SU759930A1 - X-ray spectrometer for investigating monocrystals - Google Patents

Description

The invention relates to an apparatus -) re for precision measurements of crystal lattice distortions of single crystals, in particular, to X-ray multichip spectrometers for measuring internal stresses in single crystals subjected to various external influences (temperature, doping, epitaxy, etc.).

A X-ray spectrometer is known, which contains an X-ray source, a slot device with three crystographic holders for.,

two monochromators and a crystal under investigation, means for rotating and fixing the angular positions of crystals and a quantum counter £ .13 · 20

The spectrometer works as follows.

The beam from the x-ray tube falls on an asymmetrically reflecting first crystal, the result of which is a wide beam with a small angular divergence. The second crystal is located in an antiparallel position with respect to the first, and a reflection from the black

2

corresponds to symmetric Bragg diffraction. This crystal is used to isolate the spectral line. The third crystal under study reflects at the same Bragg angle as the first crystal, but under conditions of symmetric diffraction. The method for determining the radius of curvature is based on measuring the angular width кач of the rocking curve from a sample, depending on the linear width of the area of the crystal under investigation irradiated with an x-ray beam.

The beam width is measured using limiting slots installed between the second and third crystals. If is the maximum angle of misorientation between the elements of the crystal surface localized at two edges of the irradiated area, and the E is the width of the irradiated area, then the radius of curvature is determined from the relation

This spectrometer has a number of disadvantages: the design of the spectrometer provides for measuring the curvature of atomic planes only along the angular

759930

the width of the Bragg maximum, which _to a large extent depends on the magnitude and distribution of the microstresses in the crystal, in particular, if the assignments of the inter-block distance (4 ^) are enclosed in the interval +

- ^l ^ shkE · (64 ^ - increment, about ³

when struck by structural defects), the angular width of the swing curve will be

.ten

where 6 is the diffraction angle.

The spectrometer scheme does not allow one to isolate the contributions of each of the terms and the total broadening of D®, which is reduced. _ the accuracy of the measurement of curvature and, accordingly, stress.

The measurement of large radii of curvature (K 7,500 m) 'on the spectrometer is carried out by increasing the parameter B with a slit device. This leads to the averaging of information on the stress distribution in the crystal volume and to an increase in the contribution to the broadening of the diffraction cycle of the strain of DMS1 / o1), i.e. to a decrease in measurement accuracy.

The limit value of the measured radius of curvature of the crystallographic planes for the device does not exceed 1.5 "10 * m. ' thirty

The closest technical solution is an X-ray spectrometer for the study of single crystals, containing an x-ray source, a rotating holder with a 35 "monochromator crystal, a moving

the holder of the investigated crystal microscope rotation, detek ¥ br radiation and a means of measuring the angle of rotation £ 2]. 4P

Measurement Procedure curvature samples were ob- ⁴⁰ next to the spectrometer.

Going from the source is incident ia'ybnohromator, where the selection of the most intensive spectral dubDeta K _l. Then they are 45 and separated in space} are sent to the crystal under study. Using a slit device, a non-simultaneous fall of the components onto the sample is carried out. Sleep - 50 "begin to miss, fix the angle

its reflections from the crystal, then move the stranded and find reflections for. If the sample under study is not

is bent, then the components of the doublet will differ at the same angular position of the crystal. In the case when there are out of, the beams of crystallographic planes and К * _г due to spatial separation will be будут15 £ ^ 3ВББя at different angular positions of the crystal. The difference of the reflection angles - the angle Ф - is related to the radius of curvature of sample I by the formula

'- I = δ / φ, ......... ....... ₆₅ where 5 is the distance between points on

the surface of the crystal under investigation, into which the spectral components ^{fall to the σ and} is the base distance. To significant disadvantages described

First of all, the low resolution of the installation when measuring small crystal curvatures (the limit value of the curvature radius does not exceed 600 meters), the impossibility of local (base size 5 less than 2 mm) measurements of the curvature of the planes at K? 6O0m, due to the need to increase the basic bundles K _{oh 1} and Κ _{Λ <Ζ} .

This is usually achieved by increasing the distance between the crystals (monochromator and studied) and the elongation of the collimator.

In this case, information is lost on the magnitude and nature of the distribution of local internal stresses in the material, as well as in the spectrometer.

The purpose of the invention is to improve the accuracy and resolution of the ren’t * gene Spectrometer when measuring the local curvature of the crystallographic planes.

The goal is achieved by the fact that an X-ray spectrometer for studying single crystals, containing an X-ray source, a rotatable holder with a crystal monochromator, a movable slit, a rotatable holder of the monocrystal under investigation, a radiation detector, and means of measuring angles of rotation, are refracting at least two that are X-ray transparent triangular prisms that complement each other to a quadrilateral prism and installed with the possibility of their joint and relative rotation around boiling axis offset ottraektorii ray beam.

In this case, the triangular prisms are installed between the monochromator intercrystal and the monocrystal holder under study.

In addition, the second analogous pair of triangular prisms and means for selectively introducing both pairs of prisms into the X-ray beam trajectory are introduced into the spectrometer, and the axes of rotation of both pairs of prisms are located on opposite sides of the indicated trajectory and one prism from each pair is rotatable relative to the other prism pairs in opposite directions for each pair. In addition, a crystal analyzer is installed in the spectrometer. It is mounted in a swivel holder behind the holder. 757530

the single crystal and the prisms are located between the latter and the crystal analyzer.

FIG. 1 is a schematic diagram of an X-ray spectrometer; in fig. 2 - diagram 5 of the course of the beams as they pass through one of the systems of trigonal prisms; in fig. 3 - a block of trigonal prisms, which allows the X-ray beam to be deflected both in the direction of increasing, and in the direction of decreasing Bragg angles.

X-ray beams from source 1 fall on a crystal-monochromator 2, where the spectral doublet K ^ is separated. The slit device 3, when moving along the normal to the direction of the rays reflected from the monochromator, makes it possible to isolate the components K ^ and K ^. Before reaching the sample, the rays pass through a system of prisms 4, where they undergo refraction. The rotation of the trigonal prisms relative to each other and the registration of the angles is carried out using an angle measuring device 5. The beams, * ³ reflected from the monocrystal 6 under investigation, are recorded by the detector 7. To bring the crystal 6 into the reflecting position relative to one of the components of the doublet Co <· <30 is used the rotation mechanism (lever, micrometer screw) and the reference system of angles.

Measurements on spectrometer carried out as follows. 35

Triangular prisms are joined together so that they form a single rectangular prism (angle | b = 0), the large edge of which is perpendicular to the beam Ko, · The beam “<* is separated from the doublet reflected from the monochromator using slit 3. The single crystal 6 under study is set to the reflecting position with respect to the beam Κ _Λ ,, while detector 7 fixes a maximum on the diffraction peak of the line,

which serves as the starting point of the angle increment of 4 ⁵ due to

sample curvature. After the angular position of the maximum K #, is found, the slit 3 is moved and passed

component. If single crystal

6 is curved, then the detector 7 will not register reflections, or (in case of small bends) a part of the diffraction peak from

on the decline of the reflection curve. Removal to the maximum intensity of reflection is carried out by turning

triangular prisms 4 one relative-0 th other (the crystal under study remains fixed at the angle at which detector 7 will register the maximum intensity value of the beam reflected from sample 6, 65

Changing the angle of incidence of the beam K *. crystal 6 occurs as a result of multiple refraction in triangular prisms at β / 0. If at a certain angle β detector 7 has detected the maximum intensity, this means that the beam has deviated from its direction at] b = 0 (the prisms are connected) through an angle which is determined from the formula

where c £ is the unit decrement of the X-ray refractive index for the substance from which the prisms are made, ca is the minimum angle at the apex of the trigonal prism, related to the linear dimensions of the prism by the formula 1d </ ^ b / a, where b is the base width and a is the length in the plane of reflection of the spectrometer. The values of the angle | b are measured on the scale of the angle meter 5.

The angle 4 * is connected with the radius of curvature of the investigated crystal by the ratio

(2)

where 5 is the distance on the surface of the crystal between the points at which the components of the doublet fall.

To prove the formula (1) we turn to figure 2. Here ,

EA,>& ₄ > EC, denote the angles between the incident beam (solid line) and the corresponding inner and outer faces of the trigonal prisms. The dotted line shows a beam that has passed a rectangular prism without refraction, i.e. the case of trigonal prisms brought together ((b = 0). The equation for determining the angle Ф has the form

(3)

Where

Respectively for angles, E ^

we have

~ | ϊ>

_{(ί ()}

Since in the X-ray part of the spectrum, then, limiting ourselves to terms of the first order of smallness by ά ¹ , from (3) and (4) we obtain formula (1)

Two trigonal prisms, shown in figure 2, one of which rotates relative to another wok7 759930

The axis A will always deflect the x-ray beam in one direction (figure 2 shows a case of deflection in the area of increasing the angle of reflection), i.e., using a system of only two trigonal prisms, allows only ⁵ curvature to be measured

one sign (in Figure 2, the concavity of the cryvian is positive). To measure the curvature of the opposite sign, it is necessary to introduce another system of two trigonal prisms located either above or below the first system and having a different axis of mutual rotation. .

Fig. 3 shows a block of trigonal Drizm, which allows deflecting an X-ray 15 beam both towards large and small Bragg angles.

(And c B - axis · rotation systems, prisms). '

To obtain the deflection of the beam in the right direction, it is enough to raise 20 or lower the entire unit by the thickness of one prism and make a turn around the axis A or B by the corresponding angle £>. The selection of the necessary working system of prisms is carried out with 25

using a radiation detector: a drop in and ^x intensity with increasing angle of rotation of the prisms (b. indicates the need to change this system of prism to the upper (lower) one.

. We illustrate the possibility of obtaining small (less than 0.1 arc-sec.) Deviations of the x-ray beam by the example of Cu, K, * radiation passing through a system of prisms made by beryllium and having a low 35

absorption coefficient () ^ = 2.49 cm '*), The single decrement of the refractive index _of cp for beryllium at Ά = 1.54 A is> 5.25x1ο * ⁶ . With the value of the angles of -4 ° and $ = 1 ° (measurements?) Dd with an error of ± 2 angular seconds is carried out using a angle meter of the type UN), we obtain the minimum value of the angle 'P, equal to 10 "4 arc seconds. The latter at' basic distance 5 = 2mm allows, measure radii of curvature K _tyh . = 0, C>

X1 0 ³ km.

Since expression (1) includes the tangents of the corresponding angles, then already at = 70 ° the angle <P is sp 0.5 ang. Second, i.e. It reaches uglovo- permit ^{communication} of conventional spectrometers.

Using the proposed spectrometer, local curvatures of crystallographic planes are measured at a base distance of $ <2mm. At the same time, the 55th prism of the beam by an angle P practically does not change the value of 5, since d 5 = £? , where 2 is the distance from the output face of the prism to the surface of the investigated crystal. $ d When 'Ρ _ηιαχ = 0.5 arcsec. and E = 100mm increment d 5 * will be 2.5x10 '"' * Mm.to.e. a lot less than 5.

. Thus, using the proposed spectrometer is achieved by

increasing the limit of measurement of small bends of crystallographic planes.

Elok trigonal prisms can also be used for precision measurement of the relative change in the lattice parameter (Δα / α) in the case when measurements are taken on a three-crystal spectrometer with a crystal analyzer.

In this case, prisms are installed between the crystal under study and the analyzer crystal. This allows you to measure the value of &&> a with an accuracy of · 10 '“; relative units

Claims (4)

Claim " 1. X-ray spectrometer for the study of single crystals, "* containing an X-ray source, a rotatable holder with a monochromator crystal, a movable slit, a rotatable holder of the monocrystal under investigation, a radiation detector, means of measuring angles of rotation, characterized in that, in order to improve accuracy and resolution , at least two X-ray-transparent refracting triangular prisms, which complement each other to a quadrilateral prism, are inserted into the spectrometer and are installed with the possibility of their joint and relative rotation about a common axis offset from the path of the x-ray beam. 2. The spectrometer according to claim 1, which is based on the fact that triangular prisms are installed between the monochromator crystal and the holder of the single crystal under study. 3. Spectrometer on the PP. 1 and 2, differing in the fact that a second similar pair of triangular prisms and means of selectively introducing both pairs of prisms into the X-ray beam trajectory are introduced into it, with the axes of rotation of both pairs of prisms located on opposite sides From the indicated trajectory and one prism from each pair are made turning relative to the other prism of the corresponding pair in opposite directions for each pair. 4. Spectrometer on the PP. 1 and 3, that is, by introducing an analyzer crystal installed behind the holder of the monocrystal under investigation and a prism located between the holder and the analyzer crystal.