Electrical, Optical, Structural, and Analytical Properties of Very Pure GaN

2002 ◽  
Vol 743 ◽  
Author(s):  
D. C. Look ◽  
J. R. Sizelove ◽  
J. Jasinski ◽  
Z. Liliental-Weber ◽  
K. Saarinen ◽  
...  
Keyword(s):  
Activation Energy ◽  
Hall Effect ◽  
Excited States ◽  
Vacancy Concentration ◽  
Strong Line ◽  
Threading Dislocation ◽  
Charge Balance ◽  
Acceptor Concentration ◽  
Flat Surfaces ◽  
The Difference

ABSTRACTPresent hydride vapor phase epitaxial growth of GaN on Al2O3 can produce material of very high quality, especially in regions of the crystal far from the substrate/epilayer interface. In the present study, we characterize a 248-μm-thick epilayer, which had been separated from its Al2O3 substrate and etched on top and bottom to produce flat surfaces. Temperature-dependent Hall-effect data have been fitted to give the following parameters: mobility μ(300) = 1320 cm2/V-s; μ(peak) = 12,000 cm2/V-s; carrier concentration n(300) = 6.27 × 1015 cm−3; donor concentration ND = 7.8 × 1015 cm−3; acceptor concentration NA = 1.3 × 1015 cm−3; and effective donor activation energy ED = 28.1 meV. These mobilities are the highest ever reported in GaN, and the acceptor concentration, the lowest. Positron annihilation measurements give a Ga vacancy concentration very close to NA, showing that the dominant acceptors are likely native defects. Secondary ion mass spectroscopic measurements show that ND is probably composed of the common donors O and Si, with [O] > [S1]. Transmission electron microscopy measurements yield threading dislocation densities of about 1 × 107 cm−2 on the bottom (N) face, and < 5 × 105 cm−2 on the top (Ga) face. Photoluminescence (PL) spectra show a strong donor-bound exciton (D°X) line at 3.47225 eV, and a weaker one at 3.47305 eV; each has a linewidth of about 0.4 meV. In the two-electron satellite region, a strong line appears at 3.44686 eV, and a weaker one at 3.44792 eV. If the two strong lines represent the same donor, then ED,n=1 – ED,n=2 = 25.4 meV for that donor, and the ground-state activation energy (EC – ED,n=1) is (4/3)25.4 = 33.9 meV in a hydrogenic model, and 32.7 meV in a somewhat modified model. The measured Hall-effect donor energy, 28.1 meV, is smaller than the PL donor energy, as is nearly always found in semiconductors. We show that the difference in the Hall and PL donor energies can be explained by donor-band conduction via overlapping donor excited states, and the effects of non-overlapping excited states which should be included in the n vs. T data analysis (charge balance equation).

Effect of Cu doping on the electrical Properties of ZnTe by Vacuum Thermal Evaporation

2018 ◽  
Vol 31 (3) ◽  
pp. 20
Author(s):  
Sarmad M. M. Ali ◽  
Alia A.A. Shehab ◽  
Samir A. Maki
Keyword(s):  
Activation Energy ◽  
Electrical Conductivity ◽  
Hall Effect ◽  
Carrier Concentration ◽  
Hall Mobility ◽  
Cu Doping ◽  
Before And After ◽  
Hall Effect Measurements ◽  
Evaporation Technique ◽  
P Type

In this study, the ZnTe thin films were deposited on a glass substrate at a thickness of 400nm using vacuum evaporation technique (2×10-5mbar) at RT. Electrical conductivity and Hall effect measurements have been investigated as a function of variation of the doping ratios (3,5,7%) of the Cu element on the thin ZnTe films. The temperature range of (25-200°C) is to record the electrical conductivity values. The results of the films have two types of transport mechanisms of free carriers with two values of activation energy (Ea1, Ea2), expect 3% Cu. The activation energy (Ea1) increased from 29meV to 157meV before and after doping (Cu at 5%) respectively. The results of Hall effect measurements of ZnTe , ZnTe:Cu films show that all films were (p-type), the carrier concentration (1.1×1020 m-3) , Hall mobility (0.464m2/V.s) for pure ZnTe film, increases the carrier concentration (6.3×1021m-3) Hall mobility (2m2/V.s) for doping (Cu at 3%) film, but  decreases by increasing Cu concentration.

Microscopic Interpretation of Arrhenius Parameters

2018 ◽  
Author(s):  
Niels Engholm Henriksen ◽  
Flemming Yssing Hansen
Keyword(s):  
Activation Energy ◽  
Transition State ◽  
Transition State Theory ◽  
Average Energy ◽  
Zero Point ◽  
State Theory ◽  
Exponential Factor ◽  
Quantum Tunnelling ◽  
Microscopic Interpretation ◽  
The Difference

This chapter reviews the microscopic interpretation of the pre-exponential factor and the activation energy in rate constant expressions of the Arrhenius form. The pre-exponential factor of apparent unimolecular reactions is, roughly, expected to be of the order of a vibrational frequency, whereas the pre-exponential factor of bimolecular reactions, roughly, is related to the number of collisions per unit time and per unit volume. The activation energy of an elementary reaction can be interpreted as the average energy of the molecules that react minus the average energy of the reactants. Specializing to conventional transition-state theory, the activation energy is related to the classical barrier height of the potential energy surface plus the difference in zero-point energies and average internal energies between the activated complex and the reactants. When quantum tunnelling is included in transition-state theory, the activation energy is reduced, compared to the interpretation given in conventional transition-state theory.

Second Activation Energy in the Fractional Quantum Hall Effect

1987 ◽  
Vol 56 (9) ◽  
pp. 3005-3008 ◽  
Author(s):  
Junichi Wakabayashi ◽  
Satoru Sudou ◽  
Shinji Kawaji ◽  
Kazuhiko Hirakawa ◽  
Hiroyuki Sakaki
Keyword(s):  
Activation Energy ◽  
Hall Effect ◽  
Quantum Hall Effect ◽  
Quantum Hall ◽  
Fractional Quantum Hall Effect ◽  
Fractional Quantum ◽  
Fractional Quantum Hall

Thermogravimetric Analysis of Glucose-Based and Fructose-Based Carbohydrates

2013 ◽  
Vol 805-806 ◽  
pp. 265-268 ◽  
Author(s):  
Fang Ming Cui ◽  
Xiao Yuan Zhang ◽  
Li Min Shang
Keyword(s):  
Activation Energy ◽  
Thermogravimetric Analysis ◽  
Kinetic Parameters ◽  
Degree Of Polymerization ◽  
Experiment Data ◽  
Pyrolysis Characteristics ◽  
The Difference ◽  
Kinetic Calculations

Thermogravimetric analysis (TGA) was employed to study the pyrolysis characteristics of four glucose-based and three fructose-based carbohydrates. Kinetic parameters were calculated based on the experiment data. The results indicated that the starting and maximal pyrolysis temperatures of the glucose-based carbohydrates were increased steadily as the rising of their degree of polymerization (DP). The fructose-based carbohydrates exhibited similar pyrolysis behaviors as the glucose-based carbohydrates, but the difference was smaller. Kinetic calculations revealed that the activation energy values of the glucose-based carbohydrates were higher than those of the fructose-based carbohydrates, indicating the glucose-based carbohydrates were more difficult to decompose than the fructose-based carbohydrates.

Relevance of the Entropy Factor in Stereoselectivity Control of Asymmetric Photoreactions

Synlett ◽  
2020 ◽  
Vol 31 (13) ◽  
pp. 1259-1267
Author(s):  
Tadashi Mori
Keyword(s):  
Activation Energy ◽  
Excited States ◽  
Weak Interactions ◽  
Supramolecular Interactions ◽  
Thermal Reactions ◽  
Thermodynamics And Kinetics ◽  
Control Concept ◽  
Entropy Factor ◽  
Fine Tune

Entropy as well as enthalpy factors play substantial roles in various chemical phenomena such as equilibrium and reactions. However, the entropy factors are frequently underestimated in most instances, particularly in synthetic chemistry. In reality, the entropy factor can be in competition with the enthalpy factor or can even be decisive in determining the overall free or activation energy change upon molecular interaction and chemical transformation, particularly where weak interactions in ground and/or excited states are significant. In this account, we overview the importance of the entropy factor in various chemical phenomena in both thermodynamics and kinetics and in the ground and excited states. It is immediately apparent that many diastereo- and enantioselective photoreactions are entropy-controlled. Recent advances on the entropy-control concept in asymmetric photoreactions are further discussed. Understanding the entropy-control concept will pave the way to improve, fine-tune, and even invert the chemo- and stereoselectivity of relevant chemical phenomena.1 Introduction2 Role of Entropy in Supramolecular Interactions3 Selected Examples of Entropy-Driven Thermal Reactions4 Classical Examples of Entropy Control in Photoreactions5 Entropy-Driven Asymmetric Photoreactions6 Advances in Entropy Control7 Perspective

Hydrogen Incorporation in A-Si:H: Temperature and Doping Type Dependence

1990 ◽  
Vol 192 ◽  
Author(s):  
M.J.M. Pruppers ◽  
K.M.H. Maessen ◽  
F.H.P.M. Habraken ◽  
J. Bezemer ◽  
W.F. Van Der Weg
Keyword(s):  
Activation Energy ◽  
Glow Discharge ◽  
Gas Phase ◽  
Hydrogen Concentration ◽  
Hydrogen Content ◽  
Hydrogen Incorporation ◽  
Undoped Material ◽  
Measured Activation Energy ◽  
Measured Activation ◽  
The Difference

ABSTRACTPhosphorus, boron and compensation doped hydrogenated amorphous silicon films were deposited in a glow discharge at different substrate temperatures in the range 50–330°C. Gas phase doping levels were 1%. At the lower temperatures the hydrogen concentration in the B doped and compensated doped films is larger than in the P and undoped films. For higher deposition temperatures the H concentration of the B doped films appeared to be smaller than in the other materials. The difference in hydrogen content of the doped and undoped material, deposited at various temperatures, is considered as a function of the measured activation energy for conduction in these films. This difference varies in much the same way with the activation energy as the hydrogen content in films deposited at one substrate temperature, but with varying gas phase dopant levels. This represents strong evidence that, apart from the deposition temperature, the hydrogen concentration in glow discharge a-Si:H is determined by the position of the Fermi level.

Energetics and structural effects in the fragmentation of protonated esters in the gas phase

1981 ◽  
Vol 59 (14) ◽  
pp. 2133-2145 ◽  
Author(s):  
Jan A. Herman ◽  
Alex. G. Harrison
Keyword(s):  
Activation Energy ◽  
Gas Phase ◽  
Methyl Formate ◽  
Carbonyl Oxygen ◽  
Original Structure ◽  
Proton Affinities ◽  
Acetate Methyl ◽  
Ether Oxygen ◽  
The Difference ◽  
Tertiary Alkyl

A series of formate (methyl through butyl) and acetate (methyl through pentyl) esters have been protonated in the gas phase by the Brønsted acids H3+, N2H+, CO2H+, N2OH+, and HCO+. Carbonyl oxygen protonation is 87–97 kcal mol−1 exothermic for H3+ and 47–57 kcal mol−1 exothermic for the weakest acid HCO+, permitting a study of the effect of protonation exothermicity on the decomposition modes of the protonated esters. With the exception of protonated methyl formate, three decomposition modes, (a) to (c) are observed.[Formula: see text]Reaction (a) is unimportant for formates; for acetates it is the sole decomposition channel for the methyl ester, but is less important for higher acetates. The dependence of the relative importance of this reaction mode on the protonation exothermicity indicates an activation energy considerably in excess of ΔH0, presumably because the reaction involves a symmetry-forbidden 1,3-H shift for the carbonyl protonated ester. For the higher acetates where the difference in the proton affinities of the carbonyl and ether oxygens is less, acyl ion formation results, in part, from protonation at the ether oxygen. For protonated methyl formate the major fragmentation reaction yields CH3OH2+ + CO; this reaction also appears to have an activation energy considerably in excess of the ΔH0. For the remaining esters either reaction (b) or (c) is the major decomposition mode. The competition between these two channels depends strongly on the protonation exothermicity and the relative activation energies. From the reaction competition we conclude that 1,2-H shifts occur in the case of primary alkyl esters yielding more stable secondary or tertiary alkyl ions. This rearrangement appears to occur after the excess energy has been partitioned between the alkyl ion and the neutral acid since the extent of further fragmentation of the alkyl ion reflects the original structure of the alkyl group.

scholarly journals Designing bioinspired surfaces for water collection from fog

2018 ◽  
Vol 377 (2138) ◽  
pp. 20180269 ◽  
Author(s):  
Dev Gurera ◽  
Bharat Bhushan
Keyword(s):  
Flat Surface ◽  
Unit Area ◽  
Water Repellency ◽  
Vertical Axis ◽  
Collection Rate ◽  
Flat Surfaces ◽  
Single Cone ◽  
Water Collection ◽  
The Difference ◽  
Conical Surfaces

A systematic study is presented on various water collectors, bioinspired by desert beetles, desert grass and cacti. Three water collecting mechanisms including heterogeneous wettability, grooved surfaces, and Laplace pressure gradient, were investigated on flat, cylindrical, conical surfaces, and conical array. It is found that higher water repellency in flat surfaces results in higher water collection rate and inclination angle (with respect to the vertical axis) has little effect. Surfaces with heterogeneous wettability have higher water collection rate than surfaces with homogeneous wettability. Both cylindrical and conical surfaces resulted in comparable water collection rate. However, only the cone transported the water droplets to its base. Heterogeneity, higher inclination and grooves increased the water collection rate. A cone has a higher collection rate per unit area than a flat surface with the same wettability. An array of cones has higher collection rate per unit area than a single cone, because droplets in a conical array coalesce, leading to higher frequency of droplets falling. Adding heterogeneity further increases the difference. Based on the findings, scaled-up designs of beetle-, grass- and cactus-inspired surfaces and nets are presented. This article is part of the theme issue ‘Bioinspired materials and surfaces for green science and technology’.

scholarly journals Isochronal Phase Transformation in Bimodal Ti-55531

Metals ◽  
2019 ◽  
Vol 9 (7) ◽  
pp. 790 ◽  
Author(s):  
Fuwen Chen ◽  
Guanglong Xu ◽  
Kechao Zhou ◽  
Hui Chang
Keyword(s):  
Mechanical Properties ◽  
Heat Treatment ◽  
Activation Energy ◽  
Phase Transformation ◽  
Microstructure Evolution ◽  
Continuous Heating ◽  
Interface Curvature ◽  
The Difference ◽  
Treatment Procedures ◽  
And Control

Bimodal microstructures where globular α and acicular α phases are embedded in the β matrix are commonly used in industry-relevant Ti-55531. To optimize the performance of Ti-55531 through heat treatment, it is crucial to understand and control the phase transformation in the as-received bimodal Ti-55531 as well as its microstructure evolution. In this work, the isochronal phase transformations and microstructure evolution in the bimodal Ti-55531 during the continuous heating were systematically studied by combining dilatometry, XRD phase analyses, and SEM observation. The β → α transformation occurred at 678 K only with the acicular α. When the temperature was higher than 788 K, α → β transformation took place in two separate stages (i.e., αacicular → β and αglobular → β transformation). The dissolution of αglobular occurred after the dissolution of αacicular was completed. Due to the difference in the chemical composition and interface curvature between αacicular and αglobular, the average activation energy for αacicular → β transformation was lower than that for the αglobular → β transformation. The isochronal phase transformation and microstructure evolution during continuous heating in the present work could be used to optimize heat treatment procedures for desired mechanical properties.

scholarly journals Exercise tolerance during flat over-ground intermittent running: modelling the expenditure and reconstitution kinetics of work done above critical power

2019 ◽  
Vol 120 (1) ◽  
pp. 219-230
Author(s):  
Christian Vassallo ◽  
Adrian Gray ◽  
Cloe Cummins ◽  
Aron Murphy ◽  
Mark Waldron
Keyword(s):  
Critical Power ◽  
Specific Model ◽  
Threshold Velocity ◽  
Positioning Systems ◽  
Flat Surfaces ◽  
Constant Work Rate ◽  
The Difference ◽  
Uptake Velocity ◽  
Work Done ◽  
W Prime

Abstract Purpose We compared a new locomotor-specific model to track the expenditure and reconstitution of work done above critical power (W´) and balance of W´ (W´BAL) by modelling flat over-ground power during exhaustive intermittent running. Method Nine male participants completed a ramp test, 3-min all-out test and the 30–15 intermittent fitness test (30–15 IFT), and performed a severe-intensity constant work-rate trial (SCWR) at the maximum oxygen uptake velocity (vV̇O2max). Four intermittent trials followed: 60-s at vV̇O2max + 50% Δ1 (Δ1 = vV̇O2max − critical velocity [VCrit]) interspersed by 30-s in light (SL; 40% vV̇O2max), moderate (SM; 90% gas-exchange threshold velocity [VGET]), heavy (SH; VGET + 50% Δ2 [Δ2 = VCrit − VGET]), or severe (SS; vV̇O2max − 50% Δ1) domains. Data from Global Positioning Systems were derived to model over-ground power. The difference between critical and recovery power (DCP), time constant for reconstitution of W´ ($$\tau_{{W^{\prime}}}$$τW′), time to limit of tolerance (TLIM), and W´BAL from the integral (W´BALint), differential (W´BALdiff), and locomotor-specific (OG-W´BAL) methods were compared. Results The relationship between $$\tau_{{W^{\prime}}}$$τW′ and DCP was exponential (r2 = 0.52). The $$\tau_{{W^{{\prime}}}}$$τW′ for SL, SM, and SH trials were 119 ± 32-s, 190 ± 45-s, and 336 ± 77-s, respectively. Actual TLIM in the 30–15 IFT (968 ± 117-s) compared closely to TLIM predicted by OG-W´BAL (929 ± 94-s, P > 0.100) and W´BALdiff (938 ± 84-s, P > 0.100) but not to W´BALint (848 ± 91-s, P = 0.001). Conclusion The OG-W´BAL accurately tracked W´ kinetics during intermittent running to exhaustion on flat surfaces.

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