Volume 32(1) - Winter 2016

X-ray topography is a powerful technique for evaluating crystal defects such as dislocations, stacking faults, scratches, and so on. High–performance electronics devices such as microprocessors, solid-state memories, imaging processors are fabricated on dislocation-free Si single crystal wafers. However, device fabrication processes often induce dislocations in the Si wafers that can affect the device’s performance. Because X-ray topography can evaluate these crystal defects efficiently, it plays an important role in the Si industry. Recently, composite semiconductors—for example, SiC-based materials—have been highlighted due to their higher band gap energies and higher breakdown voltages, features superior to those of Si for achieving higher-efficiency power devices. These devices are sought to improve the utilization efficiency of electric energy and reduce carbon dioxide emissions in order to prevent global warming. Although a lot of effort has been devoted to developing growth technology for achieving low-dislocation density crystals, even the highest quality crystals still have many dislocations, in the range of hundreds to thousands per cm². These dislocations can degrade the device’s performance. Therefore, quantitative measurement of the dislocation density is crucial for controlling fabrication yields and improving device reliabilities. Recently, a high-resolution and high-speed X-ray topography measurement instrument called XRTmicron has been released that allows users to acquire high-quality topography digital images. New software that analyzes the obtained digital topography images to count dislocations and identify their types has been developed. In this note, the operation of the software will be introduced.

X-ray fluorescence spectrometry (XRF) is well known as an analysis method with high precision by means of non-destructive and no contact analysis, and is therefore widely used for process and quality control at production sites.

In particular, total reflection X-ray fluorescence spectrometry (TXRF) developed in the 1970s is a special energy dispersive type XRF which excites elements only on the surface of sample.

TXRF has been one of the standard methods for wafer contamination analysis. However, TXRF has recently been gaining attention as a new technique for analysis of environmental samples.

Benchtop TXRF spectrometers are manufactured by a few companies in the world, but no models other than the original NANOHUNTER has the highly advanced functions such as auto alignment of the optical system. The new TXRF spectrometer NANOHUNTER II, which is improved by the employment of newly developed components, is introduced here.

X-ray fluorescence spectrometry is one of the common instrumental analysis techniques for routine quality control. This is due to high precision and easy sample preparation compared to other instrumental analytical methods. It is also a powerful analytical tool in the field of research and development for the analysis of advanced materials and products with the recent improvement of data processing of fundamental parameter method.

Rigaku has released a new high power sequential type Wavelength Dispersive X-ray Fluorescence (WDXRF) spectrometer ZSX Primus IV with tube above optics to the ZSX Primus family which meets wide variety of recent application needs.

The advantages of tube above optics have been recognized in the fields more widely due to its safe measurement and easy sample preparation for pressed pellets without using binder and protect film.

The new ZSX Primus IV has been developed as a successor of ZSX Primus II with higher performances and many additional software features.

Quality control is a top priority for the pharmaceutical industry. RMID (raw material identification) is an important part of quality control. Since health authorities of many countries including Japan joined PIC/S recently, quick and reliable RMID is becoming more important.

In the field of RMID, IR (infrared) and NIR (near infrared) spectrometry were used earlier than Raman spectroscopy. However, these analytical methods have limitations in the types of materials they can analyze. Raman spectroscopy can solve the many limitations or problems that were encountered in the past and is now widely recognized as a useful method for material identification.

One of the important advantages of Raman spectroscopy over IR and NIR spectroscopy is the fact that water does not cause interference, allowing measurement of moist samples and even aqueous solutions.

Another advantage is that the Raman spectroscopy enables direct material identification through a glass bottle or a transparent bag, thus minimizing the risk of contamination. In addition, Raman spectroscopy has an advantage over NIR spectroscopy regarding the ease of material identification. This advantage is due to the abundant, yet sharp and well resolved, spectral peaks in the Raman spectra. These sharp and abundant peaks in Raman allow for material identification without the need to build time consuming chemometric models as is required in NIR spectroscopy. Finally, inorganic materials are normally easier to analyze by Raman spectroscopy than by NIR spectroscopy which shows very weak peaks for inorganic materials.

The general preparation method of fusion bead, equipment, reagents and other important considerations were described in the previous article “Sample preparation for X-ray fluorescence analysis IV Fusion bead method—part 1 basic principles.” In this article, the preparation methods of various applications such as ferroalloy, sulfide and carbide are described.

Conventionally, these samples had been prepared as fusion beads after they were oxidized completely by mixing with a strong acid followed by drying. However, raising the temperature of the strong acids such as nitric acid degrades the working environment and the surrounding equipment corrodes due to its oxidizing power. Therefore, it has been necessary to work in a well-ventilated environment.

In the preparation method described here, oxidation reaction progresses slowly in the platinum crucible by oxidizing agent or oxidation catalyst without the use of strong acids. Thus it is possible to prepare fusion beads in a short time in a conventional environment. It should be noted that the described procedure assumes that grain size of the powder samples and the drying temperature of the samples and reagents are those for common fusion bead preparation methods.

If the grain size of the sample is coarse and the fusion bead is prepared without spreading the flux on the bottom of the platinum crucible, the sample will be oxidized insufficiently and form an alloy with the platinum in the crucible and cause irreversible damage. In this case, recasting of crucible may be required. For this reason, it is necessary to perform sample preparation carefully. Other additional analytical considerations regarding measurement of fusion bead are described at the end.

The previous series have discussed single crystal X-ray analysis of small molecules. This series will discuss structure analysis of proteins using X-ray diffraction. The explanation will focus in particular on differences between structure analysis of proteins and that of small molecules.

In structure analysis of proteins or small molecules, the purpose of single crystal X-ray analysis is to determine molecular structure and the basic principle is the same. However, there are considerable differences in the method pursuing each stage of structure analysis. These differences can be attributed primarily to differences in the size of the molecules. Whereas small molecules normally have a molecular weight ranging from a few hundred to thousand daltons, while that of proteins ranges from a few thousand to million daltons. There also are large differences in the components of the molecules and their chemical degrees of freedom. The atomic species comprising small molecules, and their framework, are diverse and there are no limitations in principle, however proteins are basically made up of 20 amino acids of known structure. Furthermore, the proteins of any living organisms on the earth are all comprised of L-amino acids alone, with just a few exceptions, and thus their absolute configurations are known. Also, an α-helix, which is one distinctive structure of proteins, is always a right-handed helix when tracing from the N-terminus to the C-terminus.

Despite the large amount of structure-related information which exists beforehand as described above, it is not unusual for structure analysis of a new protein to take a few years, including the stages of expression and purification of the target molecule. Why is this troublesome task carried out? The reason is that various benefits can be obtained once the structure of a protein has been determined.

X-ray diffraction is an analytical method for the characterization of the crystalline structure of a material, where the X-ray intensity (I) variation is recorded as a function of diffraction angle (2θ). The diffraction region where 2θ≦10° is called the Small Angle X-ray Scattering (SAXS) area, and the area where 2θ≧5° is called the Wide Angle X-ray Scattering (WAXS) or the Wide Angle X-ray Diffraction (WAXD) area. Since the X-ray diffraction method enables evaluation of various physical properties, it is widely applicable to qualitative analysis (crystal phase identification), quantitative analysis, crystal structure analysis, orientation analysis, particle size analysis and so on.

In general, with the powder X-ray diffraction method, measurement is performed by irradiating X-rays onto a large area of the sample surface, approx. 10 mm×2–3 mm. On the other hand, in order to perform an analysis of a tiny sample, or to analyze something like a micro area of a rock specimen, it is necessary to narrow the X-ray irradiation field to approx. 0.01 mm–1 mm. In the past, because these measurements used the slit collimation method to form a narrow beam by inserting a slit into the incident optical system, X-ray intensity was low and therefore measurements took a long time. However, with the latest X-ray diffractometers, which take advantage of the remarkable progress in technology for components such as the X-ray sources, optical components, detectors and so on, performing high-sensitivity measurements even for tiny samples has been made possible. In this article, various examples of characterizations realized by the state-of-the-art “SmartLab μHR” diffractometer system, equipped with cutting-edge technologies, such as the ultra-high brilliance microfocus X-ray source, a magnificent optic system,

Dr. Satoshi Omura of Kitasato Univerisity and his collaborator, Dr. William C. Campbell of Merck, were awarded the 2015 Nobel Prize in Physiology or Medicine “for their discoveries concerning a novel therapy against infections caused by roundworm parasites”. What they discovered is the breakthrough medicine ivermectin which cures onchocerciasis, an insect-borne disease caused by the parasite Onchocerca volvulus.

Onchocerciasis is estimated to affect 18 million people every year primarily in tropical regions such as West and Central Africa. Once infected, intense itching, rash, scarring and visual impairment occur, and in severe cases blindness is resulted. It is estimated nearly 300,000 people lose their eyesight to every year to onchocerciasis.