SU857816A1 - X-ray spectrometer - Google Patents

Description

This invention relates to X-ray spectrometers designed to study the actual structure of single crystals, in particular for precise measurement of the crystal lattice deformation after various types of external influences on the sample (temperature, doping, epitaxi, etc.). The id / do deformation is associated with increment x-ray angle of reflection. Adfdo -u9 ®o / where & d / dg.d-do / dg- is the relative change in the interplanar, bone distance for this family of crystallographic areas thkE} of the studied sample (d) H of an undeformed crystal of a standard ( do) d 0 is the angle of reflection from the .hkfti planes of the crystal under study; 0 (3 is the angle of reflection from the reference. The most accurate method for measuring the deformation of the crystal lattice is currently the three-crystal spectrometer method. The spectrometer known, consisting of an x-ray source, a collimator, crystal carriers for two monochromator crystals and one analyzer, is rotating mechanically. and linear displacements of the X-ray tube, collimator and crystal carriers, as well as the radiation detector. The second monochromator crystal and analyzer crystal are mounted on the main When the spectrometer is in operation, the X-ray beam from the radiation source falls on the first crystal monochromator, which, with the help of the turning mechanisms, is placed in a reflecting position at which the diffracted beam passes through the analyzer crystal and the second crystal monochromator. Both crystals are brought into a reflecting position with respect to the beam coming from the first monochromator crystal.

The determination of the angular increment l, due to the difference in the parameters of the gratings of the second monochromator and analyzer, is performed as follows on a spectrometer of this type. The x-ray reflected from the first monochromator crystal is directed to the second monochromator crystal (which serves as a reference when measuring Sid / dp), the reflection from which is recorded by a radiation detector. Then, in parallel to the reflecting face of the standard, a thin crystal under investigation is placed, capable of transmitting a portion of the radiation incident on the standard and reflected from it. If the crystal under investigation is not in the reflecting position, then the detector captures only a beam diffracted on a standard, the intensity of which is weakened due to photoelectric absorption in the sample. In the case when the crystal under study reflects and the period of its lattice coincides with the period of the standard lattice (ie, d d / do 0), the detector located at the output of the diffracted beam detects a sharp decrease in intensity (extinction minimum). This minimum is due to the double reflection of the x-ray beam from the crystal under investigation: the first reflection occurs on the input face of the sample, the second on the opposite one, from which the beam diffracted on the standard is reflected. At ud / dg O, the reflection angles for both crystals are the same. If the sample under study is deformed (ud / dgi O), the rays are not reflected simultaneously, but only after turning the crystal under study at an angle lb associated with the deformation by the ratio

i9: - uol (6ioi j9o) This non-simultaneity is registered by the detector as the appearance of two minima against the background of the intensity of reflection from the reference.

Using the design of the spectrometer, the angles are measured at the same time with the same alignment of the instrument elements, thus avoiding the instrumental errors associated with the alignment of the standard and the sample under study 1.

However, this spectrometer has the following disadvantages;

1. The device design provides for multiple reflection from the crystals when measuring ud / d and imposes strict requirements on the thickness of the test samples (the x-ray beam must pass through the crystal twice). This reduces the accuracy of measurement, since for thin samples, an increase in l 9 makes a significant contribution to the bending of the crystallographic planes, due either to the processing of the crystals or to their mounting on the spectrometer. Moreover, on the described instrument it is impossible to isolate and evaluate the contributions to & from uniform deformation and bending.

2. The distance between the crystal holders of the standard and the sample under study should be much smaller than the linear dimensions of the reflecting face of the crystal so that at a given diffraction angle the beam can be reflected twice from the crystal.

3. The parallel displacements of crystals used in the transition to other reflection orders also lead to the need for a close arrangement of the crystals at small reflection angles, which does not allow

5 to investigate many of the properties of crystals directly on the spectrometer (for example, to conduct heat treatment of the sample, in particular, to determine the coefficients of thermal

0 expanded and.

The closest to the present invention is an X-ray spectrometer for the precision measurement of the strain of the crystal lattice, containing successively located

5 x-ray source, crystal holder of a monochromator, collimator, crystal carriers of the investigated crystal and crystal analyzer with the mechanisms of their rotation

0 and measure the angles of rotation and the detector G.

When this device is operated, the X-rays coming from the radiation source are monochromatized by a stationary monochromator crystal. The target device located after this crystal selects the spectral component K that falls on the crystal under study. After reflection from the crystal under investigation, the beam hits the analyzer crystal and then is detected by the detector. The reflecting faces of all three crystals are mutually parallel and are located at a Rag angle to the radiation source.

When measuring the deformation, the reflection from the reference crystal is first detected, the angle of reflection from the reference is fixed by the indicator associated with the analyzer crystal. Indicator indications in this case give a reference point (Q) of the angular increment. The reflection angle of the sample under study from it is also noted by the indicator of the crystal-analyzer, the difference in the indications of the indicator, converted into angular units, corresponds to the increment of the Bragg angle.

(The 3ott 0o scheme of the spectrometer does not impose any restrictions on the thickness of the samples under study and allows you to adjust the distance between the crystals at any angle of diffraction. Since the rays in the device undergo a single reflection from the crystals, the curvature of the sample under study does not affect the increment of ai 2.

The disadvantage of the spectrometer is the low accuracy of the alignment of the crystals in the azimuthal direction, which causes an instrumental error in measuring the reflection angles and, accordingly, the deformation of the crystal lattice. Azimuthal misorientation of crystals causes an angular shift of the Bragg maximum. So, if the angle between the normal and the reflecting face of the sample and the vertical axis of rotation of the crystal in the Bragg direction is 90 + сЛ, also with zero deformation, the analyzer will record an increment of -c / 1t (J9.

The exact value of the angle is usually. not known, since it depends on many factors. Among them, the main one is the azimuthal divergence of the primary X-ray beam, the minimum value of which when using slit collimators exceeds 1 °. The amount of deviation of the reflecting facet from the principal axis of rotation of the crystal is also affected by the accuracy of manufacturing the mechanisms in the crystal carriers, by means of which the azimuthal adjustment is made, the discrepancy between the normals to the reflecting crystallographic plane and the cut surface of the sample, and the non-parallelism of the axes of rotation of the crystals in the spectrometer. Together, these factors cause the azimuthal misalignment 0.5

In practice, the azimuthal deflection has all three crystals. There is a more complex functional relationship between the measured increment of Lb and the misorientation angles. The design of the spectrometer does not contain elements controlling the angles of deflection of the reflecting faces of the crystals in the azimuthal direction, which, with the above reasons for inaccurate alignment of the crystals, does not allow to achieve the calculated accuracy of measuring the strain of the crystal lattice corresponding to the accuracy of determining the increment of reflection angles.

The purpose of the invention is to improve the accuracy of measuring the strain of the crystal lattice.

The goal is achieved by the fact that a X-ray spectrometer containing successively located X-ray source, monochromator crystal holder, collimator, crystal holders of the investigated crystal and analyzer crystal with the mechanisms of their rotation and measurement of the angles of rotation and detector, is placed between the radiation source and the crystal radiator. monochromator installed two flat mirrors with a mechanism for their rotation, located each relative to the double angle of total external reflection of the x-ray beam, and the normals to the reflecting surfaces of the mirrors lie in a plane passing through the focus of the source and the axis of rotation of the monochromator, an additional collimator and means for its linear displacement relative to the surface are installed above one of the mirrors , and between the collimator,

5, located after the monochromator, and the crystal holder of the crystal under study, one more flat mirror with the means of its rotation relative to the X-ray beam is installed so that the normal to the reflecting surface of the mirror lies in the plane passing through the axis of rotation of the monochromator and the crystal under study.

Figure 1 shows the general principle of the proposed X-ray spectrometer; Fig. 2 shows the path of the rays in a system of flat mirrors for full external reflection located in front of the crystal.

0 monochromator; on fig.Z - variant of the mutual orientation of the investigated crystal and crystal analyzer, as well as x-rays when measuring the deformation of the crystal

5 lattices.

The X-ray spectrometer contains an X-ray source 1, a device 2 of its linear nepeMeDje vertically, flat mirrors 3,

0 3, mechanism 4 of rotation of flat mirrors, slit device 5, mechanism 5 displacement (1 slit device relative to flat mirrors, crystal monochromator 7, slot device 8, flat mirror 9, mechanism 5 nst 10 of rotation of a flat mirror, crystal 11 under study, crystallizer 12 detector 13 radiation.

The X-ray source 1 is connected to the linear displacement device 2 vertically. On the path from the source there are two flat mirrors 3 and 3 for direct external shielding of the beams with the mechanism 4 that the mirrors rotate relative to the primary beam axis, the slit device 5 and the associated with it, the movement mechanism 6 relative to the surface of the mirrors. Next are the crystal-monochromator 7, a slit device 8, a flat mirror 9 for complete external reflection and means 10 for turning it relative to the x-ray beam, the crystal 11 under study, an analyzer crystal 12 and a detector 13

Claims (2)

1. Authors testimony of the USSR 487338, cl. G 01 N 23/20, 1973. 2. Skupov V.D. and Uspenska G.I. Combined spectrometer for measuring the deformation in single crystals. Instruments and experimental technique., 1975, 2, p.210-213 (prototype).