241 research outputs found
Zum Leitungsmechanismus im System Cu-Te
The authors report measurements of electrical conductivity, Hall effect and infrared absorption of compact samples and evaporated layers of Cu2Te. These investigations show an extraordinary high number of phase-transitions. Opposite to the similar compound Ag2Te quasi-metallic conduction in the crystals is to be concluded from the results. On the other hand the investigations of very thin evaporated layers indicate in the system Cu-Te a phase with semiconducting properties. This phase is assumed to be enforced only in the evaporated layers, but not to exist in the crystals
Optische Untersuchungen über die Halbleitereigenschaften von As- und Zn3As2- Schichten
One of the fundamental constants of semiconductors is the energy gap [Delta]E between the top of the valence band and the bottom of the conduction band. For its determination electrical and optical methods are equally convenient. In this paper the authors report on optical measurements of [Delta]E on thin layers of As and some Zn-As-alloys. X-ray- and optical investigations on these layers, produced in high vacuum, confirm their crystalline structure, their homogeneity and in the case of Zn3As2 the formation of the compound Zn3As2. The optical oonstants of As and Zn3As2 are calculated by means of the Maxwell-theory from reflection- and transmission-curves in the spectral region from 0,5 to 2,7 [my]. Assuming the threshold wavelength belonging to an absorption constant K = 1 mm^-1 the authors obtain for As [lambda]g = 1,16 [my] corresponding to [Delta]E = 1,07 eV and for Zn3As2 [lambda]g = 2,44 [my], which corresponds to 0,51 eV. The experimental results are discussed in comparison with previous electrical and optical measurements on the amorphous As
Strong Influence of the diffuse component on the lattice dynamics in Pb(MgNb)O
The temperature and zone dependence of the lattice dynamics in
Pb(MgNb)O is characterized using neutron inelastic
scattering. A strong correlation between the diffuse and phonon scattering is
measured. The lattice dynamics in Brillouin zones where the diffuse scattering
is strong is observed to display qualitatively different behavior than those
zones where the diffuse scattering is weak. In the (220) and (200) zones, where
there is a weak diffuse component, the dynamics are well described by coupled
harmonic oscillators. Compared with SrTiO, the coupling is weak and
isotropic, resulting in only a small transfer of spectral weight from one mode
to another. A comparison of the scattering in these zones to the (110) zone,
where a strong diffuse component is present, reveals a strong coupling of the
diffuse (or central) component to the acoustic mode. We speculate that the
coupling to the central peak is the reason for several recent conflicting
interpretations of the lattice dynamics based on data from zones with a strong
diffuse component.Comment: 7 pages, 7 figure
Zero-field spin-splitting and spin lifetime in n-InSb/In1-xAlxSb asymmetric quantum well heterostructures
The spin-orbit (SO) coupling parameters for lowest conduction subband due to
structural (SIA) and bulk (BIA) inversion asymmetry are calculated for a range
of carrier densities in [001]-grown delta-doped n-type InSb/In1-xAlxSb
asymmetric quantum wells using the established 8 band k.p formalism [PRB 59,8
R5312 (1999)]. We present calculations for conditions of zero bias at 10 K. It
is shown that both the SIA and BIA parameters scale approximately linearly with
carrier density, and exhibit a marked dependence on well width when alloy
composition is adjusted to allow maximum upper barrier height for a given well
width. In contrast to other material systems the BIA contribution to spin
splitting is found to be of significant and comparable value to the SIA
mechanism in these structures. We calculate the spin lifetime for spins
oriented along [11-0] based on D'yakonov-Perel mechanism using both the theory
of Averkiev et al. [J. Phys.:Condens. Matter 14 (2002)] and also the rate of
precession of spins about the effective magnetic field, taking into account all
three SO couplings, showing good agreement.Spin lifeime for this direction is
largest in the narrow wells over the range of moderate carrier densities
considered, which is attributed to the reduced magnitude of the k-cubic BIA
parameter in narrow wells. The inherently large BIA induced SO coupling in
these systems is shown to have considerable effect on the spin lifetime, which
exhibits significant reduction in the maximum spin lifetime compared to
previous studies which consider systems with relatively weak BIA induced SO
coupling. The relaxation rate of spins oriented in the [001] direction is
dominated by the k-linear SIA and BIA coupling parameters and at least an order
of magnitude greater than in the [11-0] direction.Comment: 18 pages 12 figure
Behavior of high dose O+-implanted Si/Ge/Si structures
The synthesis of a buried oxide layer in multilayer Si/Ge/Si structures by the implantation of high doses of 200 keV O+ ions is studied by Rutherford backscattering analysis. The presence of Ge is found to have a minimal effect upon the mass transport of excess oxygen and interstitial silicon. Infrared transmission spectroscopy and x-ray photoelectron spectroscopy confirm that the oxygen atoms bond preferentially to silicon forming silicon dioxide and SiOx, where x<2, with no evidence for Ge—O bonding
Relaxor ferroelectricity and colossal magnetocapacitive coupling in ferromagnetic CdCr2S4
Multiferroic materials, which reveal magnetic and electric order, are in the
focus of recent solid state research. Especially the simultaneous occurrence of
ferroelectricity and ferromagnetism, combined with an intimate coupling of
magnetization and polarization via magneto-capacitive effects, could pave the
way for a new generation of electronic devices. Here we present measurements on
a simple cubic spinel with unusual properties: It shows ferromagnetic order and
simultaneously relaxor ferroelectricity, i.e. a ferroelectric cluster state,
reached by a smeared-out phase transition, both with sizable ordering
temperatures and moments. Close to the ferromagnetic ordering temperature the
magneto-capacitive coupling, characterized by a variation of the dielectric
constant in an external magnetic field, reaches colossal values of nearly 500%.
We attribute the relaxor properties to geometric frustration, which is well
known for magnetic moments, but here is found to impede long-range order of the
structural degrees of freedom.Comment: 4 pages, 3 figure
Characterization of an electroactive polymer for overcharge protection in secondary lithium batteries
International School of Materials Science and Technology "Ettore Majorana" on Polycrystalline Semiconductors : Physical Properties and Applications
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