Real-time Observation of Nanowire Formation by Means of GISAXS

Tomoaki Kawamura, Satyaban Bhunia, *Seiji Fujikawa and Yoshio Watanabe
Material Science Laboratory, *University of Hyogo

@Nanowires composed of several semiconductor materials have recently been attracting many interests due to their promising potential for nano-technology applications such as photonics, quantum computing and bio / medical engineering. Several nanowires have been grown using the vapor-liquid-solid (VLS) mechanism in a gaseous environment and evaluated after the growth, using electron-based microscopic techniques, such as SEM and TEM. Since electron-based techniques are limited in vacuum, usual monitoring tool, for example, RHEED and LEED can not be applied to observe nanowire growth, and details of the growth is still unclear. In contrast with the electrons, x-ray has larger permeability with the materials, and is often used for monitoring crystal growth in solid, liquid and gases.
@In this work, we evaluated nanowire growth with using GISAXS (Grazing Incidence Small Angle X-ray Scattering) since this technique can be applied fro evaluating nano-structures in a gaseous and liquid environment. Figure 1 shows the experimental layout for GISAXS measurement. X-rays were impinged at the grazing condition and scatterings from the nanowires were observed with the digital x-ray CCD camera every several seconds. Figure 2 shows the GISAXS image obtained just after the nanowire growth. Obviously, clear scatterings along qy and qz direction were observed, suggesting dense nanowires on the substrate. Theoretical calculations with using DWBA (Distorted Wave Born Approximation), shown in Fig. 3 (a) and (b), suggests x-rays were scattered mainly by the hexagonal objects than hemispheres. This was consistent with the results of SEM observation which clearly showed vertical nanowires with hexagonal cross-section.

[1] T. Kawamura, et al., Proc. of XTOP 2004, Prague, September 2004.
[2] S. Bhunia, et al., Appl. Phys. Lett. 83 (2003) 3371.

Fig.1 Experimental layout of GISAXS.
Fig.2 GISAXS image after nanowires formation (Ts=400)
Fig.3 Calculated GISAXS image by DWBA approximation. (a) hemisphere, (b) hexagonal pillar.