DETERMINATION OF VIBRATIONAL-ENERGY RELAXATION RATES OF C-H,D,T STRETCHING MODES ON HYDROGEN, DEUTERIUM, AND TRITIUM-TERMINATED H,D,T C(111) AND H,D,T/C(110) DIAMOND SURFACES USING MOLECULAR-DYNAMICS SIMULATION - THERMAL EFFECT/

Molecular dynamics simulations were carried out to determine the vibra tional energy relaxation rates for C-H,D,T stretches on hydrogen-, deu terium-, and tritium-terminated H,D,T/C(111) and H,D,T/C(110) diamond surfaces at high temperatures based on the Bloch-Redfield theory and t he calculated power spectra of fluctuating force along C-H,D,T stretch es. The lifetime of C-H stretches on H/(110) surfaces at room temperat ure was found to be 0.8 ps, which is much shorter than the calculated lifetime of 30 ps on a H/C(111) surface attributed to 1:3 resonance. T his is due to the blueshift of the 1:2 resonance domain in the force p ower spectra for a H/C(110) surface. The lifetimes of C-H stretches on a H/C(110) surface and C-D,T stretches on both D,T/C(111) and D,T/C(1 10) surfaces, which all undergo 1:2 resonance energy relaxation, are a ll on the time scale of tenths of a picosecond at room temperature and are approximately inversely proportional to the square of the tempera ture at high temperatures. For C-H stretches on a H/C(111) surface, th e lifetimes at high temperatures are shortened much further not only b y the rise in the temperature but also due to the thermal broadening o f the resonance peaks in the force power spectra. The characteristics of power spectra and the resulting relaxation rates were analyzed usin g a simple model of a constrained diatomic bond in a harmonic bending potential field. The present results suggest that, since the resonance frequencies of C-H stretches are located within the border region bet ween the 1:2 and 1:3 resonance domains, the vibrational energy relaxat ion of C-H stretches may differ by more than an order of one on differ ent monohydrided low index unreconstructed diamond surfaces in contras t to the lifetimes of C-D,T stretches on these diamond surfaces, which are all on the same time scale at a given temperature. (C) 1998 Ameri can Institute of Physics. [S0012-9606(98)71040-2].