摘要:

In order to investigate the relative importance of short‐range order and local topology in determining the vibrational properties of group IV semiconductors, we introduce a cluster Bethe lattice method. A cluster of atoms with any desired configuration is treated exactly. The rest of the system is treated within the Bethe Peierls Approximation, which retains the short‐range tetrahedral order. Main features of perfect crystaol density of states are already present in small clusters. A few cases of effects of disorder are studied.

ISSN:0094-243X    

DOI:10.1063/1.30763

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

Experiments on the propagation of sound waves in fused silica glass (Suprasil W) below 1K have been carried out to test theories of the glassy state. The tunneling state model1,2postulates the the existence of a broad distribution of two‐level systems in all glasses which are capable of resonantly scattering phonons, thus accounting for the low phonon thermal conductivities of amorphous dielectrics. Additionally, this model predicts the temperature and frequency dependence of the reciprocal decay length, or absorption, of a phonon:1,3

ISSN:0094-243X    

DOI:10.1063/1.30764

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

An anomalous quasielastic component has been observed in the light scattering spectra of several heavy metal oxide glasses. This component consists of a depolarized ’’central peak’’ of frequency width less than &angupr;0.5 cm−1, depending on temperature and composition. Observations are reported here for eight different compositions, all containing either transition metal or rare earth oxides. The integrated intensity for glasses whose major constituent is Tb2O3correlates well with Tb concentration, while the linewidth is insensitive to Tb concentration as well as host composition.

ISSN:0094-243X    

DOI:10.1063/1.30765

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

Examples of perfectly four‐coordinated networks satisfying periodic boundary conditions are constructed by a pseudo‐random process, starting from a crystalline region. The unphysical features (high density, large deviations from the tetrahedral bond‐angle) are removed by systematic modification of the bonding scheme. The vibrational spectra are calculated, using a valence‐force potential, and the neutron scattering is computed by a phonon‐expansion approximation.

ISSN:0094-243X    

DOI:10.1063/1.30766

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

The disorder induced far infrared and microwave absorption characteristic of amorphous materials is shown to depart from the general frequency squared dependence between 0.1 and 10 cm−1in glassy As2Se3and SiO2. The absorption is also temperature dependent in this frequency region. These results are discussed in terms of a simple illustrative model which invokes a coupling of the photons to a Debye‐like density of low frequency modes through the mechanism of a spatially fluctuating electronic charge.

ISSN:0094-243X    

DOI:10.1063/1.30767

出版商:AIP    

年代:1976

数据来源: AIP

ISSN:0094-243X    

DOI:10.1063/1.30768

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

This paper reviews some of our recent work which demonstrated that substitutional doping of a‐Si can a‐Ge is possible. Bothn‐ andp‐type specimens of a‐Si can be prepared with room temperature conductivities varying over some ten orders of magnitude, corresponding to a shift in the Fermi level position of about 1.2 eV. This control of the properties has enabled the density of states to be determined over an increased energy range. The results of thermoelectric power measurements onn‐type samples are described and discussed in terms of the normal electronic contribution for extended state conduction and a phonon drag effect. The doping of a‐Si also suggests device applications and the recent production of an amorphousp‐njunction is briefly discussed.

ISSN:0094-243X    

DOI:10.1063/1.30769

出版商:AIP    

年代:1976

数据来源: AIP

ISSN:0094-243X    

DOI:10.1063/1.30770

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

Anabinitiocalculation of the electronic structure in amorphous silicon based on Henderson’s 61‐atom quasiperiodic lattice model has been made by using the method of linear combinations of atomic orbitals. The use of the Gaussian technique makes it quite easy to evaluate all the necessary multicenter integrals and the lattice summation is carried out to convergence. The calculated density of states is in good agreement with experiments. The band structures of silicon in two polycrystalline forms have been calculated also by the same method. Comparison of their density of states with that of amorphous silicon is discussed with special reference to distortion from the perfect tetrahedral coordination.

ISSN:0094-243X    

DOI:10.1063/1.30771

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

Recently measured photoemission spectra on SixGe1−xO2films show definite trends asxvaries from 0 to 1. Calculations are presented which reproduce these trends and shed light on the nature of the electronic levels in these systems.

ISSN:0094-243X    

DOI:10.1063/1.30772

出版商:AIP    

年代:1976

数据来源: AIP