Laufzeitmessungen in Fluoren-Einkristallen / Transit Time Measurements in Fluorene Single Crystals

1977 ◽  
Vol 32 (6) ◽  
pp. 580-587
Author(s):  
H. Eckhardt
Keyword(s):  
Single Crystals ◽  
Transit Time ◽  
Low Temperatures ◽  
Pulse Shape ◽  
Room Temperature ◽  
Trap Depth ◽  
Drift Mobility ◽  
Temperature Ranges ◽  
Increasing Temperature ◽  
Shallow Traps

Abstract The hole drift mobility in single crystals of fluorene was determined by transit time measurements. At room temperature the mobility along the c-axis is (0,82 ± 0,14) cm2/Vs and in the abplane (0,72 ± 0,1) cm2/Vs. In the temperature ranges 200K<T<300K and 165K<T<300K μc and μab have been found to be ~T-1,5 and ~T-1,0, respectively. In both cases the mobility reaches a constant value for low temperatures (100 K). In the range 300 K<T<345 K μ decreases very strongly with increasing temperature {μ~T-5). Traps, especially deep and shallow surface traps, influence the pulse heighth and the pulse shape. From the change of the pulse shape with temperature a trap depth EH = 0,4 eV for shallow traps is determined.

Photoleitung in 2,3-Dimethylnaphthalin bei gepulster Lichteinstrahlung / Transient Photocurrents in 2,3-Dimethylnaphthalene Single Crystals

1976 ◽  
Vol 31 (3-4) ◽  
pp. 251-258
Author(s):  
W.-W. Falter
Keyword(s):  
Electric Field ◽  
Single Crystals ◽  
Pulse Shape ◽  
Applied Field ◽  
Room Temperature ◽  
Cleavage Plane ◽  
Trap Depth ◽  
Surface Region ◽  
Deep Hole ◽  
Hole Trapping

Hole currents are observed by illuminating 2,3 DN single crystals with 347 nm and 337 nm. The probability of generating free holes is a function of temperature and electric field-strength. In the cleavage plane of the crystals the mobility does not depend on the direction of the applied field and amounts to 2.6·10-1 cm2/Vsec at room temperature, which exceeds the related value measured perpendicularly to the plane by a factor of four. The temperature-dependence of the mobility indicates shallow hole-trapping exspecially close to the surface. The trap depth is estimated to be 10-2 eV. Temperature also influences the pulse shape, by which one can conclude that hole traps of 0.2 eV and ≲ 0.1 eV exist in a thin surface layer. Photocurrents exited with 347 nm increase stronger than quadratically with the electric field. Deep hole traps, being also restricted to the surface region of the crystals, are made responsible for this fact.

Plastic Deformation of Mo(Si,Al)2 Single Crystals with the C40 Structure

1996 ◽  
Vol 460 ◽  
Author(s):  
M. Moriwaki ◽  
K. Ito ◽  
H. Inui ◽  
M. Yamaguchi
Keyword(s):  
Single Crystals ◽  
Deformation Behavior ◽  
Basal Slip ◽  
Room Temperature ◽  
Slip Systems ◽  
Temperature Range ◽  
Al Content ◽  
Partial Dislocations ◽  
Increasing Temperature ◽  
Critical Resolved Shear Stress

ABSTRACTThe deformation behavior of single crystals of Mo(Si,Al)2 with the C40 structure has been studied as a function of crystal orientation and Al content in the temperature range from room temperature to 1500°C in compression. Plastic flow is possible only above 1100°C for orientations where slip along <1120> on (0001) is operative and no other slip systems are observed over whole temperature range investigated. The critical resolved shear stress for basal slip decreases rapidly with increasing temperature and the Schmid law is valid. Basal slip appears to occur through a synchroshear mechanism, in which a-dislocations (b=1/3<1120>) dissociate into two synchro-partial dislocations with the identical Burgers vector(b*1/6<1120>) and each synchro-partial further dissociates into two partials on two adjacent planes.

scholarly journals Photoconductivity of activated carbon fibers

1991 ◽  
Vol 6 (5) ◽  
pp. 1040-1047 ◽  
Author(s):  
K. Kuriyama ◽  
M.S. Dresselhaus
Keyword(s):  
Activated Carbon ◽  
Surface Area ◽  
Carbon Fibers ◽  
Low Temperatures ◽  
Room Temperature ◽  
High Surface ◽  
Localized States ◽  
Activated Carbon Fibers ◽  
Disordered Carbon ◽  
Increasing Temperature

The conductivity and photoconductivity are measured on a high-surface-area disordered carbon material, i.e., activated carbon fibers, to investigate their electronic properties. This material is a highly disordered carbon derived from a phenolic precursor, having a huge specific surface area of 1000–2000 m2/g. Our preliminary thermopower measurements show that the dominant carriers are holes at room temperature. The x-ray diffraction pattern reveals that the microstructure is amorphous-like with Lc ≃ 10 Å. The intrinsic electrical conductivity, on the order of 20 S/cm at room temperature, increases by a factor of several with increasing temperature in the range 30–290 K. In contrast, the photoconductivity in vacuum decreases with increasing temperature. The magnitude of the photoconductive signal was reduced by a factor of ten when the sample was exposed to air. The recombination kinetics changes from a monomolecular process at room temperature to a bimolecular process at low temperatures, indicative of an increase in the photocarrier density at low temperatures. The high density of localized states, which limits the motion of carriers and results in a slow recombination process, is responsible for the observed photoconductivity.

Variation of sticking probabilities with temperature and coverage, and desorption spectra for nitrogen on tungsten films

1967 ◽  
Vol 297 (1450) ◽  
pp. 321-335 ◽  
Keyword(s):  
Low Temperatures ◽  
Room Temperature ◽  
Continuous Distribution ◽  
Kcal Mole ◽  
Initial Value ◽  
Precursor State ◽  
Heats Of Adsorption ◽  
Sticking Probabilities ◽  
Increasing Temperature ◽  
Pressure Changes

From 78 to 150°K, and at coverages < 8 x 10 14 molecules/cm 2 , the sticking probability s of nitrogen on tungsten films (= 0·9) is independent of both temperature and coverage, whereas at temperatures above 150°K it is a function of both these variables. These results are interpreted in terms of a physically adsorbed precursor state with a heat of adsorption of ca . 3 kcal/mole. It is concluded that only a fraction of molecules colliding with the surface enter this state and that it is this fraction which determines the initial value of s at low temperatures. The decrease of s with increasing temperature above 150°K is a consequence of the inactivity of some planes, such as the (110), at the higher temperatures. Desorption spectra were obtained by warming films from 78°K to room temperature and recording the subsequent pressure changes as a function of time. From these data the distribution of site energies for the weakly held adsorbate (the αγ state) was evaluated, indicating a continuous distribution with heats of adsorption varying between 6 and 20 kcal/mole.

High-Temperature Absorption of the 3.39 μm He-Ne Laser Line by Acetylene, Ethylene, and Propylene

1980 ◽  
Vol 34 (1) ◽  
pp. 81-84 ◽  
Author(s):  
T. Koike ◽  
W. C. Gardiner
Keyword(s):  
Room Temperature ◽  
Spectroscopic Analysis ◽  
Laser Line ◽  
Absorption Process ◽  
Line Broadening ◽  
Chemical Behavior ◽  
Time Resolved ◽  
Temperature Ranges ◽  
Increasing Temperature ◽  
Line Positions

Absorptivity measurements for the 3.39 μm He-Ne laser line are reported for acetylene, ethylene, and propylene over the temperature ranges 1500 to 3000 K (acetylene), 1000 to 2000 K (ethylene), and 700 to 2300 K (propylene). In contrast to the behavior of other hydrocarbons, the absorptivities of acetylene and ethylene increase with increasing temperature. The conventional spectroscopic analysis of line positions based upon high-resolution infrared spectroscopy at room temperature and approximate line-broadening theory indicate that no absorption at all would be expected for acetylene or ethylene. The time-resolved absorption profiles and computer models of the chemical behavior expected for shock-heated test gas confirm that the absorption is really due to these molecules, but must be attributed to some heretofore unidentified absorption process.

PHONON-DRAG EFFECT OF ULTRA-THIN FeSi2 AND MnSi1.7/FeSi2 FILMS

2011 ◽  
Vol 25 (22) ◽  
pp. 1829-1838 ◽  
Author(s):  
Q. R. HOU ◽  
B. F. GU ◽  
Y. B. CHEN ◽  
Y. J. HE
Keyword(s):  
Electrical Resistivity ◽  
Seebeck Coefficient ◽  
Single Crystals ◽  
Thermoelectric Power ◽  
Power Factor ◽  
Low Temperatures ◽  
Room Temperature ◽  
Phonon Drag ◽  
Drag Effect ◽  
Thermoelectric Power Factor

Phonon-drag effect usually occurs in single crystals at very low temperatures (10–200 K). Strong phonon-drag effect is observed in ultra-thin β- FeSi 2 films at around room temperature. The Seebeck coefficient of a 23 nm-thick β- FeSi 2 film can reach -1.375 mV/K at 343 K. However, the thermoelectric power factor of the film is still small, only 0.42×10-3 W/m-K2, due to its large electrical resistivity. When a 27 nm-thick MnSi 1.7 film with low electrical resistivity is grown on it, the thermoelectric power factor of the MnSi 1.7 film can reach 1.5×10-3 W/m-K2 at around room temperature. This value is larger than that of bulk MnSi 1.7 material in the same temperature range.

Electrical resistivity of gallium single crystals at low temperatures

1951 ◽  
Vol 209 (1099) ◽  
pp. 542-550 ◽  
Keyword(s):  
Electrical Resistivity ◽  
Specific Heat ◽  
Single Crystals ◽  
Low Temperatures ◽  
Room Temperature ◽  
Resistivity Measurements ◽  
Characteristic Temperatures ◽  
The Ideal

Electrical resistivity measurements on single crystals of gallium grown to conform approximately to the three axial directions have been extended to low temperatures, detailed investigation being made over the range 20.4 to 4.2° K. The anisotropy of this property increases in this region where the resistivity ratios for the three specimens are approximately 1: 2.1: 8 compared with 1: 2.1 6 : 6.5 5 at room temperature. The ‘ideal’ resistivity is proportional to T n , where n ≃ 4.45 for the range 5 to 12° K and decreases to about 3.9 for the range 12 to 20.4° K. The characteristic temperatures as derived from Grüneisen’s expression show relatively small differences for the three axial directions but decrease with decrease in temperature. Comparable variations with temperature are observed in the characteristic temperatures derived previously from specific heat measurements on gallium.

Plastic Behavior and Deformation Structure of Silicide Single Crystals with Transition Metals at High Temperatures

1993 ◽  
Vol 322 ◽  
Author(s):  
Y. Umakoshi ◽  
T. Nakashima ◽  
T. Nakano ◽  
E. Yanagisawa
Keyword(s):  
Brittle Fracture ◽  
Slip System ◽  
Single Crystals ◽  
Low Temperatures ◽  
Plastic Behavior ◽  
Deformation Structure ◽  
Secondary Slip ◽  
Ambient Temperatures ◽  
Brittle Transition ◽  
Increasing Temperature

AbstractThe mechanical and plastic behaviors of refractory silicide single crystals with Cllb (MoSi2), C40 (CrSi2, TaSi2 and NbSi2), D88 (Ti5Si3) and Cl (CoSi2 and (Co0.9Ni0.1)Si2) structures were investigated. The C40–type silicides were deformed by (0001)<1120> slip. Their yield stress decreased sharply with increasing temperature but NbSi2 and TaSi2 which were deformable even at low temperatures, exhibited anomalous strengthening around 1350°C. Deformation of Ti5Si3 whose ductile-brittle transition occurred around 1300°C was controlled by twins and the brittle fracture occurred on the basal plane. In CoSi2 the {001}<100> slip was only activated at ambient temperatures but addition of Ni activated {110}<110> slip as secondary slip system and improved the ductility. The creep behavior of MoSi2 and CrSi2 single crystals were also investigated and was found to be controlled by the viscous and glide motion of dislocations.

Annealing of Cold-Rolled Fe-40A1 Single Crystals

1996 ◽  
Vol 460 ◽  
Author(s):  
Y. Yang ◽  
I. Baker
Keyword(s):  
Single Crystals ◽  
Differential Scanning Calorimeter ◽  
Room Temperature ◽  
Plastic Strains ◽  
Temperature Ranges ◽  
Cold Rolled

ABSTRACTSingle crystals of Fe-40A1 were cold-rolled to plastic strains in the range 5% to 48%. Discs cut from the rolled crystals at different rolling strains were heated at 10 K/min in a differential scanning calorimeter from room temperature to 973 K. Three exothermic peaks were observed in the temperature ranges of 440–550 K, 610–650 K, and 860–930 K, all the peaks shifting to lower temperatures with increasing strain. The origins of these peaks are discussed in terms of the disorder and vacancies introduced during rolling.

Time-of-Flight Measurement on a-Ge:H and a-SiGe:H Alloys

1992 ◽  
Vol 258 ◽  
Author(s):  
E.Z. Liu ◽  
D. Pang ◽  
W. Paul ◽  
J.H. Chen
Keyword(s):  
Room Temperature ◽  
Transport Model ◽  
Drift Mobility ◽  
Band Tail ◽  
High Quality ◽  
Hopping Transport ◽  
Flight Measurement ◽  
Order Of Magnitude ◽  
Temperature Ranges ◽  
Electron Drift Mobility

ABSTRACTWe report TOF measurements on high quality intrinsic a-Ge:H and a-SiGe:H films of E04=1–4.eV in temperature ranges of 200 to 280 and 230 to 300K, respectively. Complete charge collection is achieved in all measurements. For a-Ge:H films, the (μτ)e product obtained from the Hecht plot is (5±3)×10-8 cm2/V above 240K and decreases at lower temperatures. The electron transit signal is dispersive at all temperatures. The a obtained from ttV-1/αis 0.23 at 200K and approaches 1.0 at 260K. The electron drift mobility μd shows activated behavior, with an energy of 0.37±0.05eV, and has an extrapolated room temperature value of 0.03 cm2/Vs. Compared to a-Ge:H, μd of a-SiGe:H alloy samples is lower by one order of magnitude but has a similar activation energy. These results are consistent with a band tail hopping transport model.

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