Patent Application
20200350138
This application relates generally to x-ray sources.
Laboratory x-ray sources generally bombard a metal target with electrons, with the deceleration of these electrons producing Bremsstrahlung x-rays of all energies from zero to the kinetic energy of the electrons. In addition, the metal target produces x-rays by creating holes in the inner core electron orbitals of the target atoms, which are then filled by electrons of the target with binding energies that are lower than the inner core electron orbitals, with concomitant generation of x-rays with energies that are characteristic of the target atoms. Most of the power of the electrons irradiating the target is converted into heat (e.g., about 60%) and backscattered electrons (e.g., about 39%), with only about 1% of the incident power converted into x-rays. Melting of the x-ray target due to this heat can be a limiting factor for the ultimate brightness (e.g., photons per second per area per steradian) achievable by the x-ray source.
Transmission-type x-ray sources configured to generate microfocus or nanofocus x-ray beams generally utilize targets comprising a thin sputtered metal layer (e.g., tungsten) over a thermally conductive, low density substrate material (e.g., diamond). The metal layer on one side of the target is irradiated by electrons, and the x-ray beam comprises x-rays emitted from the opposite side of the target. The x-ray spot size is dependent on the electron beam spot size, and in addition, due to electron bloom within the target, the x-rays generated and emitted from the target have an effective focal spot size that is larger than the focal spot size of the incident electron beam. As a result, transmission-type x-ray sources generating microfocus or nanofocus x-ray beams generally require very thin targets and very good electron beam focusing.
Conventional reflection-type x-ray sources irradiate a surface of a bulk target metal (e.g., tungsten) and collect the x-rays transmitted from the irradiated target surface at a take-off angle (e.g., 6-30 degrees) relative to the irradiated target surface, with the take-off angle selected to optimize the accumulation of x-rays while balancing with self-absorption of x-rays produced in the target. Because the electron beam spot at the target is effectively seen at an angle in reflection-type x-ray sources, the x-ray source spot size can be smaller than the electron beam spot size in transmission-type x-ray sources.
Certain embodiments described herein provide an x-ray target. The x-ray target comprises a thermally conductive substrate comprising a surface and at least one structure on or embedded in at least a portion of the surface. The at least one structure 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 millimeter 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 microns to 50 microns. The at least one second material is configured to generate x-rays upon irradiation by electrons having energies in an energy range of 0.5 keV to 160 keV.
Certain embodiments described herein provide an x-ray source. The x-ray source comprises an x-ray target comprising a thermally conductive substrate comprising a surface and at least one structure on or embedded in at least a portion of the surface. The at least one structure 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 millimeter 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 microns to 50 microns. The at least one second material is configured to generate x-rays upon irradiation by electrons having energies in an energy range of 0.5 keV to 160 keV. 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 the at least one structure.
Certain embodiments described herein provide a reflection-type x-ray source which 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., utilizing less rigorous electron beam focusing as compared to that used in transmission-type x-ray sources).
Certain embodiments described herein advantageously provide a reflection-type x-ray source with a high brightness of x-rays while avoiding the deleterious effects of excessive heating of the target. By using a cooled substrate and a high thermal conductivity first material (e.g., diamond) in thermal communication with the substrate and having a target layer of a second material deposited on the first material, heat can advantageously be removed from the target layer at a rate faster than would be achieved by removing the heat through bulk target material.
Certain embodiments described herein advantageously provide a reflection-type x-ray source with multiple target materials within a “sealed tube” source. By configuring the x-ray source to use an electron beam to irradiate a selected target material of the multiple target materials, with each target material generating 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 so that the x-ray source can be optimized for different applications, without having to open the x-ray source to change targets and to pump down the x-ray source each time.
In certain embodiments, the target 10 is configured to transfer heat away from the at least one structure 30. For example, the surface 22 of the substrate 20 can comprise at least one thermally conductive material and the remaining portion of the substrate 20 can comprise the same at least one thermally conductive material and/or another one 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 conducting 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 comprises elements with atomic numbers less than or equal to 14. The surface 22 of the substrate 20 is electrically conductive in certain embodiments and is configured to be in electrical communication with an electrical potential (e.g., electrical ground) and is configured to prevent charging of the surface 22 due to electron irradiation of the target 10. In certain embodiments, the target 10 comprises a heat transfer structure in thermal communication with the substrate 20 and configured to transfer heat away from the target 10. Examples of heat transfer structures include but are not limited to, heat sinks, heat pipes, and fluid flow conduits configured to have a fluid coolant (e.g., liquid; water; deionized water; air; refrigerant; heat transfer fluid such as Galden® Perfluoropolyether fluorinated fluids marketed by Solvay S.A. of Brussels, Belgium) flow therethrough and to transfer heat away from the substrate 20 (e.g., at a rate similar to the power loading rate of the target 10 from the electron irradiation).
In certain embodiments, the thermally conductive first material 32 is configured to be adhered (e.g., joined; 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 can be soldered or brazed onto the surface 22 with a thermally conductive soldering or brazing material, examples of which include but are not limited to: CuSil-ABA® or Nioro® brazing alloys marketed by Morgan Advanced Materials of Windsor, Berkshire, United Kingdom; gold/copper braze alloys. As schematically illustrated in
Examples of the first material 32 include but are not limited to, at least one of: diamond, silicon carbide, beryllium, and sapphire. While
In certain embodiments, the at least one second material 42 of the at least one layer 40 is selected to generate x-rays having a predetermined energy spectrum (e.g., x-ray intensity distribution as function of x-ray energy) upon irradiation by electrons having energies in the energy range of 0.5 keV to 160 keV. Examples of the at least one second material 42 include but are not limited to, at least one of: 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 including one or more thereof. In certain embodiments, the thickness t of the second material 42 is the largest extent of the second material 42 in the direction 38 perpendicular to the portion of the surface 22, and can be in a range of 2 microns to 50 microns, 2 microns to 20 microns, 2 microns to 15 microns, 4 microns to 15 microns, 2 microns to 10 microns, or 2 microns to 6 microns. In certain embodiments, the thickness t of the at least one second material 42 is substantially uniform across the whole area of the layer 40, while in certain other embodiments, the thickness t of the at least one second material 42 varies across the area 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, the second thickness larger than the first thickness).
In certain embodiments, the thickness t of the at least one second material 42 is selected as a function of the kinetic energy of the at least one electron beam irradiating the at least one structure 30. The electron penetration depth of electrons within a material is dependent 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 to be less than the electron penetration depth of the electrons in the at least one second material 42. For example, the continuous slowing down approximation (CSDA) can provide an estimate of the electron penetration depth for the electrons of a selected kinetic energy incident on the at least one second material 42, and the thickness t of the at least one second material 42 can be selected to be in a range of 50% to 70% of the CSDA estimate.
The at least one second material 42 in certain embodiments is configured to be in electrical communication with an electrical potential (e.g., electrical ground) and is configured to prevent charging of the at least one second material 42 due to electron irradiation. For example, electrically conductive soldering or brazing material (not shown in
In certain embodiments, as schematically illustrated by
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 stress 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, each of the length L and the width W of the first material 32 can be less than 2 millimeters.
In certain embodiments, the first material 32 (e.g., diamond) can be cut (e.g., laser-cut) from a wafer or other structure (e.g., in strips). While
In certain embodiments, the first materials 32 of two or more of the structures 30 can be the same as one another (e.g., all the first materials 32 the same as one another), the first materials 32 of two or more of the structures 30 can be different from one another, the second materials 42 of two or more of the structures 30 can be the same as one another, and/or the second materials 42 of two or more of the structures 30 can be different from one another (e.g., all the second materials 42 different from one another). The x-rays generated by at least two of the structures 30 can have spectra (e.g., intensity distributions as functions of x-ray energy) that are different from one another (e.g., all the spectra from the different structures 30 can be different from one another). In certain embodiments, some or all of the structures 30 can comprise at least one third material 44 between the first material 32 and the second material 42, and the third materials 44 of two or more of the structures 30 can be the same as one another and/or the third materials 44 of two or more of the structures 30 can be different from one another.
In certain embodiments, each of the structures 30 has a corresponding long dimension (e.g., length La, Lb, Lc) along a first direction 34a, 34b, 34c parallel to the portion of the surface 22 and a corresponding short dimension (e.g., width Wa, Wb, Wc) 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 structures 30 can be equal to one another (e.g., all the long dimensions equal to one another), the long dimensions of two or more of the structures 30 can be non-equal to one another, the short dimensions of two or more of the structures 30 can be equal to one another (e.g., all the short dimensions equal to one another), and/or the short dimensions of two or more of the structures can be non-equal to one another. In certain embodiments, each of the layers 40 has a corresponding thickness (e.g., ta, tb, tc) in a direction 38 perpendicular to the portion of the surface 22. The thicknesses of two or more of the structures 30 can be equal to one another (e.g., all the thicknesses equal to one another) and/or the thicknesses of two or more of the structures 30 can be non-equal to one another (e.g., all the thicknesses non-equal to one another). Adjacent structures 30 of certain embodiments are spaced from one another by separation distances in a direction parallel to the portion of the surface 22, and the separation distances are in a range greater than 0.02 millimeter, 0.02 millimeter to 4 millimeters, 0.2 millimeter to 4 millimeters, 0.4 millimeter to 2 millimeters, 0.4 millimeter to 1 millimeter, or 1 millimeter to 4 millimeters. The separation distance between a first two adjacent structures 30 and the separation distance between a second two adjacent structures 30 can be equal to one another or non-equal to one another.
As schematically illustrated in
The electron source 50 further comprises electron optics components (e.g., deflection electrodes; grids; etc.) configured to receive the electrons emitted from the electron emitter, to accelerate the electrons to a predetermined electron kinetic energy (e.g., in a range of 0.5 keV to 160 keV), to form (e.g., shape and/or focus) the at least one electron beam 52, and to direct the at least one electron beam 52 onto the target 10. Example configurations of electron optics 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 at a positive voltage relative to the electron source 50) to accelerate and/or otherwise modify the electron beam 52.
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 can 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 1.5× to 2× of the thickness t of the at least one second material 42).
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 the at least one structure 30 at a non-zero angle θ (e.g., impact angle) relative to the direction 38 perpendicular to the portion of the surface 22 or to the at least one layer 40 of the structure 30 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 center line 56 of the at least one electron beam 52 can be 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 substantially perpendicular to the portion of the surface 22. The at least one electron beam 52 can have a rectangular-type beam profile, an oval-type beam profile, or another type of beam profile.
In certain embodiments, as schematically illustrated in
In certain embodiments, an x-ray system 200 comprises the x-ray source 100 as described herein and at least one x-ray optic 60 configured to receive x-rays 62 from the x-ray source 100 propagating along a propagation direction having a take-off angle ψ (e.g., angle of a center line 64 of an acceptance cone of the at least one x-ray optic 60, the angle 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 can be configured to receive x-rays 62 emitted from the x-ray source 100 (e.g., through a window substantially transparent to the x-rays 62) and the take-off angle ψ can be in a plane perpendicular to the plane defined by the center line 56 of the electron beam 52 and the direction 38. In certain embodiments, the take-off angle ψ is selected such that the electron beam spot 54, when viewed along the center line 64 at the take-off angle ψ, is foreshortened (e.g., to appear to be substantially symmetric; to appear to have an aspect ratio of 1:1). For example, the focal spot from which x-rays 62 are collected by the at least one x-ray optic 60 can have a full-width-at-half maximum focal spot size (e.g., width of the region of the focal spot at which the x-rays 62 have an intensity of at least one-half of the maximum intensity of the x-rays 62) that is less than 20 microns, less than 15 microns, or less than 10 microns.
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 can comprise at least one of a polycapillary-type or single capillary-type optic, with an inner reflecting surface having a shape of one or more portions of a quadric function (e.g., portion of an ellipsoid and/or portions of mirrored paraboloids facing one another). The x-ray system 200 can comprise multiple x-ray optics 60, each optimized for efficiency for a specific x-ray energy of interest, and can be configured to selectively receive x-rays 62 from the x-ray target 10 (e.g., 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 disclosed herein can 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 in its entirety by reference herein.
In certain embodiments, the at least one structure 30 comprises a plurality of structures 30 separate from one another (see, e.g.,
As schematically illustrated in
As schematically illustrated in
The x-rays 62 emitted from 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 among the different structures 30, thereby advantageously avoiding adjustments of the position and/or orientation of the at least one x-ray optic 60 to account for different positions of the x-ray focal spot. In certain embodiments, a combination of the selectively directed electron beam 52 and the selectively movable stage 320 can be used.
While conventional sealed-tube x-ray sources typically provide focal spot sizes of about 1 millimeter and low brightness, certain embodiments described herein can provide an x-ray source that has a much smaller focal spot size and much higher brightness. Certain embodiments described herein utilize at least one electron beam 52 focused and incident onto the structure 30 with a spot size (e.g., full-width-at-half-maximum 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/μm2 to 100 W/μm2 (e.g., 0.3-0.8 W/μm2; 2.5 W/μm2; 8 W/μm2; 40 W/μm2) and the x-ray brightness (e.g., proportional to the electron beam power density) is in a range of 0.5×1010 photons/mm2/mrad2 to 5×1012 photons/mm2/mrad2 (e.g., 1-3×1010 photons/mm2 photons/mm2; 1×1011 photons/mm2/mrad2; 3×1011 photons/mm2/mrad2; 2×1012 photons/mm2/mrad2).
In addition, by having multiple structures 30 that are selectively impinged by the at least one electron beam 52, certain embodiments described herein can provide such small focal spot sizes and higher brightnesses with the flexibility to select an 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 having to break vacuum, replace one x-ray target with another, and pump down to return to vacuum conditions). By moving the x-ray target 10 with 1 micron or sub-micron 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.
By providing multiple selectable x-ray spectra, certain embodiments described herein can advantageously be used in various types of x-ray instrumentation that utilize a microfocus x-ray spot, including but not limited to: 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.
For the simulations of
As shown by these simulation results, the example targets 10 in accordance with certain embodiments described herein exhibit higher brightnesses than do conventional targets. For a tungsten layer with an impact angle of 60 degrees and a take-off angle of 5 degrees and for the three electron beam energies (25 kV, 35 kV, 50 kV), Table 1A shows the brightnesses (photons/electron/m2/steradian) of x-rays having energies 8-10 keV and Table 1B shows the brightnesses photons/electron/m2/steradian) of x-rays having energies greater than 3 keV. These results were made assuming that the example target 10 exhibits four times the heat dissipation than the conventional target and with a correction of 1.3 times to account for higher electron scattering at the incident angle of 60 degrees as compared to 0 degrees.
For a copper layer with an impact angle of 60 degrees and a take-off angle of 5 degrees and for the three electron beam energies (25 kV, 35 kV, 50 kV), Table 2A shows the brightnesses (photons/electron/m2/steradian) of x-rays having energies 7-9 keV and Table 2B shows the brightnesses photons/electron/m2/steradian) of x-rays having energies greater than 3 keV. These results were made assuming that the example target 10 exhibits four times the heat dissipation than the conventional target and with a correction of 1.3 times to account for higher electron scattering at the incident angle of 60 degrees as compared to 0 degrees.
Various configurations have been described above. Although this invention has been described with reference to these specific configurations, the descriptions are intended to be illustrative of the invention and are not intended to be 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 sequence and are not necessarily limited to any particular disclosed sequence. Features or elements from various embodiments and examples discussed above may be combined with one another to produce alternative configurations compatible with embodiments disclosed herein. Various aspects and advantages of the embodiments have been described where 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 should be recognized that the 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.
The present application is a continuation from U.S. patent application Ser. No. 16/518,713 filed Jul. 22, 2019 which claims the benefit of priority to U.S. Provisional Appl. No. 62/703,836, filed Jul. 26, 2018 which is incorporated in its entirety by reference herein.
| Number | Date | Country | |
|---|---|---|---|
| 62703836 | Jul 2018 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 16518713 | Jul 2019 | US |
| Child | 16866953 | US |
