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WO2005004188A2 - Perfectionnements a l'imagerie en champ lointain - Google Patents

Perfectionnements a l'imagerie en champ lointain Download PDF

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Publication number
WO2005004188A2
WO2005004188A2 PCT/GB2004/002699 GB2004002699W WO2005004188A2 WO 2005004188 A2 WO2005004188 A2 WO 2005004188A2 GB 2004002699 W GB2004002699 W GB 2004002699W WO 2005004188 A2 WO2005004188 A2 WO 2005004188A2
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WIPO (PCT)
Prior art keywords
aperture
wave function
diffraction pattern
function
intensity
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Ceased
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WO2005004188A3 (fr
Inventor
John Marius Rodenburg
Helen Mary Louise Faulkner
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Sheffield Hallam University
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Sheffield Hallam University
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Publication of WO2005004188A3 publication Critical patent/WO2005004188A3/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
    • H01J37/26—Electron or ion microscopes; Electron or ion diffraction tubes
    • H01J37/295—Electron or ion diffraction tubes
    • H01J37/2955—Electron or ion diffraction tubes using scanning ray
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J2237/00—Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
    • H01J2237/26—Electron or ion microscopes
    • H01J2237/2614—Holography or phase contrast, phase related imaging in general, e.g. phase plates

Definitions

  • the present invention relates to far-field imaging, and in particular to improvements to far-field imaging in electron microscopy.
  • Microscopy is used to investigate the structure of objects that cannot be resolved by the eye.
  • Light microscopy is known, using lenses to magnify radiation in the form of light, and different techniques of electron microscopy are used to achieve higher magnification and investigate other aspects of an object, for example crystal structure.
  • Electron microscopy can resolve smaller distances than light microscopy because a wavelength of a beam of electrons can be much lower than a wavelength for visible radiation.
  • a beam of electrons at 100 keV has a wavelength of around 0.0037 nm, compared to a wavelength of visible radiation in a range of the order of a few hundred nm. This allows for resolution of much lower values of d than light microscopy.
  • An electron microscope comprises a source of electrons 101 for an electron beam 102, 103 and one or more lenses 104 to focus the electron beam 102, 103.
  • the lens 104 is typically a magnetic lens or an electrostatic lens. In this example, the lens 104 is configured to focus the electron beam on the image plane 107.
  • Beams 103 that are paraxial come to a Gaussian focus 105 on the image plane 107.
  • beams 102 that are at higher angles come to a focus 106 prematurely, and so the image on the image plane 107 is not fully focussed.
  • Prior art solutions have included using apertures to remove high angle beams 102. However, this introduces diffraction of the electron beam as it passes through the aperture, and also limits the resolution of the microscope, as high angle beams are required to obtain low values for d. For an electron microscope operating at 100 keV, the value of ⁇ is around 0.037 A, but values of d that can be obtained are much higher owing to the removal of the high angle electrons from the beam by the aperture.
  • a further problem in obtaining meaningful data from high angle beams is the stability of the lenses. Magnetic or electrostatic lenses require large power supplies, and minute fluctuations in the power supply lead to fluctuations in the lens. High angle beams are required to interfere with transmitted beams in order to obtain meaningful data, but this interference, especially for high-angle beams, is difficult to establish and remain constant in the presence of lens instabilities.
  • the largest angle up to which meaningful data can be obtained is known as the information limit. Chromatic variations in the beam can similarly restrict the information limit, because changes in wavelength alter the path lengths of high- angle beams, thus dephasing them with respect to each other.
  • An electron source 201 is used to produce an electron beam 202.
  • An aberrated lens 203 is used to bring the beam to a focus 204 at a distance from an object to be imaged 205.
  • the electron beam 202 is transmitted through the object, and interactions with the object 205, such as electron scattering, alter the characteristics of the electron beam 202.
  • a reference wave it is considered theoretically possible to deconvolve a diffraction pattern formed in the far field plane 206 to obtain an exit wave function of the beam after interaction with an object, and hence to image the object.
  • holographic methods have some drawbacks relating to the number of measurements that must be taken to deconvolve the diffraction pattern formed in the far field, and the detector size required is prohibitively large if significant improvements to the resolution are to be obtained.
  • the object In the Gabor geometry, the object must be substantially transparent (weak phase) in order to provide a strong reference wave, whereas this usually not true in practice.
  • the diffraction pattern formed in the far-field is sometimes referred to as a Gabor hologram, or a Ronchigram.
  • the diffraction plane on which the diffraction pattern is formed is also referred to as the micro- diffraction plane or the nano-diffraction plane.
  • the wave function of the far-field diffraction pattern comprises a modulus component and a phase component, but only the intensity of the far-field diffraction pattern can be measured, which corresponds to the square of the modulus component. Without knowing the phase component of the wave function, it is difficult to work out the wave function of the electron beam as it exits in the object to be imaged.
  • FIG. 3 there is illustrated schematically a prior art technique for obtaining information about the imaged object from a far-field diffraction pattern.
  • An incoming beam of radiation 301 is incident on an object to be imaged 302.
  • the transmitted beam 303 has interacted with the object and has a wave function 304.
  • a far-field diffraction pattern 306 is formed in the far- field diffraction plane 305.
  • the intensity of the far-field diffraction pattern 305 can be measured.
  • a wave function for the far-field diffraction pattern 306 can be estimated.
  • An estimated wave function for the exit wave of the radiation as it exits the object is then determined by inverse Fourier transformation of the estimated wave function for the far-field diffraction pattern.
  • the estimated wave function for the exit wave of the radiation as it exits the object can be modified using a measured intensity of the exit wave function of the radiation as it exits the object.
  • the algorithm used is known as the Gerchberg- Saxton algorithm. Iterations of this process solve the wave function for the exit wave of the radiation as it exits the object.
  • to measure the intensity of the exit wave function of the radiation as it exits the object requires use of an imaging lens, with the resolution constrains discussed above, and so this process cannot be used to obtain high magnification information about the object.
  • FIG 4 there is illustrated schematically the prior art Fienup algorithm for obtaining a wave function of radiation.
  • An object to be imaged 401 has a wave function. It is known that the wave function of an area outside the object 402 is zero. The area of the object 401 over which the wave function is greater than zero is known as the support.
  • An intensity of a diffraction pattern 404 can be measured in the far-field.
  • an estimate is made of a phase of a wave function of the diffraction pattern in the far-field, and the estimate of the phase is combined with the known intensity to estimate a wave function of the diffraction pattern.
  • an estimate of a wave function of the object can be made. The estimate is corrected at each iteration by removing data from the regions outside the support 401 where the wave function is known to be zero 402.
  • This method has been demonstrated as a possible means for performing lens-less microscopy, although it suffers many major problems.
  • an aperture must be employed, an area of the aperture relating to the support, and an area outside the aperture relating to the area outside the support.
  • the aperture must be sharp and of irregular shape, otherwise certain ambiguities can arise during the reconstruction of the image. In the presence of noise, convergence is not guaranteed and cannot in general be checked.
  • the requirement of a finite support means that a large field of view cannot be investigated, whereas in most practical situations it would be advantageous to image large areas of the object function.
  • the inventors have devised a method for far-field imaging that includes an aperture that can be scanned across an object to be imaged, or located in very near proximity to the specimen. Radiation is passed through the object and the aperture to form a diffraction pattern in the far-field. The intensities of the diffraction patterns are recorded for at least two aperture positions. Using the intensity measurements and known information about the aperture, an exit wave function of the object is determined. The exit wave function of the object is used to provide high resolution information regarding the object.
  • a method of constructing image data for a region of an object comprising: analyzing an intensity data of a diffraction pattern arising from said region, said intensity data arising from a function of a known aperture, wherein said aperture can be moved to at least two different positions relative to said object.
  • said intensity data of said diffraction pattern is measured in a far-field of an electron microscope.
  • said analysis comprises at least one Fourier transformation.
  • said analysis is an iterative process.
  • said analysis comprises estimating a wave function.
  • said analysis comprises only using data where a value for an aperture transmission is substantially greater than zero.
  • an estimated phase of said diffraction pattern is combined with said intensity data of said diffraction pattern to form an estimate of a wave function of said diffraction pattern.
  • said analysis comprises transforming said estimate of said wave function of said diffraction pattern to obtain an estimate of a wave function of said region of said object.
  • an exit wave function of said region of an object is estimated.
  • said analysis comprises transforming said estimated exit wave function of said object using a known aperture transmission function.
  • said analysis comprises: correcting a wave function of said diffraction pattern using said intensity data of said diffraction pattern; and preserving a phase of said wave function of said diffraction pattern.
  • said diffraction pattern arises from interaction of radiation from a radiation source with said object.
  • a method for obtaining image data for an object comprising:
  • the method comprises
  • step (a) performing the inverse operation of step (ix);
  • said transformations of steps (ix) and (c) comprise a Fourier transformation.
  • said transformations of steps (vii) and (a) comprise an inverse Fourier transformation.
  • said transformation of steps (viii) and (b) comprises dividing an estimate of a wave function for said object by an aperture transmission function of said aperture.
  • said division is not performed where said aperture transmission function of said aperture approaches zero.
  • said aperture transmission function of said aperture comprises complex data.
  • said diffraction patterns are obtained where said aperture is in more than two positions.
  • said phase of said first diffraction pattern is preserved during step (d).
  • said phase of said second diffraction pattern is preserved during step (x).
  • a method of constructing image data comprising:
  • said transformation of steps (e) and (k) is an inverse Fourier transformation.
  • said transformation of steps (h) and (m) is a Fourier transformation.
  • said transformation of steps (g) and (I) comprises dividing an estimate of a wave function for said object by an aperture transmission function of said aperture.
  • said division is not performed where said aperture transmission function of said aperture approaches zero.
  • said aperture transmission function of said aperture comprises a complex wave function.
  • the method measuring an intensity of a diffraction pattern arising from further aperture positions.
  • a method of imaging a sample comprising:
  • said electromagnetic source comprises a coherent electromagnetic source.
  • the electromagnetic source comprises an incoherent source.
  • said mask is placed between said sample and said electromagnetic source.
  • said mask is placed between said sample and said electromagnetic source.
  • a method for obtaining image data for an object comprising:
  • said transformation of step (e) comprises a Fourier transformation
  • said transformation of step (g) comprises an inverse Fourier transformation
  • step (h) is not performed where said aperture transmission function of said aperture approaches zero.
  • said average value in step (i) comprises a mean.
  • said mean is weighted by a modulus of each said aperture transmission function at each aperture position.
  • an algorithm comprising:
  • said algorithm is used to obtain a refined value for ⁇ ⁇ (r) and a refined value for
  • said algorithm is used to construct image data.
  • said transformation in step (a) comprises an inverse Fourier transformation; and said transformation in step (c) comprises a Fourier transformation; and said transformation in step (e) comprises an inverse Fourier transformation; and said transformation in step (g) comprises a Fourier transformation.
  • said modification of ⁇ (k) in step (d) preserves a phase of 2 (k); and said modification of ⁇ k) in step (h) preserves a phase of ⁇ (k).
  • said transformation in step (c) comprises dividing by a first complex function, and multiplying by a second complex function; and ignoring values for " ii ) where said first complex function is substantially zero.
  • said transformation in step (d) comprises dividing by a second complex function, and multiplying by a first complex function; and ignoring values for " ⁇ (r) where said second complex function is substantially zero.
  • (k) represents a wave function of radiation in diffraction space where a aperture is in a first position
  • ⁇ 2 (k) represents a wave function of radiation in diffraction space where a aperture is in a second position; and represents an exit wave function of radiation where said aperture is in said first position
  • ⁇ 2 (r) represents an exit wave function of radiation where said aperture is in second position
  • a computer program comprising program instructions for causing a computer to form the process of any preceding claims.
  • said computer program is stored on a data carrier.
  • apparatus for obtaining image data for an object comprising: a radiation source; and a holder, configured to locate said object to be imaged; and an aperture; and means to moveably position said aperture relative to said object in at least a first position and a second position; and a detector, configured to detect an intensity of a far-field diffraction pattern arising from an interaction between said radiation and said object; and means to process said intensity data.
  • said means to detect an intensity of radiation comprises a CCD detector.
  • said radiation source comprises a coherent radiation source.
  • said radiation source comprises an incoherent radiation source.
  • said object is located between said radiation source and said aperture.
  • said aperture is located between said radiation source and said object to be imaged.
  • said means to move said aperture comprises a micro-actuator.
  • said means to process said intensity data comprises: a microprocessor; and a data carrier comprising instructions for said microprocessor to perform an analysis of said data; and a data input device configured to allow a user to input instructions; and means to instruct a movement of said aperture via said aperture movement means.
  • the apparatus further comprises at least one lens located between said aperture and said detector, said lens configured to alter a camera length of said apparatus.
  • the apparatus further comprises at least one lens located between said object and said radiation source.
  • apparatus for constructing image data for a region of an object comprising: means to analyze an intensity data of a diffraction pattern arising from said region, said intensity data arising from a function of a known aperture, wherein said aperture can be moved to at least two different positions relative to said object.
  • apparatus for obtaining image data for an object comprising:
  • (viii) means to transform said estimate of said wave function for said object where said aperture is in said first position to an estimate of a wave function for said object where said aperture is in said second position;
  • (ix) means to transform said wave function of said object where said aperture is in said second position to obtain an estimate of said wave function of said diffraction pattern where said aperture is in said second position;
  • (x) means to modify said wave function of said diffraction pattern when said aperture is in said second position using said measured intensity of said second diffraction pattern
  • apparatus for obtaining image data for an object comprising:
  • (f) means to modify each said wave function in diffraction space using said measured intensity patterns at each said aperture position, whilst preserving a phase of each said wave function in diffraction space to obtain a corresponding respective refined wave function in diffraction space for each said aperture position;
  • (h) means to obtain a corresponding respective value of said exit wave function for each said aperture position
  • Figure 1 illustrates schematically the prior art problem of achieving a low value for d.
  • Figure 2 illustrates schematically prior art Gabor holography.
  • Figure 3 illustrates schematically a prior art technique for obtaining information about the imaged object from a far-field diffraction pattern.
  • Figure 4 illustrates schematically the prior art Fienup process for obtaining a wave function of radiation.
  • Figure 5 illustrates schematically a process for obtaining a far-field diffraction pattern.
  • Figure 6 illustrates schematically an alternative arrangement for obtaining a far-field diffraction pattern where the aperture is located below the object.
  • Figure 7 illustrates schematically an algorithm for obtaining a wave function of an object.
  • Figure 8 illustrates schematically a process of obtaining an exit wave function of an object.
  • Figure 9 illustrates schematically an alternative process of obtaining an exit wave function of an object.
  • Figure 10 illustrates schematically apparatus for far-field imaging of an object.
  • Detailed Description There will now be described by way of example a specific mode contemplated by the inventors. In the following description numerous specific details are set forth in order to provide a thorough understanding. It will be apparent however, to one skilled in the art, that the present invention may be practiced without limitation to these specific details. In other instances, well known methods and structures have not been described in detail so as not to unnecessarily obscure the description.
  • radiation denotes energy from a source, and includes electromagnetic radiation, emitted particles such as electrons, and acoustic waves. Radiation can be represented by a wave function.
  • a wave function comprises a real part and an imaginary part. It can be represented by its modulus and phase.
  • ⁇ //(r)* is the complex conjugate of ⁇ (r),
  • the modulus of the wave function is determined from the square root of the intensity.
  • far-field is used to denote a region which is a relatively long distance from a wave function of interest.
  • Diffraction space is also known as Fourier space.
  • aperture is used to describe a localized transmission function of radiation that can be represented by a complex variable in two dimensions having a modulus value between 0 and 1 , for example an aperture in a mask or a region where an electron beam is brought substantially to a focus.
  • 0(r) is an exit wave function of radiation after interaction with an object. If an aperture is displaced some distance away from the exit of the object, this function may have undergone Fresnel propagation to the plane of the aperture. It can be represented as a complex function.
  • P(r - R ) is an aperture transmission function where an aperture is in a first position, and can be represented as a complex function. Its complex value is given by modulus and phase alterations it introduces to a perfect plane wave incident upon it.
  • P(r - R 2 ) is an aperture transmission function where an aperture is in a second position, and can be represented as a complex function Its complex value is given by modulus and phase alterations it introduces to a perfect plane wave incident upon it.
  • the aperture transmission function may be different for each different aperture position relative to the object.
  • ⁇ (r) is an exit wave function of radiation is it exits the aperture and the object where an aperture is in a first position.
  • ⁇ (r) is an exit wave function of radiation is it exits the aperture and the object where an aperture is in a second position.
  • ⁇ (k) is a wave function of radiation in diffraction space where the aperture is in a first position.
  • ik) is a wave function of radiation in diffraction space where the aperture is in a second position.
  • ⁇ j is the square of the modulus of a wave function of the radiation in diffraction space where the aperture is in a first position, and is measured as an intensity of a measured diffraction pattern.
  • ⁇ 2 is the square of the modulus of a wave function of the radiation in diffraction space where the aperture is in a second position, and is measured as an intensity of a measured diffraction pattern.
  • k is a vector co-ordinate in diffraction space.
  • r is a vector co-ordinate in real space.
  • R ⁇ and R 2 are vector co-ordinates representing positions to which an aperture is shifted in real space in a first position and a second position.
  • a radiation source 501 is used to produce a beam 502 of radiation.
  • the beam 502 passes through an aperture 503.
  • the propagated beam passes through an object 505, where further interactions with the specimen further alter the wave function of the beam 506.
  • the altered wave function ⁇ (r) 506 is a complex wave function.
  • the resultant diffracted radiation forms a diffraction pattern in the far-field 507, the intensity of which can be measured.
  • Fig. 6 there is illustrated schematically an alternative arrangement for obtaining a far-field diffraction pattern where the aperture is located below the object.
  • a first interaction of the radiation 502 is with the object 503, which forms a complex wave function O (r) 601.
  • the resultant complex wave function 506 is related to 0(r) and P(r - R ) by equation 2.
  • An intensity of an electron diffraction pattern is measured where an aperture is positioned relative to an object to be imaged in a first position (position 1).
  • An intensity of an electron diffraction pattern is then measured where an aperture is positioned relative to an object to be imaged in a second position (position 2). From these measurements, and from the known aperture positions, it is possible to work out a wave function for the object that is to be imaged, and therefore to obtain image data relating to the object.
  • Example 1 Referring to figure 7 herein, there is illustrated schematically an algorithm for obtaining a wave function of an object.
  • a measured intensity of the diffraction pattern where the aperture is in the first position ⁇ W) 701 forms the basis of an estimate of the complex wave function of the diffraction pattern.
  • an intensity value it does not give information about the phase of the wave function in diffraction space. Therefore, an estimate of the phase is made, and combined 702 with the square root of the measured intensity 701 to give an estimate of the wave function of the radiation in diffraction space ⁇ (k) 703 where the aperture is in position 1.
  • the estimate of the phase may be at random.
  • An inverse Fourier transformation 704 is performed on ⁇ (k) 703 to obtain an estimate of the exit wave function of the radiation as it exits the aperture and the object ⁇ (r) 705 where the aperture is in position 1.
  • ⁇ ⁇ (r) is a product of the wave function of the radiation as it exits the object 0(r) and the aperture transmission function P(r - R ) where the aperture is in position 1 (equation 2).
  • a Fourier transformation 708 is performed on fair) 707 to give an estimate of the wave function of the radiation in diffraction space ( :) 709 where the aperture is in position 2.
  • the intensity of this diffraction pattern has been measured ] ⁇ 2 (&)
  • 711 is used to correct the estimated wave function 2 i ) 709. However, in this correction the phase component ⁇ 2 ik) 709 is preserved.
  • An inverse Fourier transformation 712 is performed on the corrected diffraction pattern wave function 2 ik 709 to obtain a new estimate of fair) 707.
  • fair is transformed 713 using a similar equation to equation 4 to obtain a revised estimate of ⁇ _i ) 705.
  • a Fourier transformation 714 is then performed on 705 to obtain a revised estimate of iik) 703.
  • steps 704, 706, 708, 710, 712, 713, and 714 are iterated to obtain refined exit wave functions 705 and fair) 707.
  • the refined wave functions ⁇ . (r) 705 and fair) 707 can be related to the exit wave function of the object using known P(r - R 2 ) and P(r - R ), to obtain an exit wave function Oir) of radiation after interaction with an object. From Oir), image data relating to the structure of the object can be obtained.
  • FIG. 8 there is illustrated schematically a process of obtaining an exit wave function of an object.
  • the image of the dog 801 represents the modulus component of an exit wave function Oir), and the image of the bird 802 represents a phase component of a object wave function Oir).
  • These images 801 , 802 represent the information that is required to obtain an image of the object.
  • a first aperture position 803 and a second aperture position 804 are shown here as circles for the purposes of illustration only. In most circumstances, an aperture transmission function would comprise a complex wave function.
  • the exit wave function iir comprises a modulus component 805 and a phase component 806.
  • the wave function in diffraction space iik) where the aperture is in position 1 also comprises a diffraction pattern intensity 807 and phase information 808.
  • the diffraction pattern intensity 807 is all that can be measured.
  • the diffraction pattern intensity is not shown to scale in this illustration.
  • the object exit wave function intensity 801 and phase 802 can be reconstructed to give an object intensity 809 where the aperture is in position 1 and position 2, and an object phase where the aperture is in position 1 and position 2.
  • the intensity portion of the object 809 and the phase portion of the object 810 can only be obtained for the first and second aperture position.
  • this technique is not limited to two aperture positions. Third and further aperture positions may also be introduced to obtain image data for a larger object area, and to improve the accuracy of the revised values for ⁇ ir) and fair).
  • the above example also requires making an estimate of a wave function, or a phase component of a wave function.
  • an estimate is made of the phase of iik) 703. It will be appreciated that the estimate is required to provide an estimated wave function that is then refined by the iterative algorithm shown in figure 7.
  • the estimate of the phase of ⁇ ⁇ ik) 703 is made to provide a wave function that can then be used to obtain refined Oir).
  • the estimate need not be of a phase of ⁇ ( ) 703.
  • An estimate could be made of a phase of 2 ik) 709, and combined 710 with the square root of the measured intensity 711 to provide an estimate of ⁇ C ⁇ ) 709.
  • an estimate could be made of ⁇ ir) 705 or iir) 707 and used as a starting point for the algorithm.
  • Example 2 An aperture is positioned relative to an object to be imaged in several positions.
  • an aperture is positioned relative to the object in a first, a second, a third, a fourth and a fifth position, although it will be appreciated that any number of aperture positions greater than two may be used. Some overlap is required between the aperture positions.
  • An intensity of a corresponding respective diffraction pattern is then measured for each aperture position. From these measurements, and from the known aperture positions, it is possible to work out a wave function for the object that is to be imaged, and therefore to obtain image data relating to the object.
  • FIG. 9 there is illustrated schematically an alternative process of obtaining an exit wave function of an object.
  • An estimate is made of an exit wave function of an object O(r) 901.
  • This estimate of (9(r) 901 is multiplied 902, 903, 904, 905, 906 by an aperture transmission function at each aperture position to obtain estimates for the exit wave function at each aperture position, (r) 907, fa(r) 908, (r) 909, ⁇ r) 910, and 5 ir) 911.
  • a Fourier transform is applied 912, 913, 914, 915, 916 to each exit wave function i r) 907, ⁇ 2 (r) 908, ⁇ 3 (r) 909, ⁇ 4 (r) 910, and ⁇ s (r) 911.
  • a Fourier transform is applied 932, 933, 934, 935, 936 to the refined values of values (k) 917, 2 (&) 918, k) 919, ⁇ 4 (£) 920, and (k) 921.
  • the exit wave functions ⁇ iir) 907, (r) 908, (r) 909, ⁇ f) 910, and ⁇ s (r) 911 can be transformed 937, 938, 939, 940, 941 to give refined values for 0(r) 901.
  • Many values for each aperture transmission function will approach zero, as the aperture only covers a certain area of the object.
  • the transformations 937, 938, 939, 940, 941 are only made for each aperture transmission function where their values are significantly greater than zero.
  • the values of Oir) 901 can then be combined as a mean, or a mean weighted by a modulus of the aperture transmission function at each aperture position, to obtain a refined estimate of Oir). Further iterations proceed using the refined estimate of Oir).
  • An area of image data obtained by this method is an area spanned by a union of all aperture position areas.
  • the aperture positions will in certain cases overlap with each other, and a greater degree of overlap will improve a convergence of the algorithm for estimating Oir) because more independent measurements of intensity of each diffraction pattern of the object at different aperture positions provide more information.
  • the estimate of the wave function Oir is made for convenience.
  • an estimated wave function may be made for any of the wave functions as a starting point for the algorithm.
  • an estimated phase can be made for of each of (k) 917, ⁇ 2 (k) 918, (k) 919, (k) 920, and ⁇ ( ⁇ ) 921.
  • the apparatus comprises a radiation source 1001 , configured to emit radiation 1002.
  • the radiation 1002 interacts with an object to be imaged 903 to give an object wave function 1004.
  • the radiation then passes through an aperture 1005.
  • Interactions between the radiation 1002 and the aperture 1005 further modify the radiation to give a complex exit wave function ⁇ ir) 1006.
  • the position of the aperture 1005 can be altered with respect to the position of the object 1003 using an actuator 1007.
  • the actuator 1007 comprises a piezoelectric actuator capable of moving at Angstrom resolution over a field of up to 1 ⁇ m.
  • the diffracted electron beam 1008 forms a diffraction pattern in the far-field space, the intensity of which can be measured using a CCD detector 1009.
  • a CCD detector 1009 By moving the aperture 1005 using the actuator 1007, diffraction pattern intensities can be measured using the CCD detector 1009 where the aperture 1005 is in a first position, a second position, and if desired further positions.
  • the size of the CCD detector array required relates to the size of the aperture. As the aperture size is reduced, a size of allowed features in the far- field diffraction pattern increase. It has been determined that a CCD array of 2000 x 2000 pixels corresponds to a resolution of around 1 /2000 th of the aperture size. Using an aperture size of 50 A gives an estimated resolution of 0.25 A, compared to a resolution in a conventional transmission electron microscope of around 2 A.
  • a control unit 1010 is used to control the position of the aperture 1005 and to process the diffraction pattern intensity data obtained from the CCD detector 1009.
  • the control unit 1010 comprises a microprocessor 1011 , a memory 1012, a data storage device 1013, a display 1014, a data inputting device 1015, and a device 1016 for receiving data from the CCD detector 1009 and transmitting data to control the actuator 1007.
  • the data input device 1015 is used to instruct the microprocessor 1011 to move the aperture 1005 to a known first position. Once the aperture 1005 is at the first position, the object of the image 1003 is subjected to radiation 1002, and an intensity of a first diffraction pattern is obtained using the CCD detector 1009. The intensity data of the first diffraction pattern is stored in the memory 1012.
  • the aperture 1005 is then moved to a second position using the actuator 1007, controlled by the microprocessor 1011.
  • the object to be imaged 1003 is then subjected to radiation 1002, and a second diffraction pattern intensity is measured using the CCD detector 1009.
  • the second diffraction pattern intensity data is stored in the memory 1012.
  • the microprocessor 1011 processes the first diffraction pattern intensity data and the second diffraction pattern intensity data using instructions stored in the data storage 1013 to obtain an exit wave function O(r) of radiation after interaction with the object 1005.
  • the exit wave function can be used to obtain image data relating to the object 1005
  • the radiation source 1001 comprises a coherent radiation source.
  • the radiation source 1001 also produces substantially monochromatic electromagnetic radiation.
  • the aperture 1005 is positioned above the object to be imaged 1003, such that the radiation 1002 passes through the aperture 1005 before it interacts with the object to be imaged 1003.
  • the radiation source comprises an incoherent radiation source.
  • the radiation 1002 is not transmitted through the object 1003.
  • the radiation 1002 interacts with the object of the image 1003 such that the object emits other forms of radiation that can form diffraction patterns in the far-field.
  • the object may be subjected to x-ray radiation, and emit photoelectrons.
  • the photoelectrons form a diffraction pattern in the far-field, the intensity of which can be measured to provide data relating to the object.
  • an electron lens is mounted after the object 1003 and the aperture 1005 to alter a camera length of the apparatus for far-field imaging of an object.
  • an electron lens is mounted between the radiation source 1001 and the object 1003 to condense the radiation onto the region of the object to be imaged.

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  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Analysing Materials By The Use Of Radiation (AREA)

Abstract

La présente invention a trait à un procédé et un appareil pour l'imagerie en champ lointain comportant une petite ouverture qui peut soit être balayée à travers un objet pour la formation d'image, ou située très proche du spécimen. Le rayonnement traverse l'objet et l'ouverture pour former une image de diffraction dans le champ lointain. Les niveaux d'intensité des images de diffraction sont enregistrés pour au moins deux position d'ouverture. Au moyen des mesures d'intensité et d'information connue concernant l'ouverture, une fonction d'onde de sortie de l'objet est déterminée. La fonction d'onde de sortie de l'objet est utilisée pour assurer une information de haute résolution concernant l'objet.
PCT/GB2004/002699 2003-06-30 2004-06-23 Perfectionnements a l'imagerie en champ lointain Ceased WO2005004188A2 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB0315245A GB2403616A (en) 2003-06-30 2003-06-30 Diffraction pattern imaging using moving aperture.
GB0315245.1 2003-06-30

Publications (2)

Publication Number Publication Date
WO2005004188A2 true WO2005004188A2 (fr) 2005-01-13
WO2005004188A3 WO2005004188A3 (fr) 2005-08-18

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PCT/GB2004/002699 Ceased WO2005004188A2 (fr) 2003-06-30 2004-06-23 Perfectionnements a l'imagerie en champ lointain

Country Status (2)

Country Link
GB (1) GB2403616A (fr)
WO (1) WO2005004188A2 (fr)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2008142360A1 (fr) * 2007-05-22 2008-11-27 Phase Focus Limited Imagerie tridimensionnelle
US7792246B2 (en) 2004-04-29 2010-09-07 Phase Focus Ltd High resolution imaging

Families Citing this family (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2481589B (en) 2010-06-28 2014-06-11 Phase Focus Ltd Calibration of a probe in ptychography
GB201020516D0 (en) 2010-12-03 2011-01-19 Univ Sheffield Improvements in providing image data
GB201107053D0 (en) 2011-04-27 2011-06-08 Univ Sheffield Improvements in providing image data
GB201201140D0 (en) 2012-01-24 2012-03-07 Phase Focus Ltd Method and apparatus for determining object characteristics
GB201207800D0 (en) 2012-05-03 2012-06-13 Phase Focus Ltd Improvements in providing image data

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Publication number Priority date Publication date Assignee Title
GB8612099D0 (en) * 1986-05-19 1986-06-25 Vg Instr Group Spectrometer
US5866905A (en) * 1991-05-15 1999-02-02 Hitachi, Ltd. Electron microscope
JP3422045B2 (ja) * 1993-06-21 2003-06-30 株式会社日立製作所 組成及び格子歪測定用電子顕微鏡及びその観察方法

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7792246B2 (en) 2004-04-29 2010-09-07 Phase Focus Ltd High resolution imaging
WO2008142360A1 (fr) * 2007-05-22 2008-11-27 Phase Focus Limited Imagerie tridimensionnelle
KR101455338B1 (ko) * 2007-05-22 2014-11-03 페이즈 포커스 리미티드 3차원 영상화
US9116120B2 (en) 2007-05-22 2015-08-25 Phase Focus Limited Three dimensional imaging

Also Published As

Publication number Publication date
WO2005004188A3 (fr) 2005-08-18
GB2403616A (en) 2005-01-05
GB0315245D0 (en) 2003-08-06

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