Intrinsic Optical and Electrical Properties of Strain-Adjusted Short-Period SimGen Superlattices

1993 ◽  
Vol 298 ◽  
Author(s):  
Janos Olajos ◽  
Jesper Engvall ◽  
Hermann G. Grimmeiss ◽  
Erich Kasper ◽  
Horst Kibbel ◽  
...  
Keyword(s):  
Low Temperatures ◽  
Room Temperature ◽  
Optical And Electrical Properties ◽  
Interband Absorption ◽  
Optical Transitions ◽  
Photocurrent Spectroscopy ◽  
Photogenerated Electrons ◽  
Short Period ◽  
Systematic Shift ◽  
Good Agreement

AbstractInterband optical transitions are observed in a series of strain-adjusted, short-period Si/Ge superlattices by means of photocurrent spectroscopy, infrared absorption, photo (PL)- and electroluminescence (EL). The onsets of the interband absorption in the energy range of 0.7 - 0.9 eV are in good agreement with the observed PL and EL. Bandgap-related EL is observed in mesa diodes at room temperature, whereas the PL disappears at about 40K. In samples, annealed at growth temperatures (550°C) and higher, a systematic shift of the bandgap is observed which is discussed in terms of a process involving interdiffusion of the Si and Ge atoms. Photocurrent measurements at low temperatures support the model from PL studies suggesting that the photogenerated electrons are immobile in the SLS at low temperatures and have to be thermally ionized from shallow levels.

Ordering of Oxygen Atoms in YBA2CU3O6+X and its Effects on Superconducting Properties

1987 ◽  
Vol 99 ◽  
Author(s):  
Keikichi Nakamura ◽  
Takeshi Hatano ◽  
Shozo Ikeda ◽  
Keiichi Ogawa
Keyword(s):  
Experimental Data ◽  
Oxygen Content ◽  
Low Temperatures ◽  
Room Temperature ◽  
Orthorhombic Phase ◽  
Superconducting Phase ◽  
Superconducting Transition ◽  
Superconducting Properties ◽  
Good Agreement ◽  
Oxygen Atoms

ABSTRACTOrdering of oxygen atoms in YBa2Cu3O6+x has been analysed by employing statistical thermodynamics ana the results are compared with the experimental data. The axial lengths a and b at room temperature were determined experimentally as a function of oxygen content and were found to show good agreement with the calculated lengths a and b. Special care was taken in the above experiment to dope oxygen atoms into the sample at low temperatures, typically 400° C. The superconducting transition temperature of the sample doped with oxygen at 400°C(starting material:YBa2Cu3O6.1.(decreases linearly with decreasing the oxygen content from 6+x=6.9(92 K) to 6.38(30 K) and decreased sharply around 6+x=6.35(5 K). No distinct superconducting phase corresponding to further ordered orthorhombic phase has been observed in this case.

Room Temperature Optical Studies of GaAs/AlGaAs Coupled Double Quantum Wells

1987 ◽  
Vol 102 ◽  
Author(s):  
C. Jagannath ◽  
B. Elman ◽  
Emil S. Koteles ◽  
Y. J. Chen ◽  
S. Brown ◽  
...  
Keyword(s):  
Optical Properties ◽  
Quantum Wells ◽  
Electric Fields ◽  
Low Temperatures ◽  
Room Temperature ◽  
Double Quantum ◽  
Optical Transitions ◽  
Photoluminescence Excitation ◽  
Optical Studies

ABSTRACTRoom temperature photoreflectance (PR) spectroscopy has been utilized to study the effect of electric fields on the optical properties of GaAs/AlGaAs coupled double quantum wells (CDQWs). The behavior of optical transitions when subjected to electric fields ranging from 0 to 2×105V/cm, was found to be similar to that observed at low temperatures using photoluminescence excitation spectroscopy. Large shifts in the energies of spatially indirect transitions were observed when the CDQW was subjected to modest bias voltages.

Dislocation structures around SiO2 Particles in aged Cu-Cr-SiO2

1978 ◽  
Vol 36 (1) ◽  
pp. 594-595
Author(s):  
N.J. Long ◽  
M.H. Loretto ◽  
C.H. Lloyd
Keyword(s):  
Flow Stress ◽  
Single Crystals ◽  
Room Temperature ◽  
Thin Foil ◽  
Age Hardening ◽  
Dispersion Strengthening ◽  
Accurate Picture ◽  
The Matrix ◽  
Very High ◽  
Good Agreement

IntroductionThere have been several t.e.m. studies (1,2,3,4) of the dislocation arrangements in the matrix and around the particles in dispersion strengthened single crystals deformed in single slip. Good agreement has been obtained in general between the observed structures and the various theories for the flow stress and work hardening of this class of alloy. There has been though some difficulty in obtaining an accurate picture of these arrangements in the case when the obstacles are large (of the order of several 1000's Å). This is due to both the physical loss of dislocations from the thin foil in its preparation and to rearrangement of the structure on unloading and standing at room temperature under the influence of the very high localised stresses in the vicinity of the particles (2,3).This contribution presents part of a study of the Cu-Cr-SiO2 system where age hardening from the Cu-Cr and dispersion strengthening from Cu-Sio2 is combined.

scholarly journals Review of Multi-Physics Modeling on the Active Magnetic Regenerative Refrigeration

2021 ◽  
Vol 26 (2) ◽  
pp. 47
Author(s):  
Julien Eustache ◽  
Antony Plait ◽  
Frédéric Dubas ◽  
Raynal Glises
Keyword(s):  
Magnetic Field ◽  
Low Temperatures ◽  
Room Temperature ◽  
State Of The Art ◽  
Vapor Compression ◽  
Crucial Step ◽  
Potential Alternative ◽  
Vapor Compression Refrigeration ◽  
Preliminary Study ◽  
Physics Modeling

Compared to conventional vapor-compression refrigeration systems, magnetic refrigeration is a promising and potential alternative technology. The magnetocaloric effect (MCE) is used to produce heat and cold sources through a magnetocaloric material (MCM). The material is submitted to a magnetic field with active magnetic regenerative refrigeration (AMRR) cycles. Initially, this effect was widely used for cryogenic applications to achieve very low temperatures. However, this technology must be improved to replace vapor-compression devices operating around room temperature. Therefore, over the last 30 years, a lot of studies have been done to obtain more efficient devices. Thus, the modeling is a crucial step to perform a preliminary study and optimization. In this paper, after a large introduction on MCE research, a state-of-the-art of multi-physics modeling on the AMRR cycle modeling is made. To end this paper, a suggestion of innovative and advanced modeling solutions to study magnetocaloric regenerator is described.

scholarly journals On the measurement of the ratio of the specific heats using small volumes of gas.—The ratios of the specific heat of air and of hydrogen at atmospheric pressure and a temperatures between 20°C. and —183°C

1925 ◽  
Vol 107 (743) ◽  
pp. 510-543 ◽  
Keyword(s):  
Systematic Error ◽  
Low Temperatures ◽  
Room Temperature ◽  
Expansion Chamber ◽  
Small Vessels ◽  
Specific Heats ◽  
Large Expansion ◽  
Before And After ◽  
The One ◽  
Chamber Capacity

Introduction .—In nearly all the previous determinations of the ratio of the specific heats of gases, from measurements of the pressures and temperature before and after an adiabatic expansion, large expansion chambers of fror 50 to 130 litres capacity have been used. Professor Callendar first suggests the use of smaller vessels, and in 1914, Mercer (‘Proc. Phys. Soc.,’ vol. 26 p. 155) made some measurements with several gases, but at room temperature only, using volumes of about 300 and 2000 c. c. respectively. He obtained values which indicated that small vessels could be used, and that, with proper corrections, a considerable degree of accuracy might be obtained. The one other experimenter who has used a small expansion chamber, capacity about 1 litre, is M. C. Shields (‘Phys. Rev.,’ 1917), who measured this ratio for air and for hydrogen at room temperature, about 18° C., and its value for hydroger at — 190° C. The chief advantage gained by the use of large expansion chambers is that no correction, or at the most, a very small one, has to be made for any systematic error due to the size of the containing vessels, but it is clear that, in the determinations of the ratio of the specific heats of gases at low temperatures, the use of small vessels becomes a practical necessity in order that uniform and steady temperature conditions may be obtained. Owing, however, to the presence of a systematic error depending upon the dimensions of the expansion chamber, the magnitude of which had not been definitely settled by experiment, the following work was undertaken with the object of investigating the method more fully, especially with regard to it? applicability to the determination of this ratio at low temperatures.

Defect Structure of MEV Si Implantation in GaAs

1988 ◽  
Vol 126 ◽  
Author(s):  
S.-Tong Lee ◽  
G. Braunstein ◽  
Samuel Chen
Keyword(s):  
Free Surface ◽  
Defect Structure ◽  
Room Temperature ◽  
Surface Region ◽  
Peak Position ◽  
Lattice Disorder ◽  
Depth Profiles ◽  
Trim Calculation ◽  
Good Agreement

ABSTRACTThe defect and atomic profiles for MeV implantation of Si in GaAs were investigated using He++ channeling, TEM, and SIMS. Doses of 1–10 × 1015Si/cm2 at 1–3 MeV were used. MeV implantation at room temperature rendered only a small amount of lattice disorder in GaAs. Upon annealing at 400°C for 1 h or 800°C for 30 a, we observed a ‘defect-free’ surface region (- 1 μ for 3 MeV implant). Below this region, extensive secondary defects were formed in a band which was 0.7 μ wide and centered at 2 μ for 3 MeV implant. These defects were mostly dislocations lying in the [111] plane. SIMS depth profiles of Si implants showed the Si peak to be very close to the peak position of the defects. The experimental profiles of Si were compared to the TRIM calculation; generally good agreement existed among the peak positions.

scholarly journals The behaviour of visual purple at low temperature

1941 ◽  
Vol 179 (977) ◽  
pp. 151-159 ◽  
Keyword(s):  
Aqueous Solution ◽  
Low Temperature ◽  
Low Temperatures ◽  
Room Temperature ◽  
Absorption Curve ◽  
Quantum Yields

Visual purple is soluble and stable in a mixture of glycerol and water (3:1). At room temperature the spectrum of such a solution is identical with that of the aqueous solution. At — 73° C the peak of the absorption curve is higher and narrower than at room temperature, and it is shifted towards longer waves. The product of photodecomposition at — 73° C has a spectrum in ­ dependent of pH and is at low temperatures thermostable and photostable, but at room temperature it decomposes therm ally to indicator yellow. The primary product appears to be identical with transient orange. The quantum yields of the photoreaction at low and at room temperature are of the same order.

Optical Transitions in Chalcogenide Glasses From the Point of View of a Barrier-Cluster Model

2008 ◽  
Vol 39-40 ◽  
pp. 253-256
Author(s):  
Ivan Baník
Keyword(s):  
Optical Absorption ◽  
Low Temperatures ◽  
Cluster Model ◽  
Chalcogenide Glasses ◽  
Temperature Shift ◽  
Point Of View ◽  
Optical Transitions ◽  
Influence Of Temperature ◽  
Exponential Tails ◽  
Influence Of Temperature On

A barrier-cluster model of chalcogenide glasses is employed to analyze optical transitions near the absorption edge. The influence of temperature on the optical absorption is studied. The model is used to explain the temperature shift of exponential tails of the optical absorption and the temperature dependence of the optical forbidden-band width at low temperatures.

Analysis of Thermal Variation of Length and Refractive Index of Lead Fluoride to Study its Optical Properties

1989 ◽  
Vol 172 ◽  
Author(s):  
T. S. Aurora ◽  
D. O. Pederson ◽  
S. M. Day
Keyword(s):  
Refractive Index ◽  
Room Temperature ◽  
Linear Thermal Expansion ◽  
Small Variation ◽  
Published Data ◽  
Thermal Variation ◽  
Lead Fluoride ◽  
Superionic Phase Transition ◽  
Lorenz Relation ◽  
Good Agreement

AbstractLinear thermal expansion and refractive index variation have been measured in lead fluoride with a laser interferometer as a function of temperature. Data has been analyzed using the Lorentz-Lorenz relation. Molecular polarizability, band gap, variation of refractive index with density, and strain-polarizability parameter have been studied as a function of temperature. They exhibit a small variation with temperature except near the superionic phase transition where the variation appears to be more pronounced. The results are in good agreement with the published data near room temperature.

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