December 2014 Archives

X-ray ptychography is known as a promising lensless imaging method. Compared with other similar techniques, it can give a rather wide viewing area with the same high-spatial-resolution in nano scale, by combining multiple coherent diffraction measurements from the illumination of several overlapping regions on the sample. However, this apparently has to assume a highly sophisticated scanning/positioning instrumentation. The method may suffer also from partial-coherence effects and fluctuations. Dr. A. Menzel (Paul Scherrer Institut, Switzerland) and his colleagues have recently published an interesting report on fast measurement. The authors discussed ptychographic on-the-fly scans, i.e., collecting diffraction patterns while the sample is scanned with constant velocity. It was found that such a scan can be used as a model for a state mixture of the probing radiation and helps to achieve reliable image recovery. The feasibility of on-the-fly measurements in traditional scanning transmission X-ray microscopy is already known. This time, the research team was successful in applying these to X-ray ptychography, which usually uses reconstruction algorithms assuming diffraction data from a static sample. Such problems were discussed in detail. For more information, see the paper, "On-the-fly scans for X-ray ptychography", P. M. Pelz et al., Appl. Phys. Lett., 105, 251101 (2014).

A team led by Professor Harald Ade (North Carolina State University, USA) has reported that grazing resonant soft X-ray scattering (GRSoXS), a technique measuring diffusely scattered soft X-rays from grazing incidence, can reveal the statistical topography of buried thin-film interfaces. So far, in wide variety of material systems, the internal structures of layered systems, particularly interfaces between different materials, have been critical to their functions. However, the analysis of buried interfaces has always presented some difficulties. It is known that X-ray electric field intensity distribution along the depth can be controlled by a change of either the incidence angle or the X-ray energy. The research team was able to manipulate it by scanning the X-ray energy, and succeeded in identifying the microstructure at different interfaces of a model polymer bilayer system such as PMMA/PEG. The authors attempted to gauge the feasibility of the technique for further practical systems like an organic thin-film transistor, PS[100nm]/PBTTT[50nm]/Si. For more information, see the paper, "Topographic measurement of buried thin-film interfaces using a grazing resonant soft x-ray scattering technique", E. Gann et al., Phys. Rev. B90, 245421 (2014).

Professor P. S. Pershan (Harvard University, USA) has recently published an interesting review paper on X-ray studies of the interface between liquid metals and their coexisting vapor. For more information, see the paper, "Review of the highlights of X-ray studies of liquid metal surfaces", P. S. Pershan, J. Appl. Phys., 116, 222201 (2014).

In addition to large-scale X-ray facilities such as synchrotrons and X-ray FELs, there have been increasing demands for much more compact X-ray sources with high brilliance, ultra short pulse properties and coherence. Dr. W. S. Graves (Massachusetts Institute of Technology, USA) and his colleagues have proposed a design for a compact X-ray source based on inverse Compton scattering. The source consists of a 1m linuc and an ultra short pulse laser. The whole size of the source including X-ray experiment space is nearly 4m. The colliding laser is a Yb:YAG solid-state amplifier producing 1030 nm, 100 mJ pulses at 1 kHz repetition rate. The calculation shows that X-ray intensity at 12.4 keV is 5×10¹¹ photons/second in a 5% bandwidth. For more information, see the paper, "Compact x-ray source based on burst-mode inverse Compton scattering at 100 kHz", W. S. Graves et al., Phys. Rev. STAB, 17, 120701 (2014).