X-RAY APPARATUS

Abstract

An X-ray optical system incorporates a refractometer, interferometer, spectrometer, diffractometer or imaging device for analyzing a sample. The X-ray optical system is configured with a monochromator which is fabricated from low atomic mass metal borates MxByOz crystals, wherein M is low atomic mass metal, and x, y, z are respective atom numbers of metal, borate and oxygen in chemical formula. The metal borates include borates of lithium (Li), sodium (Na) or stronium (Sr).

Claims

1. An X-ray optical system, which incorporates a refractometer, interferometer, spectrometer, diffractometer or imaging device for analyzing a sample, comprising a monochromator fabricated from a group of low atomic mass metal borates MxByOz, wherein M is low atomic mass metal, and x, y, z are respective atom numbers of metal, borate and oxygen.

2. The X-ray optical system of claim 1, wherein the low mass-metal is one of lithium (Li), sodium (Na) or stronium (Sr).

3. The X-ray optical system of claim 1, wherein the x, y and z atomic numbers vary in accordance with a desired chemical formula of the selected metal borate.

4. The X-ray optical system of claim 1, wherein the monochromator operates in a reflective mode or transmissive mode.

5. The X-ray optical system of claim 1, wherein the monochromator is a single crystal or polycrystal.

6. The X-ray optical system of claim 1 further comprising: an X-ray source emitting a polychromatic X-ray beam which is incident on the monochromator reflecting a filtered monochromatic beam; and a X-ray detector spaced upstream from the sample and detecting the monochromatic beam.

7. The X-ray optical system of claim 6, wherein the monochromator is located upstream or downstream from a sample.

8. The X-ray optical system of claim 6, wherein the X-ray source is selected from conventional tubes, rotation anode systems, or synchrotron.

9. The X-ray optical system of claim 7, wherein the sample is one of solid, gas or liquid.

10. The X-ray system of claim 6 further comprising an analyzer configured identically to the monochromator and located immediately upstream from the detector.

11. A method of monochromatizing X-ray radiation, comprising: emitting a polychromatic beam of X-ray radiation along a path; and spectrally and spatially filtering the polychromatic beam by a monochromator selected from low atomic mass number metal borates, thereby forming a monochromatic beam.

12. The method of claim 11 further comprising detecting the monochromatic beam.

13. The method of claim 11, wherein the metal borates include Li, Na or Sr borates.

14. The method of claim 11 further comprising locating the monochromator along the path upstream or downstream from a sample to be analyzed.

15. The method of claim 11, wherein the monochromator operates in a reflective mode or transmissive mode.

Description

DESCRIPTION OF THE DRAWINGS

[0019] Various aspects of the disclosure are discussed below with reference to the accompanying figures, which are not intended to be drawn to scale. The figures are included to provide an illustration and a further understanding of the various aspects and embodiments, and are incorporated in and constitute a part of this specification, but are not intended as a definition of the limits of any particular embodiment. The drawings, together with the remainder of the specification, serve to explain principles and operations of the described and claimed aspects and embodiments. In the figures, each identical or nearly identical component in various figures is represented by a like numeral. For purposes of clarity, not every component may be labeled in every figure. In the figures:

[0020] FIG. 1 illustrates a measured rocking curve for 400 reflection from an almost ideal silicon (Si) single crystal wafer;

[0021] FIG. 2 is an exemplary optical schematic of X-ray diffractometer of the known prior art;

[0022] FIGS. 3A 3C illustrates calculated intrinsic rocking (reflection) curves of LBO, Si and Ge, respectively;

[0023] FIG. 4 is an exemplary optical schematic of a double-crystal spectrometer with a single monochromator manufactured from an LBO crystal;

[0024] FIG. 5A 5C illustrate respective measured (experimentally obtained) rocking curves of respective LBO, Si and Ge.

SPECIFIC DESCRIPTION

[0025] Described herein are optical schematics of X-ray diffractometers used in X-ray spectrometry, diffractometry, reflectometry, interferometry and imaging. In particular, the shown schematics each are include a monochromator configured in LBO crystals and operating in a reflective or transmissive mode. The LBO monochromator offers several advantages, including a narrow rocking curve, high reflectivity and high mechanical integrity.

[0026] FIG. 3A 3C illustrate respective calculated intrinsic rocking (reflection) curves, in relative units, i.e. intensities reflected from atomic planes versus the angle of incidence of a monochromatic X-ray beam. In particular, the curves are calculated for strongest symmetric 111 reflection of CuKa.sub.1 X-ray in Bragg geometry for respective single crystal plates of LBO (FIG. 3A), Si (FIG. 3B) and Ge (FIG. 3C). In symmetrical Bragg geometry, reflecting atomic planes, such as (111), are parallel to the upstream surface of the monochromator or a sample to be tested. As can be seen, the intrinsic rocking curve of LBO has a FWHM, which is almost three times less than that of Si, and almost 6 times less than that of Ge. The theoretical peak reflectivity and linear absorption parameters of the LBO are also better than those of respective Si and Ge as summarized in the following table.

TABLE-US-00001 TABLE 1 Parameters for the theoretical crystal intrinsic rocking (reflection) curves. LiB.sub.3O.sub.5 Si Ge Single crystals Reflecting crystallographic plane (hkl) (111) Energy and wavelength for incident Cu- 8.0478 keV and 0.15406 nm Ka.sub.1 radiation Calculated Bragg angle Theta, deg of arc 11.77 14.22 13.64 Parameters of calculated intrinsic reflection curves FWHM, arcsec 2.53 7.6 16.7 Peak reflectivity, relative units 0.96 0.94 0.93 Linear absorption coefficient, cm.sup.−1 20 141 353

[0027] FIG. 4 illustrates an exemplary optical schematic of a single-crystal X-ray spectrometer 40. The spectrometer 40 includes an X-ray source 30 selected from conventional tubes, rotation anode systems and synchrotrons. While the scope of the invention includes all of the above-mentioned types of X-ray source 30, preferably, the source is a hard energy source emitting hard X-rays, but the latter does not exclude the possibility of working with soft X-rays. The polychromatic X-ray radiation is incident on a monochromator 32 at an angle of incidence Θ.

[0028] In accordance with a main concept of the invention, monochromator 32 is made of borates of lithium (LiB.sub.3O.sub.5) or strontium (SrB.sub.4O.sub.7) or sodium borates. A material for a monochromator can be selected single-crystal or polycrystalline. For the purpose of convenience, this description further refers to LBO single crystal, but the entire disclosure relates to a group of borates of low atomic mass metals including additional compounds each having different chemical formulas. For example, LBO besides LiB.sub.3O.sub.5 may include LiBO.sub.2 and Li.sub.2B.sub.4O.sub.7. Thus, for the purposes of generalization, the metal borates covered in this disclosure are referred to as M.sub.xB.sub.yO.sub.z, wherein M is Li, Na and Sr, and x, y. z are numbers of atoms in a chemical formula of a compound.

[0029] The monochromator 32 is a reflector which selects a narrow spectral band of broadband X-ray beam from source 30 and reflects this intense monochromatic beam on a single-crystal sample 34. The angle of incidence equals to the reflection angle at reflecting plane of monochromator 32, so that the shown diffraction schematic of monochromator is symmetric. The angle of incidence Θ at reflecting plane of monochromator 32 equals to or it is close to an angle of incidence Φ at receiving/upstream reflecting plane of single-crystal sample 34, so that the shown diffraction schematic is called non-dispersive. However, sample 34 may represent not only single crystals but also polycrystalline materials, liquids and even gases; for analysis of these samples, a wide range of angles of incidence is utilized. Thus, the monochromatic X-ray beam irradiates single-crystal sample 34 at incidence angle Φ; the sample 34 reflects the incident beam at the same angle. A detector 38 is set at an angle 2Φ relative to incident beam position to collect X-ray photons reflected from the single-crystal sample 34.

[0030] A variation of the optical schematic of FIG. 4 may include a triple-crystal X-ray spectrometer in symmetric diffraction scheme. Specifically, this scheme includes monochromator, such as LBO or borates of sodium (Na) or strontium (Sr), receiving a polychromatic beam of X-rays from the X-ray source. The monochromator reflects the desired monochromatic beam which is incident on the sample to be examined similarly to the schematic of FIG. 4. The monochromatic beam reflected from the sample is further incident on an analyzer crystal, which is identical to the monochromator. The analyzer reflects the received X-rays onto the detector. The use of the analyzer provides background reduction, as well as improving resolution of rocking curves collected for the sample.

[0031] FIGS. 5A 5C illustrate respective rocking curves for strongest, 111 reflections measured in count per second with changing angle of incidence of the monochromatic radiation. In particular, the experiments were conducted on −0.7 mm thick, flat LBO, Si and Ge crystal plates in symmetrical Bragg geometry with monochromatic Cu—Ka.sub.1 X-rays. Parameters of these rocking curves are shown in table 2.

TABLE-US-00002 TABLE 2 Parameters of measured 111 reflection curves displayed at FIG. 6A-6C. Measured values, Cu-Ka.sub.1, 4x Ge 220 monochromator Peak max Peak integral Reflection FWHM, intensity, intensity, curve sec cps cps LBO 111 7.9 68400 165 Si 111 9.8 126500 376 Ge 111 17.2 185900 983

[0032] The values of the measured FWHM and peak integral intensity change among LBO, Si and Ge in line with a change of respective values calculated for intrinsic reflection curves shown in Table 1 and FIGS. 3A 3C. Observed absolute differences between measured and calculated FWHM values for each crystal are explained by optical aberrations related to Ge 220 monochromator and limit of minimal angular step specific to utilized model of X-ray diffractometer. However, the measured peak maximum intensity for LBO is lower than that of the calculated reflection curve. This is explained by uncertainties in calculations of atomic scattering factor for Li and temperature factors for Li, B and O atoms in LBO crystal, and also due to the experimental nature of the measured LBO crystal plate with (111) orientation, which is unusual for this material.

[0033] Peak maximum intensity of LBO 111 reflection may be increased 1.5-2.6 times by asymmetric Bragg diffraction, i.e. a reflection of X-rays from (111) atomic planes which are not parallel to the surface of LBO crystal plate. For this purpose, as an example, the monochromator 32 at FIG. 4 is intentionally cut from LBO crystal so that its reflecting (111) atomic planes create an angle with the surface of the monochromator plate; this angle is slightly less than Bragg angle for 111 reflection, thus minimizing an angle of incidence relative to crystal surface. This type of monochromator is referred to as the asymmetric monochromator.

[0034] Having thus described several aspects of at least one example, it is to be appreciated that various alterations, modifications, and improvements will readily occur to those skilled in the art. For example, the sample to be analyzed may located upstream from the monochromator. Such alterations, modifications, and improvements are intended to be part of this disclosure, and are intended to be within the scope of the examples discussed herein. Accordingly, the foregoing description and drawings are by way of example only.