摘要:

We compare the moments and continued fraction technique to other methods developed within the same tight binding framework. We give some typical results for ideal networks and for a vacancy. A theorem is given which relates the properties of the four coordinated even networks and the twelve coordinated systems.

ISSN:0094-243X    

DOI:10.1063/1.30791

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

This paper calculated the densities of valence and conduction states for simplified crystalline models of amorphous As2S3and As2Se3. The results are in fairly good agreement with experimental data. The changes of the density of valence states (DOVS) and the optical gap upon varying the bond angle, the bond length and the interlayer distance are also calculated for As2S3. The change of the DOVs by the decrease of the bond angle is found to be similar to the pressure‐induced change of the DOVS observed by Minomura et al.

ISSN:0094-243X    

DOI:10.1063/1.30792

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

The nuclear spin‐lattice relaxation timeT1of11Band23Na have been measured in the following insulating glasses: B2O3, Na2B4O7, (Na2O)0.3(SiO2)0.7. In all cases relaxation has been shown previously to be dominated by a strong quadrupolar mechanism.T1is observed to decrease between 1.2K and 273K and to be nearly field independent up to 55kG. In view of the available experimental results, the various models which have been proposed to account for NMR relaxation in glasses are shown to be unsatisfactory.

ISSN:0094-243X    

DOI:10.1063/1.30793

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

Quadrupolar‐broadened NMR spectra were obtained for 0‐17, B‐10, and B‐11 in B2O3glass using samples specially enriched in 0‐17 and B‐10. Lineshape analysis of the 0‐17 spectra indicates the presence of two oxygen sites. Site one has coupling constant Qcc=4.69 MHz and asymmetry parameter &eegr;=0.58, corresponding to oxygen atoms in boroxol rings; site two is characterized by Qcc=5.6 MHz and a large distribution in &eegr; about the value &eegr;=0.2, corresponding to oxygen atoms connecting boroxol rings. From one of the features of the B‐10 spectrum, the distribution of the boron coupling constants is obtained centered about the value Qcc=5.51 MHz (corresponding to Qcc=2.64 MHz for B‐11). A distribution about &eegr;=0.12 is postulated for the boron asymmetry parameter which fits the remainder of the spectrum. These distributions are shown to agree with the B‐11 spectrum.

ISSN:0094-243X    

DOI:10.1063/1.30794

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

An E.S.R. study of amorphous silicon films evaporated under U.H.V. conditions is presented. The question of whether the ESR signal arises from randomly distributed individual spins or spin clusters is investigated using several experimental tests : a) Dependence of the line‐width on spin concentration, b) Temperature dependence of the susceptibility from 5 to 120 °K, c) Influence of evaporating at oblique incidence. Present results are compatible with a random distribution of individual spins 1/2.

ISSN:0094-243X    

DOI:10.1063/1.30795

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

For differently prepared and for ion‐bombarded samples the behavior of linewidth, lineshape and saturation has ben studied. A close relation between the temperature dependent part of the linewidth and the hopping conductivity is found. The temperature independent contribution at low temperatures varies considerably with preparation conditions, but only little with spin density. At constant temperature the saturation power increases with rising conductivity of the samples indicating that the spin‐lattice relaxation is strongly enhanced by hopping.

ISSN:0094-243X    

DOI:10.1063/1.30796

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

We report on measurements of the electron spin resonance (ESR) signal from amorphous Si (a‐Si) with spin concentrations as low as 3×1016cm−3. The a‐Si was prepared by the glow discharge decomposition of silane gas. From a study of the linewidth, lineshape, saturation and spin susceptibility and from their variation with temperature we present evidence that even for samples with &angupr;1016spins cm−3, there are some spins that undergo an antiferromagnetic spin exchange interaction. The Curie‐Weiss &Vthgr; in the relation &khgr; =C/(T+&Vthgr;) is found to be 1.3±0.4 K. We find that &Vthgr; is independent of spin concentration in our samples and within experimental uncertainties agrees with the &Vthgr; reported for evaporated and sputtered films with as many as 8×1019spins cm−3. The constancy of &Vthgr; in samples differing by more than three orders of magnitude in spin concentration implies the existence of spin clusters in a‐Si.

ISSN:0094-243X    

DOI:10.1063/1.30797

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

Structural investigations on amorphous AsxTe1−xthin films and bulk glass samples have been performed as a function of composition ′x′ and heat treatment. Spectra of amorphous AsxTe1−xin the composition range 0.10?×?0.57 show quadrupole doublets, characterized by fairly well defined splittings. Data obtained for a total of six compositions in the specified range, show that the quadrupole splitting (QS) increases smoothly as ′x′ decreases suggesting the lack of chemical ordering in this system. Kinetics of crystallization atx=0.30 and 0.50 were systematically investigated. The amorphous to crystalline transformation in the Te rich phase (x=0.30) leads to Te in two chemical evironments, Te metal and monoclinic As2Te3. In the As rich phase (x=0.50), the process of crystallization reveals intermediate phases.

ISSN:0094-243X    

DOI:10.1063/1.30736

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

A brief review of the electronic and vibrational structure of amorphous As is presented. Using the random network model as a proto‐type for the structure of the amorphous phase, theoretical electron and phonon densities of states are calculated. The influences of topology on these state densities are examined by using ’’cluster‐Bethe‐lattice’’ techniques. These results are then used to interpret the experimental X‐ray photomeission and infra‐red absorption measurements on amorphous As. It is shown that As is one of a small class of unique materials which exhibit an isomorphism between their electronic and vibrational excitations.

ISSN:0094-243X    

DOI:10.1063/1.30737

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

The coordinates of a three‐fold coordinated random network model containing 533 atoms, and constructed to simulate the structure of amorphous As, have been computer refined by moving atoms in an iterative scheme (i) to minimize the variations in the nearest neighbor bond length, (ii) to relax the structure to one of lowest local energy. The resulting bond and dihedral angle distributions, as well as the RDF, will be presented and discussed in the light of experimentally observed properties of amorphous As.

ISSN:0094-243X    

DOI:10.1063/1.30738

出版商:AIP    

年代:1976

数据来源: AIP