Volume 32(2) - Summer 2016

A scientific discipline, which investigates crystal structures by means of the X-ray diffraction method, is called X-ray crystallography or simply crystallography. It originated in a discovery of the phenomena that X-rays are diffracted by crystals, and it has a history of more than one hundred years. Various analytical techniques based on X-ray diffraction have been developed along with the developments of X-ray sources, beam-collimating optics, detectors, mathematical algorithms and computers. X-ray diffraction techniques are used to determine the positions of atoms in a crystal with an accuracy in the order of 10⁻⁴ nm (1 nm＝10⁻⁶ mm). They are also used for the identification of crystalline phases of various materials and the quantitative phase analysis subsequent to the identification. X-ray diffraction techniques are superior in elucidating the three-dimensional atomic structure of crystalline solids. The properties and functions of materials largely depend on the crystal structures. X-ray diffraction techniques have, therefore, been widely used as indispensable means in materials research, development and production.

This article has been written for the people who are beginning X-ray analysis of crystalline powder samples using the diffraction method. In X-ray powder diffraction measurements, so-called an X-ray diffraction pattern is recorded, in which many peaks called diffraction lines queue on the abscissa calibrating the diffraction angle. We often hear that it is much more difficult to understand what this diffraction pattern means when the pattern is compared, for examples, with infra-red spectra or the TG-DTA curve in thermal analysis. If we can understand how this diffraction pattern is generated when X-rays irradiate a crystal, it will become much easier to understand the relationship between the X-ray diffraction pattern and the crystal structural information. One purpose of this article is to elucidate the mechanism of X-ray diffraction by the crystal. The knowledge required in reading this article is limited to the mathematics of trigonometric function and the physical principle of the superposition of waves. Imagination and inference by readers will suffice to understand this article.

Rigaku Oxford Diffraction single’s crystal diffraction systems are controlled with the user-inspired CrysAlis^Pro software. CrysAlis^Pro integrates and interfaces seamlessly with not only our own equipment but also with third party data collected on other diffraction systems. It delivers precise system control and superior X-ray data quality and analysis.

EasyX is an easy to use software package for completely integrated measurement and analysis of X-ray diffraction data. Crystalline phases can be automatically measured, identified, and quantified in just three clicks. EasyX is well suited for the analysis of industrial materials in the laboratory and on the production floor. It offers the best functionality and usability not only to XRD professionals but also to users with only general analytical laboratory experience. The computational part of EasyX is the same as that of PDXL, our industry leading analysis software so both beginners and experienced users can be sure of the highest quality analyses. EasyX is fully integrated with the MiniFlex 300/600 series of benchtop XRD systems. Operation and full analysis is completely turn-key and fully compatible with Rigaku’s CFR part 11 regulatory software solutions.

With your success utmost in our minds, the XtaLAB Synergy has been developed for single crystal X-ray diffraction. Using a combination of leading edge components and user-inspired software tied together through a highly parallelized architecture, the XtaLAB Synergy produces fast, precise data in an intelligent fashion.

SAXS (Small Angle X-ray Scattering) is a powerful tool for nano-scale structural analysis covering a broad range of applications from research and development to quality control. The technique targets a broad range of materials, from periodic and non-periodic structures including solid, liquid, liquid crystal and gels to research in advanced functional materials such as carbon fiber reinforced plastics (CFRP), nano-particle (NP) sizing, and coarse-structure analysis of macromolecules. Advanced functional materials, used increasingly in today’s nanotechnology-focused research, have nanoscale fine structural features that must be well-controlled. SAXS measurement and analysis is used for atomic and molecular-scale structure evaluations, but it can also be used for measurement of diffuse scattering caused from boundaries of electron density inhomogeneity. In the case of a periodic structure having 10 nm spacing, a diffraction peak is observed around 0.4 degrees in two theta using copper Kα emission line (λ＝0.15418 nm). This is an example of small angle scattering, or scattering which occurs at lower angles—typically less than 5 degrees.

Rigaku’s new product, NANOPIX, gets its name from “Nano Particle Inspection by X-rays”. It is optimized for SAXS measurement such as scattering occurs at low scattering angles. Moreover, It has been developed for not only the SAXS but also the atomic-scale structures that are in higher scattering angles around 20–30 degrees. Including both SAXS and WAXS, this new instrument is developed for multi-scale structure analysis of materials which have hierarchical structures.

Sample preparation methods for X-ray fluorescence analysis (XRF) featuring powder samples were discussed in the previous issues. Preparation of metal samples is introduced in this issue. XRF is superior to ICP and optical emission spectroscopy in reproducibility. However most of analysis errors in XRF can be caused by nature of sample itself and sample preparation, as in the case of powder samples discussed before. Analysis errors of metal samples come from (1) internal segregation, (2) defective surface, (3) surface roughness and uneven surface, (4) surface transformation, (5) metallurgical history, etc. Consideration of these points will provide more accurate analysis results.

In order to elucidate various biological phenomena occurring in vivo, it is essential to determine the structure of proteins. This article will focus on expression of proteins for X-ray analysis.

For performing structure analysis, the first challenge is to establish an expression system. Structure analysis requires large amounts of proteins with high purity, so it is essential to establish a large-scale protein expression and purification systems. Even target proteins that are only present in trace amounts in vivo can be overexpressed as recombinant proteins using genetic engineering techniques and appropriate hosts. In such cases, it is crucial to select an appropriate expression system from numerous existing protein expression systems. Some expression systems cannot be used or are more difficult to use, depending on whether the protein of interest is of prokaryotic or eukaryotic origin. For multi-domain proteins or proteins expected to undergo large structure change, regions containing only certain domains can be selectively expressed to suppress structure change. For rapid purification of the expressed proteins, in most cases, purification tags are generally added to the N- and/or C-terminals of proteins. Sometimes, the expressed proteins do not fold properly and are expressed as “inclusion bodies”, which cannot be directly used as starting materials for purification. As can be seen, there are many challenges to be overcome to obtain proteins that can be used as starting materials for structure analysis.

Stress analysis using X-ray diffraction is a well-known, effective technique for nondestructive evaluation of residual stresses in the surface of materials. Among X-ray stress analyses, the sin2 ψ method is the most widely used and very common, especially in the industrial field. In this method, residual stress is calculated by assuming a plane stress condition as the stress state on the surface of materials. In detail, it is calculated by multiplying the X-ray stress constant specific to materials by the slope of a regression line between observed diffraction angle (2θ) and the sin2 ψ function. As a result, it is not necessary to obtain the information on crystal lattice spacing (d-value) in the strain-free condition d0, which is very difficult to know beforehand. This is why use of the sin2 ψ method has become widespread as an effective analysis method.

On the other hand, in manufacturing processes such as surface modification, thermal processing, and fabrication, the stresses applied to the surface of materials may not only be an equi-biaxial stress state but also a biaxial or a triaxial stress state. Therefore, the need for more accurate inspection or evaluation of the stress state in the surface of materials is increasing; namely, biaxial or triaxial stress analysis is strongly required.

The Direct Refinement Solution (DRS) method proposed here is an effective technique for biaxial or triaxial stress analysis. This method calculates stresses using an equation that most faithfully represents the relationship between stress and strain in isotropic elastic bodies.

Since the stress state on the surface of actual materials must be assumed for the stress calculation, the DRS method has been developed to improve accuracy in the calculations. As one of its applications, this method is capable of analyzing stresses on the basis of a single Debye-Scherrer obtained by the single exposure technique. This technique is employed in our new portable X-ray stress analyzer SmartSite RS, designed for on-site measurements that require compact and

The development of new functional thin films and the fabrication of functional devices using these materials are the outgrowth of emerging demands for high efficiency, energy-saving, lightweight devices to further the pursuit of comfort and convenience in daily life. The “Smartphone” is a typical example, where numerous functional thin film based devices are employed, such as, display screens, backlighting, batteries, data storage  devices, etc. Characterization of functional thin films is necessary in terms of not only the phase identification of composing materials but also further crystallographic characterization of constituent crystals, such as their textures or orientation relationships with substrates, lattice distortions, film thicknesses etc., since these physical parameters are closely correlated with the devices’ performance.

A 2-dimensional (2D) detector enables various kinds of XRD measurements to be performed in a remarkably short time, covering a wide range of reciprocal space and thus, enables us to perform certain measurements with laboratory equipment that have previously been performed only at synchrotron facilities. Recently, the hybrid pixel array 2-dimensional detector (HPAD) has come into use for measurements with in-house XRD systems. The Rigaku SmartLab™ X-ray diffractometer can also be equipped with the latest HPAD, the “HyPix-3000”.(2) This detector is equipped with direct X-ray detection pixel array sensors, which enable capabilities such as high sensitivity, wide-dynamic range, and high spatial resolution.

Examples of X-ray analysis of modern functional thin film materials using 2D detectors are presented in this short series of articles. The article, Part 1 is focused on examples of polycrystalline thin films specimens, where how to effectively collect weak signals from thin films is crucial for the analysis. The forthcoming Part 2 article will be dedicated to cases featuring the analysis of epitaxial thin films with complex domain structures.

Total Reflection X-ray Fluorescence (TXRF) is a method that can be used for high sensitive elemental analysis on solid sample surface, and has been widely used for detecting contamination on wafer to improve fabrication process yield in the semiconductor industry. On the other hand, there has been increasing need for liquid sample analysis such as contaminated water along with a movement to use TXRF analysis technique in the environmental field.

The TXRF analysis can reduce background intensity, because primary X-rays irradiated with very low glancing angle are totally reflected on the sample surface, and scattered X-rays do not enter the detector. Moreover, the spectra with high S/N ratio can be obtained since only the topmost sample surface is excited to generate fluorescent X-rays. Wide range of elements from Al to U can be analyzed qualitatively and quantitatively by the energy dispersive detector, and it is common to utilize built-in relative sensitivity coefficients for quantitative analysis without using standard samples. Actual example of quantitative analysis of