Growing wetting films: An x-ray study

The growth kinetics of thin liquid films, completely wetting a solid substrate, are studied. The film thickness is perturbed and reduced by a short thermal pulse. Subsequently the time dependence of the growth process was monitored by x-ray reflectivity measurements in the region of total external reflection. The examined sample systems are CBrCl3 films on top of silicon, germanium, and glass wafers and CBrCl3 on glass/gold and glass/silver substrates. The observed growth kinetics of the wetting layer are discussed in the framework of two models that were adapted to the experimental conditions, particularly the finite temperature stability of the experimental setup. From the growth law l(t) proportional to 1-exp(-t/tau)(n) fitted to the data, time constants tau and dynamic exponents n are determined. n depends on the dimension of the growth mechanism. Various systems with quite different substrate-adsorbate interactions can be explained quantitatively within this model.