Metastable Phenomena in the Thermally Activated Conductivity of Hydrogenated Amorphous Germanium (a-Ge:H)

1993 ◽  
Vol 297 ◽  
Author(s):  
T. DrÜsedau ◽  
D. Pang ◽  
E. Sauvain ◽  
P. Wickboldt ◽  
E.Z. Liu ◽  
...  
Keyword(s):  
Cooling Rate ◽  
Room Temperature ◽  
Equilibrium Temperature ◽  
Cooling Curves ◽  
Thermally Activated ◽  
Heating And Cooling ◽  
Higher Temperature ◽  
Hydrogenated Amorphous ◽  
Hydrogenated Amorphous Germanium ◽  
Good Agreement

The activated conductivity of a-Ge:H between room temperature and 460K was investigated using heating and cooling rates in the range between .001 and 0.1 K/s. A splitting of the cooling curves obtained at different rates, which defines the so called equilibrium temperature TE, is observed mainly between 420 and 430K. Taking into consideration that TE depends on the maximum cooling rate, the present results are in good agreement with those reported by Eberhardt et al. The higher cooling rate always leads to the lower conductivity at any temperature below TE. These effects can be rationalized in terms of a reversible shift of the Fermi level towards midgap at higher temperature. Though reversible changes of the mobility cannot be excluded, they cannot account for our set of experimental data. Rather, changes in the density of electronic states within the mobility gap can explain the effects observed.

scholarly journals Design of Ag-Ge-Zn braze/solder alloys: Experimental thermodynamics and surface properties

2017 ◽  
Vol 53 (3) ◽  
pp. 295-302 ◽  
Author(s):  
S. Delsante ◽  
D. Li ◽  
R. Novakovic ◽  
G. Borzone
Keyword(s):  
Cooling Rate ◽  
Room Temperature ◽  
Slow Heating ◽  
Experimental Investigations ◽  
Spectroscopy Analysis ◽  
Heating And Cooling ◽  
Experimental Thermodynamics ◽  
Liquid Phases ◽  
Dsc Analyses ◽  
S Model

The experimental investigation of the Ag-Ge-Zn phase diagram was performed by using combined microstructural and Differential Scanning Calorimeter (DSC) analyses. The samples were subjected to thermal cycles by a heat-flux DSC apparatus with heating and cooling rate of 0.5 or 0.3?C/min. The microstructure of the samples, both after annealing and after DSC analysis, was studied by optical and scanning electron microscopy coupled with EDS (Energy Dispersive Spectroscopy) analysis. Considering the slow heating and cooling rate adopted, the isothermal section at room temperature was established. No ternary compounds were observed. On the basis of the experimental investigations the invariant reactions were identified. Combining the thermodynamic data on the Ag-Ge, Ag-Zn and Ge-Zn liquid phases by means of Butler?s model the surface tension of Ag-Ge-Zn alloys was calculated.

Grain Boundary Relaxation in 18-Carat Yellow Gold

2012 ◽  
Vol 184 ◽  
pp. 283-288 ◽  
Author(s):  
Ann Kathrin Maier ◽  
Iva Tkalcec ◽  
Daniele Mari ◽  
Robert Schaller
Keyword(s):  
Activation Parameters ◽  
Relaxation Peak ◽  
Dislocation Model ◽  
Mechanical Loss ◽  
Thermally Activated ◽  
Heating And Cooling ◽  
Boundary Relaxation ◽  
Higher Temperature ◽  
Amplitude Dependency ◽  
Second Peak

Au60Ag30Cu10(in at%) gold alloy exhibits a mechanical loss spectrum composed of a Zener peak due to Cu atoms in the solid solution and of a second relaxation peak at higher temperature or lower frequency. It is shown that this second peak is related to the presence of grain boundaries as it is absent in the spectrum of a single crystal. This mechanical loss peak, which is stable and reproducible in heating and cooling cycles, is thermally activated with an activation enthalpy of 2.35 eV and an apparent limit relaxation time of 9.6·10-17s. As it is hard to imagine that a whole grain should slip at once along a touching grain, the relaxation peak is interpreted by a dislocation model, which may account not only for the activation parameters but also for the stress amplitude dependency of the peak.

The DSC Investigation on Phase Transformations of Directionally Solidified (DS) and Powder Metallurgy (PM) Ni-Base Superalloys

2018 ◽  
Vol 941 ◽  
pp. 1035-1040
Author(s):  
Liang Zheng ◽  
Yu Feng Liu ◽  
Michael J. Gorley ◽  
Zu Liang Hong ◽  
Sarah Day ◽  
...  
Keyword(s):  
Particle Size ◽  
Phase Transformation ◽  
Powder Metallurgy ◽  
Phase Change ◽  
Phase Transformations ◽  
Cooling Rate ◽  
Cooling Curves ◽  
Directionally Solidified ◽  
Transformation Temperatures ◽  
Heating And Cooling

The phase transformations of the directionally solidified (DS) and powder metallurgy (PM) Ni-base superalloys were investigated by JMatPro, synchrotron XRD (SXRD) and differential scanning calorimetry (DSC). The minor phases, such as MC, eutectic γ′ and Ni5Hf, and γ matrix with secondary γ′ existed in as-cast microstructure of DS DZ22. However, only γ matrix was found in PM625 alloy powders. The phase change in both heating (melting) and cooling (solidification) process was investigated by DSC on DZ22 test bar and PM625 alloy powders respectively. The DSC experiment with different heating/cooling rates (5-40°C/min) was performed on DS superalloy DZ22. The results indicated that the heating/cooling rate had obvious effect on the DSC results of the phase transformation temperatures of liquidus, MC carbides, solidus, eutectic (γ+γ′) and secondary γ′. The heating and cooling DSC curves shifted to high and low temperature direction respectively, accompanied by the heating/cooling rate increased. However, the average values of specific peaks of heating and cooling curves are relatively consistent which is close to the equilibrium phase change temperatures of the alloy and makes the results comparable. Besides the average value method, the liquidus temperature of the alloy (0°C/min) can also be obtained by method of linear-fit/extrapolating from 5-40°C/min heating/cooling rates or inflection point deviate from the baseline of DSC cooling curves which could minimize the heating/cooling rate effects. The DSC experiment was carried out on PM625 superalloy powders with different particle size range (0-355μm), the results indicated that the particle size had minor effect on liquidus and solidus temperatures of DSC heating curves, the differences were less than 2°C. The change in phase transformation temperatures under different heating/cooling rate should be considered for selecting the process parameter (heat treatment, HIP or casting) for manufacturing Ni-base superalloy components.

A Transient Technique to Measure the Temperature Coefficient of Resistance for Thin Film Resistors

1989 ◽  
Vol 111 (2) ◽  
pp. 143-148 ◽  
Author(s):  
Bahgat Sammakia ◽  
Phillip Vadala ◽  
Thomas Homa
Keyword(s):  
Thin Film ◽  
Temperature Coefficient ◽  
Room Temperature ◽  
Conventional Technique ◽  
Temperature Coefficient Of Resistance ◽  
Moderate Amount ◽  
Transient Technique ◽  
Thin Film Resistors ◽  
Higher Temperature ◽  
Good Agreement

The temperature coefficient of resistance (TCR) is defined as: TCR=(R2−R1)R1×1(t2−t1) where R2 and R1 are the resistances measured at temperatures t1 and t2, respectively. The conventional TCR measurement method consists of measuring resistance at room temperature, then heating the resistor to a known higher temperature, then measuring the resistance again. This technique is very accurate and repeatable, however it is slow and cumbersome because it takes a moderate amount of time for the sample to reach steady state in an oven before the resistance can be measured. The present study proposes a new transient technique for measuring TCR. Thin film resistors are heated by passing a constant electric current through them. At an arbitrarily set time, the resistor temperature is estimated from the known transient conduction solution for a uniform flux surface imbedded in a semi-infinite medium. Measurements of the resistance at that time, along with the resistance at the initial (usually room) temperature will now permit the calculation of TCR. The method was found to be very fast, repeatable, and in good agreement with the conventional technique.

Metastable Defects in a-Si:H from Bond-length Disorder

1996 ◽  
Vol 420 ◽  
Author(s):  
Qiming li ◽  
R. Biswas
Keyword(s):  
Bond Length ◽  
Defect Formation ◽  
Defect Density ◽  
Relaxation Times ◽  
Thermally Activated ◽  
Equilibrium Defects ◽  
Induced Defects ◽  
Hydrogenated Amorphous ◽  
Good Agreement

AbstractA model of metastable defect formation via H-rebonding in hydrogenated amorphous silicon is developed where the defect density and defect formation energy are controlled by the bond-length disorder of the material. Dangling bond defects are created by H motion from SiH bonds to weak Si-Si bonds. The model predicts formation energies for thermal and light-induced defects in good agreement with experiment. The relaxation of thermal equilibrium defects is stretched exponential, with stretch parameters varying approximately linearly with temperature and relaxation times that are thermally activated- in good agreement with experiment. The annealing of light-induced defect densities also shows relaxation behavior. The model accounts for barriers of ≈ 1.5 eV for H diffusion. The energetics of the H*2 complex will also be discussed. The rms bond-length deviation is a new parameter that controls the quality of the material.

scholarly journals A CRITICAL REVIEW OF THE PEIERLS MECHANISM

1967 ◽  
Vol 45 (2) ◽  
pp. 983-1016 ◽  
Author(s):  
Pierre Guyot ◽  
John E. Dorn
Keyword(s):  
Activation Volume ◽  
Prismatic Slip ◽  
Thermally Activated ◽  
Covalently Bonded ◽  
Higher Temperature ◽  
Fe Alloys ◽  
Increasing Temperature ◽  
Peierls Model ◽  
Volume Stress ◽  
Good Agreement

A thorough review is made of the application of the Peierls model to the macroscopic plastic deformation of ionic crystals, metals, alloys, and covalently bonded crystals. The effects of the shape of the Peierls hill, kink–kink energies, and the frequency terms on the stress–temperature and activation volume–stress relationships are extended and discussed. Theory is compared with experimental results, giving special emphasis to recent advances. Single-crystal data for [Formula: see text] {110} thermally activated slip in Ta and Mo at low temperatures agree well with the dictates of the Peierls mechanism. Deformation characteristics of polycrystalline Fe alloys containing either 2 wt.% Mn or 11 at.% Mo agree with expectations based on the Peierls mechanism only at temperatures below about 200 °K. At higher temperatures, the effective stress decreases more slowly and the activation volume increases more rapidly with increasing temperature than can be accounted for by the Peierls mechanism. Over this higher temperature range, however, the experimental data are in good agreement with Escaig's mechanism based on the recombination of dissociated screw dislocations. It is also shown that low-temperature [Formula: see text] {123} slip in AgMg, prismatic slip in Ag plus 33 at.% Al, and in Mg plus 6–12 at.% Li occurs by the Peierls mechanism.

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.

Mass spectrometric study of allyl radical, allyl bromide and 1,5-hexadiene interactions with oxides; Cobalt suboxide Co3O4

1979 ◽  
Vol 44 (7) ◽  
pp. 2009-2014 ◽  
Author(s):  
Jana Nováková ◽  
Zdeněk Dolejšek
Keyword(s):  
Room Temperature ◽  
Allyl Bromide ◽  
Catalytic Properties ◽  
Mass Spectrometric Study ◽  
Spectrometric Study ◽  
Flow Conditions ◽  
Allyl Radical ◽  
Knudsen Flow ◽  
Thermally Activated ◽  
Radical Interaction

Products of (a) allyl radical interaction with unheated Co3O4, (b) thermally activated 1,5-hexadiene or thermally activated allyl bromide with unheated Co3O4, (c) moderately heated Co3O4 with unheated 1,5-hexadiene or allyl bromide were studied under Knudsen flow conditions. Cobalt suboxide Co3O4, a typical catalyst of deep oxidations yielded acrolein in reaction with allyl radicals as early as at the room temperature of the catalyst. A similar acrolein formation was also observed in the allyl radical interaction with other oxides exhibiting different catalytic properties. It appears that acrolein is in general the primary product of the allyl radical interaction with the oxides. The results are discussed and compared with previous data obtained with MoO3.

Variable Temperature Measurement on Operating Pentacene-Based OTFT

2008 ◽  
Vol 1091 ◽  
Author(s):  
Hung-Keng Chen ◽  
Po-Tsun Liu ◽  
Ting-Chang Chang ◽  
S.-L. Shy
Keyword(s):  
Conduction Mechanism ◽  
Variable Temperature ◽  
Electrical Measurement ◽  
Isokinetic Temperature ◽  
Trap States ◽  
Band Tail ◽  
Thermally Activated ◽  
Multiple Trapping ◽  
Higher Temperature ◽  
Release Model

AbstractVariable temperature electrical measurement is well-established and used for determining the conduction mechanism in semiconductors. There is a Meyer¡VNeldel relationship between the activation energy and the prefactor with a Meyer¡VNeldel energy of 30.03 meV, which corresponds well with the isokinetic temperature of about 350 K. Therefore, the multiple trapping and release model is properly used to explain the thermally activated phenomenon. By the method, an exponential distribution of traps is assumed to be a better representation of trap states in band tail. Samples with higher temperature during measurement are observed to show better mobility, higher on-current and lower resistance, which agree well with the multiple trapping and release model proposed to explain the conduction mechanism in pentacene-based OTFTs.

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