Observation of 2D nanostructures using X-ray reciprocal-lattice space imaging

Research&Utilization Division, Japan Synchrotron Radiation Research Institute / SPring-8* Chiba University** Tokyo Institute of Technology***
â—‹Osami Sakata* Masashi Nakamura** Takayuki Watanabe*** Hiroshi Funakubo***

We proposed x-ray reciprocal-lattice space imaging (X-ReSI) as an obvious-at-a-glance analysis method for 1D nanostructures such as NiO nanowires on a sapphire surface[1] and Bi nanolines in Si[2]. The success pushed us to applying X-ReSI to observing 2D structures of a sample surface in solution and a thin film. X-ReSI combined higher-energy and monochromatic synchrotron x-rays in grazing incidence with a 2D detector. An X-ReSI pattern is taken from a sample fixed at an angular position with one-time exposure.
A sample examined was a single-crystal Au (111) working electrode; the reference electrode used was Hg|Hg2SO4|0.5M H2SO4. Diffraction patterns were recorded with an imaging plate detector. The 1 1 L and 1 -1 L crystal truncation rods (CTR) were intersected at L=6.3 with the Ewald sphere. A batch of images around the 0 1 6.3 CTR indicates that the surface of the Au electrode was reconstructed. We, moreover, recorded a series of x-ray patterns in the vicinity of a surface structural phase transition between the reconstructed and the bulk-terminated surface. During the transition, change in crystal domain shapes of surface intermediates as well as its smaller lattice distortion was observed.
Other samples were 50 nm- and 3 nm-thick Bi4Ti3O12(100) and (010) films epitaxially grown on TiO2 (101). Observation of about a hundred spots recorded at a fixed sample position implies that X-ReSI is also applicable for a 2D nanostructure. Similar patterns obtained from the two samples suggest that the sample have the same crystal structure. Measurements were performed at beamline BL13XU, SPring-8. 25 keV x-rays were incident on sample surfaces at an angle of 0.1 degree.
[1]Sakata et al, Appl. Phys. Lett. 84, 4239 (2004).
[2]Sakata et al. Phys. Rev. B 72, 121407(R) (2005).