The reflection high-energy electron diffraction (RHEED) is a powerful tool for surface studies and widely used for surface structural analysis in monitoring epitaxial growth. In this article, it is described that RHEED is developed as a tool in surface studies such as structure determination of crystal surfaces, evolution of surface structures by epitaxial growth and monitoring thin film growth processes. Recent novel RHEED techniques for surface structural analysis are also described.

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  Surface x-ray diffraction is a valid method of studying the atomic-scale structure and morphologies of surface and interface. It has been developed to be a powerful tool with the evolution of synchrotron light sources and is being widely used in light of growing importance of surface and interface in science and technology. In this review paper, first, I review the basics of surface x-ray diffraction briefly and then introduce recent progresses in the method of structural analysis and experimental techniques: iterative phase-retrieval method for the direct structural analysis, coherent surface x-ray diffraction for studying inhomogeneous structures, and high-speed measurement techniques for monitoring dynamics at surface and interface. Finally, I briefly mention some future aspects.

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  Total-reflection high-energy positron diffraction (TRHEPD) is a surface-sensitive tool owing to the total reflection of positrons. Since the sign of the crystal potential energy for positrons is positive, opposite to that for electrons, the positron beam at a grazing incidence is totally reflected at a crystal surface. The penetration depth of the positron beam in the total reflection region is estimated to be about a few Å, which corresponds to the thickness of 1-2 atomic layers. Thus, the positron beam in the total reflection region sees only the topmost surface layer of the crystal. Slightly over the critical angle for the total reflection, the positon beam also sees the underlying surface layer. Adjusting the glancing angle of the incident positron beam, the diffraction intensity selectively contains information about the topmost and the underlying surface layers without any effect from the bulk. Therefore, the TRHEPD is very useful for structure determinations of crystal surface and two-dimensional atomic sheet adsorbed on the substrate. In this paper, we will show the surface-sensitivity of the TRHEPD. Shown is also the recent result of silicene, two-dimensional atomic sheet of silicon, using the TRHEPD.

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  This review written in Japanese is directed to graduate students willing to be part of the emerging field of ultrafast structural dynamics. It provides them with all the basic assumptions and experimental tricks of femtosecond optical spectroscopy and diffraction techniques. The progress in the development of femtosecond X-ray and electron probes during the last twenty years has been tremendous, which provides us with the temporal and spatial resolutions required to observe atoms in motion. Recently, these direct observation of atomic motion with femtosecond X-ray and electron diffraction techniques has gain much attention in the fields of material physics, chemistry or even biology. One good example involves the developments of X-ray free electron laser (XFEL). The table-top femtosecond electron diffraction setups, on the other hand, have comparable brightness and temporal resoution as the facility-top XFELs with proper calibation. This review is mainly focused on generation of ultrashort electron pulses, characterization of the pulses and application for the femtosecond electron diffraction measurements. We now have in hand the ultrafast structural ‘cameras’ ready to be applied for the study of an endless list of dynamical phenomena at the atomic level of inspection.

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  Low-energy electron diffraction (LEED) apparatuses with field-emission (FE) tips were developed. The FE tips were fabricated by field-assisted gas etching to obtain an atomically sharp tip apex. These tips emit single-spot electron beams. Using the FE beams in conjunction with a lensless system, we observed backscattered electrons at the surface of few-layer graphene grown on SiC(0001). The obtained hexagonal patterns at sample biases of 93 V, 54 V, and 28 V were interpreted as diffraction spots derived from the graphene, the SiC(0001) substrate, and a buffer layer, respectively. On the basis of the opening angle of FE, the irradiated areas were estimated to be 350 nmφ when the sample bias was 100 V. Since the FE beams were easily focused by a magnetic lens, a LEED apparatus with the focused FE beams was also examined. This approach might be useful for improving the sharpness of LEED patterns.

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