Differential phase contrast microanalysis using energy loss spectrometers

Abstract

To provide techniques for performing DPC imaging and EELS that satisfy dose constraints.SOLUTION: Systems, components and methods for generating differential phase contrast (DPC) data are described. The methods include operations for directing a beam of electrons through a material sample disposed in a microscope column, where interactions of the material sample and the beam of electrons produce a scattered portion of the beam of electrons. The methods include directing the scattered portion onto an energy filter, the energy filter being configured to disperse the scattered portion along a dispersal axis by energy and to 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 comprising EELS data. The operations also include generating differential phase contrast data using the detector data.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] (CROSS REFERENCE TO RELATED APPLICATIONS) This application claims the benefit of U.S. Provisional Application No. 18 / 453,978, filed August 22, 2023, the disclosure of which is incorporated by reference in its entirety herein.

[0002] (Technical field) SUMMARY OF THE DISCLOSURE Embodiments of the present disclosure are directed to charged particle microscope systems, and algorithms and methods for their operation. In particular, some embodiments are directed to techniques for microanalysis, including differential phase contrast. [Background technology]

[0003] In a scanning electron microscope (STEM), a beam of electrons is focused on a sample to generate various signals from which characteristic information about the sample can be derived. Electron energy loss spectroscopy (EELS) is one example, and high angle dark field scattering (HAADF) is another. Differential phase contrast (DPC) involves scanning the beam over the sample to generate characteristic interferograms that can be used to derive structural information, such as crystal structure information (similar to diffraction) and bonding information. Differential phase contrast offers the advantage of directly imaging the magnetic structure of the atoms that make up the sample, allowing intuitive image analysis and direct measurement of material parameters from the image.

[0004] Typically, differential phase contrast (DPC) is implemented using a segmented detector, and a differential signal is generated as the beam sweeps forward and backward across the sample. Typically, the differential signal is generated from the difference of detector signals from opposing detector segments on opposite sides of a central position, for example using a quadrant detector. For this reason, differential phase contrast techniques typically involve the introduction of a specialized segmented detector downstream of the sample, similar to those used in bright-field (BF) STEM imaging, except that the detector is split into opposing segments along one or more axes. Compared to HAADF, both DPC and EELS measure electrons scattered at relatively small angles by atoms of the sample. Thus, the common techniques of DPC and EELS do not allow simultaneous measurements without sacrificing one in favor of the other. For example, a segmented detector can include an aperture to allow a portion of the scattered electrons to pass to the EELS spectrometer. Alternatively, two consecutive measurements can be performed at any location of the sample to collect EELS and DPC data separately. Due to the increasing resolution of instruments, the progressively smaller structures of materials to be measured, and the improvement of cryopreservation techniques, samples of interest are becoming more and more sensitive to charged particle exposure. This sensitivity imposes a constraint on the total dose that can be used at a given sample location in DPC imaging and EELS analysis. Therefore, techniques to perform DPC imaging and EELS that meet the dose constraints need to be developed. Summary of the Invention

[0005] In one aspect, an electron microscope system includes an electron source configured to emit a beam of electrons, a microscope column optically coupled to the electron source and configured to receive the beam of electrons from the electron source, and an energy filter coupled to the microscope column and configured to receive the electrons of the beam of electrons from the microscope column. The system includes 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. The operations include directing the beam of electrons through a material sample disposed within the microscope column, where interaction of the material sample with the beam of electrons generates scattered portions of the beam of electrons. The operations include directing the scattered portions to an energy filter configured to disperse the scattered portions along a dispersion axis by energy and direct a subset of the scattered portions toward a detector of the energy filter. The operations include generating detector data using the subset of the scattered portions incident on the detector, where the detector data includes EELS data. The operations further include generating differential phase contrast (DPC) data using the detector data.

[0006] In some embodiments, generating the detector data also includes defocusing one or more components of the energy filter and using the detector to generate an angle resolved EELS (AR-EELS) image. Generating the DPC data can include determining a first centroid of a region of the AR-EELS image in energy-momentum coordinate space. Generating the DPC data can include mapping the first centroid of the AR-EELS image from the energy-momentum coordinate space to a momentum-momentum coordinate space. Additionally, generating the DPC data can include determining a second centroid in the momentum-momentum coordinate space.

[0007] In some embodiments, generating the DPC data can further include determining a displacement μ of the second center of mass relative to a reference position of the first center of mass in momentum-momentum coordinate space. Additionally, generating the DPC data can include using the displacement to generate a DPC vector image and generating a scalar iDPC image of the material sample by at least partially integrating the DPC vector image.

[0008] Defocusing one or more components of the energy filter may include changing one or more operating parameters of one or more electronic optical elements of the energy filter or moving the detector, and may further include determining an angle α corresponding to an angle of incidence of the subset of scatterers with respect to a detection surface of the detector.

[0009] Generating the detector data can include generating a first AR-EELS image using the detector. Generating the detector data can include altering one or more components of the microscope column to cause a rotation of a diffraction pattern generated by an interaction of the beam of electrons with the material sample. Additionally, generating the detector data can include generating a second AR-EELS image from the rotated diffraction pattern using the detector.

[0010] In some embodiments, generating the DPC data includes determining a first centroid of a region in the first AR-EELS image, the first centroid being defined relative to a first energy-momentum coordinate space. Generating the DPC data can include determining a second centroid of a region in the second AR-EELS image, the second centroid being defined relative to a second energy-momentum coordinate space. Additionally, generating the DPC data can include determining a third centroid of the region, the third centroid being defined relative to a momentum-momentum coordinate space. The first energy-momentum coordinate space and the second energy-momentum coordinate space can be substantially orthogonal. The region can correspond to a zero-loss peak of the scattering portion. The region can correspond to a plasmon resonance region of the scattering portion. The region can correspond to an inner shell electron excitation region of the scattering portion.

[0011] 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 operations of the aforementioned aspect.

[0012] In a third aspect, a method of generating DPC data includes the operations of the aforementioned aspects. The method can be implemented automatically (e.g., without human intervention), semi-automatically (e.g., with limited human intervention), and / or manually. For example, the method can be initiated by a human user using a charged particle microscope system, after which the operations of the aforementioned aspects can be implemented as one or more computer-implemented algorithms. The method can conclude with a user action, such as generating visualization data from a subset of the EELS data and corresponding DPC data.

[0013] The terms and expressions employed are used as terms of description and not as terms of limitation, and in using such terms and expressions there is no intention to exclude any equivalents of the features or portions thereof shown and described, but it is understood that various modifications are possible within the scope of the claimed subject matter. Thus, although the subject matter claimed herein has been specifically disclosed by embodiments and optional features, it should be understood that modifications and variations of the concepts disclosed herein may be made by those skilled in the art, and such modifications and variations are deemed to be within the scope of the present disclosure as defined by the appended claims. [Brief description of the drawings]

[0014] The foregoing aspects and many of the attendant advantages of the present disclosure will become more readily appreciated as the same become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, in which:

[0015] [Figure 1] FIG. 1 is a schematic diagram illustrating an exemplary charged particle microscope system according to some embodiments of the present disclosure.

[0016] [Diagram 2] 1A-1C are schematic diagrams illustrating an exemplary differential phase contrast technique according to some embodiments of the present disclosure.

[0017] [Diagram 3] 1 is a schematic diagram illustrating example differential phase contrast detector data according to some embodiments of the present disclosure;

[0018] [Figure 4] 1 is a schematic diagram illustrating example EELS data including momentum-spatial information according to some embodiments of the present disclosure.

[0019] [Diagram 5] FIG. 1 is a schematic diagram illustrating one example backprojection technique for extracting momentum-spatial information from EELS data according to some embodiments of the present disclosure.

[0020] [Figure 6] FIG. 4 is a block flow diagram illustrating an example process for generating differential phase contrast data using the example system of FIGS. 1-3, according to some embodiments of the present disclosure.

[0021] In the drawings, like reference numbers refer to like parts throughout the various views unless otherwise specified. Not every instance of an element is necessarily labeled, so as to reduce clutter in the drawings where appropriate. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles being described. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] While exemplary embodiments have been shown and described, it will be understood that various modifications are possible 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. For ease of explanation, the embodiments of the present disclosure focus on transmission electron microscopes and associated instruments. As such, the embodiments are not limited to such instruments, but rather, analytical instrument systems are contemplated in which a scanning beam of charged particles is used to generate detector data. Similarly, the embodiments of the present disclosure focus on EELS spectrometer systems for generating detector data, although additional and / or alternative detector modalities are contemplated.

[0023] 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 a sample. The basic principle of STEM-DPC is that electrons in a beam can interact with the electromagnetic field in a material. DPC techniques involve measuring the phase shift of the electron beam resulting from such interaction. The phase shift can then be correlated with the local magnetization or polarization of the sample. The resolution of current STEM instruments allows direct imaging of atomic-scale information, from which bulk-scale parameters such as sample thickness and lattice strain can be derived. Detailed mathematical derivations of various techniques, including DPC, integral DPC (iDPC), differential DPC (dDPC), center of mass (COM), integral COM (iCOM), differential COM (dCOM), etc., have been described in the art. Without going into detailed mathematical derivations of the key equations for each technique, the reader is referred to the following peer-reviewed publications that describe theoretical and experimental aspects of such techniques using segmented brightfield detectors in STEM systems:

[0024] Ivan Lazic, Eric GT Bosch, and Sorin Lazar. “Phase contrast STEM for thin samples: Integrated differential phase contrast.” Ultramicroscopy 160 (2016): 265-280.

[0025] Ivan Lazic and Eric GTBosch, Analytical Review of Direct Stem Imaging Techniques for Thin Samples.In: Peter W. Hawkes, editor, Advances in Imaging and Electron Physics, Vol. 199, Burlington: Academic Press, 2017, pp. 75-184.ISBN: 978-0-12-812091-0.

[0026] Emrah Yucelen, Ivan Lazic, and Eric GT Bosch. “Phase contrast scanning transmission electron microscopy imaging of light and heavy atoms at the limit of contrast and resolution.”Scientific Reports 8, no. 1 (2018): 1-10.

[0027] 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, the method can include directing a beam of electrons through a material sample disposed within an objective section of a microscope column, where interaction of the material sample with the beam of electrons generates scattered portions of the beam of electrons. The method can include focusing the scattered portions onto an energy filter configured to disperse the scattered portions along an energy dispersion axis and direct a subset of the scattered portions towards a detector of the energy filter. The method can include generating detector data using the subset of the scattered portions incident on the detector, where the detector data includes EELS data. Additionally, the method can also include generating differential phase contrast (DPC) data using the detector data.

[0028] Advantageously, the disclosed technique allows for the generation of DPC data using a system without a split STEM detector, while providing energy loss selection that allows element and transition specific imaging that is not otherwise available in regular DPC data, thereby combining the capabilities of EELS and DPC. In an illustrative example, the EELS-DPC technique involves analyzing the incident electron beam using an energy filter in front of a camera or detector (e.g., as part of an energy loss spectrometer). 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, along which the raw signal can be projected onto a spatially defined vertical axis on the detector surface. Importantly, such projections can be used to determine DPC vector components, which can then be used to pre-calculate configuration directions from which COM information can be derived. In some embodiments, energy spectra can be recorded from which DPC components can be generated without the split detectors or cameras used in STEM systems.

[0029] Microscopic microanalysis at the atomic scale, such as convergent beam electron diffraction (CBED), can involve focusing a beam of electrons onto a sample and imaging the disk projection with a detector positioned at a distance from the sample where 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 derive physical and chemical information, such as crystal structure, composition, and sample thickness. Unlike DPC, CBED uses image information contained in the detector data, such as fringes, or Kikuchi lines, to derive crystallographic information.

[0030] An embodiment of the present disclosure includes generating DPC data using detector data generated by an EELS spectrometer, where 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 projection typically used to generate an EELS spectrum in momentum-energy coordinate space reduces the order of magnitude from the two momentum dimensions (q1 and q2) present in a CBED disk to a single momentum dimension (q1) and an energy-loss dimension (E). In EELS spectroscopy, the energy-loss dimension is favored as an approach to extract electronic structure information about the sample, which is at least in part a result of energy-dispersive filtering of electrons through a prism that forms part of the EELS spectrometer.

[0031] For at least this reason, a key challenge of this approach is to invert the projection from momentum-energy space to momentum-momentum space, so that a shift of the beam disk (e.g., a diffraction disk for CBED) relative to a neutral position corresponding to the absence of a sample can be utilized 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, so that multiple momentum dimensions can be preserved in the data. The data can be mapped into coordinate space using a characteristic angle α where the momentum dimensions q1 and q2 are orthogonal and combined with the axial dimension of the energy loss (E). Center of mass (COM) measurements using the geometry of the detector data at a given value of energy loss can be used to generate a data cube of DPC data, in which DPC information can be constructed as a function of spatial dimensions within the sample (e.g., using one-, two-, or three-dimensional coordinates) or as a function of energy loss. Advantageously, measuring energy-resolved DPC data allows filtering of the data to interrogate specific elements in the sample, as well as specific energy transitions in the sample.

[0032] FIG. 1 is a schematic diagram illustrating an exemplary 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 exemplary TEM system 100 are omitted for simplicity and to focus the description on embodiments of the present disclosure and techniques for increasing sample information in spectra with relative background information, as described in more detail with reference to FIGS. 2-5B. The exemplary TEM system 100 includes an electron source section, a TEM column including an objective section 105, and a detector section 110. The present disclosure focuses on techniques for improving the performance of the detector section 110, focusing on embodiments of the present disclosure including one or more electron energy loss spectroscopy (EELS) spectrometers 115.

[0033] Briefly, the electron source section includes electronics configured to energize a source of charged particles 205 (see FIG. 2), which may include a high voltage field emitter or other source of emitted electrons, such that a beam of electrons is formed and conducted through a vacuum to the TEM column. The TEM column includes beam-forming components, including electromagnetic and / or electrostatic lenses, and a number of apertures for controlling the characteristics of the beam of electrons. The TEM column components include condenser lenses, objective lenses, projector lenses, aberration correctors, deflectors, astigmatism correctors, etc., and corresponding apertures. The sample section 107 houses a sample 225 (see FIG. 2) through which the electron beam can be transmitted. For EELS microanalysis, the beam can be focused (e.g., through the action of one or more objective lenses) on the sample for spot mode analysis, or the beam can pass through the sample in parallel illumination mode (or at least partially defocused) to collect data from a relatively large sample area.

[0034] In some embodiments, the sample section 107 includes an objective lens 109 such that the sample is immersed in the objective field of view of the objective lens. Advantageously, disposing the sample in the objective field of view of the objective lens can provide good resolution, on the order of about 0.05 nm, for STEM mode operation. In this context, immersion in the objective field of view refers to disposing the sample in the magnetic field of the objective lens that extends 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.

[0035] In some embodiments, the charged particle microscope system 100 operates in a STEM mode. For example, in a magnetic field-free (e.g., non-immersion) STEM mode, an objective lens is not used to focus the charged particles on the sample. In some systems, a small focusing lens upstream of the specimen can function as a probe-forming lens, and a Lorentz lens downstream of the specimen can function as a first imaging lens to provide at least some of the functions of the objective lens. In a field-free STEM mode, detector data can be generated with a spatial resolution of about 0.5 nm. On the other hand, in a field-immersion STEM mode, in which an objective lens is used to focus the charged particles on the sample, the spatial resolution can be improved by an order of magnitude, but the magnetic field in the vicinity of the sample can complicate the generation of DPC data using an energy loss spectrometer, based at least in part on the effect of the field-immersion magnetic field on the local magnetic field in the sample.

[0036] 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 micro-analysis. For example, the imaging section may include, among others, a scintillator screen, binoculars, a transmission electron microscope (TEM) detector (e.g., a pixelated electron detector, a secondary electron detector, a camera, and an electron energy loss spectroscopy (EELS) spectrometer 115. The EELS spectrometer 115 functions at least in part as an energy filter by focusing the electron beam onto a magnetic dispersive element (also called a "prism") that exerts a force on the electrons proportional to the electron's energy. In this manner, electrons that have transferred energy to the sample (e.g., by inelastic collision) may be redirected through the magnetic dispersive element to 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 may be derived. In some embodiments, as described in more detail with reference to FIG. 2, the EELS spectrometer(s) 115 further include one or more optical elements, such as electromagnetic lenses and / or accelerators, to condition and / or focus the scattered electrons on the detector.

[0037] 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 an example of the charged particle microscope system 100 of FIG. 1 and includes a microscope 201 that corresponds to at least a portion of the source section, TEM column, sample section 107, and possibly detector section 110 of the charged particle microscope system 100. The example system 200 also includes a spectrometer 115, which in the illustrated embodiment is represented by components of an EELS spectrometer. The example system 200 also includes elements of a control system 210 that are operably coupled to the microscope 201 and the spectrometer 115.

[0038] The microscope 201 may include a charged particle source 205 configured to generate a beam of charged particles 215 (e.g., electrons or ions) of a first energy E1. A few particles may be scattered by the sample. The scattering events may include inelastic scattering, through which the scattered particles lose energy (e.g., ΔE). In the technique of electron energy loss spectroscopy (EELS), an EELS spectrometer 115 is used to measure the energy of the inelastically scattered electrons, from which the energy loss ΔE can be derived. The electrons that have lost energy during the inelastic scattering event travel through the TEM column and through the EELS spectrometer with an energy of E1-ΔE. As will be described in more detail with reference to Figures 3-5, the magnitude of the deviation from the energy E1 may be measured by a detector 245 of the EELs spectrometer 115 in energy space.

[0039] The spectrometer 115 may include charged particle optical elements such as a dispersive element 235 and one or more electromagnetic and / or electrostatic elements 240 (e.g., lenses, accelerators, quadrupoles, hexapoles, octopoles, etc.). The dispersive element 235 may comprise one or more magnetic and / or electrostatic dispersive elements (also referred to as "prisms"). The spectrometer 115 may be post-column (positioned after the TEM column as in FIG. 2) or in-column operably coupled to the TEM column. The elements 235 and 240 may be calibrated to select an energy that is the same as or different from the beam energy E1. In this manner, the charged particles may be filtered and a subset may be transmitted to the element 240 and then directed to the detector 245 of the spectrometer 115.

[0040] In some embodiments, the element 240 also focuses the charged particles onto the detector 245. The detector 245 can generate detector data. The detector 245 can be a pixelated detector. Thus, the detector 245 can be configured to generate an electrical signal in response to receiving the charged particles at the detector surface. In some embodiments, the detector 245 can be configured for electron counting such that the detector 245 responds to individual charged particles. Advantageously, a single particle counter configuration can improve the signal-to-noise characteristics of the detector 245 relative to an integrator configuration that generates a signal proportional to the particle flux over a given collection period. As described in more detail with reference to FIGS. 3-6, the detector data can include an EELS spectrum resulting from the interaction of the beam of charged particles 215 with atoms 227 of the sample 225. For example, if the microscope 201 is operating in a STEM mode (e.g., scanning TEM, or STEM in a SEM) and the sample 225 is thinned to allow transmission of the beam, the electron beam can be focused to a point within the sample 225 that allows measurement of single atoms, or groups of atoms, on the nanometer scale.

[0041] The beam of charged particles 215 can be focused on the sample 225 and / or on a plane at a given distance relative to the sample or within the sample and scanned (e.g., according to a raster pattern) over the surface of the sample 225. In coordination with the movement of the beam, the EELS spectrometer 115 can be used to generate detector data, as described in more detail with reference to FIG. 3. The imaging mode can be energy selective (e.g., imaging zero-loss peaks, plasmon resonance peaks, inner shell electron excitation regions, etc., of the EELS spectrum), such that the detector data is defined in momentum-energy coordinate space, as described in more detail with reference to FIG. 3. Interaction of the beam of charged particles 215 with atoms of the sample 227 can shift the momentum and / or energy of the particles. In this way, according to embodiments of the present disclosure, DPC and / or COM techniques can be performed based at least in part on processing of energy loss spectroscopy data.

[0042] Other components of system 200 can function to attenuate, redirect, absorb, or otherwise filter out from the detector data unscattered 250 or weakly scattered charged particles 255 (e.g., electrons that pass through sample 225 without being scattered). For example, element 230 can apply a force (e.g., a magnetic force) to the electrons proportional to their energy, which redirects electrons having an energy of about E1 away from the beam axis and toward an absorber material or other surface inside microscope 201.

[0043] Control system 210 may include one or more machines (e.g., computing devices) operably coupled to control circuitry disposed within microscope 201 and / or spectrometer 115. In an illustrative example, control circuitry may include an arrangement of circuit components connected to a power source and configured to control the supply of power (e.g., voltage and / or current) to source 205, elements 220, 230, 235, 240, and / or detector 245. In this manner, the process of generating DPC data using elements 220, 230, 235, 240, and / or detector 245 may be orchestrated by 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.).

[0044] The one or more machines may include, but are not limited to, a personal computer, a laptop, a tablet, a server, an application specific machine (ASM), and the like. In some embodiments, the control system 210 includes user-interactive elements, such as a display and input peripherals (e.g., a mouse and keyboard), through which a user can reversibly implement the DPC-EELS mode according to the operations described with reference to FIG. 3 . In an illustrative example, a user can select an interactive graphical element 211 on a user interface (e.g., within an application, browser environment, etc.) that initiates the DPC-EELS mode. To return the system 200 to a previous state, the user can select an interactive graphical element 211 that initiates a recalibration of elements 220, 230, 235, and / or 240 back to the elements. To that end, a process of the present disclosure (e.g., example process 300 of FIG. 3) can include operations for receiving user interaction data (e.g., via an interactive user interface), where the interaction data corresponds to an action by the user to initiate a recalibration of one or more elements of the charged particle microscope system, or vice versa. Similarly, a process of the present disclosure can include generating user interface data configured to modify a display (e.g., of the control system 210) to present the interactive user interface.

[0045] FIG. 3 is a schematic diagram illustrating example detector data according to some embodiments of the present disclosure. Elements of the system 200 of FIG. 2 are shown in isolation to focus the discussion on the technique for generating the detector data. Thus, the example detector data can be generated using the example system 100 of FIG. 1 and / or the example system 200 of FIG. 2. Unlike the typical operation of an EELS spectrometer (e.g., spectrometer 115 of FIG. 1), the technique of the present disclosure involves scanning a beam of charged particles 215 across the sample according to a scan pattern 305. Interaction of the beam of charged particles 215 with atoms 227 of the sample can result in momentum shifts 310 and / or energy losses 315 of the charged particles. Such information can be used to generate DPC data, as described in more detail with reference to FIGS. 5-6.

[0046] 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, a first atom 227-1 may be relatively lighter than a second atom 227-2, which may cause the second atom 227-2 to have a relatively greater effect on the trajectories of the constituent particles that make up the beam of charged particles 215 than the first atom 227-1. Similarly, atoms that have characteristic inelastic transitions associated with the atoms' electrons, such as excitation and / or ionization transitions, may experience a characteristic energy loss, represented by a shift in the detector data on the energy axis relative to the zero-loss position.

[0047] The elements 235 and 240 can be configured to direct at least a subset of the charged particles from the sample location through the optical element 230 to the detector 245. In typical EELS operation, electrons are focused on the detector as an approach to reduce momentum-space dimensional information to improve the signal-to-noise characteristics of the energy loss spectrum. In some embodiments of the present disclosure, the energy dispersive component 320 of the beam of charged particles 215 is directed onto the detector 245 without being focused on the detector's surface. To that end, the elements 235 and / or 240 may be defocused from an initial "focused" configuration and / or can be operated in a defocused configuration. Defocusing in this context can include changing the operating parameters of one or more of the elements 235 and / or 240 or moving the detector 245 relative to the elements 240. Examples of operating parameters include, but are not limited to, the focal length of the element 240 and / or parameters that affect the operation of the energy dispersive element 235. For example, the dispersive element 235 can be configured to generate a diverging component 320 from the outlet 330 in imaging mode, or a converging component 320 from the outlet 330 in spectroscopic mode. In imaging mode, the component 320 is integrated by the detector, while in spectroscopic mode, the spatial position on the detector correlates with the energy loss with reference to the zero-loss peak position, which allows defining the origin of the energy loss spectrum. The imaging mode can apply energy selection by a 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.

[0048] Advantageously, defocusing the energy dispersion component 320 allows momentum information to be preserved in the detector data that would otherwise be lost by projecting it onto the energy axis (e.g., as part of the EELS data cube). As described in more detail with reference to FIGS. 4-6, momentum information can be extracted from the energy loss data via one or more geometric transformations applied to the energy loss data and / or data generation operations. Thus, embodiments of the present disclosure include approaches for generating and / or processing energy loss data to extract momentum-spatial information to be used in DPC, as well as COM techniques for imaging phase contrast information and other physical and chemical properties of a sample.

[0049] FIG. 4 is a schematic diagram illustrating example EELS data 400 including momentum-space information according to some embodiments of the present disclosure. The example data 400 represents detector data generated using a STEM or TEM system with an energy loss spectroscopy device (e.g., spectrometer 115 of FIG. 1) operating in a spectroscopy mode. In this image, intensity measured in counts or any other units is represented by a patterned fill, with brighter areas of the data 400 representing areas of higher charged particle flux. The example data 400 includes a region of a zero-loss peak 405 and a region of a phonon resonance peak 410. As described in more detail with reference to FIG. 3, the zero-loss peak 405 can be used to define the origin of the energy loss dimension, so that calibrations used to correlate energy loss with positions on the detector 245 can be referenced to the position of the zero-loss peak 405. In some embodiments, the spectroscopy mode can include configuring elements 235 and 240 to focus the charged particles in momentum space onto the detector while maintaining the energy dispersion. The resulting data produces a one-dimensional energy loss spectrum rather than the two-dimensional data shown.

[0050] However, the exemplary data 400 still represents a partial dimensionality reduction by integrating the momentum distribution along a second momentum dimension, referred to as "q2", which can 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, by recovering the momentum-space information, energy loss spectroscopy data, such as data 400, for example, can be used in DPC and COM techniques. With reference to FIG. 3, by defocusing the spectrometer, it is possible to preserve the momentum information of the pattern projected onto the detector, where charged particles of substantially equal energy are incident at different positions on the energy loss axis due at least in part to the momentum distribution along q2. In this way, back projection from the q1-E plane to the q1-q2 plane allows the momentum-momentum space data to be restored, from which phase contrast information can be derived.

[0051] Additionally or alternatively, the example data 400 can be used directly to extract momentum information of the charged particles relative to q1. Where q1 and q2 define a coordinate space with E, the techniques of the present disclosure include generating energy loss spectroscopy data for multiple system configurations, such that two or more sets of data can provide momentum information at q1 and q2 separately. As will be described in more detail with reference to FIG. 6, data can be generated in the q2-E coordinate space by rotating the beam of charged particles prior to entering the spectrometer.

[0052] FIG. 5 is a schematic diagram illustrating an example backprojection technique for extracting momentum-space information from example energy loss spectroscopy data 500, according to some embodiments of the present disclosure. As described with reference to FIG. 4, the example data 500 includes a zero-loss peak 505 region projected onto momentum-energy coordinate space. The technique of FIG. 5 includes mapping the example data 500 from the q1-E plane onto the q1-q2 coordinate space using a three-dimensional coordinate system defined by q1, q2, and E. As shown, the zero-loss peak 505 region is illustrated as an ellipse for simplicity to facilitate explanation. In some embodiments, the example data 500 includes information about other energy loss regions, such as the phonon resonance 410 region illustrated in FIG. 4.

[0053] The illustrated backprojection involves transforming two-dimensional data from the q1-E coordinate space to the q1-q2-E coordinate space so that various features of the example data 500 can be used in 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 a line connecting the centroid 510 of the q1-E plane with the q1-q2 plane, where the line is aligned at an angle 525, α, with respect to the q2 axis.

[0054] The backprojected centroid 520, where a line intersects the q1-q2 plane, encodes information about the interaction of the beam of charged particles 215 with the atoms 227 of the sample at a given beam position on the sample 225. Thus, the backprojection in the q1-q2 coordinate space can be used to generate DPC data. Although the centroid 510 of the q1-E plane is shown to lie on the energy (E) axis and the centroid 520 of the q1-q2 plane is shown to lie on the q2 axis, the locations of the respective centroids 510-520 may differ from those shown. For example, the centroid 510 of the q1-E plane may be off-axis in the q1 dimension. Similarly, the centroid 520 of the q1-q2 plane may be off-axis in the q1 dimension. Advantageously, backprojecting the data 500 into the q1-q2-E coordinate space provides energy resolved momentum information. In this way, the energy-selective imaging capabilities of EELS can be combined with the phase-contrast imaging capabilities of DPC and COM techniques.

[0055] FIG. 6 is a block flow diagram illustrating an example process 600 for generating differential phase contrast data using the example system of FIGS. 1-2, according to some embodiments of the present disclosure. One or more operations constituting the example process 600 can be performed and / or initiated by a computer system and / or other machine operatively coupled with components of an analytical instrument (e.g., the example system 100 of FIG. 1) and / or additional systems or subsystems, including, but not limited to, a characterization system, a network infrastructure, a database, a controller, a relay, a power system, and / or a user interface device. Thus, the operations can be stored as machine-executable instructions on one or more machine-readable media that, when executed by a computer system, cause the computer system to perform at least some of the constituent operations of the process 600. As illustrated in FIG. 2, the constituent operations of the process 600 can precede, intervene, and / or follow operations omitted herein, such as sample and / or instrument preparation, operations performed prior to operation 605, which form at least a part of an analytical method for processing a sample to generate data. Thus, in some embodiments, operations of the example process 600 are omitted, repeated, reordered, and / or substituted.

[0056] In operation 605, the example process 600 includes directing a beam of charged particles (e.g., beam of charged particles 215 of FIG. 2) through a material sample (e.g., sample 225 of FIG. 2). The sample can be disposed in an objective section of a microscope column (e.g., objective section 105 of FIG. 1). As described in more detail with reference to FIGS. 2-5, interaction of the material sample with the charged particle beam can result in scattered portions of the beam. The scattered portions can include particles that are elastically scattered and / or particles that are inelastically scattered. Since there is a non-zero probability that a given charged particle undergoes both elastic and inelastic collisions, a particle that has lost energy from the sample can also undergo an elastic collision resulting in a change in momentum, or vice versa. In the context of the example process 600, operation 605 can include focusing the beam of charged particles on the sample and translating the beam across the sample according to a scan pattern (e.g., scan pattern 305 of FIG. 3). Similarly, operation 605 can include focusing the beam to a location within the sample or a location away from the sample.

[0057] At operation 610, the example process 600 includes directing the scattered portions to an energy filter (e.g., spectrometer 115 of FIG. 1). As described in more detail with reference to FIGS. 1-3, the energy filter can 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 can include focusing the scattered portions at least partially onto the energy filter. In some embodiments, an energy selector (e.g., a selector slit) can be disposed in the beam path or the energy filter can be configured to select a given energy or range of energies, such that operation 610 can include directing a subset of the scattered portions toward a detector of the energy filter.

[0058] In operation 615, the example process 600 includes generating detector data using the scattered portions incident on a detector (e.g., detector 245 of FIG. 2). As described in more detail with reference to FIGS. 2-5, the detector data may include EELS data if the charged particle beam is an electron beam. Operation 615 may also include defocusing one or more components of an energy filter and using the detector to generate an angle-resolved EELS (AR-EELS) image. As described in more detail with reference to FIGS. 4-5, AR-EELS is a technique in which scattering of electrons is measured in one momentum dimension (q) and one angular dimension (ω), and the angle is correlated to energy loss via one or more parameters of an energy filter (e.g., element 235 of FIG. 2).

[0059] In operation 620, the example process 600 includes generating DPC data using the detector data. Generating the DPC data can include determining a first centroid (e.g., centroid 510 in FIG. 5 ) of a region (e.g., region 505 in FIG. 5 ) of the AR-EELS image. Additionally, operation 620 can include mapping the first centroid of the AR-EELS image from an energy-momentum coordinate space (e.g., q1-E) to a momentum-momentum coordinate space (e.g., q1-q2) and determining a second centroid in the momentum-momentum coordinate space (e.g., centroid 520 in FIG. 5 ). In some embodiments, the first centroid is located along an energy loss axis (E) of the AR-EELS image and the second centroid is located at the origin of the momentum and energy loss axes (e.g., q1-E in FIG. 5 ).

[0060] As described with reference to FIG. 4, generating detector data can include using a detector to generate a first AR-EELS image, modifying one or more components of the microscope column to induce a rotation in a diffraction pattern generated through the interaction of the beam of electrons with the material sample, and using a detector to generate a second AR-EELS image from the rotated diffraction pattern. Modifying the one or more components can include adjusting electromagnetic properties of one or more charged particle optical elements (e.g., elements(s) 230 of FIG. 2) to induce a rotation of the beam relative to the beam axis that preserves the momentum distribution of the charged particles that make up the beam in momentum space (e.g., q1-q2). In this way, momentum information can be projected onto the q2 of the detector data, from which q2 momentum information can be extracted for use in DPC and COM techniques, also as a function of position within the sample resolved with respect to energy loss. For example, the tendency of charged particles to enter a helical trajectory in the presence of a magnetic field aligned with the beam axis can be exploited to induce a rotation by modifying one or more electromagnetic elements of the projector lens system to move the sample and / or move it downstream relative to the sample.

[0061] Thus, generating the DPC data may further include determining a first centroid of the region in the first AR-EELS image, the first centroid being defined with respect to the first energy-momentum coordinate space (q1-E), determining a second centroid of the region in the second AR-EELS image, the second centroid being defined with respect to the second energy-momentum coordinate space (q2-E), and determining a third centroid of the region, the third centroid being defined with respect to the momentum-momentum coordinate space (q1-q2). As illustrated in FIG. 5, the first and second energy-momentum coordinate spaces may be substantially orthogonal. Thus, operation 620 may include rotating the beam 90 degrees about the beam axis as part of generating the two AR-EELS images. In the context of an example system of the present disclosure (e.g., example system 200 of FIG. 2), the planar coordinate spaces can be oriented at an angle relative to one another in the three-dimensional space defined by the planar spaces. In the detector data, the planar coordinate spaces can be parallel due to the reduced dimensionality of the projection onto the detector by the optics of the spectrometer (e.g., spectrometer 115 of FIGS. 1 and 2).

[0062] In some embodiments, generating the DPC data can include applying an integral (inverse gradient) to generate an iDPC image of the electrostatic potential field of the sample using the centroid information generated in operation 620. For example, generating the DPC data can include determining a displacement μ of the second centroid relative to a reference position of the first centroid in momentum-momentum coordinate space. The reference position can include the centroid of the corresponding pattern in q1-q2 space in the absence of the sample, a calibrated "zero point position", etc., such that μ is a vector quantity defined relative to the origin in momentum-momentum coordinates. In some embodiments, generating the DPC data can apply a differential (divergence) to generate a dDPC image of the charge density field of the sample using the centroid information generated in operation 620.

[0063] In the following equations, q1 is x and q2 is y, based on a two-dimensional Cartesian coordinate system. Similar coordinates can be used, for example r-θ, or any coordinate system that describes a plane defined by two vectors. The equations treat the two momentum axes independently and use any energy range from a first energy E to a second energy E+ΔE. For an energy selection (E,E+ΔE), the detector data is a function of the momentum in the x direction and is described by:

number

number

[0064] (outside 1) Using the COM of TIFF2025031585000004.tif7128, the following formula can be derived:

number

[0065] The above equation can be rearranged by switching the order of the integrals to give the following:

number

[0066] The resulting term is k xcan be understood as the DPC component (q1) in the direction, but this time for the selected energy range (E,E+ΔE). Integrating over the range of electron energies from zero to infinity gives the unfiltered DPC component:

number

[0067] Similarly, after rotating the CBED pattern in front of the filter by 90° (π / 2rad), in this example, q2, i.e., k y The same situation occurs for the direction. Within the energy selection (E, E+ΔE), the detector data are k y It is a function of directional momentum and is described by the following equation:

number

[0068] k y In line with (Outside 0002) Using the COM of TIFF2025031585000009.tif8128, the following formula can be derived:

number

[0069] The above equation can be rearranged by switching the order of the integrals to give the following:

number

[0070] The resulting term is k y can be understood as the DPC component in the direction (q2), but this time for the selected energy range (E,E+ΔE). Integrating over the range of electron energies from zero to infinity gives the unfiltered DPC component:

number

[0071] In the techniques of this disclosure, the above formulas can be applied to coordinate space data, as described in more detail with reference to FIG. 5, and / or to the projection of momentum data into one momentum dimension (q1 or q2), as described with reference to FIG.

[0072] Further, the iDPC and dDPC methods may also include DPC vector images using displacements. Detailed formulas are described in the literature cited in the use of split STEM detectors and referenced in the previous paragraph of this disclosure. In the DPC vector images, the displacement vector μ may vary with position on the sample (e.g., in Cartesian xyz coordinates), and thus generating the DPC vector image may include determining a number of displacements that correlate with positions on the sample through a scan pattern (e.g., scan pattern 305 of FIG. 3 ), from which pixels of the DPC vector image may be defined. In this manner, a scalar image of the material sample may be generated at least in part by integrating (e.g., applying an inverse gradient) the DPC vector image to generate an iDPC image. In some embodiments, a scalar image of the material sample may be generated at least in part by differentiating (e.g., applying a divergence) the DPC vector image to generate a dDPC image.

[0073] In some embodiments, the energy resolved momentum information can be used to generate energy resolved DPC data. For example, operation 620 can include selecting a region of the AR-EELS image(s) such that the DPC data corresponds to a zero loss peak of the EELS data. Similarly, the region can be selected such that the DPC data corresponds to a plasmon resonance peak and / or a core electron excitation region of the EELS data. Thus, the region can be selected to include one or more edges in the EELS data, which can be correlated to particular elements, such that the DPC data can highlight particular elements, transitions, etc.

[0074] In the preceding specification, 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 be apparent to one skilled in the art that the embodiments may be practiced without the specific details. Furthermore, well-known features may be omitted or simplified so as not to obscure the described embodiments. Although the exemplary embodiments described herein are centered around energy loss spectroscopy systems, and in particular EELS systems, these are meant to be non-limiting exemplary embodiments.

[0075] Some embodiments of the present disclosure include a system including one or more data processors and / or logic circuitry. In some embodiments, the system includes a non-transitory computer-readable storage medium storing instructions that, when executed on the one or more data processors and / or logic circuitry, cause the one or more data processors and / or logic circuitry to perform some or all of one or more methods and / or some or all of one or more processes and workflows disclosed herein. Some embodiments of the present disclosure include a computer program product tangibly embodied in a non-transitory machine-readable storage medium that includes instructions configured to cause one or more data processors and / or logic circuitry to perform some or all of one or more methods and / or some or all of one or more processes disclosed herein.

[0076] The terms and expressions used are used as terms of description and not as terms of limitation, and in using such terms and expressions, there is no intention to exclude any equivalents of the features or portions thereof shown and described, but it is understood that various modifications are possible within the scope of the claims. Thus, although the present disclosure includes specific embodiments and optional features, it should be understood that modifications and variations of the concepts disclosed herein can be made by those skilled in the art, and such modifications and variations are considered to be within the scope of the appended claims.

[0077] When a term is used without an explicit definition, it is understood that the ordinary meaning of the word is intended unless the term has a special and / or specific meaning in the field of charged particle microscope systems or other related fields. The term "about" or "substantially" is used to indicate a deviation from a described characteristic, within which there is little or no effect on the corresponding function, characteristic, or attribute of the described structure. In an illustrative example where a 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 not be equal within acceptable limits, such as manufacturing tolerances or confidence intervals inherent in the operation of the system. Similarly, when a geometric parameter such as alignment or angular orientation is described as "about" 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 strictly described condition (e.g., not strictly perpendicular) within acceptable limits. For dimensional values ​​such as diameter, length, width, etc., the term "about" can be understood to describe a deviation of up to ±10% from the described value. For example, a dimension of "approximately 10 mm" can describe a dimension between 9 mm and 11 mm.

[0078] This specification provides exemplary embodiments and is not intended to limit the scope, applicability, or configuration of the present disclosure. Rather, the description following the exemplary embodiments provides those skilled in the art with an enabling description to realize various embodiments. It should be understood that various changes can be made in the function and arrangement of elements without departing from the spirit and scope as set forth in the appended claims. Specific details are given herein to provide a thorough understanding of the embodiments. However, it will be understood that the embodiments may be practiced without these specific details. For example, specific system components, systems, processes, and other elements of the present disclosure may be shown in schematic diagram form or omitted from the illustrated diagrams so as not to obscure the embodiments in unnecessary detail. In other cases, well-known circuits, processes, components, structures, and / or techniques may be shown without unnecessary detail.

Claims

1. 1. An electron microscope system, comprising: an electron source configured to emit a beam of electrons; a microscope column optically coupled to the electron source and configured to receive the beam of electrons from the electron source; an energy filter coupled to the microscope column and configured to receive electrons of the beam of electrons 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, the operations including: directing the beam of electrons through a material sample disposed within the microscope column, where interaction of the beam of electrons with the material sample produces scattering portions of the beam of electrons; directing the scattered portions to the energy filter, the energy filter being configured to disperse the scattered portions along an energy dispersion axis and direct a subset of the scattered portions towards a detector of the energy filter; generating detector data using the subset of the scatter incident on the detector, the detector data including EELS data; and and generating differential phase contrast (DPC) data using the detector data. Electron microscope system.

2. Producing detector data includes: defocusing one or more components of the energy filter; and and generating an angle-resolved EELS (AR-EELS) image using the detector. The system of claim 1 .

3. Generating the DPC data includes: determining a first center of gravity of a region of the AR-EELS image in energy-momentum coordinate space; mapping the first centroid of the AR-EELS image from the energy-momentum coordinate space to a momentum-momentum coordinate space; determining a second center of gravity in the momentum-momentum coordinate space; The system of claim 2.

4. Generating the DPC data includes: determining a displacement μ of the second center of gravity relative to a reference position of the first center of gravity in the momentum-momentum coordinate space; generating a DPC vector image using the displacements; and generating a scalar iDPC image of the material sample by at least partially integrating the DPC vector image. The system of claim 3.

5. Defocusing the one or more components of the energy filter may include: modifying one or more operating parameters of one or more electro-optical elements of the energy filter; or moving the detector. The system of claim 2.

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 scatterers with respect to a detection surface of the detector.

7. Producing detector data includes: generating a first AR-EELS image using the detector; and modifying one or more components of the microscope column to produce a rotation in a diffraction pattern produced through the interaction of the beam of electrons with the material sample; and generating a second AR-EELS image from the rotated diffraction pattern using the detector. The system of claim 1 .

8. Generating the DPC data includes: determining a first center of gravity of a region in the first AR-EELS image, the first center of gravity being defined with respect to a first energy-momentum coordinate space; determining a second centroid of the region in the second AR-EELS image, the second centroid being defined with respect to a second energy-momentum coordinate space; determining a third center of gravity of the region, the third center of gravity being defined with respect to momentum-momentum coordinate space; The system of claim 7.

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. A non-transitory machine-readable storage medium storing machine-executable instructions that, when executed by a machine, cause the machine to perform operations, the operations including: directing a beam of electrons through a material sample disposed within an objective section of a microscope column, where interaction of the beam of electrons with the material sample produces scattered portions of the beam of electrons; directing the scattered portions to an energy filter, the energy filter operatively coupled to the microscope column and configured to disperse the scattered portions along an axis of dispersion by energy and direct a subset of the scattered portions towards a detector of the energy filter; generating detector data using the subset of the scatter incident on the detector, the detector data including EELS data; and generating detector data using the detector data to generate digital phase contrast (DPC) data; One or more non-transitory machine-readable storage media.

13. Producing detector data includes: defocusing one or more components of the energy filter; and generating an angle-resolved EELS (AR-EELS) image using the detector. The medium according to claim 12.

14. Generating the DPC data includes: determining a first centroid of an area of ​​the AR-EELS image; mapping the first center of gravity of the AR-EELS image from an energy-momentum coordinate space to a momentum-momentum coordinate space; determining a second center of gravity in the momentum-momentum coordinate space; The medium according to claim 13.

15. Producing detector data includes: generating a first AR-EELS image using the detector; and modifying one or more components of the microscope column to produce a rotation in a diffraction pattern produced through the interaction of the beam of electrons with the material sample; and generating a second AR-EELS image from the rotated diffraction pattern using the detector. The medium according to claim 12.

16. Generating the DPC data includes: determining a first center of gravity of a region in the first AR-EELS image, the first center of gravity being defined with respect to a first energy-momentum coordinate space; determining a second centroid of the region in the second AR-EELS image, the second centroid being defined with respect to a second energy-momentum coordinate space; determining a third center of gravity of the region, the third center of gravity being defined with respect to momentum-momentum coordinate space; The medium according to claim 15.

17. Generating the DPC data includes: determining a displacement μ of the third center of gravity relative to a reference position of the second center of gravity in the momentum-momentum coordinate space; generating a DPC vector image using the displacements; and generating a scalar dDPC image of the material sample by differentiating the DPC vector image. The medium according to claim 16.

18. 17. 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 according to claim 16 , wherein the region corresponds to an inner shell electron excitation region of the scattering portion.

Images