Volume 29(1) - Winter 2013

Pressure is one of the important parameters that define the structure and state of materials.

A high-pressure diamond anvil cell (DAC) is commonly used to measure the “in-situ analysis” of the structural change against pressure in the X-ray diffraction experiment. In a DAC experiment, it is necessary to enclose the sample in a space less than ~200 μm in diameter in order to apply high pressure.  The diameter of the X-ray beam should be smaller than the window of the DAC. There are thus three issues that make this experiment difficult to perform using a laboratory X-ray system. A small X-ray beam requires a large amount of collimation that significantly reduces flux, the window for the DAC absorbs X-rays, and finally the sample size has to be small and this reduces the diffraction intensities. Because of these restrictions, it is often believed that a synchrotron radiation X-ray source is needed to observe the X-ray diffraction in a DAC experiment.

However, recent changes in fundamental technologies related to X-ray sources and X-ray detectors allow us to obtain single crystal structures from crystals as small as a few microns in diameter with a laboratory system.  These new laboratory configurations improve the S/N of the DAC experiment to allow elucidation of structural information in the laboratory.

The combination of a microfocus rotating anode X-ray generator (MicroMax-007HF) and a multilayer focusing optic system (VariMax), produces a brilliance that is an order of magnitude better than that of the combination of the conventional rotating anode X-ray generator and graphite monochromator. This high brilliant X-ray source is integrated in the latest single crystal systems. The DAC experiment can easily be measured with such a system.
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The elemental analysis of environmental samples is essential for the heath of human beings and an accurate and rapid analysis technique is demanded.

ICP-OES (Inductively Coupled Plasma Optical Emission Spectrometry) and AAS (Atomic Absorption Spectrometry) for elemental analysis are typical wet chemistry techniques. On the other hand, X-ray fluorescence (XRF) spectrometry has three advantages: easy sample preparation, high reproducibility and rapid analysis. It has also been widely used for environmental applications.

The energy dispersive X-ray fluorescence spectrometer NEX CG with polarized optics enables data measurements with low background and high peak-to-background ratio (P/B ratio). Therefore, trace amounts of hazardous elements contained in environmental samples can be analyzed with high sensitivity.  Moreover, the scattering fundamental parameter method corrects for the influence from non-measurable components in samples such as coal fly ash, soils and biological samples by using Compton and Thomson scattering intensities from a Mo secondary target.

In this paper, the analyses of hazardous and the other elements in a variety of environmental samples such as polluted soil and biological samples are introduced.

A newly developed DualSource RAPID II system utilizes two types of sealed tubes X-ray sources: for Cu radiation a 30 W micro-focus sealed tube generator with multilayer optics is used (MicroMax-003) and for Mo radiation a 3 kW sealed tube with a curved monochromator (SHINE) is used. It is well known that selecting a suitable X-ray source is essential to successful experiments. The Cu source is useful for absolute structure determination and resolving crystals with large unit cells. On the other hand, a Mo source is applicable to crystals that have high absorption or where very high-resolution data is needed, for example for a charge density study.

This DualSource system enables us to collect data using two different wavelengths within one system and one data collection. It is especially recommended for users who largely deal with various kinds of samples because an appropriate source can easily be selected for a particular sample.

The large detector aperture allows us to collect a wide 2θ range of data rapidly. The large aperture combined with Mo data collection produces diffraction resolution up to 0.45 Å, which is applicable for charge density studies. The combination of dual wavelength and a large aperture image plate system provides many advantages for various diffraction experiments.

A new sequential benchtop wavelength-dispersive X-ray fluorescence spectrometer, the Supermini200, has been released.

The Supermini200 successfully inherits all of the superior characteristics of the Supermini, such as an energy and space-saving design, good sensitivity due to a high powered 200 W tube, high spectral resolution utilizing WDX optics and highly flexible and feature-rich operation software.

Improvements to the spectrometer include:

• Easier operation using an “EZ Analysis” window
• SQX Scatter FP method for powder samples (optional)
• Oxygen analysis supported by SQX analysis
• Universal Power Supply for worldwide wall outlets

This article introduces the latest WDX spectrometer from Rigaku.

SmartStudio is a platform that seamlessly integrates various Rigaku software modules involved with operating the SmartLab diffractometer as well as analyzing data obtained from the SmartLab. It enhances the communication between the application software modules and increases ease of use. For example, the data generated from one Rigaku application software module can be sent to another software module with a single mouse click using the Launcher, an interface that serves as the starting point for application software modules.  Also, various processes from measurement to analysis are automatically executed by using a rec

Structural information of a protein molecule is very important for investigating protein function. MAD phasing continues to play a crucial role in the structure determination of novel proteins. In addition, the conventional method of heavy atom derivatization for the purpose of phasing still plays a crucial role in protein crystallography in novel protein structure determination.  Here, we introduce a product that improves the efficiency of protein structure determination using an X-ray fluorescence attachment and a dual wavelength X-ray system.
 

Due to the recent development of fundamental technologies of X-ray generators and detectors, such as X-ray focusing optics and area detectors, the size of the measurable crystals by a laboratory source has been dramatically reduced. In these days, a crystal of a few microns can sometimes be measured. However, obtaining quality diffraction data from such a small crystal, namely a microcrystal, requires special attention that is not necessary for a regular sized crystal. In particular, the handling of a microcrystal becomes more troublesome as the size of the crystal becomes smaller. The retrospective glass fiber and glue seems to be a better method than today’s conventional loop type mounts for a microcrystal. In this article, techniques and tools to measure diffraction data out of a microcrystal are introduced.
 

TXRF spectrometers are widely used as evaluation instruments for measuring contamination in the semiconductor fabrication process. This is mainly because the TXRF technique allows non-destructive analysis for almost all elements (Na~U) in the periodic table.

TXRF spectroscopy is possible due to the property of X-rays as they irradiate a flat surface, such as a Si wafer or glass. Each material has a unique critical angle. If the incident angle of the X-rays is above the critical angle, the X-rays penetrate the surface deeply; if the incident angle is smaller than the critical angle, the X-rays are reflected off the surface totally, or what is termed total reflection. In the total reflection condition, any ?uorescence X-rays will occur only from contamination on the surface and the surface material will not add background noise to the measurement. The penetration depth of the incident X-rays under the conditions of total reflection is theoretically around 5 nm, and thus TXRF is classified as a surface analysis. TXRF’s outstanding S/N ratio makes the detection of contamination on the surface of a sample possible with high sensitivity.
 

High-voltage and high-efficiency power devices are in strong demand as a way of decreasing energy consumption in a wide range of industrial and consumer products. Wide band gap semiconductors such as SiC, GaN, and diamond are candidates for producing these next generation power devices. Table 1 indicates the basic physical properties for these materials compared to Si. These materials have a much higher breakdown voltage and are expected to be used in future equipment requiring compact and low-loss conversion devices.  Among these materials, SiC is the most promising candidate and is expected to be used in a wide range of power device applications in the near future.

The band gap of SiC is approximately three times greater than Si and has a breakdown electric field strength nearly 10 times higher than Si as shown in Table 1. These characteristics result from the extremely strong atomic bonds in the crystal. Due to the strong atomic bonds, SiC will not melt at its original composition, even at high temperatures.  Even at a temperature of more than 2,800°C, at 100 atm, SiC remains in a phase in which a Si melt containing approximately 19%C coexists with solid graphite. Unlike Si, a direct crystal growth method from the melt is not possible with SiC. This poses significant difficulties in growing the large-diameter single crystals required for device production. For these reasons, single crystals are now mainly grown by the sublimation method (modified Lely method). SiC sublimes at approximately 2,500°C and grows on a single crystal seed placed in an environment of approximately 2,200°C. The sublimation rate determines crystal growth rate. Since this process involves extremely high temperatures, it entails various problems, including impurities migrated into the substrate crystal and crystal defects caused by thermal stress. In addition, SiC has many polytypes with different atomic layer stacking. It is important to control proper crystal polytype growth and avoid twinning. Recent improvements in crystal growth methods have solved many of these problems. In particular, the occurrences of micropipes, crystal defects that can fatally damage device performance, have been reduced to near zero. Current methods are capable of producing 6-inch large-diameter wafers. However, crystal growth process at such high temperatures is difficult and expensive. In addition, growth crystals still contain numerous defects, including dislocations.  Further technological advances are required, including investigations of other methods such as solution growth and gas phase growth.

Since the crystal growth is a high temperature process, it is difficult to control the impurity concentrations during bulk single crystal growth, which is essential for semiconductor device fabrication. The most important progress was achieved by introducing a step-flow epitaxy, which is homoepitaxial growth using the CVD method. The step-flow mechanism that induces crystal growth along the steps on the atomic surface using a hexagonal SiC crystal wafer 4° to 8° off-cut relative to the c plane. This method can produce epitaxial layers with satisfactory crystallinity even at 1,500°C, which is much lower than the growth temperature of the single crystal. This method also allows precise control of both p and n conductivity that are the key for the device performance. It is now possible to acquire commercial SiC devices according to these improvements.