desorption rates become significantly slower with increasing number of empty sites on the surface. This is to be expected since the repulsion between the adsorbed groups decreases as the number of empty sites increases for the most densely packed surfaces. The desorption rates were also found to increase with increasing temperature which is also observed experimentally (Fig. ). The same trend has previously been shown on Al2O3, were higher temperature decreases the amount of surface methyl groups. Figure shows the kinetics when a pulse of inert gas is added between TMA and NH3. Adding the extra pulse between the TMA and NH3