Mobility of tungsten clusters and microstructure of tungsten films on amorphous carbon substrates

The cluster density, size and spatial distribution of tungsten clusters during deposition onto amorphous carbon (a-C) substrates at a deposition rate of 0.005 nm s^-1 are investigated. The effect of interparticle forces in producing preferred spacings between clusters and the influence of such forces on coalescence are determined. It is shown that the distribution of tungsten clusters on a-C is non-random and the mobility of tungsten clusters decreases with increasing size. A minimum centre-to-centre spacing value is observed. Venables' correlation function of 1973 and Schmeisser's modification to Venables' correlation function proposed in 1974 are applied to the experimental results. Venables' correlation function predicts the nearest-neighbour distance distribution consistently for deposits with cluster number density less than 3.0*10¹² cm^-2 while Schmeisser's modified correlation function does not produce a good fit to the data. The microstructure of tungsten films of varying thickness for a deposition rate of 0.25 nm s ^-1 is also studied by electron microscopy and electron diffraction.