WO1996037898A1

WO1996037898A1 - The equipment for x-ray beam conditioning

Info

Publication number: WO1996037898A1
Application number: PCT/SK1996/000009
Authority: WO
Inventors: Dusan KORYTÁR
Original assignee: Korytar Dusan
Priority date: 1995-05-23
Filing date: 1996-05-20
Publication date: 1996-11-28
Also published as: SK68395A3

Abstract

The equipment for X-ray beam conditioning is formed by a compact monochrocollimator consisting of at least three diffractors (51) formed by the walls of the crystal material (11) in the leading channels (4). The arrangement is such that the successive diffraction cones of the diffractors (51) share at least one generator and that for each of the diffractors (51) the angle between the successive generators is just the vertex angle of its diffraction cone.

Description

The equipment for x-ray beam conditioning

BACKGROUND OF THE INVENTION Field of the Invention

The presented invention relates to the equipment for X-ray beam conditioning, mainly for apparatus for X-ray diffractometiy.

Brief Description of the Related Art

To achieve high angular resolution crystal monochromaτors or monochrocollimators significantly decreasing the angular divergence and wavelength spread of the X-ray beam coming from the X-ray tube are used in various areas of X-ray diffractometry. This decrease is due to the diffraction in one, usually horizontal plane. The angular setting for a given wavelength according to the X-ray tube used and for a given crystal (mostly silicon or germanium) is given in the first approximation by the Bragg law. The X-ray beam formed in this way falls at the sample attached to a precise goniometer allowing to measure with high angular resolution the diffraction curves characterizing the structure of a sample.

Significant improvement of the above parameters of the beam from the X-ray generator is provided already by the so called non-dispersive setting of the sample and monochromator with one, either symmetrical or asymmetrical diffraction. This setting preserves high intensity of the X-ray beam but the necessity to use further monochromator and tedious readjustment when changing to another diffraction represent a meaningful disadvantage.

Even more pronounced decrease of the angular divergence and of the wavelength spread is provided sequentially by monochrocollimators with two, three, or .four successive diffractions utilizing the dispersion setting, too.

At present the advanced high resolution diffractometers utilize for the monochromatization and collimation three or four symmetrical or asymmetrical coplanar diffractions.

The monochrccollimator with three diffractions is based on two independent goniometers. A channel-cut monolithic block with two diffractions in non-dispersive setting is attached to the first one, and to the second one a single crystal with the third diffraction set dispersively. The monochrocollimator with four diffractions uses two goniometers, too. A monolithic block with two diffractors in non-dispersive setting is attached to each of them while these two blocks are arranged dispersively relatively one to the other. The advantage of this monochrocollimator is also the fact that the outcoming X-ray beam continues in the direction of the beam falling at the monochrocollimator from the X-ray generator. The disadvantage of these monochrocollimators is the necessity to use two goniometers and emerging from this demands on the size of the equipment, on the precise and tedious adjustment of both goniometers, as well as on mechanical and thermal stability required by very precise setting of the angular position of the individual diffracting planes.

SUMMARY OF THE INVENTION

The drawbacks mentioned above are to a large extent removed by the equipment for X-ray beam conditioning, the incoming and outcoming beams being mainly in the same direction, which is based on the principle that this monochrocollimator is compact It contains at least three diffractors formed by the crystal walls of the leading channels. The arrangement of the diffractors is such that the succesive diffraction cones of symmetrical diffractors or deformed diffraction cones of asymmetrical diffractors share at least one generator. At the same time, for each of the diffractors the angle between the successive generators is just the vertex angle of its diffraction cone. Alternatively, it is possible to form at least one reflector on the crystal walls in the leading channels between the successive diffractors. The reflection cones of this reflector share at least one generator with neighbouring diffractors or reflectors. At the same time, for each reflector the angle between the successive generators is just the vertex angle of the corresponding reflection cone. The monochrocollimator is monolithic, formed from the only crystal. Coupling of the vertex angles of the diffraction cones of successive symmetrical or asymmetrical diffractors and/or between a symmetrical and an asymmetrical diffractor can be provided also by a rigid joint of two equal crystal materials or different ones. The joint is formed at the cut faces of these materials.

The main advantage of the monochrocollimator according to the invention is the fact that due to its compact form there is no need of two goniometers to adjust the angular position of two separate crystal blocks, which allows its miniaturization. In due course it has higher mechanical and thermomechanical stability and allows higher precision of the measurements and at the same time simpler manipulation and shorter time to prepare the measurements When using the asymmetrical diffractors it allows the beam comρress ion or expansion in one direction at the decreased loss of intensity.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in more detail in the enclosed drawings from which Fig.1 shows a monolithic monochrocollimator where four symmetrical diffractors are prepared in one crystal

Fig. 2 shows a monohthic monochrocolli mator where four symmetrical diffractors and one reflector are prepared in one crystal

Fig.3 shows a compact monochrocollimator prepared by joining two different crystal materials and consisting of two symmetrical and one asymmetrical diffractors.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The equipment for X-ray beam conditioning, called also the moncchrocollimator, is attached either to the body of the goniometer or directly in the X-ray tube of the X-ray diffractometer. As the example it was prepared according to Fig.1 for the wavelength λ=0.178892 nm. Based on the Bragg law it is possible to choose suitable combination of the lattice parameter, diffraction vectors, and the outward normals to the active surfaces of the diffractors for a given wavelength and for the required angular resolution and wavelength dispersion of the beam outcoming the monochrocollimator.

Germanium monocrystal (a=0.565745 nm) is used as the crystal material and successive diffractions of (220) and (440) types are chosen. As the outward normals to the active surfaces are s^I =(-0.788;-0.616;0.000), s^II =(0.788;0.616;0.000), s^III =(0.999;0.040;0.013), s^IV =(-0.999;-0.040;-0.013), according to these parameters are into the monocrystal 11 cut the precisely oriented leading channels 4 , which are surface-treated to high planarity and crystal perfection.

The primary beam from the X-ray generator, about 1 mm wide, and with high angular divergence and wavelength dispersion falls in the channel 4 onto the crystal wall 11. in the position of the entrance diffractor 51 and after multiple diffractions at successive diffractors 51 comes out of the monochrccollimator in the direction of the primary beam as the secondary beam 3 with significantly decreased angular divergence and wavelength dispersion (spread) within the K_α1 line. Secondary beam 3 conditioned in this way probes the measured sample (e.g. semiconductor substrate, heterostructure, multilayer, polycrystalline layer) attached to the goniometer of a high resolution diffractometer.

A monocrystal of silicon 12 is used as the crystal material in the example depicted in Fig.2. The leading channels 4 are formed in such a way that for example after the second diffraction at the diffractor 52 the X-ray beam 21 passing through the transition channel 4 hits the wall of the monocrystal sihcon 12 under the angle lower than the critical angle (about 0.26 deg) by which fact the total reflection occurs and the small change of the direction of the passing X-ray beam 21 enables together with the further diffractions at diffractors 52 the optimal setting of the parameters of the secondary beam 3.

In the example depicted in Fig, 3 the monochrocollimator consists of two different monocrystal materials, namely monocrystal of germanium 11 and silicon 12, faces of which , cut under precisely adjusted angles, are bonded forming a rigid joint 7. The cut angles correspond to the vertex angles of their diffraction cones. The primary beam 2 after two symmetrical diffractions at walls of the germaniiim crystal 11 in transition channel 4 hits the asymmetric diffractor 53 in the transition channel 4 at the wail of the silicon crystal 12 which causes its about 100 times compression in which way the secondary beam 3 is adequately formed before its incidence at the tested sample. Industrial Exploitation

The monochrocollimator according to the invention is advantageously exploitable at high resolution diffractometers and reflectometers used to characterize monocrystal and polycrystal materials and layers , as well as multilayers. It may be used for neutron and γ- radiation considering the corresponding wavelengths.

Claims

1 The equipment for X-ray beam conditioning, the incoming and outcoming beams being mainly in the same direction, characterized by the fact that this monochrccollimator is compact and contains at least three diffractors (51,52,53) formed by the walls of the crystal material (11,12) in the leading channels (4) in such a way that the successive diffraction cones of symmetrical diffractors (51,52) or deformed cones of the asymmetric diffractors (53) share at least one generator and that for each of the diffractors (51,52,53) the angle between the successive generators is just the vertex angle of its diffraction cone.

2. The equipment as claimed in claim 1 , characterized by the fact that at least one reflector (6) is formed on the crystal walls (11,12) in the leading channels (4) between diffractors

(51,52,53) in such a way that the reflection cones of the reflector {6) share with the neighbouring diffractors (51,52,53) and/or reflectors (6) at least one generator, the angle of the generators being for every of the reflectors (6) just the vertex angle of its reflection cone.

3. The equipment as claimed in claim 1 or in claims 1 and 2 characterized by the fact that the monochrocollimator is monohthic, formed from the only crystal.

4. The equipment as claimed in claim 1 characterized by the fact that the coupling of the vertex angles of the diffraction cones of the successive symmetrical diffractors (51) or asymmetric diffractors (53) and/or between asymmetrical and asymmetrical diffractor (53) is provided by a rigid joint (7) of two equal materials (11) or different ones (11,12) formed at their cut faces.