C. H. Mak

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

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 1.2×101±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 2.8×100±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...

Surface diffusion of hydrogen on Ru(001) studied using laser‐induced thermal desorption

The surface diffusion coefficient for hydrogen on Ru(001) at low coverage was measured using laser‐induced thermal desorption techniques. In the temperature range between 260 and 330 K, the diffusion coefficients displayed Arrhenius behavior with an activation barrier Ediff=4.0±0.5 kcal and a preexponential factor D0=6.3×10−4 cm2/s. Agreement between the experimental and theoretical parameters suggests that hydrogen diffuses on the surface by moving from a threefold site to a neighboring threefold site via a twofold site. Surface contaminants such as carbon and oxygen were observed to produce dramatic effects on the hydrogen surface diffusion rate.

Low-temperature dynamical simulation of spin-boson systems

The dynamics of spin-boson systems at very low temperatures has been studied using a real-time path-integral simulation technique, which combines a stochastic Monte Carlo sampling over the quantum fluctuations with an exact treatment of the quasiclassical degrees of freedom. To a large degree, this special technique circumvents the dynamical sign problem and allows the dynamics to be studied directly up to long real times in a numerically exact manner. This method has been applied to two important problems: (1) crossover from nonadiabatic to adiabatic behavior in electron-transfer reactions, (2) the zero-temperature dynamics in the antiferromagnetic Kondo region 1/2K1, where K is Kondos parameter.

Crossover from Fermi Liquid to Wigner Molecule Behavior in Quantum Dots

The crossover from weak to strong correlations in parabolic quantum dots at zero magnetic field is studied by numerically exact path-integral Monte Carlo simulations for up to eight electrons. By the use of a multilevel blocking algorithm, the simulations are carried out free of the fermion sign problem. We obtain a universal crossover governed only by the density parameter

Large-scale simulations of the two-dimensional melting of hard disks

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Monte Carlo studies of diffusion on inhomogeneous surfaces

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Coverage dependence of the surface diffusion coefficient for hydrogen on Ru(001)

{r}_{s}g{r}_{c}

Effects of coadsorbed carbon monoxide on the surface diffusion of hydrogen on Ru(001)

, the data are consistent with a Wigner molecule description, while, for

Surface diffusion of hydrogen on carbon‐covered Ru(001) surfaces studied using laser‐induced thermal desorption

{r}_{s}l{r}_{c}

DYNAMICAL SIMULATION OF CURRENT FLUCTUATIONS IN A DISSIPATIVE TWO-STATE SYSTEM

, Fermi liquid behavior is recovered. The crossover value