Characterization of conducting molecular films on silicon: Auger electron spectroscopy, X-ray photoelectron spectroscopy, atomic force microscopy and surface photovoltage

Complex analysis of atomic composition and surface structure of thin multilayer LB corbathiene CRB.films and cast films of regio-regular head-to-tail coupled poly 3-dodecylthiophene. PDDT. was performed using Auger electron spec- troscopy AES., X-ray photoelectron spectroscopy and Atomic force microscopy AFM.techniques. AES and XPS studies verified the film bulk and surface atomic composition expected from their chemical structure. AFM investigations showed the uniformity on micron scale of the surfaces of the films under study with roughness less than 5 nm and 10 nm for the LB and cast films, respectively. A pronounced photovoltage signal was observed in the structures composed of the films deposited on n-Si substrates and semitransparent Au layer deposited on top of the films. No significant photovoltage was observed in similar structures using p-Si substrates. The photovoltage values attained 0.5 V under monochromatic visible light irradiation of total energy density less than 0.1 mW cmy2. The photovoltage spectral variation was monitored and related to the films and n-Si substrate optical absorption features. q1999 Elsevier Science B.V. All rights reserved.