WO2010102103A1

WO2010102103A1 - Production and use of indium/indium oxide nanostructures

Info

Publication number: WO2010102103A1
Application number: PCT/US2010/026204
Authority: WO
Inventors: Nicholas John Edgington; Thomas Ellsworth Mcwhorter
Original assignee: Quantum Confined Ltd
Current assignee: Quantum Confined Ltd
Priority date: 2009-03-04
Filing date: 2010-03-04
Publication date: 2010-09-10
Anticipated expiration: 2011-09-04

Abstract

An electrical device using metal nanocones and a method for handling nanocones. The electrical device includes a conductive element having a metallic spherical section, a metallic conical section integrally connected to the spherical end, and a tip section integrally connected to the conical section and narrowing in width as the tip section extends from the conical section. The electrical device includes a first electrode connected to the metallic spherical section, a second electrode disposed proximate the tip section, and a gate electrode applying an electric field to the metallic conical section and the tip section. The method includes filling a first surface containing nanocones with a polymerizable medium, polymerizing the medium to encapsulate the nanocones in the medium, and removing the polymerized medium from the first surface.

Description

TITLE OF THE INVENTION

PRODUCTION AND USE OF INDIUM/INDIUM OXIDE NANOSTRUCTURES

BACKGROUND OF THE INVENTION

Field of Invention

The invention relates to methods and systems for producing indium/indium oxide nano-structures.

Discussion of the Background

Indium is a soft metal with an atomic weight of 114.82 grams per mole and three electrons in its outer shell. Its melting point is 156.6 ⁰C. The boiling point of indium is 2072 ⁰C. Indium is electrically conductive and is increasingly used to replace lead for soldering because of its low melting point and its non-toxic nature. Indium Oxide (Ln₂O₃) is a ceramic material that is electrically insulating. It is formed by the reaction of indium metal and oxygen, typically at a high temperature, since indium resists oxidation under normal ambient conditions.

A "nano-structure" is a structure formed of one or more elements with at least one dimension that is approximately 1000 nanometers ("nm") or smaller, and can in some examples be on the order of the dimension of a few atoms. The behavior of nanostructures is often radically different from the behavior of larger structures of the same materials due to quantum confinement effects. Changes in the behavior of nanostructures are especially prevalent in the electrical, electromagnetic and optical properties as the scale of the nanostructures decreases to 100 nm or less. When energy in the form of light, an electrical current, or mechanical stress is added to certain types of semiconductor materials, the electrons in the valence band can be excited and raised to a higher energy level in a conduction band. When these electrons are moved into the conduction band, a "hole" in the valence band is left behind. The physical distance between the electron and the hole is referred to in the art as the "exciton Bohr radius." If any of the dimensions of a semiconductor nanostructure are approximately equal to or smaller than the exciton Bohr radius of the material, the nanostructure is considered to be a quantum confined structure. As noted above, quantum confined materials exhibit different behavior than bulk materials in many respects.

Many concepts have been proposed for development of future generations of ultra- fast, ultra-small computers involving nanoelectronics. One component of many proposed nanoelectronic circuits is a single electron transistor. Figure 1 shows an example of a single electron transistor built in Bell Laboratories in 1987. Components of this device include a Coulomb island, an electrode and a counter electrode isolated from each other by one or more insulating barriers, and a gate electrode. The gate electrode in Figure 1 is offset from the Coulomb island by a small gap. The gate electrode controls an amount of charge introduced to the Coulomb island. Electric current flows through the device from the electrode to the counter-electrode as in a conventional circuit, but here in the single electron transistor, the current is limited by the stepwise hopping of electrons onto and off of the Coulomb island. This design in Figure 1 is a 2-dimensional design wherein structural elements (sometimes overlapping) are all in essentially the same plane.

SUMMARY OF THE INVENTION

The invention overcomes the problems and disadvantages of prior work as described in the various embodiments below.

In one embodiment of the invention, there is provided a metal nanostructure including a metallic spherical section, a metallic conical section integrally connected to the spherical end, and a tip section integrally connected to the conical section and narrowing in width as the tip section extends from the conical section.

In one embodiment of the invention, there is provided a method for making the metal nanostructure. The method includes providing a source of metal to a reactor having an oxide susceptor; exposing the metal and the oxide susceptor to a plasma, and forming the metallic nanostructures on the oxide susceptor during the plasma exposing.

In one embodiment of the invention, there is provided a system for producing metallic nanostructures. The system includes a reactor chamber configured to be exhausted and purged, an oxide susceptor inside or integral with a wall of the reactor chamber, a metal source configured to provide a source of metal inside the reactor chamber for growth of the metallic nanostructures, a heating device configured to heat at least one of the metal and susceptor, and a plasma discharge device configured to generate a plasma in the reactor in proximity to the susceptor.

In one embodiment of the invention, there is provided an electrical device having 1) a conductive element including a metallic spherical section, a metallic conical section integrally connected to the spherical end, and a tip section integrally connected to the conical section and narrowing in width as the tip section extends from the conical section, 2) a first electrode connected to the metallic spherical section, 3) a second electrode disposed proximate the tip section, and 4) a gate electrode applying an electric field to at least the tip section.

In one embodiment of the invention, there is provided a method for handling nanocones. The method includes filling a first surface containing nanocones with a polymerizable medium, polymerizing the medium to encapsulate the nanocones in the medium, and removing the polymerized medium from the first surface. It is to be understood that both the foregoing general description of the invention and the following detailed description are exemplary, but are not restrictive of the invention.

BRIEF DESCRIPTION OF THE FIGURES A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:

Figure 1 is a schematic of one example of a known single electron transistor; Figure 2 is an electron microscope photograph of a nanocone of the present invention;

Figure 3 is a schematic showing a system for producing nanocones of the present invention;

Figure 4 is a schematic depicting one embodiment of the nanocone formation process of the present invention; Figure 5 is a schematic illustrating another system for producing nanocones of the present invention; and

Figure 6 is a schematic of one embodiment of a nanocone-based device of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is for the production and use of cone-and-sphere nanostructures including indium metal cores and a monatomic layer of indium oxide coating the outer surface ("nanocones"). Referring now to the drawings, wherein like reference numerals designate identical, or corresponding parts throughout the several views, one preferred embodiment of the present invention, as represented in Figure 2, Figure 2 is an electron microscope photograph of one nanocone of the present invention. Figure 2 shows the tip, metal cone, and metal sphere elements of the nanocones of the present invention. Analysis of the resulting structure shows a core of indium metal with a monatomic layer of indium oxide (In₂O₃) coating the outer surface. An indium oxide layer exists especially on the surface of the metal tip and cone. An oxide layer also usually exists on the outside of the sphere.

Figure 3 is a schematic showing a system for producing nanocones of the present invention. Accordingly, in one embodiment of the present invention, nanocones are prepared in a quartz tube. In the configuration shown in Figure 3, two electrodes are clamped to the outside of the quartz tube. The electrodes in this example are about 200 mm apart. A small piece of indium metal (e.g., about 2 milligrams) is positioned inside the tube and in this example midway between the two electrodes. As shown in Figure 3, a vacuum pump attached to one end of the tube evacuates the quartz tube. The pressure is maintained inside the tube by a metered supply of 1-2% helium in nitrogen. For example, the tube can be evacuated to a pressure of 60-70 milliTorr and then backfilled up to about 2 Torr with the 1- 2% helium in nitrogen purge. Further, a helium/nitrogen purge flow through the tube at a rate of about 1-2 lpm can yield a pressure in the tube was of 1 -2 Torr.

For formation of the indium nanocones of the present invention, a portion of the tube near the indium metal was heated from the outside to a temperature of about 1000-1500 ⁰C using in this example an oxy/propane flame, and 30,000 V DC was applied across the electrodes to generate a plasma arc inside the quartz tube. The plasma arc appeared blue in color, due to the presence of indium in the plasma. The voltage (and thus the plasma arc) was maintained until the blue color disappeared, then continued for about an additional 30 minutes, before the plasma arc was terminated. The quartz capillary tube was found to contain indium/indium-oxide nanocones. While described in this example with regard to the formation of indium/indium-oxide nanocones, other metals besides indium or along with indium could be used. Such as for example, in one embodiment of the present invention, the cones can be formed from sources of Sn, Zn, and/or Al. Sn for example has a boiling point of 2600 °C, slightly higher than In. Sn has a melting point of 232 ⁰C, slightly higher than In. Accordingly, it is expected that the reactor temperatures given above as 1000-1500 ⁰C for In would be approximately that needed for Sn nanocone formation. Zn for example has a boiling point of 907 °C, substantially lower than In. However, Zn has a melting point of 419 ⁰C, slightly higher than In. Accordingly, it is expected that the reactor temperatures given above as 1000-1500 ⁰C for In would be significantly reduced for the formation of Zn nanocones. Al for example has a boiling point of 2467 ⁰C, higher than In. Al has a melting point of 660 °C, higher than In. Accordingly, it is expected that the reactor temperatures given above as 1000-1500 ⁰C for In would be approximately that needed for Al nanocone formation.

In particular, indium/indium-oxide nanocones (using the formation process described above) were found to be present in a coating on the inside of the quartz tube which also contained fine silicon particles. The indium/indium-oxide nanocones typically were found with their narrower ends attached to the inner wall of the quartz tube, and thus having a long axis of the cone perpendicular to the tube wall. Nanocones as collected from the inner sides of the quartz tube were typically randomly oriented. In one manufacturing embodiment of the present invention, a molten thermoplastic or liquid self-curing polymeric material such as polyimide is cast as a film across a surface where the nanocones have been formed. The polymer is hardened and then peeled from the surface with the nanocones becoming embedded in a polymer sheet. This approach is expected to cause much less breakage of cones and is expected to maintain the cones in a uniform orientation, which is advantageous for many applications. Figure 4 is a schematic depicting one embodiment of the nanocone formation process of the present invention. The theory for nanocone formation presented here is not provided to limit the invention but rather is described here to provide an illustrative teaching of how the indium/indium-oxide nanocones of the present invention are formed when indium vapor or ions are condensed at discrete points on the quartz tube wall. Oxygen atoms in the quartz tube provide a diffusion limited source of oxygen to the condensed indium. In particular, oxygen atoms in the quartz tube evolve from electrical or thermal breakdown of the quartz (Figure 4A). In this model, oxygen reacts with the outer surface of the indium starting at the sides of the condensed indium. The oxide forms a barrier to further indium deposition, so subsequent indium deposition continues on the end of the growing structure which is most distant from the quartz wall. As more and more indium is deposited, the structure grows in length (Figures 4B and 4C), since the indium metal is deposited on the unoxidized distal end of the cone. As the structure grows, the area where unoxidized indium is deposited becomes farther and farther away from the quartz source of oxygen, so the ratio of the rate of deposition of indium to the rate of surface oxidation becomes greater and greater. Therefore, the indium/indium oxide nanocone structure increases in diameter as it grows from the tube wall. Eventually, the rate of indium deposition increasingly outpaces the rate at which the surface can oxidize, and a spherical "snow ball" of indium metal is formed (Figure 4D). While exact details are not known, there may also be an electrical phenomenon present in the cone formation as positively charged indium ions attracted to the end of the cone may cause the cone to become positively charged. The positive charging may cause oxygen atoms to be released from the surface of the quartz and to flow along the surface of the cone.

In various manufacturing processes of the present invention, nanocones are produced in reactors having different geometrical configurations. In general, these reactors provide 1) an indium supply (e.g., an indium source and a high temperature heating region to vaporize the indium or alternatively a gaseous source of indium could be provided), 2) a high temperature reaction zone, 3) a condensation point upon which the vapor-phase indium can condense, 4) a limited supply of oxygen to the base of the growing indium, and optionally 5) a plasma source. In the example above, vaporized indium provided the gas phase indium source.

However, in other embodiments, a metal organic carrier gas could be used such as trimethyl- indium for the source of indium. Other metal organic carrier gasses such as for example triisopropyl-indium could also be used. These chemicals under appropriate conditions, where for example the organic components of the metal organic are not substantially incorporated into the cones, can be used in one embodiment of the invention. In the example above, an external flame was used to heat the indium inside the quartz tube. However, in other embodiments, the indium metal could be heated using an infrared heater, laser heating, electrical induction heater, electrical resistance heater or other devices for heating the indium and the gas inside the reactor. In the example above, the quartz material provided the limited supply of oxygen to the base of the growing nanocone. However, in other embodiments, other solid sources of oxygen such as thermally grown silicon dioxide on silicon, vapor deposited or sputter deposited silicon dioxide pads could be used. Moreover, other solid sources of oxygen such as borosilicate glass could be used in applications where the purity of the resultant indium/indium-oxide nanocones was not considered as critical or where lower formation temperatures were desired.

Figure 5 is a schematic illustrating another system for producing nanocones of the present invention. In one embodiment of the present invention, a susceptor (e.g., a quartz plate) is used in the high temperature reaction zone to provide a plurality of sites for nanocone formation. The susceptor could be placed horizontally in a chamber containing the 1-2% helium in nitrogen gas at 1-2 Torr. The plasma arc would be maintained across the surface of the susceptor. The susceptor could contain the indium metal source, or a separate plate could locate the indium metal source in the high temperature reaction zone. In this embodiment, nanocones would be formed on the susceptor (e.g., a flat quartz plate surface) for subsequent collection therefrom. In this embodiment, one would be able to collect nanocones without the need to break the quartz reactor tube.

There are many potential uses for the indium/indium-oxide nanocones of the present invention. The indium/indium-oxide nanocones can be used as a component of single electron transistors, field emitters, and a host of other possible microelectronic and micromechanical applications.

Figure 6 shows a transistor made from one of the indium/indium-oxide nanocones of the present invention. The device shown in Figure 6 is analogous to the single electron device shown in Figure 1. If the diameter of the point of the nanocone is small enough, the device n Figure 6 acts as a single electron transistor. If the point is not small enough to be a single electron transistor, the device would still function as a small field effect transistor (FET).

In one embodiment of the present invention, there is provided a method for the formation of a nanocone-based electronic device. In this embodiment, nanocones are collected using the polymer-based technique described above. The polymer-encased nanocones then have one side of the polymer encasement (for example the side with the spherical ends of the nanocones) partially etched to expose a base of the spherical ends of the nanocones. The etching can be accomplished using any number of conventional plasma etching processes such as for example oxygen plasma etching. A reducing plasma etching process may be used at the end of the oxygen plasma etching to remove and clean the exposed indium surfaces. At this point, metal deposition deposits contacting metal pads which after patterning provide for the depicted bottom electrode in Figure 6.

The polymer encasement is processed from the opposite side. Here, etching such as plasma oxygen etching is used to remove enough of the surface polymer that the narrowing tip sections of the nanocones are exposed. The plasma processing could then form or deposit an oxide on the surface of the exposed tip sections. At this point, metal deposition deposits metal pads which after patterning provide for the depicted gate electrode in Figure 5. The gate electrode could be patterned to partially or completely encircle the tip sections of each respective nanocone. Following the gate electrode formation, a deposited insulation is formed over the gate electrode, which is subsequently patterned to expose the end tips of the nanoocones. A field oxide (or a residual amount of the deposited insulation formed over the gate electrode) is formed (or remains) over the end tips of the nanocones. At this point, metal deposition deposits metal pads which after patterning provide for the depicted upper counter electrode in Figure 6.

In general, the above device formation would work for any of the metal nanocones provided by the present invention. In other devices besides the device of Figure 6, the collection or encapsulated or non-encapsulated nanocones are positioned on an appropriate base material or a substrate. Conventional techniques can be used to selectively etch away the polymeric layers, leaving the nanocones in place for subsequent patterning and device development. Once in place, for example, thin films of conductors and insulators are deposited and patterned, as needed, to form the electrode, counter-electrode, and gate electrode.

If the existing oxide on the as-grown indium/indium-oxide nanocones is not thick enough to provide sufficient insulation, further oxidation could occur by placement of the as- grown indium/indium oxide nanocones in an oxidizing atmosphere either before or after the indium/indium oxide nanocones are placed into the electronic device(s). Additional oxidation would have the added benefit of reducing the diameter of the metal core inside the tip, which may enhance or particularize quantum confinement effects in the single electron transistor devices. Additional insulation for example could be provided by chemical or physical vapor pressure deposition of silicon oxides and nitrides on the indium/indium-oxide nanocones. U.S. Pat. No. 4,098,923 (the entire contents of which are incorporated by reference) describes the pyrolytic deposition of silicon dioxide from a reaction with silane and oxygen in a vacuum furnace tube. While U.S. Pat. No. 4,098,923 is directed to the deposition of silicon dioxide on silicon wafers, the deposition conditions (temperatures and flow rates of oxygen and silane) described therein or similar conditions could be used in the present invention for the deposition of silicon dioxide on the metal cone structures. U.S. Pat. No. 5,068,124 (the entire contents of which are incorporated by reference) describes the plasma enhanced chemical vapor deposition of silicon dioxide using a number of different oxygen sources and silane in a radio frequency plasma environment at temperatures of 250 to 600 ⁰C. Similar process conditions could be used in the present invention to deposit silicon dioxide on the metal cone structures.

Thus, given the above descriptions of the invention, the invention includes a number of generalized embodiments. In a nanostructure embodiment, the invention provides for a metal nanostructure which includes a metallic spherical section, a metallic conical section integrally connected to the spherical end, and a tip section integrally connected to the conical section and narrowing in width as the tip section extends from the conical section.

In various aspects of the nanostructure embodiment, the tip section can extend to a pointed end having a diameter in a range of 5-50 nm. The spherical section, the conical section, and the tip section can have a total length in a range from 200-1000 nm. The spherical section can have a diameter less than 100 nm. The metallic core can include at least one of indium metal, zinc, tin, or aluminum.

In various aspects of the nanostructure embodiment, an insulation can be formed or can exist after formation on the spherical section, the conical section, and/or the tip section. The tip section can include a pointed end having dimensions small enough to exhibit quantum confined states in the pointed end. A plurality of nanocones can all have a spherical section, a conical section, and a tip section. The plurality of nanocones can be collected to form a set of oriented nanocones. The plurality of nanocones can be a plurality of indium/indium-oxide nanocones.

In a method embodiment, the invention provides for a process for producing metallic nano structures which includes providing a source of metal to a reactor having an oxide susceptor; exposing the metal and the oxide susceptor to a plasma; and forming the metallic nanostructures on the oxide susceptor during the plasma exposing. In various aspects of the method embodiment, the metallic nanostructures can be formed on a ceramic oxide susceptor including at least one of quartz, amorphous silica, or borosilicate. The metallic nanostructures can be formed on a ceramic oxide susceptor inside the reactor. The plasma can be maintained inside the reactor in proximity to the oxide susceptor. As a result, there can be formed on the susceptor a plurality of nanocones having a metallic spherical section, a metallic conical section integrally connected to the spherical end, and a tip section integrally connected to the conical section and narrowing in width as the tip section extends from the conical section.

In various aspects of the method embodiment, the metal inside the reactor can be heated to a temperature where the metal is vaporized into the plasma. For indium, the temperature is in a range from 1000-1500 ⁰C. In other aspects, a plurality of indium/indium- oxide nanocones having a metallic spherical section, a metallic conical section integrally connected to the spherical end, and a tip section integrally connected to the conical section and narrowing in width as the tip section extends from the conical section are formed on a susceptor in the reactor. For collection, as noted above, the metal nanostructures can be encapsulated in a polymer; and removing the polymer from the susceptor removes and collects the metal nanostructures .

In a system embodiment, the invention provides for a system for producing metallic nanostructures. The system includes a reactor chamber configured to be exhausted and purged, an oxide susceptor inside or integral with a wall of the reactor chamber, a metal source configured to provide a source of metal inside the reactor chamber for growth of the metallic nanostructures, a heating device configured to heat at least one of the metal and susceptor, and a plasma discharge device configured to generate a plasma in the reactor in proximity to the susceptor. In various aspects of the system embodiment, there is included a vacuum pump for evacuation of the reactor chamber, and/or a purge gas supply for supply gas containing at least one of helium, argon, neon, xenon, krypton, and a combination thereof to the reactor chamber. The oxide susceptor can be made of quartz, amorphous silica, borosilicate. The oxide susceptor can be disposed inside the reactor chamber or along the wall of the reactor chamber. The oxide susceptor can be a part of the wall of the reactor chamber. For example, the reactor chamber can be a quartz reactor tube, and the susceptor can be a surface of the quartz reactor tube.

In various aspects of the system embodiment, the heating device can be an external heater externally heating the reactor chamber and/or a laser or irradiation heating device heating the metal inside the reactor chamber directly. In various aspects of the system embodiment, the metal source can be an elemental metal or a gas source carrier of the metal. The metal source can be indium, zinc, tin, or aluminum.

In a device embodiment, the invention provides for an electrical device having 1) a conductive element including a metallic spherical section, a metallic conical section integrally connected to the spherical end, and a tip section integrally connected to the conical section and narrowing in width as the tip section extends from the conical section, 2) a first electrode connected to the metallic spherical section, 3) a second electrode disposed proximate the tip section, and 4) a gate electrode applying an electric field to at least the tip section. In various aspects of the device embodiment, the gate electrode is configured such that a voltage supplied to the gate electrode controls or switches on and off current flow between the first and second electrodes, as the supplied voltage generates the electric field which in one embodiment increases a probability that an electron entering the metallic spherical section will tunnel into the second electrode. In various aspects of the device embodiment, insulation is provided on a surface of the metallic conical section or the tip section. The insulation can be an indium oxide layer, and the metallic spherical section and the metallic conical section in this example would be indium. The insulation can be a deposited insulation layer formed on the surface of the metallic conical section or the tip section. In various aspects of the device embodiment, insulation is provided between the gate electrode and the conical section of indium. In this example, the insulation can be a deposited insulation layer formed on the cone or its tip (e.g., the deposited silicon oxide and silicon nitride layers discussed above).

In various aspects of the device embodiment, the gate electrode partially or completely encircles a part of the tip section. The tip section can extend to a pointed end having a diameter in a range of 5-50 nm. The spherical section, the conical section, and the tip section can have a total length in a range from 100-1000 nm. The spherical section can have a diameter less than 100 nm.

In another method embodiment, the invention provides for a method for handling nanocones. The method includes coating a first surface containing nanocones with a polymerizable medium, polymerizing the medium to encapsulate the nanocones in the medium, and removing the polymerized medium from the first surface.

In various aspects of this method for handling, the polymerized medium is transferred to a second surface, and the polymerized medium is dissolved to deposit the nanocones on the second surface.

In various aspects of this method for handling, the polymerizable medium is filled around regions of nanocones having a metallic spherical section, a metallic conical section integrally connected to the spherical end, and a tip section integrally connected to the conical section and narrowing in width as the tip section extends from the conical section. This permits an oriented collection of the nanocones to be formed in which tip sections of the nanocones and metallic spherical sections of the nanocones are respectively on opposite sides of the polymerized medium.

Numerous modifications and variations of the invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.

Claims

CLAIMS:

1. An electrical device comprising: a conductive element including, a metallic spherical section, a metallic conical section integrally connected to the spherical end, and a tip section integrally connected to the conical section and narrowing in width as the tip section extends from the conical section; a first electrode connected to the metallic spherical section; a second electrode disposed proximate the tip section; and a gate electrode applying an electric field to the metallic conical section and the tip section.

2. The device of Claim 1, wherein the gate electrode is configured such that a voltage supplied to the gate electrode controls or switches on and off current flow between the first and second electrodes.

3. The device of Claim 1 , further comprising: an insulation provided on a surface of the metallic conical section or the tip section.

4. The device of Claim 3, wherein: the insulation comprises an indium oxide layer; and the metallic spherical section and the metallic conical section comprise indium.

5. The device of Claim 3, wherein the insulation comprises a deposited insulation layer formed on the surface of the metallic conical section or the tip section.

6. The device of Claim 1, further comprising: insulation provided between the gate electrode and the indium metal of the conical section.

7. The device of Claim 6, wherein the insulation comprises a deposited insulation layer.

8. The device of Claim 1, wherein the gate electrode partially encircles a part of the tip section.

9. The device of Claim 1, wherein the gate electrode completely encircles a part of the tip section.

10. The device of Claim 1, wherein the tip section extends to a pointed end having a diameter in a range of 5-50 nm.

1 1. The device of Claim 1, wherein the spherical section, the conical section, and the tip section have a total length in a range from 200-1000 nm.

12. The device of Claim 1, wherein the spherical section has a diameter less than 100 nm.

13. A method for handling nanocones, comprising: filling a first surface containing nanocones with a polymerizable medium; polymerizing the medium to encapsulate the nanocones in the medium; and removing the polymerized medium from the first surface.

14. The method of Claim 13, further comprising: transferring the polymerized medium to a second surface to place the nanocones on the second surface.

15. The method of Claim 13, wherein filling comprises: filling the polymerizable medium around regions of nanocones having a metallic spherical section, a metallic conical section integrally connected to the spherical end, and a tip section integrally connected to the conical section and narrowing in width as the tip section extends from the conical section.

16. The method of Claim 15, further comprising: forming an oriented collection of the nanocones in which tip sections of the nanocones and metallic spherical sections of the nanocones are respectfully on opposite sides of the polymerized medium.