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WO2008018923A2 - Fabrication de nanostructures isolées et/ou d'ensembles de nanostructures - Google Patents

Fabrication de nanostructures isolées et/ou d'ensembles de nanostructures Download PDF

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Publication number
WO2008018923A2
WO2008018923A2 PCT/US2007/007101 US2007007101W WO2008018923A2 WO 2008018923 A2 WO2008018923 A2 WO 2008018923A2 US 2007007101 W US2007007101 W US 2007007101W WO 2008018923 A2 WO2008018923 A2 WO 2008018923A2
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WIPO (PCT)
Prior art keywords
nanostructures
nanostructure
substrate
article
dimension
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Ceased
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PCT/US2007/007101
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WO2008018923A3 (fr
Inventor
Qiaobing Xu
Jiming Bao
Federico Capasso
George M. Whitesides
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Harvard University
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Harvard University
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Publication of WO2008018923A2 publication Critical patent/WO2008018923A2/fr
Publication of WO2008018923A3 publication Critical patent/WO2008018923A3/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B81—MICROSTRUCTURAL TECHNOLOGY
    • B81C—PROCESSES OR APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OR TREATMENT OF MICROSTRUCTURAL DEVICES OR SYSTEMS
    • B81C1/00—Manufacture or treatment of devices or systems in or on a substrate
    • B81C1/00015—Manufacture or treatment of devices or systems in or on a substrate for manufacturing microsystems
    • B81C1/00023—Manufacture or treatment of devices or systems in or on a substrate for manufacturing microsystems without movable or flexible elements
    • B81C1/00031—Regular or irregular arrays of nanoscale structures, e.g. etch mask layer
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y20/00—Nanooptics, e.g. quantum optics or photonic crystals
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B08—CLEANING
    • B08B—CLEANING IN GENERAL; PREVENTION OF FOULING IN GENERAL
    • B08B17/00—Methods preventing fouling
    • B08B17/02—Preventing deposition of fouling or of dust
    • B08B17/06—Preventing deposition of fouling or of dust by giving articles subject to fouling a special shape or arrangement
    • B08B17/065—Preventing deposition of fouling or of dust by giving articles subject to fouling a special shape or arrangement the surface having a microscopic surface pattern to achieve the same effect as a lotus flower
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
    • G01N21/63—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light optically excited
    • G01N21/65—Raman scattering
    • G01N21/658—Raman scattering enhancement Raman, e.g. surface plasmons
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B2207/00—Coding scheme for general features or characteristics of optical elements and systems of subclass G02B, but not including elements and systems which would be classified in G02B6/00 and subgroups
    • G02B2207/101—Nanooptics

Definitions

  • the present invention relates to methods for fabricating nanostructures and articles associated therewith and, more specifically, to methods for fabricating isolated nanostructures and/or arrays of nanostructures.
  • Nanostructures with different geometries in a range of materials have been successfully synthesized using chemical methods; however, these nanostructures may not be uniform in size and geometry.
  • the integration of these nanostructures into devices, e.g., optical devices, is also challenging due to the difficulty of selecting and manipulating specific nanostructures.
  • Nanostructures fabricated by nanosphere lithography have been used for chemosensing and biosensing. This technique, although very useful, can only produce nanostructures with limited flexibility in dimensions and geometries.
  • Electron beam lithography is widely used to fabricate metal nanostructures for studying surface plasmon coupling and subwavelength optical waveguiding.
  • Electron-beam lithography is, however, still not conveniently available to general users; and it is also challenging to fabricate structures with sub-30 nanometer width and with a high aspect ratio. Advances in the field that could, for example, enable the fabrication of nanostructures with well-controlled dimensions would find application in a number of different fields.
  • a method of fabricating a nanostructure comprises providing an article having a surface, depositing a first material on at least a portion of the surface of the article, encapsulating at least a portion of the first material in an encapsulating material, cutting the encapsulating material in a direction that intersects at least a portion of the first material, thereby forming a cut portion, and removing the encapsulating material from the cut portion, thereby forming an isolated nanostructure comprising the first material.
  • a method of fabricating a nanostructure comprises providing a substrate formed in an article material having a surface defining a plurality of indentations, depositing a first material on at least a portion of the surface of the substrate, cutting the substrate in a direction that intersects at least a portion of the first material, thereby forming a cut portion, removing any substrate from the cut portion, and forming an isolated nanostructure comprising the first material.
  • a method of positioning a plurality of isolated nanostructures on a surface comprises providing a structure comprising a plurality of nanostructures positioned in a particular arrangement in association with a first material, at least a portion of each nanostructure embedded in the first material, positioning the structure on a surface, removing the first material from the surface, and allowing the plurality of nanostructures to remain on the surface in the particular arrangement, wherein each nanostructure is physically isolated from another nanostructure in the particular arrangement.
  • a method of making a device comprising a nanostructure comprises providing a precursor article having three principle intersecting axes, wherein at least a first dimension of the precursor article, along a first axis passing through the precursor article, is smaller than 1 micron and at least a second dimension of the precursor article, along a second axis perpendicular to the first axis passing through the precursor article, is larger than 100 microns, separating, from the precursor article, a nanostructure, wherein the nanostructure has three principle intersecting axes, wherein at least a first dimension of the nanostructure, along a first axis passing through the nanostructure, is smaller than 1 micron and at least a second dimension of the nanostructure, along a second axis perpendicular to the first axis passing through the nanostructure, is smaller than 1 micron, and positioning the nanostructure in association with a plurality of other components to form a functional component of a functional device.
  • a method of fabricating a nanostructure comprises providing a supporting article, positioning a precursor article in supported relationship with the supporting article, and separating, from the precursor article, a nanostructure, wherein the nanostructure has three principle intersecting axes, wherein at least a first dimension of the nanostructure, along a first axis passing through the nanostructure, is smaller than 1 micron and at least a second dimension of the nanostructure, along a second axis perpendicular to the first axis passing through the nanostructure, is smaller than 1 micron.
  • a method of forming a composite structure comprises providing a first structure comprising a plurality of first nanostructures positioned in a particular arrangement in association with a first material, at least a portion of each first nanostructure embedded in the first material, and positioning a dielectric material adjacent the first structure.
  • the method also includes positioning a second structure adjacent the dielectric material such that the dielectric material is positioned between the first and second structures, wherein the second structure comprises a plurality of second nanostructures positioned in a particular arrangement in association with a second material, at least a portion of each second nanostructure embedded in the second material, and allowing the plurality of first and second nanostructures to remain in their respective arrangements, wherein each nanostructure is not in direct physical contact with another nanostructure in the arrangements.
  • the invention provides a series of articles.
  • Articles may include ones that are made by a process of any preceding method.
  • a composite structure in one particular embodiment, includes a first conductive nanostructure, wherein the first nanostructure has three principle intersecting axes, wherein at least a first dimension of the first nanostructure, along a first axis passing through the first nanostructure, is smaller than 500 nm and at least a second dimension of the first nanostructure, along a second axis perpendicular to the first axis passing through the first nanostructure, is smaller than 500 nm.
  • the composite structure also includes a second conductive nanostructure positioned adjacent but not in physical contact with the first nanostructure, wherein the second nanostructure has three principle intersecting axes, wherein at least a first dimension of the second nanostructure, along a first axis passing through the first nanostructure, is smaller than 500 nm and at least a second dimension of the second nanostructure, along a second axis perpendicular to the first axis passing through the second nanostructure, is smaller than 500 nm.
  • a dielectric material may be positioned between the first and second nanostructures.
  • the first and second nanostructures may be positioned less than 1 micron apart.
  • FIG. 1 shows a method of fabricating isolated nanostructures, according to one embodiment of the invention
  • FIGS. 2 A and 2B are SEM images of isolated nanostructures fabricated by the method shown in FIG. 1, according to another embodiment of the invention.
  • FIG. 3 shows another method of fabricating isolated nanostructures, according to another embodiment of the invention.
  • FIGS. 4A-4O are SEM images of various isolated nanostructures, according to another embodiment of the invention.
  • FIGS. 4P and 4Q are schematic diagrams of stacked nanostructures according to another embodiment of the invention.
  • FIG. 5 shows another method of fabricating isolated nanostructures, according to another embodiment of the invention
  • FIGS. 6A and 6B are SEM images of isolated nanostructures, according to another embodiment of the invention.
  • FIG. 7A shows an experimental setup for measuring scattering spectra of single nanostructures, according to another embodiment of the invention.
  • FIG. 7B shows scattering spectra of four randomly-selected nanostructures, according to another embodiment of the invention.
  • FIGS. 8A-8C shows dark field optical images of gold nanowires having different dimensions, according to another embodiment of the invention.
  • FIGS. 8D-8F show scattering spectra of the gold nanowires of FIGS. 8A-8C, respectively, according to another embodiment of the invention
  • FIGS. 9A-9C show Finite-Difference Time-Domain simulations of scattering spectra of gold nanowires, according to another embodiment of the invention
  • FIG. 9D shows a comparison between scattering spectra obtained from experiments and simulations, according to another embodiment of the invention
  • FIG. 10 shows a method of fabricating nanostructures, according to another embodiment of the invention.
  • FIG. 1 IA shows a photograph of patterned square-loop shaped nanostructures, according to another embodiment of the invention.
  • FIG. 1 IB shows a dark-field optical microscopy image of the nanostructures of FIG. 1 IA, according to another embodiment of the invention
  • FIG. 11C shows an SEM image of an array of closed-loop holed nanostructures, according to another embodiment of the invention
  • FIG. 1 ID shows an IR transmission spectrum measured through an array of the nanostructures shown in FIG. 1 IB, according to another embodiment of the invention
  • FIG. 12A shows a dark-field optical image of L-shaped gold nanostructures on a CaF 2 substrate, according to another embodiment of the invention.
  • FIGs. 12B-12D show transmission spectra of the nanostructures of FIG. 12A using different incidents of light polarization, according to another embodiment of the invention
  • FIG. 13 shows a transmission spectrum of L-shaped nanostructures with polarization parallel to either of the two arms of the nanostructure, according to another embodiment of the invention
  • FIG. 14A shows a bright-field optical image of an epoxy article including U- shaped nanostructures positioned on a hole of a copper sheet, according to another embodiment of the invention.
  • FIG. 14B shows an SEM image of the U-shaped nanostructures of FIG. 14 A, according to another embodiment of the invention.
  • FIGs. 14C-14E show transmission spectra of the U-shaped nanostructures of FIGs. 14A and 14B of different polarization directions of incident light, according to another embodiment of the invention.
  • FIG. 15 shows a transmission spectrum of a 100 nanometer thick epoxy article, according to another embodiment of the invention.
  • FIG. 16A shows a SEM image of U-shaped nanostructures supported on a CaF 2 substrate, according to another embodiment of the invention.
  • FIG. 16B shows a transmission spectrum of the U-shaped nanostructures of FIG. 16A, according to another embodiment of the invention.
  • FIGs. 17A and 17B are images of a composite structure including stacked nanostructures separated by a dielectric film, according to another embodiment of the invention.
  • a precursor material is provided and a nanostructure is formed by separating a portion of the precursor article (which becomes the nanostructure) from the precursor article. This separation can take place by positioning the precursor article in supported relationship with a supporting article, and effecting separation by slicing, cutting, or the like.
  • the resulting nanostructure can take a variety of forms, as described in greater detail below.
  • the nanostructure can include at least one portion having an aspect ratio of at least 5:1, 10:1, 25:1, 50:1, 100: 1 , or greater where aspect ratio is the ratio between a dimension of the article along a first axis compared to a dimension of the article along a second axis perpendicular to the first axis.
  • the nanostructure can be positioned in association with a plurality of other components to form a functional component of a functional device.
  • a functional device can be, for example, an electronic device, a sensor, or essentially any other device that can utilize such a nanostructure.
  • the nanostructure once formed by separation from a precursor article, is moved from a position and/or location from which it is separated to another position defining a location of such a functional device.
  • Article as used herein takes its common meaning as would be understood by those of ordinary skill in the art. That is, it is a piece of material, significantly more than just an isolated molecule or a relatively small number of molecules.
  • isolated nanostructures and/or arrays of nanostructures of the invention can be fabricated by depositing a material (e.g., a metal) on a surface having a plurality of protrusions or indentations. At least a portion of the deposited material may be embedded in an encapsulating material, and the encapsulating material can be cut, for instance, to form a thin slice that includes the deposited material at least partially embedded therein. In some instances, the slice can be positioned on a surface in a desired arrangement.
  • a material e.g., a metal
  • the encapsulating material can be removed from the surface to form one or more isolated nanostructures of the deposited material.
  • the encapsulating material is not removed and an array of nanostructures (e.g., nanostructures that are positioned in a predetermined (e.g., ordered) arrangement) can be used to form a composite structure.
  • dimensions of the nanostructures of the invention can be controlled to, e.g., 15 run, to form nanostructures having a variety of shapes and geometries (e.g., wires, rings, and cylinders). Nanostructures can also be formed in a variety of materials, including metals, ceramics, and polymers.
  • nanostructures of the invention can also be fabricated over large areas (e.g., greater than 1 mm 2 ). In some cases, these nanostructures may be positioned in association with other components, e.g., to form a functional component of a device.
  • FIGS. IA- IH show one method of fabricating isolated nanostructures and/or arrays of nanostructures (which may be isolated or embedded in an encapsulating material) according to an embodiment of the invention.
  • substrate 10 includes a plurality of protrusions 14 and indentations 16 that form the features of the substrate.
  • the protrusions or indentations may be formed by any suitable process, such as photolithography, molding, or etching, as described in more detail below.
  • the dimensions of protrusions 14 and the spacing between the protrusions can be easily controlled by such processes.
  • the spacing between the features is denoted JC. In some cases, this spacing can define a cross-sectional dimension of the nanostructures formed.
  • a material 20, which may be the material used to form the nanostructures, can be deposited on the surface of substrate 10.
  • Material 20 may be deposited to cover all, or, portions, of the protrusions and/or indentations of the substrate.
  • FIG. 1C shows the removal of protrusions 20 from the surface of the substrate, leaving material 20 remaining on the indentation portions. In other embodiments, however, removal of the protrusions may not be required.
  • the widths of material 20 on the surface of the substrate may be defined by the spacing x between the protrusions in the original pattern of features on the substrate.
  • substrate 10 may be coated with an encapsulating material 26, which may be in the form of a pre-polymer. After curing the pre-polymer, and removing the polymer from the substrate, an article 28 which includes portions of material 20 can be formed, as shown in FIG. IE. If desired, material 20 may be encapsulated in a material (e.g., encapsulating material 26) to form article 30 (FIG. IF). Article 30 may be cut, e.g., with a microtome or another suitable apparatus, to form cut portions 34. The cut portions may have a thickness z, which can be controlled down to, e.g., 15 nanometers, in some embodiments.
  • the cut portions may include a plurality of nanostructures 38 embedded therein.
  • a cut portion is a precursor article for a plurality of isolated nanostructures (e.g., nanostructures that are not embedded (either partially or completely) in a material).
  • one or more cut portions can be positioned on a surface, and encapsulating material 26 may be removed (partially or completely) from the surface, as discussed in more detail below.
  • the pattern of isolated nanostructures 38 on surface 40 e.g., a silicon surface, a TEM grid, or a single crystal CaF 2 surface
  • the nanostructures may have dimensions of x, y and z, the length x of the nanostructure defined by the spacing between the protrusions (FIG. IA), the width y defined by the thickness of material 20 deposited on substrate 10 (FIG. IB), and the height z defined by the thickness of the cut portions (FIG. IG).
  • FIGS. 2A and 2B show SEM images of isolated nanostructures formed by the method described in FIG. 1.
  • FIG. 2A shows gold nanowires with dimensions of 2 microns (x) x 40 nanometers (y) * 50 nanometers (z).
  • the insets show high magnification images of the same samples.
  • FIG. 2B shows gold nanowires with dimensions of 2 microns (x) ⁇ 10 nanometers (y) * 100 nanometers (z).
  • dimensions of the nanostructures can be controlled by varying the thickness of materials deposited on a substrate and the thicknesses of portions cut from an article.
  • nanostructures having high aspect ratios can be fabricated using the methods of fabrication described herein.
  • the aspect ratio of a nanostructure is the ratio of minimum lateral dimension of any raised portion of the structure to the height of the structure.
  • FIG. 2B shows nanostructures having an aspect ratio of 10 : 1.
  • nanostructures including isolated nanostructures having aspect ratios of at least 5:1, at least 10:1, at least 20:1, at least 50:1, or at least 100:1 can be fabricated by methods of the invention.
  • FIGS. 3A-3H show another method of fabricating isolated nanostructures and/or arrays of nanostructures according to another embodiment of the invention.
  • substrate 50 which includes a plurality of features 52 (e.g., protrusions)
  • mold 56 which includes a plurality of inverse features 58 (e.g., indentations).
  • the mold may be brought into contact with material 60 (e.g., a pre-polymer), and the material may fill, or coat, at least a portion of the indentations of the mold. Although not required, the material may be molded against surface 62. Layer 64, which may include an adhesive layer (e.g., silver) may optionally be deposited on the surface prior to molding.
  • material 60 e.g., a pre-polymer
  • Layer 64 which may include an adhesive layer (e.g., silver) may optionally be deposited on the surface prior to molding.
  • material 70 which may be the material in which the nanostructures are formed, can be deposited on substrate 50. All, or portions, of material 70 can be encapsulated in an encapsulating material 72, as shown in FIG. 3D.
  • surface 62 can be removed from substrate 50. In some cases, this removal can be aided by the differential adhesion between layer 64 and surface 62 (e.g., layer 64 may be more adhesive to surface 62 than to encapsulating material 72). Of course, this differential adhesion may depend on the material properties of the surface and encapsulating material, and these materials may be chosen accordingly.
  • FIG. 3F shows article 74 after the removal of layer 64.
  • article 72 may be cut, e.g., in the direction of arrows 76, to form one or more cut portions 80.
  • the cut portions can include a plurality of nanostructures 82 embedded therein.
  • cut portion 80 may be positioned on surface 84, and encapsulating material 72 may be separated or removed (partially or completely) to form a plurality of isolated nanostructures 82 on the surface.
  • a plurality of nanostructures can be fabricated in a single step (e.g., in a single cutting step).
  • these nanostructures can be positioned essentially simultaneously on a surface in a single step. It should be understood that while in some embodiments the encapsulating material (e.g., encapsulating material 72 of FIG. 3F) is removed from the isolated nanostructures, in other embodiments, the encapsulating material is not removed from the nanostructures.
  • nanostructures embedded in an encapsulating material can be used to form a composite structure.
  • the encapsulating material may be flexible such that in these and other embodiments, the composite structure can have a curved surface. As shown in FIG.
  • the pattern of nanostructures formed on a surface may be determined, at least in part, by the pattern of features on substrate 50.
  • isolated nanostructures may manipulated to different parts of the surface (e.g., by various methods such as magnetic forces, capillary forces, electrostatic forces, and the like).
  • isolated nanostructures (and/or arrays of nanostructures) may be positioned in association with other components to form a functionally component of a device, as discussed in more detail below.
  • FIGs. 4A-4O show SEM images of isolated gold nanorings on a substrate fabricated by the method shown in FIG. 3.
  • the diameter of the nanorings of FIGs. 4 A and 4B were approximately 3 microns, and the widths and heights of the nanorings were 40 nanometers and 200 nanometers, respectively.
  • FIG. 4B shows a high magnification SEM of the sample shown in FIG. 4A.
  • FIGs. 4C-4K show high aspect ratio isolated gold nanorings on a silicon substrate after removing the encapsulating material (an epoxy matrix) with oxygen plasma at 0.9 Torr, 70 W for 20 min.
  • the aspect ratio is the ratio of minimum lateral dimension of any raised portion of a surface feature (e.g., height) to indentation depth (e.g., thickness of the wall of the ring).
  • the wall thickness and the height of the rings were about 40 nm and 500 nm, respectively; thus, these structures had an aspect ratio of 12.5.
  • FIGs. 4C-4E show circular rings
  • FIGs. 4F-FH show square nanorings
  • FIGs. 4I-4K show double rings.
  • FIGs. 4D, 4G, and 4J show top views of the free-standing nanostructures;
  • FIGs. 4E, 4H, and 4K show top views of the nanostructures lying on a silicon substrate on their sides to indicate the heights of the structures.
  • FIGs. 4L-4O show SEM images of various nanorings with different aspect ratios.
  • the images were taken at angles that show the differences in height of the structures.
  • the nanorings can be fabricated to have even higher aspect ratios.
  • a nanoring having a diameter of 2 microns, a width of 10 nm, and a height of 1 micron can have an aspect ratio of 100: 1.
  • a plurality of such nanostructures can be formed essentially simultaneously. These nanostructures may useful, for instance, in applications requiring large surface areas.
  • material 70 was deposited on all sides of features 52 of the substrate.
  • the resulting nanostructures formed included nanorings in the shape of these features (e.g., in the shape of the circumferences of the protrusions).
  • material 70 can be deposited on only portions of protrusions 52.
  • material deposited on only half of the surfaces of the protrusions can form structures such as semi-circular rings.
  • the shapes of nanostructures can depend not only on the features of the substrate, but also on the method and/or amount of material deposited on the substrate.
  • a second material can be deposited on top of material 70.
  • complex multilayer nanostructures can be formed.
  • a first material may be coated on at least a portion of the substrate and a second material may be coated on another portion of the substrate.
  • the first and second portions overlap such that at least a portion of the second material is on top of the first material.
  • the first and second portions do not overlap, e.g., the first material may cover a first side of a cube and the second material may cover a second side of the cube.
  • the first and/or second materials may be conductive, semiconductive, or insulative.
  • additional layers may be deposited. For instance, alternating metallic and non-metallic materials may be deposited to form various multilayer nanostructures. Such structures may be useful for forming functional nano-scaled devices.
  • a composite structure can be formed by providing a first structure comprising a plurality of first nanostructures positioned in a particular arrangement in association with the first material, at least a portion of each first nanostructure embedded in the first material.
  • nanostructures 82 are positioned in an array within encapsulating material 72.
  • the first structure (cut portion 80) may optionally be positioned on a surface.
  • a dielectric material can be positioned adjacent the first structure.
  • a thin film of a dielectric material may be deposited on top of the first structure by various methods such as deposition, or by slicing a thin layer of dielectric material and positioning it on top of the first structure.
  • the film of dielectric material may have various thicknesses such as, for example, less than 1 mm, less than 500 microns, less than 200 microns, less than 100 microns, less than 1 micron, less than 500 nanometers, less than 300 nanometers, less than 200 nanometers, less than 100 nanometers, or less than 50 nanometers.
  • the combined first structure and film of dielectric material can then be used as a substrate for positioning a second structure (e.g., a second cut portion) that may include a plurality of second nanostructures positioned in a particular arrangement in association with a second material, at least a portion of each second nanostructure embedded in the second material.
  • a second cut portion 80 may be positioned on top of a first cut portion 80 to form stacked nanostructures.
  • the second nanostructures are different from the first nanostructures.
  • the first nanostructures may have a open loop or closed loop structure, and the second set of nanostructures may be in the form of a straight wire or a rod-shaped nanostructure.
  • Other combinations of shapes of nanostructures can also be used.
  • the plurality of first nanostructures may be the same or different from one another.
  • the shapes and arrangements of nanostructures can be controlled at least in part by features (e.g., protrusions and/or indentations) on the substrate that are used to form the nanostructures.)
  • the plurality of first and second nanostructures may remain in their respective arrangements, wherein each nanostructure is not in direct physical contact with another nanostructure in the arrangement.
  • the nanostructures can remain in their respective arrangements due to the encapsulating material, which is not removed from the nanostructures.
  • the encapsulating material is removed from the nanostructures.
  • the first material may be removed from the first structure and/or the second material may be removed from the second structure.
  • a portion of the encapsulating material is removed from the first and/or second structure.
  • all of the encapsulating material is removed.
  • isolated composite structures e.g., stacked nanostructures
  • the first and/or second nanostructures may have a variety of sizes and/or cross-sectional dimensions.
  • at least one of the nanostructures has a cross-sectional dimension of less than or equal to 500 nanometers, less than or equal to 300 nanometers, less than or equal to 200 nanometers, less than or equal to 100 nanometers, or less than or equal to 50 nanometers.
  • stacked nanostructures can be separated by a dielectric material.
  • a first nanostructure may be positioned adjacent a second nanostructure and the first and second nanostructures may be in direct physical contact with one another.
  • conductive or semiconductive films can be positioned between first and second nanostructures.
  • the material positioned between the first and second nanostructures may be chosen at least in part by one or more of the following: its optical properties, electron conductivity, permeability, and permittivity.
  • the intervening material may be chosen such that it is transparent in the wavelength of interest.
  • the material used to form the first and/or second nanostructures may also be chosen at least in part by one or more of its optical properties, electron conductivity, permeability, and permittivity.
  • a composite structure includes a first nanostructure (e.g., a conductive nanostructure), wherein the first nanostructure has three principle intersecting axes, wherein at least a first dimension of the first nanostructure, along a first axis passing through the first nanostructure, is smaller than 500 run (or 400 nm, 300 nm, 200 nm, 100 nm, or 50 nm) and at least a second dimension of the first nanostructure, along a second axis perpendicular to the first axis passing through the first nanostructure, is smaller than 500 nm (or 400 nm, 300 nm, 200 nm, 100 nm, or 50 nm).
  • a first nanostructure e.g., a conductive nanostructure
  • the first nanostructure has three principle intersecting axes, wherein at least a first dimension of the first nanostructure, along a first axis passing through the first nanostructure, is smaller than 500 run (or 400 nm, 300 nm, 200 nm
  • the composite structure includes an array of such first nanostructures.
  • the composite may also include a second nanostructure (e.g., a conductive nanostructure) positioned adjacent but not in physical contact with the first nanostructure (e.g., an intervening material such as a dielectric material and/or a conductive material can be positioned between the first and second nanostructures).
  • a second nanostructure e.g., a conductive nanostructure
  • an intervening material such as a dielectric material and/or a conductive material can be positioned between the first and second nanostructures.
  • more than one layer of material is positioned between the first and second nanostructures.
  • the second nanostructure may have three principle intersecting axes, wherein at least a first dimension of the second nanostructure, along a first axis passing through the first nanostructure, is smaller than 500 nm (or 400 nm, 300 nm, 200 nm, 100 nm, or 50 nm) and at least a second dimension of the second nanostructure, along a second axis perpendicular to the first axis passing through the second nanostructure, is smaller than 500 nm (or 400 nm, 300 nm, 200 nm, 100 nm, or 50 nm).
  • the first and second nanostructures may be positioned at various distances from one another (e.g., measured by the two closest points between the first and second nanostructures). Such a distance may be, for example, less than 1 mm (e.g., such that the first and second nanostructures are positioned less than 1 mm apart), less than 500 microns, less than 200 microns, less than 100 microns, less than 50 microns, less than 1 micron, less than 500 nm, less than 250 nm, less than 200 nm, less than 100 nm, less than 50 nm, or less than 30 nm.
  • the distance between the structures may depend in part by, for example, the dimensions of the first and second nanostructures. For some applications, the distance may also be chosen such the nanostructures can couple to incident light magnetically.
  • Composite structures described herein may be flexible. In some cases, the composite structure has a curved surface (e.g., in the shape of cylinder).
  • first and second nanostructures are aligned such that they share a common principle axis.
  • the structures, if positioned on top of one another, may share the same z-axis.
  • Examples of stacked nanostructures are shown in FIGs. 4P and 4Q.
  • FIGs. 4P and 4Q show first nanostructure 86 and second nanostructure 88 sharing the same z-axis.
  • the nanostructures may be offset from one another relative to the z-axis (e.g., the second nanostructure may not be positioned directly above the first nanostructure in some embodiments).
  • arrays of these nanostructures can be formed.
  • the nanostructures of these arrays may be embedded or not embedded in a matrix material.
  • first nanostructures and second nanostructures can be formed.
  • greater than or equal to 2 greater than or equal to 6, greater than or equal to 10, greater than or equal to 15, greater than or equal to 20, greater than or equal to 50, or greater than or equal to 100 alternating layers can be formed.
  • a first layer may have negative permittivity and a second layer may have negative permeability.
  • such structures may have a negative index of refraction (e.g. in the infrared range).
  • FIG. 5 shows another method of fabricating isolated nanostructures and/or arrays of nanostructures according to another embodiment of the invention.
  • substrate 90 which is formed in material 92, may include a plurality of indentations 94.
  • Material 100 may be deposited on at least a portion of the surface of substrate 90, including in all, or portions of, indentations 94.
  • a section of substrate 90 may be cut, e.g., with a thickness of z, as shown in FIG. 5C. This process can form one or more cut portions 104 including nanostructures 102 embedded in material 92.
  • Material 92 may be removed (partially or completely) from the cut portion to form isolated nanostructures 102.
  • Nanostructures of the invention may have a variety of shapes and dimensions.
  • nanostructures may depend, at least in part, on the patterns of features on a substrate (e.g., including the shapes, spacing, and density of the protrusions and/or indentations).
  • Non-limiting examples of nanostructure shapes include lines (e.g., wires), pillars, disks, squares, triangles, rings, tubes, cylinders, and irregular shapes.
  • nanostructures having curved surfaces e.g., circles, rings, L-, C-, and U-shapes, which may be difficult to fabricate using conventional nanofabrication techniques, may be fabricated using methods described herein.
  • nanostructures have a "closed-loop" structure; that is, one in which the nanostructure forms a closed loop or perimeter when viewed from above, such as an O- (circular closed-loop), ⁇ - (triangular closed-loop), or G- (square closed-loop) shape (e.g., as shown in FIGs. 4A-4K).
  • nanostructures may have an "open-loop" structure.
  • Open loop structures are curved structures that are not completely closed when viewed from above and have at least two end portions that are not connected. Examples of open loop structures are ones having a U-, L-, or C-shape. Arrays of such structures can also be fabricated.
  • Nanostructures described herein can have varying cross-sectional dimensions.
  • a nanostructure may have at least one cross-sectional dimension (e.g., a length, width, height, or diameter) of less than 10 microns, less than 1 micron, less than 0.5 micron, less than 0.1 micron, less than 50 nm, less than 20 nm, or less than 10 nm.
  • at least two cross-sectional dimensions of the nanostructure may be less than 10 microns, less than 1 micron, less than 0.5 micron, less than 0.1 micron, less than 50 nm, less than 20 nm, or less than 10 nm.
  • a nanostructure has three principle intersecting axes (e.g., axes on the same plane as the length, width, and height of the nanostructure), at least a first dimension of the nanostructure, along a first axis passing through the nanostructure, being smaller than 1 micron (or, alternatively, smaller than 0.1 micron, or smaller than 10 nm) and at least a second dimension of the nanostructure, along a second axis perpendicular to the first axis passing through the nanostructure, being smaller than 1 micron (or, alternatively, smaller than 0.1 micron, or smaller than 10 nm).
  • nanostructures can be etched to form even smaller structures after they have been formed by methods described herein.
  • the nanostructures described herein may be substantially uniform in size and/or composition. For instance, greater than 70%, greater than 80%, greater than 90%, greater than 95%, or greater than 99% of the nanostructures fabricated may be substantially uniform in size and/or composition (e.g., the dimensions of the nanostructures may be within ⁇ 1%). In some instances, nanostructures with the above characteristics can be fabricated essentially simultaneously (e.g., in a single step). Monodispersed nanostructures have use in a variety of applications.
  • a nanostructure of the invention may comprise a metal.
  • the metal film includes a transition element.
  • metals include copper (Cu), platinum (Pt), palladium (Pd), gold (Au), nickel (Ni), indium (In), tin (Sn), silver (Ag), lead (Pb), bismuth (Bi), cadmium (Cd), zinc (Zn), antimony (Sb), chromium (Cr), and titanium (Ti).
  • metals such as ones from Groups 3-15 of the Periodic Table of Elements, can be used to form nanostructures.
  • other materials such as semi-conductors (e.g., elements from Groups 13-16 of the Periodic Table of Elements such as Si, Ga, and As) can also be used.
  • organic materials such as polymers (e.g., conductive polymers) and carbon can be used to form nanostructures, such as polymeric or carbon nanowires.
  • nanostructures such as polymeric or carbon nanowires.
  • Carbon nanowires of the invention may have different characteristics that carbon nanowires fabricated by chemical synthesis techniques.
  • Combinations of materials such as the ones listed above can also be used; for example, polymers may be combined with a magnetic material to form magnetically-susceptible nanostructures.
  • Materials used to form nanostructures may be conductive, semi-conductive, or insulating.
  • nanostructures are formed from a precursor article (e.g., a cut portion) sectioned from a larger article.
  • the dimensions of a precursor article may depend on the size of the substrate, the thickness of the article from which the precursor article was portioned, and/or the instrument used to section the precursor article.
  • the precursor article may have at least one cross-sectional dimension (e.g., a length, width, height, or diameter) of less than 10 microns, less than 1 micron, less than 0.1 micron, less than 50 nm, less than 20 nm, or less than 10 run.
  • a precursor article has three principle intersecting axes (e.g., axes on the same plane as the length, width, and height of the cut portion), at least a first dimension of the precursor article, along a first axis passing through the precursor article, being smaller than 1 micron (or, alternatively, smaller than 0.1 micron, or smaller than 20 nm) and at least a second dimension of the precursor article, along a second axis perpendicular to the first axis passing through the precursor article, being smaller than 1 micron (or, alternatively, smaller than 0.1 micron, or smaller than 20 nm).
  • at least one cross-sectional dimension of the nanostructure is essentially the same as a cross-sectional dimension of the precursor article.
  • a plurality of precursor articles may be formed from a single article, and each of these precursor articles may vary in size (e.g., thickness).
  • a material e.g., a material used to form the nanostructures
  • An appropriate method may depend on the type of material to be deposited (e.g., a metal compared to an organic material).
  • Examples of methods for depositing conductive or semi-conductive materials include electroplating, vacuum deposition, and thermal evaporation.
  • methods for depositing organic materials include vapor deposition, spin coating, printing, and stamping.
  • methods involving solvent evaporation can be used, e.g., coating a surface with a solution of the material dissolved in a solvent and allowing the solvent evaporate.
  • Such methods can coat all, or portions of, a surface with a material. For instance, dipping the substrate in the material may cause the material to cover all of the substrate. Using a microfluidic network to deliver materials to a surface can cause only portions of the substrate to be covered by the material.
  • materials e.g., films or layers
  • Materials deposited on a substrate can cover all or portions of a substrate.
  • the portions of the substrate covered by the material can influence the shape of the nanostructure formed, as discussed above.
  • a material is deposited such that it completely covers the substrate, e.g., to form a continuous layer.
  • a material may be deposited to form a discontinuous layer.
  • collimated material e.g., gold
  • non-collimated material deposition can be used to form thin films on all surfaces of the substrate.
  • material can be deposited at an angle (e.g., less than or equal to 15°, less than or equal to 30°, less than or equal to 45°, less than or equal to 60°, less than or equal to 75°, or less than or equal to 90°) relative to the substrate such that the film is deposited on only certain portions of the substrate (e.g., on certain portions of the protrusions and/or indentations).
  • Depositing material at an angle may be performed multiple times at different positions on a single substrate to form free standing structures having different shapes. For example, features in the shape of a cube may be treated with deposition material to selectively coat two sides of the cube to form free-standing structure in the shape of an "L" using methods described herein.
  • a material deposited on a substrate can have various thicknesses.
  • the thickness of the material deposited may define a cross-sectional dimension of the nanostructure formed in that material.
  • a layer of material may have a thickness of, e.g., equal to or less than 1 micron, equal to or less than 100 nanometers, equal to or less than 50 nanometers, equal to or less than 40 nanometers, equal to or less than 30 nanometers, equal to or less than 20 nanometers, or equal to or less than 10 nanometers.
  • a substrate may include a surface having a variety of features defined therein by protrusions (i.e., raised portions) and/or indentations (i.e., recessed portions).
  • the substrate may include features having a variety of lateral dimensions.
  • the substrate may include at least one feature with a lateral dimension of less than about 100 microns, less than about 50 microns, less than about 10 microns, less than about 5 microns, less than about 1 micron, or less than 0.25 microns.
  • the substrate may be fabricated using various methods such as e-beam lithography, which can be combined with reactive etching steps to create even smaller features.
  • a substrate may include one or more different patterns of features including lines, circles, squares, triangles, pyramids, cylinders, and irregular shapes.
  • the patterns include lines, circles, squares, triangles, pyramids, cylinders, and irregular shapes.
  • the pattern of the features on the substrate can control the pattern of nanostructures formed in a cut portion (e.g., embedded nanostructures), and/or the pattern of isolated nanostructures formed on a surface.
  • a substrate can substantially smooth, i.e., the substrate may not include protrusions or indentations. These types of substrates may be useful, for example, for forming nanostructures in the form of long wires. Substrates without protrusions and/or indentations may also be suitable for certain material deposition techniques (e.g., depositing a material used to form a nanostructure using a microfluidic system). Additionally, a substrate may be planar, or it may be curved. Numerous protrusions and/or indentations may be present on a substrate.
  • a single substrate may include more than 5000 isolated protrusions and/or indentations, more than 10 6 isolated protrusions and/or indentations, or more than 10 9 isolated protrusions and/or indentations.
  • a substantially equivalent number of nanostructures can be fabricated from one cut portion.
  • one isolated protrusion and/or indentation may be used to form one isolated nanostructure of a cut portion.
  • the same protrusions and/or indentations of a substrate can be used to form several cut portions, and, therefore, multiple numbers or arrays of nanostructures can be fabricated from one substrate.
  • a single substrate including 1000 isolated protrusions and/or indentations may be cut 100 times to form 10 5 isolated (or embedded) nanostructures.
  • Such protrusions and/or indentations may be used form arrays of nanostructures (which may be isolated or embedded in a matrix/encapsulating material).
  • the nanostructures may be positioned at various distances from one another in the array, which may depend on the distances between the protrusions and/or indentations on the substrate.
  • Different types of arrays of nanostructures can be formed. For example, hexagonal arrays, face-centered cubic arrays, and other types of arrays of nanostructures can be fabricated.
  • the nearest distance between two nanostructures in an array is, for example, less than 1 mm, less than 500 microns, less than 200 microns, less than 100 microns, less than 50 microns, less than 1 micron, less than 500 nm, less than 250 nm, less than 200 nm, less than 100 nm, less than 50 nm, or less than 30 nm.
  • the distance between structures, as well as the size of the nanostructures themselves, can form unit cells (e.g., a simplest repeating unit) of different sizes. Different sizes of units cells can have different properties. For instance, smaller unit cells can be used to select smaller wavelengths of light for optical applications (e.g., optical filters).
  • the protrusions and/or indentations may form a "patterned area" on the substrate.
  • the patterned area may be larger than 1 mm 2 , larger than 0.5 cm 2 , larger than 1 cm 2 , larger than 2 cm 2 , or larger than 5 cm 2 .
  • this patterned area of the substrate can be cut in such a way to form a patterned area of nanostructures within the cut portion.
  • the patterned area of nanostructures within the cut portion may have an area that is substantially equivalent to the patterned area of the substrate.
  • the nanostructures of the cut portion may be transferred to a surface to form isolated nanostructures, e.g., arranged in the form of the pattern.
  • An individual feature included in the protrusions and/or indentations of a surface can have various aspect ratios in some embodiments of the invention, e.g., depending on the method in which the features are made.
  • the aspect ratio of a feature is the ratio of minimum lateral dimension of any raised portion of a surface feature to indentation depth.
  • An individual feature may have an aspect ratio of greater than or equal to 2, greater than or equal to 5, greater than or equal to 10, greater than or equal to 20, greater than or equal to 50, or greater than or equal to 100 in some instances.
  • a substrate or article (including a nanostructure material associated with the substrate or article) can be cut or sectioned by a variety of methods.
  • a particular method of cutting may depend on the physical properties of the substrate, e.g., the hardness, elasticity, or crystallinity of the surface.
  • substrates can be cut by fractioning the substrate.
  • a sharp cutting edge such as a microtome, can be used.
  • Several different microtomes are known in the art, including those made by Leica. These microtomes can be equipped with different types of cutting edges including diamond knives and trimming blades.
  • microtomes may be suitable for cutting extremely hard and brittle materials such as ceramics (including oxides (e.g., glass, alumina, zirconia), non- oxides (e.g., carbides, borides, nitrides, and suicides) and composites (e.g., particulate reinforced composites, and combinations of oxides and non-oxides)).
  • Ceramics including oxides (e.g., glass, alumina, zirconia), non- oxides (e.g., carbides, borides, nitrides, and suicides) and composites (e.g., particulate reinforced composites, and combinations of oxides and non-oxides)).
  • Semiconductors e.g., silicon, GaAs, etc.
  • super conducting oxides e.g., silicon, GaAs, etc.
  • nanocrystalline ceramics can also be cut.
  • microtomes are suitable for cutting polymers (e.g., epoxies, acrylates
  • tungsten carbide knives may be suitable for cutting certain polymers.
  • glass or diamond knives can be used.
  • these instruments can be used at low temperatures, e.g., below - 100 0 C. Such temperatures may be important, e.g., for cutting elastomers and thermoplastics which may not be cut satisfactorily at ambient temperatures.
  • the angle of the cutting edge can also be varied, e.g., to modify a cut portion.
  • Portions of a substrate or article can be cut serially or in parallel.
  • a plurality of nanostructures may be fabricated essentially simultaneously.
  • greater than 1000, greater than 10 4 , greater than 10 5 , greater than 10 6 , or greater than 10 7 nanostructures may be fabricated essentially simultaneously (e.g., in a single cutting step or a single removal step).
  • encapsulating materials may have physical properties (e.g., hardness) that make it appropriate for cutting, e.g., with a microtome or another suitable apparatus.
  • Another consideration when choosing a suitable encapsulating material is compatibility with the material used to form the nanostructures. In some cases, for example, an encapsulating material can be easily and quickly removed or separated from the nanostructures, e.g., without destroying or damaging the nanostructures.
  • An encapsulating material may be removed by appropriate methods such as etching in an oxygen plasma or using an appropriate solvent that can dissolve the encapsulating material.
  • an encapsulating material may be chosen based on its ability to adhere to the material used to form the nanostructure, e.g., such that additional adhesion layers are not required.
  • an encapsulating material is polymeric.
  • Polymeric materials suitable for use in fabrication of the substrate may have linear or branched backbones, and may be crosslinked or noncrosslinked, depending upon the particular polymer and the degree of formability or hardness desired of the substrate.
  • a variety of polymeric materials are suitable for such fabrication, including epoxy polymers (e.g., Araldite 502), acrylate polymers, and silicone polymers.
  • Epoxy polymers are characterized by the presence of a three-member cyclic ether group commonly referred to as an epoxy group, 1, 2-epoxide, or oxirane.
  • diglycidyl ethers of bisphenol A may be used, in addition to compounds based on aromatic amine, triazine, and cycloaliphatic backbones.
  • Another example includes the well-known Novolac polymers.
  • silicone polymers suitable for use include those formed from precursors including the chlorosilanes such as methylchlorosilanes, ethylchlorosilanes, and phenylchlorosilanes, and the like.
  • Another example of a silicone polymer is poly(dimethylsiloxane) (PDMS).
  • an encapsulating material may include a ceramic. Ceramics may include oxides (e.g., glass, alumina, zirconia), non-oxides (e.g., carbides, borides, nitrides, and suicides) and composites (e.g., particulate reinforced composites, and combinations of oxides and non-oxides). A variety of different materials may be used as substrates for depositing materials. In some cases, the material used to form the substrate may be the same as the encapsulating material, such as those listed above. Materials used to form a substrate may be chosen based on its ability to be conformed to form features on the substrate (e.g., by patterning, molding, or other suitable techniques). Features of a substrate may be formed according to a variety of methods.
  • oxides e.g., glass, alumina, zirconia
  • non-oxides e.g., carbides, borides, nitrides, and suicides
  • composites e.g.,
  • the features of a substrate can be micromachined from a material such as a semi-conductor.
  • the features can be formed lithographically by providing a surface, depositing a film of material onto the surface, coating an exposed surface of the material with resist, irradiating the resist according to a predetermined pattern, removing irradiated portions of the resist from the material surface, contacting the material surface with a reactant selected to react chemically therewith and selected to be chemically inert with respect to the resist such that portions of the material according to the predetermined pattern are degraded, removing the degraded portions, and removing the resist to uncover portions of the material formed according to the predetermined pattern to form the mold surface.
  • Negative or positive resist may be used, and the procedure can be adjusted accordingly.
  • a surface may be provided, and coated with resist. Then portions of the resist may be irradiated according to a particular predetermined pattern. Irradiated portions of the resist may then be removed from the substrate to expose portions of the substrate surface according to the predetermined pattern, and the substrate may be contacted with a plating reagent such that exposed portions according to the predetermined pattern are plated. Then, the resist may be removed to uncover portions of the exposed substrate according to the predetermined pattern bordered by plated portions of the substrate to form the features.
  • Other methods of forming features include etching, stamping, molding, and the like.
  • a method of fabricating features on a substrate by molding may be as follows.
  • a template consisting of an exposed and developed photoresist pattern on silicon is prepared (This type of fabrication is described in any conventional photolithography text, such as Introduction to Microelectronic Fabrication, by Richard C. Jaeger, Gerold W. Neudeck and Robert F. Pierret, eds., Addison- Wesley, 1989). Templates such as electron microscopy grids or other corrugated materials may also be used.
  • the template is placed in a container such as a petri dish.
  • PDMS-Sylgard Silicone Elastomer 184 and Sylgard Curing Agent 184 (Dow Corning Corp., Midland, Michigan) is poured into the petri dish. It is not necessary to put the mixture of PDMS-elastomer and curing agent under vacuum to remove dissolved dioxygen.
  • the PDMS can be cured at room temperature for 30 to 60 min. This cure can be followed by additional curing at 65 0 C for approximately 1-2 hours or until the polymer is rigid. After cooling to room temperature, the PDMS-stamp is carefully peeled from the template and can be used as a substrate.
  • multiple substrates can be formed from a single template (or mold).
  • positioning includes providing a structure, such as a cut portion of an article, including a plurality of nanostructures positioned in a particular arrangement in the structure. At least a portion of each nanostructure in the structure can be embedded in the structural material (e.g., an encapsulant material). For instance, the sides of the nanostructures may be encapsulated in the structural material, with the tops and bottoms of the nanostructures exposed. In other embodiments, all surfaces of the nanostructures may be embedded in the structural material.
  • the cut portion may be positioned on a surface, e.g., by methods using capillary, magnetic, or electrostatic forces.
  • the cut portion may float at a fluid/air interface or may be suspended in a fluid, and a surface may be brought underneath the cut portion in the fluid and pulled back carefully to let the cut portion sit on the surface.
  • nanostructures may be directly transferred to the surface.
  • a hollow loop may be used to position a cut portion on a surface.
  • the cut portion may float at a fluid/air interface or may be suspended in a fluid, and the cut portion may be picked up in a drop of water using a loop (e.g., 2 mm in diameter) and positioned on a surface.
  • a loop e.g., 2 mm in diameter
  • methods of positioning nanostructures enable the transfer of nanostructures to various types of surfaces having different compositions (e.g., metallic, semi-conductive, and polymeric surfaces), and/or surfaces having different shapes and/or geometries (e.g., flat surfaces, curved surfaces, surfaces having multiple faces (e.g., a cube), and surfaces already patterned with features).
  • surfaces having different compositions e.g., metallic, semi-conductive, and polymeric surfaces
  • surfaces having different shapes and/or geometries e.g., flat surfaces, curved surfaces, surfaces having multiple faces (e.g., a cube), and surfaces already patterned with features.
  • the structural material of the portion may be removed from the surface by methods such as plasma oxidation and/or removal using a solvent (e.g., dissolving the structural material in an appropriate solvent that does not dissolve the nanostructures). Heat and/or sonication may also be applied to aid removal.
  • removal of the structural material from a cut portion may occur before positioning the cut portion or the nanostructures on a surface.
  • the nanostructure is at least partially embedded in an interior portion of the cut portion (e.g., a precursor article), and a nanostructure may be removed or separated from the interior portion of the cut portion. In other cases, a nanostructure may be removed or separated from the exterior surface of the cut portion.
  • a solvent e.g., dissolving the structural material in an appropriate solvent that does not dissolve the nanostructures.
  • Heat and/or sonication may also be applied to aid removal.
  • removal of the structural material from a cut portion may occur before positioning the cut portion or the nanostructures on a surface.
  • the nanostructure is at least partially
  • the plurality of nanostructures remain on the surface in the particular arrangement that they were in when embedded in the cut portion.
  • adjacent nanostructures are not in direct physical contact with one another and nanostructures are separated from one another via the structure material (encapsulating material).
  • each nanostructure may be physically isolated from another nanostructure in that particular arrangement, e.g., to form isolated nanostructures.
  • adjacent nanostructures are not in direct physical contact with one another and the nanostructures are separated from each other via a non-solid substance (e.g., a liquid or air).
  • a second material different material from the encapsulating material can be used to at least partially embed the nanostructures.
  • a first set of nanostructures can be positioned on a surface, and a second set of nanostructures can be positioned relative to the first set of nanostructures.
  • a first set of nanostructures may include a set of parallel nanowires.
  • a second set of nanowires may be positioned substantially perpendicular to the first set of nanowires, as shown in FIG. 6B.
  • first and second sets of nanostructures can be positioned at different positions relative to one another.
  • the first and second sets of nanostructures may be positioned at an angle of 30°, 60°, or 75° relative to one another.
  • third or more sets of nanostructures can be positioned on the same surface.
  • a first set may include nanostructures having particular shapes and/or dimensions
  • the second set may include nanostructures having shapes and/or dimensions different from that of the first set.
  • complex nanostructures and/or nanostructure networks can be fabricated.
  • Nanostructures of the invention can be used in a variety of applications. For instance, nanostructures may be used as sensors, tags or probes, electrodes, switches, or transistors. In some cases, nanostructures can be integrated into a functional component of a functional device. The structural, chemical, and/or electronic properties of the nanostructures can be used to create devices of a variety of types. In addition, structural, chemical, and/or electronic changes associated with nanostructures can modulate the properties of the nanostructures. In some cases, enhancements in local fields and strong scatterings of nanostructures can be used in a number of applications, including surface-enhanced Raman scattering, subwavelength optical waveguiding, biolabeling, and biosensing.
  • Nanostructures of noble metals show different colors due to their surface plasmon resonances. These particles interact strongly with visible light through the resonant excitation of the collective oscillations of their conduction electrons. As a result of these oscillations, local electromagnetic fields near the particle can be many orders of magnitude higher than the incident fields; these strong, oscillating fields generate intense scattered light around the wavelength of the resonant peak.
  • the magnitude, peak wavelength, and spectral bandwidth of the plasmon resonance of a nanostructure may depend on the size, shape, composition, and local environment of the nanostructure. As such, the plasmon resonances of nanostructures of the invention can be easily tuned by varying such parameters. The differences in optical properties of such nanostructures are illustrated in Examples 3-5.
  • the differences in surface-enhanced Raman scattering (SERS) of nanostructures can be used in certain applications (e.g., sensing). Since vibrational information is very specific for certain materials (e.g., the size, shape, composition, and local environment of a nanostructure), it can provide a fingerprint by which the nanostructure can be identified. Compared with some metal nanoparticles, nanostructures of the invention, which may have, e.g., sharp corners and/or large surfaces areas, can greatly enhance electric fields and can have increased total SERS efficiency.
  • nanostructures in the form of metal nanowires can be used as waveguides to propagate light under subwavelength scales.
  • the ability to engineer plasmon resonances may optimize the nanowire sizes for different colors of light.
  • nanostructures may be appropriately functionalized (e.g., with a coating of material) to impart desired characteristics (e.g., surface properties) to the nanostructures.
  • the nanostructure may be functionalized or derivatized to include compounds, functional groups, atoms, or materials that can alter or improve properties of the nanostructure.
  • Nanostructures are particularly suitable for chemical functionalization on their exterior surfaces, as is well known.
  • a nanostructure may be functionalized with functional groups which can specifically interact with an analyte.
  • the functional groups may include compounds, atoms, or materials that can alter or improve properties such as compatibility with a suspension medium (e.g., water solubility, water stability, i.e., at certain pH ranges), photo-stability, and biocompatibility.
  • Nanostructures may be modified using species such as self-assembled monolayers (SAMs). Nanostructures can be modified with any of a variety of SAM- forming materials, such as those described in U.S. Patent No. 5,512,131 of Kumar, et al., published April 30, 1996 and incorporated herein by reference.
  • SAMs self-assembled monolayers
  • nanostructure may be modified with functional groups that interact with an analyte to form a bond with the analyte, such as a covalent bond (e.g., carbon-carbon, carbon-oxygen, oxygen-silicon, sulfur-sulfur, phosphorus-nitrogen, carbon-nitrogen, metal-oxygen or other covalent bonds), an ionic bond, a hydrogen bond (e.g., between hydroxyl, amine, carboxyl, thiol and/or similar functional groups, for example), a dative bond (e.g., complexation or chelation between metal ions and monodentate or multidentate ligands), or the like.
  • the interaction may also comprise Van der Waals interactions.
  • the interaction comprises forming a covalent bond with an analyte.
  • the functional group may also interact with an analyte via a binding event between pairs of biological molecules.
  • the functional group may comprise an entity, such as biotin that specifically binds to a complementary entity, such as avidin or streptavidin, on a target analyte.
  • Such interactions with an analyte may cause the nanostructure to have a detectable change in property (e.g., optical scattering, color, or size) that can allow the detection of the interaction.
  • the analyte may be a chemical or biological analyte.
  • the term "analyte,” may refer to any chemical, biochemical, or biological entity (e.g., a molecule) to be analyzed.
  • nanostructures of the invention may have high specificity for the analyte, and may be, e.g., a chemical, biological, explosives sensor, or a small organic bioactive agent (e.g., a drug, agent of war, herbicide, pesticide, etc.).
  • a nanostructure may comprise a functional group that acts as a binding site for an analyte.
  • the binding site may comprise a biological or a chemical molecule able to bind to another biological or chemical molecule in a medium, e.g., in solution.
  • the binding site may be capable of biologically binding an analyte via an interaction that occurs between pairs of biological molecules including proteins, nucleic acids, glycoproteins, carbohydrates, hormones, and the like.
  • an antibody/peptide pair an antibody/antigen pair, an antibody fragment/antigen pair, an antibody/antigen fragment pair, an antibody fragment/antigen fragment pair, an antibody/hapten pair, an enzyme/substrate pair, an enzyme/inhibitor pair, an enzyme/cofactor pair, a protein/substrate pair, a nucleic acid/nucleic acid pair, a protein/nucleic acid pair, a peptide/peptide pair, a protein/protein pair, a small molecule/protein pair, a glutathione/GST pair, an anti-GFP/GFP fusion protein pair, a Myc/Max pair, a maltose/maltose binding protein pair, a carbohydrate/protein pair, a carbohydrate derivative/protein pair, a metal binding tag/metal/chelate, a peptide tag/metal ion-metal chelate pair, a peptide/NTA pair, a lectin/carbohydrate pair,
  • the nanostructures may be used in applications such as drug discovery, the isolation or purification of certain compounds, and/or implemented in assays or high-throughput screening techniques (e.g., sensing arrays).
  • nanostructures can be positioned in association with a plurality of other components to form a functional component of a functional device.
  • a nanostructure e.g., a carbon nanowire or a semi-conductive polymer nanowire
  • a biomolecule e.g., biotin
  • the nanostructure may be positioned on a surface proximate a source and a drain to form a field-effect transistor. Detection of the analyte may be measured by the difference in current flowing across the nanostructure when the nanostructure is exposed to the analyte and in the absence of the analyte.
  • Patterned arrays of nanostructures described herein can also have applications in nanopho tonics.
  • such' structures may be used to form negative index of refraction materials (NIMs), frequency-selective surfaces (FSS), infrared optical polarizers, and nanostructures for surface-enhanced Raman spectroscopy.
  • NIMs negative index of refraction materials
  • FSS frequency-selective surfaces
  • infrared optical polarizers infrared optical polarizers
  • nanostructures for surface-enhanced Raman spectroscopy for surface-enhanced Raman spectroscopy.
  • Frequency-selective surfaces are two-dimensional periodic arrays of structure (e.g., metallic structures) that transmit or reflect radiation at specific frequencies.
  • FSS are useful in, for example, beam-splitters, filters, and polarizers.
  • the reflection or transmission is strongest when the wavelength of the incident electromagnetic field resonates with the metallic structures comprising the FSS.
  • This resonant frequency is mainly determined by the size and shape of the unit elements of the FSS, while the bandwidth of resonance— as well as total reflectivity or transmittance— depend on density and periodicity of unit elements.
  • n.ffl (1) is resonance wavelength
  • the wire is approximated as a simple electric dipole.
  • L becomes the tip to tip distance for the half wavelength resonance condition.
  • high order or harmonic resonances at shorter wavelength for example, ⁇ r /2
  • ⁇ r /2 can also be excited in open loop nanostructures even at normal incidence with proper polarization of incident light. Accordingly, harmonic modes in L-shaped and U-shaped structures can be observed.
  • nanostructures e.g., arrays of nanostructures that may be isolated and/or embedded in a material
  • a FSS can couple to incident light magnetically if it includes, for example, open loop nanostructures such as split-ring and/or U-shaped structures, because the magnetic field perpendicular to the plane of the nanostructures can induce circulating electrical current in them.
  • U-shaped metallic structures may have a magnetic resonance at infrared wavelengths.
  • nanostructures described herein are used to form negative index of refraction materials.
  • NIMs can be formed by, for example, assembling a first set of nanostructures having a negative permittivity adjacent a second set of structures having a negative permeability.
  • the first and second sets of nanostructures may be positioned such that they are not in direct physical contact with one another (e.g., such that a current cannot substantially pass from one a nanostructure of the first set to a nanostructure of the second set).
  • the first and second sets of nanostructures are separated from each other by a dielectric film.
  • nanostructures e.g., open loop nanostructures
  • the open loop nanostructures and thin wire structures may each be conductive (e.g., formed of a conductive material such as gold), and a dielectric material such as a thin film polymer or ceramic may be positioned between the two structures.
  • the dielectric material may be chosen such that it does not interfere with (e.g., absorb) the wavelength of interest.
  • the particular encapsulating material may also be chosen such that is does not interfere with the wavelength of interest.
  • U-shaped nanostructures and nanowires are used to form a negative index material.
  • U-shaped nanostructures may be a simplified version of an initial split-ring structure for the construction of materials with negative index.
  • the fundamental mode of the U-shaped nanostructure can magnetically couple to the incident field, since a magnetic field normal to the U plane will induce the same current pattern shown in FIG. 14D.
  • a composite structure may have a negative index of refraction as it combines split-ring structures (e.g., a U-shaped nanostructure having negative permittivity) with metal wire structures (e.g., a straight-wire shaped nanostructure having negative permeability). Due to the size scale of these nanostructures, this composite structure may be selective towards wavelengths in the infrared region.
  • These structures can be used as, for example, optical filters. In certain embodiments, as the wavelength of interest enters the mid-infrared
  • the sizes of features (of the nanostructures) necessary for functional FSS may be on the order of the wavelength of light (Eq. 1).
  • methods of fabricating patterned (e.g., metallic) nanostructures described herein can be used.
  • a composite structure comprising nanostructures described herein are selective towards wavelengths in the mid-infrared region (MIR) (e.g., 4-20 ⁇ m), near-infrared (NIR) region (e.g., 0.8-4 ⁇ m), or the visible region (e.g., 0.8-0.4 ⁇ m).
  • MIR mid-infrared region
  • NIR near-infrared
  • visible region e.g., 0.8-0.4 ⁇ m
  • three dimensional FSS and/or NIM can be formed using nanostructures described herein.
  • nanostructures are positioned on surfaces having multiple faces, e.g., a cube, as well as curved surfaces, such as a cylinder.
  • Nanowires can be fabricated according to the scheme illustrated in FIG. 1.
  • a thin layer (-500 nm) of positive photoresist (Shipley 1805, www.microchem.com) was spin- coated at 4000 rpm for 40 s on a Si/SiO 2 substrate ( ⁇ 100 >, N/phosphorus or P/boron doped, 1-10-cm, from Silicon Sense; Nashua, NH) and baked on a hotplate at 115 0 C for 5 min.
  • This layer of photoresist was exposed through a chrome mask patterned with 2- ⁇ m lines spaced by 2 ⁇ m in a Karl Suss mask aligner with a UV-light source (365-405 nm) to generate lines of photoresist after development (CD-26, www.microchem.com).
  • a gold film with thickness between 10 and 40 nm on this patterned substrate using e-beam evaporation the photoresist was removed by lift-off using acetone.
  • a layer of an Araldite-based epoxy prepolymer ( ⁇ 500 ⁇ m) was coated on this substrate and cured at 60 0 C overnight.
  • the epoxy was purchased from Electron Microscope Science (Araldite 502 kit; Fort Washington, PA). The epoxy was prepared by mixing different components included in a kit in the following amounts: 5 mL of diglycidyl ether of bisphenol-A
  • the epoxy block containing the embedded metal film was trimmed with a razor blade to an area of -0.5 mmx 0.5 mm with the aid of microscope; the trimming exposed the metal layer.
  • Thin epoxy film sections were sliced from the sample using a microtome with a diamond knife, with water in the sample-collecting boat (Ultracut microtome, Leica MZ6). The sectioning speed was set at 1 mm/s.
  • the thin, sectioned polymer sections containing embedded metal nanowires floated on the surface of water.
  • a solid substrate e.g., a TEM grid or a silicon wafer
  • the film was picked up in a drop of water with a loop ( ⁇ 2 mm in diameter) and deposited on a solid substrate.
  • the epoxy component of a section transferred to a solid substrate was removed with oxygen plasma (250 mTorr, 70 w barrel etcher) by exposing for 300 s. Gold nanowires were left on the substrate, as shown in FIG. 2.
  • FIG. 2 shows SEM images of typical free-standing gold nanowires viewed in an angle.
  • FIG. 2A shows gold nanowires with dimensions of ⁇ 2 ⁇ m (length) by 40 nm (width) by 50 nm (height).
  • FIG. 2B shows gold nanowires with dimensions of ⁇ 2 ⁇ m (length) by 10 nm (width) by 100 nm (height); these nano wires had a high aspect ratio of 10:1.
  • the insets show high magnification images of the same samples.
  • the orientations of FIG. 2A and 2B were at a 45° oblique angle.
  • the SEM images were obtained using a LEO 982 SEM operating at 2 kV.
  • This example illustrates a method of fabricating isolated structures such as nanowires according to certain embodiments of the invention.
  • This example also shows that nanostructures having high aspect ratios (e.g., 10:1) can be fabricated with well- controlled dimensions using such a method.
  • This example illustrates a method of fabricating isolated structures such as nanorings according to certain embodiments of the invention.
  • Nanorings can be fabricated according to the scheme illustrated in FIG. 3.
  • a poly(dimethyl siloxane) (PDMS) mold having desired features e.g., the negative of the structures used to form the nanorings
  • desired features e.g., the negative of the structures used to form the nanorings
  • the SU8 substrate can be patterned with desired features (e.g., the positive of the structures used to form the nanorings) which can be fabricated by conventional photolithography using standard procedures for soft- lithography.
  • a 2- ⁇ m-thick layer of SU8 photoresist (SU8-5 purchased from MicroChem Corp.; Newton, MA) film can be coated on a silicon wafer ( ⁇ 100>, N/phosphorus or P/boron doped, 1-10 ⁇ -cm, from Silicon Sense; Nashua, NH) by spin- coating the prepolymer at 3000 rpm for 30s.
  • the films of SU8 can be patterned by photolithography.
  • the patterned surface can be coated with a release layer (e.g., using Tridecafluoro-tetrahyrooctyl-trichorosilane from United Chem. Tech; Bristol, PA), and molded with PDMS (Dow Coming's Sylgard 184 kit, mixing catalyst and prepolymer in a ratio of 1 :10).
  • the PDMS mold can be replicated into an Araldite-based epoxy by molding the epoxy precursor against the PDMS master on a 15 nm thick silver coated silicon substrate. This silver layer was used to facilitate the lift-off of the epoxy from the silicon substrate due to its poor adhesion with silicon substrate.
  • the epoxy was cured at 60 0 C for 12 h.
  • the epoxy which was composed of a diglycidyl ether of bisphenol-A (isopropylidenediphenol), was purchased from Electron Microscope Science (Araldite 502 kit; Fort Washington, PA).
  • the epoxy was prepared by the mixing different components included in a kit in the following amounts: 5 mL of diglycidyl ether of bisphenol-A (isopropylidenediphenol) (Araldite 502), 5.5 mL of dodecenyl succinic anhydride (DDSA), and 0.3 mL of benzyldimethylamine (BDMA).
  • the epoxy was coated directly with a gold film by sputtering.
  • the epoxy slab comprising the gold film was trimmed with a razor blade to an area of -0.2 mmx 0.2 mm.
  • the patterned plane was aligned parallel to the edge of a diamond knife with the aid of microscopy so that the sample could be cut uniformly.
  • Thin epoxy film sections of the sample were sliced using a microtome (Ultra microtome, Leica RM2165) with water filling in the sample-collecting boat of the diamond knife (DiatomeTM, Ultra 35°).
  • the sectioning speed was set at 1 ⁇ m/s with a selected section thickness, which can be precisely controlled by the instrument.
  • a solid substrate e.g., a TEM grid or silicon wafer
  • the polymer film can be picked up in a drop of water with a loop ( ⁇ 2 mm in diameter) and deposited onto the substrate.
  • the epoxy sections that were transferred onto a solid substrate were removed with oxygen plasma (250 mTorr, 70 w barrel etcher) for 300 s.
  • Gold nanorings were left on the substrate, as shown in FIG. 4.
  • FIGS. 4 A and 4B show SEM images of patterned isolated gold nanorings on a silicon substrate after removing the epoxy with oxygen plasma.
  • FIG. 4B shows a high magnification SEM image of the structures shown in FIG. 4A. SEM images were obtained using a LEO 982 SEM operating at 2 kV. This example illustrates a method of fabricating isolated structures such as nanorings according to certain embodiments of the invention. This example also shows that nanostructures having different geometries can be fabricated with well-controlled dimensions using such a method. EXAMPLE 3
  • FIG.7A outlines an apparatus that can be used to record the scattering spectra of individual nanowires (e.g., nanowires shown in FIG. 2 fabricated using the method discussed in Example 1).
  • This dark-field illumination maximized the scattering from the nanoparticles, and minimized the background scattering from the substrate.
  • the collected light then passed through a polarizer parallel to the short axis of the nanowire (y direction) and focused on the plane of the entrance slit of a single- grating monograph (Triax 550, Jobin Yvon Horiba); this apparatus enabled video imaging of the nanowires and measurements of their spectrum.
  • the polarizer enabled selection of surface plasmon resonances with polarization traverse to the long axis of the wire.
  • An individual nanowire, or a small group of wires, could be selected for analysis by adjusting the width and height of the slit.
  • the as-obtained spectra depended on the spectrum of the incident white light, the focusing and collecting optics, and the response of the spectrometer.
  • the nanowire sample was replaced with a broad-band white-light target (which has a constant scattering response over wide range of frequencies) and its scattering spectrum was obtained using the same procedure.
  • the as-obtained spectrum of the nanowires was then normalize to the reference spectrum of the broad-band target.
  • FIG. 7B shows the normalized scattering spectra of four randomly selected nanowires in a single sample.
  • the scattering spectra of the four nanowires were displaced vertically to show reproducibility.
  • the nanowires measured were 2 ⁇ m long, 20 nm wide, and 50 nm high. This plot shows that the variation in position of the resonance peak among the nanowires was negligible.
  • the spectral variation between nanowires from separate cut portions of the same thickness was also negligible.
  • nanowires with different cross-sectional dimensions can have different optical properties.
  • the nanowires shown in FIG. 8 were fabricated using the method described in
  • Nanowires with different cross-sectional dimensions were fabricated by changing the thicknesses of the metal film deposited on the articles (e.g., to change the heights of the nanowires) and by changing the thickness of the cut portions (e.g., to change the widths of the nanowires).
  • the nanowires were all 2 ⁇ m long (x).
  • the dimensions of the cross-sections are marked in each figure by y and z (the thickness of gold film and the thickness of the cut portion, respectively). The sizes of nanowires appear larger than their actual dimensions, due to optical diffraction.
  • FIGS. 8A-8C show color, dark-field, optical images of nanowires with different cross-sections, obtained using a standard optical microscopic system with dark-field illumination (Nikon 43300-522 with CCD camera). All optical images were taken under the same conditions with polarization perpendicular to the long axis of the nanowires. For each set of wires with the same width (y), the color shows a red-shift with increasing height (z).
  • FIGS. 8D-8F show the scattering spectra of gold nanowires corresponding to those in FIGS. 8A-8C.
  • Emission spectra were collected simultaneously from four nanowires during each measurement in order to increase the signal-to-noise ratio, and to average the small spectral variation from wire to wire.
  • the spectrum shifts to longer wavelengths with increasing height (z) for the same set of wires with fixed width (y). This spectral observation agrees well with the optical color images.
  • nanowires with different cross-sectional dimensions fabricated using methods of the invention can have different optical properties.
  • Such nanowires may be useful for a number of applications, including surface-enhanced Raman scattering, subwavelength optical waveguiding, biolabeling, and biosensing.
  • the configuration of the simulation was similar to that of the experiment (e.g., as shown in FIG. 2A), except that in the simulation, the nanowire was suspended in air rather than supported on a substrate.
  • an incident exciting plane wave was launched at the same angle (60°).
  • the scattering amplitude at individual wavelengths was calculated, and the far- field scattered field was obtained.
  • FIGS. 9A-9C shows the results of these FDTD simulations.
  • the resonance peak shifted to a longer wavelength as the height increased.
  • the dimensions of the cross-section are marked in each figure by y and z. Simulations and experiments showed the same trend in the red shift of the spectra as the z/y ratio increased. Since the polarization of the incident field was at 60° with respect to z axis in the z-y plane, it excited two modes of surface plasmons, polarized along the z direction and the y direction, respectively. The total scattering spectrum arose from the plasmons excited by the z and y components of the incident electric field.
  • FIG. 9D plots the dependence of the wavelength of maximum plasmon scattering against the z/y aspect ratio of the nano wires for the experimental measurements and simulations.
  • Both the experimental data and the FDTD simulation showed a similar red shift when the aspect ratio of the cross-section of the nanowire increased.
  • the resonance peaks of the experimental data were, however, uniformly at longer wavelengths than those of the simulations. This discrepancy likely reflects the fact that the simulations assumed that the nanowires were suspended in air, rather than supported on a silicon substrate. Similar effects have been reported in the literature.
  • This example describes a procedure for fabricating closed-loop structures over large areas.
  • FIG. 10 shows an example of a scheme 200 for the fabrication of square closed- loop shaped nanostructures extending over large areas (e.g., ⁇ 9 mm 2 ).
  • epoxy substrates 210 patterned with ⁇ 2 x 2 ⁇ m square post features 216 were fabricated by casting epoxy prepolymer on a PDMS mold 218 using soft-lithographic procedures on a layer 220 (e.g., a 15-nm-thick film of gold) supported on a substrate 222 (e.g., test-grade silicon wafer with a top layer 224 of SiO 2 ).
  • the gold layer facilitates separation of epoxy from the Si/SiO 2 : gold adheres poorly to Si/SiO 2 in the absence of an adhesion- promoting layer such as Ti or Cr.
  • a gold film 226 (e.g., 40-nm thick) was deposited on selected sides of these square posts on the epoxy substrate using line of sight or shadow (angle) deposition by electron beam evaporation. Embedding the metal-coated epoxy substrate in more epoxy of the same kind generated an epoxy article 228 including the topographically structured thin gold film. At step 230, the epoxy article was peeled off from the silicon surface.
  • the epoxy article was trimmed into a smaller article 232 with an area of 2 mm by 1.5 mm with a razor blade, and this article was cut/sectioned in a plane parallel to the patterned surface (in the direction of arrows 236) using an ultramicrotome (Leica UCT) equipped with a diamond knife (Diatome, 45° knife angle).
  • the edge of the knife and face of the epoxy article must be carefully aligned in order to obtain articles of uniform thickness over a large area ( ⁇ 3 mm 2 ). Alignment requires several steps; a detailed procedure for microtome alignment is described in more detail below.
  • Cut/sectioned epoxy articles 240 were collected on the surface of water contained in the sample trough mounted to the backside of the diamond knife. These thin epoxy sectioned articles were transferred onto a solid substrate 244 (e.g., TEM grid or single crystal CaF 2 ) by submerging small sections of the substrate in the trough, and pulling it toward the surface in a way that allowed the floating polymer film containing the gold nanostructures to settle on it.
  • the adhesion between the gold nanostructures and the substrate was not very robust and in some cases, the nanostructures separated from the substrate on rinsing the surface with laboratory solvents.
  • the nanostructures can be stabilized on the surface by coating a thin film (e.g., -50 nm) of, for example, silicon dioxide or silicon nitride on the silicon substrate prior to transferring the sectioned article onto the substrate.
  • FIG. 1 IA is a digital image of the square loop-shaped nanostructures 248 formed by the method described above on a silicon (Si(IOO)) substrate patterned over a ⁇ 9 mm 2 area; this area 250 reflects the self-assembly of three individual epoxy slabs 252, 254, and 256 (each 3 mm 2 ) into an ordered rectangle.
  • FIG. 1 IB is a dark field optical microscopy image of the square-loop shaped nanostructures. The SEM images in FIG.
  • nanostructures 248 with a wall thickness of ⁇ 50-nm, and with 100-nm height. These two dimensions correspond to the thickness of the gold film deposited by e-beam evaporation, and of the thickness of the sectioned epoxy article generated by the microtome. The following materials were used to fabricate the nanostructures described above.
  • Araldite 502 epoxy was purchased from Electron Microscope Science (Fort Washington, PA).
  • the epoxy was prepared by mixing different components included in the kit in the following amounts: 5 mL of diglycidyl ether of bisphenol-A (isopropylidenediphenol) (Araldite 502), 5.5 mL of dodecenyl succinic anhydride (DDSA), and 0.3 mL of benzyldimethylamine (BDMA).
  • a number of substrates transparent in the mid-infrared were used to support arrays of both L-shaped and closed loop nanostructure arrays. The infrared permissive substrates were submerged in water during the sample (sectioned epoxy article) collection process and therefore was chosen based in part by its resistance to attack or dissolution by water.
  • Calcium fluoride (CaF 2 , Harrick Scientific, 19-mm diameter single-crystal disc, 2-mm thick) is slightly soluble in water and transmits light from 1.5 to 9 ⁇ m.
  • Zinc selenide Zinc selenide (ZnSe, International Crystal Laboratories, Garfield, NJ) is insoluble in water and transmits light from 0.6 to 16 ⁇ m.
  • KRS-5 thallium bromide iodide
  • the nanostructures were observed by SEM measurements using a LEO 982 SEM operating at 2 kV.
  • the following are a set of instructions that can be used to align an edge of a knife to a face of an epoxy article to obtain articles of uniform thickness over a large area ( ⁇ 3 mm 2 ). Correct alignment may be critical for obtaining high uniformity across a mm 2 area section.
  • the alignment of the microtome can require several steps.
  • top and bottom edges of the block are parallel to each other and to the knife edge, the shadow will appear across the entire width of the block at the lower edge and leave the top edge at the same time. 3. If the shadow appears on the lower edge at one side of the block before the other side, the edge of the block is not parallel to the knife.
  • FIG. 1 ID is an IR transmission spectrum of the closed loop nanostructures (shown by line 260). A single major resonant peak at 11 ⁇ m independent of the polarization of the incident infrared light, and with a transmittance at a wavelength of maximum scattering of 45%, was observed. In some cases involving FSS work, ⁇ r ⁇ rie ff C (eq.
  • each induced dipole also has an effective length / equal to C/2, which results the same resonance wavelength, ⁇ 11 ⁇ m.
  • two dipoles are induced by the electrical field; each dipole involves half of the total length of the loop; this equality explains why only a single resonance peak is observed, whose position is independent of the polarization of the incident light. In this explanation, the interaction between the two dipoles is neglected. This argument is applicable to FSS of a simple closed structures.
  • a Nicolet Fourier-transform infrared spectrometer in transmission mode was used to characterize the sample optically.
  • a piece of aluminum foil ( ⁇ 200 ⁇ m thick) with a punched hole directly in front of the sample was used to support the sample.
  • the small hole enabled the incident beam ( ⁇ 1 mm 2 diameter) to transmit through the substrate area with the nanostructure array thereby increasing the signal to noise ratio.
  • 128 scans with a resolution of 4 cm *1 were averaged.
  • a separate spectrum of the clean substrate was collected and subtracted from the spectrum of the FSS surface.
  • FDTD Finite-Difference Time-Domain
  • xfdtd back-scattering
  • R back-scattering
  • an incident Gaussian pulse excites the structure, and the back scattered electrical field in time domain was calculated.
  • the ratio of the power spectrum of scattered field to the power spectrum of the incident field yielded the scattering spectrum in frequency domain.
  • the reflectance spectrum for an FSS array is linearly proportional to a single unit with the constant of proportionality dependent on the density of unit structure, if the weak interaction between the units is neglected.
  • the reflectance spectra were plotted with y-axis values reversed and rescaled to match the experimentally measured transmittance spectra.
  • the objective of the simulation was not to provide absolute transmittance, but to confirm the main features of transmission spectrum, such as its resonance position, and its linewidth.
  • gold nanostructures were approximated by a wire with cross-section 50-nm wide * 100-nm height, as determined during fabrication.
  • the structures were approximated as an ideal rectangle, L or U (angle set to 90° for adjoining arms).
  • the dimensions for these structures in the simulation were set according to SEM measurements.
  • the n ⁇ is calculated from eq. 2; the n ⁇ -for ZnSe substrate is 1.8, the n ⁇ for CaF 2 is 1.2, and n ⁇ -l .2 for polymer.
  • open-loop nanostructures can be used to form frequency selective surfaces (FSS) that have resonances that are dependant upon the polarization of an electric field.
  • FSS frequency selective surfaces
  • the nanostructures may be supported by a substrate.
  • L-shaped open loop nanostructures were fabricated by modifying the metal deposition procedure of Example 6. Shadow evaporation from a single direction was used to coat two sides of a template of square epoxy posts selectively. In such a procedure, a single shadow evaporation with the sample mounted 60° from the plane for line-of-sight evaporation onto a single corner was used to generate L-shaped nanostructures. The U-shaped nanostructures were supported on CaF 2 substrate.
  • FIG. 12A is a dark-field optical microscopic image of L-shaped nanostructures 270 patterned over a ⁇ 3 mm 2 area after removal of the epoxy matrix, used as an encapsulating material, with an oxygen plasma. These nanostructures have a wall thickness of- 50-nm, and 100-nm height.
  • the spectrum exhibits two dominant transmission stop-bands 272 and 274 in the mid-infrared region centered at 8.4 ⁇ m and 4.8 ⁇ m, respectively, with maximum transmissions of 67% and 82%.
  • the L-shaped structure is less isotropic than a square structure with respect to excitations produced by polarized incident light.
  • linearly polarized light was used by inserting a broadband wire polarizer in the path of the incident beam.
  • the 8.4 ⁇ m long wavelength resonance is observed when the polarization of incident light is parallel to the line connecting the two ends of the L- structure, as shown in FIG. 12C (line 276).
  • FIG. 12D shows a single resonant peak at 4.8 ⁇ m (line 280) when the polarizer is rotated by 90° such that the polarization is now perpendicular to the diagonal line connecting the two ends of the L.
  • the inset diagram illustrates the polarization direction (arrows 284) and induced current flow (arrows 286) in the L-shaped nanostructure 288 for the two polarizations of the incident light.
  • FIG. 12C shows the first current pattern (fundamental mode, half wavelength resonance) oscillating between the two tips of the L when the E field points from one tip of the L to the other tip.
  • / in eq. (1) is the sum of the lengths of both arms of the L-shaped nanostructure. This current distribution is responsible for the 8.4- ⁇ m resonance.
  • FIG. 12D When the polarization of the incident light is perpendicular to the line connecting the two ends of the "L" (FIG. 12D), a relatively symmetric current pattern is induced, in which the "L” is effectively split into two antenna (two dipoles) oscillating in phase. The length for each dipole is about half of the total length. This current pattern is responsible for the 4.8 ⁇ m resonance.
  • This 4.8 ⁇ m resonance is the harmonic mode of 8.4 ⁇ m mode. With this polarization, only the 4.8 ⁇ m mode is excited, and the fundamental mode at 8.4 ⁇ m is suppressed. At any other arbitrary polarization, both modes will be excited.
  • FIG. 13 shows transmission spectra of the L shaped nanostructure with polarization parallel to either of the two arms.
  • open-loop nanostructures can be used to form frequency selective surfaces (FSS) that have resonances that are dependant upon the polarization of an electric field.
  • the nanostructures may be supported by the encapsulating (matrix) material used to embed the nanostructures, instead of a substrate.
  • U-shaped open loop nanostructures were fabricated by modifying the metal deposition procedure of Example 6. Shadow evaporation from multiple directions was used to coat three sides of a template of square epoxy posts selectively. In such a procedure, three consecutive shadow evaporations from three edges of the square template were used to generate U-shaped nanostructures.
  • the nanostructures were not positioned on a substrate after sectioning. Instead, the nanostructures were supported by the epoxy material between the nanostructures (i.e., epoxy matrix was not removed with an oxygen plasma after sectioning to form the article).
  • FIG. 14A is a bright field optical image of an epoxy article 289 (100 nm thick) including U-shaped nanostructures sitting on a hole ( ⁇ 1 mm diameter) in a copper sheet ( ⁇ 100 ⁇ m thick).
  • FIG. 14B is a dark field optical image of the array of U shaped nanostructures 290 of FIG. 14A in the epoxy matrix.
  • the inset is a high-magnification SEM image of a single U-shaped nanostructure with a wall thickness of- 50-nm, and 100-nm height.
  • the transmission spectra of this sample was measured directly (see FIG. 15) using a piece of epoxy film with same thickness as a reference to subtract out absorption features due to the epoxy. As shown in FIG. 14C, three distinct resonant peaks from this sample was observed in the mid-IR region at 5.15 ⁇ m, 6.5 ⁇ m, and 14.75 ⁇ m, respectively.
  • FIGs. 14D and 14E are transmission spectra of the U-shaped nanostructures with the polarization of the incident light parallel (FIG. 14D) or perpendicular (FIG. 14E) to the line connecting the two ends of the U.
  • the inset diagrams illustrate the polarization direction (arrows 292) and induced current flow (arrows 294) in the U-shaped nanostructure 296 for the two polarizations of the incident light.
  • the U-shaped nanostructure was not isotropic with respect to the polarization of incident light, and the observed number and location of the resonance was dependent on the polarization of the incident light.
  • the right inset of FIG. 14D shows the current distribution for the given polarization.
  • the length (used in eq. 1) for this dipole oscillation is the total length of the U.
  • the left inset of FIG. 14D is the current pattern responsible for the harmonic mode.
  • There are three dipole oscillators excited along the wire. The length of each oscillator is about the third of the total length; the resonant frequency is approximately three times higher than the resonant frequency of the fundamental dipole mode (i.e. half wavelength resonance).
  • the inset of FIG. 14E shows the current pattern when the E-field vector of the light is perpendicular to the open side. In this case, two symmetric dipoles are induced, and the length is half of the total length for each dipole.
  • FIG. 16A and 16B show the effect of choosing an unsuitable substrate for supporting certain nanostructures.
  • FIG. 16A shows an array of U-shaped nanostructures supported on a CaF 2 substrate.
  • FIG. 16B is a transmission spectrum of the nanostructures of FIG. 16A. As shown in FIG. 16B, two strong resonant peaks from 2- 10 ⁇ m (5.25 ⁇ m and 6.75 ⁇ m, respectively). Eq. 1 indicates that one should observe the fundamental mode (longest wavelength resonance) at ⁇ >10 ⁇ m when 1 is defined as the total length of U ( ⁇ 6 ⁇ m).
  • these particular nanostructures may be prepared in the absence of a substrate by maintaining the matrix between the nanostructures.
  • Example 8 The procedure described in Example 8 was used to fabricate an array of U-shaped nanostructures embedded in an epoxy.
  • the U-shaped nanostructures had a wall thickness of- 50-nm, and a 100-nm height.
  • a block of epoxy that did not contain nanostructures was then sectioned to a thickness of 150 ran.
  • This sectioned epoxy article was positioned on top of the array of U-shaped nanostructures, and this combined article was used as a substrate for depositing an array of metal nanowires.
  • the metal nanowires were formed using the procedure described in Example 1, except the wires were continuous along one axis.
  • FIG. 17A shows the nanostuctures fabricated over a large area (greater than 1 mm 2 ).
  • FIG. 17B shows a magnified view of the structure of FIG. 17A.
  • the composite structures includes U-shaped nanostructures 324 embedded in epoxy. Positioned on top of the U-shaped nanostructures are parallel gold nanowires 328, having a width of 40 nm and a height of 50 nm.
  • a reference to "A and/or B", when used in conjunction with open-ended language such as “comprising” can refer, in one embodiment, to A only (optionally including elements other than B); in another embodiment, to B only (optionally including elements other than A); in yet another embodiment, to both A and B (optionally including other elements); etc.
  • At least one of A and B can refer, in one embodiment, to at least one, optionally including more than one, A, with no B present (and optionally including elements other than B); in another embodiment, to at least one, optionally including more than one, B, with no A present (and optionally including elements other than A); in yet another embodiment, to at least one, optionally including more than one, A, and at least one, optionally including more than one, B (and optionally including other elements); etc.

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Abstract

L'invention concerne des procédés servant à fabriquer des nanostructures et des articles associés à celles-ci. Dans certains modes de réalisation, une nanostructure isolée (par exemple, un nanocâble métallique) ou un ensemble de nanostructures peut être fabriqué par dépôt d'une matière (par exemple, un métal) sur une surface ayant une pluralité de saillies ou d'indentations. Au moins une partie de la matière déposée peut être incorporée dans une matière d'encapsulation, et la matière d'encapsulation peut être découpée, par exemple, pour former une tranche mince comprenant la matière déposée au moins partiellement incorporée dans celle-ci. Dans certains cas, la tranche peut être positionnée sur une surface dans une configuration désirée. La matière d'encapsulation peut être retirée de la surface pour former une ou plusieurs nanostructures isolées de la matière déposée. Avantageusement, les dimensions des nanostructures peuvent être contrôlées, par exemple, à 15 passes, pour former des nanostructures ayant une diversité de formes et de géométries (par exemple, câbles, anneaux, et cylindres). Les nanostructures peuvent également être formées dans une diversité de matières, comprenant des métaux, des céramiques, et des polymères. De plus, des nanostructures peuvent également être fabriquées sur des surfaces importantes (par exemple, supérieure à 1 mm2). Dans certains cas, ces nanostructures sont positionnées en association avec d'autres composants, par exemple, pour former un composant fonctionnel d'un dispositif.
PCT/US2007/007101 2006-03-22 2007-03-22 Fabrication de nanostructures isolées et/ou d'ensembles de nanostructures Ceased WO2008018923A2 (fr)

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US20090061170A1 (en) * 2007-09-03 2009-03-05 Tokyo Ohka Kogyo Co., Ltd. Anisotropic film and method of manufacturing anisotropic film
EP2144297A1 (fr) * 2008-07-07 2010-01-13 Technische Universiteit Delft Dispositif solaire et procédé de génération d'électricité
KR101378117B1 (ko) 2012-06-26 2014-03-26 인텔렉추얼디스커버리 주식회사 나노링 어레이를 사용한 표면증강 라만산란법 기반 바이오센서 및 그 제조 방법
WO2014022330A3 (fr) * 2012-07-31 2014-03-27 Northwestern University Nanofeuilles dispersibles pour spectrométrie laser de l'effet raman exalté de surface
WO2014028380A3 (fr) * 2012-08-13 2014-05-08 President And Fellows Of Harvard College Imagerie multispectrale utilisant des nanofils de silicium
WO2014179891A1 (fr) * 2013-05-09 2014-11-13 Idit Technologies Corp. Optique diffractive de réseaux de nano-structures pour un affichage de mouvements et d'animations
DE102013017018A1 (de) * 2013-10-14 2015-04-16 Siegert Thinfilm Technology Gmbh Verfahren zum Herstellen einer Struktur sowie insbesondere eine nach diesem Verfahren hergestellte Struktur
US9631291B2 (en) 2013-01-29 2017-04-25 Hewlett-Packard Development Company, L.P. Controlling dimensions of nanowires
CN111948267A (zh) * 2020-08-20 2020-11-17 哈尔滨工业大学 一种利用超长纳米线制备电化学纳米点阵列电极的方法
US11198314B2 (en) 2013-05-10 2021-12-14 Nanotech Security Corp. Nanostructure array diffractive optics for RGB and CMYK color displays
US12174530B1 (en) * 2016-10-21 2024-12-24 Iowa State University Research Foundation, Inc. Nano-patterning methods including: (1) patterning of nanophotonic structures at optical fiber tip for refractive index sensing and (2) plasmonic crystal incorporating graphene oxide gas sensor for detection of volatile organic compounds
WO2025022240A3 (fr) * 2023-07-21 2025-03-20 3M Innovative Properties Company Substrat nanostructuré, chimiquement différencié et sans film appliqué sur un substrat rigide

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US6902807B1 (en) * 2002-09-13 2005-06-07 Flex Products, Inc. Alignable diffractive pigment flakes
JP4719464B2 (ja) * 2002-05-08 2011-07-06 エージェンシー フォー サイエンス，テクノロジー アンド リサーチ マイクロ／ナノ構造を基板上にインプリントする方法

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20090061170A1 (en) * 2007-09-03 2009-03-05 Tokyo Ohka Kogyo Co., Ltd. Anisotropic film and method of manufacturing anisotropic film
EP2144297A1 (fr) * 2008-07-07 2010-01-13 Technische Universiteit Delft Dispositif solaire et procédé de génération d'électricité
KR101378117B1 (ko) 2012-06-26 2014-03-26 인텔렉추얼디스커버리 주식회사 나노링 어레이를 사용한 표면증강 라만산란법 기반 바이오센서 및 그 제조 방법
WO2014022330A3 (fr) * 2012-07-31 2014-03-27 Northwestern University Nanofeuilles dispersibles pour spectrométrie laser de l'effet raman exalté de surface
WO2014028380A3 (fr) * 2012-08-13 2014-05-08 President And Fellows Of Harvard College Imagerie multispectrale utilisant des nanofils de silicium
CN104969000A (zh) * 2012-08-13 2015-10-07 哈佛大学校长及研究员协会 使用硅纳米线的多光谱成像
US9631291B2 (en) 2013-01-29 2017-04-25 Hewlett-Packard Development Company, L.P. Controlling dimensions of nanowires
WO2014179891A1 (fr) * 2013-05-09 2014-11-13 Idit Technologies Corp. Optique diffractive de réseaux de nano-structures pour un affichage de mouvements et d'animations
US11198314B2 (en) 2013-05-10 2021-12-14 Nanotech Security Corp. Nanostructure array diffractive optics for RGB and CMYK color displays
DE102013017018A1 (de) * 2013-10-14 2015-04-16 Siegert Thinfilm Technology Gmbh Verfahren zum Herstellen einer Struktur sowie insbesondere eine nach diesem Verfahren hergestellte Struktur
US12174530B1 (en) * 2016-10-21 2024-12-24 Iowa State University Research Foundation, Inc. Nano-patterning methods including: (1) patterning of nanophotonic structures at optical fiber tip for refractive index sensing and (2) plasmonic crystal incorporating graphene oxide gas sensor for detection of volatile organic compounds
CN111948267A (zh) * 2020-08-20 2020-11-17 哈尔滨工业大学 一种利用超长纳米线制备电化学纳米点阵列电极的方法
CN111948267B (zh) * 2020-08-20 2023-07-18 哈尔滨工业大学 一种利用超长纳米线制备电化学纳米点阵列电极的方法
WO2025022240A3 (fr) * 2023-07-21 2025-03-20 3M Innovative Properties Company Substrat nanostructuré, chimiquement différencié et sans film appliqué sur un substrat rigide

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