Strain relaxation of GeSi alloy with low dislocation density grown on low-temperature Si buffers

We have developed a low-temperature (LT) growth technique. Even with Ge fraction x upto 90%, the total thickness of fully relaxed GexSi1-x buffers can he reduced to 1.7 mu m with dislocation density lower than 5 x 10(6) cm(-2). The surface roughness is no more than 6 nm. The strain relaxation is quite inhomogeneous From the beginning. Stacking faults generate and form the mismatch dislocations in the interface of GeSi/LT-Si. (C) 1999 Elsevier Science B.V. All rights reserved.

Low-temperature heat capacities and derived thermodynamic functions of cyclohexane

The low-temperature heat capacities of cyclohexane were measured in the temperature range from 78 to 350 K by means of an automatic adiabatic calorimeter equipped with a new sample container adapted to measure heat capacities of liquids. The sample container was described in detail. The performance of this calorimetric apparatus was evaluated by heat capacity measurements on water. The deviations of experimental heat capacities from the corresponding smoothed values lie within +/-0.3%, while the inaccuracy is within +/-0.4%, compared with the reference data in the whole experimental temperature range. Two kinds of phase transitions were found at 186.065 and 279.684 K corresponding solid-solid and solid-liquid phase transitions, respectively. The entropy and enthalpy of the phase transition, as well as the thermodynamic functions {H-(T)- H-298.15 K} and {S-(T)-S-298.15 K}, were derived from the heat capacity data. The mass fraction purity of cyclohexane sample used in the present calorimetric study was determined to be 99.9965% by fraction melting approach.

Low-temperature heat capacities and standard molar enthalpy of formation of aspirin

Molar heat capacities (C-p,C-m) of aspirin were precisely measured with a small sample precision automated adiabatic calorimeter over the temperature range from 78 to 383 K. No phase transition was observed in this temperature region. The polynomial function of Cp, vs. T was established in the light of the low-temperature heat capacity measurements and least square fitting method. The corresponding function is as follows: for 78 Kless than or equal toTless than or equal to383 K, C-p,C-m/J mol(-1) K-1=19.086X(4)+15.951X(3)-5.2548X(2)+90.192X+176.65, [X=(T-230.50/152.5)]. The thermodynamic functions on the base of the reference temperature of 298.15 K, {DeltaH(T)-DeltaH(298.15)} and {S-T-S-298.15}, were derived.

Low-temperature heat capacity and thermodynamic properties of crystalline carboxin (C12H13NO2S)

Carboxin was synthesized and its heat capacities were measured with an automated adiabatic calorimeter over the temperature range from 79 to 380K. The melting point, molar enthalpy (Delta(fus)H(m)) and entropy (Delta(fus)S(m)) of fusion of this compound were determined to be 365.29 +/- 0.06K, 28.193 +/- 0.09 kJ mol(-1) and 77.180 +/- 0.02 J mol(-1) K-1, respectively. The purity of the compound was determined to be 99.55 mol% by using the fractional melting technique. The thermodynamic functions relative to the reference temperature (298.15 K) were calculated based on the heat capacity measurements in the temperature range between 80 and 360 K. The thermal stability of the compound was further investigated by differential scanning calorimetry (DSC) and thermogravimetric (TG) analysis. The DSC curve indicates that the sample starts to decompose at ca. 290degreesC with the peak temperature at 292.7degreesC. The TG-DTG results demonstrate the maximum mass loss rate occurs at 293degreesC corresponding to the maximum decomposition rate. (C) 2003 Elsevier B.V All rights reserved.

Low-temperature heat capacity and standard molar enthalpy of formation of 9-fluorenemethanol (C14H12O)

Low-temperature heat capacities of the 9-fluorenemethanol (C14H12O) have been precisely measured with a small sample automatic adiabatic calorimeter over the temperature range between T = 78 K and T = 390 K. The solid-liquid phase transition of the compound has been observed to be T-fus = (376.567 +/- 0.012) K from the heat-capacity measurements. The molar enthalpy and entropy of the melting of the substance were determined to be Delta(fus)H(m) = (26.273 +/- 0.013) kJ (.) mol(-1) and Delta(fus)S(m) = (69.770 +/- 0.035) J (.) K-1 (.) mol(-1). The experimental values of molar heat capacities in solid and liquid regions have been fitted to two polynomial equations by the least squares method. The constant-volume energy and standard molar enthalpy of combustion of the compound have been determined, Delta(c)U(C14H12O, s) = -(7125.56 +/- 4.62) kJ (.) mol(-1) and Delta(c)H(m)degrees(C14H12O, s) = -(7131.76 +/- 4.62) kJ (.) mol(-1), by means of a homemade precision oxygen-bomb combustion calorimeter at T = (298.15 +/- 0.001) K. The standard molar enthalpy of formation of the compound has been derived, Delta(f)H(m)degrees (C14H12O, s) = -(92.36 +/- 0.97) kJ (.) mol(-1), from the standard molar enthalpy of combustion of the compound in combination with other auxiliary thermodynamic quantities through a Hess thermochemical cycle. (C) 2004 Elsevier Ltd. All rights reserved.

Low-temperature heat capacity and thermodynamic properties of crystalline 2-chloro-5-trichloromethylpyridine

The low-temperature heat capacities of 2-chloro-5-trichloromethylpyridine were measured with a high-precision automated adiabatic calorimeter in the temperature range from 80 K to 345 K. A solid-liquid phase transition was observed from 318.57 K to 327.44 K with peak temperature 324.67 K; the molar enthalpy and entropy of phase transition, DeltaH(m) and DeltaS(m), were determined to be 14.50 +/-0.02 kJ mol(-1) and 44.66 +/- 0.07 kJ K-1 mol(-1), respectively. The thermal stability was investigated through thermogravimetric analysis (TG). The TG and DTG results reveal that 2-chloro-5-trichloromethylpyridine starts to lose mass at 332 K due to evaporation and completely changes into vapour at 483 K under the present experimental conditions.

Low temperature heat capacity and thermal stability of nanocrystalline nickel

The heat capacity (C-p) of nanocrystalline nickel (nc-Ni, 40 mn crystallite size) has been measured over the temperature range of 78-370 K with a high-resolution automated adiabatic calorimeter. The measured results are compared with the C-p values of the corresponding coarse-grained crystal, and an enhancement of heat capacity of the nanocrystalline nickel was observed to be 2-4% in the temperature range between 100 and 370 K. The thermal stability of the nanocrystalline nickel sample was determined by a differential scanning calorimeter and a thermogravimetric system. The melting point of nc-Ni is the same as that of the corresponding coarse-grained crystalline nickel and the sample is stable at temperature lower than 500 K. (C) 2002 Elsevier Science B.V. All rights reserved.

Photo-sensitized oxidation in natural water via .OH radicals

A method is presented for determining production and consumption rates of .OH radicals produced photochemically in natural surface waters. It is based on the determination of the kinetics by which the concentration of a specified trace compound decreases during irradiation. In samples from Lake Greifensee (Switzerland) low production rates for .OH limit its possible effects. In addition, fast consumptions by the natural dissolved organic solutes and by the bicarbonate protect organic micropollutants from oxidation by .OH. Neither direct nor indirect H2O2 photolysis was a significant source of .OH in the lakewater studied lacking iron, whereas nitrate photolysis could have been a source. Comparison with reaction kinetic formulations allows generalizations for other types of waters.

Atomic force microscopic study of low temperature induced disassembly of RecA-dsDNA filaments

The assembly and disassembly of RecA-DNA nucleoprotein filaments on double-stranded DNA (dsDNA) or single-stranded DNA (ssDNA) are important steps for homologous recombination and DNA repair. The assembly and disassembly of the nucleoprotein filaments are sensitive to the reaction conditions. In this work, we investigated different morphologies of the formed nucleoprotein filaments at low temperature under different solution conditions by atomic force microscopy (AFM). We found that low temperature and long keeping time could induce the incomplete disassembly of the formed nucleoprotein filaments.

Low-temperature synthesis of oil-soluble CdSe, CdS, and CdSe/CdS core - Shell nanocrystals by using various water-soluble anion precursors

Colloidal CdSe and CdS quantum dots were synthesized at low temperatures (60-90 degrees C) by a two-phase approach at a toluene-water interface. Oil-soluble cadmium myristate (Cd-MA) was used as cadmium source, and water-soluble Na2S, thiourea, NaHSe, Na2SeSO3, and selenourea were used as sulfur and selenium sources, respectively. When a cadmium precursor in toluene and a selenium precursor in water were mixed, CdSe nanocrystals were achieved at a toluene-water interface in the range of 1.2-3.2 nm in diameter. Moreover, we also synthesized highly luminescent CdSe/CdS core-shell quantum dots by a two-phase approach using poorly reactive thiourea as sulfur source in an autoclave at 140 degrees C or under normal pressure at 90 degrees C. Colloidal solutions of CdSe/CdS core-shell nanocrystals exhibit a photoluminescence quantum yield (PL QY) up to 42% relative to coumarin 6 at room temperature.

The complex kinetics of protein folding in wide temperature ranges

The complex protein folding kinetics in wide temperature ranges is studied through diffusive dynamics on the underlying energy landscape. The well-known kinetic chevron rollover behavior is recovered from the mean first passage time, with the U-shape dependence on temperature. The fastest folding temperature T-0 is found to be smaller than the folding transition temperature T-f. We found that the fluctuations of the kinetics through the distribution of first passage time show rather universal behavior, from high-temperature exponential Poissonian kinetics to the relatively low-temperature highly nonexponential kinetics. The transition temperature is at T-k and T-0, T-k, T-f. In certain low-temperature regimes, a power law behavior at long time emerges. At very low temperatures ( lower than trapping transition temperature T< T-0/(4&SIM;6)), the kinetics is an exponential Poissonian process again.

Electrochemical deposition of silver in room-temperature ionic liquids and its surface-enhanced Raman scattering effect

The use of room-temperature ionic liquids (RTILs) as media for electrochemical application is very attractive. In this work, the electrochemical deposition of silver was investigated at a glassy carbon electrode in hydrophobic 1-n-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF6) and hydrophilic 1-n-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF4) RTILs and in KNO3 aqueous solution by cyclic voltammetric and potentiostatic transient techniques. The voltammograms showed the presence of reduction and oxidation peaks associated with the deposition and dissolution of silver from AgBF4 in both BMIMPF6 and BMIMBF4, resembling the redox behavior of AgNO3 in KNO3 aqueous solution. A crossover loop was observed in all the cyclic voltammograms of these electrochemical systems, indicating a nucleation process. From the analysis of the experimental current transients, it was shown that the electrochemical deposition process of silver in these media was characteristic of 3D nucleation with diffusion-controlled hemispherical growth, and the silver nucleation closely followed the response predicted for progressive nucleation in BMIMPF6 and instantaneous nucleation in KNO3 aqueous solution, respectively.

Low temperature preparation of ceria solid solutions doubly doped with rare-earth and alkali-earth and their properties as solid oxide fuel cells

A series of solid electrolytes, (Ce(0.8)Ln(0.2))(1 - x)MxO2 - delta(Ln = La, Nd, Sm, Gd, M:Alkali-earth), were prepared by amorphous citrate gel method. XRD patterns indicate that a pure fluorite phase is formed at 800 degreesC. The electrical conductivity and the AC impedance spectra were measured. XPS spectra show that the oxygen vacancies increase owing to the MO doping, which results in the increase of the oxygen ionic transport number and conductivity. The performance of ceria-based solid electrolyte is improved. The effects of rare-earth and alkali-earth ions on the electricity were discussed. The open-circuit voltages and maximum power density of planar solid oxide fuel cell using (Ce0.8Sm0.2)(1 - 0.05)Ca0.05O2 - delta as electrolyte are 0.86 V and 33 mW . cm(-2), respectively.

A new preparation of zinc sulfide nanoparticles by solid-state method at low temperature

A novel solid-state method of the preparation of zinc sulfide nanoparticles is reported. By solid-state reaction of zinc acetate and thioacetamide at low temperature, zinc sulfide nanoparticles of different sizes were prepared. The temperature of preparation varied from room temperature to 300 degrees C. The particles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), differential thermal analysis (DTA), and photoluminescence spectrum. X-ray diffraction patterns revealed that the particles exhibited pure zinc-blende crystal structure and that particle size increased with increasing temperature. The TEM micrograph showed that the mean particle size was about 40 nm for the sample heated at 100 degrees C. A blue shift was observed in the photoluminescence emission spectrum. A possible mechanism of the reaction corresponding to our observation is proposed, (C) 2000 Elsevier Science Ltd. All rights reserved.

Low temperature preparation and fuel cell properties of rare earth doped barium cerate solid electrolytes

The solid electrolytes, BaCe(0.8)Ln(0.2)O(2.9) (Ln: Gd, Sm, Eu), were prepared by the sol-gel method. XRD indicated that a pure orthorhombic phase was formed at 900 degrees C. The synthesis temperature by the sol-gel method was about 600 degrees C: lower than the high temperature solid phase reaction method. The electrical conductivity and impedance spectra were measured and the conduction mechanism was studied. The grain-boundary resistance of the solid electrolyte could be reduced or eliminated by the sol-gel method. The conductivity of BaCe0.8Gd0.2O2.9 is 7.87 x 10(-2) S.cm(-1) at 800 degrees C. The open-circuit voltage of hydrogen-oxygen fuel cell using BaCe0.8Gd0.2O2.9 as electrolyte was near to 1 V and its maximum power density was 30 mW.cm(-2).