Temperature measurement of reflected shock wave by using chemical indicator

This report describes a new method for measuring the temperature of the gas behind the reflected shock wave in shock tube, corresponding to the reservoir temperature of a shock tunnel, based on the chemical reaction of small amount of CF4 premixed in the test gas. The final product C2F4 is used as the temperature indicator, which is sampled and detected by a gas chromatography in the experiment. The detected concentration of C2F4 is correlated to the temperature of the reflected shock wave with the initial pressure P-1 and test time tau as parameters in the temperature range 3 300 K < T < 5 600 K, pressure range 5 kPa < P1 <12 kPa and tau similar or equal to 0.4 ms.

Temperature Dependence of the Tribological Properties of Laser Re-Melted Al-Cu-Fe Quasicrystalline Plasma Sprayed Coatings

The aim of this study was to investigate the effect of temperature on tribological properties of plasma-sprayed Al-Cu-Fe quasicrystal (QC) coating after laser re-melting treatment. The laser treatment resulted in a more uniform, denser and harder microstructure than that of the as-sprayed coatings. Tribological experiments on the coatings were conducted under reciprocating motion at high frequency in the temperature range from 25 to 650 degreesC. Remarkable influence of temperature on the friction behavior of the coating was recorded and analyzed. Microstructural analysis indicated that the wear mechanisms of the re-melted QC coatings changed from abrasive wear at room temperature, to adhesive wear at 400 degreesC and severe adhesive wear at 650 degreesC owing to the material transfer of the counterpart ball. It was also observed that the ratio of the icosahedral (i)-phase to beta-Al-50(Fe,CU)(50) phase in the coating was higher after test at 400 'C than that at 650 'C. The variation of the ratio UP of coating and of the property of the counterpart ball and coating with the temperature are the two main factors influencing the wear mechanisms and value of the friction coefficient.

Quantum Efficiency And Temperature Coefficients Of Gainp/Gaas Dual-Junction Solar Cell

GaInP/GaAs dual-junction solar cell with a conversion efficiency of 25.2% has been fabricated using metalorganic chemical vapor deposition (MOCVD) technique. Quantum efficiencies of the solar cell were measured within a temperature range from 25 to 160A degrees C. The results indicate that the quantum efficiencies of the subcells increase slightly with the increasing temperature. And red-shift phenomena of absorption limit for all subcells are observed by increasing the cell's work temperature, which are consistent with the viewpoint of energy gap narrowing effect. The short-circuit current density temperature coefficients dJ (sc)/dT of GaInP subcell and GaAs subcell are determined to be 8.9 and 7.4 mu A/cm(2)/A degrees C from the quantum efficiency data, respectively. And the open-circuit cell voltage temperature coefficients dV (oc)/dT calculated based on a theoretical equation are -2.4 mV/A degrees C and -2.1 mV/A degrees C for GaInP subcell and GaAs subcell.

Temperature dependence of thermal properties of Ag8In14Sb55Te23 phase-change memory materials

The dependence of thermal properties of Ag8In14Sb55Te23 phase-change memory materials in crystalline and amorphous states on temperature was measured and analyzed. The results show that in the crystalline state, the thermal properties monotonically decrease with the temperature and present obvious crystalline semiconductor characteristics. The heat capacity, thermal diffusivity, and thermal conductivity decrease from 0.35 J/g K, 1.85 mm(2)/s, and 4.0 W/m K at 300 K to 0.025 J/g K, 1.475 mm(2)/s, and 0.25 W/m K at 600 K, respectively. In the amorphous state, while the dependence of thermal properties on temperature does not present significant changes, the materials retain the glass-like thermal characteristics. Within the temperature range from 320 K to 440 K, the heat capacity fluctuates between 0.27 J/g K and 0.075 J/g K, the thermal diffusivity basically maintains at 0.525 mm(2)/s, and the thermal conductivity decreases from 1.02 W/m K at 320 K to 0.2 W/m K at 440 K. Whether in the crystalline or amorphous state, Ag8In14Sb55Te23 are more thermally active than Ge2Sb2Te5, that is, the Ag8In14Sb55Te23 composites bear stronger thermal conduction and diffusion than the Ge2Sb2Te5 phase-change memory materials.

Homoepitaxial growth of ZnO films via low-temperature liquid-phase epitaxy

Homoepitaxial ZnO films have been grown via liquid-phase epitaxy (LPE) on (000 1) oriented ZnO substrates. X-ray rocking curve revealed the high quality of the ZnO films with a FWHM of 40 arc sec. Films of thickness about 20 gm were gown in the temperature range 700-720 degrees C. The growth rate of ZnO films was estimated to be 0.3 mu m h(-1). Atomic force microscope analysis showed that the surface roughness of ZnO films was very low, which further confirmed the high crystallinity of ZnO films. (c) 2006 Elsevier B.V. All rights reserved.

Low temperature growth of c-axis oriented AlN films on gamma-LiAlO2 by radio frequency magnetron sputtering

Aluminum nitride (AlN) films were prepared on gamma-LiAlO2 substrates by radio frequency (rf) magnetron sputtering. The influence of substrate temperature (T-s) and nitrogen (N-2) concentration on film growth was investigated. The X-ray diffraction (XRD) results reveal that highly c-axis oriented AlN films can be obtained in the temperature range from room temperature (RT) to 300 degrees C. A smoother surface and a crystalline quality decrease with increasing N-2 concentration have been observed by XRD and atomic force microscopy (AFM) for the films deposited at lower substrate temperature. On the contrary, the degradation of the surface smoothness and the higher crystalline quality can be observed for the films deposited at a higher substrate temperature with N-2-rich ambient. The growth mechanism which leads to different crystalline quality of the films is discussed. (C) 2008 Elsevier B.V. All rights reserved.

Responses of dark respiration in the light to desiccation and temperature in the intertidal macroalga, Ulva lactuca (Chorophyta) during emersion

Dark respiration (nonphotorespiratory mitochondrial CO2 release) in the light (R-L) of the intertidal macroalga Ulva lactuca (Chorophyta) during emersion was investigated with respect to its response to variations in temperature and desiccation. R-L was estimated by CO2 gas-exchange analysis using the Kok effect method, whereas dark respiration in darkness (R-D) was determined from CO2 release at zero light. Rates of R, were significantly and consistently lower than those of R-D in emersed U. lactuca across all the temperature and desiccation levels measured. This demonstrated that dark respiration was partially depressed in the light, with the percentage inhibition ranging from 32 to 62%. Desiccation exerted a negative effect on R-L and R-D at a high temperature, 33 degrees C, whereas it had much less effect on respiration at low and moderate temperatures, 23 and 28 degrees C. In general, R-L and R-D increased with increasing temperature in U. lactuca during all stages of emersion but responded less positively to temperature change with increasing desiccation. Additionally, the Q(10) value (i.e. the proportional increase of respiration for each 10 degrees C rise in temperature) for R-L calculated over the temperature range of 23 to 33 degrees C was significantly higher than that for R-D in U. lactuca during the initial stages of emersion. Respiratory carbon loss as a percentage of gross photosynthetic carbon gain increased with increasing temperature and/or desiccation but was significantly reduced when estimated using R-L rather than R-D. It is suggested that measurements of R-L and how it changes in a variable environment are as important as estimates of R-D and photosynthesis in determining simultaneous balance between photosynthetic carbon uptake and respiratory carbon loss and in modeling the net daily carbon gain for an intertidal macroalga.

Quantum efficiency and temperature coefficients of GaInP/GaAs dual-junction solar cell

GaInP/GaAs dual-junction solar cell with a conversion efficiency of 25.2% has been fabricated using metalorganic chemical vapor deposition (MOCVD) technique. Quantum efficiencies of the solar cell were measured within a temperature range from 25 to 160A degrees C. The results indicate that the quantum efficiencies of the subcells increase slightly with the increasing temperature. And red-shift phenomena of absorption limit for all subcells are observed by increasing the cell's work temperature, which are consistent with the viewpoint of energy gap narrowing effect. The short-circuit current density temperature coefficients dJ (sc)/dT of GaInP subcell and GaAs subcell are determined to be 8.9 and 7.4 mu A/cm(2)/A degrees C from the quantum efficiency data, respectively. And the open-circuit cell voltage temperature coefficients dV (oc)/dT calculated based on a theoretical equation are -2.4 mV/A degrees C and -2.1 mV/A degrees C for GaInP subcell and GaAs subcell.

Influence of the growth temperature of the high-temperature AlN buffer on the properties of GaN grown on Si(111) substrate

We have studied the influence of the growth temperature of the high-temperature (HT) AIN buffer layer on the properties of the GaN epilayer which was grown on Si(111) substrate by metalorganic chemical vapor deposition (MOCVD). It was found that the crystal quality of the GaN epilayer strongly depends on the growth temperature of the HT-AIN buffer. The growth temperature of the AIN buffer to obtain high-quality GaN epilayers lies in a narrow window of several tens of degrees. When the temperature is lower than a certain temperature range, the appearance of AIN polycrystals results in the deterioration of the crystal quality of the AIN buffer layer, which is greatly disadvantageous to the coalescence of the GaN epilayer. Although the AIN buffer's crystal quality is improved as the growth temperature increases, the Si outdiffusion from the substrate is also enhanced when the temperature is higher than a certain temperature range, which will demolish the subsequent growth of the GaN epilayer. Therefore, there exists an optimum growth temperature range of the AIN buffer around 1080degreesC for the growth of high-quality GaN epilayers. (C) 2003 Elsevier B.V. All rights reserved.

Anomalous temperature dependence of photoluminescence from stoichiometric GD(2)O(3-x) film

A stoichiometric Gd2O3-x thin film has been grown on a silicon (10 0) substrate with a low-energy dual ion-beam epitaxial technique. Gd2O3-x shares Gd2O3 structures although there are many oxygen deficiencies in the film. The photoluminescence (PL) measurements have been performed in a temperature range 5-300 K. The detailed characters of the peak position, the full-width at half-maximum (FWHM) and the peak intensity at different temperature were reported. An anomalous intensity behavior of the PL spectra has been observed, which is similar to that of some other materials such as porous silicon and silicon nanocrystals in silicon dioxide. Therefore, we suggest that the nanoclusters with the oxygen deficiencies contribute to the PL emission and employ the model of singlet-triplet exchange splitting of exciton to discuss the four peaks observed in the experiment. (C) 2003 Elsevier B.V. All rights reserved.

Temperature-independent fiber Bragg grating strain sensor using bimetal cantilever

A new packaged fiber Bragg grating using bimetal cantilever beam as the strain agent is presented. The grating is two-point attached on one specific surface of the bimetal beam which consists of two metallic material with different thermal-expansion coefficient. Thereby the grating can be compressed or stretched along with the cantilever beam while temperature varies and temperature compensation can be realized. At the same time, grating chirping can be avoided for the particular attaching method. Experiment results demonstrated that the device is able to automatically compensate temperature induced wavelength shift. The temperature dependence of Bragg wavelength reduced to -0.4 pm/degrees C over the temperature range from -20 to 60 degrees C. This fiber grating package technique is cost effective and can be used in strain sensing. (c) 2005 Elsevier Inc. All rights reserved.

Temperature dependence of absorption edge in MOCVD grown GaN

We have studied the temperature dependence of absorption edge of GaN thin films grown on sapphire substrate by metal-organic chemical vapor deposition using optical absorption spectroscopy. A shift in absorption edge of about 55 meV has been observed in temperature range 273-343 K. We have proposed a theoretical model to find the energy gap from absorption coefficient using alpha = alpha(max) + (alpha(min) - alpha(max))/[1 + exp 2(E - E-g + KT)/KT]. Temperature dependence of band gap has also been studied by finding an appropriate theoretical fit to our data using E-g(T) = E-g(273 K) - (8.8 x 10(-4)T(2))/(483 + T) + 0.088 (Varshni empirical formula) and E-g(T) = E-g(273 K)-0.231447/[exp(362/T)-1] + 0.082 relations. It has been found that data can be fitted accurately after adding a factor similar to 0.08 in above equations. Debye temperature (483 K) and Einstein temperature (362 K) in the respective equations are found mutually in good agreement.

Measurement of small-signal and large-signal responses of packaged laser modules at high temperature

In this paper, the pulsed injection method is extended to measure the chip temperature of various packaged laser modules, such as the DFB laser modules, the FP laser modules, and the EML laser modules. An optimal injection condition is obtained by investigating the dependence of the lasing wavelength on the width and period of the injection pulse in a relatively wide temperature range. The small-signal frequency responses and large-signal performances of packaged laser modules at different chip temperature are measured. The adiabatic small-signal modulation characteristics of packaged LD are first extracted. In the large-signal measurement, the effects of chip temperature, bias current and driving signal on the performances of the laser modules are discussed. It has been found that the large-signal performances of the EML modules depend on the different red-shift speeds of the DFB and EAM sections as chip temperature varying, and the optimal characteristics may be achieved at higher temperature.