Volume 24(1) - Winter 2008

In order to solve various problems in materials, there are very high demands for crystal structure analysis.  However, most materials used in industries are in powdery or polycrystalline states, and it is often quite hard to obtain single crystals for some materials. Structure analysis from X-ray powder diffraction can be applied not only for crystal structure analysis of a material which is hard to obtain suitable single crystals, but also can be used for structure analysis under special conditions and/or in-situ observations that are difficult for single crystal structure analysis.

In recent years, to overcome the hurdles of structure analysis from X-ray powder diffraction, researchers in universities and X-ray instrument manufactures have developed experimental hardware and application software.  They have improved the performances of hardware such as a reduction of measurement time by increasing the brightness of an X-ray source and enhancing the sensitivity of a detector, and a reduction of calculation time by enhancing the performance of the application software.  Structure analysis from X-ray powder diffraction is now treated as a routine work, where research of powder diffractometry is active. In the beam line ID31 of ESRF that is managed by Prof. Andy Fitch, it is possible to automatically take up to 50 diffraction data of samples sealed in capillaries for structure determination using a special robot sample changer in one night. As a result of the improvements in research environment, the number of reported crystal structure analyses using powder diffractometry has been greatly increased.

In what follows, we would like to show examples of successful complicated crystal structure analysis using powder diffraction technique.
 

There are growing demands for mineral resources around the world, and rapid and accurate elemental analysis is required at a satellite laboratory in a mining site for quality check, geological resource survey, etc.  One of the Rigakus solutions for such requirements is the compact-size light-weight benchtop wavelength dispersive X-ray fluorescence spectrometer (WDX), Supermini.

Although a benchtop energy dispersive X-ray fluorescence spectrometer (EDX) is commonly used for an elemental analysis, WDX, with its superior spectral resolution and light-element sensitivity, is more suitable for the analysis of rocks and minerals, because they usually contain a large number of light- and heavy- element oxide components,

Supermini is equipped with a newly developed high power air cooled 200-W X-ray tube, which has about 4 to 6 times higher sensitivity than that of a former benchtop spectrometer. This enables an XRF analysis of a sample with high precision. This paper reports the results of an XRF analysis of rocks using a Supermini spectrometer.
 

Ultima IV is an advanced and versatile X-ray diffraction system equipped with a precision-engineering horizontal- sample X-ray diffractometer together with a conventional X-ray generator and a sealed-off X-ray tube.  Ultima IV is specially designed to allow for simple and reproducible changeovers form one selected configuration to another and vice versa.

A variety of configurations from a conventional model for an analysis of powder samples to an advanced model for the characterization of thin film samples can easily be selected by selecting and combining a goniometer, an optical system, a slit, a detector and various special-purpose attachments.

In recent years, with new developments in industrialized countries, there are increasing demands for the analysis of rare metals and other mineral resources. Supermini, a 200-W benchtop wavelength dispersive X-ray fluorescence spectrometer (WDX), has been developed to meet these demands. Supermini is a compact sized benchtop instrument without requiring cooling water, and this makes it easy to install and operate. Elements from light elements including Na and F to heavy elements can be analyzed with high precisions.

D/teX Ultra is a high-speed one-dimensional X-ray detector using a state-of-the-art semiconductor device, and has a superior X-ray detection capability and energy resolution than a conventional one-dimensional semiconductor X-ray detector. The advantages of a D/teX Ultra detector include: a drastic reduction of the measurement time, an acquisition of high-intensity diffraction data, and a reduction of background intensity.  Therefore, D/teX Ultra is one of the most, if not the most, advanced detectors, and it can be used for the measurements of a large number of samples and an insitu dynamical study of phase transition as a function of temperature or humidity. The detector can be used and mounted on a horizontal-sample general-purpose X-ray diffractometer, namely Ultima IV, a theta/theta rotating anode XRD system, TTRAX III.

There is a flood of high-tech functional devices made up of thin films. Cell phones and personal computers are integrated units of thin film devices, so are TV displays, recording media such as CD/DVD, their write/playback apparatuses, etc. X-ray measurement techniques are widely used for characterizing various thin-film materials and devices.

When a sample is “thin film,” there are precautions and constraint conditions, characteristics for a thin film.  For example, when a thin film has a strong preferred orientation, only one set of specific lattice planes can be detected.  This is one of the reasons why measurements of thin films are more difficult compared with that of a powder sample. This article will overview this series for the basic techniques for X-ray characterizations of thin films.
 

Since W. von Laue discovered X-ray diffraction using a zinc sulfide single crystal in 1912, single crystals including Si, Ge, LiF, etc. have been used as analyzing crystals for X-ray analysis. However, as the research and applications of X-rays advanced, the wavelength region also extended significantly. Analyzing crystals made of single crystals can no longer cover all X-ray analysis requirements.  A new type of analyzing crystals is each made of a periodic layer structure with a period longer than the wavelength of X-rays. For example, if two different kinds of thin layers are overlaid alternately to form a periodic multilayer structure, the multilayer can be used as an analyzing crystal for X-ray analysis. In fact, such a structure was proposed a long time ago after the discovery of X-ray diffraction. However, it was not until the 1970s that scientists were able to make multilayer devices because of the advances of sophisticated ultra thin-film deposition techniques such as electronbeam evaporation, sputtering deposition, etc. The development of multilayer X-ray optical devices has advanced rapidly since the 1970s. In 1980s, the Osmic, Inc. (now Rigaku Innovative Technologies, RIT) in the US commercialized multilayer devices for X-ray fluorescence analysis under the brand name of “Ovonyx”. The multilayer optical devices have now been widely used in X-ray diffraction, X-ray fluorescence, and X-ray projection/ imaging technologies.

A multilayer optical device is also called “artificial lattice,” “artificial multilayer film”, or “artificial stacked film”. In this article, we call it “multilayer optics,” or simply, “multilayer.”