METAL ATOM CERAMIC BINDING-ENERGIES

The binding of vapor-deposited metal and metal oxide films to Al2O3(0001) and fused silica was investigated using thermal desorption spectroscopy combined with mass spectrometric detection of the desorbed species. The experimental value for E(d), the activation energy of desorption, is compared with H(L), the calculated bond enthalpy value for an adsorbed metal-surface oxygen bond. For Ga and Ga2O on Al2O3(0001) and fused silica, the calculated value 2H(L)(Ga-O) = 200.6 kj.mol-1 agrees with experimental E(d) values and indicates that two gallium-oxygen bonds are broken in the desorption process (E(d) = 2H(L)). For Pb and Sn on Al2O3(0001) and fused silica, the calculated values 3H(L) (Pb-O) and 3H(L)(Sn-O) agree with experimental E(d) values (E(d) = 3H(L)). For Cr adsorbed on Al2O3, H(L)(Cr-O) = 111.1 kJ.mol-1 is calculated for one Cr-surface oxygen bond. This value agrees, within experimental error, with Stubican's values for the activation energy of surface diffusion for Cr of 110 +/- 12, 121 +/- 12, and 119 +/- 12 kJ.mol-1 on Al2O3, MgO, and MgAl2O4, respectively. A calculated value of 3H(L)(Cr-O) = 333.3 kJ.mol-1 agrees within experimental error with literature values for activation energy of volume diffusion of Cr in Al2O3, MgO, and MgAl2O4. Agreement between experiment and theory suggests that in these cases the surface bond breaking process involved in desorption and/or diffusion is described by an integral number of metal-oxygen bonds similar to those in an appropriately chosen bulk oxide model. This agreement suggests that the binding model may be useful in predicting and/or correlating appropriate metal-ceramic interactions.