Total current electron spectroscopy (TCS) that uses a probing beam of low energy electrons was applied to study electronic charge transfer at interfaces between Cu-phthalocyanine (CuPc) films thermally deposited in situ onto ZnO, oxidized and crystalline silicon substrates. Analysis of the TCS data provided us also with new data on the density of unoccupied electron states (DOUS) of the CuPc films at 0-25 eV above E-F. A most significant electronic charge transfer from the CuPc film to SiO2/n-Si and n-Si(1 0 0) was observed and the polarization layer extended up to 10 nm into the CuPc film bulk. the electronic structure of the CuPc molecules on n-Si(1 0 0) and on ZnO(0 0 0 1) was perturbed within 1-2 nm of the deposit due to interaction with the substrates. Admission of O-2 and NO2 at 10(-5) Pa and 300 K resulted in a reversible decrease and increase of the film surface potential, respectively. Formation of TC peaks related to O-orbitals on the gas adsorption on the CuPc surface was also registered. (C) 2003 Elsevier Science B.V. All rights reserved.