We calculate finite-size effects of the Gaussian model in a Lx(d-1) box geometry with free boundary conditions in one direction and periodic boundary conditions in d-1 directions for 2 infinity ). Finite-size scaling is found to be valid for d<3 and d>3 but logarithmic deviations from finite-size scaling are found for the free energy and energy density at the Gaussian upper borderline dimension d*=3. The logarithms are related to the vanishing critical exponent 1-alpha-nu=(d-3)/2 of the Gaussian surface energy density. The latter has a cusplike singularity in d>3 dimensions. We show that these properties are the origin of nonscaling finite-size effects in the mean spherical model with free boundary conditions in d > or =3 dimensions. At bulk T(c), in d=3 dimensions we find an unexpected nonlogarithmic violation of finite-size scaling for the susceptibility chi approximately L3 of the mean spherical model in film geometry, whereas only a logarithmic deviation chi approximately L2 ln L exists for box geometry. The result for film geometry is explained by the existence of the lower borderline dimension d(l)=3, as implied by the Mermin-Wagner theorem, that coincides with the Gaussian upper borderline dimension d*=3. For 3 or =T(c).

In this paper, both excitonic and defect-related information of ZnS nanobelts and nanowires have been investigated by a temperature-dependent photoluminescence (PL) spectrum. PL spectra of ZnS nanobelts and nanowires differ significantly in the ultraviolet (UV) and visible emission regions. In UV emission regions, due to high-quality crystals, free exciton B (FXB), free exciton A (FXA), FXA-one longitudinal optical (LO) phonon replica are observed in ZnS nanobelts, as well as free-to-bound (e, A) with its one LO phonon replica, while neutral-donor bound exciton (Do, X) and free-to-bound (e, A) are observed in ZnS nanowires at 10 K. The peak and relative intensity of the FX and (Do, X) versus temperature follow well with conventional empirical relations. In the visible emission regions, weak donor–acceptor pair (DAP) and self-activated (SA) emission from ZnS nanowires are commonly observed, but the Y band emission is only observed at 10 K in ZnS nanobelts. The Y band emission disappears at some temperature lower than 50 K. The peak position and full width at half maximum of DAP and SA emission bands display different temperature dependences. Detailed study on temperature-dependent PL spectra of ZnS nanobelts and nanowires provides crucial information on the nature of the electronic states and recombination mechanisms in these nanostructures.

Using material chip technology, large area n-on-p planar junctions with various boron implantation doses have been fabricated on an Hg 1−x Cd x Te (x = 0.291) film, similarly grown using molecular beam epitaxy, for the mid-infrared wavelength range. The current-voltage characteristics of p-n junctions have been measured on a cold stage at 77 K and an optimized ion implantation dose has been discovered. Zero bias resistance of all the junctions has been calculated and shows distinct dependence upon the boron implantation doses.