IN SITU INVESTIGATION OF ALUMINUM GALLIUM ARSENIDE/GALLIUM ARSENIDE MULTILAYER STRUCTURES UNDER INERT AND REACTIVE MEDIA BY ATOMIC FORCE MICROSCOPY

摘要

In this paper we describe the analytical benefits of in situ preparation and imaging under inert and reactive media using an AlGaAs/GaAs superlattice structure as a well-defined model sample. Imaging under inert organic liquids like toluene has been made possible by means of a home-built sample holder which has been designed for mechanical mounting of small-scale, cleaved specimens and which works without polymer seals in the liquid cell. The results show that sensitive surfaces can be protected from atmospheric influences without the need for ultrahigh-vacuum conditions. Contrast development on the AlGaAs/GaAs system by preferential oxidation on the AlGaAs layers could be completely suppressed by covering the cross-sectional cleavage surface with toluene. In situ studies of corrosion processes on oxidized AlGaAs/GaAs cleavage surfaces have shown that 0.01 and 0.001 M HCl lead to pitting, while 0.1 M HCl results in a clear contrast inversion of the original corrugation of 0.3-0.6 mm. The described in situ imaging capability significantly enhances the information content of atomic force microscopy (AFM) images, since it allows assignment of chemical information to topographical features primarily seen in AFM images.