New temperature fluctuation method for direct determination of thermal activation energy of deep levels in semiconductors

A new method is suggested where the thermal activation energy is measured directly and not as a slope of an Arrhenius plot. The sample temperature T is allowed to fluctuate about a temperature T0. The reverse-biased sample diode is repeatedly pulsed towards zero bias and the transient capacitance C1 at time t1 is measured The activation energy is obtained by monitoring the fluctuations in C1 and T. The method has been used to measure the activation energy of the gold acceptor level in silicon.

Thermal activation parameters for low temperature deformation of alpha-hafnium

Abstract is not available.

Acid-Catalyzed Thermal Rearrangement of Gamm,Delta-Unsaturated Ketones

Thermal activation of gamma,delta-unsaturated ketones (1, 9 and 12) in the presence of a catalytic amount of propionic acid causes a rearrangement to give new gamma,delta-unsaturated ketones (2, 10 and 14) via an intramolecular ene reaction followed by a retro-ene reaction.

High-temperature deformation processing of Ti-24Al-20Nb

Power dissipation maps have been generated in the temperature range of 900 degrees C to 1150 degrees C and strain rate range of 10(-3) to 10 s(-1) for a cast aluminide alloy Ti-24Al-20Nb using dynamic material model. The results define two distinct regimes of temperature and strain rate in which efficiency of power dissipation is maximum. The first region, centered around 975 degrees C/0.1 s(-1), is shown to correspond to dynamic recrystallization of the alpha(2) phase and the second, centered around 1150 degrees C/0.001 s(-1), corresponds to dynamic recovery and superplastic deformation of the beta phase. Thermal activation analysis using the power law creep equation yielded apparent activation energies of 854 and 627 kJ/mol for the first and second regimes, respectively. Reanalyzing the data by alternate methods yielded activation energies in the range of 170 to 220 kJ/mol and 220 to 270 kJ/mol for the first and second regimes, respectively. Cross slip was shown to constitute the activation barrier in both cases. Two distinct regimes of processing instability-one at high strain rates and the other at the low strain rates in the lower temperature regions-have been identified, within which shear bands are formed.

Resistivity Maxima in Lithium Fast-Ion Conductors at High Pressure

The resistivity of two types of lithium fast-ion conductors, Li16-2xZnx(GeO4)4 (x=1,2) and Li3+xGexV1-xO4 (x=0.25,0.6,0.72), showed pronounced maxima as a function of pressure. For the first type, ln(ρ / ρ0) peaked at values of 0.12 (x=1) and 0.35 (x=2) near 20 kbar and decreased thereafter up to 80 kbar. Thermal activation energies and prefactors also showed corresponding maxima. For the second type, ln(ρ / ρ0) increased to 3-4 between 20 and 32 kbar. Near 80 kbar, ρ decreased (for x=0.25) by a factor of 250. The results are interpreted in terms of negative activation volumes.

Impression creep of zinc and the rate-controlling dislocation mechanism of plastic flow at high temperatures

The impression creep behaviour of zinc is studied in the range 300 to 500 K and the results are compared with the data from conventional creep tests. The steady-state impression velocity is found to exhibit the same stress and temperature dependence as in conventional tensile creep with the same power law stress exponent. Also studied is the effect of indenter size on the impression velocity. The thermal activation parameters for plastic flow at high temperatures derived from a number of testing techniques agree reasonably well. Grain boundary sliding is shown to be unimportant in controlling the rate of plastic flow at high temperatures. It is observed that the Cottrell-Stokes law is obeyed during high-temperature deformation of zinc. It is concluded that a mechanism such as forest intersection involving attractive trees controls the high-temperature flow rather than a diffusion mechanism.

Properties of the gold related acceptor level in silicon

The apparent thermal activation energy of 0.56 eV and the electron thermal capture cross section of 2.0 × 10-16 cm2 are measured for the gold related acceptor level in p+ nn+ silicon diodes by isothermal current transient and DLTS techniques. Using the emission and capture rate data and a degeneracy ratio of 2, the energy separation of the trap level from the conduction band is calculated and found to have the same temperature dependence as the band gap indicating that the acceptor level is pinned with respect to the valence band a t Ev + 0.637 eV.

Slim P‐E hysteresis loop and anomalous dielectric response in sol-gel derived antiferroelectric PbZrO3 thin films

Sol-gel derived PbZrO3 (PZ) thin films have been deposited on Pt(111)/Ti/SiO2/Si substrate and according to the pseudotetragonal symmetry of PZ, the relatively preferred (110)t oriented phase formation has been noticed. The room temperature P‐E hysteresis loops have been observed to be slim by nature. The slim hysteresis loops are attributed to the [110]t directional antiparallel lattice motion of Pb ions and by the directionality of the applied electric field. Pure PZ formation has been characterized by the dielectric phase transition at 235 °C and antiferroelectric P‐E hysteresis loops at room temperature. Dielectric response has been characterized within a frequency domain of 100 Hz–1 MHz at various temperatures ranging from 40 to 350 °C. Though frequency dispersion of dielectric behaves like a Maxwell–Wagner type of relaxation, ω2 dependency of ac conductivity indicates that there must be G‐C equivalent circuit dominance at high frequency. The presence of trap charges in PZ has been determined by Arrhenius plots of ac conductivity. The temperature dependent n (calculated from the universal power law of ac conductivity) values indicate an anomalous behavior of the trapped charges. This anomaly has been explained by strongly and weakly correlated potential wells of trapped charges and their behavior on thermal activation. The dominance of circuit∕circuits resembling Maxwell–Wagner type has been investigated by logarithmic Nyquist plots at various temperatures and it has been justified that the dielectric dispersion is not from the actual Maxwell–Wagner-type response.

Low-temperature deformation behaviour of polycrystalline copper

Low-temperature plastic flow in copper was investigated by studying its tensile and creep deformation characteristics. The dependence of the flow stress on temperature and strain rate was used to evaluate the thermal activation energy while the activation area was derived from the change-in-stress creep experiments. A value of 0.6 eV was obtained for the total obstacle energy both in electrolytic and commerical copper. The activation areas in copper of three selected purities fell in the range 1200 to 100 b2. A forest intersection mechanism seems to control the temperature dependent part of the flow stress. The increase in the athermal component of the flow stress with impurity content in copper is attributed to a change in the dislocation density. The investigation also revealed that thermal activation of some attractive junctions also takes place during low-temperature creep. The model of attractive junction formation on a stress decrement during creep, yields a value of 45±10 ergs cm-2 for the stacking fault energy in copper.

Silver- and Gold-Related Deep Levels in Gallium Arsenide

Characterization of silver- and gold-related defects in gallium arsenide is carried out. These impurities were introduced during the thermal diffusion process and the related defects are characterized by deep-level transient spectroscopy and photoluminescence. The silver-related center in GaAs shows a 0.238 eV photoluminescence line corresponding to no-phonon transition, whereas its thermal ionization energy is found to be 0.426 eV. The thermal activation energy of the gold-related center in GaAs is 0.395 eV, but there is no corresponding luminescence signal.

On the High Frequency Dielectric Behavior of Castor Oil

The low frequency dielectric behavior of castor oil (a vegetable oil) has been analyzed quite exhaustively in the context of its application as impregnant in capacitors. For the sake of completeness and in order to understand the relaxation phenomena in this liquid dielectric, this high frequency dielectric study was undertaken. In order to compare its properties with a liquid dielectric used in similar application and whose high frequency behavior has been quite well analyzed, Arochlor 1476 was studied. It is observed that both liquids have distributed relaxation times. The distribution parameters together with the two distinct relaxation times have been calculated by measuring the average relaxation time. It has been found that the distinct relaxation times thus calculated represent the dielectric behavior quite satisfactorily. The average dipole moments, dipole radii and thermal activation energies for dipole relaxation have also been evaluated.

Isomerisation of 1-methylene-2-methyl-2-(2-oxopropyl)-cyclohexanes to 2-methylene-1-methyl-1-(2-oxopropyl)-cyclohexanes by ene and retro-ene reaction

Thermal activation of the normal Claisen products, the enones 4 7 and 14 in the presence of a catalytic amount of propionic acid generated the isomeric enones 6 9 and 15 via the sequential intramolecular ene-reaction of the enol tautomer followed by 1,5-hydrogen transfer (or retro ene-reaction) of the resultant acetyl cyclopropane intermediate. conversion of the enones 9 and 15 into the corresponding cyclohexenones 10 and 16 established the structures of the rearrangement products.

Hot deformation and microstructural evolution in an alpha(2)/O titanium aluminide alloy Ti-25Al-15Nb

Deformation processing and microstructural development of an alpha(2)/O aluminide alloy Ti-25Al-15Nb (at.%) was studied in the temperature range of 950 to 1200 degrees C and strain rate range of 10(-3) to 100 s(-1). Regions of processing and instability were identified using dynamic materials model. Dynamic recrystallization (DRX) of alpha(2)/O phase and p phase were seen to occur in the region of 950 to 1050 degrees C/0.001 to 0.05 s(-1) and 1125 to 1175 degrees C/0.001 to 0.1 s(-1), respectively. Unstable flow was seen to occur in the region of 1050 to 1190 degrees C/10 to 100 s(-1). Thermal activation analysis showed that DRX of alpha(2)/O and beta was controlled by cross-slip.