It is well known that surface stress and strain play important roles in surface reconstruction, surface topography and surface nanostructure growth. If we can control the surface stress and strain applied externally to the surface, it may become one of the key techniques for the fabrication of novel functional nanostructures. In order to understand the effect of external stress and strain on the surface nanostructures and topography, we have developed a dual-probe scanning probe microscope (SPM) which can be operated under ultrahigh vacuum environment and elevated temperatures with in-situ external stress/strain application capability. The main observation modes are scanning tunneling microscopy (STM) and dynamic mode atomic force microscopy (DFM). The external tensile stress and strain can be applied to the center of the surface by a nanometer-scale pushing device using a UHV stepping motor.
Using this novel SPM, we have succeeded in the observation of high resolution surface imaging on Si(111) and Si(001) with STM mode. In the case of Si(111), we have not observed any topographical or superstructural change induced by the applied stress and strain. On the contrary, as for Si(001) and Ge(001) surfaces, we have observed a stress-induced surface modification.
In the case of Si(001) surface, it is well known that the dimerized surface has a compressive stress perpendicular to the dimer bond and a tensile stress along the dimer direction. Webb et al. have already demonstrated that it is possible to control the surface domain population by applying external stress [1]. After surface flush cleaning in UHV, the n-type (P-doped) Si(100) surface showed evenly distributed double-domains of 1×2 and 2×x1 ones, which were clarified by STM and LEED observation. At the elevated temperatures, we have succeeded in the observation of domain redistribution on Si(100) surface induced by applying a uni-axial stress with atomic resolution.
References:
[1] F. K. Men, W. E. Packard, and M. B. Webb, Phys. Rev. Lett. 61, 2469 (1988)
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