WO2016005516A1

WO2016005516A1 - Method and device for x-ray analysis

Info

Publication number: WO2016005516A1
Application number: PCT/EP2015/065739
Authority: WO
Inventors: Anatoliy Slobodskky; Taras Slobodskky; Wolfgang Hansen
Original assignee: Universität Hamburg
Priority date: 2014-07-10
Filing date: 2015-07-09
Publication date: 2016-01-14
Also published as: WO2016005516A9; DE102014109671B3

Abstract

A method for evaluating signals at an x-ray analysis device suitable for analysing a sample of crystalline substances, characterized by the following method steps: irradiating the sample with x-ray radiation, recording the scattered x-ray radiation using a detector, repeating the recording with a modified stress parameter for the sample, subtracting at least one pair of recordings at different stress parameters, analysing at least one difference image in respect of whether one or more reflections within the recorded Debye-Scherrer rings have a greater change in intensity than the surrounding reflections of the Debye-Scherrer rings, performing a quantitative analysis in relation to the extent of which crystals contained in the sample are rotated.

Description

Method and device for X-ray analysis

The present invention relates to a method for the evaluation of scatter signals on an X-ray analysis device as well as a device for X-ray analysis of a sample with crystalline substances.

The Debye-Scherrer method is used to study and identify crystalline substances in powder form. In the method known for 100 years, randomly arranged crystals are bombarded with monochromatic X-ray beams in a layer. For the scattered X-ray light, circular patterns form in the diffractogram. When the X-rays hit a crystalline particle sample just to satisfy the Bragg condition, the X-rays are diffracted and mutually reinforce each other in a constructive interference. Starting from the lattice planes on the scattering crystals, a cone forms, which shows up as a circular pattern on the diffractogram or a digital detector. As the wavelength of incident X-rays changes, cones with different angles of aperture are created and correspondingly different Debye-Scherrer rings are formed in the image. Using the Bragg condition, the recorded Debye-Scherrer rings provide information about the spacing of the lattice planes and allow conclusions to be drawn about the present crystal system with its respective lattice constants.

DE 10 2012 217 419 A1 discloses an analysis method for X-ray diffraction measurement data. In the known analysis method, peak positions and integrated intensities of a diffraction X-ray beam are determined on the basis of X-ray diffraction beam measurement data, counting the number of determined peaks of the diffraction X-ray beam. Finally, a quantitative analysis of the quantities of material contained in the sample can be carried out by evaluating integrated intensities of the diffraction x-ray beam. DE 101 60 326 A1 discloses a method and a device for determining a plurality of crystallographic directions in the orientation of single crystals. This is measured by rotating the single crystal in a single direction with the aid of an energy-resolving detector. The energy-dissipating detector is positioned in such a way that the energy of the beams diffracted at different network levels is registered in the detector and from whose energy the orientation of the different network levels in the single crystal is calculated.

From EP 2 112 505 Bl an X-ray diffractometer for the mechanically correlated adjustment of source, detector and sample position has become known. For this purpose, a linkage is provided, in which source, sample position and detector are arranged together and can be adjusted.

From DE 10 2012 111 504 AI an X-ray analysis apparatus has become known, which is able to load various measurement methods from a memory in a computer and execute there.

EP 1 650 558 A1 has disclosed an X-ray diffractometer in which diffracted and fluorescent X-ray radiation can be detected simultaneously with an X-ray detector using non-monochromatic X-ray light.

WO 2006/047267 A2 discloses a method and a device for suppressing fluctuations in the measurement signals of an X-ray analysis system. From US 2013/0089182 AI an evaluation system is known, can be detected with the plastic deformation on the surface of treated materials.

From Taras Slobodskyy et al. J.D. D: Appl. Phys. 46 (2013) 475104 (5pp) has disclosed that X-ray diffraction signals of individual Cu ("pseudo-crystalline nanocrystallites inside a thin-film solar cell absorber layer") have been reported. In, Ga) Se2 nanocrystals can be detected and analyzed for stresses.

DE 698 22 556 T2 has disclosed polybenzazole fibers with a high tensile modulus of elasticity and a process for their preparation. For analysis, a small-angle X-ray scattering is used, in which a mechanical stress on the fiber is varied. The measurements and evaluation methods give no indication of rotation of individual crystals.

US 2014/0093052 A1 has disclosed an in-situ measurement of an electrochemical cell in which small-angle scattering is used to detect changes in the battery cell during charging and discharging. The measurements and evaluation methods give no indication of rotation of individual crystals.

From Herklotzm, Markus et al "Advances in in-situ powder diffraction of battery materials: a case study often he new beamline P02.1 at DESY, Hamburg" (Journal of Applied Crystallography (2013), 46, pp. 1117-1127) For example, Figures 6 and 7 also disclose a study of altering the Debye-Scherrer rings, comparing load and unload changes become. The changes do not allow any conclusions about individual crystals or their rotation.

From A. Bjeoumikhov et al., "Capillary optics for real-time X-ray diffractometry," published in the Journal of X-Ray Science and Technology 13 (2005), pp. 185-190, it has become known to use a CCD camera for In-situ powder diffraction can be used on a small number of crystals, and rotation of individual crystals is not observed.

The invention has for its object to provide a method for the evaluation of scattering signals and a device for X-ray analysis, which provide additional information about the behavior of crystals and in particular of nanocrystals in the sample.

According to the invention the object is achieved by a method having the features of claim 1 and a device having the features of claim 8. Advantageous embodiments form the subject of the dependent claims.

The method according to the invention is provided and intended for the evaluation of signals on an X-ray analysis device which is suitable for the analysis of a sample of crystalline substances. The method according to the invention provides for a series of individual steps. First, the sample to be analyzed is irradiated with X-radiation and recorded the scattered X-radiation with a detector. In a subsequent step, a stress parameter, which can also be understood as a stress parameter, is changed for the sample and the recording of the scattered X-radiation is repeated. In a subsequent step, the records are subtracted in pairs at different stress parameters. The resulting difference images relate respectively to two different values of the stress parameter. In a subsequent step, at least one of the difference images is analyzed as to whether one or more regions within the recorded Debye-Scherrer rings have greater intensity or intensity variations than the remaining Debye-Scherrer rings. By recording at different values of the stress parameter, individual crystals, ie individual sections within the Debye-Scherrer rings, can change their position in the sample. Disproportionately large intensities or intensity changes will occur as a result of these positionally altered crystals. In repeated recording, essentially only the values for the stress parameter in the sample have been changed. Other parameters, such as irradiation angle, detector angle, orientation of the sample or the like, are not changed or only in a systematic manner. If the position of the crystals in the sample with the stress parameter remained unchanged, there would be no change in the recorded image. The difference image would be, apart from natural fluctuations in the measurement, without change. The invention is based on the recognition that stress parameters can lead to significant changes in the difference images. By changing the stress parameters, individual crystals, while maintaining their position, change their orientation in the crystal. In the method according to the invention, at least one difference image is analyzed as to whether one or more reflections within the indicated Debye-Scherrer rings have a greater intensity change than the surrounding reflections of the Debye-Scherrer rings. Also, a quantitative analysis is made of the degree to which crystals contained in the sample are rotated. With the method according to the invention, it is evaluated to what extent crystals contained in the sample are rotated by a change in the stress parameter. In a preferred embodiment, the stress parameter consists of an applied voltage or a current flowing through the sample. Voltage and / or current may be applied to the sample in a time constant or periodic manner. Other preferred stress parameters are electrical and / or magnetic fields which act on the sample. Likewise, electromagnetic waves, standing or running on the sample can be applied. Furthermore, mechanical forces can also be used as stress parameters for the sample. In the case of the stress parameters, it is sometimes known that these, such as a pressure, can also lead to a change in the lattice constants in a crystal without the crystal changing its orientation. In the method according to the invention, changes in the Debye-Scherrer rings, which are caused by a change in the lattice constant of the crystal due to the stress parameters, are not taken into account and, for example, excluded from the results. In general, the local intensities and / or intensity changes occurring in the difference images are so great that they can not be caused by a change in the lattice constants, the stress parameters.

In a preferred development of the method, an analysis of the difference images distinguishes between two possible types of behavior. In one type of behavior, an area of the Debye-Scherrer rings loses intensity while an adjacent area increases in intensity. In the other type of behavior, the local intensity varies from a single region of the ring. Depending on which type of intensity or change in intensity occurs in the differential image, it can be determined as a function of the stress parameters about which axis a rotation takes place in the sample. A particularly preferred method for evaluating the difference images is also the determination of the number of areas varying in brightness. This can provide information on how many of the crystals in the sample are rotated under the stress parameter in the sample. This can provide information about the quality of the sample, for example the efficiency of a solar cell.

The object of the invention is also achieved by a device for X-ray analysis of a sample with crystalline substances. The device has a detector for detecting X-ray radiation scattered on the sample in a two-dimensional recording. Further, the apparatus has a sampling device designed to apply different stress parameters to the sample. Furthermore, the evaluation unit is designed to subtract from each other at least one pair of records of an altered stress parameter for the sample captured images to a differential image. According to the invention, the evaluation unit is also designed to evaluate at least one difference image as to whether one or more regions within the recorded Debye-Scherrer rings have greater intensity and / or intensity changes than the remaining regions of the Debye-Scherrer rings. As already explained above for the method, it can be evaluated with the device according to the invention for X-ray analysis as to whether and to what quantitative extent crystals contained in the sample are rotated by a change in the stress parameter.

In a preferred embodiment, the evaluation unit is equipped with a memory which is designed to store a plurality of the difference images. In particular, a series of difference images allows a detailed detailed analysis to what extent and with what dependence on a varying stress parameter individual crystals rotate.

In a preferred embodiment, the sample device is designed to change stress parameters for the sample. When changing the stress parameters, the other parameters for recording the acquired image are not varied, so that every significant signal in the difference image is caused by the variation of the stress parameter.

In a preferred development, the sample device is designed to vary a voltage or a current of the sample. For this purpose, the sample device can be provided, for example, with electrical contacts, via which the voltage or the current can be applied as a parameter to the sample.

Likewise, the sample device can be designed to apply an electrical or magnetic field acting on the sample as a stress parameter to the sample. The orientation of the field can also be a varying stress parameter. In a further embodiment, the field is designed as an electromagnetic wave, which may be a standing or an ongoing electromagnetic wave. It is also possible that the sample device is designed to generate a mechanical force as a varying stress parameter on the sample.

A preferred embodiment of the invention is to use the method according to the invention for a crystal provided as a solar cell in order to define a critical number of regions of the recorded Debye-Scherrer rings with greater intensity and / or intensity change and to use the crystal only as a solar cell. if the number of measured areas is smaller as a critical number of areas. The intended use of the method according to the invention is based on the insight that crystals provided as solar cells sometimes have a different efficiency in power generation. One of the decisive factors is whether and to what extent crystals in the solar cell can rotate under a stress parameter, such as an applied DC voltage. If many crystals can rotate, it is to be expected that the sample has a lower efficiency than solar cell.

The invention will be explained in more detail below with reference to some examples. 1 is a schematic representation of the structure for X-ray analysis with schematically drawn diffraction vectors and a two-dimensional detector,

2 shows a schematic view of the effect of a rotation about a q _x -axis and the effect of the scattering image on the detector,

Fig. 3 is a schematic view of the Debye-Scherrer rings, and

4 a corresponding difference image,

5a-b, the difference images and two detailed views of the difference images and

Fig. 6 shows the intensity distribution in the difference image. FIG. 1 shows an X-ray source 10 in a schematic view with a collimated X-ray beam 12 impinging on a sample layer 14. The scattered X-ray radiation hits, as schematically illustrated, on the detector 16, the corresponding points pi correspond to p ₃ on the detector 16 to the different diffraction vectors qi-q. ₃

FIG. 2 shows a schematic view of the effect of a crystal 18 rotating about an axis, here the q _x axis. It can be clearly seen that in the reciprocal space the detector 16 has a curved surface and the scattering image 20 of the crystal 18 moves with the movement of the q-vector through the detector. The reciprocal space is essentially the Fourier transformed space of the waves.

Fig. 3 shows the images obtained in the structure of FIG. 1 to individual Debye-Scherrer rings 22. The measured sample is a solar cell of the type Cu (In, Ga) Se ₂ (CIGS). The solar cell contains, among other layers, an active CIGS layer with a thickness of 1 μm. The images were obtained with an X-ray energy of 8 kEV (λ = 1.55 A), wherein the X-ray beam was collimated to a diameter of 500 μιη. A DC voltage of -1.2 V to + 1.2 V was changed step by step on the sample.

The difference image shown in FIG. 4 corresponds to a voltage at 0 V and a voltage at 0.915 V. Of the differential image shown, the points marked 1 and 2 are of particular interest. They lie on the 112 diffraction ring and have increased significantly in intensity. This means that corresponding crystals have rotated by the applied voltage in an angular position that meets the diffraction condition. Point 3 is on the (220) / 204 diffraction ring. At this point, the diffraction intensity has clear decreased, that is, that a crystal has moved out of its diffraction condition by the applied voltage. Point 4 lies on the same diffraction ring as. The intensity profile of this point consists of two adjacent regions with different signs. This pattern corresponds to the rotation of the corresponding crystallites in the detector plane, as already described. Such signals are statistically expected.

Of particular interest is region 5, which is contained in the molybdenum ring and contains two lines. Since the crystals in this layer are much smaller and contributions from individual crystals overlap, they can not be distinguished. Therefore, the region 5 is due to a piezoelectric change in the lattice constant due to the applied voltage.

FIGS. 5a and 5b show detail enlargements of individual points appearing in the difference image. Figure 5a shows a point created by rotation of the crystal perpendicular to the detector plane. This point is characterized by having a large intensity change. Fig. 5b shows a colon with a decrease in intensity, for example in the region A and an increase in intensity, for example in the region Z. Such a colon in the difference image corresponds to a crystal rotation about an axis which lies in the detector plane.

6 shows in the lower area the intensity of a diffraction pattern of a solar cell at 0 V and the difference image with a voltage of 0.915 V applied to the solar cell. The difference shown is increased by the size 20 and shifted upward by 6 units. It can be clearly seen that a structure in the differential image occurs due to the applied voltage of 0.915 V. The invention makes it possible to measure and analyze the behavior of individual crystals in a polycrystalline material by applying a stress parameter to a sample. This allows, for example, the conclusion of crystal rotation in the sample or even very low concentrations of rotating crystals in the sample. Furthermore, the invention provides a non-destructive measuring method for detecting rotating crystallites in a sample. In this way, during the preparation and process management, conclusions can be drawn on the individual process parameters. Also, the amount of rotating crystals in a layer can be quantified, as well as the rotation speed. Even preferred directions, clustering of rotating crystals and other statistical information can provide information about material properties and optimal process control. Especially with solar cells, the invention allows conclusions to be drawn on the efficiency of the solar cell by analyzing differential diffraction patterns.

Claims

claims

1. A method for evaluating signals on an X-ray analysis apparatus which is suitable for analyzing a sample of crystalline substances, characterized by the following method steps:

Irradiating the sample with X-radiation,

Recording the scattered X-radiation with a detector,

Repeating the recording with an altered stress parameter for the sample,

Subtract at least one pair of records at different stress parameters,

Analyzing at least one difference image as to whether one or more reflections within the recorded Debye-Scherrer rings have a greater intensity change than the surrounding reflections of the Debye-Scherrer rings,

Quantitative analysis of the degree to which crystals contained in the sample are rotated.

2. Method according to claim 1, characterized in that the stress parameter to be applied is a voltage applied to the sample and / or a current flowing through the sample.

3. The method according to claim 1, characterized in that the stress parameter to be applied has an electric and / or magnetic field acting with the sample.

4. The method according to claim 3, characterized in that the field is designed as an electromagnetic wave.

5. The method according to claim 1 to 4, characterized in that the stress parameter to be applied has a mechanical force.

6. The method according to any one of claims 1 to 5, characterized in that a distinction is made in the analysis between difference images, in which two adjacent areas vary in intensity and in which a range varies in intensity.

7. The method according to any one of claims 1 to 6, characterized in that in the difference images, the number of varying in the brightness ranges is counted.

8. Apparatus for X-ray analysis of a sample with crystalline substances, with

a detector for detecting X-ray radiation scattered on the sample in a two-dimensional recording,

a sample device, which is designed to apply different stress parameters to the sample, and

- An evaluation unit which is adapted to create from at least one pair of records at a changed stress parameter, a difference image, wherein

- The evaluation unit is also designed to evaluate at least one difference image to see whether one or more reflections within the recorded Debye-Scherrer rings have a greater change in intensity than the surrounding areas of the Debye-Scherrer rings, and

- The evaluation unit is also designed to determine a proportion of crystals rotated in the sample.

9. Apparatus according to claim 8, characterized in that the evaluation unit has a memory which is designed to store a series of differential images.

10. Apparatus according to claim 8 or 9, characterized in that the sample device is designed to change stress parameters for the sample.

11. Device according to one of claims 5 to 7, characterized in that the sample device is designed to vary a voltage or a current across the sample.

12. Device according to one of claims 8 to 11, characterized in that the sample device is designed to apply an acting with the sample electric or magnetic field as a stress parameter to the sample.

13. The apparatus according to claim 12, characterized in that the field is designed as an electromagnetic wave.

14. Device according to one of claims 8 to 13, characterized in that the sample device is designed to produce a varying stress parameter, in particular in the form of a mechanical force.

15. Use of the method according to one of claims 1 to 7, characterized in that for a provided as a solar cell crystal, a critical number of areas within the recorded Debye-Scherrer rings is defined with greater intensity and the crystal only as a solar Cell is used when the number of measured areas is less than the critical number.