Heat conductivity and thermomagnetic effects in Ag2Te at low temperatures

The heat conductivity and thermomagnetic effects are investigated in Ag₂Te of stoichiometric composition and compositions with excess Te and Ag in the 5–100 K domain. Experimental results are compared with a theoretical model of the heat conductivity that takes account of intraphonon processes and phonon scattering by the boundaries and point defects.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 41–45, June, 1990.     

Thermoelectric power of electron-irradiated graphite at low temperatures

The thermoelectric power (TEP) of very well oriented, nearly single-crystal graphite irradiated at 333 K by 3 MeV electrons was measured along the basal plane direction above 5 K. Changes in the low-temperature dependence of the TEP after different stages of annealing, at 410 and 520 K, have also been investigated. Analysing carefully the experimental data, the phonondrag component S_ph of the TEP is extracted and compared with the theory of Jay-Gerin and Maynard. As a check of the concentration of the irradiation defects, deduced from this analysis, measurements of the thermal conductivity were made on the same samples. The results are found to be in good agreement.     

Magnetooptical effects in ferromagnetic metals at low temperatures

Zeroth-order and first-order Boltzmann kinetic equations are found for the frequency-dependent transverse-conductivity tensor for inelastic scattering of electrons, with an account of thermal oscillations of the scattering centers. At low temperatures this tensor, which is linear in the spin-orbit interaction, depends exponentially on the temperature. A relation is found between the magnetooptical effects in ferromagnetic metals and the topology of the Fermi surfaces; from this relation, qualitative conclusions can be drawn regarding the effect of this topology on the magnetooptical effects and regarding the sign of the anomalous magnetooptical parameter (which depends on whether hole or electronic conductivity predominates).Translated from Izvestiya VUZ. Fizika, No. 4, pp. 86–90, April, 1970.     

Environmental effects on the tensile deformation of polymers at low temperatures

General experimental results are presented on the environmental effect exerted by nitrogen and argon on the tensile deformation of polymers in the neighborhood of 80° K. The primary features are the large dependence of tensile strength on strain rate and the occurrence of crazing, both of which are absent in helium and vacuum environments. The fracture stress in N₂ and Ar may be less or greater than that in He and vacuum in accordance with the strain rate being low or high, respectively. A brief theory for the low-temperature environmental crazing is presented. A central part of the theory is related to the fact that the adsorption of N₂ and Ar on all polymers around 80° K substantially reduces their surface free-energy by about 25 to 75%.     

A kinetics and dynamics study on the auto-ignition of dimethyl ether at low temperatures and low pressures

Though the combustion chemistry of dimethyl ether (DME) has been widely investigated over the past decades, there remains a dearth of ignition data that examines the low-temperature, low-pressure chemistry of DME. In this study, DME/‘air’ mixtures at various equivalence ratios from lean (0.5) to extremely rich (5.0) were ignited behind reflected shock waves at a fixed pressure (3.0 atm) over the temperature range 625–1200 K. The ignition behavior is different from that at high-pressures, with a repeatable ignition delay time fall-off feature observed experimentally in the temperature transition zone from the negative temperature coefficient (NTC) regime to the high-temperature regime. This could not be reproduced using available kinetic mechanisms as conventionally homogeneous ignition simulations. The fall-off behavior shows strong equivalence ratio dependence and disappears completely at an equivalence ratio of 5.0. A local ignition kernel postulate was implemented numerically to quantifiably examine the inhomogeneous premature ignition. At low temperature, no pre-ignition occurs in the mixture. A conspicuous discrepancy was observed between the measurements and constrained UV simulations at temperatures beyond the NTC regime. A third O₂ addition reaction sub-set was incorporated into AramcoMech 3.0, together with related species thermochemistry calculated using the G3/G4/CBS-APNO compound method, to explore the low-temperature deviation. The new reaction class does not influence the model predictions in IDTs, but the updated thermochemistry does. Sensitivity analyses indicate that the decomposition of hydroperoxy-methylformate plays a critical role in improving the low-temperature oxidation mechanism of DME but unfortunately, the thermal rate coefficient has never been previously investigated. Further experimental and theoretical endeavors are required to attain holistic quantitative chemical kinetics based on our understanding of the low-temperature chemistry of DME.     

A systematic study of the electron mobility in V-shaped quantum wires at low temperatures

We present a systematic study of the electron mobility in V-shaped AlGaAs/GaAs quantum wires taking into account the impurity (background, remote and interface) and the acoustic-phonon scattering. The electron scattering rates are calculated for wires with electron concentrations up to 10⁶ cm⁻¹ and temperatures up to 40 K by using Fermi’s golden rule. The effects of the interface roughness scattering and the alloy scattering are also discussed. The energy eigenstates and eigenvalues of the system under study are calculated using a finite difference method. We analyze the importance of each scattering mechanism on the mobility of several quantum wires of different qualities as a function of the electron concentration and the temperature.     

Cems study of corrosion on iron foil at low temperatures

Conversion electron Mössbauer measurements with a proportional counter at 6.3, 78 and 300 K have been done to investigate the corrosion of the surface of iron foils, which consists of small particles of γ-Fe₂O₃. When the average particle sizes of the corroded layer are approximately 4 and 5 nm, magnetic hyperfine splitting was observed in the spectra at 6.3 and 78 K. However, for a corroded layer composed of smaller particles, the splitting was noticed only at 6.3 K. The anisotropy constantK of the small particles was estimated using the magnetic hyperfine fields obtained from the spectra at 6.3 and 78 K.     

A comment on the acoustic properties of glasses at low temperatures

The acoustic attenuation and sound velocity change due to the resonant interaction in glasses are calculated. The standard results are extended to all the domain ?ω, ?Γ₂ ? kT whatever the ratio of the frequency ω/2π and the linewidth Γ₂ is. These results, although in contradiction with previous calculations, are in agreement with experiments.     

Heavy doping effects on donor-acceptor spectra of polar semiconductors at low temperatures

The heavy doping effects on donor-acceptor (DA)-pair spectra at small DA-pair distances R are investigated, basing on an effective screened impurity potential model given by Morgan and on the results of the R-dependent electron (hole)—longitudinal optical phonon interaction energy obtained by Kartheuser et al. It is suggested that the deviation of the electron—hole recombination energy by dense impurities (or at small R), found from the energy of the emitted photon for a zero-phonon transition, results from the band-gap narrowing effect.At large R, we have found that the energy gap of the pure ZnSe crystal is equal to 2.827 eV, in good agreement with observed results. Finally, at small R, our numerical results applied to ZnSe doped with ln and Li impurities are compared with other theories and with observed results.     

A note on the depth dependence and current density effects upon the radiation damage in graphite

This note is in two parts. The first describes the surprisingly large depth at which the radiation damage can be observed after irradiating graphite with²MeV⁴He⁺ ions. The second part deals with the dependence of the induced damage with the deposited power density at sample temperatures up to 1250°C.     

Arrangement of ferric and ferrous ions at low temperatures in FeCl3 intercalated graphite

Previous work has shown that electrons donated by the graphite to the FeCl₃ intercalant freeze onto some Fe³⁺ ions to change them into Fe²⁺ ions at low temperatures. We show that the created Fe²⁺ ions are not randomly situated. Indirect evidence suggesting the formation of a specific chemical superlattice of Fe³⁺ and Fe²⁺ ions is presented. A method for direct observation of this superlattice is suggested.     

Relaxation in glasses at low temperatures

JETP Letters - The interaction between tunneling system inherent in amorphous solids is established to be responsible for the universal behavior of their kinetics and thermodynamic properties at...     

Transitions in glasses at low temperatures

Length-temperature measurements from ?180°C to the glass transition temperature have been made on a poly(vinyl alkyl ether) series, poly(ethylene terephthalate), and a tetrafluoroethylene-trifluoropropylene copolymer series.

Consistent with low frequency dynamic measurements, the poly(vinyl alkyl ethers) exhibit a glass-glass transition? Tgg [1] between Tg and Tg ?70°C with evidence of another at about ?160 to ?180°C. With increasing side-chain length, the expansion coefficient below Tg- and the magnitude of the g-g transition increase, and the value of the Simha-Boyer free-volume product decreases, suggesting retention of excess free volume by the flexible pendant group. This behavior is analogous to that observed for poly(alkyl methacrylates) except that the latter system exhibited two g-g transitions, the lower of which coincided with Tgg [1] observed here.

Poly(ethylene terephthalate) samples, both amorphous and crystalline, exhibit two T > Tg transitions at about ?85 and ?40°C. Dynamic results resolve only one relaxation in this temperature range.

The glass temperatures of the tetrafluoroethylene-trifluoropropylene copolymer series, as determined by both dilatometry and differential scanning calorimetry, extrapolate to a Tg, for 100% amorphous PTFE of 11-16°C. Two g-g transitions, present in each homo-polymer, persist in the copolymers, indicating that only a small number of molecular units are involved. The magnitude of these relaxations, however, as measured by the change in expansion coefficient, is dependent on copolymer composition.     

Optoelectrical investigations on MOS-sandwiches at low temperatures

MOS-structures are irradiated with light of energy from 1.5 to 6 eV at different temperatures (300, 77, 12 K) while the resulting photocurrent is measured. At high photon energies (hv>4 eV) the threshold energy and the scattering mean free path for electrons at the Si — SiO₂-interface are determined. They are independent from temperature. At low photon energies (hv<3 ev)=" electrons=" are=" released=" from=" traps=" with=" energy=" levels=" 1.2=" and=" 1.9=" ev=" below=" the=" si-conduction=" band.=" the=" trap=" concentration=" is=" 4.8="> 10¹³ cm^–3. The capture cross section is measured in a rather direct way. The temperature and electrical field dependence of this cross section is explained by a trapping model.     

Optoelectrical investigations on MOS-sandwiches at low temperatures

MOS-structures are irradiated with light of energy from 1.5 to 6 eV at different temperatures (300, 77, 12 K) while the resulting photocurrent is measured. At high photon energies (hv>4 eV) the threshold energy and the scattering mean free path for electrons at the Si — SiO₂-interface are determined. They are independent from temperature. At low photon energies (hv<3 eV) electrons are released from traps with energy levels 1.2 and 1.9 eV below the Si-conduction band. The trap concentration is 4.8 10¹³ cm^–3. The capture cross section is measured in a rather direct way. The temperature and electrical field dependence of this cross section is explained by a trapping model.     

Dynamic scanning force microscopy at low temperatures on a van der Waals surface: graphite (0001)

The (0001) surface of highly oriented pyrolytic graphite is studied by scanning force microscopy in both contact and dynamic mode. Low temperatures were necessary for the dynamic mode measurements in order to achieve the required signal to noise ratio. At 22 K, atomic scale structures with 2.46 Å periodicity and trigonal symmetry of the individual maxima were obtained in both modes. Since graphite exhibits a van der Waals surface in good approximation, this result shows that comparatively weak forces of van der Waals type are sufficient for successful imaging in the dynamic mode on the atomic scale. However, since the positions of the observed maxima correspond to the ones found by scanning tunneling microscopy and contact scanning force microscopy, but not to the positions of the carbon atoms, it also opens new questions on the imaging mechanism in the dynamic mode.