MICROFOCUS X-RAY SOURCE FOR THE GENERATION OF HIGH FLUENT, LOW ENERGY X-RAY

Abstract

One X-ray source comprising: at least one enclosure configured to contain a first area at a pressure of less than one atmosphere (atm) and configured to separate the first area from an environment outside the at least one enclosure, wherein the at least one enclosure includes a window for x-ray transmission with an x-ray transmittance of more than or equal to 20% for at least some x-rays with an x-ray energy of less than 1 keV; an electron source in the at least one housing, wherein the electron source is configured to produce at least one electron beam; an anode arrangement within the at least one housing, configured to generate X-rays in response to electron bombardment by at least some of the electrons of the at least one electron beam from the electron source; at least one X-ray optic in the at least one housing, wherein the at least one X-ray optic is configured to receive at least a portion of the X-rays from the anode arrangement and to direct at least a portion of the received X-rays towards the window to generate an X-ray beam.

Description

CLAIMING PRIORITY

[0001] This application claims priority over U.S. Preliminary Application No. 63 / 299,341, which was filed on January 13, 2022, and is incorporated herein in its entirety by reference. BACKGROUND area

[0002] The present application discloses X-ray sources for generating X-rays by electron bombardment. Description of the state of the art

[0003] A widely used method and system for generating X-rays involves bombarding an anode with energetic electrons generated by an electron column. The anode material, such as copper (Cu) or molybdenum (Mo), is selected based on its X-ray spectral properties (e.g., its characteristic fluorescent X-ray emission). Because electrons interact strongly with matter (e.g., with the gas the electrons pass through on their way from the electron column to the anode), the electron column and the X-ray anode are located in a container with a vacuum greater than 10⁻⁶. -6Torr. Since the use of X-rays inside a vacuum chamber is extremely impractical for many applications (e.g., materials characterization / analysis / imaging), the vacuum chamber typically includes an X-ray / vacuum window. This window allows X-rays to pass through while separating the high-vacuum region inside the chamber, containing the electron column and anode, from the low- or no-vacuum region outside. Such conventional X-ray / vacuum windows have high transmittance for higher-energy X-rays but low transmittance for lower-energy X-rays.

[0004] US 2019 / 0145917A1 relates to an X-ray spectrometer system comprising an X-ray source, an optical X-ray system, a mount, and an X-ray spectrometer. The optical X-ray system is configured to receive, focus, and spectrally filter X-rays to produce an X-ray beam with a second spectrum. The second spectrum is attenuated compared to the first spectrum in an energy range above a predetermined energy, and the X-ray beam has a focus in a predetermined focal plane.

[0005] US 2020 / 0035440A1 relates to an X-ray source comprising an X-ray target and an electron source. The X-ray target comprises a thermally conductive substrate with a surface and at least one structure on or embedded in at least a portion of the surface. This structure comprises a thermally conductive first material in contact with the substrate and a second layer over the first material. This second layer comprises at least one further material that generates X-rays when irradiated by electrons. The electron source is configured to generate electrons in at least one electron beam and direct it to strike the structure.

[0006] WO 2019 / 236 384 A1 relates to an X-ray spectrometer comprising X-ray optics configured to receive X-rays of different energies, an X-ray detector that records the spatial distribution of the X-rays, and a mosaic crystal structure and / or a multilayer arrangement that influences the spectral distribution of the X-rays. The X-ray spectrometer further comprises an X-ray detector for receiving X-rays from the X-ray optics and recording a spatial distribution of the X-rays.

[0007] DE 196 33 860 A1 relates to a method for generating high-intensity X-rays of varying energies. Electrons are emitted from a cathode, accelerated, and directed onto a rotating anode, where they initiate X-rays. The X-rays are focused using a glass capillary optic, and the focal spot on the rotating anode is positioned and held precisely on the optical axis of the glass capillary optic. SUMMARY

[0008] In certain embodiments, an X-ray source comprises at least one housing configured to contain a first region at a pressure of less than one atmosphere and configured to separate the first region from an environment outside the housing. The housing includes a radiolucent window with a transmittance of at least 20% for at least some X-rays with an X-ray energy of less than 1 keV. The X-ray source further comprises an electron source within the housing. The electron source is configured to generate at least one electron beam.The X-ray source further comprises an anode assembly within the at least one housing, configured to generate X-rays in response to electron bombardment by at least some of the electrons from the at least one electron beam originating from the electron source. The X-ray source further comprises at least one X-ray optic within the at least one housing. The at least one X-ray optic is configured to receive at least some of the X-rays from the anode assembly and to direct at least some of the received X-rays onto the window to form an X-ray beam. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1A and Fig. Figure 1B schematically shows cross-sectional views of two exemplary X-ray sources for generating X-rays in accordance with certain embodiments described herein. Fig. Figure 2 schematically shows a perspective view of part of an example of an X-ray transparent window in accordance with certain embodiments described herein. Fig. Figure 3 schematically shows an exemplary electron source in accordance with certain embodiments described herein. Fig. Figure 4 schematically shows part of an exemplary anode arrangement in accordance with certain embodiments described herein. Fig. Figure 5 schematically shows an example of an X-ray optic in accordance with certain embodiments described herein. DETAILED DESCRIPTION

[0009] X-ray sources with conventional X-ray / vacuum windows are incompatible with applications requiring low-energy X-rays (e.g., less than 1 keV). Low-energy X-rays offer advantages for many applications (e.g., large ionization cross-sections for most elements in the periodic table, especially for low-atomic elements, known as low-Z elements). For many applications, low-energy X-rays with specific spectral properties are desirable (e.g., a narrow spectral bandwidth to generate photoelectrons with low kinetic energy and a narrow energy distribution; specific X-ray energies to optimize the ionization cross-sections of selected elements). High-flux, low-energy X-rays, particularly those with energies below 1 keV, outside the vacuum chamber may be desirable and / or critical for various applications.

[0010] Conventional X-ray sources struggle to meet these desirable properties because the requirements of the X-ray system and the vacuum system conflict. To increase the X-ray flux for low-energy X-rays (e.g., to allow more low-energy X-rays to pass through the window), it may be desirable to have a window with high transmittance for low-energy X-rays and a window large enough to allow low-energy X-rays propagating over a wide emission angle to pass through. While a thin window made of low-Z elements can provide high transmittance for low-energy X-rays, such thin windows are typically fragile, especially if the thin window is large enough to receive low-energy X-rays over a wide emission angle.Furthermore, such a large, thin window would have to withstand various harsh conditions during the manufacture and processing of the X-ray source (e.g., baking at high temperatures, pressure differences between the two sides of the window, transport from the manufacturer to the customer).

[0011] To generate characteristic X-rays with energies below 1 keV while simultaneously producing less bremsstrahlung, anode materials consisting predominantly of low-Z elements (e.g., boron to fluorine) may be desirable, as the amount of bremsstrahlung produced by the anode materials is proportional to the average atomic number (Z) of the anode materials. Since it may be desirable to have an electrically conductive path (e.g., to ground) from the anode material to prevent charging by the incident electrons, and low-Z bulk materials are typically insulators (with the exception of boron and carbon), metals with an atomic number greater than 12 (the atomic number of magnesium) are often used as anode materials, resulting in significant bremsstrahlung.

[0012] Fig. Figure 1A schematically shows a cross-sectional view of an exemplary X-ray source 100 for generating X-rays in accordance with certain embodiments described herein. The exemplary X-ray source 100 comprises at least one housing 110 (e.g., a vacuum vessel) configured to provide a first region 112 in a vacuum (e.g., pressure of less than 10 -4 Torr; less than less than 10 -6 Torr; less than less than 10 -8The at least one housing 110 contains a first region 112 from a second region 170 (e.g., the environment) outside the housing 110. The housing 110 includes an X-ray-transparent window 120 with an X-ray transmittance of more than or equal to 20% for at least some X-rays with an X-ray energy of less than 1 keV (e.g., less than 0.5 keV; less than 0.3 keV). The exemplary X-ray source 100 further includes an electron source 130 (e.g., an electron column) within the housing 110, configured to produce at least one electron beam 132 (e.g., a collimated electron beam, a focused electron beam, a converging electron beam). The exemplary X-ray source 100 further comprises an anode arrangement 140 in the at least one housing 110, which is configured such that it emits X-rays 142 (e.g.a divergent X-ray beam) is generated in response to electron bombardment by at least some of the electrons of the at least one electron beam 132 from the electron source 130. The exemplary X-ray source 100 further comprises at least one X-ray optic 150 within the at least one housing 110, configured to receive (e.g., collect) at least a portion of the X-rays 142 from the anode arrangement 140 and to direct at least a portion of the received X-rays 142 onto the window 120 to form an X-ray beam 152 (e.g., a collimated X-ray beam, a focused X-ray beam, a converging X-ray beam). The at least one X-ray optic 150 may comprise at least one monocapillary lens, at least one polycapillary lens, a pair of KB mirrors, a zone plate, a plurality of monocapillary lenses nested along a common axis, or a Wolter optic.In certain embodiments, the at least one X-ray optic 150 comprises a reflective mirror optic in which at least a part of the mirror surface has a square surface profile in at least one direction (e.g. elliptical; parabolic; hyperbolic; ellipsoidal; paraboloidal; hyperboloidal).

[0013] In certain embodiments, the X-ray beam 152 has a cross-sectional area perpendicular to the direction of propagation of the X-ray beam 152, and the cross-sectional area is a function of the distance from the at least one X-ray optic 150 (e.g., the cross-sectional area at a first location at a first distance from the at least one X-ray optic 150 differs from the cross-sectional area at a second location at a second distance from the at least one X-ray optic 150, the second distance being greater than the first distance). The cross-sectional area can have a minimum value (e.g., a minimum area compared to the cross-sectional areas at all other locations along the direction of propagation of the X-ray beam 152 from the at least one X-ray optic 150) at a position 160 (e.g.,focal point of the at least one X-ray optic 150; position of the smallest beam waist of the X-ray beam 152), wherein the position 160 is at or near the window 120 (e.g., at a location within 30 millimeters in front of the window 120; within 20 millimeters in front of the window 120; within 5 millimeters in front of the window 120; within 2 millimeters in front of the window 120; within 1 millimeter in front of the window 120; the position 160 may be within the first region 112, coincident with the window 120, or outside the at least one housing 110). For example, the X-ray beam 152 may have a cross-sectional width (e.g.,diameter) in a range of 3 micrometers to 300 micrometers, 10 micrometers to 1 millimeter, less than 2 millimeters, less than 200 micrometers and / or less than 50 micrometers and / or a cross-sectional area in a range of 100 square micrometers to 5 square millimeters (e.g. 0.004 square millimeters to 5 square millimeters; 0.01 square millimeters to 5 square millimeters).

[0014] Fig. Figure 1B schematically shows a cross-sectional view of another example of an X-ray source 100 in accordance with certain embodiments described herein. The at least one housing 110 of Fig. 1B comprises a first housing 110a (e.g., a first vacuum vessel) and a second housing 110b (e.g., a second vacuum vessel). The first housing 110a is configured to contain the first area 112 under vacuum (e.g., pressure of less than 10). -4 Torr; less than 10 -6 Torr; less than 10 -8The first housing 110a contains a first region 112 (less than 1 Torr) and is configured to separate the first region 112 from the second region 170 (e.g., the environment) outside the first housing 110a. The first housing 110a also contains the electron source 130, the anode assembly 140, and the at least one X-ray optic 150. The second housing 110b is configured to contain a third region 180 under vacuum, with the window 120 located between the first region 112 and the third region 180. In certain embodiments, the second housing 110b is rigidly connected to the first housing 110a. In certain embodiments, the second housing 110b is detachable from the first housing 110a.

[0015] In certain embodiments, the second housing 110b comprises at least one second X-ray optic 182 within the third area 180, wherein the at least one second X-ray optic 182 is configured to receive at least some of the X-rays of the X-ray beam 152 transmitted through the window 120 and adjusts the received X-rays (e.g., with respect to their spectral properties and / or angular distribution) to transmit a second X-ray beam 184 (e.g., a collimated X-ray beam; a focused X-ray beam; a converging X-ray beam). The at least one second X-ray optic 182 may comprise at least one monocapillary lens, at least one polycapillary lens, a pair of KB mirrors, a zone plate, a plurality of monocapillary lenses nested along a common axis, or a Wolter optic.In certain embodiments, the at least one second X-ray optic 182 comprises a reflective mirror optic in which at least a portion of the mirror surface has a square surface profile in at least one direction (e.g., elliptical, parabolic, hyperbolic, ellipsoid, paraboloid, hyperboloid). For example, the at least one second X-ray optic 182 may have an ellipsoidal surface (e.g., with a first focus within 2 millimeters of the window 120 and a second focus within 2 millimeters of an opening of the second housing 110b) or a pair of substantially symmetrical paraboloidal surfaces (e.g., a first paraboloidal surface with a first focus within 2 millimeters of the window 120 and a second paraboloidal surface with a second focus within 2 millimeters of an opening of the second housing 110b).For example, the at least one second X-ray optic 182 can be configured to receive (e.g., collect) X-rays from the X-ray beam 152 transmitted through the window 120 (e.g., diverging X-rays) and to direct at least some of the X-rays received from the window 120 so that they form the second X-ray beam 184 (e.g., a collimated X-ray beam; a focused X-ray beam; a converging X-ray beam).

[0016] The second housing 110b may further include at least one vacuum valve 186 at the opening of the second housing 110b, configured to controllably separate the third area 180 from the second area 170 (e.g., the environment). The at least one vacuum valve 186 may be a gate valve (e.g., manually or pneumatically operated) and may be used to protect the window 120 (e.g., during vacuum baking of the X-ray source 100) and / or to facilitate the transport and storage of components within the second housing 110b.

[0017] In certain embodiments, the at least one vacuum valve 186 can be opened controllably so that the second X-ray beam 184 from the at least one second X-ray optic 182 can propagate out of the second housing 110b (e.g., to a sample that is analyzed downstream of the at least one vacuum valve 186). In certain embodiments, the window 120 can open the first region 112 in which a first vacuum pressure prevails (e.g., less than 1 Torr; less than 10 -4 Torr; less than 10 -6 Torr; less than 10 -8to separate the first window (Torr) from the third window (180), where a second vacuum pressure prevails that is lower than atmospheric pressure but higher than the first vacuum pressure (e.g., in a range of 1 Torr to 500 Torr; in a range of 20 Torr to 200 Torr). Such a configuration avoids a large pressure difference across window 120, and window 120 can be sufficiently thin to transmit a substantial portion of the low-energy X-rays, despite having a greater width (e.g., 1 millimeter or more).

[0018] In certain embodiments (e.g., as in the Fig. 1A and Fig. (as shown in Figure 1B) the electron source 130, the anode arrangement 140 and the at least one X-ray optics 150 are located in a single chamber within the first region 112, while in certain other embodiments the first region 112 comprises a plurality of chambers with walls between two or more of the electron source 130, the anode arrangement 140 and the at least one X-ray optics 150.

[0019] Fig. Figure 2 schematically shows a perspective view of part of an example of an X-ray-transparent window 120 in accordance with certain embodiments described herein. In certain embodiments, the at least one housing 110 comprises one or more metal walls 111 (e.g., made of stainless steel) surrounding the first region 112, which is under vacuum pressure (e.g., less than 1 Torr; less than 10 -4 Torr; less than 10 -6 Torr; less than 10 -8Torr) and is sealed against the second area 170 (e.g., at ambient pressure) outside the housing 110. In certain embodiments, as in Fig. As shown in Figure 2, at least one of the walls 111 comprises an aperture 114 extending through the wall 111, and the window 120 is mounted and sealed above the aperture 114 (e.g., the window 120 is configured to seal the first area 112 against the second area 170 or against the second housing 110b). The aperture 114 may, for example, have a substantially square or substantially rectangular shape with a transverse width in the range of 0.1 millimeters to 10 millimeters (e.g., a first width in a first transverse direction of 200 micrometers and a second width in a second transverse direction substantially perpendicular to the first transverse direction of about 2 millimeters). The transverse width of the aperture 114 may be smaller than the transverse width of the window 120 (e.g., to facilitate mounting the window 120 on the wall 111). In certain embodiments, as shown in Figure 2, the aperture 114 may be smaller than the transverse width of the window 120 (e.g., to facilitate mounting the window 120 on the wall 111). Fig. As shown in Figure 2, the window 120 is attached to an outer surface of the wall 111 (e.g., a surface facing the second area 170), while in certain other embodiments, the window 120 is attached to an inner surface of the wall 111 (e.g., a surface facing the first area 112). The window 120 can, for example, be manufactured on and supported by a silicon frame (e.g., with a thickness in the range of 200 to 400 micrometers), which is sealed to the wall 111 with a vacuum-compatible adhesive (e.g., epoxy sealant; TorrSeal®, available from Kurt J. Lesker Co. of Jefferson Hills, PA), an O-ring seal, or by brazing. In certain embodiments, the window 120 is secured to the wall 111 with a vacuum-tight bellows between the window 120 and the wall 111.

[0020] In certain embodiments, the window 120 is configured to withstand (e.g. maintain) a pressure difference between the first area 112 inside the at least one housing 110 (e.g., at a first pressure of less than 1 atmosphere) and the second area 170 outside the at least one housing 110 (e.g., at a second pressure that is greater than the first pressure).

[0021] In certain embodiments, the window 120 comprises a substrate 122 (e.g., a frame) and a radiolucent element 124 (e.g., a membrane; a plate) attached to the substrate 122. The substrate 122 can be attached (e.g., mounted and sealed) to the wall 111 surrounding the aperture 114, and the element 124 can be attached (e.g., mounted and sealed) to the substrate 122 above the aperture 114. The element 124 can have a thickness of less than 1 micrometer, less than 0.2 micrometers, and / or less than 0.05 micrometers. The materials of the transmission element 124 and the substrate 122 can be the same or different. In certain embodiments, where the materials of the transmission element 124 and the substrate 122 are different from each other, the transmission element 124 and the substrate 122 can be attached to each other with a vacuum-tight seal.

[0022] In certain embodiments, the radiolucent element 124 of the window 120 has a radiolucency of more than 20% for X-rays with energies in a range (e.g., bandwidth) of less than 1 keV. In certain embodiments, the element 124 has at least one dimension (e.g., a first width perpendicular to the direction of propagation of the X-ray beam 152; a second width perpendicular to the direction of propagation of the X-ray beam 152 and perpendicular to the first width) of less than or equal to 5 millimeters (e.g., less than or equal to 1 millimeter; less than or equal to 0.3 millimeters; less than or equal to 0.1 millimeters). In certain embodiments, the element 124 is configured such that at least part of the X-ray beam 152 can propagate from the at least one X-ray optic 150 in the first area 112 inside the at least one housing 110 to the second area 170 outside the at least one housing 110 (see e.g. ). Fig. 1A). The element 124 can comprise at least one low-Z material (e.g., diamond, graphene, aluminum, aluminum hydroxide, silicon, silicon carbide, silicon nitride, lithium fluoride, boron carbide, beryllium, beryllium oxide) and can have a thickness of less than 500 nanometers (e.g., less than 100 nanometers, less than 50 nanometers). In certain embodiments, the element 124 comprises a metal layer (e.g., with a thickness of less than or equal to 100 nanometers) on the at least one low-Z material, the metal layer being configured to ensure sufficiently high transmittance of the X-ray beam 152 (e.g., greater than or equal to 20% at a thickness of 20 nanometers) and spectral filtering of the X-ray beam 152. Examples of metals compatible with certain embodiments described here include: Al, Ti, Cr, Fe, Co, Re, Rh, Pd, Ag and La.In certain embodiments, the metal layer can be configured to prevent low-energy photons (e.g., less than 50 eV) generated within the region 112 from escaping through the window 120.

[0023] In certain embodiments, the radiolucent window 120 comprises a plurality of radiolucent elements 124 to simplify the alignment of the X-ray beam 152 onto the window 120. In certain embodiments, the at least one housing 110 comprises a plurality of radiolucent windows 120, wherein the individual windows 120 comprise different radiolucent elements 124 and have different spectral X-ray transmittance properties (e.g., such that the X-rays transmitted through the different windows 120 have different spectral properties). For example, the at least one X-ray optic 150 can be moved such that the X-ray beam 152 strikes and passes through a selected radiolucent element 124 from the plurality of radiolucent elements 124.Another example is that the multiple radiolucent elements 124 can be mounted on a flange that is connected to the at least one housing 110 by an assembly comprising a bellows that can be adjusted (e.g., moved) so that the X-ray beam 152 strikes and passes through a selected radiolucent element 124 of the multiple radiolucent elements 124 (e.g., a selected window 120 of the plurality of windows 120 in a path of the X-ray beam 152) and a strut configured to prevent the bellows from collapsing due to the force of the ambient pressure on one side of the bellows and the vacuum pressure on the other side of the bellows.

[0024] In certain embodiments, the aperture 114 of the at least one housing 110 and the window 120 are in a fixed position relative to other parts of the at least one housing 110, while in certain other embodiments, the aperture 114 and the window 120 are configured to be movable relative to other parts of the at least one housing 110. For example, the at least one housing 110 may include a bellows between a first section and a second section of the at least one housing 110, the first section comprising the aperture 114 (with the window 120 attached above the aperture 114) and being mechanically connected to a table configured to set a position of the aperture 114 and the window 120 relative to the X-ray beam 152. The table may (e.g.,along a single direction or along two or three mutually orthogonal directions) such that the aperture 114 and / or the window 120 is located at or near a minimum cross-sectional area (e.g. waist) of the X-ray beam 152.

[0025] Fig. Figure 3 schematically shows an exemplary electron source 130 that is compatible with certain embodiments described herein. In certain embodiments, the electron source 130 is configured to generate at least one electron beam 132 comprising electrons with a range of kinetic energies (e.g., a range from 0.5 keV to 5 keV; a range from 5 keV to 50 keV). The electron source 130 may, for example, comprise an electron-optical column 134 with at least one cathode 136 and an electron-optical subsystem 138. The at least one cathode 136 may be configured to emit electrons (e.g., with at least one electron emitter, including, but not limited to, helical tungsten wires or threads, carbon nanotubes, dispensers, lanthanum hexaboride, etc.).The electron-optical subsystem 138 can comprise one or more gratings and / or electrodes configured to direct, accelerate, and / or shape the electrons emitted from the at least one cathode 136 to form the at least one electron beam 132, and to set a position and / or orientation of the at least one electron beam 132 relative to the anode arrangement 140. In certain embodiments, the electron-optical column 134 is configured to focus the at least one electron beam 132 onto a surface of the anode arrangement 140, the size of the focal spot being in at least one direction (e.g., substantially perpendicular to the propagation direction of the electron beam) within a range of less than or equal to 200 micrometers, less than or equal to 50 micrometers, and / or less than or equal to 10 micrometers.In certain embodiments, the electron focal spot has an elongated shape with an aspect ratio in the range of 1.5 to 10. The at least one cathode 136 and the electron-optical subsystem 138 can be configured to be electrically connected to the control electronics outside the at least one housing 110 via one or more electrical feedthroughs (not shown).

[0026] Fig. Figure 4 schematically shows a portion of an exemplary anode arrangement 140 in accordance with certain embodiments described herein. In certain embodiments, the anode arrangement 140 comprises at least one anode 146 with at least one target structure 144, which comprises one or more materials selected for their properties in generating X-rays (e.g., desired spectral properties) when bombarded (e.g., struck) by the at least one electron beam 132. The at least one anode 146 may further comprise an electrically conductive substrate 147 that is in thermal contact with the at least one target structure 144.In certain embodiments, the substrate 147 is configured to absorb thermal energy from the at least one target structure 144, wherein the thermal energy is generated by the electron bombardment of the at least one target structure 144 by the at least one electron beam 132, and to dissipate thermal energy and / or direct it away from the at least one target structure 144.

[0027] In certain embodiments, the at least one anode 146 has an electrically conductive path from the at least one target structure 144 to the substrate 147, and the substrate 147 has an electrically conductive path to ground, such that the substrate 147 is configured to prevent the at least one target structure 144 from becoming electrically charged by the at least one electron beam 132. In certain embodiments, the at least one target structure 144 comprises at least one ceramic layer 148, which is in thermal contact with the substrate 147 and has a thickness sufficiently thin to allow electrons to tunnel through the at least one ceramic layer 148 to the substrate 147 (e.g., with a thickness in the range of 0.1 microns to 10 microns) to prevent the at least one ceramic layer 148 from becoming electrically charged by the at least one electron beam 132.In certain embodiments, the at least one ceramic layer 148 comprises at least one material configured to generate X-rays 142 with predetermined X-ray spectral properties in response to bombardment by the at least one electron beam 132. In certain embodiments, the at least one ceramic layer 148 has a surface facing the at least one electron beam 132, wherein the surface has a surface normal direction oriented at an angle (e.g., in a range of 0 degrees to 80 degrees) relative to the propagation direction of the at least one electron beam 132.

[0028] For example, the at least one ceramic layer 148 can comprise at least one material (e.g., boride, carbide, nitride, oxide, fluoride) containing at least one low-Z element (e.g., lithium, beryllium, boron, carbon, nitrogen, oxygen, fluorine). The at least one low-Z element can generate X-rays 142 with (i) characteristic K-lines or L-lines, X-ray energies of less than 1 keV, and narrow spectral linewidths (e.g., less than 2 eV), and (ii) a high intensity ratio of characteristic K-line or L-line X-rays 142 to bremsstrahlung X-rays.In certain embodiments, the spectral linewidth of the X-rays 142 is sufficiently narrow to optimize the photoelectron production cross-section, kinetic energy, and chemical state analysis for X-ray photoelectron spectroscopy, and the intensity ratio of the K-line X-rays 142 to the bremsstrahlung X-rays is sufficiently high to obtain a quasi-monochromatic X-ray spectrum. In certain embodiments, the spectral linewidth of the X-rays 142 is sufficiently narrow to optimize the signal-to-noise ratio for the X-ray fluorescence analysis of characteristic low-energy fluorescence X-rays for applications in semiconductor thin-film and materials metrology, wherein the intensity ratio of the K-line X-rays 142 to the bremsstrahlung X-rays is sufficiently high to obtain a quasi-monochromatic X-ray spectrum.In certain applications, the energy of the K-line X-ray radiation 142 is chosen so that the fluorescence cross-section of a particular element of interest is optimized above the absorption edge of the element (e.g. 100 eV above the absorption edge).

[0029] In certain embodiments, the at least one target structure 144 comprises at least one layer containing at least one element in the third or fourth row of the periodic table or at least one compound of such an element with a low-Z element (e.g., BeO, B4C, MgO, Al2O3, SiC, CaB6, diamond / graphite, LiF, and TiB2). In the case of compounds with low electrical conductivity, the substrate 147 can form an electrically conductive path (e.g., to ground) to prevent electrical charging of the at least one anode 146 by the at least one electron beam 132. For example, the at least one target structure 144 can comprise a ceramic layer 148 containing MgO (e.g., configured to generate MgK and L X-ray emission line X-rays and O-K X-ray emission line X-rays) on an underlying diamond structure of the substrate 147 in thermal connection with a metal part (e.g., Cu) of the substrate 147 (e.g.,the diamond structure on or embedded in a surface of the metal part of the substrate 147). The at least one target structure 144 can comprise at least one thermally and / or electrically conductive layer between the MgO ceramic layer 148 and the diamond structure and / or between the diamond structure and the metal part of the substrate 147.

[0030] In certain embodiments, the at least one target structure 144 further comprises at least one additional target structure 144 (e.g., spaced apart from the target structure 144 comprising the low-Z element), wherein the at least one additional target structure 144 comprises at least one metal (e.g., Ti, Sc, V, Cr, Cu, Fe, Co, Ni, Zr, Mo) configured to generate X-rays 142 with predetermined spectral properties (e.g., characteristic X-rays with energies less than or equal to 1 keV; characteristic X-rays with energies greater than 1 keV). Examples of other additional target structures 144 compatible with certain embodiments described herein are described in the USPatents numbered 10,658,145, 10,401,309, 10,352,880, 10,349,908, 10,304,580, 10,297,359, 10,295,485, 10,269,528, 9,874,531, 9,823,203, 9,719,947, 9,594,036, 9,570,265, 9,543,109, 9,570,265, 9,449,781, 9,448,190 and 9,390,881, each of which is incorporated herein in its entirety by reference.

[0031] In certain embodiments, the at least one target structure 144 comprises a plurality of target structures 144 (e.g., on a common substrate 147), wherein the materials of the target structures 144 are configured to be bombarded by the at least one electron beam 132 and to generate X-rays 142 with predetermined spectral properties, wherein the X-rays from different materials have different spectral properties from one another (e.g., different K- and L-X-ray emission lines). Individual target structures 144 can, for example, comprise individual thin layers containing elements selected to generate characteristic X-rays with energies of less than 1 keV.Individual target structures 144 can, for example, comprise MgO, SiC and CaB6, where MgO is used to generate Mg K and L emission line X-rays and O K emission line X-rays, SiC to generate C Ka emission line X-rays with 288 eV energy and Si Lα emission line X-rays with 98 eV energy, and CaB6 to generate Ca Lα emission line X-rays with 345 eV energy and B Kα emission line X-rays with 198 eV energy.

[0032] In addition to the characteristic X-rays with energies of less than 1 keV, the at least one target structure of certain embodiments provides characteristic X-rays with higher energies, which can be useful for many experiments (e.g., generating photoelectrons with higher kinetic energy using Ca Kα line X-rays than with Ca L-line X-rays). For example, Al2O3 can provide Kα line X-rays with energies greater than 1 keV, and Mo can provide K-line and L-line X-rays with energies greater than 1 keV, in addition to their respective characteristic lines with energies less than 1 keV.

[0033] In certain embodiments, the at least one electron beam 132 and / or the at least one anode 146 are configured to be moved (e.g., positioned) such that the at least one electron beam 132 strikes the at least one target structure 144 at angles in a range of 30 degrees to 90 degrees with respect to a surface normal of the at least one target structure 144. At smaller angles of incidence, the penetration depth of the incident electrons 132 into the at least one target structure 144 and the X-ray generation from deeper regions of the at least one target structure 144 can be reduced, resulting in less attenuation of the X-rays from the X-ray generation point to the surface of the target structure.

[0034] In certain embodiments, the anode arrangement 140 is mechanically connected to a table 149, which is configured to set a position and / or orientation of the at least one target structure 144 relative to the at least one electron beam 132 from the electron source 130. For example, the table 149 can be configured to move the at least one target structure 144 along a single direction or along two or three directions (e.g., orthogonal to each other) and / or to rotate the at least one target structure 144 about a single axis or about two or three axes (e.g., orthogonal to each other). In certain embodiments, a first section of the table 149 is located inside the at least one housing 110 and a second section of the table 149 is located outside the at least one housing 110 (e.g.,The first part and the second part communicate operationally with each other via an electrical and / or mechanical feedthrough attached to the or a component of the at least one housing 110). In certain embodiments comprising a plurality of target structures 144, the table 149 is configured to move the plurality of target structures 144 relative to the at least one electron beam 132 within the at least one housing 110 (e.g., to select one of the target structures 144 to be irradiated by the at least one electron beam 132).

[0035] Fig.Figure 5 schematically shows an example of at least one X-ray optic 150 in accordance with certain embodiments described herein. In certain embodiments, the at least one X-ray optic 150 comprises at least one functional (e.g., X-ray-reflecting) surface 154, which has at least one segment with a square shape (e.g., ellipsoidal, hyperboloidal, paraboloidal) and extends at least partially around an axis 156 at an axial angle of more than or equal to 30 degrees (e.g., more than 60 degrees, more than 90 degrees, more than 180 degrees), surrounds the axis 154, and is axially symmetrical. The at least one functional surface 154 may have at least one coating made of at least one material (e.g.,The at least one functional surface 154 comprises a single-layer or multi-layer coating that differs from the material of the at least one functional surface 154, wherein the at least one coating is configured to achieve a sufficiently high X-ray reflectance and / or sufficiently large critical angles. The at least one functional surface 154 can comprise a plurality of square surfaces (e.g., a Wolter optic). In certain other embodiments, the at least one X-ray optic 150 comprises at least one transmission zone plate.

[0036] The at least one X-ray optic 150 of certain embodiments is configured to receive (e.g., collect) at least some of the diverging X-rays 142 generated by the anode arrangement 140 in response to the at least one electron beam 132 (e.g., a focused electron beam) incident on the at least one target structure 144, and to direct at least some of the received X-rays 142 to form and emit the X-ray beam 152 (e.g., a collimated X-ray beam; a focused X-ray beam; a converging X-ray beam). The X-ray beam 152 may, for example, be convergent with a minimum cross-sectional width of less than or equal to 1 millimeter (e.g., less than or equal to 0.2 millimeters; less than 0.05 millimeters) in at least one direction in a plane perpendicular to the propagation direction of the X-ray beam 152.

[0037] In certain embodiments, the at least one X-ray optic 150 is configured such that it is aligned (e.g., positioned and / or oriented) such that a minimum cross-sectional area (e.g., the waist at position 160) of the X-ray beam 152 is located at or near the window 120. For example, the at least one X-ray optic 150 can be adjusted by at least one linear and / or rotary motion stage 159. Example ranges for the dimensions of the waist of the X-ray beam 152 at position 160 include, among others: less than 2 millimeters in at least one direction in the cross-sectional plane, less than 200 micrometers in at least one direction in the cross-sectional plane, and / or less than 50 micrometers in at least one direction in the cross-sectional plane. For example, in the case of a converging X-ray beam 152, the minimum cross-sectional width of the X-ray beam 152 (e.g.,The position 160 at which the X-ray beam 152 is focused; the position 160 of the minimum waist of the X-ray beam 152) at the window 120 (e.g., coincident with) or at a distance from a surface of the window 120 (e.g., a surface facing the first region 112 inside the at least one housing 110; a surface facing the second region 170 outside the at least one housing 110) by a distance of less than 2 millimeters, less than 200 micrometers, and / or less than 50 micrometers. The at least one second X-ray optic 182 may be similar to the at least one X-ray optic 150 (e.g., having essentially the same shape and geometric parameters).

[0038] By locating the position 160 of the minimum cross-sectional width of the X-ray beam 152 at or near the window 120, certain embodiments allow the window 120 to be small enough to possess sufficient mechanical strength to maintain a pressure differential between the first region 112 inside the at least one housing 110 and the second region 170 outside the at least one housing 110, while also providing an X-ray transmittance of more than or equal to 20% for a substantial portion of the X-ray beam 152 with an X-ray energy of less than 1 keV. In certain embodiments, the at least one X-ray optic 150 can also result in a significantly greater X-ray flux transmitted through the window 120 than would be the case without the at least one X-ray optic 150.In certain embodiments, at least part of the X-ray beam 152 is transmitted through the window 120 for use outside the at least one housing 110. In certain embodiments, the at least one X-ray optic 150 also controls the input X-ray spectrum (e.g., preferred suppression of X-rays with energies above a preselected X-ray energy using a reflection mirror optic with a selected maximum angle of incidence or using a mirror optic with a surface coated with multiple layers).

[0039] In certain embodiments, the at least one X-ray optic 150 is mechanically connected to a table 159, which is configured to set a position and / or orientation of the at least one X-ray optic 150 relative to the at least one target structure 144 (e.g., relative to the X-rays 142 from the anode arrangement 140). For example, the table 159 can be configured to move the at least one X-ray optic 150 along a single direction or along two or three directions (e.g., orthogonal to each other) and / or to rotate the at least one X-ray optic 150 about a single axis or about two or three axes (e.g., orthogonal to each other).For example, the table 159 can be located entirely within the at least one housing 110, or a first part of the table 159 can be located within the at least one housing 110 and a second part of the table 159 can be located outside the at least one housing 110 (e.g., the first section and the second section are in operational communication with each other via an electrical and / or mechanical feedthrough attached to, or forming part of, the at least one housing 110). In certain embodiments comprising a plurality of X-ray optics 150, the table 159 is configured to move the plurality of X-ray optics 150 relative to the X-rays 142 within the at least one housing 110 (e.g., to select at least one of the X-ray optics 150 to receive the X-rays 142).

[0040] In certain embodiments, the table 159 is configured to adjust the position and / or orientation of the at least one X-ray optic 150 relative to other parts of the X-ray source 100 (e.g., the anode assembly 140; the window 120) such that the X-ray beam 152 passes through the window 120 into the second area 170 (e.g., the minimum waist of the X-ray beam 152 is at or near the window 120). In certain embodiments, adjusting the propagation direction of the X-ray beam 152 so that the X-ray beam 152 strikes the window 120 includes adjusting the position and / or orientation of the at least one X-ray optic 150 (e.g., using the table 159). In certain embodiments, adjusting the propagation direction of the X-ray beam 152 further includes adjusting the position and / or orientation of the anode assembly 140 (e.g., using the table 159).using the table 149) and / or adjusting the position and / or orientation of the at least one electron beam 132 (e.g., using the electron-optical subsystem 138). For example, aligning the converging X-ray beam 152 to pass through the window 120 may involve mechanically positioning the at least one X-ray optic 150 while the position of the focused electron beam 132 remains stationary on the anode assembly 140, mechanically or electronically moving the focused electron beam 132 on the anode assembly 140 while the at least one X-ray optic 150 remains stationary, or a combination of both.

[0041] In certain embodiments, the X-ray source 100 further comprises an X-ray detector within the first region 112, configured to be located upstream of the window 120. The X-ray detector can be configured to facilitate the alignment of the at least one X-ray optic 150 in the first region 112 to focus the X-ray beam 152 at the desired position (e.g., at or on the window 120). The X-ray detector can comprise a direct electronic array detector or a scintillation screen that can be observed with a CCD-based observation system and can include a hole that can be positioned at the desired focus position and through which the X-ray beam 152 can propagate. In certain embodiments, the X-ray detector can be mounted on a table configured to allow the X-ray detector to be moved controllably (e.g.,into the path of the X-ray beam 152 or out of the path of the X-ray beam 152).

[0042] Although commonly used terms are employed to describe the systems and procedures of certain embodiments for ease of understanding, these terms are used here in their broadest, most reasonable sense. Although various aspects of the disclosure are described with respect to illustrative examples and embodiments, the disclosed examples and embodiments should not be interpreted as limiting. Conditional expressions such as "may," "might," "could," or "may" are, unless expressly stated otherwise or understood differently in the context, generally intended to express that certain embodiments include certain features, elements, and / or steps, while other embodiments do not.Such conditional formulations are therefore not intended to imply that features, elements, and / or steps are in any way required for one or more embodiments. In particular, the terms "includes" and "containing" are to be understood as referring to elements, components, or steps in a non-exclusive manner and indicating that the elements, components, or steps mentioned may be present, used, or combined with other elements, components, or steps that are not expressly mentioned.

[0043] Quantitative statements or conditions such as "at least one of X, Y and Z" are, unless expressly stated otherwise, to be understood in the generally used context as meaning that an element, term, etc. can be either X, Y or Z.

[0044] The terms "approximately", "about", "in general", and "essentially" used here refer to a value, quantity, or characteristic that is close to the specified value, quantity, or characteristic and yet fulfills a desired function or achieves a desired result. For example, the terms "approximately", "about", "in general", and "essentially" can refer to a quantity that is within ±10%, within ±5%, within ±2%, within ±1%, or within ±0.1% of the specified quantity.As a further example, the terms "generally parallel" and "essentially parallel" refer to a value, magnitude, or characteristic that deviates from exact parallel by ±10 degrees, ±5 degrees, ±2 degrees, ±1 degree, or ±0.1 degrees, and the terms "generally perpendicular" and "essentially perpendicular" refer to a value, magnitude, or characteristic that deviates from exact perpendicular by ±10 degrees, ±5 degrees, ±2 degrees, ±1 degree, or ±0.1 degrees. The ranges disclosed here also include all overlaps, subranges, and combinations thereof. Expressions such as "up to," "at least," "greater than," "less than," "between," and the like include the specified number. As used herein, the meaning of "ein", "ein" and "besagtes" includes the plural unless the context clearly indicates otherwise.While the structures and / or methods are discussed here in the form of elements characterized by ordinal adjectives (e.g., first, second, etc.), the ordinal adjectives are used merely as labels to distinguish one element from another, and the ordinal adjectives are not used to denote any order of these elements or their use.

[0045] Several configurations have been described above. It should be understood that the embodiments disclosed herein are not mutually exclusive and can be combined in various arrangements. Although this invention has been described with reference to these specific configurations, the descriptions are intended to illustrate the invention and are not meant to be limiting. Various modifications and applications are available to those skilled in the art without departing from the true spirit and scope of the invention. For example, in any method or process disclosed herein, the actions or operations comprising the method / process can be carried out in any suitable sequence and are not necessarily limited to any particular disclosed sequence.Features or elements from various embodiments and examples described above can be combined to create alternative configurations compatible with the embodiments disclosed herein. Various aspects and advantages of the embodiments have been described where appropriate. It is to be understood that not all of these aspects or advantages can necessarily be achieved in accordance with any particular embodiment. For example, it should be apparent that the various embodiments can be carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein, without necessarily achieving other aspects or advantages that may be taught or suggested herein.

Claims

[1] One X-ray source comprising: at least one enclosure configured to contain a first area at a pressure of less than one atmosphere (atm) and configured to separate the first area from an environment outside the at least one enclosure, wherein the at least one enclosure includes a window for x-ray transmission with an x-ray transmittance of more than or equal to 20% for at least some x-rays with an x-ray energy of less than 1 keV; an electron source in the at least one housing, wherein the electron source is configured to produce at least one electron beam; an anode arrangement within the at least one housing, configured to generate X-rays in response to electron bombardment by at least some of the electrons of the at least one electron beam from the electron source; at least one X-ray optic in the at least one housing, wherein the at least one X-ray optic is configured to receive at least a portion of the X-rays from the anode arrangement and to direct at least a portion of the received X-rays onto the window to generate an X-ray beam. [2] The X-ray source according to claim 1, wherein a cross-sectional area of ​​the X-ray beam has a local minimum value at a focal point of the at least one X-ray optic. [3] The X-ray source according to claim 2, wherein the value at the focal point is in a range of 100 square micrometers to 5 square millimeters. [4] The X-ray source according to claim 2, wherein the focal point is located within 30 millimeters of the window. [5] The X-ray source according to claim 2, wherein the focal point is located within the first region. [6] The X-ray source according to claim 2, wherein the focal point coincides with the window. [7] The X-ray source according to claim 2, wherein the focal point is located outside the at least one housing. [8] The X-ray source according to claim 1, wherein the X-ray-transparent window has an X-ray transmittance of more than or equal to 20% for at least some X-rays with an X-ray energy of less than 0.5 keV. [9] The X-ray source according to claim 1, wherein the X-ray-transparent window has an X-ray transmittance of more than or equal to 20% for at least some X-rays with an X-ray energy of less than 0.3 keV. [10] The X-ray source according to claim 1, wherein the X-ray-transmitting window comprises a plurality of X-ray-transmitting elements, wherein the at least one X-ray optic or the X-ray-transmitting window is configured such that the X-ray beam hits a selected X-ray-transmitting element of the plurality of X-ray-transmitting elements. [11] The X-ray source according to claim 1, wherein the X-ray-transparent window comprises at least one X-ray-transparent element selected from the group consisting of: diamond, graphene, aluminum, aluminum hydroxide, silicon, silicon carbide, silicon nitride, lithium fluoride, boron carbide, beryllium, beryllium oxide. [12] The X-ray source according to claim 1, wherein the at least one electron beam comprises a focused electron beam and the X-rays generated by the anode arrangement comprise a divergent X-ray beam. [13] The X-ray source according to claim 1, wherein the X-ray beam from the at least one X-ray optic comprises a focused X-ray beam. [14] The X-ray source according to claim 1, wherein the X-ray beam from the at least one X-ray optic has a cross-sectional area perpendicular to the direction of propagation of the X-ray beam from the at least one X-ray optic, wherein the cross-sectional area is a function of the distance from the at least one X-ray optic. [15] The X-ray source according to claim 1, wherein the at least one housing comprises: a first housing configured to contain the first region at a pressure of less than 1 atmosphere (atm) and configured to separate the first region from the second region outside the first housing, the first housing containing the electron source, the anode arrangement and the at least one X-ray optic; and a second enclosure designed to contain a third area, with the window located between the first area and the third area. [16] The X-ray source according to claim 15, which further comprises at least a second X-ray optic within the third area, which is configured to receive X-rays of the X-ray beam transmitted through the window and to direct at least some of the received X-rays out of the window to form a second X-ray beam. [17] The X-ray source according to claim 15, wherein the second housing further comprises at least one vacuum valve configured to controllably separate the third area from the second area. [18] The X-ray source according to claim 1, wherein a wall of the at least one housing has an aperture extending through the wall, and the window is positioned and sealed above the aperture. [19] The X-ray source according to claim 18, wherein the window comprises a substrate and an X-ray transparent element, wherein the substrate is attached to a part of the wall surrounding the aperture and the element is attached to the substrate above the aperture. [20] The X-ray source according to claim 19, wherein the at least one housing comprises a bellows between a first section and a second section of the at least one housing, wherein the first section comprises the aperture and is in mechanical connection with a table configured to set a position of the aperture and the window relative to the X-ray beam. [21] The X-ray source according to claim 1, wherein the electron source comprises an electron-optical column with at least one cathode configured to emit electrons and an electron-optical subsystem configured to direct, accelerate and / or shape the electrons emitted by the at least one cathode to form the at least one electron beam, and to set a position and / or orientation of the at least one electron beam relative to the anode arrangement. [22] The X-ray source according to claim 21, wherein the electron-optical column is configured to focus the at least one electron beam onto a surface of the anode arrangement with a focal spot size in at least one direction which is substantially perpendicular to the propagation direction of the electron beam, wherein the focal spot size is in a range of less than or equal to 200 micrometers. [23] The X-ray source according to claim 1, wherein the anode arrangement comprises at least one anode, which includes at least one X-ray generating target structure and an electrically conductive substrate in thermal connection with the at least one target structure, wherein the at least one X-ray generating target structure is configured to generate X-rays when bombarded by the at least one electron beam, and wherein the substrate is configured to dissipate and / or transfer thermal energy from the at least one target structure. [24] The X-ray source according to claim 23, wherein the at least one anode has an electrically conductive path from the at least one X-ray generating target structure to the substrate and the substrate has an electrically conductive path to the ground. [25] The X-ray source according to claim 23, wherein the at least one X-ray generating target structure comprises at least one ceramic layer which is in thermal contact with the substrate and has a thickness in the range of 0.1 microns to 10 microns. [26] The X-ray source according to claim 25, wherein the at least one ceramic layer comprises at least one element selected from the group consisting of lithium, beryllium, boron, carbon, nitrogen, oxygen and fluorine. [27] The X-ray source according to claim 23, wherein the at least one X-ray generating target structure comprises a first target structure comprising at least one X-ray generating material selected from the group consisting of the following materials: BeO, B4C, MgO, Al2O3, SiC, CaB6, diamond / graphite, LiF, and TiB2. [28] The X-ray source according to claim 27, wherein the at least one X-ray generating target structure further comprises a second target structure spaced apart from the first target structure, wherein the second target structure comprises at least one metal selected from the group consisting of: Ti, Sc, V, Cr, Cu, Fe, Co, Ni, Zr, Mo. [29] The X-ray source according to claim 1, wherein the at least one X-ray optic comprises at least one X-ray reflecting surface having at least one square segment extending at least partially about an axis at an axial angle of more than or equal to 30 degrees. [30] The X-ray source according to claim 29, wherein at least one X-ray reflecting surface comprises a first material and the at least one X-ray optic further comprises at least one layer on the at least one surface, wherein the at least one layer comprises a second material which is different from the first material.

Images