Vorsch effect reduction in dispersive optical systems

Abstract

To solve a problem of a conventional technique.SOLUTION: In the present disclosure, systems, methods, algorithms, and non-transitory media storing computer readable instructions for reducing the Boersch effect using dispersion optics are described in various embodiments. The charged particle optical device may include a Wien filter arranged on the beam axis. The Wien filter can be configured to disperse the particles of the charged particle beam by energy in a dispersion plane. The dispersion plane may be parallel to the beam axis. The device includes an optical element disposed on the beam axis on the downstream side of the Wien filter. The optical element may be configured to focus the charged particle beam towards the beam axis. The device may also include a selector. The selector may be arranged on the beam axis at a position substantially coinciding with a third intersection plane downstream of the optical element.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] (Reference to Related Application) This application claims priority from U.S. Provisional Application No. 18 / 767,485, filed July 9, 2024, the disclosure of which is incorporated herein by reference in its entirety.

[0002] (Technical field) Embodiments of the present disclosure are directed to charged particle optical systems, and algorithms and methods for their operation. In particular, some embodiments are directed to techniques for attenuating the Borsch effect in dispersive optical systems. In particular, some embodiments are directed to techniques for attenuating the Borsch effect in dispersive optical systems. [Background technology]

[0003] Charged particle microscopy and microanalysis involve exposing materials to a beam of electrons. The interaction of the electrons with the sample generates various types of detectable signals that can be used for imaging and analysis. Transmission electron microscopy (TEM) imaging and microanalysis can provide atomic-level detail, including images of the atomic and molecular structure of nanomaterials and crystalline materials.

[0004] TEM analysis of materials at progressively smaller length scales, such as on the order of angstroms to tens of angstroms, involves loss spectroscopy, such as electron energy loss spectroscopy (EELS). EELS relies in part on the narrow beam energy distribution, which is described with reference to the width of the zero-loss peak. The Boersch effect is one phenomenon that explains the increased energy spread (e.g., wider beam energy distribution) due at least in part to Coulomb interactions between particles in charged particle beams. Therefore, there is a need to develop components, systems, and methods to reduce the Boersch effect, for example, to improve the energy resolution of charged particle beam sources. Summary of the Invention

[0005] In various embodiments, aspects of the present disclosure include systems, methods, algorithms, and non-transitory media storing computer-readable instructions for reducing the Boeche effect using dispersive optics. In a first aspect, a charged particle optical device includes a Wien filter disposed on a beam axis. The Wien filter can be configured to disperse particles of a charged particle beam by energy in a dispersive plane. The dispersive plane can be parallel to the beam axis. The device includes an optical element disposed on the beam axis downstream of the Wien filter. The optical element can be configured to focus the charged particle beam toward the beam axis. The device can also include a selector. The selector can be disposed on the beam axis downstream of the optical element at a position substantially coincident with a third intersecting plane.

[0006] In some embodiments, the charged particle beam defines a first intersecting plane at a first point on the beam axis within the dispersion filter and a second intersecting plane downstream of the first intersecting plane at a second point on the beam axis. The second point may substantially coincide with an exit from the dispersion filter. The Wien filter may include a bifocal Wien filter.

[0007] In some embodiments, the Wien filter is characterized by an excitation parameter φ. This position can correspond to values ​​of the excitation parameter φ greater than about 3π / 4. This position can correspond to values ​​of the excitation parameter φ ranging from π to about 3π / 2. This position can correspond to a value of the excitation parameter φ of about 4.3.

[0008] In some embodiments, the optical element is further configured to accelerate particles of the charged particle beam. The charged particle beam can be characterized by a first beam current of about 5 nA to about 50 nA at the entrance to the dispersion filter and a second beam current of greater than about 60 pA below the energy selector. Downstream of the selector, the charged particle beam can be characterized by an energy distribution with a half-width at one-hundredth of the maximum of about 40 meV to about 200 meV. In some embodiments, the selector defines an aperture having a characteristic width of about 0.3 μm to about 1.3 μm.

[0009] In a second aspect, a charged particle beam system includes a charged particle source. The charged particle source can be configured to generate a charged particle beam substantially coincident with a beam axis. In one or more embodiments, the system can include the monochromator of the first aspect. The monochromator can include a Wien filter disposed on the beam axis. The Wien filter can be configured to disperse particles of the charged particle beam by energy in a dispersion plane parallel to the beam axis. The monochromator can include an optical element disposed on the beam axis downstream of the Wien filter. The optical element can be configured to focus the charged particle beam toward the beam axis. The monochromator can include a selector disposed on the beam axis downstream of the optical element and substantially coincident with a third intersecting plane. The system can also incorporate a condenser lens disposed on the beam axis downstream of the spectrometer and configured to focus particles of the charged particle beam on the beam axis.

[0010] In some embodiments, the system includes input optics. The input optics can be configured to receive a charged particle beam from a charged particle source. The input optics can also be configured to focus the charged particle beam toward a beam axis. The input optics can be positioned on the beam axis between the charged particle source and the spectrometer.

[0011] In a third aspect, a process for reducing the Boersch effect using dispersive optics includes generating a charged particle beam. The process also includes dispersing charged particles of the charged particle beam. The process also includes narrowing the energy distribution of the beam. In some embodiments, dispersing the charged particle beam can include modifying one or more parameters of a dispersive element of the preceding aspect in one or more embodiments. The one or more parameters of the dispersive element can include an electric field of a Wien filter, a magnetic field of a Wien filter, and / or one or more parameters of an accelerator forming part of the monochromator. Modifying the one or more parameters can include setting the Wien filter to operate according to an excitation parameter, φ, having a value from about 0.5π to about 1.5π. In some embodiments, the excitation parameter is about 4.3.

[0012] The processes of the third aspect, in one or more embodiments, may be performed automatically (e.g., as a computer-implemented method), pseudo-automatically (e.g., with human initiation and / or limited input from a user), and / or manually (e.g., with direction from a user of the systems and devices of the preceding aspect). To this end, the processes of the third aspect may be stored, at least in part, as machine-readable instructions on one or more machine-readable storage media. Machine execution of such instructions enables systems and / or devices of the present disclosure to perform one or more operations of the third aspect.

[0013] The terms and expressions used are used as terms of description and not of limitation. Furthermore, there is no intention to exclude equivalents of the functions shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the subject matter described in the claims. Thus, while the subject matter claimed herein has been specifically disclosed by embodiments and optional features, modifications and variations of the concepts disclosed herein are accessible to 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. For example, the above-described aspects and various embodiments can be combined with one or more other aspects and / or embodiments of the same or other aspects. [Brief explanation 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.

[0015] [Figure 1] FIG. 1 is a schematic diagram illustrating a transmission electron microscope (TEM) system according to some embodiments of the present disclosure.

[0016] [Figure 2] 1 is a schematic diagram illustrating an example of a monochromated electron source configured for use in a transmission electron microscope (TEM) system in accordance with the current state of the art.

[0017] [Figure 3] FIG. 1 is a schematic diagram illustrating an example of a monochromated electron source configured for use in a transmission electron microscope (TEM) system in accordance with an embodiment of the present disclosure.

[0018] [Figure 4] 1 is a schematic diagram illustrating an example of a monochromated charged particle source configured for use in a transmission electron microscope (TEM) system, where the excitation parameter "φ" does not attenuate the Boersch effect, in accordance with the current state of the art.

[0019] [Figure 5] FIG. 1 is a schematic diagram illustrating an example of a monochromated charged particle dispersion source in which an excitation parameter “φ” is used to reduce the influence of the Boersch effect, according to an embodiment of the present disclosure.

[0020] [Figure 6A] 1A-1C are data plots illustrating analytical data for dispersion, Boersch effect, and normalized beam energy distribution (FWHM), respectively, for a distributed monochromatic electron source configured for use in a transmission electron microscope (TEM) system in accordance with an embodiment of the present disclosure. [Figure 6B] 1A-1C are data plots illustrating analytical data for dispersion, Boersch effect, and normalized beam energy distribution (FWHM), respectively, for a distributed monochromatic electron source configured for use in a transmission electron microscope (TEM) system in accordance with an embodiment of the present disclosure. [Figure 6C] 1A-1C are data plots illustrating analytical data for dispersion, Boersch effect, and normalized beam energy distribution (FWHM), respectively, for a distributed monochromatic electron source configured for use in a transmission electron microscope (TEM) system in accordance with an embodiment of the present disclosure.

[0021] [Figure 7] FIG. 1 is a block flow diagram illustrating an example of a process for generating a monochromatic beam of charged particles, according to some embodiments of the present disclosure.

[0022] [Figure 8A] 3 is an example of an energy distribution graph simulated in accordance with the current state of the art for the electron source of FIG. 2. [Figure 8B] 3 is an example of an energy distribution graph simulated in accordance with the current state of the art for the electron source of FIG. 2.

[0023] [Figure 9A] 4 is an example of a simulated energy distribution graph for the electron source of FIG. 3 in accordance with an embodiment of the present disclosure. [Figure 9B] 4 is an example of a simulated energy distribution graph for the electron source of FIG. 3 in accordance with an embodiment of the present disclosure.

[0024] 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, to reduce clutter in the drawings where necessary. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles being described. DETAILED DESCRIPTION OF THE INVENTION

[0025] While exemplary embodiments have been illustrated and described, it will be understood that various changes can be made thereto without departing from the spirit and scope of the present disclosure. The following describes embodiments, components, and methods for reducing the Boersch effect in a charged particle microscope system. The disclosed embodiments include a transmission electron microscope incorporating an improved electron-optical device. The improved electron source can include a monochromator configured to narrow the energy distribution of the monochromatized beam around a target energy. The monochromator includes a dispersive element disposed on the beam axis, the dispersive element configured to disperse particles of the charged particle beam by energy in a dispersive plane parallel to the beam axis. The electron-optical device can include a selector disposed downstream of the spectrograph at a position corresponding to an intersecting plane on the beam axis. This intersecting plane corresponds to a third intersecting plane of the charged particle beam downstream of the monochromator entrance on the beam axis. The blocking portion can include an electron-opaque material and define an aperture substantially aligned with the beam axis, as described in more detail with reference to FIG. 3 .

[0026] Embodiments of the present disclosure include systems, methods, algorithms, and non-transitory media storing computer-readable instructions for reducing the Boersch effect using dispersive optics. An exemplary implementation includes a method for modifying one or more operating parameters of an energy-dispersive monochromator, where the monochromator is characterized by an excitation parameter ("φ") greater than about 3π / 4 (e.g., φ≈4.3). Further details about the Boersch effect, excitation parameters, and monochromator operation are provided below.

[0027] The disclosed techniques improve the energy resolution of charged particle beam systems, enabling more precise and accurate measurements of energy-dependent material properties, such as molecular bonding information and inner-shell electronic transitions. Examples of energy loss spectroscopy include electron energy loss spectroscopy (EELS). In electron energy loss spectroscopy, an electron beam is transmitted through a sample, and the inelastic scattering of electrons is measured. Inelastic scattering involves the transfer of energy between the electrons and the sample, which can be measured using a spectrometer configured to generate an energy loss spectrum of the electrons transmitted through the sample. Analysis of the energy loss spectrum can provide detailed material information (e.g., bonding style, elemental composition), even for samples of light elements that are difficult to analyze.

[0028] Electrons that pass through a sample without inelastically scattering (electrons that lose little or no energy to the sample) form a zero-loss peak, or "ZLP," in the energy-loss spectrum. The width of the zero-loss peak primarily reflects the energy distribution of the electron source. It is typically around 0.2 eV to 2.0 eV, but can be narrower with monochromated sources. Valence electron information, such as plasmon resonances and interband transitions, can be derived from energy-loss spectrum information within approximately 50 eV of the zero-loss peak. Core electron information, such as core ionization, can be obtained from more than 100 eV away from the zero-loss peak. Furthermore, imaging using a ZLP can improve the spatial resolution of microscopy images by selectively filtering scattered electrons.

[0029] Trace analysis of light elements, organic materials, and / or molecular samples requires detailed information about bonds, thus utilizing valence electron information. This technique, called "vibrational EELS," examines the stretching, bending, pinching, and other atomic and molecular bond transitions that appear in the energy loss spectrum in the range from approximately 0.05 eV to approximately 1 eV above the zero-loss peak. Thus, the width of the zero-loss peak is a limiting factor in vibrational EELS, due at least in part to background effects caused by the zero-loss peak. As explained in more detail with reference to Figures 9A-10B, the width of the zero-loss peak at the "1 / 100 limit" is a metric (including other metrics such as full width at half maximum (FWHM)) used to describe the energy distribution of a monochromated electron source. The 1 / 100 limit corresponds to a value for the energy distribution of the electron beam that is 100 times smaller than the peak of the zero-loss peak (e.g., 0 eV loss).

[0030] The improved width of the zero-loss peak at the 1 / 100 limit can be achieved, at least in part, by attenuating the Boersch effect further upstream of the selective surface. Narrowing the energy distribution of charged particles emitted from the emission source can also improve the performance (e.g., signal-to-noise ratio and signal-to-background ratio) of the charged particle spectroscopy system. In an exemplary embodiment, a charged particle optical device according to the present disclosure can be configured to output an electron beam with an energy deviation of about 200 meV or less from a target energy at the 1 / 100 limit, depending on the combination of operating parameters of the source, monochromator, and additional and / or alternative optical elements.

[0031] Typical approaches to generating chromatic electron beams include the use of alpha or omega monochromators, which utilize a curved electron beam path and multiple electromagnetic prisms, but these involve structural and operational complexities. Such sources typically exhibit widths of 80 meV or more at the 1 / 1000 limit (e.g., 86 meV for alpha monochromators, although smaller widths can be achieved at the expense of probe current, potentially significantly affecting EELS performance). In this context, the "width" of the zero-loss peak refers to the distance from the center to the edge of the zero-loss peak.

[0032] Such devices involve complex arrangements of multiple charged particle optical elements, typically significantly limiting beam current. In this approach, alpha or omega monochromator devices are designed as independent modules (e.g., retrofit modules) rather than in-situ monochromator device usage. Therefore, there is a need for monochromator sources and their application techniques with zero-loss peak half-widths of approximately 200 meV or less at the 1 / 100 limit. A quantitative discussion of the reduction of the Boersch effect in electron monochromators is presented below. In particular, the derivation of a mathematical formula for optimally reducing the Boersch effect in monochromators is presented. As a first example, a double-focusing Wien filter is described, followed by a generalization to any dispersive charged particle optical device.

[0033] FIG. 1 is a schematic diagram illustrating a transmission electron microscope (TEM) 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 brevity, in order to focus the description on embodiments of the present disclosure, as described in more detail with reference to FIGS. 3A-5 (in contrast to the exemplary system depicted in FIGS. 2A and 2B ), and to describe techniques for enhancing the energy resolution of monochromated beams of charged particles. The exemplary TEM system 100 includes an electron source section 110, a TEM column including an objective section, and an imaging section. This disclosure focuses on the electron gun section 110. Briefly, the electron source section 110 includes electronics configured to power an electron source, which may include a high-voltage field emission source or other emitting electron source, such that an electron beam is formed and directed through a vacuum into the TEM column.

[0034] The TEM column contains beam-shaping components such as electromagnetic and electrostatic lenses and multiple apertures to control the electron beam characteristics. TEM column components include condenser lenses, objective lenses, and projector lenses, along with corresponding apertures. The imaging section contains 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 microanalysis. For example, the imaging section may include a scintillator screen, binoculars, or a transmission electron microscope (TEM) detector (e.g., a pixelated electron detector, a secondary electron detector, a camera, an electron energy loss spectroscopy (EELS) spectrometer, etc.).

[0035] As described in more detail with reference to FIGS. 2-5, the TEM system 100 can include a charged particle optical device 115 . The charged particle optical device 115 may include one or more monochromators, one or more electromagnetic lenses, one or more electrostatic lenses, one or more charged particle acceleration elements, one or more charged particle deceleration elements, and / or one or more apertures and / or slits that block and / or attenuate portions of the electron beam (e.g., foils defining the slits or apertures may be of an appropriate thickness to allow some electrons to penetrate the foil at scattering angles and / or energy losses that do not perturb the resulting EELS spectrum. The configuration of the components of the charged particle optical device 115 enables the exemplary TEM system 100 to produce a monochromated electron beam that is characterized by improved (e.g., relatively narrow) energy resolution, as measured at the 1 / 100 limit of the half-width, compared to existing systems that are more complex in structure and operation. Furthermore, the charged particle optical device 115 enables the exemplary TEM system 100 to perform measurements with improved spatial and / or energy resolution at relatively high currents of 10 pA or more, higher than those currently available in comparable optical devices, without including a more complex alpha-type monochromator.

[0036] FIG. 2 is a schematic diagram illustrating an example of a monochromated electron beam source configured for use in a transmission electron microscope (TEM) system in accordance with the current state of the art. The electron beam is generated by a source such as a hot cathode Schottky electron source, a field emission (FEG) source (e.g., a Schottky FEG source, or a cold cathode FEG (CFEG) source). The outer extent of the beam is shown to simplify the illustration and focus the discussion on the dispersive elements downstream of the source; however, it is understood that electrons are also emitted between the illustrated lines (e.g., as shown in FIG. 3). In the illustrated dispersive monochromator, the electron beam passes through a half-π Wien filter configured to spatially disperse electrons by energy in a dispersive plane parallel to the beam axis (e.g., the "xz" plane). The illustrated half-π Wien filter is an example of a "double-focusing" Wien filter, focusing in a YZ plane (not shown) orthogonal to the illustrated XZ plane. The term "half-π" in this context refers to the excitation parameter ρ, which is described in more detail in the next paragraph.

[0037] The selector can be placed downstream of the spectrometer to selectively block portions of the electron beam with energies different from the target energy ("U"). Alternatively, the selector can be placed at the exit of a Wien filter (e.g., plane 335 in Figure 3). In the example source 200 of Figure 2, the selector is placed at the focal plane, and each individual energy is focused in the dispersion direction (X) and also in the non-dispersion direction (Y), depending on the electron energy. Due to the dispersion of the electron beam, the selector can selectively block electrons with energies that deviate from the target energy ("U ± ΔU") beyond an acceptable range, where "ΔU" refers to the deviation from the target energy. Placing the selector at the cross plane of the beam axis where the electron beam diverges improves the energy resolution of the monochromator, at the expense of a reduced beam current after the selector. The configuration of Figure 2 has the disadvantage of reduced beam current for oscillatory EELS. The relative prominence of noise in the region of the zero-loss peak increases with decreasing beam current. Furthermore, the Boersch effect increases with increasing beam current, as explained with reference to Figures 6A-6C below. Therefore, the Boersch effect can be understood to set an upper limit on the beam current above which the energy resolution of the monochromator is compromised. The width of the selector aperture can also depend, at least in part, on the desired energy resolution of the monochromator, which is coupled to the beam current through the Boersch effect.

[0038] 3 is a schematic diagram illustrating an example of a monochromatized electron beam source 300 configured for use in a transmission electron microscope (TEM) system according to embodiments of the present disclosure. The example source 300 includes a source 305 from which electrons 310 (also referred to as "primary electrons" or "beam electrons") are emitted as an electron beam, a dispersive element 315, a selector 320, and an optical element 325 substantially aligned with the beam axis A. While FIG. 3 is illustrated as a monochromatized electron source, embodiments of the present disclosure are not limited to electron sources and include other charged particle sources, such as ion sources.

[0039] The exemplary source 300 may include at least some components of the source of Figure 2, such as a dispersion filter and an accelerator. However, in contrast to the source of Figure 2, the deviation "ΔU" from the target energy may be significantly reduced, based at least in part on modifying the excitation parameter "φ," which causes the electrons 310 of the beam to exhibit different spatial and energy characteristics (e.g., velocity) in the space between the source 305 and the selector 320, thereby reducing the Boersch effect and improving the energy resolution of the exemplary source 300 compared to the source of Figure 2.

[0040] In the exemplary source 300, one or more operating parameters of the dispersive element 315 and / or the source 305 are modified so that the electron beam 310 exhibits a first intersection 330 and a second intersection 335 within the dispersive element 315, and a third intersection 340 plane substantially co-located with the selector 320. The selector 320 can define an aperture having a characteristic width from about 0.1 μm to about 5 μm, including fractions, interpolations, and subranges thereof (e.g., from about 0.3 μm to about 1.3 μm). Widths smaller than 0.3 μm can cause beam aberrations due at least in part to interactions between the beam and the material of the selector 320, excessively limiting the beam current and potentially damaging the selector 320. Widths larger than 1.3 μm can impair the effectiveness of the monochromator by causing too wide an energy range of charged particles to pass through the selector 320. Nevertheless, larger aperture widths can be used for relatively small monochromatizations (e.g., ΔU at FWHM between about 0.3 eV and about 0.8 eV). When selector 320 is located at the exit of dispersive element 315, the aperture width (e.g., slit width) can be between about 50 nm and about 1.0 μm, including subranges, fractions, and interpolated values ​​thereof.

[0041] In some embodiments, the first crossover 330 and the second crossover 335 occur within a segment of the beam axis A that corresponds to the dispersive filter 317 (e.g., an electromagnetic prism or a Wien filter). In some embodiments, the first crossover 330 occurs within a segment of the beam axis A that corresponds to the filter 317, and the second crossover 335 occurs outside the segment of the beam axis A that corresponds to the filter 317 (e.g., within an accelerator segment). In some embodiments, the second crossover 335 may occur substantially at the exit of the filter 317, as described in more detail with reference to FIG. 5 . The exit is the boundary opposite the source 305.

[0042] 3 is not drawn to scale, if the exemplary source 300 can reduce the impact of the Boersch effect on the energy distribution (e.g., ΔU) through a combination of dispersive element 315 and / or source 305 operating parameters, the electron beam 310 may experience increased divergence downstream of selector 320 and optical element 325. To this end, the TEM systems of the present disclosure may include column optics (e.g., the TEM column section of FIG. 1) configured to condition, shape, and shape the electron beam 310. These and other issues are described in more detail below with reference to FIGS. 4-6C.

[0043] 4 is a schematic diagram illustrating an example of a monochromated charged particle dispersive source 400 configured for use in a transmission electron microscope (TEM) system, in which the excitation parameter "φ" does not significantly attenuate the Boersch effect. The example source 400 includes a charged particle source 405, a beam-limiting aperture 410, a dispersive element 415, and a cutoff 420 positioned along the beam axis A at the exit of the dispersive element 415. The example source 400 is a specific example of the example source 300 of FIG. 3, with the selector 320 of FIG. 3 omitted, to focus the discussion on the effect of the excitation parameter φ on the operation of the dispersive element 415.

[0044] The dispersive element 415 can be or include a dispersive Wien filter or other electromagnetic element that applies a magnetic field in a direction opposite to the electric field. The two forces are balanced so that the charged particles 425 experience a deflection force (e.g., a Lorentz force, or F) that is proportional to the energy deviation (ΔU) of the charged particles 425. One or more charged particle optical elements can be included between the source 405 and the source aperture 410, but are omitted for clarity.

[0045] For a charged particle 425 whose velocity is aligned along the beam axis A and whose magnetic and electric fields are perpendicular to the beam axis A, if the charged particle 425 has an energy that deviates from the target energy (e.g., when the Wien filter is calibrated), the charged particle 425 will be deflected off-axis and will be incident on the cutoff 420. If the charged particle 425 has an energy that is substantially equal to the target energy, the deflection force will be substantially zero and the charged particle will pass through the cutoff 420 opening and towards the optics of the TEM column.

[0046] Aperture 410 limits the beam current from source 405. To this end, exemplary source 400 is configured to define a first beam intersection at cutoff 420 such that charged particles incident on dispersive element 415 at an off-axis position or trajectory are focused toward the first beam intersection where the aperture in cutoff 420 is located. Typically, dispersive element 415 is configured to operate with an excitation parameter, φ, of about 0.5π. For values ​​greater than 0.5π, dispersion typically increases with φ, as described in more detail with reference to FIG. 6A.

[0047] FIG. 5 is a schematic diagram illustrating an example of a monochromated charged particle dispersive source 500 in which an excitation parameter “φ” is used to reduce the effects of the Boersch effect, according to an embodiment of the present disclosure. The example source 500 includes a charged particle source 505, a beam-limiting aperture 510, a dispersive element 515, and a cutoff 520. For ease of comparison with the example source 400 of FIG. 4 , the path of an example beam is illustrated, and parallel beams of equivalent energy are shown to illustrate the general behavior of the example source 500. The example source 500 is a specific example of the example source 300 of FIG. 3 , omitting the selector 320 of FIG. 3 to focus the discussion on the effect of the excitation parameter φ on the operation of the dispersive element 515.

[0048] 4, in source 500, dispersive element 515 can be or can include a dispersive Wien filter or other electromagnetic element that applies a magnetic field in a direction opposite to the electric field. The two forces are balanced so that charged particle 525 experiences a deflection force (e.g., Lorentz force or F) that is proportional to the energy of the charged particle 525. One or more charged particle optical elements can be included between source 505 and source aperture 510, but are omitted for clarity.

[0049] For a charged particle 525 whose velocity is aligned with the beam axis A and whose magnetic and electric fields are perpendicular to the beam axis A, if the charged particle 525 has an energy that deviates from the target energy (e.g., when the Wien filter is calibrated), the charged particle 525 will be deflected off-axis and will be incident on the cutoff 520. If the charged particle 525 has an energy that is substantially equal to the target energy, the deflection force will be substantially zero and the charged particle will pass through the cutoff 520 aperture and proceed towards the optics of the TEM column.

[0050] In contrast to the exemplary source 400 of FIG. 4 , one or more operating parameters of the exemplary source 500 are specified such that the excitation parameter φ has a value of approximately 3π / 4 or greater. The resulting deflection force induces a sinusoidal trajectory in the charged particles. This is explained in more detail with reference to FIGS. 6A-6C . The force acting on charged particles entering the dispersive element 515 at an off-axis position creates a first beam intersection 530 between the beam-limiting aperture 510 and the cutoff 520. Charged particles 525 that deviate from a predetermined energy U by ΔU, and are not subject to the Boersch effect, are deflected so that the beam follows a trajectory 540 that defines a second intersection 535 at the cutoff 520. For charged particles 525 subject to the Boersch effect, the deflection force imparts a trajectory 545 that intersects the cutoff 520, indicating that the charged particles 525 are blocked by the cutoff 520. A mathematical treatment of the Boersch effect is explained below with reference to FIGS. 6A-6C . 5, there is a third crossover (e.g., third crossover 340 in FIG. 3) due to the focusing effect of the optics downstream of the Wien filter (e.g., accelerator in FIG. 3). This third crossover can correspond to a location of selector 340 outside of dispersive element 515, for example, downstream of dispersive element 515 (e.g., as an alternative to cutoff 520).

[0051] As explained in more detail with reference to Figures 8-9B, specifying excitation parameters of approximately 3π / 4 or greater reduces the effects of the Boersch effect and improves the width of the beam's energy distribution. For energy-dispersive beams, this improvement also corresponds to improved spatial resolution (e.g., beam width), which in turn translates into improved spatial resolution for imaging (zero-loss TEM) and microanalysis techniques (EELS mapping).

[0052] 6A-6C are data plots illustrating analytical data for dispersion, the Boersch effect, and the normalized beam energy distribution (FWHM), respectively, for a dispersive monochromator electron source configured for use in a transmission electron microscope (TEM) system according to an embodiment of the present disclosure. The next two sections describe the mathematical treatment of the influence of the excitation parameter ("φ") on the magnitude of the Boersch effect in an energy-dispersive monochromator and derive the relationship between the excitation parameter and the monochromator's performance in a TEM system. To that end, various mathematical expressions and discussions of physical phenomena are provided, but embodiments of the present disclosure are not limited to any particular physical mechanism or mathematical formulation. Section 1 below describes an exemplary embodiment of a double-focusing Wien filter, which is described in more detail with reference to Figures 2-5 above. Section 2 describes the general case of energy-dispersive optics and extends the treatment in Section 1 to systems and techniques other than double-focusing Wien filters.

[0053] 1. Double focus Wien filter

[0054] In a first example, the charged particle beam mainly comprises electrons. In this example, the same expressions apply: η=(e / (2m)) 1 / 2 , where e is the elementary charge of the electron and m is the mass of the electron; a straight optical axis identified as the "z" axis in Cartesian or cylindrical coordinate space; and The equation for the beam voltage of the Wien filter = U + ΔU = U(1 + κ) (κ = ΔU / U), where U = the nominal beam voltage below the electron source (e.g., U is defined as the potential of the electron source) and the energy of the electrons is eU or e(U o +dU) (nominal energy U o and for an electron source with energy spread dU);

[0055] Typically, U is less than 10 kV, so the non-relativistic approximation is adequate, as is the SCOFF approximation (which assumes a beam incidence angle perpendicular to the magnetic field B, resulting in zero quadrupole field). Combined effects of the approximations include the negligibility of peripheral regions at the entrance and exit of the Wien filter.

[0056] Magnetic dipole field B y is the vector potential (outside 1) TIFF2026010670000002.tif866. The dipole field E that can cancel out the magnetic dipole field of nominal energy x =2ηByU 1 / 2 Next, the quadrupole potential φ2=a2(x 2 -y 2 ) can be applied. The Wien filter is (outside 2) Double focusing can be achieved by setting TIFF2026010670000003.tif854. In a simplified model of electron-electron interaction, each electron experiences a constant electric field E, which is generated by its neighboring electrons (different for each electron), as it passes through the Wien filter. z , B The evolution parameter "z" is used in the model.

[0057] The Hamiltonian H(x,y,p,q,z) of the SCOFF Wien filter is

number

[0058] where A z =-xB y and

number

[0059] The evolution parameters are chosen so that z = 0 at the slit plane, and the electron energy at the slit plane is E z,B The Wien filter can be assumed to run from z=-L to z=0, with the beam crossing and energy selection slit at z=0.

[0060] At the filter entrance plane z=-L, the electron energy is e[U(1+κ)+E z,B E is equal to L. z,B Electrons experiencing different values ​​of θ travelling through the slit with the same energy can enter the filter with a distribution of energies. These incident energy variations can be relatively small compared to the energy dispersion of electrons at the beam source.

[0061] The Hamilton formula is shown below:

number

[0062] For the relevant basis rays, the Hamiltonian can be truncated to:

number

[0063] In this case, the excitation parameters (Outside 3) TIFF2026010670000008.tif1350 is in inverse metric units (m- 1 ) Considering a subset of the basis rays (e.g. excluding the field rays), the x(z),y(z) ray can be described mathematically as:

number

number

[0064] In this case, the ray parameters α, β, κ, Ez,B Here, we define a new basis ray x for the Boersch effect. B (z) is the constant Coulomb force E between the electrons adjacent to it z,B (which differs for each electron) is introduced as an approximation of x in the energy selection plane. B When (z)=0, the Boersch effect is maximally reduced. The axis is (outside 4) The expression follows TIFF2026010670000011.tif1270. α and β are the image-side angles in the plane z=0.

[0065] base ray x B (z) allows us to approximately introduce the Boersch effect. Hamilton's equation leads to the equation of motion:

number

number

[0066] This is a linear non-homogeneous differential equation and can be solved using the "variation of constants method". Thus,

number

[0067] and for the central ray, starting from x(-L)=x′(-L)=0, the x position of the slit plane is given by:

number

[0068] Therefore, the variance "D" is

number

[0069] That is,

number

[0070] The Wien filter excitation parameter φ is defined as φ = KL, and the approximate Boersch effect is given by

number

number

[0071] Figures 6A-6C show the variation of the dispersion and Boersch effect as a function of the excitation parameter φ, as described in Equations 2.12 and 2.13. From the above derivation, for values ​​around φ = 4.5, the Boersch effect is nearly zero and the dispersion is relatively small (e.g., about 30% of the peak value of the dispersion around φ = 2.3).

[0072] The Wien filter axial coma B2 is expressed by the following formula:

number

[0073] Axial coma was found to be proportional to dispersion. This is where beam aberrations affect the energy resolution of a monochromator. The data in Figures 6A-6C are for U=1 kV, Wien filter length L=50 mm, slit current=10 nA, and brightness reduction β r =5 10 7 A / (V m 2 ·sr), corresponding to the assumed optimal aperture angle and optimal slit width values.

[0074] The probe size at the slit plane was approximated using a simple square-root summing method. The full width at half maximum (FWHM) of the energy distribution and the shape of the long tail (highly affected by the Boersch effect) significantly affect the energy distribution of the beam under the slit (e.g., approximately 0.1% of the maximum). Therefore, using a value of φ smaller than the value at which the approximate Boersch effect is zero (e.g., φ = 4 rather than φ = 4.5) improves the monochromator's performance in terms of the Boersch effect and dispersion. Note that the values ​​and curves described here are generated under the assumption that the slit is located at z = 0 and that the ambient magnetic field is ignored. Therefore, the monochromator's performance will vary depending on various assumptions made in the simulation, such as whether or not the ambient optical field is considered, or whether or not the selection slit is moved.

[0075] 2. General Case of Dispersive Optical Systems

[0076] To that end, the Wien filter can be generalized to cases where an ambient light field is included, where the slit plane is at a different position, where there is a line focus within the slit rather than a point focus, etc. Also, because dispersion can also occur with magnetic and electrostatic prisms, the monochromator can be generalized to devices with a curved optical axis. In that case, the optical axis can be defined as the central ray of nominal energy. The distance coordinate along the centerline is defined as "z", and "x,y" are the corresponding orthogonal curvilinear coordinates. If the optical axis is in the xz plane, the non-relativistic Hamiltonian H(x,y,p,q,z) is given mathematically by:

number

[0077] The principal dispersion is generated and magnified in the xz plane. The incorporation of the Boersch effect adds significant complexity to the analytical description of dispersion through relativistic treatment. For at least this reason, a nonrelativistic approximation is maintained in the general case, even for monochromators at ground potential. Suppression of the Boersch effect is important for oscillatory EELS performed at beam energies below 80 kV, where the relativistic approximation is usually appropriate. At the slit plane, it is the same as before z = 0. For the Wien filter discussed in Section 2, optical designers typically ignore values ​​of φ greater than π. This is because, at least in the dispersion equation 2.10 above, the integral term sin(Kz) = sin(φz / L) becomes negative for some values ​​of z. A negative dispersion value indicates compromised dispersion and appears to offer no benefit to the monochromator's performance.

[0078] In most cases, the beam energy is stable (constant) in the region where the Boersch effect is calculated, and in that case φB=-E z,B z can be used. An exception to this approximation occurs in systems where an accelerator is placed between the monochromator and the energy-selecting slit. Acceleration increases the average distance between the charged particles. This means that the Borsch potential generalizes to:

number

[0079] In the following explanation, we assume that the beam energy from the monochromator entrance surface to the slit surface is constant, but U(z) 3is variable. The matrix A can be generalized to A(z), but in general (including in the peripheral region) analytical expressions for xα(z) and yβ(z) are more complicated and sometimes unavailable. Combining equations and using non-relativistic approximations, z = z slit and x α =x α Applying (zslit) gives:

number

[0080] where z 開始 <0. The dispersion equation for a dispersive device is ψ 1s It can be expanded when (z) is a dispersion generating function, which has a non-zero value inside the dipole Wien filter and / or prism and can take any sign. The general Hamiltonian (3.1) can be expanded by adding the Boersch effect term, so that κ becomes κ-(E z,B / U)z. This is the same as in the previous section. And, as in the previous section, the "changing constants" method can be adopted, which generalizes Equation 3.3.

number

number

number

[0081] In typical monochromator designs, the approach is to maximize dispersion as an approach to optimize the half-width of the energy distribution. Thus, in designs that use multiple prisms, such as curved-axis monochromators (e.g., alpha and omega types), (outside 6) The sign of TIFF2026010670000028.tif1674 is the same for all prisms. Equation 3.6 (when the entire integral is z<0) shows that the approximate Boersch effect can be largely zero or negligible in monochromators with multiple prisms, such as the curved-axis monochromator to which the techniques of this disclosure are applied.

[0082] 7 is a block flow diagram of an exemplary process 700 for generating a monochromatic beam of charged particles, according to some embodiments of the present disclosure. As described with reference to FIGS. 1-6C, one or more operations comprising exemplary process 500 may be performed by a computer system operatively coupled to components of a charged particle microscope (e.g., TEM system 100 of FIG. 1) and / or additional systems or subsystems, including, but not limited to, a characterization system, a network infrastructure, a database, and a user interface device. To that end, the operations may be stored as machine-executable instructions on one or more machine-readable media.

[0083] For example, operations of example process 700 can be repeated, reordered, and / or omitted as part of performing an oscillation EELS workflow. To this end, the operations of example process 700 are described as being performed by a system, with the understanding that the operations include the generation and communication of control signals between a processor or other logic circuitry and electronic or electromechanical elements of a charged particle microscope. The operations of example process 700 are described in the context of an electron microscope for clarity. Embodiments of the present disclosure include processes for generating monochromated ion beams and other charged particle configurations, such as dual beam systems.

[0084] The exemplary process 700 includes generating a charged particle beam in operation 705. Electron beam 310 in FIG. 3 is an example of a charged particle beam in operation 705. Generating the charged particle beam includes adjusting a high-voltage supply coupled to an emitter source (e.g., source 305 in FIG. 3 ) to provide power to the emitter source. As one skilled in the art would understand, operation 705 can be preceded by one or more operations and / or sub-operations, such as evacuating the environment surrounding the source to a high or ultra-high vacuum or completing internal calibration tests, cleaning cycles, or other processes that form part of the operation of the charged particle microscope system. To this end, for example, in some embodiments of exemplary process 700, generating a charged particle beam refers to modifying the operation of the source (e.g., via one or more control instructions executed by a computer system) to facilitate microanalysis, such as oscillation EELS, when the electron microscope switches from one operating mode (e.g., TEM imaging mode) to another operating mode (e.g., spot mode EELS).

[0085] The exemplary process 700 includes dispersing charged particles of a charged particle beam in operation 710. As described in more detail with reference to FIGS. 2-5, energy dispersion of the charged particles (e.g., electrons 310 in FIG. 3) can be achieved by modifying one or more parameters of a dispersive element (e.g., dispersive element 315 in FIG. 3), including the electric field of a Wien filter, the magnetic field of a Wien filter, and / or one or more parameters of an accelerator (e.g., including multiple annular electrodes separated from each other by a dielectric). To this end, a monochromator can be included as part of a charged particle optical device, such as electron optical device 115 in FIG. 1, to selectively filter, block, or otherwise remove regions of the energy distribution of the charged particles emitted from the source (e.g., using dispersive element 315 and selector 320 in FIG. 3). Advantageously, operation 710 can attenuate, reduce, or substantially eliminate the impact of the Boersch effect on the energy distribution, as described in more detail with reference to FIGS. 5-6C and shown in the comparative data of FIGS. 8A-9B. In some embodiments, the operation of the dispersive element is characterized by an excitation parameter φ having a value from about 0.5π to about 1.5π, including subranges, fractions, and interpolations (e.g., about 0.75π). In one example, the excitation parameter is about 4.3.

[0086] As part of generating a monochromatic beam of charged particles, the exemplary process 700 includes narrowing the energy distribution of the beam in operation 715. In some embodiments, narrowing the energy distribution includes selectively blocking, redirecting, absorbing, or attenuating the charged particles using a selector (e.g., selector 320 of FIG. 3 ) located on or near a beam axis (e.g., beam axis A). As described in more detail with reference to FIGS. 3 and 5 , the selector can be located substantially co-located with the third intersection of the charged particle beam, such that the beam dispersed in a plane substantially perpendicular to the axis includes charged particles having a range of energies according to a spatial distribution relative to the beam axis (e.g., as described with reference to FIG. 2 ). To that end, the selector can remove charged particles from the beam having energies outside an acceptable deviation from the target energy U. This allows the monochromatic beam to exit the source with an improved energy distribution compared to prior art techniques in which the energy distribution is broadened due to the Boersch effect in the selector.

[0087] Figures 8A-10B show a series of comparative examples developed for the charged particle optical device of Figures 2-5. The presented data were generated by simulating the device components using a Monte Carlo (stochastic) simulation technique that includes physical models of Coulomb interactions and the Boersch effect. The presented examples show monoenergetic electron sources configured to operate at different values ​​of the excitation parameter "φ." Thus, the simulations illustrate sources configured to generate monoenergetic electron beams characterized by FWHMs between about 5 meV and about 30 meV and beam currents between about 10 pA and about 200 pA. Figures 8A-8B correspond to sources operated according to parameters typical of current technology (φ ≈ π / 2) and are described with reference to Figures 2 and 4. Figures 9A-9B correspond to sources operated in accordance with embodiments of the present disclosure described with reference to Figures 3 and 5. The graphs plot normalized intensity versus differential energy, expressed as a relative value to the target energy U, which can be understood to correspond to beam energies between about 1 kV and about 500 kV.

[0088] Figures 8A-8B show example energy distribution graphs simulated according to the current state of the art for the electron source of Figure 2. The data in Figures 8A-8B were generated using excitation parameter φ values ​​of approximately π / 2, beam energy at the Wien filter of approximately 500 V, and beam current at the Wien filter of approximately 20 nA. The half-width of the energy distribution at a monochromated probe current of 56 pA was determined to be approximately 18 meV, and the half-width at 1 / 10 of the maximum was determined to be approximately 106 meV. Figure 8B shows the same data on a logarithmic scale, demonstrating that the energy distribution half-width at 1 / 100 of the maximum at approximately 250 meV 805 overlaps well with the range of energy differences that provide meaningful information for vibrational EELS.

[0089] 9A-9B are example energy distribution graphs simulated for the electron source of FIG. 3 in accordance with an embodiment of the present disclosure. The data in FIGS. 9A-9B were generated using an excitation parameter φ value of approximately 4.3. The half-width of the energy distribution at a monochromated probe current of 84 pA was determined to be approximately 15 meV, and the half-width at 1 / 10 of the maximum was determined to be approximately 43 meV, corresponding to an improvement of approximately 60%. FIG. 9B shows the same data on a logarithmic scale, showing that the half-width 905 of the energy distribution at 1 / 100 of the maximum 810 at approximately 130 meV is narrow enough to distinguish the beam energy from the energy range that provides meaningful information for vibrational EELS. The parameters used in simulating the data in FIGS. 9A-9B indicate that a higher current (e.g., approximately 1.5 times) beam can exhibit an improvement in energy resolution of approximately 40% to 60%, at least in part, by reducing the effects of the Boersch effect in monochromated sources.

[0090] In the preceding description, various embodiments have been described. For purposes of explanation, specific configurations and details have been presented to provide a thorough understanding of the embodiments. However, it will be apparent to those skilled in the art that embodiments may be practiced without the specific details. Additionally, well-known features may be omitted or simplified so as not to obscure the described embodiments. While the exemplary embodiments described herein focus on charged particle source components and systems, particularly transmission electron microscope electron source systems, these are intended to be non-limiting exemplary embodiments. Embodiments of the present disclosure are not limited to such systems, but rather are directed to analytical instrument systems capable of analyzing a wide variety of material samples to determine chemical, biological, physical, structural, or other properties, including, but not limited to, chemical structure, trace element composition, and the like. A monochromatic beam of charged particles interacts with the sample to generate a detectable signal.

[0091] 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 including 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 including 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.

[0092] The terms and expressions used are used as terms of description, not of limitation, and are not intended to exclude equivalents of the functions shown and described or portions thereof, but recognize that various modifications are possible within the scope of the claims. Thus, while the present disclosure includes specific embodiments and optional functions, it should be understood that those skilled in the art may make modifications and variations to the concepts of the present disclosure, and that such modifications and variations are considered to be within the scope of the appended claims.

[0093] When terms are used without explicit definition, they are understood to be used in their ordinary sense unless they have a special and / or specific meaning in the context of charged particle microscope systems or other related fields. The terms "about" or "substantially" are used to indicate that deviations from a stated characteristic have little or no effect on the corresponding function, characteristic, or attribute of the described structure. In illustrated examples, when one dimensional parameter is described as "substantially equal" to another dimensional parameter, the term "substantially" is intended to reflect that the two compared parameters may differ within tolerances, such as manufacturing tolerances or the confidence interval inherent in the operation of the system. Similarly, when a geometric parameter such as alignment or angular orientation is described as "approximately" normal, "substantially" normal, or "substantially" parallel, the terms "about" or "substantially" are intended to reflect that the alignment or angular orientation may differ from the precisely stated condition (e.g., not exactly normal) within a tolerance range. For numerical values ​​such as diameter, length, and width, the term "about" can be interpreted to mean a deviation from the stated value within ±10%. For example, the dimension "approximately 10 mm" can represent a dimension between 9 mm and 11 mm.

[0094] This specification provides exemplary embodiments and is not intended to limit the scope, applicability, or configuration of the disclosure. Rather, the following description of exemplary embodiments will provide those skilled in the art with an effective description for implementing various embodiments. It is 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 set forth in the description to provide a thorough understanding of the embodiments. However, it will be understood that the embodiments can be practiced without these specific details. For example, certain system components, systems, processes, and other elements in the disclosure may be omitted from illustrations or shown in schematic form so as not to obscure the embodiments with unnecessary detail. Additionally, prominent circuits, processes, components, structures, and / or techniques may be shown without unnecessary detail.

Claims

1. a Wien filter arranged on the beam axis, the Wien filter configured to disperse particles of the charged particle beam by energy in a dispersion plane parallel to the beam axis; an optical element disposed on the beam axis downstream of the Wien filter and configured to focus the charged particle beam toward the beam axis; a selector disposed on the beam axis at a position downstream of the optical element and substantially corresponding to a third intersecting plane; Charged particle optical device.

2. 2. The charged particle optical device of claim 1, wherein the charged particle beam defines a first intersecting plane at a first point on the beam axis within the Wien filter and a second intersecting plane that substantially coincides with an exit from the Wien filter at a second point on the beam axis downstream of the first intersecting plane.

3. 10. The charged particle optical device of claim 1, wherein the Wien filter comprises a double-focusing Wien filter.

4. 2. The charged particle optical device of claim 1, wherein the Wien filter is characterized by an excitation parameter φ, the positions of which correspond to values ​​of the excitation parameter φ greater than about 3π / 4.

5. 5. The charged particle optical device of claim 4, wherein the excitation parameter φ is at a position corresponding to a range of values ​​from about π to about 3π / 2.

6. 6. The charged particle optical device of claim 5, wherein the position corresponds to a value of the excitation parameter φ of about 4.

3.

7. The charged particle optical device of claim 1 , wherein the optical element is further configured to accelerate particles of the charged particle beam.

8. 2. The charged particle optical device of claim 1, wherein the charged particle beam at the entrance of the Wien filter is characterized by a first beam current of about 5 nA to about 50 nA and a second beam current below the selector of greater than about 60 pA.

9. 9. The charged particle optical device of claim 8, wherein downstream of the selector, the energy distribution of the charged particle beam has a half-width at 1 / 100 of the maximum from about 40 meV to about 200 meV.

10. 10. The charged particle optical device of claim 1, wherein the selector defines an aperture having a characteristic width from about 0.3 μm to about 1.3 μm.

11. a charged particle source configured to generate a charged particle beam substantially aligned with the beam axis; a monochromator comprising a Wien filter disposed on the beam axis, the Wien filter configured to disperse particles of the charged particle beam by energy in a dispersion plane parallel to the beam axis; an optical element disposed on the beam axis downstream of the Wien filter and configured to focus the charged particle beam toward the beam axis; a selector disposed on the beam axis downstream of the optical element at a position substantially corresponding to a third intersecting plane; and a focusing lens disposed on the beam axis downstream of the monochromator and configured to focus particles of the charged particle beam toward the beam axis. Charged particle beam system.

12. 12. The charged particle beam system of claim 11, wherein the charged particle beam defines a first intersecting plane at a first point on the beam axis within the Wien filter and a second intersecting plane downstream of the first intersecting plane at a second point on the beam axis that substantially coincides with an exit from the Wien filter.

13. 12. The charged particle beam system of claim 11, wherein the Wien filter comprises a double-focusing Wien filter.

14. 14. The charged particle beam system of claim 13, wherein the Wien filter is characterized by an excitation parameter, φ, and its positions correspond to values ​​of the excitation parameter φ greater than about 3π / 4.

15. 15. The charged particle beam system of claim 14, wherein the positions correspond to values ​​of the excitation parameter φ from about π to about 3π / 2.

16. 16. The charged particle beam system of claim 15, wherein the position corresponds to a value of the excitation parameter φ of about 4.

3.

17. The charged particle beam system of claim 11 , wherein the optical element is further configured to accelerate the particles of the charged particle beam.

18. 12. The charged particle beam system of claim 11, wherein the charged particle beam is characterized by a first beam current of about 5 nA to about 50 nA at an entrance to the Wien filter, wherein the charged particle beam is characterized by a second beam current of greater than about 60 pA at an exit of the Wien filter, and downstream of the monochromator, the charged particle beam is characterized by an energy distribution having a half-width at one-hundredth of maximum of about 80 meV to about 200 meV.

19. The charged particle beam system of claim 11, wherein the selector defines an aperture having a characteristic diameter of from about 0.3 μm to about 1.3 μm.

20. 12. The charged particle beam system of claim 11, further comprising input optics configured to receive the charged particle beam from the charged particle source and focus the charged particle beam toward the beam axis, the input optics being positioned on the beam axis between the charged particle source and the monochromator.

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