阅读说明：本技术 Talbot-lau x射线源和干涉测量系统 (TALBOT-LAU X-ray source and interferometry system ) 是由 云文兵 西尔维娅·贾·云·路易斯 雅诺什·科瑞 大卫·维恩 于 2019-08-05 设计创作，主要内容包括：本公开涉及TALBOT-LAU X射线源和干涉测量系统。提供了一种x射线源,以及采用该x射线源的x射线干涉测量系统。x射线源包括靶,所述靶包括衬底和多个结构。衬底包括导热的第一材料和第一表面。多个结构位于第一表面的至少一部分上或嵌入在第一表面的至少一部分中。结构彼此分开并与衬底热连通。结构包括与第一材料不同的至少一种第二材料,该至少一种第二材料被配置为在由具有0.5keV至160keV的能量范围内的能量的电子照射时生成x射线。x射线源还包括电子源,其被配置为生成电子,并且引导电子以撞击靶并且沿着相对于第一表面的该部分的表面法线的非零角度处的方向照射至少一些结构。(The present disclosure relates to a TALBOT-LAU X-ray source and an interferometric system. An x-ray source and an x-ray interferometry system employing the x-ray source are provided. The x-ray source includes a target including a substrate and a plurality of structures. The substrate includes a thermally conductive first material and a first surface. A plurality of structures is located on or embedded in at least a portion of the first surface. The structures are separated from each other and in thermal communication with the substrate. The structure includes at least one second material different from the first material, the at least one second material configured to generate x-rays when irradiated by electrons having an energy in an energy range of 0.5keV to 160 keV. The x-ray source also includes an electron source configured to generate electrons and direct the electrons to strike the target and illuminate at least some structures along a direction at a non-zero angle relative to a surface normal of the portion of the first surface.)

1. An x-ray source, comprising:

a target, the target comprising:

a substrate comprising a first material that is thermally conductive and a first surface; and

a plurality of structures on or embedded in at least a portion of the first surface, the structures being separate from one another and in thermal communication with the substrate, the structures comprising at least one second material different from the first material, the at least one second material being configured to generate x-rays when irradiated by electrons having an energy in an energy range of 0.5keV to 160 keV; and

an electron source configured to generate the electrons and direct the electrons to strike the target and strike at least some of the structures along a direction at a non-zero angle relative to a surface normal of the portion of the first surface, the angle and kinetic energy of the electrons being configured such that at least some of the electrons have an electron penetration depth within the target sufficient to penetrate the first surface and strike at least two of the structures.

2. The x-ray source of claim 1, further comprising an x-ray window comprising the target, at least some of the x-rays passing through the first material and through a second surface of the target.

3. The x-ray source of claim 1, wherein the angle is greater than 20 degrees.

4. The x-ray source of claim 1, wherein the angle is in a range of 40 degrees to 85 degrees.

5. The x-ray source of claim 1, wherein the angle is in a range of 40 degrees to 60 degrees.

6. The x-ray source of claim 1, wherein the angle is equal to 60 degrees.

7. The x-ray source of claim 1, wherein an energy deposition from the electrons to the structure is greater than an energy deposition from the electrons to the substrate.

8. The x-ray source of claim 1, wherein the substrate comprises a second surface opposite and substantially parallel to the first surface, and the substrate has a thickness in a range of 250 to 3000 microns between the first and second surfaces.

9. The x-ray source of claim 8, wherein the structure extends from the first surface toward the second surface to a depth in a range of 1 micron to 30 microns.

10. The x-ray source of claim 8, wherein the structure extends from the first surface toward the second surface to a depth in a range of 2 microns to 10 microns.

11. The x-ray source of claim 8, wherein the x-rays pass through the second surface of the substrate to at least one optical element.

12. The x-ray source of claim 1, wherein at least some of the structures each extend a width along the first surface in at least one lateral direction in a range of 0.5 microns to 5 microns.

13. The x-ray source of claim 1, wherein at least some of the structures are separated from each other along the first surface by a separation distance greater than 0.3 microns.

14. The x-ray source of claim 13, wherein the separation distance is in a range of 1 to 2 microns.

15. The x-ray source of claim 1, wherein the first material comprises at least one of: diamond, silicon carbide, beryllium, and sapphire.

16. The x-ray source of claim 1, wherein the first material has a thermal conductivity in a range between 20W/m-K and 2500W/m-K and comprises an element having an atomic number less than or equal to 14.

17. The x-ray source of claim 1, wherein the at least one second material comprises at least one of: tungsten, gold, and molybdenum.

18. The x-ray source of claim 1, wherein the target further comprises at least one interface layer between the first material and the at least one second material, the at least one interface layer comprising at least one third material different from the first material and the at least one second material.

19. The x-ray source of claim 18, wherein the at least one third material comprises at least one of: titanium nitride, iridium, and hafnium oxide.

20. The x-ray source of claim 1, wherein the target further comprises at least one layer covering the structure at the first surface.

21. The x-ray source of claim 20, wherein the at least one layer is electrically conductive and/or seals the structure between the at least one layer and the substrate.

22. The x-ray source of claim 20, wherein the at least one layer comprises the first material.

23. The x-ray source of claim 1, wherein the x-rays are in an energy range of 2keV to 85 keV.

24. The x-ray source of claim 1, wherein the x-rays are emitted from the target in a beam comprising a plurality of beamlets, each of the plurality of beamlets propagating from a respective one of the plurality of structures.

25. The x-ray source of claim 1, further comprising at least one optical element positioned such that at least some of the x-rays pass through the first material and to or through the at least one optical element, wherein the at least one optical element comprises a solid material that is substantially transparent to the at least some of the x-rays.

26. An x-ray interferometry system comprising an x-ray source as claimed in claim 1.

27. The x-ray interferometry system of claim 26, having a Talbot-Lau interferometry configuration.

28. The x-ray interferometry system of claim 27, comprising a Talbot x-ray microscope.

Technical Field

The present application relates generally to x-ray sources.

Background

Laboratory x-ray sources typically bombard a metal target (target) with electrons whose deceleration produces Bremsstrahlung x-rays of all energies, from zero to electron kinetic energy. In addition, metal targets generate x-rays by creating holes in the core electron orbital of the target atom, which are then filled with electrons of the target having a binding energy lower than the core electron orbital, with the concomitant generation of x-rays having energies characteristic of the target atom. Most of the power of the electrons illuminating the target is converted into heat (e.g., about 60%) and backscattered and/or reflected electrons (e.g., about 39%), with only about 1% of the incident power being converted into x-rays. Melting of the x-ray target due to this heat can be a limiting factor in the ultimate brightness (e.g., number of photons per area per second per steradian) that the x-ray source can achieve.

Disclosure of Invention

Certain embodiments described herein provide an x-ray source comprising a target comprising a substrate and a plurality of structures. The substrate includes a thermally conductive first material and a first surface. A plurality of structures is located on or embedded in at least a portion of the first surface. The structures are separated from each other and in thermal communication with the substrate. The structure includes at least one second material different from the first material, the at least one second material configured to generate x-rays when irradiated by electrons having an energy in an energy range of 0.5keV to 160 keV. The x-ray source also includes an electron source configured to generate electrons and direct the electrons to strike the target and illuminate at least some structures along a direction at a non-zero angle relative to a surface normal of the portion of the first surface. The angle and kinetic energy of the electrons are configured such that at least some of the electrons have an electron penetration depth within the target sufficient to penetrate the first surface and irradiate the at least two structures.

Drawings

Fig. 1A and 1B schematically illustrate cross-sectional views of a portion of an example x-ray source, in accordance with certain embodiments described herein.

Fig. 1C schematically illustrates a cross-sectional view of a portion of an example x-ray source, wherein at least one optical element includes a target, in accordance with certain embodiments described herein.

Fig. 2A-2C schematically illustrate example targets configured to improve x-ray distribution from the target, according to certain embodiments described herein.

Fig. 3A-3C illustrate results of simulated calculations of an electron beam of 30keV impinging on a first surface of a target according to certain embodiments described herein.

Detailed Description

Certain embodiments described herein advantageously provide a micropatterned x-ray beam configured for use in an imaging system employing a Talbot-Lau interferometric configuration (e.g., a Talbot x-ray microscope). Examples of such Talbot-Lau imaging systems include, but are not limited to: medical imaging systems, such as radiography, tomosynthesis (e.g., for limited angle tomography to detect cancerous breast tissue), Computed Tomography (CT) (e.g., total tomography), absorption-based x-ray microscopy, where the target feature of interest and the detector are placed on the same Talbot edge, and x-ray dose sensitive applications, such as pediatric x-ray imaging and scheduled breast x-ray radiography; analysis of plastics and polymer blends (e.g., three-dimensional visualization of polymer blend structure); imaging/tomography of interfaces between two or more materials with elements of low atomic number, for example, implants in soft tissue (e.g., dermal fillers) and samples in a hydrated environment.

Various configurations of Talbot-Lau imaging systems that may use x-ray sources according to certain embodiments described herein are disclosed in U.S. patent nos. 9,719,947, 9,874,531, 10,349,908, and 10,352,880, and U.S. patent application publication nos. 2015/0117599a1 and 2016/0320320a1, which are incorporated herein in their entirety.

Fig. 1A and 1B schematically illustrate cross-sectional views of a portion of an example x-ray source 10, in accordance with certain embodiments described herein. The source 10 includes a target 20 and an electron source 30. The target 20 includes a substrate 22, the substrate 22 including a thermally conductive first material and a first surface 24. The substrate 22 also includes a plurality of structures 26 on or embedded in at least a portion of the first surface 24. The structures 26 are spaced apart from each other and in thermal communication with the substrate 22. The structure 26 includes at least one second material different from the first material, and the at least one second material is configured to generate x-rays when irradiated by electrons having an energy in a range of energies from 0.5keV to 160 keV. The electron source 30 is configured to generate electrons 32 and direct the electrons 32 to strike the target 20 and illuminate at least some of the structures 26 along a first direction 34 at a non-zero angle relative to a surface normal 28 of the portion of the first surface 24. The angle and kinetic energy of the electrons 32 are configured such that at least some of the electrons 32 have an electron penetration depth within the target 20 sufficient to penetrate the first surface 24 and irradiate the at least two structures 26. In certain embodiments, the x-ray source 10 further includes at least one optical element 40 (e.g., an x-ray window including the target 20). The at least one optical element 40 may be positioned such that at least some x-rays 50 are transmitted to or through the at least one optical element 40 (e.g., at least some x-rays 50 are transmitted through the first material or through the at least one optical element 40).

Various configurations of the target 20, substrate 22, and plurality of structures 26 according to certain embodiments described herein are disclosed in U.S. patent nos. 9,719,947, 9,874,531, 10,349,908, and 10,352,880, and U.S. patent application publication nos. 2015/0117599a1 and 2016/0320320a1, which are incorporated herein in their entirety.

In certain embodiments, the substrate 22 comprises a body (e.g., a wafer; a plate, a sheet) comprising a thermally conductive first material (e.g., having a thermal conductivity in a range between 20W/m-K and 2500W/m-K; between 150W/m-K and 2500W/m-K; between 200W/m-K and 2500W/m-K; and/or between 2000W/m-K K and 2500W/m-K) and comprising an element having an atomic number less than or equal to 14. For example, the first material may include at least one of: diamond, beryllium, and sapphire. In certain other embodiments, the first material may include at least one of: copper, doped graphite, metal alloys, metal composites, graphite, diamond-like carbon, silicon, boron nitride, and silicon carbide. In certain embodiments, the body of the substrate 22 includes a first surface 24 and a second surface 25, and the second surface 25 is opposite the first surface 24 (e.g., as schematically shown in fig. 1A and 1B). The second surface 25 of some embodiments is generally parallel to the first surface 24 (e.g., as schematically shown in fig. 1A and 1B), while in some other embodiments the first surface 24 and the second surface 25 are not parallel to each other. For example, the second surface 25 may be at a non-zero angle relative to the first surface 24, the non-zero angle being in a range of greater than zero and less than 15 degrees, or in a range of 15 degrees to 45 degrees.

The substrate 22 of some embodiments is planar and has a substantially planar first surface 24 and a substantially planar second surface 25 (e.g., as schematically shown in fig. 1A and 1B), while in some other embodiments the substrate 22 is non-planar and/or at least one of the first surface 24 and the second surface 25 is curved, stepped, or otherwise deviates from being planar. Although fig. 1A and 1B schematically illustrate an example substrate 22 in which surface normals 28 are uniform across first surface 24 (e.g., different sub-portions of first surface 24 have surface normals that are parallel to each other and point in the same direction as each other), surface normals 28 may be non-uniform across first surface 24 (e.g., different sub-portions of first surface 24 have surface normals that are non-parallel and point in different directions from each other).

In certain embodiments, the substrate 22 has a thickness T (e.g., between the first surface 24 and the second surface 25) in the range of: 100 to 250 microns, 250 to 3000 microns, 250 to 1000 microns, or less than 1000 microns. The thickness T of the substrate 22 of some embodiments is uniform across the substrate 22, while in other some embodiments the thickness of the substrate 22 is different in different portions of the substrate 22.

In certain embodiments, the at least one second material of structure 26 is selected to produce x-rays having a predetermined energy spectrum (e.g., an x-ray intensity distribution as a function of x-ray energy) when irradiated by electrons having an energy in the energy range of 0.5keV to 160 keV. Examples of the at least one second material include, but are not limited to, at least one of: tungsten, gold, molybdenum, chromium, copper, aluminum, rhodium, platinum, iridium, cobalt, tantalum, titanium, rhenium, silicon carbide, tantalum carbide, titanium carbide, boron carbide, and alloys or combinations comprising one or more thereof. Although fig. 1A and 1B schematically illustrate a structure 26 having a rectangular cross-section including substantially straight sides, any other shape (e.g., regular; irregular; geometric; non-geometric) having straight, curved, and/or irregular sides is also compatible with certain embodiments described herein. In certain embodiments, the structures 26 extend from the first surface 24 toward the second surface 25 to a depth D in the range_z: 1 to 30 microns, 2 to 10 microns, 3 to 7 microns, 2 to 4 microns, or less than 7 microns. In certain embodiments, depth D_zThe choice is based at least in part on the kinetic energy of the electrons 32, as the electron penetration depth depends on the electron kinetic energy and the material through which the electrons travel. For example, for a structure 26 comprising gold, for 20keV electrons, the depth D_zCan be selected in the range of 2 to 4 micrometers and with a depth D for 40keV electrons_zMay be selected in the range of 4 microns to 6 microns.

Although not shown in the cross-sectional views of fig. 1 and 1B, in certain embodiments, the structures 26 are arranged in a one-dimensional array across a portion of the substrate 22 (e.g., aligned with each other in a direction parallel to the first surface 24). For example, the structure 26 may comprise elongated strips or "lines" of at least one second material that are spaced apart from and substantially parallel to each other (e.g., for a one-dimensional Talbot-Lau imaging system). In certain other embodiments, the structures 26 are arranged in a two-dimensional array across a portion of the substrate 22 (e.g., aligned with each other along two directions that are perpendicular to each other and parallel to the first surface 24). For example, the structure 26 may include a block, hexagonal (e.g., "honeycomb") prism, or "dot" (e.g., cylinder) of at least one second material that is spaced apart from one another in two lateral directions (e.g., for a two-dimensional Talbot-Lau imaging system). In certain embodiments, the structures 26 are arranged in a mixture of one-dimensional and two-dimensional arrays.

In certain embodiments, at least some of the structures 26 each extend a width W along the first surface 24 in at least one lateral direction (e.g., a direction parallel to the first surface 24). For example, FIG. 1B shows a width W₁And has a spacing distance S between the structures 26 in a first lateral direction (e.g., a first direction parallel to the first surface 24; a first direction in a plane defined by the surface normal 28 and the direction 34 of electron irradiation)₁Structure 26 of (a). The width of the structure 26 in a second lateral direction perpendicular to the first lateral direction may be in the range of 0.5 microns to 10 millimeters; in the range of 0.5 microns to 5 millimeters; in the range of 0.5 microns to 1 millimeter; in the range of 0.2 mm to 3 mm. In certain embodiments (e.g., where the structures 26 are arranged in a one-dimensional array or a two-dimensional array), the width W of at least some of the structures 26 in the first lateral direction₁A separation distance S in a range of 0.5 to 2 microns, in a range of 1 to 3 microns, in a range of 1 to 5 microns, or in a range of less than 5 microns, and between at least some of the structures 26 in the first lateral direction₁In a range of greater than 0.3 microns, in a range of 0.3 microns to 2 microns, in a range of 1 micron to 2 microns, or in a range of 1 micron to 4 microns. In certain embodiments, the duty cycle (e.g., the ratio of the width W to the sum of the width W and the spacing distance S, in a lateral direction of the first surface 24) of the structures 26 is 33%, 50%, in a range of 20% to 40%, in a range of 40% to 60%, or in a range of 50% to 70%. In certain embodiments (e.g., where structures 26 are arranged in a two-dimensional array), structures 26 also have a width W₂And a spacing distance S between the structures 26 in a second lateral direction (e.g., a second direction parallel to the first surface 24; a second direction perpendicular to a plane defined by the surface normal 28 and the direction of electron irradiation 34)₂. In certain embodiments, the width W of at least some of the structures 26 in the second lateral direction₂A separation distance S in a range of 0.5 to 2 microns, in a range of 1 to 3 microns, in a range of 1 to 5 microns, or in a range of less than 5 microns, and between at least some of the structures 26 in the second lateral direction₂In a range greater than 0.3 microns, in a range from 0.3 microns to 4 microns, or in a range from 1 micron to 2 microns. In certain embodiments (e.g., where the structures 26 are arranged in a linear type array), the structures 26 have a width substantially greater than W₁Width W of₂And the structures 26 are arranged such that their width W₂Aligned with each other (e.g., forming a "dashed line" or "dashed line" array), or arranged such that the structures 26 are perpendicular to their width W₂Are shifted, offset or staggered relative to each other in the transverse direction. Spacing distance S between at least some of the structures 26₂In the range of 0.2 to 0.4 microns, in the range of 0.3 to 0.7 microns, or in the range of less than 2 microns. In certain embodiments, the separation distance S₁、S₂Is sufficiently large to facilitate (e.g., enhance; improve) heat transfer from structure 26 to substrate 22, and from substrate 22 to a heat sink in thermal communication with substrate 22. In certain embodiments in which the electron penetration depth and/or electron mean free path in the first and second materials as a function of electron kinetic energy is known, the size of the target 20 (e.g., depth D)_zOne or more of width W, separation distance S) and electron propagation direction 34 are selected such that at least some electrons 32 propagate through two or more structures 26.

The specific embodiment of the design may vary depending on the intended application. For example, for mammography or absorption-based submicron resolution 3D x radiographs of a semiconductor sample, the x-ray source of certain embodiments can use electron acceleration voltages in the range of 20keV to 70 keV. In certain such embodiments, the at least one second material of the structure 26 may be molybdenum, tungsten, and/or rhodium. Width W₁(and width W if a two-dimensional array₂) Can be used forTo be in the range of 0.3 to 1 micron, in the range of 0.5 to 1.5 microns, or in the range of 1 to 2 microns. Depth D of structure 26_zMay be selected to be less than half of a continuous deceleration approximation (CSDA) estimate of the electron's penetration depth at its kinetic energy through the first material (e.g., diamond), and may be in the range of 1 to 3 microns, 2 to 5 microns, or 4 to 10 microns. For another example, x-ray microphotographs and medical CT applications, the x-ray source of certain embodiments may use higher electron acceleration voltages (e.g., up to 120keV or up to 160 keV). In certain such embodiments, the at least one second material of structure 26 may be tungsten. Width W₁(and W if a two-dimensional array₂) May be in the range of 0.3 to 1 micron, in the range of 0.5 to 1.5 microns, or in the range of 1 to 3 microns. Depth D of structure 26_zMay be in the range of 2 microns to 5 microns, in the range of 4 microns to 8 microns, or in the range of 6 microns to 12 microns.

In certain embodiments, the target 20 further comprises at least one interfacial layer between the first material and the at least one second material, and the at least one interfacial layer comprises a third material different from the first material and the at least one second material. Examples of the at least one third material include, but are not limited to, at least one of: titanium nitride (e.g., for use with a first material comprising diamond and a second material comprising tungsten), iridium (e.g., for use with a first material comprising diamond and a second material comprising molybdenum and/or tungsten), chromium (e.g., for use with a first material comprising diamond and a second material comprising copper), beryllium (e.g., for use with a first material comprising diamond), and hafnium oxide. In certain embodiments, the at least one interfacial layer has a thickness in a range of 1 to 5 nanometers, in a range of 2 to 30 nanometers, or in a range of 2 to 50 nanometers. In certain embodiments, the at least one third material is selected to provide a diffusion barrier configured to prevent (e.g., prevent; reduce; inhibit) diffusion of the at least one second material (e.g., tungsten) into the first material (e.g., diamond). For example, the diffusion barrier layer may be graded from a carbide material to at least one third material at the interface with the diamond first material. In certain embodiments, the at least one third material is configured to enhance (e.g., improve; promote) adhesion between the at least one second material and the first material and/or to enhance (e.g., improve; promote) thermal conductivity between the at least one second material and the first material.

In certain embodiments, the target 20 further includes at least one layer covering the structure 26 at the first surface 24. The at least one layer of certain embodiments includes a conductive material (e.g., doped diamond; nickel; aluminum) configured to be in electrical communication with electrical ground or another potential to prevent charging of the first surface 24 due to electron irradiation of the target 20, and/or an encapsulation material (e.g., first material; diamond; beryllium; sapphire) configured to encapsulate the structure 26 between the at least one layer and the substrate 22.

In certain embodiments, the electron source 30 comprises an electron emitter having a dispenser cathode (e.g., impregnated tungsten), tungsten filament, lanthanum hexaboride (LaB)₆) A cathode, carbon nanotubes that are configured or arranged (e.g., via thermionic emission or field emission) to emit electrons 32 (directed to impinge on the target 20). An example dispenser cathode according to certain embodiments described herein is sold by Spectra-Mat corporation of Watsonville, california (e.g., a thermionic emitter comprising a porous tungsten matrix impregnated with barium aluminate).

The electron source 30 further includes electron-optical components (e.g., deflection electrodes; grids; electrostatic lenses; magnetic lenses, etc.) configured to deflect, shape, and/or focus electrons 32 emitted from the electron emitter to accelerate the electrons to a predetermined electron kinetic energy and direct the electrons 32 onto the target 10. Example configurations of electron-optical components according to certain embodiments described herein include, but are not limited to, single-grid configurations, double-grid configurations, and triple-grid configurations. In some embodiments, the electron optical components are configured to limit the location at which electrons are drawn from the electron emitter by setting a retardation field, while other downstream electron optical components are used to draw electrons through the retardation field. In certain embodiments, the target 20 is configured to function as an anode (e.g., set at a positive voltage relative to the electron source 30) to accelerate and/or otherwise modify the trajectory of the electrons 32. In certain embodiments, the target 20 is configured as a grounded window that serves as a source.

In certain embodiments, the electron source 30 is positioned relative to the target 20 such that the electrons 32 strike the first surface 24 at a non-zero angle θ relative to the surface normal 28 of the portion of the first surface 24. For example, the angle θ may be greater than 20 degrees, in the range of 40 degrees to 85 degrees, in the range of 30 degrees to 70 degrees, or in the range of 40 degrees to 60 degrees. As shown in fig. 1A and 1B, the angle θ is equal to 60 degrees. In certain embodiments in which the structures 26 are arranged in one or more one-dimensional (e.g., linear) arrays, the projection of the electron beam centerline onto the first surface 24 of the target 20 is parallel to a first lateral dimension (e.g., a shorter width W)₁) And orthogonal to the second lateral dimension (e.g., longer width W)₂) To facilitate electron travel through more than one structure 26. In certain embodiments in which structures 26 are arranged in one or more two-dimensional arrays, the central electron beam projection may be diagonal to the array dimension. In certain embodiments, electrons 32 (e.g., in one or more electron beams) can be deflected and/or moved relative to the first surface 24 of the target 20 by one or more electromagnetic assemblies (e.g., one or more electrodes and/or electrode elements) to illuminate different structured areas on the target 20. In certain other embodiments, the electrons 32 may be deflected and/or moved relative to the first surface 24 of the target 20 by mechanically moving one or more components of the electron source 30 (e.g., some or all of the electron source 30 is mounted on a mechanical flexure system). In certain embodiments, the deflection and/or movement of the electrons 32 relative to the first surface 24 may modify the angle of incidence at which the electrons 32 strike the first surface 24, while in certain other embodiments, the angle of incidence is substantially unchanged by the deflection and/or movement of the electrons 32.

In certain embodiments, the electrons 32 striking some of the structures 26 may be arranged as a single electron beam or as multiple electron beams, and the one or more electron beams may each have a rectangular beam profile, an elliptical beam profile, or other type of beam profile. In certain embodiments, at least some of the electrons 32 strike different structures 26 at the same angle θ as one another (e.g., the electrons 32 are incident at each structure 26 of the plurality of structures 26 at substantially the same angle θ as one another, as schematically illustrated in fig. 1A), while in certain other embodiments, at least some of the electrons 32 strike different structures 26 at different non-zero angles θ as one another. In certain embodiments in which at least some of the structures 26 are separated from each other along a lateral direction of the target 20 (e.g., a direction parallel to the first surface 24), the electron source 30 is positioned relative to the target 20 such that a centerline of the electrons 32 lies in a plane defined by the surface normal 38 and the lateral direction (e.g., as schematically shown in fig. 1A).

In certain embodiments, the kinetic energy of electrons 32 striking structure 26 is in the range of 0.5keV to 160keV, 2keV to 85keV, 35keV to 85keV, 20keV to 70keV, 20keV to 120keV, 20keV to 160keV, or any other range selected to provide x-rays having a predetermined energy spectrum. In certain embodiments, the angle θ and the electron kinetic energy are selected such that at least some of the electrons 32 have an electron penetration depth within the target 20 sufficient to penetrate the first surface 24 and strike the at least two structures 26. In certain embodiments, the width W, separation distance S, and duty cycle (e.g., W/(W + S)) are selected to correspond to the incident beam energy and angle θ such that most electrons encounter more than one structure 26. In certain such embodiments, dimensions W and S are sufficiently small such that the electron penetration distance (e.g., average electron stopping distance), which is a function of both material and electron energy, extends at least W/(sin θ) of the second material (e.g., tungsten) and S/(sin θ) of the first material (e.g., diamond) of structure 26 at a predetermined electron acceleration voltage (e.g., the electron penetration distance is greater than (W + S)/(sin θ)). In certain embodiments, θ is 60 degrees.

For example, referring to FIG. 1B, it schematically illustrates the first surface 24 separated from each other by a separation distance S along a transverse direction thereof₁May be selected using a continuous deceleration approximation (CSDA) estimate of electron penetration depthThe kinetic energy of the electrons 32 causes at least some of the electrons 32 to propagate through the first structure 26a, through the portion of the substrate 22 between the first and second structures 26a, 26b, and to the second structure 26 b. In certain embodiments, the thickness T of the target 20 is configured to be less than a CSDA estimate of the electron penetration depth of the electrons 32 in the first material of the substrate 22, thereby avoiding (e.g., preventing; reducing; suppressing) deeper portions of the first material and/or absorption of the first material of x-rays generated by the structure 26 from contributing to the resulting x-rays from the x-ray generation.

In certain embodiments, x-rays 50 are generated in each structure 26 illuminated by electrons 32. As schematically illustrated in fig. 1A, in certain embodiments, x-rays 50 are emitted from target 20 in a beam comprising a plurality of sub-beams 52a, 52 b.

Although fig. 1A schematically illustrates x-rays 50 being generated only by structures 26 and being emitted from structures 26, electron irradiation also generates x-rays from substrate 22 (e.g., regions of substrate 22 between structures 26), and these x-rays generated within substrate 22 may adversely degrade the resulting overall x-ray distribution (e.g., reducing the discrimination of structures 26 as individual x-ray emitters, which facilitates use of x-ray source 10 in a Talbot-Lau imaging system). For example, it is expected that the spatial distribution of x-rays (e.g., structure 26 acting as a spatially distinct x-ray source) may be degraded by x-rays generated by the substrate, and that the energy spectrum of x-rays (e.g., x-rays having an intensity that is a function of the x-ray energy that is characteristic of the at least one second material of structure 26) may be degraded by x-rays generated by the first material.

Fig. 2A-2C schematically illustrate an example target 20 configured to improve x-ray distribution from the target 20, according to certain embodiments described herein. As schematically shown in fig. 2A, the target 20 includes at least one layer 60 located at a position between the structure 26 and the second surface 25 of the target 20. The at least one layer 60 includes an x-ray absorbing material (e.g., gold) embedded within the substrate 22 having a thickness T_a(e.g., in the range of 10 to 30 microns) and includes pores directly below structure 26 (e.g., with 3 microns therebetween)Distance and 2 micron line). For example, the at least one layer 60 can be formed by depositing a uniform layer on the back surface of the substrate 22, etching the layer 60 to form the desired microstructure, and then forming additional substrate material over the layer 60 on the back surface. Alternatively, the top of the substrate and the bottom of the substrate may be formed separately, the top having the structure 26 and the bottom having the at least one layer 60, and the two substrate portions may be joined together (e.g., adhered; clamped).

In certain embodiments, the at least one layer 60 effectively blocks much of the x-rays generated in the substrate 22 while allowing transmission of the x-rays 50 generated in the structure 26. The at least one layer 60 has a thickness T defined by the at least one layer 60_aDivided by the transverse width W of the hole_hThe aspect ratio is defined and the aspect ratio of the at least one layer 60 may be lower than that of a conventional G0 absorption grid of a Talbot-Lau imaging system.

As schematically shown in FIG. 2B, at least one layer 60 comprises an x-ray absorbing material (e.g., gold) deposited on second surface 25 having a thickness T_b(e.g., in the range of 10 to 60 microns) and includes a groove 62 directly below structure 26 having a lateral width W_hAnd a depth in the range of 3 microns to 100 microns. In certain embodiments, the at least one layer 60 also functions as a filter configured to reduce the energy bandwidth of the x-rays 50 (e.g., to filter the x-rays 50 to have a bandwidth of ± 15% around the x-ray energy of interest). As schematically shown in FIG. 2C, at least one layer 60 comprises an x-ray absorbing material (e.g., gold) deposited on second surface 25, having a thickness T_b(e.g., in the range of 10-60 microns) and includes an aperture 64, the aperture 64 having a lateral width sufficiently wide such that x-rays from the plurality of structures 26 may propagate through the aperture 64. In certain such embodiments, at least one layer 60 defines an outer boundary (e.g., perimeter) of the region through which x-rays from the plurality of structures 26 are emitted from the second surface 25 of the target 20.

In some configurations, the target may include a thin layer of x-ray generating material (e.g., gold; tungsten; molybdenum) on a top surface of a substrate (e.g., diamond) and a plurality of structures on a bottom surface of the substrate that function as x-ray absorbing layers to define individual x-ray emitters.

In certain embodiments, as schematically illustrated in fig. 1A, at least one optical element 40 is configured to receive at least some of the x-rays 50 emitted from the target 20. For example, the at least one optical element 40 includes a window portion of a housing wall of the x-ray source 10 (e.g., a solid material that is substantially transparent to at least some x-rays 50 emitted from the target 20) and is spaced apart from the substrate 22 of the target 20. In certain embodiments, as schematically illustrated in fig. 1C, the window portion comprises the target 20 (e.g., a housing wall of the x-ray source 10 comprises the substrate 22 such that a first surface 24 of the substrate 22 faces an area within the housing and a second surface 25 faces an area outside the housing). By having the window portion include the substrate 22, at least some of the x-rays that pass through the first material also pass through the window portion and are emitted from the target 20 (e.g., pass through the second surface 25). Although fig. 1C schematically shows that only the edge of the substrate 22 is mechanically coupled to the housing of the x-ray source 10, in certain embodiments, the substrate 22 is mounted to a portion of the housing wall that is substantially transparent to at least some of the x-rays 50 emitted from the second surface 25 of the substrate 22. For example, the second surface 25 of the substrate 22 may be mounted to an inner surface of the portion of the housing wall.

As another example, the at least one optical element 40 includes a grating (e.g., G1) of a Talbot-Lau imaging system and/or a sample analyzed by the Talbot-Lau imaging system. As another example, the at least one optical element 40 includes an aperture and/or x-ray optics configured to receive x-rays 50 and modify (e.g., focus; deflect; filter) the x-rays. Various optical elements according to certain embodiments described herein are disclosed in U.S. patent nos. 9,719,947, 9,874,531, 10,349,908, and 10,352,880, and U.S. patent application publication nos. 2015/0117599a1 and 2016/0320320a1, each of which is incorporated herein in its entirety.

In certain embodiments, the electron source 30 and the at least one optical element 40 are positioned on opposite sides of the target 20 (e.g., the electron source 30 faces the first surface 24 and the at least one optical element 40 faces the second surface 25; see, e.g., FIG. 1A), which corresponds to a transmissive x-ray source 10 configuration. In certain other embodiments, the electron source 30 and the at least one optical element 40 are positioned on the same side of the target 20 (e.g., the electron source 30 faces the first surface 24 and the at least one optical element 40 faces the first surface 24), which corresponds to a reflective x-ray source 10 configuration.

In certain embodiments, the angle of incidence θ of the electrons 32 to the first surface 24 is configured to advantageously increase energy deposition in the structure 26 as compared to energy deposition within the substrate 22. In some such embodiments, the fraction of total energy deposition deposited in structure 26 (e.g., the ratio of energy deposition to total energy deposition in structure 26) is increased by a factor (e.g., 2X to 5X).

Fig. 3A-3C illustrate results of simulated calculations of an electron beam of 30keV impinging on the first surface 24 of the target 20 according to certain embodiments described herein. Fig. 3A shows a plot of total deposition energy (in arbitrary units) from electrons striking the first surface 24 of the target 20 as a function of the angle of incidence θ (in degrees measured from the surface normal 28 of the first surface 24). At normal incidence (θ ═ 0), the total deposited energy in the target 20 is at its maximum, with about 15% of the energy lost to backscattered and/or reflected electrons. The total deposition energy in the target 20 monotonically decreases with larger angles of incidence due to an increasing amount of backscattered and/or reflected electrons having an increasing proportion of the total impact energy incident on the target 20. Fig. 3B shows a graph of the ratio of the total deposition energy in the target 20 to the total impact energy incident on the target 20, which further shows this monotonic decrease in the total deposition energy of the angle of incidence due to backscattered and/or reflected electrons. To account for the backscattering of electrons at higher angles of incidence, the electron loading power may be increased at higher angles.

Furthermore, as shown in fig. 3A, at normal incidence (θ ═ 0), the deposition energy in substrate 22 (i.e., the fraction of the impact energy deposited in substrate 22) is greater than the deposition energy in structure 26 (i.e., the fraction of the impact energy deposited in structure 26). The deposition energy in substrate 22 also monotonically decreases with larger incidence angles, passing through the deposition energy in structure 26 at an incidence angle of about 53 degrees, while the deposition energy in structure 26 has a maximum between 45 and 60 degrees. At larger angles of incidence, electrons 32 encounter more and more of the at least one second material of structure 26, but at angles of incidence of electrons 32 greater than 20 degrees, the ratio of backscattered and/or reflected electrons increases significantly, resulting in a reduction in total energy deposition and less electron contribution to x-ray generation.

Fig. 3C shows a plot of (i) the ratio of deposition energy in substrate 22 to total deposition energy, and (ii) the ratio of deposition energy in structure 26 to total deposition energy, as a function of angle of incidence. These two ratios are equal to each other at an angle of incidence of about 47 degrees, and at higher angles of incidence, the energy deposition to structure 26 is greater than the energy deposition to substrate 22. For example, at 60 degrees θ, the energy deposited in structure 26 is 55% of the total deposited energy, while the energy deposited in substrate 22 is 45% of the total deposited energy. Although more energy is lost to backscattered and/or reflected electrons at these higher incidence angles (e.g., θ ═ 60 degrees) than at normal incidence (see fig. 3B), by depositing a greater proportion of the total deposited energy in structures 26 than in substrate 22 (with an increase in x-rays generated in structures 26 and a decrease in x-rays generated in substrate 22), certain embodiments advantageously provide higher contrast between x-ray emissions from structures 26 as compared to x-ray emissions from substrate 22 (e.g., the portion between structures 26), higher relative brightness between x-ray emissions from structures 26 as compared to x-ray emissions from substrate 22 (e.g., the portion between structures 26), and/or improved Talbot edge visibility.

In certain embodiments, structural parameters of the target 20 (e.g., lateral dimensions of the structures 26; spacing of the structures 26 across the first surface 24; distance between the structures 26; thickness of the structures 26) are selected to provide a desired tradeoff between increased interaction of electrons 32 at higher angles of incidence and reduced x-ray generation due to backscattered and/or reflected electron loss. In certain embodiments, the electron kinetic energy is selected such that an average stopping range of electrons 32 (e.g., including traveling through the first material and the second material) impacting the first surface 24 of the target 20 extends through more than one structure 26.

Various configurations have been described above. While the invention has been described with reference to these specific configurations, these descriptions are intended to be illustrative of the invention and not limiting. Various modifications and applications may occur to those skilled in the art without departing from the true spirit and scope of the invention. Thus, for example, in any method or process disclosed herein, the acts or operations making up the method/process may be performed in any suitable order and are not necessarily limited to any particular disclosed sequence. Features or elements from the various embodiments and examples discussed above may be combined with one another to create alternative configurations compatible with the embodiments disclosed herein. Various aspects and advantages of the embodiments have been described as appropriate. It is to be understood that not necessarily all such aspects or advantages may be achieved in accordance with any particular embodiment. Thus, for example, it is to be appreciated that various embodiments may 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 as may be taught or suggested herein.