Journal article
Authors list: Schlettwein, D; Meyer, JP; Jaeger, NI
Publication year: 2000
Pages: 23-30
Journal: Journal of Porphyrins and Phthalocyanines
Volume number: 4
Issue number: 1
ISSN: 1088-4246
eISSN: 1099-1409
Publisher: World Scientific Publishing
Abstract:
Thin films of phthalocyaninatomanganese (PcMn) in the thickness range of 100 nm have been prepared by vapour deposition on quartz glass substrates. The films were characterized in situ during film growth and following film deposition by measurements of the electrical conductivity under DC applied electric fields parallel to the substrate surface. The dependence of the conductivity on the average film thickness was determined and the mechanism of film growth is discussed. Without breaking the vacuum, a temperature gradient was established again parallel to the substrate surface and a thermopower was detected. Its dependence on the size of the temperature gradient gave a Seebeck coefficient of -780 mu V K-1 at 460 K. From the negative sign it is evident that electrons are the majority carriers in PcMn in a freshly prepared thin film. The temperature dependence of the Seebeck coefficient gave the thermal activation of charge carrier generation as Delta E = 0.19 eV, which is discussed in terms of the position of the Fermi energy in the films. The temperature dependence of the electrical conductivity gave an activation energy E-A = 0.38 eV considerably higher, indicating a thermal activation of charge carrier transport and hence supporting a hopping mechanism rather than delocalized transport. Under exposure to oxygen the conductivity showed a fast small increase followed by a slow large decrease, which is discussed considering surface as well as bulk interactions. Hole conduction was measured for the completely oxidized films by a positive Seebeck coefficient. Optical spectroscopy performed ex situ was used to allow further discussion of redox interactions of the films. Evidence was found for the presence of Pc(-2)Mn(+3)O-2(-1) as well as Pc(-2)Mn(+3)O(-2)Mn(+3)Pc(-2) and Pc(-2)Mn(+2) in freshly prepared films. Films exposed to air for as long as several months were completely oxidized to Pc(-2)Mn(+3)O-2(-1). Copyright (C) 2000 John Wiley & Sons, Ltd.
