SCANNING-TUNNELING-MICROSCOPY AND BARRIER-HEIGHT OBSERVATION OF STEARIC-ACID THIN-FILMS PREPARED BY HOT-WALL TECHNIQUE

Stearic acid thin films prepared by the hot-wall technique have been o bserved and barrier heights (phi) have been measured using scanning tu nneling microscopy (STM), which is operated in air. Three kinds of sub strates are used to prepare stearic acid films: highly oriented pyroly tic graphite (HOPG), gold thin film and indium-tin-oxide (ITO) film. X -ray diffraction analysis reveals that molecules in films are oriented normal to the substrate. The thickness of films we used is about 30 n m. Using STM and phi images of films, we confirmed that the film surfa ce morphology varies with the kind of substrate. Islands of stearic ac id are sparsely formed on the HOPG and gold thin film substrates; howe ver, in the case of the ITO substrate, small islands (about 3 nm) near ly cover the entire substrate surface. Under certain circumstances, it is more effective to observe the stearic acid morphology in terms of values of phi with the STM images in the constant-current mode.