Differential phase contrast microanalysis using energy loss spectrometer

Abstract

Systems, components, and methods for generating differential phase contrast (DPC) data are described. A method includes an operation for directing an electron beam through a material sample disposed in a microscope barrel, wherein interaction of the material sample and the electron beam produces a scattered portion of the electron beam. The method includes directing the scattering portion onto an energy filter configured to disperse the scattering portion by energy along a dispersion axis and direct a subset of the scattering portion toward a detector of the energy filter. The operations include generating detector data using the subset of the scattering portions incident on the detector, the detector data including EELS data. The operations also include generating differential phase contrast data using the detector data.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. non-provisional application No. 18 / 453,978, filed on August 22, 2023, the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0003] Embodiments of the present disclosure relate to charged particle microscope systems and algorithms and methods for their operation. In particular, some embodiments relate to techniques for microanalysis including differential phase contrast. Background Art

[0004] In scanning transmission electron microscopy (STEM), an electron beam is focused onto a sample and various signals are generated from which characteristic information about the sample is derived. Electron energy loss spectroscopy (EELS) is one example, high angle annular dark field (HAADF) is another. Differential phase contrast (DPC) involves scanning the beam over the sample and generating a characteristic interference pattern that can be used to derive structural information, such as crystal structure information (similar to diffraction methods) and bonding information. The advantage of differential phase contrast is that the magnetic structure of the atoms that make up the sample can be directly imaged, providing intuitive image analysis and direct measurement of material parameters from the image.

[0005] Typically, differential phase contrast (DPC) is implemented using a segmented detector, and a differential signal is generated when the beam is swept across the sample in the forward and reverse directions. The differential signal is typically generated, for example, using a quadrant detector based on the difference in detector signals from relative detector segments on opposite sides of a central position. For this reason, differential phase contrast techniques typically involve introducing a specialized segmented detector downstream of the sample, similar to the detector that will be used for bright field (BF) STEM imaging, except that the detector is also divided into relative segments along one or more axes. Compared to HAADF, both DPC and EELS measure electrons scattered by the atoms of the sample at relatively small angles. In this way, typical techniques for DPC and EELS cannot be performed simultaneously without sacrificing one of the techniques to support the other. For example, a segmented detector may include an aperture to allow a portion of the scattered electrons to pass through and reach the EELS spectrometer. Alternatively, two continuous measurements may be performed at a given point in the sample to collect EELS data and DPC data, respectively. With the advancement of instrument resolution, the gradual reduction of the material structure to be measured, and the improvement of deep cryopreservation technology, the samples of interest are becoming more and more sensitive to charged particle exposure. This sensitivity limits the total dose that can be used for DPC imaging and EELS analysis at a given sample location. Therefore, there is a need to develop techniques for performing DPC imaging and EELS that meet the dose limitations. Summary of the invention

[0006] In one aspect, an electron microscope system includes: an electron source configured to emit an electron beam; a microscope barrel optically coupled to the electron source and configured to receive the electron beam from the electron source; and an energy filter coupled to the microscope barrel and configured to receive electrons of the electron beam from the microscope barrel. The system includes a control circuit operably coupled to the microscope barrel and the energy filter, the control circuit electronically coupled to one or more non-transitory machine-readable storage media, the non-transitory machine-readable storage media storing instructions that, when executed by the control circuit, cause the electron microscope system to perform operations. The operations include directing the electron beam through a material sample disposed in the microscope barrel, wherein the interaction of the material sample and the electron beam produces a scattered portion of the electron beam. The operations direct the scattered portion toward the energy filter, which is configured to disperse the scattered portion along a dispersion axis by energy and direct a subset of the scattered portion toward a detector of the energy filter. The operations include generating detector data using the subset of the scattered portion incident on the detector, the detector data including EELS data. The operations also include generating differential phase contrast (DPC) data using the detector data.

[0007] In some embodiments, generating detector data includes: defocusing one or more components of the energy filter; and generating an angle-resolved EELS (AR-EELS) image using the detector. Generating DPC data may include determining a first centroid of a region of the AR-EELS image in energy-momentum coordinate space. Generating DPC data may include mapping the first centroid of the AR-EELS image from the energy-momentum coordinate space to momentum-momentum coordinate space. Generating DPC data may also include determining a second centroid in the momentum-momentum coordinate space.

[0008] In some embodiments, generating the DPC data further comprises determining a displacement μ of the second center of mass in the momentum-momentum coordinate space relative to a reference position of the first center of mass. Generating the DPC data may further comprise: generating a DPC vector image using the displacement; and generating a scalar iDPC image of the material sample at least in part by integrating the DPC vector image.

[0009] Defocusing the one or more components of the energy filter may include modifying one or more operating parameters of one or more electron optical elements of the energy filter or moving the detector. These operations may also include determining an angle α corresponding to the angle of incidence of the subset of the scattered portions relative to a detection surface of the detector.

[0010] Generating detector data may include generating a first AR-EELS image using the detector. Generating detector data may include modifying one or more components of the microscope column to cause a rotation of a diffraction pattern generated via the interaction of the electron beam with the material sample. Generating detector data may also include generating a second AR-EELS image from the rotated diffraction pattern using the detector.

[0011] In some embodiments, generating DPC data includes determining a first center of mass of a region in the first AR-EELS image, the first center of mass being defined for a first energy-momentum coordinate space. Generating DPC data may include determining a second center of mass of the region in the second AR-EELS image, the second center of mass being defined for a second energy-momentum coordinate space. Generating DPC data may also include determining a third center of mass of the region, the third center of mass being defined for a momentum-momentum coordinate space. The first energy-momentum coordinate space and the second energy-momentum coordinate space may be substantially orthogonal. The region may correspond to a zero-loss peak of the scattering portion. The region may correspond to a plasma resonance region of the scattering portion. The region may correspond to a core loss region of the scattering portion.

[0012] In a second aspect, one or more non-transitory machine-readable storage media store machine-executable instructions that, when executed by a machine, cause the machine to perform the operations of the aforementioned aspect.

[0013] In a third aspect, a method for generating DPC data comprises the operations of the foregoing aspects. The method may be machine-automatically implemented (e.g., without human intervention), pseudo-automatically implemented (e.g., with limited human intervention), and / or manually implemented. For example, the method may be initiated by a human user of a charged particle microscope system, after which the operations of the foregoing aspects may be implemented as one or more computer-implemented algorithms. The method may terminate, for example, at a user action of generating visualization data from a subset of the EELS data and the corresponding DPC data.

[0014] The terms and expressions that have been adopted are used as terms of description rather than limitation, and when such terms and expressions are used, it is not intended to exclude any equivalents of the features shown and described or portions thereof, but it should be recognized that various modifications are possible within the scope of the subject matter claimed. Therefore, it should be understood that although the subject matter claimed by the present disclosure has been specifically disclosed through embodiments and optional features, those skilled in the art may make modifications and changes to the concepts disclosed herein, and such modifications and changes are considered to be within the scope of the present disclosure as defined by the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The foregoing aspects of the present disclosure and many of the attendant advantages will become more readily appreciated when the following detailed description is taken in conjunction with the accompanying drawings.

[0016] Figure 1 is a schematic diagram illustrating an example charged particle microscope system according to some embodiments of the present disclosure.

[0017] Figure 2 is a schematic diagram illustrating an example differential phase contrast technique according to some embodiments of the present disclosure.

[0018] Figure 3 is a schematic diagram showing example differential phase contrast detector data according to some embodiments of the present disclosure.

[0019] Figure 4 is a schematic diagram showing example EELS data including momentum space information according to some embodiments of the present disclosure.

[0020] Figure 5 is a schematic diagram illustrating an example back-projection technique for extracting momentum space information from EELS data according to some embodiments of the present disclosure.

[0021] Figure 6 is a diagram showing a method for using a Figures 1 to 3 A block diagram of an example process for generating differential phase contrast data using an example system.

[0022] In the drawings, unless otherwise specified, the same reference numerals represent the same components in various views. Where appropriate, not all instances of components need to be labeled to reduce clutter in the drawings. The drawings are not necessarily drawn to scale, with emphasis instead on illustrating the principles being described. DETAILED DESCRIPTION

[0023] Although exemplary embodiments have been shown and described, it will be appreciated that various changes may be made therein without departing from the spirit and scope of the present disclosure. In the following paragraphs, embodiments of charged particle microscope systems, components, and methods for generating differential phase contrast data are described. To simplify the description, embodiments of the present disclosure focus on transmission electron microscopes and related instruments. To this end, embodiments are not limited to such instruments, but are contemplated for use in analytical instrument systems in which a scanning beam of charged particles is used to generate detector data. Similarly, although embodiments of the present disclosure focus on EELS spectrometer systems for generating detector data, additional and / or alternative detector modalities are also contemplated.

[0024] In scanning transmission electron microscopy (STEM), differential phase contrast (DPC) analysis is a technique for imaging the magnetic and / or electronic structure of the atoms that make up the sample. The basic principle of STEM-DPC is that the electrons in the beam can interact with the electromagnetic field in the material. The DPC technique includes measuring the phase shift of the electron beam produced by such interactions. The phase shift can then be related to the local magnetization or polarization in the sample. With the resolution of current STEM instruments, atomic scale information can be imaged directly, from which overall scale parameters such as sample thickness, lattice strain, etc. can be derived. Detailed mathematical derivations of various techniques have been described in the art, including DPC, integral DPC (iDPC), differential DPC (dDPC), center of mass (COM), integral COM (iCOM), differential COM (dCOM), etc. The detailed mathematical derivations of the main expressions of each technique are omitted, and reference is made to the following peer-reviewed publications, which describe the theoretical and experimental aspects of such techniques using segmented bright field detectors in STEM systems.

[0025] Ivan Eric GT Bosch and Sorin Lazar, “Phase contrast STEM for thin samples: Integrated differential phase contrast,” Ultramicroscopy 160 (2016): 265–280.

[0026] Ivan and Eric G. T. Bosch, “Analytical Review of Direct Stem Imaging Techniques for Thin Samples,” in: Peter W. Hawkes, ed., Advances in Imaging and Electron Physics, vol. 199, Burlington: Academic Press, 2017, pp. 75–184. ISBN: 978-0-12-812091-0.

[0027] Emrah Yücelen, Ivan and Eric GT Bosch, “Phase contrast scanning transmission electron microscopy imaging of light and heavy atoms at the limit of contrast resolution,” Scientific Reports 8, 1 (2018): 1–10.

[0028] Embodiments of the present disclosure include systems, methods, algorithms, and non-transitory media storing computer-readable instructions for generating differential phase contrast data. In an illustrative example, a method includes directing an electron beam through a material sample disposed in an objective section of a microscope barrel, wherein the interaction of the material sample and the electron beam produces a scattered portion of the electron beam. The method may include focusing the scattered portion onto an energy filter configured to disperse the scattered portion along a dispersion axis by energy and direct a subset of the scattered portion toward a detector of the energy filter. The method may include generating detector data using a subset of the scattered portion incident on the detector, the detector data including EELS data. The method may also include generating differential phase contrast (DPC) data using the detector data.

[0029] Advantageously, the techniques of the present disclosure provide DPC data generation using systems without segmented STEM detectors, while also providing energy loss options that provide element and transition specific imaging that would otherwise be unavailable in typical DPC data, thereby combining the capabilities of EELS and DPC. In an illustrative example, the techniques for EELS-DPC include using an energy filter in front of a camera or detector (e.g., as part of an energy loss spectrometer) to analyze the incoming electron beam. The energy filter can generate electron energy loss spectrum (EELS) data by applying a magnetic field that causes electron dispersion along a well-defined axis. The raw signal can be projected along this axis into a vertical axis that is spatially defined on the detector surface. Importantly, such projections can be used to determine DPC vector components and can also be used to pre-calculate component directions from which COM information can be derived. In some embodiments, an energy spectrum can be recorded, thereby generating DPC components, without the need for a segmented detector or camera that would otherwise be used in a STEM system.

[0030] Atomic-scale microscopy and microanalysis techniques, such as convergent beam electron diffraction (CBED) methods, may involve focusing an electron beam onto a sample and imaging the disk projection by placing a detector at a distance from the sample at which the electron beam is not focused. In the case of CBED microanalysis, the diffraction disk encodes information about the sample and can be analyzed to obtain physical and chemical information, such as crystal structure, composition, sample thickness, etc. Unlike DPC, the CBED method uses image information in the detector information, such as fringes or Kikuchi lines, to derive crystallographic information.

[0031] Embodiments of the present disclosure include using detector data generated by an EELS spectrometer to generate DPC data for which phase contrast information cannot be derived directly from the detector data. Instead, momentum space information is extracted from the projection of the beam onto a pixelated detector. The projections typically used to generate EELS spectra in momentum-energy coordinate space reduce the number of dimensions from the two momentum dimensions (q) present in the CBED disk to 1. 1 and q 2 ) is reduced to a single momentum dimension (q 1 The energy loss dimension (E) is preferentially considered in EELS spectra as a method of extracting information about the electronic structure of the sample, resulting at least in part from energy-dispersive filtering of the electrons through a prism that forms part of the EELS spectrometer.

[0032] For at least this reason, a significant challenge of the technique is to invert the projection from momentum-energy space back to momentum-momentum space, from which the shift in the beam disk (e.g., a diffraction disk for CBED) relative to a neutral position corresponding to the absence of the sample can be used for the DPC technique. The detector data can be generated, at least in part, by defocusing one or more optical elements of the EELS spectrometer, thereby preserving multiple momentum dimensions in the data. The data can be mapped to a coordinate space using a characteristic angle α for which the orthogonal momentum dimensions q1 and q2 are combined with the axial dimension of energy loss (E). A center of mass (COM) measurement of the shape of the detector data at a given value of energy loss can be used to generate a data cube of DPC data for which DPC information can be developed as a function of the spatial dimensions in the sample (e.g., using 1D coordinates, 2D coordinates, or 3D coordinates) and as a function of energy loss. Advantageously, measuring energy-resolved DPC data allows the data to be filtered to interrogate specific elements in the sample and specific energy transitions in the sample.

[0033] Figure 11 is a schematic diagram illustrating an example charged particle microscope system 100 according to some embodiments of the present disclosure. In the following description, details of the internal components and functions of the example TEM system 100 are omitted for simplicity, and the description is focused on the embodiments of the present disclosure (such as reference Figures 2 to 5 The present disclosure is focused on techniques for improving the performance of the detector section 110, noting embodiments of the present disclosure that include one or more electron energy loss spectroscopy (EELS) spectrometers 115.

[0034] Briefly, the electron source section includes a circuit configured to excite the charged particle source 205 (refer to Figure 2 ) electronic device, the charged particle source may include a high voltage field emission source or other emitting electron source, so that an electron beam is formed and conducted into the TEM column through a vacuum. The TEM column includes components for beam forming, including electromagnetic lenses and / or electrostatic lenses and multiple apertures to control the properties of the electron beam. The TEM column components include a condenser lens, an objective lens, a projection lens, an aberration corrector, a deflector, an stigmator, etc. and corresponding apertures. The sample section 107 accommodates the sample 225 (refer to Figure 2 ), the electron beam can be transmitted through the sample. In the case of EELS microanalysis, the beam can be focused onto the sample for point mode analysis (e.g., through the action of one or more objective lenses), or the beam can be passed through the sample in a parallel illumination mode (or at least partially defocused) to collect data from a relatively large sample area.

[0035] In some embodiments, the sample section 107 includes an objective lens 109 such that the sample is immersed in the objective field of the objective lens. Advantageously, placing the sample in the objective field of the objective lens can provide a resolution of approximately 0.05 nm for STEM mode operation. In this context, immersion in the objective field refers to placing the sample in the magnetic field of the objective lens extending into the space between the sample and the pole piece of the objective lens. Such immersion significantly reduces possible aberrations of the objective lens that would otherwise reduce the spatial resolution of the microscope.

[0036] In some embodiments, the charged particle microscope system 100 is operated in a STEM mode. For example, in a field-free (e.g., non-immersion) STEM mode, an objective is not used to focus the charged particles onto the sample. In some systems, a small focusing lens upstream of the specimen can act as a probe forming lens, and a Lorentz lens downstream of the specimen can act as a first imaging lens to provide at least some of the functions of the objective. In the field-free STEM mode, detector data can be generated with a spatial resolution of approximately 0.5 nm. In contrast, in immersion STEM mode (for which an objective is used to focus the charged particles onto the sample), the spatial resolution can be improved by up to an order of magnitude, although magnetic fields near the sample may complicate the generation of DPC data using an energy loss spectrometer, based at least in part on the effects of the immersion field on the local magnetic field in the sample.

[0037] The detector section 110 includes one or more types of detectors, sensors, screens, and / or optics configured to generate images, spectra, and other data for use in sample imaging and / or microscopic analysis. For example, the imaging section may include a scintillator screen, binoculars, a transmission electron microscopy (TEM) detector (e.g., a pixelated electron detector, a secondary electron detector), a camera, and an electron energy loss spectroscopy (EELS) spectrometer 115, among others. The EELS spectrometer 115 acts as an energy filter at least in part by focusing the electron beam onto a magnetic dispersive element (also referred to as a "prism") that exerts a force on the electrons that is proportional to the energy of the electrons. In this manner, electrons that have transferred energy to the sample (e.g., by inelastic collisions) can be redirected through the magnetic dispersive element and toward the detector. The detector may include a pixelated detector (e.g., a CCD, CMOS, or hybrid detector device configured to detect electrons) that generates two-dimensional EELS data and / or one-dimensional EELS data from which an EELS spectrum can be obtained. In some embodiments, the EELS spectrometer 115 further includes one or more optical elements, such as electromagnetic lenses and / or accelerators, to condition and / or focus the scattered electrons onto a detector, as described in reference to Figure 2 Described in more detail.

[0038] Figure 2 is a schematic diagram illustrating an example differential phase contrast system 200 according to some embodiments of the present disclosure. The example system 200 is Figure 1The example system 200 is an example of a charged particle microscope system 100 and includes a microscope 201 corresponding to a portion of a source section, a TEM column, a sample section 107, and (in some cases) a detector section 110 of the charged particle microscope system 100. The example system 200 also includes a spectrometer 115, represented by a component of an EELS spectrometer in the illustrated embodiment. The example system 200 also includes elements of a control system 210 operably coupled to the microscope 201 and the spectrometer 115.

[0039] The microscope 201 may include a charged particle source 205 configured to generate a charged particle beam 215 (e.g., electrons or ions) of a first energy E1. A portion of the particles may be scattered by the sample. The scattering event may include inelastic scattering, through which the scattered particle loses energy (e.g., ΔE). In the electron energy loss spectroscopy (EELS) technique, the EELS spectrometer 115 may be used to measure the energy of the inelastically scattered electrons, from which the energy loss ΔE may be derived. The electrons that lose energy during the inelastic scattering event travel through the TEM column and through the EELS spectrometer at an energy of E1-ΔE. The magnitude of the deviation from the energy E1 may be measured by the detector 245 of the EELS spectrometer 115 in energy space, as referenced Figures 3 to 5 Described in more detail.

[0040] Spectrometer 115 may include charged particle optical components such as a dispersive element 235 and one or more electromagnetic and / or electrostatic elements 240 (e.g., lenses, accelerators, quadrupoles, sextupoles, octopoles, etc.). Dispersive element 235 may include one or more magnetic and / or electrostatic dispersive elements (also referred to as "prisms"). Spectrometer 115 may be a post-column (e.g., Figure 2 115. The TEM column may be located after the TEM column) or it may be in the column, operably coupled to the TEM column. Elements 235 and 240 may be calibrated to select an energy that may be the same as or different from the beam energy E1. In this way, the charged particles may be filtered and a subset may be transmitted to element 240 and subsequently directed to detector 245 of spectrometer 115.

[0041] In some embodiments, element 240 also focuses the charged particles onto detector 245. Detector 245 can generate detector data. Detector 245 can be a pixelated detector. Thus, detector 245 can be configured to generate an electrical signal in response to receiving a charged particle at a detector surface. In some embodiments, detector 245 can be configured for electron counting, such that detector 245 is sensitive to individual charged particles. Advantageously, the single particle counter configuration can improve the signal-to-noise characteristics of detector 245 relative to an integrator configuration that generates a signal proportional to the particle flux within a given collection period. As described in reference Figures 3 to 6In more detail, the detector data may include an EELS spectrum resulting from the interaction between the charged particle beam 215 and the atoms 227 of the sample 225. For example, where the microscope 201 is operated in STEM mode (e.g., STEM in a scanning TEM or SEM) and the sample 225 is thinned to allow transmission of the beam, the electron beam may be focused onto a point in the sample 225 that allows measurement of individual atoms or groups of atoms on a nanometer scale.

[0042] The charged particle beam 215 may be focused onto the sample 225 and / or onto a plane at a given distance relative to or within the sample and scanned across the surface of the sample 225 (e.g., according to a raster pattern). In coordination with the beam motion, the EELS spectrometer 115 may be used to generate detector data, such as reference Figure 3 The imaging mode can be energy selective (e.g., imaging the zero-loss peak, plasmon resonance peak, core loss region, etc. of the EELS spectrum), so that the detector data is defined for the momentum-energy coordinate space, as described in reference Figure 3 The interaction of the charged particle beam 215 and the atoms of the sample 227 may change the momentum and / or energy of the particles. In this manner, according to embodiments of the present disclosure, DPC and / or COM techniques may be performed based at least in part on processing energy loss spectrum data.

[0043] Other components of the system 200 can be used to attenuate, redirect, absorb, or otherwise exclude unscattered charged particles 250 or weakly scattered charged particles 255 (e.g., electrons that pass through the sample 225 without scattering) from the detector data. For example, element 230 can apply a force (e.g., a magnetic force) to the electrons that is proportional to the energy of the electrons, which redirects electrons having an energy of about E1 away from the beam axis and into an absorbing material or other surface inside the microscope 201.

[0044] The control system 210 may include one or more machines (e.g., computing devices) operably coupled to control circuitry disposed in the microscope 201 and / or the spectrometer 115. In an illustrative example, the control circuitry may include an arrangement of circuit components connected to a power source and configured to control the application of power (e.g., voltage and / or current) to the source 205, the elements 220, 230, 235, 240, and / or the detector 245. In this manner, a process for generating DPC data using the elements 220, 230, 235, 240, and / or the detector 245 may be orchestrated by the control system 210 according to one or more operations encoded in machine-executable instructions stored on one or more machine-readable storage media (e.g., local storage media, distributed "cloud" storage media, etc.).

[0045] The one or more machines may include, but are not limited to, a personal computer, a laptop computer, a tablet computer, a server, a dedicated machine (ASM), etc. In some embodiments, the control system 210 includes user-interactive elements such as a display and input peripherals (e.g., a mouse and a keyboard), according to reference Figure 3 The user may reversibly implement the DPC-EELS mode through these user-interactive elements. In the illustrative example, the user may select an interactive graphical element 211 on a user interface (e.g., in an application, a browser environment, etc.) that initiates the DPC-EELS mode. To return the system 200 to its previous state, the user may select an interactive graphical element 211 that initiates a recalibration of the elements 220, 230, 235, and / or 240. To this end, the processes of the present disclosure (e.g., Figure 3 The example process 300 of the present disclosure may include an operation for receiving user interaction data (e.g., via an interactive user interface), wherein the interaction data corresponds to an action by a user to initiate or reverse a recalibration of one or more elements of a charged particle microscope system. Similarly, the process of the present disclosure may include generating user interface data configured to modify a display (e.g., of the control system 210) to present an interactive user interface.

[0046] Figure 3 is a schematic diagram showing example detector data according to some embodiments of the present disclosure. Figure 2 Elements of system 200 are shown separately to focus on the techniques used to generate detector data. Figure 1 The example system 100 and / or Figure 2 Example system 200 to generate example detector data. Figure 1 Compared to the typical operation of the spectrometer 115 of the present disclosure, the technique of the present disclosure includes scanning the charged particle beam 215 across the sample according to the scanning pattern 305. The interaction of the charged particle beam 215 with the atoms 227 of the sample can introduce momentum shift 310 and / or energy loss 315 in the charged particles. Such information can be used to generate DPC data, such as reference Figure 5 to Figure 6 Described in more detail.

[0047] The deflection of the beam may depend at least in part on the position of the beam 305 relative to the atoms 227, as well as the electronic and / or magnetic properties of the atoms 227. For example, the first atom 227-1 may be relatively lighter than the second atom 227-2, such that the second atom 227-2 may have a relatively greater effect on the trajectories of the constituent particles that make up the charged particle beam 215 than the first atom 227-1. Similarly, atoms having characteristic inelastic transitions associated with the electrons of the atom, such as excitation and / or ionization transitions, may result in a characteristic energy loss represented by a shift in the detector data on the energy axis relative to a zero-loss position.

[0048] Elements 235 and 240 may be configured to direct at least a subset of charged particles from the sample location via optical element 230 to detector 245. In typical EELS operation, electrons are focused onto the detector as a method of reducing dimensional information in momentum space, which is beneficial for improving the signal-to-noise characteristics of the energy loss spectrum. In some embodiments of the present disclosure, the energy dispersion component 320 of the charged particle beam 215 is directed to the detector 245 without being focused onto the surface of the detector. To this end, elements 235 and / or 240 may be defocused from an initial "focused" configuration and / or may be operated in a defocused configuration. In this context, defocusing may include modifying one or more operating parameters of elements 235 and / or 240 or moving detector 245 relative to element 240. Examples of operating parameters include, but are not limited to, parameters that affect the focal length of element 240 and / or the action of energy dispersion element 235. For example, the dispersive element 235 can be configured to generate a divergent component 320 from the outlet 330 as in an imaging mode, or to generate a converging component 320 from the outlet 330 as in a spectral mode. In the imaging mode, the component 320 is integrated by the detector, while in the spectral mode, the spatial position on the detector is related to the energy loss referenced to the zero-loss peak position, which can define the origin of the energy loss spectrum. The imaging mode can apply energy selection of the prism so that an image is generated by scanning the charged particle beam 215 over the sample, and the detector data represents the intensity of a given energy loss (e.g., zero-loss peak, edge, etc.), from which an image can be generated.

[0049] Advantageously, defocusing the energy dispersion component 320 allows momentum information to be preserved in the detector data that would otherwise be lost by projecting onto the energy axis (e.g., as part of the EELS data cube). Figures 4 to 6As described in more detail, momentum information may be extracted from energy loss data via one or more geometric transformations applied to the energy loss data and / or data generation operations. In this manner, embodiments of the present disclosure include methods for generating and / or processing energy loss data to extract momentum space information that is used in DPC and COM techniques to image phase contrast information and other physical and chemical properties of a sample.

[0050] Figure 4 4 is a schematic diagram showing example EELS data 400 including momentum space information according to some embodiments of the present disclosure. The example data 400 represents the use of an energy loss spectrometer (e.g., Figure 1 115), detector data generated by a STEM or TEM system operating in spectral mode. In the image, the intensity measured in counts or other arbitrary units is represented by a patterned fill, where brighter areas of the data 400 represent areas with higher charged particle flux. The example data 400 includes a zero-loss peak 405 area and a phonon resonance peak 410 area. As shown in reference Figure 3 As described in more detail, zero-loss peak 405 can be used to define an origin in the energy loss dimension so that a calibration used to correlate a position on detector 245 with energy loss can reference the zero-loss peak 405 position. In some embodiments, the spectral mode can include configuring elements 235 and 240 to focus charged particles onto the detector in momentum space while maintaining energy dispersion. The resulting data produces a one-dimensional energy loss spectrum, rather than the two-dimensional data shown.

[0051] However, example data 400 still represents a partial dimensionality reduction achieved by integrating the momentum distribution along a second momentum dimension (referred to as "q2"), which may be orthogonal to the plane defined by q1 and E. The information contained in the second momentum dimension is used in DPC and COM techniques. Thus, recovering the momentum space information allows energy loss spectrum data (such as example data 400) to be used in DPC and COM techniques. Reference Figure 3 , defocusing the spectrometer preserves momentum information in the pattern projected onto the detector, where charged particles of substantially equal energy are incident at different locations on the energy loss axis due, at least in part, to the momentum distribution along q2. In this way, backprojection from the q1-E plane onto the q1-q2 plane allows recovery of momentum-momentum space data from which phase contrast information can be derived.

[0052] Additionally and / or alternatively, the example data 400 can be used directly to extract momentum information about the charged particle at q1. In the case where q1 and q2 define a coordinate space of E, the disclosed techniques include generating energy loss spectrum data for multiple system configurations, through which two or more data sets can provide momentum information in q1 and q2, respectively. Figure 6 As described in more detail, rotating the charged particle beam before it enters the spectrometer can be used to generate data in the q2-E coordinate space.

[0053] Figure 5 is a schematic diagram illustrating an example back-projection technique for extracting momentum space information from example energy loss spectrum data 500 according to some embodiments of the present disclosure. The example data 500 includes a zero-loss peak 505 region projected onto momentum-energy coordinate space, as shown in FIG. Figure 4 as described. Figure 5 The technique includes mapping the example data 500 from the q1-E plane to the q1-q2 coordinate space using a three-dimensional coordinate system defined by q1, q2, and E. As shown, for ease of description, the zero loss peak 505 region is shown as an ellipse. In some embodiments, the example data 500 includes information for other energy loss regions, such as Figure 4 The phonon resonance 410 region is shown.

[0054] The backprojection shown includes transforming the two-dimensional data from the q1-E coordinate space to the q1-q2-E coordinate space so that various features in the example data 500 can be used for DPC and / or COM techniques. For example, the centroid 510 of the zero-loss peak 505 region can be mapped into the q1-q2 space 515 using the intersection of the cord connecting the centroid 510 in the q1-E plane with the q1-q2 plane, where the cord is aligned at an angle 525α relative to the q2 axis.

[0055] The back-projected centroid 520 where the cord intersects the q1-q2 plane encodes information about the interaction of the atoms 227 of the sample at a given beam position on the sample 225 with the charged particle beam 215. Thus, the back-projection in the q1-q2 coordinate space can be used to generate DPC data. Although the centroid 510 in the q1-E plane is shown to fall on the energy (E) axis, and the centroid 520 in the q1-q2 plane is shown to fall on the q2 axis, the positions of the corresponding centroids 510-520 may be different from those shown. For example, the centroid 510 in the q1-E plane may be off-axis in the q1 dimension. Similarly, the centroid 520 in the q1-q2 plane may be off-axis in the q1 dimension. Advantageously, back-projecting the data 500 into the q1-q2-E coordinate space provides energy-resolved momentum information. In this way, the energy-selective imaging capability of EELS can be implemented in combination with the phase-contrast imaging capability of DPC and COM techniques.

[0056] Figure 6 is a diagram showing a method for using a Figure 1 to Figure 2 A block diagram of an example process 600 for generating differential phase contrast data using an example system of the invention. One or more operations constituting the example process 600 may be performed by a computer system and / or an analytical instrument (e.g., Figure 1 The components of the example system 100) may be operably coupled to other machines and / or additional systems or subsystems (including but not limited to characterization systems, network infrastructure, databases, controllers, relays, power systems, and / or user interface devices) to be executed and / or initiated. Therefore, the operations may be stored in one or more machine-readable media as machine-executable instructions, which, when executed by a computer system, may cause the computer system to perform at least a portion of the constituent operations of process 600. The constituent operations of process 600 may be performed before, between, and / or after operations omitted in this specification (such as sample and / or instrument preparation, operations occurring before operation 605, etc.), which form a process for processing samples to generate such as Figure 2 To this end, in some embodiments, the operations of the example process 600 may be omitted, repeated, reordered, and / or replaced.

[0057] At operation 605, the example process 600 includes directing a charged particle beam (e.g., Figure 2 A charged particle beam 215) passes through the material sample ( Figure 2 The sample can be disposed in the objective section of the microscope tube (e.g., Figure 1 In the objective lens section 105). Figures 2 to 5As described in more detail, the interaction of the material sample and the charged particle beam may produce a scattered portion of the beam. The scattered portion may include particles that are elastically scattered and / or particles that are inelastically scattered. Since a given charged particle has a non-zero probability of experiencing both an elastic collision and an inelastic collision, a particle that loses energy to the sample may also experience an elastic collision and change momentum, and vice versa. In the context of example process 600, operation 605 may include focusing the charged particle beam onto the sample and moving the charged particle beam according to a scanning pattern (e.g., Figure 3 Operation 605 may include translating the beam across the sample (e.g., scanning pattern 305). Similarly, operation 605 may include focusing the beam to a location within the sample or away from the sample.

[0058] At operation 610, the example process 600 includes directing the scattered portion to an energy filter (e.g., Figure 1 Spectrometer 115). Figures 1 to 3 In more detail, the energy filter may be configured to disperse the scattered portions by energy along a dispersion axis (e.g., energy axis E). Directing the scattered portions onto the energy filter may include focusing the scattered portions at least partially onto the energy filter. In some embodiments, an energy selector (e.g., a selector slit) may be disposed in the beam path, or the energy filter may be configured to select for a given energy or energy range, such that operation 610 may include directing a subset of the scattered portions toward a detector of the energy filter.

[0059] At operation 615, the example process 600 includes using an incident signal on a detector (e.g., Figure 2 In the case where the charged particle beam is an electron beam, the detector data may include EELS data, such as reference Figures 2 to 5 Operation 615 may include defocusing one or more components of the energy filter and generating an angle-resolved EELS (AR-EELS) image using a detector. AR-EELS describes a technique whereby the scattering of electrons is measured in one momentum dimension (q) and one angle dimension (ω), where the angle is determined by the energy filter (e.g., Figure 2 One or more parameters of element 235) are associated with energy loss, such as reference Figures 4 to 5 Described in more detail.

[0060] At operation 620, the example process 600 includes generating DPC data using the detector data. Generating the DPC data may include determining a region of the AR-EELS image (e.g., Figure 5 of the region 505) (e.g., Figure 5Operation 620 may also include mapping the first center of mass of the AR-EELS image from the energy-momentum coordinate space (e.g., q1-E) to the momentum-momentum coordinate space (e.g., q1-q2) and determining a second center of mass in the momentum-momentum coordinate space (e.g., Figure 5 In some embodiments, the first center of mass is located along the energy loss axis (E) of the AR-EELS image, and the second center of mass is located at the origin of the momentum axis and the energy loss axis (e.g., Figure 5 q1-E).

[0061] As reference Figure 4 As described, generating detector data may include: generating a first AR-EELS image using a detector; modifying one or more components of a microscope column to cause a rotation of a diffraction pattern generated via the interaction of an electron beam and a material sample; and generating a second AR-EELS image from the rotated diffraction pattern using the detector. Modifying the one or more components may include adjusting one or more charged particle optical elements (e.g., Figure 2 The electromagnetic properties of the element 230 of the projector are modified to induce a rotation of the beam relative to the beam axis, which preserves the momentum distribution of the charged particles that make up the beam in momentum space (e.g., q1-q2). In this way, the momentum information can be projected onto q2 in the detector data, from which the q2 momentum information used in DPC and COM techniques can be extracted as a function of position in the sample, which function can also be resolved based on energy losses. The rotation can be achieved by moving the sample and / or downstream relative to the sample, by modifying one or more electromagnetic elements of the projector lens system, and by taking advantage of the tendency of charged particles to enter a spiral trajectory in the presence of a magnetic field aligned with the axis axis.

[0062] To this end, generating DPC data may further include: determining a first center of mass of a region in the first AR-EELS image, the first center of mass being defined for a first energy-momentum coordinate space (q1-E); determining a second center of mass of a region in the second AR-EELS image, the second center of mass being defined for a second energy-momentum coordinate space (q2-E); and determining a third center of mass of the region, the third center of mass being defined for a momentum-momentum coordinate space (q1-q2). Figure 5 As shown, the first energy-momentum coordinate space and the second energy-momentum coordinate space may be substantially orthogonal. In this manner, operation 620 may include rotating the beam 90 degrees about the beam axis as part of generating two AR-EELS images. In an example system of the present disclosure (e.g., Figure 2 In the context of the example system 200 of ), the planar coordinate spaces may be oriented at an angle relative to each other in the three-dimensional space defined by the planar space. In the detector data, due to the spectrometer (e.g., Figure 1 and Figure 2 The dimension of the projection of the optical device of the spectrometer 115) onto the detector is reduced and the plane coordinate space can be parallel.

[0063] In some embodiments, generating DPC data may include applying an integral (inverse gradient) to generate an iDPC image of the electrostatic potential field of the sample using the centroid information developed in operation 620. For example, generating DPC data may include determining a displacement μ of a second centroid in momentum-momentum coordinate space relative to a reference position of the first centroid. The reference position may include the centroid of a corresponding pattern in q1-q2 space in the absence of the sample, a calibrated “zero position”, etc., such that μ is a vector quantity defined relative to an origin in momentum-momentum coordinates. In some embodiments, generating DPC data includes applying a differential (divergence) to generate a dDPC image of the charge density field of the sample using the centroid information developed in operation 620.

[0064] In the following mathematical formula, q1 is referred to as x and q2 is referred to as y with reference to a two-dimensional Cartesian coordinate system. Similar coordinates (e.g., r-θ) may be used, or any coordinate system describing a plane defined by two vectors. The formula treats the two momentum axes independently using any energy range from a first energy E to a second energy E+ΔE. Within the energy selection (E, E+ΔE), the detector data is a function of momentum in the x direction as shown below:

[0065]

[0066] Where R(k x ,k y , E) is a function describing the electron energy-dependent CBED pattern behind the filter system. Note that is the complete CBED pattern that appears at the entrance of the filter, also known as the Ronchigram. This is because the filter system expands the Ronchigram in the energy direction and also in the k y Directional extrusion (projection) Ranchi diagram.

[0067] COM can be used to export the following expressions:

[0068]

[0069] The above expression can be rearranged by swapping the order of integration to obtain the following expression:

[0070]

[0071] The resulting term can be identified as k xThe DPC components in the direction (q1), but now in the selected energy range (E,E+ΔE). If we integrate over the electron energy range from zero to infinity, we obtain the unfiltered DPC components:

[0072] Similarly, after the CBED pattern in front of the filter is rotated 90° (π / 2rad), q2 or k in this example y The same situation will occur in the direction. In the energy selection (E, E+ΔE), the detector data is k y The function of momentum in direction is as follows:

[0073]

[0074] Where R(k x ,k y , E) is a function describing the electron energy-dependent CBED pattern behind the filter system. This is at least partly based on the fact that the filter system expands the Ranchi diagram in the energy direction, while now also along k x Directional extrusion (projection) Ranchi diagram.

[0075] Along k y COM can be used to export the following expressions:

[0076]

[0077] The above expression can be rearranged by swapping the order of integration to obtain the following expression:

[0078]

[0079] The resulting term can be identified as k y The DPC components in the direction (q2), but now in the selected energy range (E,E+ΔE). If we integrate over the electron energy range from zero to infinity, we obtain the unfiltered DPC components:

[0080] For the technology of the present disclosure, the above mathematical formula can be applied to coordinate space data, such as reference Figure 5 As described in more detail, and / or applied to project momentum data into a momentum dimension (q1 or q2), as referenced Figure 4 as described.

[0081] The iDPC method and the dDPC method may also include using a DPC vector image of the displacement. Detailed formulations are described in the literature sources cited with reference to the use of a segmented STEM detector and referenced in the preceding paragraphs of this disclosure. For the DPC vector image, the displacement vector μ may vary with position on the sample (e.g., in Cartesian xyz coordinates), so that generating the DPC vector image may include scanning a pattern (e.g., Figure 3 The scanning pattern 305 of the material sample is used to determine a plurality of displacements associated with locations on the sample from which pixels of the DPC vector image can be defined. In this manner, a scalar image of the material sample can be generated at least in part by integrating the DPC vector image (e.g., applying an inverse gradient) to generate an iDPC image. In some embodiments, a scalar image of the material sample is generated at least in part by differentiating the DPC vector image (e.g., applying a divergence) to generate a dDPC image.

[0082] In some embodiments, energy-resolved momentum information may be used to generate energy-resolved DPC data. For example, operation 620 may include selecting a region of the AR-EELS image such that the DPC data corresponds to a zero-loss peak of the EELS data. Similarly, a region may be selected such that the DPC data corresponds to a plasmon resonance peak and / or a core-loss region of the EELS data. To this end, a region may be selected to include one or more edges in the EELS data, where an edge may be associated with a particular element, thereby allowing the DPC data to highlight a particular element, transition, etc.

[0083] In the foregoing description, various embodiments have been described. For purposes of explanation, specific configurations and details have been set forth in order to provide a thorough understanding of the embodiments. However, it will also be apparent to one skilled in the art that the embodiments may be practiced without these specific details. In addition, well-known features may have been omitted or simplified in order not to obscure the described embodiments. Although the example embodiments described herein focus on energy loss spectroscopy systems, and specifically on EELS systems, these are meant to be non-limiting exemplary embodiments.

[0084] Some embodiments of the present disclosure include a system having one or more data processors and / or logic circuits. In some embodiments, the system includes a non-transitory computer-readable storage medium containing instructions, which, when executed on one or more data processors and / or logic circuits, cause one or more data processors and / or logic circuits to perform part or all of one or more methods disclosed herein and / or part or all of one or more processes and workflows. Some embodiments of the present disclosure include a computer program product tangibly embodied in a non-transitory machine-readable storage medium, the computer program product including instructions configured to cause one or more data processors and / or logic circuits to perform part or all of one or more methods disclosed herein and / or part or all of one or more processes.

[0085] The terms and expressions employed herein are used as terms of description rather than limitation, and when such terms and expressions are used, it is not intended to exclude any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the claims. Therefore, it should be understood that while the present disclosure includes specific embodiments and optional features, modifications and changes to the concepts disclosed herein may be made by those skilled in the art, and such modifications and changes are deemed to be within the scope of the appended claims.

[0086] When a term is used without explicit definition, it is understood that unless the term has a special and / or particular meaning in the field of charged particle microscopy systems or other related fields, the term refers to the ordinary meaning of the word. The term "about" or "substantially" is used to indicate a deviation from the stated property, wherein the deviation has little or no effect on the corresponding function, property or attribute of the described structure. In the illustrated example where one dimensional parameter is described as "substantially equal to" another dimensional parameter, the term "substantially" is intended to reflect that the two parameters being compared may be unequal within permissible limits (such as manufacturing tolerances or confidence intervals inherent to system operation). Similarly, where a geometric parameter (such as alignment or angular orientation) is described as "approximately" perpendicular, "substantially" perpendicular, or "substantially" parallel, the term "about" or "substantially" is intended to reflect that the alignment or angular orientation may differ from the precisely stated condition (e.g., not precisely perpendicular) within permissible limits. For dimensional values ​​(such as diameter, length, width, etc.), the term "about" may be understood to describe a deviation of up to ±10% from the stated value. For example, a size of "about 10 mm" may describe a size from 9 mm to 11 mm.

[0087] This description provides exemplary embodiments, and is not intended to limit the scope, applicability or configuration of the present disclosure. On the contrary, the subsequent description of the exemplary embodiments will provide enabling descriptions for realizing various embodiments to those skilled in the art. It should be understood that, without departing from the spirit and scope set forth in the appended claims, various changes may be made to the functions and arrangements of the elements. Specific details are given in the description to provide a thorough understanding of the embodiments. However, it should be understood that the embodiments may be put into practice without these specific details. For example, the specific system components, systems, processes and other elements of the present disclosure may be shown in schematic form, or omitted from the diagram, so as to avoid obscuring the embodiments due to unnecessary details. In other cases, well-known circuits, processes, components, structures and / or technologies may be shown without unnecessary details.

Claims

1. An electron microscope system, comprising: an electron source configured to emit an electron beam; a microscope column optically coupled to the electron source and configured to receive the electron beam from the electron source; an energy filter coupled to the microscope column and configured to receive electrons of the electron beam from the microscope column; and a control circuit operatively coupled to the microscope column and the energy filter, the control circuit electronically coupled to one or more non-transitory machine-readable storage media storing instructions that, when executed by the control circuit, cause the electron microscope system to perform operations including: directing the electron beam through a material sample disposed in the microscope column, wherein interaction of the material sample and the electron beam produces a scattered portion of the electron beam; directing the scattered portions onto the energy filter, the energy filter being configured to disperse the scattered portions along a dispersion axis by energy and directing a subset of the scattered portions toward a detector of the energy filter; generating detector data using the subset of the scattered portions incident on the detector, the detector data comprising EELS data; as well as Differential phase contrast (DPC) data is generated using the detector data.

2. The system of claim 1 , wherein generating detector data comprises: defocusing one or more components of the energy filter; as well as Angle-resolved EELS (AR-EELS) images were generated using the detector.

3. The system of claim 2, wherein generating DPC data comprises: determining a first centroid of a region of the AR-EELS image in energy-momentum coordinate space; mapping the first center of mass of the AR-EELS image from the energy-momentum coordinate space to the momentum-momentum coordinate space; as well as A second center of mass in the momentum-momentum coordinate space is determined.

4. The system of claim 3, wherein generating the DPC data further comprises: determining a displacement μ of the second center of mass in the momentum-momentum coordinate space relative to a reference position of the first center of mass; generating a DPC vector image using the displacement; as well as A scalar iDPC image of the material sample is generated at least in part by integrating the DPC vector image.

5. The system of claim 2, wherein defocusing the one or more components of the energy filter comprises: modifying one or more operating parameters of one or more electron-optical elements of the energy filter; or The detector is moved.

6. The system of claim 5, wherein the operations further comprise determining an angle α corresponding to an angle of incidence of the subset of the scattered portions relative to a detection surface of the detector.

7. The system of claim 1 , wherein generating detector data comprises: generating a first AR-EELS image using the detector; modifying one or more components of the microscope column to cause a rotation of a diffraction pattern generated via the interaction of the electron beam with the material sample; as well as A second AR-EELS image is generated from the rotated diffraction pattern using the detector.

8. The system of claim 7, wherein generating DPC data comprises: determining a first center of mass of a region in the first AR-EELS image, the first center of mass being defined with respect to a first energy-momentum coordinate space; determining a second center of mass of the region in the second AR-EELS image, the second center of mass being defined with respect to a second energy-momentum coordinate space; A third center of mass of the region is determined, the third center of mass being defined with respect to momentum-momentum coordinate space.

9. The system of claim 8, wherein the first energy-momentum coordinate space and the second energy-momentum coordinate space are substantially orthogonal.

10. The system of claim 8, wherein the region corresponds to a zero-loss peak of the scattering portion.

11. The system of claim 8, wherein the region corresponds to a plasmon resonance region of the scattering portion.

12. One or more non-transitory machine-readable storage media storing machine-executable instructions that, when executed by a machine, cause the machine to perform operations comprising: directing an electron beam through a material sample disposed in an objective section of a microscope column, wherein interaction of the material sample and the electron beam produces a scattered portion of the electron beam; directing the scattered portions onto an energy filter operably coupled to the microscope column and configured to disperse the scattered portions along a dispersion axis with energy and direct a subset of the scattered portions toward a detector of the energy filter; generating detector data using the subset of the scattered portions incident on the detector, the detector data comprising EELS data; as well as Digital phase contrast (DPC) data is generated using the detector data.

13. The medium of claim 12, wherein generating detector data comprises: defocusing one or more components of the energy filter; as well as Angle-resolved EELS (AR-EELS) images were generated using the detector.

14. The medium of claim 13, wherein generating DPC data comprises: determining a first centroid of a region of the AR-EELS image; mapping the first center of mass of the AR-EELS image from an energy-momentum coordinate space to a momentum-momentum coordinate space; as well as A second center of mass in the momentum-momentum coordinate space is determined.

15. The medium of claim 12, wherein generating detector data comprises: generating a first AR-EELS image using the detector; modifying one or more components of the microscope column to cause a rotation of a diffraction pattern generated via the interaction of the electron beam with the material sample; as well as A second AR-EELS image is generated from the rotated diffraction pattern using the detector.

16. The medium of claim 15, wherein generating the DPC data comprises: determining a first center of mass of a region in the first AR-EELS image, the first center of mass being defined with respect to a first energy-momentum coordinate space; determining a second center of mass of the region in the second AR-EELS image, the second center of mass being defined with respect to a second energy-momentum coordinate space; A third center of mass of the region is determined, the third center of mass being defined with respect to momentum-momentum coordinate space.

17. The medium of claim 16, wherein generating the DPC data further comprises: determining a displacement μ of the third center of mass in the momentum-momentum coordinate space relative to a reference position of the second center of mass; generating a DPC vector image using the displacement; A scalar dDPC image of the material sample is generated by differentiating the DPC vector image.

18. The medium of claim 16, wherein the first energy-momentum coordinate space and the second energy-momentum coordinate space are substantially orthogonal.

19. The medium of claim 16, wherein the region corresponds to a zero-loss peak of the scattering portion.

20. The medium of claim 16, wherein the region corresponds to a core loss region of the scattering portion.

Images