Improvements in and relating to x-ray sources

Abstract

An X-ray source for generating X-rays (11) by means of an electron impingement anode (2) comprises an electron beam generator (5) for generating an electron beam (3) along a beam axis direction. A pivoting anode assembly (1) comprises a pivot (17) and an anode surface portion (2) mounted on the pivot for receiving electrons in an electron beam, thereby generating X-rays. A suspension assembly (19) is used to apply a restoring force to the pivoting anode assembly to urge the pivoting anode assembly towards a rest position in which the anode surface portion is static relative to the pivot. A displacer assembly (21) is used to apply a periodic displacement force to the pivoting anode assembly to displace the pivoting anode assembly from the rest position. The position of the anode assembly is configured to oscillate about the rest position in movement transverse to the beam axis in response to the periodic displacement force and the restoring force, thereby oscillating the anode surface portion across the beam axis.

Description

[0001] This application claims priority to an earlier application number GB2209809.9 filed on July 4, 2022, the contents and elements of which are incorporated herein by reference for all purposes. Technical Field

[0002] The present invention relates to an X-ray source for generating X-rays by electron impact on an anode. In particular, although not limited thereto, the present invention relates to an X-ray source for use in the field of X-ray photoelectron spectroscopy (XPS). Background Art

[0003] X-ray sources usually take the form of a cathode facing an anode within a vacuum chamber (often called a "tube"). The cathode is heated to emit electrons into the vacuum. A high voltage power supply (e.g., tens of kV to over 100 kV) is applied between the cathode and anode to accelerate the electrons to the anode. This creates a flow of electric current through the tube, called an electron beam. The electrons of the electron beam collide with atoms that form the anode material (such as copper, molybdenum, or tungsten). In doing so, the colliding electron beam creates inner shell vacancies, decelerates and scatters, and in doing so, emits X-rays in several processes. A process called bremsstrahlung: electromagnetic radiation produced by the acceleration or especially deceleration of charged particles after passing through the electric and magnetic fields of atoms. In addition, "line" or "characteristic" radiation is produced by the incident electron ejecting an inner shell electron to create an inner shell vacancy, which is then filled by an outer shell electron and emits a photon with an energy equal to the energy difference between the energy levels of the outer and inner shell electrons. The spectrum of the emitted X-rays depends on the anode material and the kinetic energy of the electrons in the electron beam, which is determined by the accelerating voltage between the anode and cathode.

[0004] Only about 1% of the energy generated by the electron beam collision process is emitted as bremsstrahlung and "line" X-rays. The rest of the energy is released as heat generated at the focus on the anode. The focus is where the electron beam is directed (e.g., focused) to impact the anode using electron optics disposed between the cathode and the anode. The heat generated in the focus (E, in joules) is given by the following equation:

[0005] E=V×I×t

[0006] Here, V is the accelerating voltage between the anode and cathode in volts, I is the current of the electron beam through the tube in amperes, and t is the exposure time (seconds) from a given fixed point of the anode to the focus of the electron beam. The focus of a stationary anode can generate high temperatures. The focus temperature may be greater than the melting point of the anode material, thereby damaging the anode surface. However, by rotating the anode around a deviating electron beam axis, prior art devices allow the electron beam to scan on a circular path on the anode surface, thereby reducing the exposure time of a given point of the anode to the focus of the beam damaging the anode. However, the rotating anode arrangement is complex and difficult to implement in an ultra-high vacuum environment for continuous operation in an economical manner.

[0007] An example of an application of X-ray tubes is X-ray photoelectron spectroscopy (XPS). This is a spectroscopic technique that exploits the photoelectric effect, in which X-rays (usually characteristic line radiation) from an X-ray source are directed towards a sample material under investigation and cause photoelectrons to be emitted from the surface of this sample. This technique enables the identification of the elements present in or on the sample material. In addition, the electronic structure of the material and the density of electronic states can be deduced. By measuring the number of photoelectrons in each of the different kinetic energy ranges by a photoelectron detector, the properties of the material can be inferred: these two quantities allow the generation of a photoelectron spectrum containing spectral peaks diagnostic of the sample material.

[0008] The accuracy depends on several parameters, such as the photoelectron signal-to-noise ratio and the photoelectron peak intensity (i.e., spectral peak) from the photoelectron detector. It is known that by increasing the intensity of the X-ray irradiation of the target sample, a higher photoelectron flux can be generated. This higher flux corresponds to a higher signal at the photoelectron detector, and therefore, a higher signal-to-noise ratio can improve the measurement accuracy. The increased X-ray irradiation requires an increased electron beam current, I, in the electron beam incident on the anode. This brings up the problem of anode heating and damage, as shown above.

[0009] The present invention is designed based on the above considerations. Summary of the invention

[0010] Most generally, the present invention relates to an anode for an X-ray source, wherein the anode is located on a pivotally mounted mechanical structure that is periodically displaced from a rest or reference position and returned to said position in an oscillating manner (e.g., forced oscillation) by a suspension arrangement (e.g., a spring) that suspends the mechanical structure. This results in a simple arrangement that allows the electron beam of the X-ray source to sweep the path of the anode surface by oscillating the anode relative to the electron beam, thereby reducing the exposure time of a given point of the anode to the focus of the electron beam. This reduces the temperature rise of the anode surface. By controlling the periodic displacement, the speed and trajectory (e.g., length) of the path of the electron beam focus on the anode surface can be accurately controlled. By appropriately arranging the mechanical structure and the suspension arrangement to achieve a preferred mass distribution (e.g., moment of inertia), the dynamic response to the periodic displacement can be improved.

[0011] In a first aspect, the present invention may provide an X-ray source for generating X-rays by electron impacting an anode, comprising:

[0012] An electron beam generator, used for generating an electron beam along a beam axis direction;

[0013] A pivotable anode assembly, comprising a pivot and an anode surface portion mounted on the pivot, for receiving electrons in an electron beam to generate X-rays;

[0014] a suspension assembly for applying a restoring force to the pivoting anode assembly to urge the pivoting anode assembly toward a rest position in which the anode surface portion is static relative to the pivot axis;

[0015] a displacer assembly for applying a periodic displacement force to the pivoting anode assembly to move the pivoting anode assembly away from the stationary position;

[0016] Wherein the position of the anode assembly is used to oscillate about the stationary position in a motion transverse to the beam axis in response to the periodic displacement force and the restoring force, thereby causing the anode surface portion to oscillate across the beam axis. In this way, the dynamic interaction between the restoring force from the suspension system and the periodic displacement force of the displacer assembly, both acting on the same pivot axis of the pivoting anode assembly, determines the speed and trajectory of the impact point path of the electron beam on the anode surface. By controlling the frequency and / or magnitude of the periodic displacement force, and by controlling the restoring force from the suspension assembly, the position of the anode assembly can be caused to oscillate with a desired dynamic response to the periodic displacement. A suitable mass distribution (e.g., moment of inertia) of the anode assembly can greatly improve the energy efficiency and / or oscillation frequency of the dynamic response. The suspension assembly may include a spring suspension arrangement. For example, the suspension assembly may include one or more springs for providing the restoring force.

[0017] Preferably, the pivot is fixed or stationary relative to the suspension assembly and / or relative to the displacer assembly. Preferably, the pivot comprises a single pivot axis such that the pivoting anode assembly is adapted to pivot about the single pivot axis. The single pivot limits the movement of the anode assembly and, therefore, limits the substantially linear movement of the anode surface (e.g., movement along a very slightly curved arc), or the linear path of the trajectory of the path of the impact point of the electron beam on the anode surface. For example, the pivot may comprise a fixed or static axle or axis about which the anode assembly is adapted to rotate, such as a hinge or bearing (e.g., a flexible bearing). Alternatively, the pivot may comprise a universal joint. A universal joint may allow a longer path of movement of the anode surface (e.g., an annular or circular path, rather than an approximately linear path). Thus, the path of the impact point of the electron beam on the anode surface may become longer for a given angular deflection from the reference position. This may result in a lower average power density over the path.

[0018] Preferably, the pivot includes one or more flexible bearings for flexing about the pivot of the pivoting anode assembly. Flexible bearings have been found to be advantageous in providing a negligible "backlash" arrangement. Flexible bearings also have a very long life if angular deflection and load are maintained within suitable limits. Suitable limits may for example be about ±6°, or preferably about ±5°, or more preferably about ±4°, or more preferably about ±3°, or more preferably about ±2°. The pivoting anode assembly may be adapted to limit the angular deflection within said limits.

[0019] The pivoting anode assembly can be used to limit the load applied to the pivot (e.g., the flexible bearing, or each bearing if more than one) to less than about 650 lb (2891 N), or less than about 500 lb (2224 N), or preferably less than about 450 lb (2002 N) or less than about 425 lb (1890 N), for example, less than about 403 lb (1793 N).

[0020] The pivot may include one or more flexible bearings having a diameter between about 0.375 inches (0.952 cm) and about 0.625 inches (1.588 cm), such as about 0.5 inches (1.270 cm). The pivot may include two pairs of flexible bearings configured with mutually orthogonal axes of rotation and positioned with mutually orthogonal axes of rotation to form a universal joint that can be used to achieve the required motion accuracy of the pivoting anode assembly.

[0021] The flexible bearing may comprise a single portion comprising two rigid structures (e.g., a semi-cylindrical portion concentrically located within an outer cylindrical portion) rotationally connected by a thin bridging portion of a flat elastic material that can be repeatedly bent without decomposing. The bridging portion may be integrally formed with the two rigid structures and may be the only connection between them. The bridging portion acts as a "hinge" between the two rigid structures. From a dynamic perspective, flexible bearings have the following advantages: they have essentially zero (or negligibly low) friction and therefore do not significantly contribute to the damping of the harmonic oscillatory motion of the anode assembly. Since flexible bearings do not require lubrication, they can be used in a vacuum, which is desirable for an X-ray source.

[0022] Alternatively, the pivot may include a resilient member (e.g., a spring) to which the anode assembly is mounted (e.g., at the end of the spring). The resilient member may also serve as a suspension assembly (or at least a portion thereof). For example, the pivoting anode assembly may include a pivot mounting that is not an axle but is a spring member (e.g., a coil spring or helical spring or torsion spring) that can deform in a direction transverse to its long axis. The pivot mounting may be a mounting on the spring member, for example, at the end of the spring member or along its length. The deformation of the spring member may flex or bend to allow the anode assembly to pivot. In some examples, the spring component of the pivot may serve not only as a pivot but also as a suspension assembly. The surface movement of the anode surface portion may be sufficiently controlled to avoid significant longitudinal movement. For example, if the spring member includes a coil spring or helical spring, the displacer assembly may be used to apply a periodic displacement force to the pivoting anode assembly to displace the pivoting anode assembly to limit the displacement of the spring member, thereby limiting the excitation of the extension and compression of the spring member. In this way, suitable limits or constraints may be imposed on the extreme displacement positions of the anode surface portion. For example, when the anode surface portion reaches an extreme displacement position (eg, angular displacement), the torsion spring may act as a pivot and provide a restoring force to urge the pivoting anode assembly into its rest position.

[0023] Preferably, the pivoting anode assembly is arranged to oscillate about the stationary position such that the intersection of the electron beam axis on the anode surface portion scans a substantially linear path on the anode surface portion. In this way, the path trajectory of the electron beam focus on the anode surface can be accurately controlled to be linear by controlling or constraining the periodic displacement of the anode assembly to be constrained within (or parallel to) an oscillation plane: the oscillation plane can contain the path of the focus of the electron beam on the anode surface. A particular advantage of this arrangement is that the position of the anode assembly can be arranged to be adjustably displaced in a direction transverse to the oscillation plane, thereby allowing the oscillatory movement of the displaced anode assembly to be constrained within (or parallel to) a new oscillation plane that is substantially parallel to the previous oscillation plane. This allows the focus path of the electron beam to pass through a "fresh" new surface area of ​​the anode surface when an old surface area of ​​the anode surface previously passed through by the focus of the electron beam becomes unsuitable for use, for example due to accumulated electron impact damage.

[0024] For example, the X-ray source may include a lateral displacer for adjustably displacing the pivoting anode assembly in a direction transverse to the oscillation plane of the anode surface portion. In some aspects, the lateral displacer may include one or more stepper motors or actuators for (preferably slowly) laterally displacing the pivoting anode assembly and the suspension assembly to different positions on a plane parallel to the anode surface portion. In this way, once a particular area is consumed, a fresh area of ​​the anode surface can be used, thereby reducing the frequency of anode replacement. Accordingly, the X-ray source may include a lateral displacer for adjustably displacing the position of the anode assembly in a direction transverse to the oscillation plane to an adjustment position that allows the anode assembly to oscillate in a new oscillation plane (or parallel to a new oscillation plane) that is substantially parallel to the oscillation plane that produces the displacement. The lateral displacer may be used to adjustably displace the position of the anode assembly in a direction substantially parallel to the anode surface (e.g., the anode surface may be planar). Preferably, the lateral displacer can be used to adjustably displace the position of the anode assembly in one direction so that the focus of the electron beam continues to overlap the anode surface, or so that the distance between the electron source and the impact point of the electron beam on the anode surface remains substantially unchanged.

[0025] The surface of the anode portion presented to the electron beam generator may be generally flat or planar. Thus, side portions of the surface may be periodically moved toward the electron beam generator when the surface is tilted or tilted relative to the electron beam tip. These side portions include changing points of impact of the electron beam. Thus, the changing points of the anode surface may be periodically advanced and retracted along the electron beam axis. Ideally, the X-ray source includes a longitudinal displacer for adjustably displacing the pivoting anode assembly in a direction generally parallel to the oscillation plane of the anode surface portion to adjustably displace the anode surface portion selectively in a longitudinal direction toward the electron beam generator or longitudinally away from the electron beam generator. The longitudinal displacer may be used to adjustably displace the pivoting anode assembly in a manner that maintains a substantially constant spacing between the electron beam generator and the point of impact of the electron beam on the anode surface portion during pivoting of the anode assembly. In this way, an otherwise varying distance may remain substantially constant.

[0026] Preferably, the X-ray source includes a position sensor or transducer for determining the position of the anode surface portion as it oscillates. The position sensor or transducer may be used to determine the angular position of the pivoting anode assembly (e.g. substantially continuously, or quasi-continuously by continuously sampling the position at a sufficiently high sampling rate). The position of the anode surface varies with the angular position of the pivoting anode assembly to which it is attached. The position of any given fixed point on the anode surface may be constrained to lie on an arcuate trajectory or path defined by the angular position of the pivoting anode assembly and the radial distance of the given point from the pivot. However, the longitudinal displacer may be used to adjustably displace the pivoting anode assembly in response to the determined position of the anode surface portion, or in response to the determined angular position of the pivoting anode assembly, or in response to another determined position measurement proportional to the angular position of the pivoting anode assembly, so that the distance between the electron beam generator and the point of impact of the electron beam on the anode surface portion as the anode assembly pivots is substantially constant. In this way, an otherwise varying distance may be substantially maintained.

[0027] As a result, since the distance between the electron beam generator (e.g., electron gun) and the pivot axis is appropriately varied longitudinally during the oscillation of the pivoting anode assembly, the distance between the impact point of the electron beam and the electron beam generator is substantially constant in normal use. Since the electron beam generator typically includes electron optics for focusing the electron beam into a focal point coinciding with the surface of the anode portion, any variation in the distance between the impact point of the electron beam and the electron beam generator will mean that the anode surface will move away from the focal point of the electron beam, possibly resulting in a change in the size of the electron beam on the anode surface. The longitudinal displacer may prevent this from happening. The longitudinal displacer may include a stepper motor or an actuator (e.g., a piezoelectric element) for adjustably displacing the pivoting anode assembly longitudinally (e.g., selectively in a direction toward or away from the anode surface portion or toward or away from the electron beam generator). For example, the longitudinal displacer may include a position sensor or transducer, as described above, for generating a signal / information representative of the angular position of the pivoting anode assembly relative to the rest position. The longitudinal displacer may be used to use the angular information to control the position (extension or compression) of the actuator or stepper motor in direct proportion to the angular position.

[0028] It is noted that the angular position of the pivoting anode assembly directly translates into a corresponding position of the point of impact of the electron beam on the anode surface portion relative to the position of the point of impact when the pivoting anode assembly is in a rest position. For example, as the pivoting anode assembly oscillates, it will periodically pass through its rest position (i.e., a reference position). The longitudinal displacer may be configured to displace the pivoting anode assembly in a first direction away from the electron beam generator when the pivoting anode assembly is moved away from the reference position and in a second direction toward the electron beam generator (i.e., opposite to the first direction) when the pivoting anode assembly is moved toward the reference position.

[0029] For example, when the oscillating position of the pivoting anode assembly briefly coincides with the rest position, the radial distance from the pivot to the point of impact of the electron beam on the surface of the anode portion is set to l0. When the angular position of the pivoting anode assembly relative to the rest position is θ, the radial distance from the pivot to the point of impact of the electron beam on the surface of the anode portion is set to l. As the anode tilts by θ, the distance from the pivot point to the point of impact of the electron beam increases from l0 to l0sec(θ), and hence, the rate of change differential defines the rate of change of the radial distance as a function of the changing angular position, i.e.:

[0030]

[0031] The longitudinal displacer may be used to apply a varying longitudinal displacement (Δ) to the pivoting anode assembly such that the rate of change of the longitudinal displacement (Δ) as a function of the varying angular position is:

[0032]

[0033] Its function is to counteract the change in radial distance from the pivot axis to the point of impact of the electron beam on the surface of the anode portion caused by the change in the angular position of the pivoting anode. Integrating the rate of change of the longitudinal displacement (Δ) as a function of the changing angular position gives the value of the longitudinal displacement (Δ) at a given angular position (θ), which is:

[0034] Δ=-l0(sec(θ)-1)

[0035] The negative sign indicates that when the pivoting anode assembly deviates from the reference position, ie when the magnitude of θ increases, the displacement is in the first direction away from the electron beam generator. The longitudinal displacer can be used to apply a varying longitudinal displacement (Δ) to the pivoting anode assembly according to the equation.

[0036] The spatial distribution of the mass of the pivoting anode assembly may be asymmetric about the pivot axis. For example, the separated portions of the pivoting anode assembly may be located on opposite sides of the pivot. In this arrangement, the pivot may be located between opposite ends of the anode assembly (e.g., see Figure 5 , where there are some pivot anode structures on the right side of pivot 17, especially some water cooling pipes and connections).

[0037] Alternatively, substantially all of the mass of the pivoting anode assembly may be located on the same side of the pivot. In this alternative arrangement, the pivot may be located at one end of the anode assembly (e.g., see Figure 1 ).

[0038] Preferably, the center of mass of the pivoting anode assembly is located closer to the pivot than to the anode surface portion. It has been found that the oscillation frequency of the oscillatory motion of the anode assembly is faster due to the lower moment of inertia. The center of mass of the pivoting anode assembly is located between the pivot and the anode surface portion. Alternatively, the center of mass of the pivoting anode assembly and the anode surface can be located on opposite sides of the pivot. It has been found that carefully balancing the moment of inertia and the suspension component (e.g., the spring constant of the spring, if used in the suspension component) can improve sensitivity and mechanical efficiency. Preferably, the anode assembly is used to place most of its mass near the pivot / rotation axis so that the moment of inertia is relatively low. This means that the higher vibration frequency required to reduce the peak instantaneous temperature increase of the anode surface can be achieved by a moderate restoring force (e.g., a moderate spring constant) of the suspension component. This means that the resonant frequency of the oscillatory motion of the anode assembly can be adjusted upward or downward by changing the restoring force (e.g., spring constant) of the element (e.g., spring) upward or downward, respectively.

[0039] It is desirable to achieve the highest possible resonant frequency within the mechanical limitations of the overall structure. The purpose of achieving a high resonant frequency is to limit the peak temperature at the electron beam impact point as it passes through the anode surface. Subject to the other constraints of the structure, it is desirable to keep the center of mass of the pivoting anode assembly as close to the pivot point as possible.

[0040] Preferably, the pivotable anode assembly comprises a coolant channel for conducting a coolant fluid (e.g. water) in a direction from the pivot axis to the anode surface portion. The coolant channel is preferably also for directing the coolant fluid back to the pivot axis and away from the anode surface. This has been found to achieve the desired effect, such that the mass and flow rate of the coolant has been found to have only a minor effect on the oscillatory motion of the anode assembly (e.g. on its moment of inertia). This avoids or reduces the effect of interference on the oscillatory motion due to air space flow in the coolant flow. Preferably, the suspension assembly and the displacer assembly are such that the displacer assembly is operable to impart a driven oscillatory motion of the anode assembly at an oscillatory motion frequency corresponding to a resonant frequency. Preferably, the oscillation frequency may range from about 10 Hz to about 1 kHz. Preferably, the path length of the electron beam focus on the anode surface may range from any value up to about 10 mm. Preferably, the length of the anode assembly measured from the pivot point to the anode surface may range from about 50 mm to about 600 mm.

[0041] Preferably, the displacer assembly is used to apply the periodic displacement force to the pivotable anode assembly, the periodic displacement force having a periodicity corresponding to a resonant frequency of the pivotable anode assembly.

[0042] Ideally, the suspension assembly includes one or more springs for applying the restoring force, wherein the resonant frequency of the oscillation is substantially proportional to the value of the spring constant of the one or more springs. The desired range of the spring constant of such springs can be calculated based on the desired oscillation frequency and taking into account the subsequent loading of the pivot assembly. Alternatively, piezoelectric actuators can be used and selected to replace such springs based on their spring rate and actuation force. Similarly, in the case where a pressurized gas can be used as a spring element, a pneumatic actuator can be used instead of a spring.

[0043] The resonant frequency of the system depends on the value of the moment of inertia of the mass supported by the pivot and the value of the spring rates / constants of the support springs of the suspension system. By appropriate selection of these values, the desired resonant frequency of the oscillatory motion of the anode assembly can be achieved.

[0044] Preferably, the anode surface portion is electrically floating and maintained at a positive potential of not less than about 5 kV, or more preferably not less than about 10 kV, or more preferably in the range of about 5 kV to about 20 kV (e.g., about 15 kV). This simplifies the requirements for control electronics of the system's electron beam generator (e.g., electron gun) because if electron impact energies of about 15 keV are required, they are essentially very close to the local ground potential. A further advantage is that the energy of backscattered and secondary electrons from the anode surface is insufficient to reach the surrounding ground potential area (e.g., in XPS, this would be the analysis chamber and sample area). Therefore, in some embodiments, there is no need to enclose the anode surface within the volume of the X-ray source, except perhaps to prevent backscattered electrons and secondary electrons from entering the environment outside the X-ray source.

[0045] The displacer assembly preferably includes one or more actuators, and more preferably includes a single actuator. The actuator may include a piezoelectric actuator. The displacer assembly can be used to apply a periodic displacement force in a direction substantially parallel to the direction of the restoring force applied by the suspension assembly. For example, if the displacer assembly includes a linear actuator, and if the suspension assembly includes one or more linear (e.g., spiral) springs, the extension / contraction axis of the actuator can be substantially parallel to the longitudinal axis of the one or more linear springs. A particular advantage of this arrangement is convenience, given the limitations of other parts of the instrument. Alternatively, the displacer assembly can be used to apply a periodic displacement force in a transverse direction to the restoring force applied by the suspension assembly.

[0046] The displacer assembly can be used to apply the periodic displacement force to the anode assembly at a position laterally offset from the pivot axis so that the periodic displacement force produces a periodic displacement torque on the anode assembly about the pivot axis. The position of the actuator can be selected so that the amplitude of the required movement of the actuator corresponding to the required amplitude of movement of the anode surface is within a desired range.

[0047] The displacer assembly may be used to apply a periodic displacing force to the pivoting anode assembly to apply a torque at a location between an anode surface portion of the pivoting anode assembly and the pivot.

[0048] The displacer assembly may be configured to apply the periodic displacement force to the pivoting anode assembly to apply a torque at a location on the pivoting anode assembly, wherein the pivot axis is located between the location where the torque is applied and the anode surface.

[0049] It should be understood that the aspects and features of the invention described above are implemented in terms of an X-ray source. However, the invention may also or alternatively be manufactured and sold as an anode device for use in an X-ray source that does not include an electron beam generator but has an electron beam generator for generating an electron beam directed along a beam axis to a surface portion of the anode. In other words, the various aspects and features of the X-ray source described above with respect to the first aspect of the invention are equally applicable to the second aspect of the invention in which the electron beam generator is omitted.

[0050] For example, in a second aspect, the present invention may provide an anode device for an X-ray source having an electron beam generator, the electron beam generator being used to generate an electron beam oriented along a beam axis for generating X-rays by electrons impacting the anode device, the anode device comprising:

[0051] A pivotable anode assembly, comprising a pivot and an anode surface portion mounted on the pivot, for receiving electrons in an electron beam to generate X-rays;

[0052] a suspension assembly for applying a restoring force to the pivoting anode assembly to urge the pivoting anode assembly toward a rest position in which the anode surface portion is static relative to the pivot axis;

[0053] a displacer assembly for applying a periodic displacement force to the pivoting anode assembly to move the pivoting anode assembly away from the stationary position;

[0054] wherein the position of the anode assembly is adapted to oscillate about the stationary position in a motion transverse to the beam axis in response to the periodic displacement force and the restoring force, thereby causing the anode surface portion to oscillate across the beam axis. In this regard, the invention may be manufactured and sold as an "anode assembly": that is, as a package comprising a pivoting anode assembly, a suspension assembly and a displacer assembly, but not an electron gun. The "anode assembly" may be inserted into an existing X-ray device already having an electron beam generator, as a replacement / upgrade for an anode previously in the existing X-ray device. This allows an X-ray gun product to be upgraded with the anode assembly.

[0055] It should be understood that the above aspects and features of the present invention implement the corresponding methods of generating X-rays included in the present invention. For example, in a third aspect, the present invention may provide a method for generating X-rays by electron impacting an anode, the method comprising:

[0056] generating an electron beam directed along a beam axis;

[0057] receiving electrons from the electron beam at an anode surface portion to generate X-rays, wherein the anode surface portion is mounted on a pivoting anode assembly including a pivot, the pivoting anode assembly being mounted on a suspension assembly;

[0058] applying a restoring force to the pivoting anode assembly via the suspension assembly to urge the pivoting anode assembly toward a rest position in which the anode surface portion is static relative to the pivot axis;

[0059] applying a periodic displacement force to the pivoting anode assembly to displace the pivoting anode assembly from the rest position;

[0060] wherein the position of the anode assembly oscillates about the stationary position in motion transverse to the beam axis in response to the periodic displacement force and the restoring force, thereby causing the anode surface portion to oscillate across the beam axis.

[0061] Thus, the present invention can provide a device and method for increasing the maximum electron beam power density that the anode portion can withstand without damage, which is achieved by rapid lateral vibration of the anode surface, thereby dispersing the heat dissipation on the anode surface, thereby allowing a higher total power load at a given surface temperature. This can be used for any application when a more intense X-ray beam generated by electron impacting a target material is required than allowed by a completely stationary anode. The present invention can provide an electron impact X-ray source for use in the XPS field, where the demand for high signal levels for rapid XPS analysis leads to the use of high electron beam power densities. In prior art devices, this leads to a large temperature increase on the anode surface, ultimately leading to melting and subsequent failure of the metal surface layer. Commercial X-ray sources in current XPS instruments operate when the anode is in a fixed position. In contrast, the present invention allows the anode structure to be rapidly oscillated laterally under the electron beam, thereby exposing a larger area of ​​the anode surface, thereby reducing the average power density. Then, before damage occurs, the anode surface can withstand a higher total power, which leads to an increase in XPS signal intensity than is possible with an electron beam generator. The position of the electron beam generator is preferably fixed in space (i.e. relative to the pivot axis) so that the position of the electron beam is also fixed in space. Thus, the generated X-rays originate from an area determined by the lateral dimensions of the electron beam, rather than the lateral dimensions of the area on the anode surface irradiated by the electron beam.

[0062] In XPS, signal intensity in a small analytical field is a key metric for the performance and competitiveness of commercial XPS instruments. Various strategies are employed to achieve high intensity, including highly efficient electron optics to collect as many emitted photoelectrons as possible, to maximize the heat dissipation capability of the anode via the use of high-speed water flow within the anode structure and embedded high thermal conductivity diamonds in the area impacted by the electron beam. Even with these measures, the surface temperature of the anode can easily reach the melting point of the anode coating (usually aluminum), resulting in rapid degradation of the metal surface. It is well known that electron beam welding of high melting point materials can reach very high temperatures, so it is not surprising that aluminum is easily melted by the focused electron beam.

[0063] It is well known in the art that dispersing the electron beam on the anode surface reduces the power density, thereby reducing the anode surface temperature. A common way to achieve this is to use a rotating anode structure. This allows the electron beam to be dispersed around the circumference of the anode disk while maintaining the apparent size of the X-ray source to a desired size that is closely related to the size of the electron beam impacted. These systems typically have high melting point materials and low duty cycles to avoid continuous cooling. In XPS equipment, since the acquisition time is sometimes long, continuous operation is required, so continuous cooling is required. This brings about the difficult technical problem of cooling the anode structure rotating at high speed under ultra-high vacuum (UHV) conditions.

[0064] Compared to prior art systems, the present invention allows an increase of up to about 6 times or more in the electron beam power level at which the X-ray source can operate, and this brings significant commercial benefits. The present invention allows the anode to vibrate rapidly in a direction parallel to the anode surface. Typically, in commercial XPS instruments, the diameter of the electron beam can be 150 μm, and therefore the vibration of the anode with an "A" mm vibration amplitude will allow the power delivered to the 150 μm diameter to be dispersed to an area of ​​150 x A x1000 μm2 plus the area of ​​the point. For example, if A=1, about 9.5 times the area of ​​the anode surface is allowed to be irradiated with a constant electron beam intensity. This will allow the electron beam power to be increased to about 9.5 times, thereby generating X-ray intensity. The pivoting anode assembly can be an elongated structure (e.g., a cylindrical structure) having an anode surface located at one longitudinal end thereof, and the pivot is located at or adjacent to its other longitudinal end. For example, the longitudinal length of the pivoting anode assembly can be at least about 50 mm long, or at least about 100 mm long, or at least about 150 mm long, or at least about 200 mm long, or at least about 250 mm long, or at least about 300 mm long, or at least about 350 mm long, or at least about 400 mm long, or at least about 450 mm long. Most preferably, the longitudinal length of the pivoting anode assembly is in the range of about 50 mm to about 500 mm. For example, the longitudinal length of the pivoting anode assembly can be in the range of about 100 mm to about 450 mm, or in the range of about 200 mm to about 500 mm, or more preferably in the range of about 250 mm to about 400 mm, such as in the range of about 300 mm.

[0065] The X-ray source according to any aspect can be used to make the surface portion of the anode electrically floating and maintained at a positive potential (e.g., not less than 5kV) during use. Alternatively, the X-ray source of any aspect can be configured so that the anode is at ground potential (grounded) and the electron emitter (cathode) in the electron gun is at a negative potential. A sufficiently high negative potential value can be selected to provide the required impact energy for X-ray generation. This version of the X-ray source can be used to directly irradiate a sample with X-rays, for example, where the analytical application will accept characteristic radiation and bremsstrahlung radiation.

[0066] In yet another aspect, the present invention may provide an X-ray monochromator comprising an X-ray source according to any aspect disclosed herein. The present invention is able to compensate for the movement of the X-ray source point (i.e., the electron beam impact point on the anode surface) caused by the anode movement, meaning that the present invention is able to significantly reduce changes in intensity, energy or position changes of the reflected X-ray point on the sample surface irradiated with X-rays from the X-ray source during use.

[0067] In order to produce an X-ray radiation beam with a narrow wavelength distribution, a monochromatic optical element (e.g., a single crystal) can be used. Monochromatic optical elements work by receiving X-rays from an X-ray source and reflecting incident X-ray wavelengths that conform to the Bragg law. This allows people to select a limited wavelength of X-ray radiation on a dedicated instrument or electron beam line for further purposes. In this way, the X-ray monochromator works through a diffraction process according to the Bragg law. X-ray monochromator optical elements are similar to grating monochromators and spectrometers in the visible part of the spectrum. X-ray monochromatic optical elements may include a lattice structure selected for this purpose. If the lattice spacing of the crystal is accurately known, the observed diffraction angle can be used to select the X-ray wavelength. Since some materials (e.g., quartz) exhibit sensitive wavelength dependence of Bragg reflection, a small part of the continuous radiation spectrum can be isolated. This isolated spectral portion is considered to be effectively monochromatic, that is, its energy dispersion is narrower than the characteristic X-ray line it has been isolated. In addition, if the lattice structure is bent into a suitable shape, the isolated X-rays can be directed to a strong focus for subsequent XPS analysis.

[0068] The present invention includes any combination of the described aspects and preferred features unless such a combination is expressly impermissible or explicitly avoided. BRIEF DESCRIPTION OF THE DRAWINGS

[0069] Embodiments and experiments illustrating the principles of the present invention will now be discussed in conjunction with the accompanying drawings, in which:

[0070] Figure 1 A schematic cross-sectional view of an X-ray source is shown;

[0071] Figure 2A A schematic cross-sectional view showing a pivoting anode assembly of an X-ray source at two different angular displacements;

[0072] Figure 2B Shows the application to Figure 2A a graph of the longitudinal displacement of a pivotable anode assembly as a function of its angular displacement required to substantially reduce to zero the distance between the electron gun and its electron beam impact point on the anode;

[0073] Figure 3A A schematic cross-sectional view of an X-ray source is shown;

[0074] Figure 3B A schematic cross-sectional view of an X-ray source is shown;

[0075] Figure 4 A view showing an X-ray source;

[0076] Figure 5 for Figure 4 A cross-sectional view of an X-ray source;

[0077] Fig. 6A A schematic diagram showing the mechanical and dynamic relationships between the elements of the pivoting anode assembly;

[0078] Figure 6B shows the response to the application of a periodic displacement force, Fig. 6A A graph of the angular displacement of a pivoting anode assembly in resonance as a function of the angular frequency of the displacement force. DETAILED DESCRIPTION

[0079] Aspects and embodiments of the present invention will now be discussed in conjunction with the accompanying drawings. Other aspects and embodiments will be apparent to those skilled in the art. All documents mentioned herein are incorporated herein by reference.

[0080] Figure 1 A schematic cross-sectional view of an X-ray source according to an embodiment of the present invention is shown. The X-ray source is used to impact a surface portion of an anode 2 with an electron beam 3. The X-ray source includes an electron beam generator 5 for generating an electron beam 3 directed to the anode 2 along a beam axis. The anode 2 is mounted at the end of a pivoting anode assembly 1 for receiving electrons in the electron beam 3, thereby generating X-rays. The surface portion of the anode is electrically floating and is maintained at a positive potential of not less than 5 kV. The base end of the pivoting anode assembly is mounted on a pivot 17, which includes one or more flexible bearings for bending around the pivot axis of the pivoting anode assembly. In an alternative arrangement, the anode is at ground potential and the electron emitter in the electron gun is at a high negative potential, thereby providing the required impact energy for X-ray generation. If necessary, a high voltage insulator ( Figure 1 The anode is insulated (not shown) so as to maintain its potential at ground potential in any suitable manner, as will be apparent to those skilled in the art.

[0081] The X-ray source includes a suspension assembly 15b, which includes a plurality of springs laterally offset from the pivot 17 and configured to apply a restoring force to the pivoting anode assembly 1 to urge the pivoting anode assembly toward a stationary position (eg, Figure 1 1 ), in the rest position, the anode surface portion 2 is static relative to the pivot axis 17. The displacer assembly 21 is used to apply a periodic displacement force 27 to the pivoting anode assembly 1 to displace the pivoting anode assembly 1 from the rest position. Thus, the angular position of the pivoting anode assembly 1 is used to swing about the rest position in a motion transverse to the beam axis 3 in response to the periodic displacement force 27 and in response to a simultaneous restoring force from the suspension spring 19. This causes the pivoting anode assembly to oscillate (in a direction 23) the anode surface portion 2 at its end across the beam axis 3 of the electron beam.

[0082] Thus, the pivoting anode assembly oscillates about the rest position such that the intersection of the electron beam axis on the anode surface portion 2 scans a substantially linear path through the anode surface portion. The pivot 17 comprises a single pivot axis such that the pivoting anode assembly pivots about the single pivot axis as the angular position of the pivoting anode assembly oscillates. The angular position may be considered to be the angle subtended at the pivot by the longitudinal axis of the pivoting anode assembly 1 relative to the longitudinal axis of the anode assembly 1 when it is in its rest position.

[0083] It is noteworthy that the spatial distribution of the mass of the pivoting anode assembly 1 is asymmetric relative to the pivot axis of the pivot 17. In this example, the location of the center of mass of the pivoting anode assembly 1 is located between the pivot 17 and the anode surface portion 2. The location of the center of mass of the pivoting anode assembly is closer to the pivot than to the anode surface portion. The shape of the pivoting anode 1 is elongated so that its longitudinal dimension in the direction extending from the pivot 17 to the longitudinal axis of the anode surface portion 2 exceeds its dimension in any direction perpendicular to the longitudinal axis. In one example, the length of the pivoting anode assembly can be about 100 mm and the maximum lateral dimension (width) is about 70 mm. In contrast, in other examples, the length of the pivoting anode assembly can be about 400 mm and the maximum lateral dimension (width) is about 70 mm.

[0084] In other embodiments, as shown in FIG. 3, Figure 4 , Figure 5 As shown, the location of the center of mass of the pivotable anode assembly 1 and the location of the anode surface portion 2 are located on opposite sides of the pivot axis, with the location of the center of mass of the pivotable anode assembly being closer to the pivot axis than to the anode surface portion.

[0085] A displacer assembly is used to apply a periodic displacement force to the pivoting anode assembly, the period of the periodic displacement force corresponding to the resonant frequency of the oscillation of the pivoting anode assembly. The periodic displacement force is applied to the pivoting anode assembly at a location that is laterally offset from the longitudinal axis of the pivoting anode assembly and is also longitudinally offset from the pivot in a direction toward the anode surface portion. This results in a torque on the pivoting anode assembly at a location between the anode surface portion and the pivot. In other words, the pivot is further away from the anode surface portion than the location of the applied force. In other embodiments, such as FIG. 3, Figure 4 and Figure 5 As shown in , the periodic displacement force applies a torque to the pivoting anode assembly at a location on the anode assembly such that the pivot is located between the location where the torque is applied and the location of the anode surface. In other words, in these other embodiments, the pivot is closer to the anode surface portion than to the location where the force is applied.

[0086] The suspension assembly includes one or more springs for applying a restoring force. The resonant frequency of oscillation is substantially proportional to the value of the combined spring constant of the one or more springs. Figure 1 In the example of , two springs are used, wherein the two springs are mechanically coupled to the base end of the pivoting anode assembly, each spring being located at a position laterally offset from the longitudinal axis of the pivoting anode assembly and the pivot 17 (through the longitudinal axis of the pivot). The two springs 19 have the same size and spring constant. The displacer assembly 21 includes a single actuator, such as a piezoelectric actuator, and communicates with a control unit 25, which is configured to send control signals to the actuator to control the extension and compression of the actuator, thereby controlling the amplitude and frequency of the periodic displacement to be applied by the actuator.

[0087] In all embodiments of the present invention, appropriate positioning of the center of mass of the pivoting anode assembly relative to the pivot axis has significant benefits in reducing the moment of inertia of the pivoting anode assembly, thereby allowing rapid oscillatory movement 23 of the anode surface portion 2 with a larger angular displacement amplitude in response to relatively small periodic displacements at the resonant frequency of the mechanical system including the pivoting anode assembly and the suspension assembly mechanically coupled.

[0088] The moment of inertia of a rigid body, also known as mass moment of inertia, angular mass, second mass moment, or most accurately rotational inertia, is the amount of torque required to determine the desired angular acceleration about an axis of rotation, similar to how mass determines the force required for a desired acceleration. It depends on the distribution of the mass of the object and the axis chosen, with larger moments requiring more torque to change the body's rate of rotation. For a point mass, the moment of inertia is simply the mass times the square of the perpendicular distance from the axis of rotation. The moment of inertia of a rigid composite system is the sum of the moments of inertia of its subsystems (all about the same axis).

[0089] Fig. 6A A schematic diagram of the basic elements of the arrangement of force, motion and mass distribution according to an example of the present invention is shown. Here, the suspension assembly includes a spring with a spring constant k. The following analysis is applicable to other embodiments of the suspension system with additional springs, such as Figure 1 and Figure 3, Figure 4 and Figure 5 .

[0090] Consider a pivoting anode assembly having a mass distribution equivalent to a center of mass "m" being located a distance "h" from a pivot axis "p" of the pivoting anode assembly. An anode surface portion (not shown) defines a distal end of the pivoting anode assembly distal from the pivot. A suspension assembly includes a lateral arm "a" of length "L" extending laterally from a longitudinal axis of the pivoting anode assembly at a point adjacent the pivot axis "p" a longitudinal distance "h" from the center of mass "m". The suspension assembly includes a spring of spring constant "k" for applying a restoring force to a distal end of the lateral arm "a" to urge the pivoting anode assembly toward a rest position (as shown), wherein the pivoting anode assembly is static relative to the pivot axis. A displacer assembly (not shown) is used to apply a periodic displacement force "F" to the lateral arm "a" to displace the pivoting anode assembly from the rest position. This causes the position "x" of the center of mass "m" of the pivoting anode assembly to oscillate about the rest position in a motion transverse to its longitudinal axis in response to the periodic displacement force and the restoring force. This causes the anode surface portion (not shown) at the distal end of the pivoting anode assembly to oscillate laterally in a reciprocating direction about the longitudinal axis. The nature of this oscillation, relative to the center of mass of the pivoting anode assembly and the properties of the suspension assembly and the displacer assembly, is as follows:

[0091] Assume that the periodic displacement force "F" is in the following form:

[0092] F1=F0sin(ωt)

[0093] The torque applied to the pivoting anode assembly by this displacement force is:

[0094] T1=F1L=F0Lsin(ωt)

[0095] Assume that due to the displacement force, the spring of the suspension assembly is displaced (i.e. compressed or extended) by a displacement "y" that causes the side arm "a" to pivot about the pivot point "p" by a small angle θ, so that the spring force applied by the spring on the side arm is:

[0096] F2 = ky = kLθ The torque applied to the pivoting anode assembly by the spring force is:

[0097] T2=F2L=kL 2 θ

[0098] In response to the net effect of the applied torque T1-T2, the center of mass "m" of the pivoting anode assembly is displaced by a lateral displacement "x", causing it to experience an acceleration. The acceleration of the mass corresponds to a force, and due to its longitudinal distance "h" from the pivot point, this is equivalent to a net torque:

[0099]

[0100] Here, for small θ, we use x = hθ. The equation of motion for the center of mass "m" of the pivoting anode assembly can be defined as:

[0101]

[0102] in other words:

[0103]

[0104] If we reasonably assume, as a first approximation, that there is a damping force (F d ), the final equation of motion for the center of mass "m" of the pivotable anode assembly can be defined as:

[0105]

[0106] Here, the term α is the damping force F d = the damping constant of αdθ / dt. The solution of this differential equation is of the form:

[0107]

[0108] Here, θ0 is the amplitude factor and M is the amplitude magnification factor, where:

[0109]

[0110] at the same time,

[0111]

[0112] The response of the pivoting anode assembly to the periodic forcing provided by the displacer assembly (F) depends on the ratio of the forcing frequency to the natural frequency, ω / Ω, and the damping term ζ. Figure 6B The change in the amplitude magnification factor in response to changes in these terms is shown. The resonant drive frequency ω at which the maximum amplitude "M" (resonance) occurs Res is slightly less than the undamped natural frequency and is given by:

[0113]

[0114] It can be seen that the natural frequency Ω and the resonant driving frequency ω Res are respectively inversely proportional to the moment of inertia of the center of mass of the pivoting anode assembly, and are obtained by the following formula: m =mh 2 According to the “Parallel Axis Theorem”, when a mass system “m” rotates around an axis that is offset by a displacement “h” from the center of mass of the system, the moment of inertia of the system can be defined as the sum of the following: (1) When considering the first rotation axis passing through the center of mass of the system, the moment of inertia of the system (I CM), and (2) the moment of inertia of the center of mass of the system when considering a second axis of rotation parallel to the first axis of rotation but offset from the center of mass by a distance “h” m =mh 2 ).in other words:

[0115] I=I CM +I m =I CM +mh 2

[0116] The inventors have realised that by reducing the value of the offset distance "h", the moment of inertia (I) of the pivoting anode assembly can be reduced, thereby reducing the energy required to oscillate the anode assembly and this also results in a resonant drive frequency ω Res Higher, at this resonant drive frequency, a maximum amplitude "M" occurs in the oscillatory motion of the anode surface portion across the impinging electron beam. This has been found to be very effective in shortening the time that the electron beam spot impinges on a given surface point of the anode surface, thereby reducing the heating effect of the electron beam on the anode material at the point of impact, and allowing the electron beam intensity to be increased without overheating the anode surface. The resonant frequency and amplitude can be readily adjusted by appropriate selection of the string constant "k" and / or the side arm length "L" of the suspension assembly, and / or the amplitude (F0) of the driving force applied by the displacer assembly.

[0117] exist Figure 1In the embodiment, the X-ray source comprises a longitudinal displacer 29 coupled to the base end of the pivot and used to adjustably displace the pivot in a direction substantially parallel to the oscillation plane of the anode surface portion 2, and a pivoting anode assembly 1 connected to the pivot. The longitudinal displacer comprises an actuator (e.g., a piezoelectric element) for adjustably displacing the pivoting anode assembly longitudinally. The displacement is controlled to adjustably displace the anode surface portion 2 in a longitudinal direction toward the electron beam generator 5 or longitudinally away from the electron beam generator 5. The longitudinal displacer 29 comprises a position sensor for determining an angular position of the anode surface portion (i.e., relative to the pivot) during the oscillation of the anode surface portion. The angular position corresponds to the angular position of the pivoting anode assembly. The longitudinal displacer is used to adjustably displace the pivot 17 in response to the determined angular position of the anode surface portion, thereby displacing the pivoting anode assembly 1, so that the distance between the electron beam generator 5 and the impact point of the electron beam 3 on the anode surface portion when the anode surface portion oscillates is substantially constant. By keeping the distance constant, the point of impact of the electron beam 3 on the anode surface portion does not move along the electron beam axis 3. This keeps the focus of the electron beam on the anode surface and thus eliminates changes in the size of the focus with angular position. A position sensor is used to sense the angular position directly, and the sensing may be provided by a sensor integrated in the pivot 17, such as a strain gauge connected to the flexure of the pivot (angular displacement) or to an additional element that bends with the angular displacement of the pivot.

[0118] The longitudinal displacer converts the angular position of the pivotable anode assembly into a correction of the longitudinal distance of the location of the impact point of the electron beam on the anode surface portion relative to the impact point location when the pivotable anode assembly is in the stationary position to keep the longitudinal distance constant.

[0119] See also Figure 2A, when the pivoting anode assembly oscillates, it periodically passes through the reference position 1a at rest. The longitudinal displacer 29 is used to displace the pivot 17 in a first direction away from the electron beam generator 5 when the pivoting anode assembly moves from the reference position 1a to the position 1b with the angular displacement θ. This is used to displace the pivoting anode assembly 1 away from the electron beam generator 5. When in the rest position, the impact point "a" of the electron beam on the anode surface is spaced apart from the pivot 17 by a distance l0, and when the anode assembly 1 is in the position 1b with the angular displacement θ, the impact point "b" is spaced apart from the pivot 17 by a distance l0+Δ. This means that the impact point is close to the electron gun, and therefore, the impact point will move out of the focal area of ​​the electron beam. At this angular position, the previous impact point "a" has moved away from the electron beam along the circular arc track 24 due to the angular displacement of the anode assembly. This arc motion causes the adjacent part of the flat surface of the anode to tilt with respect to the electron gun 5, thereby bringing the impact point "b" closer to the electron gun. Accordingly, the longitudinal displacer applies a varying longitudinal displacement (Δ) to the pivoting anode assembly such that the rate at which the longitudinal displacement (Δ) changes with the varying angular position is:

[0120]

[0121] Its function is to counteract the variation in the longitudinal distance from the pivot axis 17 to the point of impact of the electron beam 3 on the anode surface portion 2 caused by the varying angular position of the pivoting anode assembly. The longitudinal displacer applies a varying longitudinal displacement (Δ) to the pivoting anode assembly at a given angular position (θ) as follows:

[0122] Δ=-lo(secθ-1)

[0123] Figure 2B This displacement is shown graphically in , with example parameters lo = 300 mm, maximum value of θ = 0.01 radians.

[0124] As the angular displacement of the anode assembly increases (or decreases) according to this relationship, the longitudinal displacer moves the anode surface 2 as a whole away from (or toward) the electron gun 5.

[0125] The pivotable anode assembly 1 includes a coolant passage 31 for conducting a coolant fluid (e.g., water) in a direction from the pivot axis to the anode surface portion 2. The coolant passage is also for conducting the coolant fluid in a direction 32 toward the pivot axis so that the coolant fluid is in thermal communication with the underside of the anode surface (i.e., the side opposite the surface portion that receives electrons from the electron beam 3), thereby allowing the coolant fluid to remove heat from the anode surface portion. A longitudinal spacing 33 within the coolant passage defines a first conduit portion in communication with the underside of the anode surface portion for directing the coolant fluid toward the anode surface portion, and a second conduit portion for directing the coolant fluid away from the anode surface. The first conduit portion and the second conduit portion may be separate conduits arranged to be in fluid communication at their respective ends adjacent to the underside of the anode surface, where the fluid flows in opposite directions as it passes from the first conduit portion through the second conduit portion while being in thermal communication with the underside of the anode surface portion. Figure 1 and Figure 3, Figure 4 , Figure 5 The X-ray source includes a lateral displacer 37 (not shown in FIG. 3 ) comprising a stepper motor and a coupling 36 connected to the pivoting anode assembly for adjustably displacing the pivoting anode assembly and the suspension assembly together in a direction 35 transverse to the plane of vibration of the anode surface portion. These components are Figure 1 and is marked as The pivoting anode assembly is used to oscillate about a stationary position so that the electron beam axis scans a substantially linear path across the anode surface portion at the intersection of the anode surface portion. Since the periodic displacement of the anode assembly is constrained to be within an oscillation plane containing the path of the focus of the electron beam on the anode surface (or parallel to the oscillation plane), the trajectory of the path of the focus of the electron beam on the anode surface is constrained to be linear. The position of the anode assembly can be adjustably displaced in a direction transverse to the oscillation plane, thereby allowing the oscillatory motion of the displaced anode assembly to be constrained in a new oscillation plane that is substantially parallel to the previous oscillation plane (or parallel to the new oscillation plane). This allows the focus path of the electron beam to pass through a "fresh" new surface area of ​​the anode surface when an old surface area of ​​the anode surface previously traversed by the focus of the electron beam becomes unsuitable for use, for example, due to accumulated electron impact damage.

[0126] To this end, the X-ray source comprises a lateral displacer 37 for adjustably displacing the pivoting anode assembly 1 in a direction 35 transverse to the oscillation plane of the anode surface portion 2. The lateral displacer 37 comprises a stepper motor 36 for displacing the pivoting anode assembly 2 and the suspension assembly 19, 30 transversely to different positions on a plane parallel to the anode surface portion 2. In this way, once a specific area has been consumed, a fresh area of ​​the anode surface can be used, thereby reducing the frequency of anode replacement. This adjustably displaces the position of the anode assembly in a direction transverse to the oscillation plane to an adjustment position that allows the anode assembly to oscillate in (or parallel to) a new oscillation plane that is substantially parallel to the oscillation plane in which the displacement is made. The anode surface 2 is flat and tilted to the electron beam axis 3, tiled towards the window 9. The lateral displacer is used to adjustably displace the position of the anode assembly in a similarly tilted direction 35 by pushing the X-ray source along an inclined sliding / supporting surface 32 substantially parallel to the anode surface to the portion where the pivot is mounted. Therefore, the anode assembly is adjusted so that the focus of the electron beam continues to coincide with the anode surface, and the distance between the electron source and the impact point of the electron beam on the anode surface remains substantially unchanged.

[0127] Example

[0128] Example 1

[0129] See also Figure 1 and Figure 3, Figure 4 and Figure 5 , the metal anode 2 is impacted by an electron beam 3 from an electron gun 5. The electron gun 5 has a focusing device inside it, which allows the lateral size and energy of the electron beam to be changed to adapt to the required working conditions. Typically, when impacting the metal anode 2, the electron beam has an energy of 15 keV and a diameter of 0.15 mm. These components are mounted in a vacuum chamber 7, which is connected to the vacuum of the XPS chamber. A thin window or baffle material 9 may be included to prohibit electrons backscattered from the metal anode 2 from reaching the XPS chamber, and the X-rays 11 generated by the electrons 3 impacting the metal anode 2 pass through the window 9 and can be used for subsequence excitation of photoelectrons for XPS analysis.

[0130] The metal anode 2 is attached to the vacuum chamber 7 via a flexible bellows 13 which allows the anode to move relative to the chamber but excludes ambient air, thereby maintaining a high or ultra-high vacuum environment suitable for operation of the electron gun 5. The metal anode 2 has internal water channels 31 which carry water 32 to the metal anode 2, and these water channels are arranged to extend to a point close to the top end of the pivoting anode assembly 1 to maximize the cooling efficiency between the areas heated by the electron beam 3. The anode is thus liquid-cooled via these coaxial water channels which supply water to the top end of the pivoting anode assembly and return the water to the outside world.

[0131] The metal anode 2 is connected to the rigid structure 15a, 15b on the vacuum chamber 7 via several elements. These are the pivot 17, the spring element 19 of the suspension assembly and the actuator 21 of the displacer assembly. The pivot axis of the pivot 17 (e.g., a hinge or a flexible bearing) is orthogonal to the plane of the figure, so that the top end of the anode assembly 1 and the metal anode 2 at the top end move as shown by the double arrow 23.

[0132] The spring element 19 of the suspension assembly is a compression coil spring in this example, but can be any suitable device that provides spring action. The actuator 21 is a piezoelectric actuator that applies a force between the rigid structure 15a, 15b and the pivot 17 mounted on the rear of the metal anode 1. The actuator 21 applies a displacement force associated with an electrical signal from an electrical signal source 25, substantially in the direction of the double-headed arrow 27. The force is periodic in time, causing the anode assembly 1 to move the metal anode 2 at its top end substantially along the path shown by the double-headed arrow 23.

[0133] For a slow rate of change of displacement force 27, the motion along path 23 will depend on the combined spring stiffness of the displacement force applied by actuator 21 and spring element 19. If the rate of change of displacement force 27 increases steadily, the amplitude of motion 23 will increase significantly as the resonant frequency of the anode assembly 1 supported by pivot 17 and spring 19 is approached. This is the preferred operating condition, where a small excitation force from actuator 21 results in a large amplitude of motion 23.

[0134] The resonant frequency of the system described depends on the moment of inertia of the mass supported by the pivot 17 and the spring rate of the support spring 19 and, to a lesser extent, on the inherent spring rate of the actuator 21. The flexible bellows 13 will also contribute to the overall spring rate of the system. This means that the resonant frequency can be adjusted up or down by adjusting the spring constant of the spring element 19 to be greater or lesser. A change in the spring constant of the spring can be achieved by simply replacing the spring.

[0135] The actuator 21 also preferably comprises a transducer to allow real-time measurement of its length / extension. The signal of the transducer can be used as a control signal for the longitudinal actuator 29.

[0136] The effect of the movement of the surface of the metal anode 2 along the path 23 is to spread out the area impacted by the electron beam 3 along a length determined by the length of the path 23. Since the position of the electron beam 3 is fixed in space, in the reference frame of the vacuum chamber 7, this means that the generated X-rays 11 appear to originate from the area where the electron beam 3 intersects the surface of the metal anode 2. The heat dissipated in the metal anode due to the impact of the electron beam is dispersed over an area (A) equal to the following formula: A = W × L + electron beam spot area; where W is the width of the electron beam 3 in a direction out of the plane of the figure, and L is twice the amplitude of the movement 23 (i.e., the "peak-to-peak" displacement). Taking a typical example, the electron beam diameter 3 can be 150μm, and twice the amplitude of the movement 23 (i.e., the "peak-to-peak" displacement) can be 1mm.

[0137] This means that the average power density in this elongated region will be reduced by a factor of 9.5. If the frequency of the motion is high enough, the electron beam power (which is the product of the electron accelerating voltage and the current in the electron beam) can be increased by approximately this factor for the same metal anode 2 surface temperature. In this way, the intensity of the X-ray beam 11, which is proportional to the electron beam current, will likewise increase. This will naturally increase the XPS signal intensity, bringing commercial benefits.

[0138] Due to the pivot 17, the path 23 of the anode tip 2 is a very shallow arc. For typical anode sizes and path lengths 23, the depth of the arc is a few micrometers. In order to keep the distance between the electron gun 5 and the impact point of the electron beam on the anode surface 2 constant, the piezoelectric element 29 extends and compresses according to the angular displacement of the anode assembly 1 from its rest (reference) position, so that the distance is constant. To this end, the piezoelectric element 29 is controlled by information of the extension / compression state of the actuator 21 of the displacement assembly provided by a position transducer in the actuator 21.

[0139] The X-rays emitted along path 11 may pass through an X-ray mirror (not shown) which is used to refocus them onto the sample surface and reduce the energy spread of the X-rays to make them more suitable for XPS analysis. The X-ray mirror assembly is sensitive to the position of the X-ray source in a direction transverse to the indicated path 11. Such small changes may cause the position of the refocused X-ray spot on the sample to change, and the X-ray energy reflection also changes with the amount of lateral displacement. Both of these effects may impair the quality of the subsequent XPS spectrum. The ability of the present invention to compensate for the movement of the X-ray source point (i.e., the electron beam impact point on the anode surface) caused by the motion of the anode means that the present invention is able to greatly reduce changes in the intensity, energy or position changes of the reflected X-ray spot on the sample surface irradiated by the X-rays from the X-ray source during use.

[0140] The extension / compression state of the actuator 21 is directly related to the angular displacement of the pivoting anode assembly. For example, referring to Figure 6a, an extension "δ" of the actuator to cause a portion of the pivoting anode assembly (or its suspension assembly) to generate a force "F" at a lateral distance "a" from the pivot axis "p", thereby causing an angular displacement "θ" to the pivoting anode assembly, is given by:

[0141]

[0142] Optimal operating conditions may be achieved at the highest vibration frequencies and amplitudes. The pivoting anode assembly may include bellows (e.g., edge-welded bellows) connected to the remainder of the X-ray gun structure via edge-welded bellows for achieving precise positioning and alignment of the anode with the electron gun using the lateral shifter described above.

[0143] Figure 5 The example shows that Figure 1 The main difference is that in Figure 1 In the embodiment, the pivot is in the displacement actuator 21 (in Figure 5 21 is the front of the insulating extension rod of the actuator 25, rather than the rear thereof. Figure 3B yes Figure 5 A simplified schematic diagram of the main elements of the design of . The differences here are represented by changes in the construction of the "suspension assemblies" 19, 30 and 30a. In this example the base 42 of the pivoting anode assembly 1 is fixed to a "swinging basket" type arrangement 30 and the basket arm 30a is attached to the rest of the frame 15b via a pivot 17. It is suspended behind the pivot 17 and has springs 19 connecting it to the frame 15a on either side of the pivot 17. These springs provide a return force to urge the "basket" to a rest position corresponding to the rest position of the anode assembly 1. By applying a periodic displacement force 27 to the base of the basket, on one side, the basket is forced to oscillate, thereby oscillating the anode assembly fixed to it. In Figure 3A In the schematic diagram of FIG. , the displacement actuator 21 rests against the bottom surface of the "swing basket" arrangement 30. Figure 3B In the schematic diagram of FIG. 3 , the displacement actuator 21 is against the side of the "swing basket" arrangement 30. An advantage of this arrangement is that the longitudinal actuator 29 is located on the moving side of the pivot point 17 and therefore does not experience the "preload" spring force of the spring 19, so the longitudinal actuator 29 can be a less robust (e.g., cheaper) actuator.

[0144] Figure 3 and Figure 5 The main difference between the designs shown is that in Figure 5 3 , the plane containing the vibration direction 23 is orthogonal to the plane containing the electron beam and the outgoing x-ray beam, rather than being coplanar as in FIG. 3 . Figure 5This feature of the design shown may be preferred because the angled end of the anode increases the longitudinal motion of the X-ray spot from the stationary position. This angled anode configuration facilitates application in X-ray monochromators. Figure 5 The anode surface in Figure 3 is not angled relative to the electron beam incident direction.

[0145] The features disclosed in the foregoing description or the following claims or in the accompanying drawings, expressed in their specific form or as a means for performing the disclosed function, or as a method or process for obtaining the disclosed results, may, as appropriate, be used alone or in any combination of these features to realize the invention in different forms.

[0146] Although the present invention has been described in conjunction with the above exemplary embodiments, many equivalent modifications and variations will be apparent to those skilled in the art when the present invention is disclosed. Accordingly, the above exemplary embodiments of the present invention are considered to be illustrative rather than restrictive. Various changes may be made to the described embodiments without departing from the spirit and scope of the present invention.

[0147] For the avoidance of any doubt, any theoretical explanations provided herein are intended to enhance the reader's understanding. The inventors do not wish to be bound by any of these theoretical explanations.

[0148] Any section headings used herein are for organizational purposes only and are not to be construed as limiting the subject matter described.

[0149] Throughout this specification, including the following claims, unless the context requires otherwise, the terms "comprises" and "comprising", and variations such as "comprises", "consisting of", and "including", will be understood to imply the inclusion of an integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

[0150] It must be noted that, as used in the specification and the appended claims, the singular forms "a," "an," and "the" include plural references unless the context clearly dictates otherwise. Ranges may be expressed herein as from "about" one particular value to "about" another particular value. When such a range is expressed, another embodiment includes from the one particular value and / or to the other particular value. Similarly, when values ​​are expressed as being approximate, by using the preceding "about," it will be understood that the particular value constitutes another embodiment. The term "about" in relation to a value is optional and means, for example, + / - 10%.

Claims

1. An X-ray source for generating X-rays by electron impact on an anode, characterized in that: include: An electron beam generator, used for generating an electron beam along a beam axis direction; A pivotable anode assembly, comprising a pivot and an anode surface portion mounted on the pivot, for receiving electrons in an electron beam to generate X-rays; a suspension assembly for applying a restoring force to the pivoting anode assembly to urge the pivoting anode assembly toward a rest position in which the anode surface portion is static relative to the pivot axis; a displacer assembly for applying a periodic displacement force to the pivoting anode assembly to move the pivoting anode assembly away from the stationary position; wherein the position of the anode assembly is adapted to oscillate about the stationary position in motion transverse to the beam axis in response to the periodic displacement force and the restoring force, thereby causing the anode surface portion to oscillate transversely across the beam axis.

2. An X-ray source according to any one of the preceding claims, characterized in that The pivoting anode assembly is adapted to oscillate about the rest position such that an intersection point of the beam axis on the anode surface portion scans a substantially linear path on the anode surface portion.

3. X-ray source according to any one of the preceding claims, characterized in that The pivot includes a single pivot axis such that the pivoting anode assembly is adapted to pivot about the single pivot axis.

4. The X-ray source according to claim 3, characterized in that The spatial distribution of the mass of the pivotable anode assembly is asymmetric with respect to the pivot axis.

5. The X-ray source according to claim 4, characterized in that The center of mass of the pivoting anode assembly and the anode surface are located on opposite sides of the pivot axis.

6. The X-ray source according to claim 4 or 5, characterized in that: The center of mass of the pivotable anode assembly is located closer to the pivot axis than to the anode surface portion.

7. The X-ray source according to any one of claims 4 to 6, characterized in that The center of mass of the pivoting anode assembly is located between the pivot axis and the anode surface portion.

8. X-ray source according to any one of the preceding claims, characterized in that The pivoting anode assembly includes a coolant passage for conducting a coolant fluid in a direction along the pivot axis to the anode surface portion.

9. The X-ray source according to claim 8, characterized in that The coolant passage is for conducting coolant fluid in a direction toward the pivot and away from the anode surface.

10. X-ray source according to any one of the preceding claims, characterized in that The displacer assembly is used to apply the periodic displacement force to the pivoting anode assembly, and the periodic displacement force has a periodicity corresponding to the resonant frequency of the pivoting anode assembly.

11. The X-ray source according to claim 10, characterized in that The suspension assembly includes one or more springs for applying the restoring force, wherein a resonant frequency of the oscillation is substantially proportional to a value of a spring constant of the one or more springs.

12. X-ray source according to any one of the preceding claims, characterized in that The anode surface portion is electrically floating and maintained at a positive potential of not less than 5 kV.

13. X-ray source according to any one of the preceding claims, characterized in that The displacer assembly includes a single actuator.

14. The X-ray source according to claim 13, characterized in that The actuator includes a piezoelectric actuator.

15. X-ray source according to any one of the preceding claims, characterized in that The pivot axis includes one or more flexible bearings for flexing about the pivot axis of the pivoting anode assembly.

16. X-ray source according to any one of the preceding claims, characterized in that The displacer assembly includes a transverse displacer for adjustably displacing the pivoting anode assembly and the suspension assembly together in a direction transverse to an oscillation plane of the anode surface portion.

17. X-ray source according to any one of the preceding claims, characterized in that A longitudinal displacer is included for adjustably displacing the pivoting anode assembly in a direction substantially parallel to an oscillation plane of the anode surface portion to adjustably displace the anode surface portion in a direction selectively longitudinally toward or longitudinally away from the electron beam generator.

18. X-ray source according to any one of the preceding claims, characterized in that The longitudinal displacer includes a position transducer for determining the position of the anode surface portion during the oscillation of the anode surface portion, and the longitudinal displacer is used to adjustably displace the pivoting anode assembly in response to the determined position of the anode surface portion so that the distance between the electron beam generator and the impact point of the electron beam on the anode surface portion during the oscillation of the anode surface portion is substantially constant.

19. X-ray source according to any one of the preceding claims, characterized in that The displacer assembly is used to apply the periodic displacement force to the pivoting anode assembly to apply a torque to the pivoting anode assembly at a location between the anode surface portion and the pivot axis.

20. An X-ray source according to any one of the preceding claims, characterized in that The displacer assembly is used to apply the periodic displacement force to the pivoting anode assembly to apply a torque to the pivoting anode assembly at a location thereon, wherein the pivot is located between the location where the torque is applied and the anode surface.

21. An X-ray monochromator, characterized in that: An X-ray source comprising the invention as claimed in any one of the preceding claims.

22. An anode device for an X-ray source having an electron beam generator, the electron beam generator being used to generate an electron beam along a beam axis direction, and being used to generate X-rays by electrons impacting the anode device, characterized in that: The anode device comprises: A pivotable anode assembly, comprising a pivot and an anode surface portion mounted on the pivot, for receiving electrons in an electron beam to generate X-rays; a suspension assembly for applying a restoring force to the pivoting anode assembly to urge the pivoting anode assembly toward a rest position in which the anode surface portion is static relative to the pivot axis; a displacer assembly for applying a periodic displacement force to the pivoting anode assembly to move the pivoting anode assembly away from the stationary position; wherein the position of the anode assembly is adapted to oscillate about the stationary position in motion transverse to the beam axis in response to the periodic displacement force and the restoring force, thereby causing the anode surface portion to oscillate transversely across the beam axis.

23. A method for generating X-rays by electron impact on a surface portion of an anode, characterized in that The method comprises: generating an electron beam along a beam axis direction; receiving electrons from the electron beam at an anode surface portion to generate X-rays, wherein the anode surface portion is mounted on a pivoting anode assembly including a pivot, and the pivoting anode assembly is mounted on a suspension assembly; applying a restoring force to the pivoting anode assembly via the suspension assembly to urge the pivoting anode assembly toward a rest position in which the anode surface portion is static relative to the pivot axis; applying a periodic displacement force to the pivoting anode assembly to displace the pivoting anode assembly from the rest position; wherein, in response to the periodic displacement force and the restoring force, the position of the anode assembly oscillates about the stationary position in a motion transverse to the beam axis, thereby causing the anode surface portion to oscillate transversely across the beam axis.

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