Abstract
The 2010 summer workshop on buried interface science with x-rays and neutrons was held at Nagoya University, Japan, on 25–27 July 2010. The workshop was organized by the Japan Applied Physics Society, which established a group to develop the research field of studying buried function interfaces with x-rays and neutrons. The workshop was the latest in a series held since 2001; Tsukuba (December 2001), Niigata (September 2002), Nagoya (July 2003), Tsukuba (July 2004), Saitama (March 2005), Yokohama (July 2006), Kusatsu (August 2006), Tokyo (December 2006), Sendai (July 2007), Sapporo (September 2007), Tokyo (December 2007), Tokyo-Akihabara (July 2009) and Hiratsuka (March 2010). The 2010 summer workshop had 64 participants and 34 presentations.
Interfaces mark the boundaries of different material systems at which many interesting phenomena take place, thus making it extremely important to design, fabricate and analyse the structures of interfaces at both the atomic and macroscopic scale. For many applications, devices are prepared in the form of multi-layered thin films, with the result that interfaces are not exposed but buried under multiple layers. Because of such buried conditions, it is generally not easy to analyse such interfaces. In certain cases, for example, when the thin surface layer is not a solid but a liquid such as water, scientists can observe the atomic arrangement of the liquid–solid interface directly by using a scanning probe microscope, of which the tip is soaked in water. However, it has become clear that the use of a stylus tip positioned extremely close to the interface might change the structure of the water molecules. Therefore it is absolutely crucial to develop non-contact, non-destructive probes for buried interfaces. It is known that analysis using x-rays and neutrons is one of the most powerful tools for exploring near-surface structures including interfaces buried under several layers. In particular, x-ray analysis using 3rd generation synchrotron radiation is highly reliable in practice, as well as being quantitative and reproducible. The use of neutron analysis complements x-ray experiments, and helps to enhance information such as contrasts in soft materials and magnetic structures, which are not always given clearly by x-rays. The techniques ensure non-contact, non-destructive measurement, and one can also use the same specimen for further analysis by other methods.
On the other hand, we are now aware that it not always straightforward to solve many realistic problems related to buried interfaces. Although advanced synchrotron x-rays and neutrons are highly useful, we still note many limitations. Collaboration with theoreticians is one of the most important directions in which to improve analysis. Over the past couple of years, scientists have argued over the existence of a depletion layer between oil and water. The argument is far from settled, even though highly sophisticated x-ray reflectometry seems to have given quite strong experimental evidence. In most cases, analysis of x-ray reflectivity depends on the model. This is good provided that one can be sure of the validity of the model, as in the case of multilayered thin films in industrial devices. However, sometimes our main interest lies in the model itself. Therefore, we should insist on introducing something new to justify the model scientifically, instead of just claiming that x-ray data can be explained by a certain model. Probably collaboration with theoretical research could be helpful. Another important direction would be to develop a method of model-free analysis.
During this workshop, participants talked about the present status of their own work. The workshop was open to those who are not particular specialists in x-ray and neutron experiments, but discussions were detailed and thorough. We discussed how buried interface research by x-ray and neutron experiments can be strengthened in the future. One of the most important extensions is high resolution in space (micro area) and time (quick and realtime). Current x-ray methods can give atomic-scale information for quite a large area on a scale of mm2–cm2, but it is also important to see a specific small area rather than the average structure of the wide area. In addition, there is a need to see unstable changing structures and related phenomena in order to understand more about the mechanism of the functioning of nano materials. Quick measurements are therefore important. Another effective extension would come with combining several x-ray and neutron techniques (reflectivity, grazing-incidence small angle scattering (GISAS), diffraction, x-ray absorption and emission spectroscopy etc). The use of coherent beams and several other new approaches are also significant.
We do not, in this current volume, intend to present what could be termed conference proceedings in a strict sense. Some papers were contributed by those who could not attend the workshop. Other papers were written on topics that were not presented during the workshop. We have always argued in favour of the significance of publishing such collections of papers; isn't it more important for young scientists to publish their results in a good ordinary journal with a high impact factor? The answer is obvious. We have already published so many papers in leading journals, and therefore, the next step would be to share information among specialists (including those who will become specialists) at a deeper level. Young scientists should contribute their work to such collections of papers, in addition to ordinary journals. In this way, almost all specialists in this field will read and respond to them. Publishing papers here will become a starting point for new discussions. I would also like to mention that almost all the papers included in this issue were reviewed thoroughly by four reviewers, who mainly make up the specialist group of the Japan Applied Physics Society. I sincerely acknowledge the efforts and assistance of all my colleagues during the editing of this issue.
This publication was financially supported by National Institute for Materials Science, Japan.
Kenji Sakurai National Institute for Materials Science Chairman of the workshop
A list of previous publications by our group:
1. J. Phys.: Condens. Matter 22 (2010) http://iopscience.iop.org/0953-8984/22/47 2. Trans MRS Japan 34 No 4 (2009) 3. 'Introduction to X-ray reflectivity' (Kodansha, 2009) [in Japanese] 4. Trans MRS Japan 33 No 3 (2008) 5. J. Phys.: Conf. Ser. 83 (2007) http://www.iop.org/EJ/toc/1742-6596/83/1 6. Trans MRS Japan 32 No 1 (2007) 7. Report on buried interface sciences with X-rays and neutrons (2006) http://www.nims.go.jp/xray/lab/hot/kaimen.pdf [in Japanese] 8. KEK Proceedings, 2006-3, 'Buried Interface Science with X-rays and Neutrons' (2006) 9. KEK Proceedings, 2004-5, 'Nano science/technology with synchrotron and neutron reflectivity' (2004) [in Japanese] 10. Trans MRS Japan 28 special issue (2003) 11. KEK Proceedings, 2001-25, 'Structural analysis of thin films and multilayers by X-ray and neutron reflectivity' (2002) [in Japanese]