METHANE ADSORPTION AND HYDROGEN ISOTHERMAL DESORPTION-KINETICS ON A C(001)-(1X1) SURFACE

Methane (CH4) adsorption and isothermal hydrogen (H-2) desorption kinetics on a C(001)-(1x1) surface have been investigated by observing the surface hydrogen coverage theta(H) which is estimated from the electron-stimulated desorption yield of H+ ions. The time evolution of theta H under CH4 exposure, in pressure and temperature ranges of 1X10(-8)-5x10(-7) Torr and 600-800 degrees C, reveals that the CH4 adsorption is a first-order reaction. The isothermal H-2 desorption is conducted in a temperature range of 1095-1270 degrees C. The time evolution of theta(H) shows that the isothermal H-2 desorption is also a first-order reaction. From Arrhenius plots of the reaction coefficients, the activation energies of CH4 adsorption and H-2 desorption are evaluated to be 7.3+/1.7 and 21+/-4.9 kcal/mol, respectively. Atomistic kinetics model for CH4 adsorption and H-2 desorption are discussed, especially in connection with a recent finding of gas source molecular beam epitaxy of diamond (001) with pure CH4 without any hydrogen or oxygen radicals. (C) 1995 American Vacuum Society.