Thermochromic vanadium dioxide (VO2) films, which are considered as intelligent window coatings, have been deposited in mixed argon/oxygen atmospheres. The properties of the films have been studied by electron energy loss spectroscopy (EELS) and ultraviolet-excited photoelectron spectrometry (UPS) at different temperatures in order to get a better understanding of the physics of the metal-semiconductor transition in thin polycrystalline VO2 films. The present article mainly discusses plasmon excitation, which is found at an electron energy loss of 1.2 eV, both in the semiconducting and the metallic phase. This is in contrast to results from a single crystalline material.