No abstract

No abstract

No abstract

No abstract

The (1ϫ1) to (2ϫ1) surface phase transition of the hydrogen-covered diamond ͑111͒ surface is investigated by core level spectroscopy, low-energy electron diffraction, and measurements of the electron affinity. The latter method is shown to be a reliable measure of the hydrogen coverage. Prolonged annealing of the surface at 1000 K converts the hydrogen-terminated (1ϫ1) structure with an electron affinity of Ϫ1.27 eV to a hydrogen-free (2ϫ1) reconstruction, increases the separation of valence-band maximum from the Fermi level E F from 0.68 to 0.88 eV, and results in a positive electron affinity of ϩ0.38 eV. Annealing the surface at high temperature ͑up to 1400 K͒ yields the same (2ϫ1) surface structure albeit with an increase in the separation of the valence-band maximum from E F to 1.42 eV and a positive electron affinity of 0.8 eV which is associated with a partial surface graphitization. An analysis of the kinetics of the thermally induced hydrogen desorption yields an activation energy of 1.25Ϯ0.2 eV. It was found that hydrogen desorption and reconstruction are surface phase transitions which are not directly linked. Instead, an intermediate phase with a high concentration of dangling bonds ͑up to 70%͒ is observed. The (1ϫ1) to (2ϫ1) phase transition is phenomenologically well described by a first-order transition provided a critical density of dangling bonds of about 70% is included in the analysis in such a way that the rate constant for reconstruction vanishes below that value. ͓S0163-1829͑99͒10407-7͔