Volume 30(1) - Winter 2014

Although high-resolution X-ray diffraction (HR-XRD) has been commonly employed for the crystallinity characterization of GaN-related materials, special care is required due to the complexities resulting from peculiar features in GaN-related materials, as explained in the preceding article.

General explanation for the application of HR-XRD techniques to the characterization of semiconductor epitaxial films or bulk single crystals can be found in various textbooks. Therefore, this article will focus on special considerations to be taken in the application of the HR-XRD technique to GaN and related optoelectronic and power-electronic device materials.

In addition, the latest hot topics in the HR-XRD characterization techniques for GaN-related materials will be shortly reviewed.

In modern society where our daily environment is supported by various electronic devices, it is critical to pursue opto-electronic or power-electronic devices with less environment impact and with higher efficiency of energy conversion to ensure a sustainable society. GaN (gallium nitride) and related materials have been a focus of attention for the issue of sustainability.

Rigaku has been receiving a large number of questions concerning characterization techniques of GaN and related materials. Rigaku’s investigation led to the conclusion that there exist specific difficulties inherent in the characterization of GaN related materials. Some of them originate from the uniqueness of the crystallographic features of GaN, and some of them are inherent to the heteroepitaxial growth of GaN films with huge lattice mismatches.

These findings were a motivation to produce a special article for the Rigaku Journal to review and highlight the topics in the characterization techniques of GaN-related materials, that show promise for optoelectronic and power electronic applications. In this article, general features of the crystallographic nature of GaN-based materials are discussed. Recent topics concerning XRD characterization techniques are the subject of the next article.

A current trend in drug delivery systems is the use of multicoated or orodispersible tablets. These new systems increase bioavailability and can improve patient compliance by removing the need to swallow. The functionality of these structured tablets is sensitive to fluctuations in the manufacturing process. The chemical formulation is important, but now the physical properties of the active ingredients and other compounds in the tablet have become important for the development, design, process optimization and quality control.

A prospective technique for the visualization and analysis of the 3-dimensional structure of pharmaceutical solids is sub-micron X-ray microscopy. Pharmaceutical applications of this technique have been limited for two primary reasons. The first reason is that the penetrating power of the X-rays used by the conventional systems is too high for small organic samples composed of the light elements such as carbon, hydrogen, oxygen and nitrogen. The small size and elemental composition of these samples make them too “transparent” to the X-rays of conventional systems, and thus limits the application areas of the existing technology to heavier samples such as electronics devices (silicon, gallium arsenide) or bones (calcium and phosphorus). The second reason is that pharmaceutical applications require both high resolution and a wide field of view, concurrently. Specifically, a resolution of a few microns is needed over the whole tablet, several millimeters, to evaluate granule deformation or micro-cracks caused by compaction during tableting. Until now, it has been difficult to satisfy these two conflicting requirements by X-ray analysis.

In order to make high resolution, large field of view measurements possible, Rigaku has developed the nano3DX, a novel X-ray microscope capable of analyzing the sub-micron structures of granules and tablets. This article reports the result of the measurements on several over-the-counter (OTC) tablets to evaluate the effectiveness of the system for pharmaceutical applications.

The previous article described data collection. When data collection is done, the next step is to determine the structure. This article discusses critical points in structure analysis.

XRF (X-ray fluorescence) analysis as a technique is widely used in academia, research and development and industry as an analysis tool for the determination of elemental composition of materials. Unlike wet chemical and other instrumental techniques which require the use of hazardous chemicals and difficult preparation methods to dissolve samples for analysis purposes, the quick, accurate, sensitive non-destructive analysis technique of XRF makes it attractive as an analytical technique, this coupled with the fact that it can be used by non-technical users and does not require expert knowledge and high skill levels to produce good, reliable, reproducible analytical data. XRF is considered to be less labor intensive and more environmentally friendly that the aforementioned methods.

XRF has many advantageous features as mentioned above but all of these features rely on a good sample to present to the XRF system.

It would not be an over statement to say that XRF analysis data quality is directly linked to the quality of the sample preparation technique.

A series of articles designed to cover all aspects of sample preparation for XRF will appear in the journal over the course of the next several months.

The XRTmicron is a topography measurement system which can reduce measurement time by one order of magnitude compared to previous systems by using a new high-brilliance microfocus X-ray source, together with an X-ray mirror optical system and high-sensitivity/high-resolution X-ray camera designed for that source. Furthermore, it can automatically perform tasks ranging from sample setting to measurement and crystal defect analysis, and thus is useful not only for R&D but also for quality control. It can also non-destructively detect problems such as dislocations and other crystal defects, threading dislocations to the surface, and defects of the epitaxial layer. By customizing the configuration of the target, optical system, detector, sample stage and loader (automatic transfer unit), the system can be applied to a diverse range of monocrystal materials including Si, SiC, GaN, Ge, GaAs, quartz, LN, LT, sapphire, rutile, and fluorite.

The newly released wavelength-dispersive X-ray fluorescence sulfur analyzer, Micro-Z ULS (Ultra Low Sulfur) meets the current needs for the analysis of sulfur in petroleum.

The sulfur content in gasoline needs to be controlled in order to reduce air pollution, lengthen the lifetime of automobile catalysts, and improve engine reliability. Many countries and regions have established regulations for gasoline sulfur (S) content in line with Euro 5(less than 10 ppm).

For compliance verification, X-ray fluorescence XRF) spectrometry is the definitive analysis tool for use at distribution terminals and refineries, as well as mobile or stationary testing laboratories.

In recent years, there has been an increasing need for an instrument which does not require the use of helium gas for situations where acquisition or delivery of helium to the analysis site is difficult.

The Micro-Z ULS was designed to meet these trends

• Optimized optics for sulfur analysis
• No need for cooling water
• Plug-in power supply system
• Simple and easy operation for daily analysis
• Helium gas is not required
• Safety method without combustion
• Meets the requirement of ASTM D2622, ISO20884 and JIS K2541-7

In X-ray diffractometry, a variety of detectors are used depending on the purpose of the measurement. In recent years, in addition to the previously used 0D detectors (scintillation counters etc.), there has been increasing use of 1D detectors in which multiple detector elements are packaged into a single unit using the latest semiconductor technology. These semiconductor 1D detectors enable measurement with high-intensity using multiple elements, high-resolution with a strip width of 100 microns or less, and a high P/B (peak/background) ratio.

The D/teX Ultra 250 1D silicon strip X-ray detector introduced here is a new type of detector that makes major improvements on previous 1D detectors, and achieves dramatically improved performance. The D/teX Ultra 250 can measure extremely high-intensity data, approximately 150 times that of a scintillation counter (SC). In addition to detection of even smaller trace components and micro-area measurements on small samples, it also enables increased speed in tasks such as multi-point measurement, in-situ measurement and reciprocal space mapping measurement. These detectors work well in a variety of fields, including R&D and quality control.

The Rigaku PlateMate is a tool that allows one to mount SBS format crystallization plates on Rigaku goniometers for in situ diffraction experiments. Protein crystallography often requires screening large numbers of crystals to identify samples suitable for X-ray data collection. Traditionally, crystallographers mounted crystalline samples in capillaries — a time consuming task often resulting in damaged crystals — to evaluate sample quality prior to cryo-freezing. The PlateMate, a tool originally designed by crystallographers at AstraZeneca and adapted by Rigaku, streamlines the screening process because it eliminates the need to harvest crystals from crystallization plates. Instead, crystals can be evaluated in situ, using existing X-ray diffraction equipment, to determine whether they are composed of protein or salt and to evaluate diffraction resolution, mosaicity and other crystal parameters. Thus, the PlateMate is a low-invasive, fast tool for benchmarking diffraction quality prior to sample harvesting and freezing.