ATOMIC-FORCE MICROSCOPY STUDY ON THE SURFACE-STRUCTURE OF OXIDIZED POROUS SILICON

We study the surface structure of porous silicon (PS) using atomic for ce microscopy (AFM), before and after oxidation in a HNO3 solution. Th e AFM image shows the PS surface with a self-affine random fractal str ucture of wires, hillocks and voids in various scales. After oxidizati on the wires and hillocks of PS structures are glazed with oxide and t he voids are filled, PS structure is altered to a simple self-affine f ractal structure of hillock clusters. The fractal dimension D of PS is around 2.3, which decreases with increasing oxidization to about 2.0 of a smooth surface for the saturated oxidization. Our direct observat ion of the fractal structure of PS from AFM data reveals a good explan ation for the recently found novel nonlinear de-response in Ag thin fi lms deposited on PS. We find the fractal surface structure of oxidized PS responds to the stepwise avalanche electric breakdown of the resis tivity of Ag thin films deposited on oxidized PS.