Desorption kinetics of hydrogen and deuterium from Si(111) 7×7 studied using laser-induced thermal desorption

Abstract

The desorption of hydrogen and deuterium from Si(111) 7×7 was studied using laser‐induced thermal desorption (LITD) and temperature programmed desorption (TPD) mass spectrometry. Isothermal LITD measurements enabled the surface coverage of hydrogen and deuterium to be monitored as a function of time. These isothermal results were used to obtain accurate desorption kinetics of hydrogen and deuterium from the high‐temperature β₁ state on Si(111) 7×7. The desorption of hydrogen displayed second‐order kinetics with an activation barrier of 61±4 kcal/mol and a preexponential factor of 1.2×10^1±1.3 cm²/s. Likewise, the desorption kinetics of deuterium displayed second‐order kinetics with an activation barrier of 59±3 kcal/mol and a preexponential factor of 2.8×10^0±1.0 cm²/s. These desorption activation barriers yield upper limits of 82.6 and 81.6 kcal/mol for the Si–H and Si–D chemical bond energies, respectively, on Si(111) 7×7. TPD results obtained as a function of hydrogen coverage were consistent with second‐order desorption kinetics. The TPD experiments were also used to measure hydrogen coverages and to calibrate the LITD signals. In addition, LITD techniques were used to study the surface diffusion of hydrogen on Si(111) 7×7. No evidence of significant hydrogen surface mobility (D≤10⁻⁹ cm²/s) was found for surface temperatures as high as 740 K.