Microscopic Structure Model Research Articles

Surface photovoltaic characterizations of porous silicon layers

The surface photovoltage properties of porous silicon layers were investigated as a function of anodization using surface photovoltage spectroscopy (SPS), combined with photoluminescence spectroscopy (PL). Fourier transform IR spectroscopy (FTIR) and scanning electron microscopy (SEM). The results show that the chemical composition, microscopic structure and photovoltaic behavior of the porous silicon layers depend strongly on the anodizing conditions. It is suggested that the chemical composition and microscopic structure model the electronic and optical properties of porous silicon. The SPS and PL experiments indicate directly the excitation and emission processes of porous silicon layers. Marked differences were observed in the SPS and PL spectra of porous silicon layers with a variety of chemical compositions and microscopic structures. These experimental observations provide a clear signature of the correlation of excitation and emission in porous silicon.

Electrical resistance-strain characteristics and structure of amorphous N iSiB thin films

The strain coefficient y and temperature coefficient of electrical resistance (TCR) and resistance stability of amorphous alloy Ni-Si-B films have been measured. These characteristics are related to the thickness of the film. The structure of the films have been examined by electron microscope. The results are discussed on the basis of microscopic columnar structure model of amorphous thin film and the Meiksin's Theory for effect of elastic strain on the electrical resistance of thin metal film.

Unexpected magnetization processes in YIG + Co films

Unidirectional properties (shifts of BH loop) were observed in (YCa) 3(FeCoGe) 5O 12 films grown on (100) GGG substrate. These shifts could be flipped by an external field (≈ 50 Oe) applied along the normal to the film or in the sample plane. The properties are similar to those of magnetic materials characterized by unidirectional anisotropy (e.g. exchange-coupled soft and hard magnetic system). The proposed domain structure model of a homogeneous sample with mixed magnetic anisotropy explains these peculiarities reasonably well. The formula for the estimation of a self-biasing field vector is given for a multi-easy axes magnet. The magnetization processes were investigated using the Faraday effect (domain structure image was analyzed visually and digitally), low frequency magnetic susceptibility technique and a vibrating sample magnetometer. The room temperature FMR spectra and the Faraday rotation spectra were analyzed, too. Microscopic theory and domain structure model are discussed for the explanation of the previously reported effects: (i) unexpectedly low and changeable domain wall velocity v ( v, which depends on the width of the applied field pulses, is in the approximate range 1 ßm/s-220 m/s); (ii) domain structure shape memory.

Dangling-bond and void-like structure in amorphous semiconductors

To explain the differences in properties between the chalcogenide glassy semiconductors and the tetrahedrally-bonded semiconductors, a microscopic structural model is given. By considering the coupling of an atom in a void to its near-by electrons, the authors find that, (i) the atom sees an effective potential with two phases: the double-well phase and the single-well phase, (ii) there exists negative Hubbard energy between an electron pair of a dangling-bond, (iii) the charged dangling-bonds have double-well structures in the configurational-coordinate space, from which they have derived an Urbach rule. Moreover, the relation of the electronic states with the spectrum of the two-level systems and the influence of an external field on the Urbach rule are also studied, and the theoretical results agree well with the experimental.

Dangling-bond and void-like structure in amorphours semiconductors

To explain the differences in properties between the chalcogenide glassy semiconductors and the tetrahedrally-bonded semiconductors, a microscopic structural model is given in this letter. Based on this model, we can not only get two-level systems, negative-U pairs, and the Urbach rule, but also account for some recent experiments.

Structure and band models for wide optical gap polysilane alloys

The microscopic structure and band models have been presented for wide optical-gap polysilane alloys. The experimentally obtained optical properties are explained by the models.

Analytic distorted wave approximation for pion scattering from nuclei

An analytic approximation to the conventional distorted wave approximation for analyses of the elastic and inelastic scattering of pions of intermediate energy from nuclei is developed. Analyses of the elastic scattering data for ${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$ on $^{12}\mathrm{C}$ using the ``best fit'' Kisslinger optical model potentials in the integral form of the scattering amplitude ascertain the relevant analytic function forms for use in analyses of inelastic scattering data. Using these functions, a separable pion-nucleon t matrix (in momentum space), and large basis (microscopic) structure models, good fits to data from the excitations of the ${2}_{1}^{+}$ (4.44 MeV) and ${3}_{1}^{\mathrm{\ensuremath{-}}}$ (9.64 MeV) states in $^{12}\mathrm{C}$ have been obtained.

Photoelastic Measurements of the Volume Expansion by theU→FandU→αTransformation in KBr

Volume expansion by the introduction and transformation of point defects in alkali halide crystals was measured using the photoelastic technique. KBr crystals containing $U$ centers were used as convenient model cases, which allow the transformation of $U$ centers into $F$ or $\ensuremath{\alpha}$ centers and hydride interstitials by uv or x irradiation. All products of these reactions can be quantitatively controlled in their formation and annealing behavior. Their concentrations can be monitored by optical absorption measurements, and their microscopic structure models are well known. Volume-expansion measurements with an improved automatic photoelastimeter were performed parallel to the formation and annealing processes, and could thus be correlated to specific center transformations. From the dilatation, which is found to be strictly proportional to the $U\ensuremath{\rightarrow}F$ transformation at room temperature, the volume expansion per $F$ center can be determined. $U\ensuremath{\rightarrow}\ensuremath{\alpha}$ conversion by uv irradiation at low temperature produces volume expansion proportional to the $\ensuremath{\alpha}$-center concentration. Thermal annealing of the $\ensuremath{\alpha}$ centers occurs in correlation with the annealing of the volume expansion. This allows the accurate determination of the volume change per vacancy ${H}^{\ensuremath{-}}$-interstitial pair. Using Eshelby's theory and previous data on the lattice parameter of KBr: KH crystals, values for the microscopic dilatations around $F$ centers and $\ensuremath{\alpha}$ centers are obtained.