STUDY OF THE STRUCTURE AND CHEMICAL NATURE OF POROUS SI AND SILOXENE BY STM, AFM, XPS, AND LIMA

In situ scanning tunneling microscopy (STM) and ex situ atomic force m icroscopy (AFM) were used to examine the surface morphology of anodize d p-Si(100) electrodes in F--containing solutions. In addition to the formation of a mainly pitted and rough surface, in situ STM observatio n of anisotropic etching of Si(100) in dilute (1 %) HF showed the form ation of well-defined features, such as peninsulas, a 27 nm wide V-gro ove, and many protruding 5 nm wide micropyramids. High-resolution in s itu STM resolved atomic features at the V-groove limiting (111) facets . Although this slightly etched Si sample contained no quantum pillars , it luminesced orange under UV irradiation, in the same way as a poro us Si layer prepared by anodization in a more concentrated HF(1:1 HF:E tOH) solution. A loosely bound surface porous Si layer as thick as 100 nm was revealed by AFM and a 2 mum2 square depression cold be fabrica ted in this layer by exerting stronger compressive force. The chemical nature of the surface film prepared by anodic etching in 1:1 HF:EtOH was further probed by x-ray photoemission spectroscopy (XPS), transmis sion Fourier transform infrared spectroscopy (FTIR), and laser ionizat ion microanalysis (LIMA) techniques. These results support the explana tion that the photoluminescence from porous Si can be caused by a chem ically modified (Si/H/O) layer on the surface (e.g., a siloxene-type m aterial).