Surface silicon-deuterium bond energy from gas-phase equilibration

The bond strength of deuterium (D) to the surface of silicon was determined to be 2.67±0.1 eV from measurements of the amount of D on the surface in equilibrium with ${\mathrm{D}}_2$ gas at various pressures. This was done by measuring the amount of D on surfaces of closed internal microcavities using nuclear reaction analysis. The binding of D to a silicon surface is significantly weaker than the Si-H bond in silane which has been assumed in the past to indicate the strength of the surface Si-H bond. The fact that the Si-D bond strength is comparable to the activation energy for thermal desorption of H from Si suggests a possible reaction path for desorption in which the first and rate-determining step is the dissociation of a Si-H bond followed by the exothermic reaction between the released H atom and a second Si-H to form a ${\mathrm{H}}_2$ molecule and two Si- dangling bonds. Our result also gives a value of 1.8 eV for the activation energy for dissociative adsorption of ${\mathrm{D}}_2$ on silicon. The number of bond sites is comparable to the number of Si atoms on the cavity surfaces calculated from the total cavity surface area determined by TEM.