HIGH BRIGHTNESS X-RAY REFLECTION SOURCE

Abstract

An X-ray target (10) comprising: a thermally conductive substrate (20) having a surface (22); and a plurality of structures (30) which are separated from one another, on or embedded in at least a portion of the surface (22), each of the at least two structures (30) of the plurality of structures (30) comprising: a thermally conductive first material (32) in thermal communication with the substrate (20), and at least one layer (40) over the first material (32), wherein the at least one layer (40) comprises at least one second material (42) that is different from the first material (32), wherein the at least one second material (42) is configured to generate X-rays when irradiated by electrons, wherein the first materials (32) of the at least two structures (30) are separated from each other and the at least one second material (42) of the at least two structures (30) are separated from each other and different from each other, and wherein the at least one layer (40) further comprises at least one third material (44) between the first material (32) and the at least one second material (42), wherein the at least one third material (44) is different from the first material (32) and the at least one second material (42), and the at least one third material (44) has a thickness between 2 nanometers and 50 nanometers and / or the at least one third material (44) comprises at least one of the following materials: titanium nitride, iridium, chromium, beryllium and hafnium oxide.

Description

PRIORITY CLAIM

[0001] This application claims priority to US Provisional Appl. No. 62 / 703,836, filed July 26, 2018, which is incorporated herein by reference in its entirety. BACKGROUNDTechnical field

[0002] This application refers generally to X-ray sources. State of the art

[0003] Laboratory X-ray sources generally bombard a metal target with electrons, with the deceleration of these electrons generating X-ray bremsstrahlung of all energies from zero up to the kinetic energy of the electrons. In addition, the metal target generates X-rays by creating holes in the inner core electron orbitals of the target atoms, which are then filled by target electrons with binding energies lower than the inner core electron orbitals, while simultaneously generating X-rays with energies characteristic of the target atoms. Most of the power of the electrons irradiating the target is converted into heat (e.g., approximately 60%) and backscattered electrons (e.g., approximately 39%), with only approximately 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 for the achievable brightness (e.g.,photons per second per area per steradian) that can be achieved by the X-ray source.

[0004] Transmission-type X-ray sources configured to produce microfocused or nanofocused X-rays generally use targets comprising a thin sputtered metal layer (e.g., tungsten) over a low-density, thermally conductive substrate material (e.g., diamond). The metal layer on one side of the target is irradiated with electrons, and the X-ray beam consists of X-rays emitted from the opposite side of the target. The size of the X-ray spot depends on the size of the electron beam spot. In addition, due to the electron bloom within the target, the X-rays generated and emitted by the target have an effective focal spot size larger than the focal spot size of the incident electron beam.Therefore, transmission-type X-ray sources producing microfocus or nanofocus X-rays generally require very thin targets and very good focusing of the electron beam.

[0005] Conventional reflection-type X-ray sources irradiate a surface of a solid target metal (e.g., tungsten) and collect the X-rays transmitted from the irradiated target surface at a takeoff angle (e.g., 6-30 degrees) relative to the irradiated target surface. The takeoff angle is chosen to optimize the accumulation of X-rays while compensating for the self-absorption of X-rays generated in the target. Because the electron beam spot on the target is effectively viewed at an angle in reflection-type X-ray sources, the size of the X-ray source spot can be smaller than that of the electron beam spot in transmission-type X-ray sources.

[0006] US 2013 / 0195246 A1 discloses an X-ray target comprising a substrate and a layer of a second (target) material, which includes projections and depressions. In a second embodiment, an intermediate layer of a first material is additionally provided between the second material and the substrate. In a third embodiment, the second material is applied directly to the substrate, and a continuous protective layer covers the second material.

[0007] US Pat. No. 5,148,462 A discloses an X-ray target comprising a diamond substrate, a second material embedded in separate structures within the substrate, and a continuous first material covering the structures of the second material. In a further embodiment, a system comprising a substrate, a second material embedded in separate structures within the substrate, and a continuous first material continuously covering the structures of the second material is described.

[0008] US Pat. No. 5,602,899 A discloses an X-ray target consisting of a housing made of a material such as molybdenum with a low thermal expansion coefficient and a diamond element embedded in the housing. In some embodiments, a metal film is applied to an outer surface of the diamond, serving as a second material to form the anode, which is receptive to the incident electron beam to generate X-rays. SUMMARY OF THE INVENTION

[0009] Certain embodiments described herein provide an X-ray target according to independent claims 1 and 17.

[0010] In one aspect, the x-ray target comprises a thermally conductive substrate having a surface and a plurality of structures separated from one another on or embedded in at least a portion of the surface. The plurality of structures comprises a thermally conductive first material in thermal communication with the substrate. The first material has a length along a first direction parallel to the portion of the surface in a range greater than 1 millimeter and a width along a second direction parallel to the portion of the surface and perpendicular to the first direction. The width is in a range of 0.2 millimeters to 3 millimeters. The at least one structure further comprises at least one layer over the first material. The at least one layer comprises at least one second material different from the first material. The at least one layer has a thickness in a range of 2 micrometers to 50 micrometers.The at least one second material is configured to generate X-rays when irradiated by electrons with energies in an energy range of 0.5 keV to 160 keV. The X-ray target further comprises at least one third material between the first material and the at least one second material, wherein the at least one third material is different from the first material and the at least one second material, and the at least one third material comprises at least one of the following materials: titanium nitride, iridium, chromium, beryllium, and hafnium oxide.

[0011] In another aspect, the x-ray target comprises a thermally conductive substrate having a surface and a plurality of structures that are separate from one another, on or embedded in at least a portion of the surface. Each of the at least two structures of the plurality of structures comprises a thermally conductive first material in thermal communication with the substrate and at least one layer over the first material, the at least one layer comprising at least one second material that is different from the first material. The at least one second material is configured to generate x-rays when irradiated by electrons. The first materials of the at least two structures are separate from one another, and the at least one second material of the at least two structures are separate and different from one another.The at least one layer further comprises at least one third material between the first material and the at least one second material. The at least one third material differs from the first material and the at least one second material. The at least one third material has a thickness between 2 nanometers and 50 nanometers and / or the at least one third material comprises one of the following materials: titanium nitride, iridium, chromium, beryllium, and hafnium oxide.

[0012] Certain embodiments described herein provide an X-ray source according to independent claims 7 and 22.

[0013] In one aspect, the x-ray source comprises an x-ray target comprising a thermally conductive substrate having a surface and a plurality of structures separated from one another on or embedded in at least a portion of the surface. The plurality of structures comprises a thermally conductive first material in thermal communication with the substrate. The first material has a length along a first direction parallel to the portion of the surface in a range greater than 1 millimeter and a width along a second direction parallel to the portion of the surface and perpendicular to the first direction. The width is in a range of 0.2 millimeters to 3 millimeters. The at least one structure further comprises at least one layer over the first material. The at least one layer comprises at least one second material different from the first material.The at least one layer has a thickness in a range of 2 micrometers to 50 micrometers. The at least one second material is configured to generate X-rays when irradiated with electrons having energies in an energy range of 0.5 keV to 160 keV. The at least one structure further comprises at least one third material between the first material and the at least one second material, wherein the at least one third material is different from the first material and the at least one second material, and the at least one third material comprises at least one of the following materials: titanium nitride, iridium, chromium, beryllium, and hafnium oxide. The X-ray source further comprises an electron source configured to generate electrons in at least one electron beam and to direct or align the at least one electron beam to impinge on the at least one structure.

[0014] In another aspect, the x-ray source comprises an x-ray target comprising a thermally conductive substrate having a surface and a plurality of structures that are separated from one another on or embedded in at least a portion of the surface. Each of the at least two structures of the plurality of structures comprises a thermally conductive first material in thermal communication with the substrate, and at least one layer over the first material, the at least one layer comprising at least one second material that is different from the first material, the first materials of the at least two structures being separated from one another, and the at least one second material of the at least two structures being separate from one another and different from one another.The at least one layer further comprises at least one third material between the first material and the at least one second material, wherein the at least one third material is different from the first material and the at least one second material. The at least one third material has a thickness between 2 nanometers and 50 nanometers and / or the at least one third material comprises at least one of the following materials: titanium nitride, iridium, chromium, beryllium, and hafnium oxide. The X-ray source further comprises an electron source configured to generate electrons in at least one electron beam and to direct the at least one electron beam to impinge on the plurality of structures.

[0015] Certain embodiments described herein further relate to a method according to independent claim 13. The method comprises irradiating a first selected structure from a plurality of structures with at least one electron beam, wherein the plurality of structures are separated from one another and are arranged on or embedded in at least a portion of the surface of a thermally conductive substrate.Each of the at least two structures of the plurality of structures comprises a thermally conductive first material in thermal communication with the substrate, at least one layer over the first material, the at least one layer comprising at least one second material different from the first material, the at least one second material configured to generate x-rays when irradiated by the first electron beam, and at least one third material between the first material and the at least one second material, the at least one third material different from the first material and the at least one second material, the at least one third material having a thickness between 2 nanometers and 50 nanometers and / or the at least one third material comprising at least one of the following materials: titanium nitride, iridium, chromium, beryllium, and hafnium oxide.The method further comprises controllably moving the substrate and / or the at least one electron beam relative to each other, and irradiating a second selected structure from the plurality of structures with the at least one electron beam. BRIEF DESCRIPTION OF THE ILLUSTRATIONS Fig. 1A-1C schematically illustrate portions of example x-ray targets in accordance with certain embodiments described herein. Fig. 2A and Fig. 2B schematically illustrate portions of example x-ray targets having a plurality of separated structures according to certain embodiments described herein. Fig. 3 schematically illustrates an example x-ray source of an example x-ray system in accordance with certain embodiments described herein. Fig. 4A and Fig.4B schematically illustrate further examples of an X-ray source according to certain embodiments described herein. Fig. 5A schematically shows an example x-ray target in accordance with certain embodiments described herein, and Fig. 5B-5I show schematically different simulation results of the brightness of different versions of the example X-ray target of Fig. 5A. DETAILED DESCRIPTION

[0016] Certain embodiments described herein provide a reflection-type X-ray source that advantageously achieves small X-ray spot sizes while using electron beam spot sizes larger than those used in transmission-type X-ray sources (e.g., using less severe electron beam focusing compared to the electron beam focusing used in transmission-type X-ray sources).

[0017] Certain embodiments described herein advantageously provide a reflection-type X-ray source with high X-ray brightness while avoiding the detrimental effects of excessive target heating. By using a cooled substrate and a first material with high thermal conductivity (e.g., diamond) in thermal communication with the substrate, and a target layer of a second material deposited on the first material, heat can advantageously be dissipated from the target layer more quickly than would be possible if the heat were dissipated through the bulk target material.

[0018] Certain embodiments described herein advantageously provide a reflection-type X-ray source having multiple target materials within a "sealed tube source." By configuring the X-ray source to use an electron beam to irradiate a selected one of the multiple target materials, each target material producing X-rays having a corresponding X-ray spectrum with different characteristic X-ray energies, the reflection-type X-ray source can advantageously provide multiple, selectable X-ray spectra, allowing the X-ray source to be optimized for different applications without requiring the X-ray source to be opened each time to change targets and pump down the X-ray source.

[0019] Fig.1A-1C schematically illustrate portions of example x-ray targets 10 in accordance with certain embodiments described herein. In each of the Fig.1A-1C, the x-ray target 10 includes a thermally conductive substrate 20 having a surface 22 and a plurality of structures 30 on or embedded in at least a portion of the surface 22. The plurality of structures 30 includes a thermally conductive first material 32 in thermal communication with the substrate 20. The first material 32 has a length L along a first direction 34 parallel to the portion of the surface 22, where the length L is in a range greater than 1 millimeter. The first material 32 also has a width W along a second direction 36 parallel to the portion of the surface 22 and perpendicular to the first direction 34, where the width W is in a range of 0.2 millimeters to 3 millimeters (e.g., 0.2 millimeters to 1 millimeter).The plurality of structures 30 further comprises at least one layer 40 over the first material 32, wherein the at least one layer 40 comprises at least one second material 42 that is different from the first material 32. The at least one layer 40 has a thickness T in a range of 1 micrometer to 50 micrometers (e.g., in a range of 1 micrometer to 20 micrometers; tungsten layer thickness in a range of 1 micrometer to 4 micrometers; copper layer thickness in a range of 2 micrometers to 7 micrometers), and the at least one second material 42 is configured to generate X-rays when irradiated by electrons with energies in an energy range of 0.5 keV to 160 keV.

[0020] In certain embodiments, the target 10 is configured to dissipate heat from the plurality of structures 30. For example, the surface 22 of the substrate 20 may comprise at least one thermally conductive material, and the remaining portion of the substrate 20 may comprise the same at least one thermally conductive material and / or another or more thermally conductive materials. Examples of the at least one thermally conductive material include, but are not limited to, metals (e.g., copper, beryllium, doped graphite), metal alloys, metal composites, and electrically insulating but thermally conductive materials (e.g., diamond, graphite, diamond-like carbon, silicon, boron nitride, silicon carbide, sapphire). In certain embodiments, the at least one thermally conductive material has a thermal conductivity in a range between 20 W / (m K) and 2500 W / (m K) (e.g.,between 150 W / (m K) and 2500 W / (m K); between 200 W / (m K) and 2500 W / (m K); between 2000 W / (m K) and 2500 W / (m K)) and includes elements with atomic numbers less than or equal to 14. The surface 22 of the substrate 20, in certain embodiments, is electrically conductive and configured to be in electrical communication with an electrical potential (e.g., electrical ground) and to prevent charging of the surface 22 due to electron irradiation of the target 10. In certain embodiments, the target 10 includes a heat transfer structure in thermal communication with the substrate 20 and configured to conduct heat away from the target 10. Examples of heat transfer structures include, but are not limited to, heat sinks, heat pipes, and fluid flow lines configured to conduct a fluid coolant (e.g.,Liquid; water; deionized water; air; coolant; heat transfer fluid such as Galden® perfluoropolyether fluorinated fluids sold by Solvay SA of Brussels, Belgium) flows therethrough and conducts heat away from the substrate 20 (e.g., at a rate similar to the power loading rate of the target 10 by the electron beam irradiation).

[0021] In certain embodiments, the thermally conductive first material 32 is configured to be adhered (e.g., bonded; fixed; brazed; soldered) to the surface 22 of the substrate 20 such that the first material 32 is in thermal communication with the substrate 20. For example, the first material 32 may be soldered or brazed to the surface 22 using a thermally conductive solder or brazing material, examples of which include, but are not limited to: CuSil-ABA ® - or Nioro ®-Brazing alloys distributed by Morgan Advanced Materials in Windsor, Berkshire, UK; gold / copper brazing alloys. As described in Fig. 1A and Fig.1B, in certain embodiments, the first material 32 is located on the surface 22 and is secured to the surface 22 by a solder or braze material (not shown) that extends along at least a portion of the first material 32 and is mechanically bonded to both the first material 32 and the surface 22. The solder or braze material may increase (e.g., improve; facilitate) the thermal conductivity between the first material 32 and the surface 22. In certain other embodiments, the first material 32 overlies the surface 22, with the solder or braze material extending along at least a portion of the first material 32 and between the first material 32 and the surface 22, being mechanically bonded to both the first material 32 and the surface 22, and increasing (e.g., improve; facilitate) the thermal conductivity between the first material 32 and the surface 22.In certain embodiments, as in . Fig. 1C, the surface 22 includes a recess 24 configured such that the first material 32 is partially inserted into the recess 24 such that the structure 30 is embedded in at least a portion of the surface 22. The first material 32 may be joined to the surface 22 by solder or brazing material (not shown) extending along at least a portion of the first material 32, mechanically bonding it to both the first material 32 and the surface 22, and increasing (e.g., improving; facilitating) the thermal conductivity between the first material 32 and the surface 22.

[0022] Examples of the first material 32 include, without limitation, at least one of: diamond, silicon carbide, beryllium, and sapphire. While Fig.1A schematically shows the first material 32 having a hemicylindrical, prism, or parallelepiped shape (e.g., ribbon; rod; strip; strut; finger; plate; sheet) with 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 length L of the first material 32 is the greatest dimension of the first material 32 in the first direction 34, and the width W of the first material 32 is the greatest dimension of the first material 32 in the second direction 36. The length L can range from greater than 1 millimeter, greater than 5 millimeters, 1 millimeter to 4 millimeters, 1 millimeter to 10 millimeters, or 1 millimeter to 20 millimeters.The width W can be in a range of 0.2 millimeters to 3 millimeters, 0.2 millimeters to 1 millimeter, 0.4 millimeters to 1 millimeter, 0.4 millimeters to 1 millimeter, 0.2 millimeters to 0.8 millimeters, or 0.2 millimeters to 0.6 millimeters. In certain embodiments, the thickness T of the first material 32 is the greatest dimension of the first material 32 in a direction perpendicular to the portion of the surface 22 and can be in a range of 0.2 millimeters to 1 millimeter, 0.4 millimeters to 1 millimeter, 0.4 millimeters to 1 millimeter, 0.2 millimeters to 0.8 millimeters, or 0.2 millimeters to 0.6 millimeters.

[0023] In certain embodiments, the at least one second material 42 of the at least one layer 40 is selected such that, when irradiated by electrons with energies in the energy range from 0.5 keV to 160 keV, it generates X-rays with a predetermined energy spectrum (e.g., X-ray intensity distribution as a function of X-ray energy). Examples of the at least one second material 42 include, but are not limited to: tungsten, chromium, copper, aluminum, rhodium, molybdenum, gold, platinum, iridium, cobalt, tantalum, titanium, rhenium, silicon carbide, tantalum carbide, titanium carbide, boron carbide, and alloys or combinations containing one or more of these.In certain embodiments, the thickness t of the second material 42 is the greatest extent of the second material 42 in the direction 38 perpendicular to the portion of the surface 22 and may range from 2 micrometers to 50 micrometers, 2 micrometers to 20 micrometers, 2 micrometers to 15 micrometers, 4 micrometers to 15 micrometers, 2 micrometers to 10 micrometers, or 2 micrometers to 6 micrometers. In certain embodiments, the thickness t of the at least one second material 42 is substantially uniform across the entire surface of the layer 40, while in certain other embodiments, the thickness t of the at least one second material 42 varies across the surface of the layer 40 (e.g., a first end of the layer 40 has a first thickness of the at least one second material 42 and a second end of the layer 40 has a second thickness of the at least one second material 42, wherein the second thickness is greater than the first thickness).

[0024] In certain embodiments, the thickness t of the at least one second material 42 is selected depending on the kinetic energy of the at least one electron beam irradiating the plurality of structures 30. The electron penetration depth of electrons in a material depends on the material and the kinetic energy of the electrons, and in certain embodiments, the thickness t of the at least one second material 42 can be selected such that it is smaller than the electron penetration depth of the electrons into the at least one second material 42. For example, the continuous deceleration approach (CETA) can be used.continuous slowing down approximation (CSDA) may provide an estimate of the electron penetration depth for the electrons of a selected kinetic energy impinging on the at least one second material 42, and the thickness t of the at least one second material 42 may be selected to be in a range of 50% to 70% of the CSDA estimate.

[0025] The at least one second material 42 is configured in certain embodiments to be in electrical connection with an electrical potential (e.g., electrical ground) and to prevent charging of the at least one second material 42 due to electron irradiation. For example, electrically conductive solder or brazing material (in the Fig.1A-1C not shown) may be used to adhere (e.g., bond; fix; solder) the structure 30 to the surface 22, and at least a portion of this solder or braze material may extend from the surface 22 to the at least one second material 42 along at least a portion of one of the sides of the first material 32, thereby providing electrical conductivity between the at least one second material 42 and the surface 22.

[0026] In certain embodiments, such as in Fig.1B, the at least one layer 40 further comprises at least one third material 44 between the first material 32 and the at least one second material 42, and the at least one third material 44 is different from the first material 32 and the at least one second material 42. Examples of the at least one third material 44 include, without limitation: titanium nitride (e.g., used with a first material 32 comprising diamond and a second material 42 comprising tungsten), iridium (e.g., used with a first material 32 comprising diamond and a second material 42 comprising tungsten), iridium (e.g., used with a first material 32 comprising diamond and a second material 42 comprising molybdenum and / or tungsten), chromium (e.g., used with a first material 32 comprising diamond and a second material 42 comprising copper), beryllium (e.g.,used with a first material 32 comprising diamond), and hafnium oxide. In certain embodiments, the thickness of the third material 44 is the greatest extent of the second material 44 in the direction perpendicular to the portion of the surface 22 and may be in a range of 2 nanometers to 50 nanometers (e.g., 2 nanometers to 30 nanometers). In certain embodiments, the at least one third material 44 is selected to provide a diffusion barrier layer configured to avoid (e.g., prevent; reduce; inhibit) the diffusion of the at least one second material 42 (e.g., tungsten) into the first material 32 (e.g., diamond). For example, a diffusion barrier layer may be graded from a carbide material at an interface with the first diamond material 32 to the at least one third material 44.In certain embodiments, the at least one third material 44 is configured to increase (e.g., improve; facilitate) the adhesion between the at least one second material 42 and the first material 32 and / or increase (e.g., improve; facilitate) the thermal conductivity between the at least one second material 42 and the first material 32.

[0027] In certain embodiments, the length L and the width W of the first material 32 can be selected to be sufficiently small to avoid (e.g., prevent; reduce; inhibit) interfacial tensions between the dissimilar first material 32 and the at least one second material 42, between the dissimilar first material 32 and the at least one third material 44, and / or between the dissimilar at least one second material 42 and the at least one third material 44. For example, the length L and the width W of the first material 32 can each be less than 2 millimeters.

[0028] In certain embodiments, the first material 32 (e.g., diamond) may be cut (e.g., laser cut) from a wafer or other structure (e.g., in strips). While Fig.1A-1C schematically illustrate certain embodiments in which the first material 32 has straight and smooth top, bottom, and side surfaces at perpendicular angles to each other. In certain other embodiments, the top, bottom, and / or side surfaces of the first material 32 are rough, irregular, or curved and / or are at non-perpendicular angles to each other. In certain embodiments, the at least one third material 44 may be applied to a top surface of the first material 32 (e.g., by a sputtering process such as magnetron sputtering). While Fig.1A-1C schematically illustrate certain embodiments in which the at least one second material 42 and the at least one third material 44 have straight and smooth top, bottom and side surfaces as well as side surfaces that are flush with the sides of the first material 32, in certain other embodiments the at least one second material 42 and / or the at least one third material 44 are rough, irregular or curved surfaces and / or the side surfaces extend beyond the top surface of the first material 32 (e.g., extending downward along the sides of the first material 32 below the top surface of the first material 32) and / or beyond one or more of the side surfaces of the first material 32 (e.g.extending outwardly in one or more directions parallel to the portion of the surface 22, such that the at least one second material 42 and / or the at least one third material 44 has a greater length and / or width than the first material 32). While. Fig. 1A-1C schematically illustrate certain embodiments in which the upper surface of the at least one second material 42 is parallel to the portion of the surface 22, in certain other embodiments the upper surface of the at least one second material 42 is not parallel to the portion of the surface 22.

[0029] The Fig. 2A and Fig. 2B schematically show portions of example X-ray targets 10 having a plurality of separated structures 30 according to certain embodiments described herein. In Fig.2A, the target 10 comprises three separate structures 30a, 30b, 30c arranged in a linear configuration, each of which comprises a respective first material 32a, 32b, 32c, at least one respective layer 40a, 40b, 40c over the respective first material 32a, 32b, 32c, and at least one respective second material 42a, 42b, 42c different from the respective first material 32a, 32b, 32c. In Fig.2B, the target 10 comprises twelve separate structures 30 arranged in a rectilinear array configuration, each of which comprises a respective first material 32, at least one respective layer 40 over the respective first material 32, and at least one respective second material 42 different from the respective first material 32. Other numbers of structures 30 (e.g., 2, 4, 5, 6, 7, 8, 9, 10, 11, or more) are also compatible with certain embodiments described herein.

[0030] In certain embodiments, the first materials 32 of two or more of the plurality of structures 30 may be the same (e.g., all first materials 32 are the same), the first materials 32 of two or more of the structures 30 may be different from each other, the second materials 42 of two or more of the structures 30 may be the same, and / or the second materials 42 of two or more of the structures 30 may be different from each other (e.g., all second materials 42 are different from each other). The X-rays generated by at least two of the structures 30 may have spectra (e.g., intensity distributions as functions of X-ray energy) that are different from each other (e.g., all spectra of the different structures 30 may be different from each other).Each of the plurality of structures 30 includes at least one third material 44 between the first material 32 and the second material 42, and the third materials 44 of the plurality of structures 30 may be the same and / or the third materials 44 of the plurality of structures 30 may be different from each other.

[0031] In certain embodiments, each of the structures 30 has a corresponding long dimension (e.g., the length L a , L b , L c ) along a first direction 34a, 34b, 34c parallel to the portion of the surface 22 and a corresponding short dimension (e.g. the width W a , W b , W c) along a second direction 36a, 36b, 36c perpendicular to the first direction 34a, 34b, 34c and parallel to the portion of the surface 22. The long dimensions of two or more of the plurality of structures 30 may be the same (e.g., all long dimensions are the same), the long dimensions of two or more of the plurality of structures 30 may be unequal, the short dimensions of two or more of the plurality of structures 30 may be the same (e.g., all short dimensions are the same), and / or the short dimensions of two or more of the structures may be unequal. In certain embodiments, each of the layers 40 has a corresponding thickness (e.g., t a , t b , t c) in a direction 38 perpendicular to the portion of the surface 22. The thicknesses of two or more of the plurality of structures 30 may be equal to one another (e.g., all thicknesses are the same) and / or the thicknesses of two or more of the structures 30 may not be equal to one another (e.g., all thicknesses are not the same). Adjacent structures 30 of certain embodiments are spaced apart from one another by separation distances in a direction parallel to the portion of the surface 22, and the separation distances range greater than 0.02 millimeters, 0.02 millimeters to 4 millimeters, 0.2 millimeters to 4 millimeters, 0.4 millimeters to 2 millimeters, 0.4 millimeters to 1 millimeter, or 1 millimeter to 4 millimeters. The separation distance between two first adjacent structures 30 and the separation distance between two second adjacent structures 30 may be equal to or unequal to one another.

[0032] As in Fig.2A, the example structures 30 are arranged in a linear configuration, wherein the structures 30 are aligned with each other (e.g., with their long dimensions along first directions 34a, 34b, 34c being parallel to each other, and with their short dimensions along second directions 36a, 36b, 36c being parallel to each other and / or coinciding with each other). In certain other embodiments, the structures 30 are not aligned with each other (e.g., have their long dimensions along the first directions 34a, 34b, 34c not parallel to each other and / or their short dimensions along the second directions 36a, 36b, 36c not parallel to each other and / or not coincident with each other). As in Fig.2B, the example structures 30 are arranged in a rectilinear array configuration, with a first set of structures 30 aligned with each other (e.g., with their long dimensions along first directions 34 parallel to each other and their short dimensions along second directions 36 parallel to each other and / or coincident with each other) and a second set of structures 30 aligned with each other and with the first set of structures 30 (e.g., with their long dimensions along first directions 34 parallel to and / or coincident with the long dimensions of the first set of structures 30). In certain other embodiments, the structures 30 of the array are not aligned with each other (e.g., not parallel to and / or not coincident with the long dimensions and / or short dimensions).Various other arrangements of the arrays of structures 30 are also compatible with certain embodiments described herein (e.g., non-rectilinear; non-aligned; non-equal separation distances; etc.). For example, a first set of structures 30 may have a first periodicity and a second set of structures 30 may have a second periodicity that differs from the first periodicity (e.g., different in one or two directions parallel to the portion of surface 22). In another example, one or both of the first set of structures and the second set of structures may be non-periodic (e.g., in one or two directions parallel to the portion of surface 22).

[0033] Fig.3 schematically illustrates an example x-ray source 100 of an example x-ray system 200 in accordance with certain embodiments described herein. The x-ray source 100 includes an x-ray target 10, as described herein, and an electron source 50 configured to generate electrons in at least one electron beam 52 and to direct the at least one electron beam 52 to impinge on one of the plurality of structures 30 of the x-ray target 10 in an electron beam spot 54 having a spot size. The electron source 50 may include an electron emitter having a donor cathode (e.g., tungsten or lanthanum hexaboride) configured to emit electrons (e.g., via thermionic or field emission) that are directed to impinge on the plurality of structures 30.The dispenser cathode of certain embodiments has an aspect ratio equal to an aspect ratio of the electron beam spot 54 impinging on the at least one structure 30. Example dispenser cathodes in accordance with certain embodiments described herein are marketed by Spectra-Mat, Inc. of Watsonville, CA (e.g., thermionic emitters impregnating a porous tungsten matrix with barium aluminate).

[0034] The electron source 50 further includes electron-optical components (e.g., deflection electrodes; grids; etc.) configured to receive the electrons emitted by the electron emitter, accelerate the electrons to a predetermined electron kinetic energy (e.g., in a range of 0.5 keV to 160 keV), shape (e.g., shape and / or focus) the at least one electron beam 52, and direct or steer the at least one electron beam 52 toward the target 10. Example configurations of electron-optical components in accordance with certain embodiments described herein include, but are not limited to, two-grid configurations and three-grid configurations. In certain embodiments, the x-ray target 10 is configured to be used as an anode (e.g.,set to a positive voltage relative to the electron source 50) to accelerate and / or otherwise modify the electron beam 52.

[0035] In certain embodiments, the kinetic energy of the at least one electron beam 52 is selected such that the electron penetration depth of the electrons of the at least one electron beam 52 within the at least one second material 42 is greater than the thickness t of the at least one second material 42. For example, the kinetic energy of the at least one electron beam 52 may be selected to correspond to a CSDA estimate of the electron penetration depth that is greater than the thickness t of the at least one second material 42 (e.g., a CSDA estimate of the electron penetration depth that is in a range of 1.5X to 2X the thickness t of the at least one second material 42).

[0036] In certain embodiments, the electron source 50 is positioned relative to the x-ray source 10 such that a center of the at least one electron beam 52 impinges on the plurality of structures 30 at a non-zero angle θ (e.g., angle of incidence) relative to the direction 38 perpendicular to the portion of the surface 22 or to the at least one layer 40 of the plurality of structures 30 that is greater than 20 degrees (e.g., in a range of 20 degrees to 50 degrees; in a range of 30 degrees to 60 degrees; in a range of 40 degrees to 70 degrees). The centerline 56 of the at least one electron beam 52 may lie in a plane defined by the direction 38 and the first direction 34, in a plane defined by the direction 38 and the second direction 36, or in another plane that is substantially perpendicular to the portion of the surface 22.The at least one electron beam 52 may have a rectangular beam profile, an oval beam profile, or another type of beam profile.

[0037] In certain embodiments, such as in Fig.3, the at least one electron beam 52 is focused onto the at least one layer 40 of the plurality of structures 30 such that the electron beam spot 54 has a maximum spot size with a full-width-at-half maximum FWHM (e.g., width of the region of the electron beam spot 54 in which the at least one electron beam 52 has an intensity of at least half the maximum intensity of the at least one electron beam 52) on the plurality of structures 30 that is smaller than the smallest dimension of the layer 40 in a direction parallel to the portion of the surface 22.For example, the maximum spot size of the electron beam spot 54 on the plurality of structures 30 in a direction parallel to the portion of the surface 22 may have a maximum width of 100 micrometers or less, 75 micrometers or less, 50 micrometers or less, 30 micrometers or less, or 15 micrometers or less. In certain embodiments, the maximum spot size at half maximum width (FWHM) has a first dimension in a direction parallel to the portion of the surface 22 (e.g., in the first direction 34) in a range of 5 micrometers to 20 micrometers and a second dimension in another direction (e.g., in the second direction 36) perpendicular to the direction and parallel to the portion of the surface 22 in a range of 20 micrometers to 200 micrometers (e.g.,the second dimension is in a range of 4X to 10X of the first dimension; the electron beam spot 54 has an aspect ratio in a range of 4:1 to 10:1).

[0038] In certain embodiments, an X-ray system 200 comprises the X-ray source 100 described herein and at least one X-ray optic 60 configured to receive X-rays 62 from the X-ray source 100 extending along a propagation direction with a take-off angle ψ (e.g., angle of a centerline 64 of a receiving cone of the at least one X-ray optic 60, wherein the angle is defined relative to a direction parallel to the portion of the surface 22) in a range of 0 degrees to 40 degrees (e.g., in a range of 0 degrees to 3 degrees; in a range of 2 degrees to 5 degrees; in a range of 4 degrees to 6 degrees; in a range of 5 degrees to 10 degrees). For example, the at least one X-ray optic 60 may be configured to receive X-rays 62 emitted by the X-ray source 100 (e.g.,through a window that is substantially transparent to the x-rays 62), and the takeoff angle ψ may lie in a plane perpendicular to the plane defined by the centerline 56 of the electron beam 52 and the direction 38. In certain embodiments, the takeoff angle ψ is selected such that the electron beam spot 54, when viewed along the centerline 64, is foreshortened at the takeoff angle ψ (e.g., to appear substantially symmetrical; to have a 1:1 aspect ratio). For example, the focal spot from which x-rays 62 are collected by the at least one x-ray optic 60 may have a maximum focal spot size across the full width at half maximum (FWHM) (e.g.,Width of the region of the focal spot in which the X-rays 62 have an intensity of at least half the maximum intensity of the X-rays 62) which is less than 20 micrometers, less than 15 micrometers or less than 10 micrometers.

[0039] Various configurations of the at least one X-ray optic 60 and the X-ray system 200 are compatible with certain embodiments described herein. For example, the at least one X-ray optic 60 may comprise at least one polycapillary-type or single-capillary-type optic with an internal reflective surface shaped like one or more portions of a quadratic function (e.g., portions of an ellipsoid and / or portions of mirrored paraboloids facing each other). The X-ray system 200 may comprise multiple X-ray optics 60, each optimized for efficiency for a particular X-ray energy of interest, and may be configured to selectively receive X-rays 62 from the X-ray target 10 (e.g., with each X-ray optic 60 paired with a corresponding structure 30 of the X-ray target 10).Various example x-ray optics 60 and x-ray systems 200 with which the x-ray source 100 described herein may be used in accordance with certain embodiments described herein are disclosed in U.S. Pat. Nos. 9,570,265, 9,823,203, 10,295,486, and 10,295,485, each of which is incorporated herein by reference in its entirety.

[0040] Fig. 4A and Fig. 4B schematically show further examples of an X-ray source 300 according to certain embodiments described herein. The X-ray source 300 includes an X-ray target 10 comprising a thermally conductive substrate 20 having a surface 22 and a plurality of structures 30 on or embedded in at least a portion of the surface 22 of the substrate 20 (see, e.g., Fig. 1A-1C and 2A-2B). The X-ray source 300 further comprises an electron source 50 (see, e.g., Fig.3) and a housing 310 containing a region 312 that is under vacuum (e.g., with a gas pressure of less than 1 Torr) and sealed from the atmosphere surrounding the housing 310. The region 312 contains the plurality of structures 30, and the at least one electron beam 52 from the electron source 50 is configured to propagate through a portion of the region 312 and impinge on a selected one of the plurality of structures 30.

[0041] In certain embodiments, the at least one structure 30 comprises a plurality of structures 30 that are separated from each other (see, for example, Fig.2A-2B), and at least one of the target 10 and the at least one electron beam 52 is configured to be controllably moved such that the at least one electron beam 52 impinges on a selected one of the plurality of structures 30 while the plurality of structures 30 remains in the sealed area 312. As described herein with respect to the Fig. 2A-2B, the second materials 42 of two or more of the plurality of structures 30 may be different from each other (e.g., all second materials 42 may be different from each other), such that the X-rays generated by at least two of the plurality of structures 30 may have spectra that are different from each other (e.g., all spectra may be different from each other), thereby advantageously providing a way to select between different X-ray spectra. Furthermore, as described herein with respect to the Fig.2A-2B, the second materials 42 of two or more of the structures 30 may be the same, thereby advantageously providing redundancy (e.g., in the event that one of the structures 30 is damaged or degraded, another of the structures 30 may be used instead). While Fig. 4A and Fig.4B schematically show the structures 30 aligned with their longitudinal dimensions along the first directions 34a, 34b, 34c perpendicular to the direction toward the at least one X-ray optics 60, one or more (e.g., all) of the structures 30 may alternatively have any other orientation relative to the direction toward the at least one X-ray optics 60 (e.g., in a plane defined by the direction toward the at least one X-ray optics 60 and the direction of the trajectory of the at least one electron beam 52). The at least one electron beam 52 may impinge on the structures 30 in a direction perpendicular to the surface 22 or to the at least one layer 40 of the structure 30 (e.g., an impingement angle of 0 degrees), as in Fig.4A, or in a direction with an incident angle θ not equal to zero (e.g., in a range of 10 degrees to 80 degrees; in a range of 10 degrees to 30 degrees; in a range of 20 degrees to 40 degrees; in a range of 30 degrees to 50 degrees; in a range of 40 degrees to 60 degrees; in a range of 50 degrees to 70 degrees; in a range of 60 degrees to 80 degrees; in a range greater than 70 degrees) relative to a direction perpendicular to the surface 22 or to the at least one layer 40 of the structure 30.

[0042] As in Fig. 4A, the electron source 50 is configured to selectively direct (e.g., deflect) the at least one electron beam 52 along a selected trajectory to impinge on a selected one of the plurality of structures 30 (e.g., using electron-optical components, such as deflection electrodes). As shown in Fig.4A, the X-ray target 10 can be aligned such that the at least one electron beam 52 impinges on the structures 30 in a direction perpendicular to the surface 22 or to the at least one layer 40 of the structure 30. In Fig. 4A, the movement of the at least one electron beam 52 is schematically indicated by the double-headed arrow, and each of the trajectories of the at least one electron beam 52 corresponding to the at least one electron beam 52 impinging on a selected one of the plurality of structures 30 is schematically indicated by a corresponding center line 56a, 56b, 56c, 56d of the at least one electron beam 52. The X-rays 62 emitted by the irradiated structure 30 and transmitted through an X-ray transparent window 314 of the housing 310 are captured by the at least one X-ray optics 60. In Fig.4A, each of the trajectories of the collected x-rays 62 corresponding to the at least one electron beam 52 impinging on a selected one of the plurality of structures 30 is schematically represented by a corresponding centerline 64a, 64b, 64c, 64d of the x-rays 62. In certain embodiments, the position and / or orientation of the at least one x-ray optic 60 can be adjusted to account for the focal spot of the x-rays 62 being located at different positions.

[0043] As in Fig. 4B, the X-ray source 300 further comprises a table 320 configured to move the X-ray target 10 relative to the electron source 50 such that a selected one of the plurality of structures 30 is struck by the at least one electron beam 52. As shown in Fig.4B, the X-ray target 10 can be aligned such that the at least one electron beam 52 impinges on the structures 30 at an incident angle θ different from zero relative to a direction perpendicular to the surface 22 or to the at least one layer 40 of the structure 30. In Fig.4B, a translation of the target 10 by the table 320 along a direction parallel to the surface 22 of the substrate 20 is schematically indicated by the double-headed arrow. In certain embodiments, the table 320 can translate the structures 30 in one direction, in two directions (e.g., perpendicular to each other), in three directions (e.g., three directions perpendicular to each other), and / or rotate the x-ray target 10 about one or more axes of rotation (e.g., two or more axes perpendicular to each other). In certain embodiments, one or more of the directions of translation of the target 10 by the table 320 can be in a direction perpendicular to the at least one electron beam 42. In certain embodiments, the table 320 includes components (e.g., actuators; sensors) located within the area 312 and other components (e.g., computer control; feedthroughs; motor) located at least partially outside the area 312.The table 320 has a sufficient range of motion to bring each of the structures 30 into a position where it is struck by the at least one electron beam 52.

[0044] The X-rays 62 emitted by the irradiated structure 30 and transmitted through an X-ray transparent window 314 of the housing 310 are collected by the at least one X-ray optic 60. In certain embodiments, the position of the source of the X-rays 62 remains unchanged when selecting between the different structures 30, thereby advantageously avoiding adjustments to the position and / or orientation of the at least one X-ray optic 60 to account for different positions of the X-ray focal point. In certain embodiments, a combination of the selectively directed electron beam 52 and the selectively movable stage 320 can be used.

[0045] While conventional sealed tube X-ray sources typically offer focal spot sizes of about 1 millimeter and low brightness, certain embodiments described herein can provide an X-ray source having a much smaller focal spot size and much higher brightness. Certain embodiments described herein utilize at least one electron beam 52 focused onto structure 30, with a focal spot size (e.g., FWHM diameter) in a range of 0.5 µm to 100 µm (e.g., 2 µm; 5 µm; 10 µm; 20 µm; 50 µm), a total power in a range of 5 W to 1 kW (e.g., 10 W; 30-80 W; 100 W; 200 W), and a power density in a range of 0.2 W / µm 2 up to 100 W / µm 2 (e.g., 0.3 - 0.8 W / µm 2 ; 2.5 W / µm 2 ; 8 W / µm 2 ; 40 W / µm 2 ) and the X-ray brightness (e.g. proportional to the electron beam power density) in a range of 0.5×10 10Photons / mm 2 / mrad 2 up to 5×10 12 Photons / mm 2 / mrad 2 (e.g., 1-3×10 10 Photons / mm 2 / mrad 2 ; 1×10 11 Photons / mm 2 / mrad 2 ; 3×10 11 Photons / mm 2 / mrad 2 ; 2×10 12 Photons / mm 2 / mrad 2 ).

[0046] Furthermore, by having multiple structures 30 selectively impacted by the at least one electron beam 52, certain embodiments described herein may provide such small focal spot sizes and higher brightnesses with the flexibility to select one X-ray spectrum from a plurality of X-ray spectra by computer-controlled movement of the at least one electron beam 52 and / or the X-ray target 10 while remaining under vacuum (e.g., without breaking the vacuum, replacing one X-ray target with another, and pumping down to return to vacuum conditions). By moving the X-ray target 10 with 1-micrometer or sub-micrometer accuracy, certain embodiments advantageously avoid re-alignment of the at least one X-ray optic 60 and / or other components of the X-ray system 200.

[0047] By providing multiple selectable X-ray spectra, certain embodiments described herein can be advantageously used in various types of X-ray instruments that utilize a microfocus X-ray spot, including, without limitation: X-ray microscopy, X-ray fluorescence (XRF), X-ray diffraction (XRD), X-ray tomography; X-ray scattering (e.g., SAXS; WAXS); X-ray absorption spectroscopy (e.g., XANES; EXAFS); and X-ray emission spectroscopy.

[0048] Fig. 5A schematically shows an example X-ray target 10 with discrete structures 30 in accordance with certain embodiments described herein, and Fig. 5B-5I show schematically different simulation results of the brightness of different versions of the example X-ray target 10 of Fig.5A in accordance with certain embodiments described herein. Each structure 30 has a metal layer 40 (e.g., tungsten; copper) on a first material 32 of diamond that is at least partially embedded in a copper substrate 20. Fig. 5B-5I compare these simulation results of the brightness with those corresponding to an exemplary conventional X-ray target with a continuous thin metal film (e.g., tungsten; copper) deposited on a continuous diamond layer on a copper substrate. The brightness in Fig. 5B-5I is defined as the number of emitted photons per unit area and unit solid angle per incident electron (e.g. photons / electron / µm 2 / Steradian).

[0049] In the simulations of the Fig. 5B, Fig. 5C, Fig. 5E, Fig. 5F, Fig. 5G and Fig.5I, each structure 30 has a width of 1 µm and the structures 30 are spaced from each other (e.g., between adjacent edges) by 2 µm (e.g., with a pitch of 3 µm and a duty cycle of 1:2), as in Fig. 5A. For the simulations in Fig. 5D and Fig. 5H, each structure 30 has a width of 1 µm and the structures 30 are spaced 1 µm apart (e.g., between adjacent edges) (e.g., with a pitch of 2 µm and a duty cycle of 1:1). According to thermal modeling calculations, the X-ray target 10 can be Fig. 5A at the same maximum temperature, an electron power density four times higher than that of a solid copper anode (e.g., 65 W versus 12.5 W). In the simulation results of the Fig.5B-5I, the power of the electron beam 52 was increased by 1.3 times at an incidence angle of 60 degrees compared to an incidence angle of 0 degrees to account for the larger proportion of stray electrons at higher incidence angles.

[0050] Fig. 5B compares the brightness of X-rays as a function of the take-off angle and for three incidence angles (0, 30, and 60 degrees) generated by a 25 kV electron beam emitted from (i) a conventional tungsten target and (ii) an example target 10 having structures 30 with a tungsten layer 40 in accordance with certain embodiments described herein with a duty cycle of 1:2. On the left side of Fig. 5B shows the brightness for X-rays with energies of 810 keV and on the right side of Fig. Figure 5B shows the brightness for X-rays with energies of 3-25 keV.

[0051] Fig.5C compares the brightness of X-rays as a function of the take-off angle and for three incidence angles (0, 30, and 60 degrees) generated by a 35 kV electron beam emitted from (i) a conventional tungsten target and (ii) an example target 10 having structures 30 with a tungsten layer 40 according to certain embodiments described herein with a duty cycle of 1:2. On the left side of Fig. 5C shows the brightness for X-rays with energies of 810 keV and on the right side of Fig. Figure 5C shows the brightness for X-rays with energies of 3-35 keV.

[0052] Fig.Figure 5D shows the brightness of X-rays as a function of the take-off angle and for three incidence angles (0, 30, and 60 degrees) generated by a 35 kV electron beam and emitted from an example target 10 having structures 30 with a tungsten layer 40 in accordance with certain embodiments described herein with a duty cycle of 1:1. On the left side of Fig. 5D shows the brightness for X-rays with energies of 810 keV and on the right side of Fig. Figure 5C shows the brightness for X-rays with energies of 3-35 keV.

[0053] Fig.5E compares the brightness of X-rays as a function of the take-off angle and for three incidence angles (0, 30, and 60 degrees) generated by a 50 kV electron beam emitted from (i) a conventional tungsten target and (ii) an example target 10 having structures 30 with a tungsten layer 40 in accordance with certain embodiments described herein with a duty cycle of 1:2. On the left side of Fig. 5E shows the brightness for X-rays with energies of 810 keV and on the right side of Fig. Figure 5E shows the brightness for X-rays with energies of 3-50 keV.

[0054] Fig.5F compares the brightness of X-rays as a function of the take-off angle and for three incidence angles (0, 30, and 60 degrees) generated by a 25 kV electron beam emitted from (i) a conventional copper target and (ii) an example target 10 having structures 30 with a copper layer 40 according to certain embodiments described herein with a duty cycle of 1:2. On the left side of Fig. 5F shows the brightness for X-rays with energies of 79 keV and on the right side of Fig. Figure 5E shows the brightness for X-rays with energies of 3-25 keV.

[0055] Fig.5G compares the brightness of X-rays as a function of the take-off angle and for three incidence angles (0, 30, and 60 degrees) generated by a 35 kV electron beam emitted from (i) a conventional copper target and (ii) an example target 10 having structures 30 with a copper layer 40 according to certain embodiments described herein with a duty cycle of 1:2. On the left side of Fig. 5G is the brightness for X-rays with energies of 79 keV and on the right side of Fig. 5G represents the brightness for X-rays with energies of 3-35 keV.

[0056] Fig.5H compares the brightness of X-rays as a function of the take-off angle and for three incidence angles (0, 30, and 60 degrees) generated by a 35 kV electron beam and emitted from an example target 10 having structures 30 with a copper layer 40 in accordance with certain embodiments described herein with a 1:1 duty cycle. On the left side of Fig. 5H shows the brightness for X-rays with energies of 79 keV and on the right side of Fig. 5H shows the brightness for X-rays with energies of 3-35 keV.

[0057] Fig.Figure 5I compares the brightness of X-rays as a function of the take-off angle and for three incidence angles (0, 30, and 60 degrees) generated by a 50 kV electron beam emitted from (i) a conventional copper target and (ii) an example target 10 having structures 30 with a copper layer 40 according to certain embodiments described herein with a duty cycle of 1:2. On the left side of Fig. 5I shows the brightness for X-rays with energies of 79 keV and on the right side of Fig. 5I shows the brightness for X-rays with energies of 3-50 keV.

[0058] As these simulation results demonstrate, the example targets 10, in accordance with certain embodiments described herein, exhibit higher brightnesses than conventional targets. For a tungsten layer with an incidence angle of 60 degrees and a takeoff angle of 5 degrees and for the three electron beam energies (25 kV, 35 kV, 50 kV), Table 1A shows the brightnesses (photons / electron / µm 2 / steradian) of X-rays with energies of 8-10 keV and Table 1B shows the brightnesses (photons / electron / µm 2 / steradian) of X-rays with energies greater than 3 keV. These results were obtained assuming that the example target 10 has four times the heat dissipation of the conventional target and with a correction of 1.3 times to account for the higher electron scattering at an angle of incidence or impact of 60 degrees compared to 0 degrees. Table 1A: Electron energy Brightness of conventional target Brightness of example target 10 Brightness ratio 25kV 1.26E-07 3.64E-07 2.90 35kV 2.28E-07 8.02E-07 3.52 50kV 3.32E-07 1.42E-06 4.27 Table 1B: Electron energy Brightness of conventional target Brightness of example target 10 Brightness ratio 25kV 3.85E-07 8.86E-07 2.30 35kV 6.12E-07 1.58E-06 2.59 50kV 8.98E-07 2.66E-06 2.96

[0059] For a copper layer with an incidence angle of 60 degrees and a take-off angle of 5 degrees and for the three electron beam energies (25kV, 35kV, 50kV), Table 2A shows the brightnesses (photons / electron / µm 2 / steradian) of X-rays with energies of 7-9 keV and Table 2B the brightnesses (photons / electron / µm 2 / steradian) of X-rays with energies greater than 3 keV. These results were obtained assuming that the example target 10 has four times the heat dissipation of the conventional target and with a correction of 1.3 times to account for the higher electron scattering at an angle of incidence or impact of 60 degrees compared to 0 degrees. Table 2A: Electron energy Brightness of conventional target Brightness of example target 10 Brightness ratio 25kV 1.85E-07 4.55E-07 2.46 35kV 2.96E-07 8.56E-07 2.89 50kV 4.69E-07 1.41E-06 3.00 Table 2B: Electron energy Brightness of conventional target Brightness of example target 10 Brightness ratio 25kV 3.67E-07 8.52E-07 2.32 35kV 5.64E-07 1.43E-06 2.53 50kV 8.32E-07 2.26E-06 2.71

[0060] Various configurations have been described above. Although this invention has been described with reference to these specific configurations, the descriptions are intended to illustrate the invention and are not intended to limit the invention. Various modifications and applications may be made by 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 acts or operations comprising the method / process may be performed in any suitable order and are not necessarily limited to any particular disclosed order. Features or elements from the various embodiments and examples described above may be combined with one another to produce alternative configurations compatible with the embodiments disclosed herein.Various aspects and advantages of the embodiments have been described where appropriate. It should be understood that not all of these aspects or advantages may necessarily be achieved in accordance with a particular embodiment. For example, it should be recognized that the various embodiments may be practiced in a manner to achieve one advantage or group of advantages taught herein without necessarily achieving other aspects or advantages that may be taught or suggested herein.

Claims

[1] An X-ray target (10) comprising: a thermally conductive substrate (20) having a surface (22); and a plurality of structures (30) which are separated from one another, on or embedded in at least a portion of the surface (22), each of the at least two structures (30) of the plurality of structures (30) comprising: a thermally conductive first material (32) in thermal communication with the substrate (20), and at least one layer (40) over the first material (32), wherein the at least one layer (40) comprises at least one second material (42) that is different from the first material (32), wherein the at least one second material (42) is configured to generate X-rays when irradiated by electrons, wherein the first materials (32) of the at least two structures (30) are separated from each other and the at least one second material (42) of the at least two structures (30) are separated from each other and different from each other, and wherein the at least one layer (40) further comprises at least one third material (44) between the first material (32) and the at least one second material (42), wherein the at least one third material (44) is different from the first material (32) and the at least one second material (42), and the at least one third material (44) has a thickness between 2 nanometers and 50 nanometers and / or the at least one third material (44) comprises at least one of the following materials: titanium nitride, iridium, chromium, beryllium and hafnium oxide. [2] The X-ray target (10) according to claim 1, wherein the first material (32) comprises diamond and / or silicon carbide. [3] The X-ray target (10) of claim 1, wherein the at least one layer (40) has a thickness (T) in a range of 1 micrometer to 20 micrometers. [4] The X-ray target (10) of claim 1, wherein the first materials (32) of the at least two structures (30) are the same. [5] The x-ray target (10) of claim 1, wherein a first structure of the at least two structures (30) is configured to generate x-rays having a first energy spectrum and a second structure of the at least two structures is configured to generate x-rays having a second energy spectrum, the second energy spectrum being different from the first energy spectrum. [6] The X-ray target (10) of claim 1, wherein the at least one second material (42) comprises at least one of the following materials: tungsten, chromium, copper, aluminum, rhodium, molybdenum, gold, platinum, iridium, cobalt, tantalum, titanium, rhenium, silicon carbide, tantalum carbide, titanium carbide, boron carbide, and alloys or combinations containing one or more of these. [7] An X-ray source (100) comprising: an X-ray target (10) comprising: a thermally conductive substrate (20) having a surface (22); and a plurality of structures (30) separated from one another, on or embedded in at least a portion of the surface (22), each of the at least two structures of the plurality of structures (30) comprising: a thermally conductive first material (32) in thermal communication with the substrate (20), and at least one layer (40) over the first material (32), the at least one layer comprising at least one second material (42) different from the first material (32), the first materials (32) of the at least two structures (30) being separate from each other and the at least one second material (42) of the at least two structures being separate from each other and different from each other; and wherein the at least one layer (40) further comprises at least one third material (44) between the first material (32) and the at least one second material (42), wherein the at least one third material (44) is different from the first material (32) and the at least one second material (42), and the at least one third material (44) has a thickness between 2 nanometers and 50 nanometers and / or the at least one third material (44) comprises at least one of the following materials: titanium nitride, iridium, chromium, beryllium and hafnium oxide, wherein an electron source (50) configured to generate electrons in at least one electron beam (52) and to direct the at least one electron beam to impinge on the plurality of structures (30). [8] The x-ray source (100) of claim 7, wherein the at least one second material (42) has a thickness (T) that is less than the electron penetration depth of the electrons into the at least one second material (42). [9] The x-ray source (100) of claim 7, wherein the at least one electron beam (52) creates an electron beam spot (54) on the plurality of structures (30), the electron beam spot (54) having a first dimension in a range between 5 and 20 micrometers in a first direction parallel to the portion of the surface and a second dimension in a second direction parallel to the portion of the surface and perpendicular to the first direction in a range between 20 and 200 micrometers. [10] The x-ray source (100) of claim 7, wherein the at least one electron beam (52) creates an electron beam spot (54) on the plurality of structures (30), the electron beam spot (52) having an aspect ratio in a range of 4:1 to 10:

1. [11] The x-ray source (100) of claim 7, wherein the at least one electron beam (52) impinges on the plurality of structures (30) such that a centerline (56) of the at least one electron beam is at a non-zero angle relative to a direction perpendicular to the portion of the surface. [12] The x-ray source (100) of claim 11, wherein the non-zero angle is in a range of 50 to 70 degrees. [13] A method comprising: Irradiating a first selected structure from a plurality of structures (30) with at least one electron beam (52), wherein the plurality of structures (30) are separated from one another and are arranged on or embedded in at least a portion of the surface (22) of a thermally conductive substrate (20), each of the at least two structures of the plurality of structures (30) comprising: a thermally conductive first material (32) in thermal communication with the substrate (20), at least one layer (40) over the first material, the at least one layer comprising at least one second material (42) different from the first material, the at least one second material (42) being configured to generate x-rays when irradiated by the first electron beam (52), and at least one third material (44) between the first material (32) and the at least one second material (42), wherein the at least one third material (44) is different from the first material (32) and the at least one second material (42), and the at least one third material (44) has a thickness between 2 nanometers and 50 nanometers and / or the at least one third material (44) comprises at least one of the following materials: titanium nitride, iridium, chromium, beryllium and hafnium oxide; controllable movement of the substrate (20) and / or the at least one electron beam (52) relative to each other; and Irradiating a second selected structure from the plurality of structures (30) with the at least one electron beam. [14] The method of claim 13, wherein the x-rays generated by irradiating the first selected structure (30) have a first energy spectrum and the x-rays generated by irradiating the second selected structure have a second energy spectrum, the second energy spectrum being different from the first energy spectrum. [15] The method of claim 13, wherein the plurality of structures (30) are located in a sealed area (312) and the controllable movement of the substrate and / or the at least one electron beam takes place while the plurality of structures remains within the sealed area (312). [16] The method of claim 13, wherein controllably moving the substrate (20) and / or the at least one electron beam (52) relative to each other comprises moving the substrate (20) along a direction parallel to the surface. [17] An X-ray target (10) comprising: a thermally conductive substrate (20) having a surface (22); and a plurality of structures (30) which are separated from one another, on or embedded in at least a portion of the surface (22), wherein the plurality of structures (30) comprises: a thermally conductive first material (32) in thermal communication with the substrate (20), the first material (32) having a length (L) along a first direction parallel to the portion of the surface (22) in a range greater than 1 millimeter and a width (W) along a second direction parallel to the portion of the surface and perpendicular to the first direction, the width (W) being in a range of 0.2 millimeters to 3 millimeters; and at least one layer (40) over the first material, the at least one layer comprising at least one second material (42) different from the first material (32), the at least one layer having a thickness (T) in a range of 2 micrometers to 50 micrometers, the at least one second material (42) being configured to generate X-rays when irradiated by electrons having energies in an energy range of 0.5 keV to 160 keV; and at least one third material (44) between the first material (32) and the at least one second material (42), wherein the at least one third material (44) differs from the first material (32) and the at least one second material (42), and the at least one third material (44) comprises at least one of the following materials: titanium nitride, iridium, chromium, beryllium and hafnium oxide. [18] The X-ray target (10) of claim 17, wherein the surface (22) comprises copper. [19] The X-ray target (10) of claim 17, wherein the at least one second material (42) comprises at least one of the following materials: tungsten, chromium, copper, aluminum, rhodium, molybdenum, gold, platinum, iridium, cobalt, tantalum, titanium, rhenium, silicon carbide, tantalum carbide, titanium carbide, boron carbide, and alloys or combinations containing one or more of these. [20] The X-ray target (10) of claim 17, wherein the X-ray beams generated by two or more of the structures (30) have intensity distributions as functions of energy that differ from each other. [21] The x-ray target (10) of claim 17, wherein the at least one second material (42) is electrically conductive and in electrical communication with an electrical potential, wherein the at least one second material (42) is configured to prevent charging of the at least one second material (42) due to electron irradiation. [22] An X-ray source (100) comprising: an X-ray target (10) comprising: a thermally conductive substrate (20) having a surface (22); and a plurality of structures (30) separated from one another, on or embedded in at least one portion of the surface (22), wherein the plurality of structures (30) comprises: a thermally conductive first material (32) in thermal communication with the substrate (20), the first material (32) having a length (L) along a first direction parallel to the portion of the surface in a range greater than 1 millimeter and a width (W) along a second direction parallel to the portion of the surface and perpendicular to the first direction, the width (W) being in a range of 0.2 millimeters to 3 millimeters; and at least one layer (40) over the first material, the at least one layer comprising at least one second material (42) different from the first material (32), the at least one layer (40) having a thickness (T) in a range of 2 micrometers to 50 micrometers, the at least one second material (42) being configured to generate X-rays when irradiated by electrons having energies in an energy range of 0.5 keV to 160 keV; and at least one third material (44) between the first material (32) and the at least one second material (42), wherein the at least one third material (44) differs from the first material (32) and the at least one second material (42), and the at least one third material (44) comprises at least one of the following materials: titanium nitride, iridium, chromium, beryllium and hafnium oxide; and an electron source (50) configured to generate electrons in at least one electron beam (52) and to direct the at least one electron beam (52) to impinge on the plurality of structures (30). [23] The x-ray source (100) of claim 22, wherein the at least one electron beam (52) on the plurality of structures (30) has a spot size (54) with a full width at half maximum (FWHM) having a maximum value of 15 micrometers or less. [24] X-ray system (200) comprising the X-ray source (100) according to claim 22. [25] The x-ray system (200) of claim 24, further comprising at least one x-ray optic (60) configured to receive x-ray beams (62) from the x-ray source (100) propagating along a propagation direction having a decay angle relative to the portion of the surface, the decay angle being in a range of 0 degrees to 40 degrees.

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