Aluminium thin films were grown on quartz substrates by metal thermal evaporation, with thicknesses between 18 and 100 nm and evaporation rates from 1 to 20 Angstrom /s. The surface morphology of the films was examined by atomic force microscopy imaging and cross-compared. The change of the estimated surface roughness with film thickness and evaporation rate was investigated and discussed. The optical transmission of the films was measured from 200 to 800 nm and correlated to the corresponding surface morphology as determined by the film thickness and evaporation rate. The goal is to optimize the use of thermally evaporated aluminium films as semitransparent electrodes in fast photoconduction experiments involving molecular stacks of discotic liquid crystals.