The sticking probability of H2 on Si(001) is immeasurably small at room temperature, indicating the presence of a large energy barrier to adsorption. Surprisingly, the final state energy distributions of H2 molecules desorbing from Si(001) show no signs of having traversed such a barrier, in apparent contradiction with microscopic reversibility. Here we report experimental and theoretical evidence resolving this long-standing puzzle. Adsorption and desorption proceeding along two distinct, microscopically reversible pathways can explain all observations.
The standard picture of desorption induced by electronic transitions (DIET) is analyzed for high excited state quenching rates. Simple dynamical considerations are found to explain the velocity distributions characterizing a large number of photodesorption and electron stimulated desorption systems. Without invoking any thermalization processes, the model predicts a Maxwell–Boltzmann velocity distribution, thus providing a theoretical justification for this distribution’s widespread use as an empirical fitting formula for velocity distributions of nonthermally desorbed species.
The exact solution for the cluster size distribution in the one-dimensional Ising model is obtained. In the thermodynamic limit the result is a simple analytical formula which gives the normalized number of clusters of different sizes. The analytical prediction is compared with Monte Carlo simulations and the energy dependence of the distribution is studied.
The alignment and polarizability of single-wall carbon nanotubes in dilute ethanol suspensions under low-frequency, alternating-current electric fields were investigated through optical polarimetry. The nematic order parameter was determined by measuring changes in the state of polarization of a laser beam transmitted through the sample. The dependence of the measured alignment on the electric field was found to be consistent with a thermal-equilibrium distribution of freely rotating, polarizable rods. The polarizability determined by fitting to this model is consistent with the classical result for a conducting ellipsoid of the dimensions of the nanotubes.
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