582 research outputs found
Lattice Properties of PbX (X = S, Se, Te): Experimental Studies and ab initio Calculations Including Spin-Orbit Effects
During the past five years the low temperature heat capacity of simple
semiconductors and insulators has received renewed attention. Of particular
interest has been its dependence on isotopic masses and the effect of spin-
orbit coupling in ab initio calculations. Here we concentrate on the lead
chalcogenides PbS, PbSe and PbTe. These materials, with rock salt structure,
have different natural isotopes for both cations and anions, a fact that allows
a systematic experimental and theoretical study of isotopic effects e.g. on the
specific heat. Also, the large spin-orbit splitting of the 6p electrons of Pb
and the 5p of Te allows, using a computer code which includes spin-orbit
interaction, an investigation of the effect of this interaction on the phonon
dispersion relations and the temperature dependence of the specific heat and on
the lattice parameter. It is shown that agreement between measurements and
calculations significantly improves when spin-orbit interaction is included.Comment: 25 pages, 12 Figures, 1 table, submitted to PR
Vibrational and Thermal Properties of ZnX (X=Se, Te): Density Functional Theory (LDA and GGA) versus Experiment
We calculated the phonon dispersion relations of ZnX (X=Se, Te) employing ab
initio techniques. These relations have been used to evaluate the temperature
dependence of the respective specific heats of crystals with varied isotopic
compositions. These results have been compared with mea- surements performed on
crystals down to 2 K. The calculated and measured data are generally in
excellent agreement with each other. Trends in the phonon dispersion relations
and the correspond- ing densities of states for the zinc chalcogenide series of
zincblende-type materials are discussed.Comment: 10 pages, submitted to PR
Treatment of Localized Morphea with Zyderm Collagen Implant
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/74946/1/j.1524-4725.1984.tb01267.x.pd
Treatment Site Reactions to Zyderm Collagen Implantation
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/98779/1/j.1524-4725.1983.tb00819.x.pd
Electronic and phononic properties of the chalcopyrite CuGaS2
The availability of ab initio electronic calculations and the concomitant
techniques for deriving the corresponding lattice dynamics have been profusely
used for calculating thermodynamic and vibrational properties of
semiconductors, as well as their dependence on isotopic masses. The latter have
been compared with experimental data for elemental and binary semiconductors
with different isotopic compositions. Here we present theoretical and
experimental data for several vibronic and thermodynamic properties of CuGa2, a
canonical ternary semiconductor of the chalcopyrite family. Among these
properties are the lattice parameters, the phonon dispersion relations and
densities of states (projected on the Cu, Ga, and S constituents), the specific
heat and the volume thermal expansion coefficient. The calculations were
performed with the ABINIT and VASP codes within the LDA approximation for
exchange and correlation and the results are compared with data obtained on
samples with the natural isotope composition for Cu, Ga and S, as well as for
isotope enriched samples.Comment: 9 pages, 8 Figures, submitted to Phys. Rev
Electronic and phononic properties of cinnabar: ab initio calculations and some experimental results
We report ab initio calculations of the electronic band structure, the
corresponding optical spectra, and the phonon dispersion relations of trigonal
alpha-HgS (cinnabar). The calculated dielectric functions are compared with
unpublished optical measurements by Zallen and coworkers. The phonon dispersion
relations are used to calculate the temperature and isotopic mass dependence of
the specific heat which has been compared with experimental data obtained on
samples with the natural isotope abundances of the elements Hg and S (natural
minerals and vapor phase grown samples) and on samples prepared from isotope
enriched elements by vapor phase transport. Comparison of the calculated
vibrational frequencies with Raman and ir data is also presented. Contrary to
the case of cubic beta-HgS (metacinnabar), the spin-orbit splitting of the top
valence bands at the Gamma-point of the Brillouin zone (Delta_0) is positive,
because of a smaller admixture of 5d core electrons of Hg. Calculations of the
lattice parameters, and the pressure dependence of Delta_0 and the
corresponding direct gap E_0~2eV are also presented. The lowest absorption edge
is confirmed to be indirect.Comment: 13 pages, 15 figure
Heat Capacity of PbS: Isotope Effects
In recent years, the availability of highly pure stable isotopes has made
possible the investigation of the dependence of the physical properties of
crystals, in particular semiconductors, on their isotopic composition.
Following the investigation of the specific heat (, ) of monatomic
crystals such as diamond, silicon, and germanium, similar investigations have
been undertaken for the tetrahedral diatomic systems ZnO and GaN (wurtzite
structure), for which the effect of the mass of the cation differs from that of
the anion. In this article we present measurements for a semiconductor with
rock salt structure, namely lead sulfide. Because of the large difference in
the atomic mass of both constituents (= 207.21 and (=32.06 a.m.u., for the natural isotopic abundance) the effects of varying
the cation and that of the anion mass are very different for this canonical
semiconductor. We compare the measured temperature dependence of , and the corresponding derivatives with respect to ( and
), with \textit{\textit{ab initio}} calculations based on the
lattice dynamics obtained from the local density approximation (LDA) electronic
band structure. Quantitative deviations between theory and experiment are
attributed to the absence of spin-orbit interaction in the ABINIT program used
for the electronic band structure calculations.Comment: 17 pages including 10 Fig
Raman and Infrared-Active Phonons in Hexagonal HoMnO Single Crystals: Magnetic Ordering Effects
Polarized Raman scattering and infrared reflection spectra of hexagonal
HoMnO single crystals in the temperature range 10-300 K are reported.
Group-theoretical analysis is performed and scattering selection rules for the
second order scattering processes are presented. Based on the results of
lattice dynamics calculations, performed within the shell model, the observed
lines in the spectra are assigned to definite lattice vibrations. The magnetic
ordering of Mn ions, which occurs below T=76 K, is shown to effect both
Raman- and infrared-active phonons, which modulate Mn-O-Mn bonds and,
consequently, Mn exchange interaction.Comment: 8 pages, 6 figure
- …