Structural phase transitions of the Si(100) surface

A Monte Carlo study of the structural phase transitions on the Si(100) surface for both the “(2×1)” and “c(2×2)” reconstruction families is carried out using the asymmetric dimer model. A second order phase transition is observed at about 250 K from a p(2×2) (layered antiferromagnetic) to a disordered (paramagnetic) state in the “2×1” family. A similar transition is observed about 800 K from a c(2×2) (ferromagnetic) to a disordered state in the “c(2×2)” family. These results are in agreement with real-space renormalization group results. The variation of the specific heat, susceptability and the absolute value of the order parameter as a function of temperature is obtained in the range 200 to 300 K for the “2×1” family and 750 to 850 K for the “c(2×2)” family. Also, the order parameter correlation function is computed for ten different temperatures in the above ranges.     

Crystal lattice energies of alkali metal halides

An empirical relation for crystal binding energy in terms of the valence level splitting of the anion and the radius of the cation has been proposed. The results are much closer to the experimental values and comparable with those obtained by different methods. The anomalously high binding energy of fluorides has been discussed.     

Dielectric studies in dilute solutions

Dielectric studies in dilute solutions of cyclohexane and benzene have been carried out in the temperature range 294–318°K. The observed data have been utilized to evaluate the relaxation times and thermodynamic parameters of these molecules. The high values ofα for 2-acetyl pyridine indicate the occurrence of more than one relaxation time. In the remaining systems, the observed lowα values indicate their rigid behaviour. The variation in the dielectric relaxation time is mostly correlated with the change in the heterocyclic configuration of the system.     

Fake double layers in double plasma devices

The double layer like potential jumps have been observed in a double plasma device. They do not correspond to a switching of plasma potential from one metastable state to another but are caused by the ionisation of a very minute amount of the gas that inevitably leaks into the system during the probe movement.     

Resolution beyond natural linewidth via flourescence in modulated beams

A new method is proposed for obtaining spectral resolution beyond the natural linewidth using excitation by a laser beam whose intensity is weakly modulated in time at a low frequency ν. Th modulated fluorescence at 2ν, is shown to posses subnatural linewidth. The resolution of two lines lying within the natural linewidth of each other is explicitly considered.     

A simple method for calculating thermal expansion of crystals

Summary A simple method based on the classical statistical mechanics is suggested for the calculation of thermal expansion of crystals. The adequacy of the procedure is tested for alkali halide crystals in conjunction with the interatomic potential of the modified Born-Mayer Type.