AFM, STS and XPS study of PVD-grown C60 fullerene films

O. AMELINES-SARRIA; P. C. DOS SANTOS CLARO; A. A. RUBERT; G. A. BENITEZ; P. L. SCHILARDI; B. BLUM; V. A. BASIUK; R. C. SALVAREZZA

Ensenada, Baja California, Mejico

Congreso; Nanomex09-Encuentro Internacional e Interdisciplinario en Nanociencias y Nanotecnología; 2009

NanoMex

Semiconducting fullerene C60 films promise many applications as photovoltaic materials. We performed atomic force microscopy (AFM), scanning tunneling spectroscopy  (STS) and X-ray photoelectron spectroscopy (XPS) studies of flat and  patterned C60 fullerene films grown by physical vapor deposition (PVD) on metallic and semiconducting surfaces at room temperature. Three-dimensional patterns were obtained by evaporating the same films with a mask in front of the substrate (Stencil Lithography). C60 evaporation from a W boat was performed at (2-4)×10-6 Torr. Film thicknesses varying from 20 to 70 nm were measured by AFM, for films grown under different experimental conditions. Grain size and morphology are dependant on film thickness, with larger grains obtained for the thinner films. STS results for C60/Si(100) show band gaps in the 1.7 eV range, consistent with the C60 band gap. Since, depending on experimental growth conditions, C60 films with metallic, semiconducting, and insulating properties have been reported, C60 films were also grown on Au and HOPG, under identical experimental conditions. STS band gaps of all C60 films are in the 1.7 eV region. Additionally, XPS measurements for C60/Si show both the Si signal and the C60 fingerprint. The above results taken together show that the C60 films on different substrates are semiconducting, and can be useful for possible optoelectronic applications due to their homogeneity.