Temperature Dependence Of Electron Transport Research Articles

Synthesis of reduced graphene oxide–Fe 3O 4 multifunctional freestanding membranes and their temperature dependent electronic transport properties

A simple and scalable method for the synthesis of reduced graphene oxide (RGO) based conductive and magnetic multifunctional films (membranes) is reported. A RGO–iron oxide (Fe 3O 4) freestanding film is fabricated using a versatile chemical route followed by vacuum infiltration. Temperature dependent electronic transport properties of the magnetic GO and RGO films were measured using a four probe technique from room temperature to 15 K. A conduction mechanism based on variable range hopping is suggested for explaining of the electronic conductivity variations. Possible applications of this multifunctional membrane are also discussed.

Deep donor state in InN: Temperature-dependent electron transport in the electron accumulation layers and its influence on Hall-effect measurements

Temperature-dependent electron transport properties in electron accumulation layers of InN are quantified by using the multilayer model. Room temperature electron densities in the electron accumulation layers are 5.83 × 1013 and 3.26 × 1014 cm−2 with Hall mobilities of 429 and 149 cm2/Vs in In- and N-polarity InN, respectively. A deep donor state with an activation energy of ∼80 meV, which is previously believed to exist in the InN bulk layer, is found to actually locate in the electron accumulation layers. The InN bulk layer shows single-shallow-donor behavior and its temperature-dependent electron mobility is in good agreement with the ensemble Monte Carlo simulation results.

Electrical, magnetic, and thermal properties of the single-grain Ag42In42Yb16icosahedral quasicrystal: Experiment and modeling

We have investigated the anisotropy of physical properties (the magnetic susceptibility, the electrical resistivity, the thermoelectric power, the Hall coefficient, and the thermal conductivity) of single-grain icosahedral $i$-Ag${}_{42}$In${}_{42}$Yb${}_{16}$ quasicrystal along the two-, three-, and fivefold symmetry directions of the crystallographic structure. The specific heat, being a scalar quantity, was determined as well. The symmetry analysis predicts that the tensorial physical properties reduce to scalars for the ideal icosahedral symmetry. The experiments have shown that the anisotropy of the electronic transport coefficients of $i$-Ag${}_{42}$In${}_{42}$Yb${}_{16}$ is either small enough to be considered within the range of the experimental uncertainty (the electrical resistivity and the thermal conductivity) or negligible (the Seebeck and the Hall coefficients). The anisotropy of the magnetization and magnetic susceptibility was also found small, originating from different Yb${}^{3+}$ magnetic fractions (of the order 10${}^{\ensuremath{-}3}$ of all Yb atoms) determined along the three symmetry directions. Our experimental results support the consideration that perfect icosahedral quasicrystals should be isotropic solids regarding their physical properties, unlike decagonal quasicrystals that are strongly anisotropic. Theoretical reproduction of the temperature-dependent electron transport coefficients of $i$-Ag${}_{42}$In${}_{42}$Yb${}_{16}$ by a spectral conductivity model was another aim of this paper.

Size- and Temperature-Dependent Charge Transport in PbSe Nanocrystal Thin Films

We report the size- and temperature-dependence of electron transport in thin films of PbSe nanocrystals. Upon increasing temperature over the range 28-200 K, the electron transport underwent a transition in mechanism from Efros-Shklovskii-variable-range-hopping (ES-VRH) to nearest-neighbor-hopping (NNH). The transition occurred at higher temperatures for films with smaller particles. The electron localization length, estimated from the ES-VRH model, was comparable to the nanocrystal size and scaled systematically with nanocrystal diameter. The activation energy from the NNH regime was also size-dependent, which is attributed both to size-dependent Coulomb effects and the size-distribution of nanocrystals.

Characterization of Nanoporous TiO2 Surface Defects by Temperature Dependent Electron Transport Studies on Dye Sensitized Solar Cells

ABSTRACTTemperature dependent, dark current-voltage characteristics (I-V-T) of dye sensitized solar cells (DSSCs) were used to study the TiO2 surface defects on photovoltaic performance. Three kinds of DSSCs were used for this study. (1) DSSC with no surface treatment, (2) DSSCs with Al2O3 and (3) HfO2 treatments. Activation energy of charge transport, obtained from the I-V-T of the three DSSCs, suggest that Al2O2 and HfO2 surface treatment on the nanoporous TiO2 effectively suppressed the electron capture by the surface states from the conduction band of TiO2 and the consecutive electron transfer to the electrolyte in which the TiO2 is permeated. The reference DSSC showed activation energy of 1.03eV while the DSSCs with Al2O3 and HfO2 surface treatment showed 1.27 and 1.31eV respectively. The higher activation energy, in case of HfO2 surface treatment, suggest that electronically active TiO2 surface states present near to the redox potential of the electrolyte was reduced and hence resulted in improved photovoltaic performance than Al2O3 treated DSSC and the reference DSSC.

Controlling Electron-Phonon Interactions in Graphene at Ultrahigh Carrier Densities

We report on the temperature dependent electron transport in graphene at different carrier densities n. Employing an electrolytic gate, we demonstrate that n can be adjusted up to 4 × 10(14) cm(-2) for both electrons and holes. The measured sample resistivity ρ increases linearly with temperature T in the high temperature limit, indicating that a quasiclassical phonon distribution is responsible for the electron scattering. As T decreases, the resistivity decreases more rapidly following ρ(T) ∼ T(4). This low temperature behavior can be described by a Bloch-Grüneisen model taking into account the quantum distribution of the two-dimensional acoustic phonons in graphene. We map out the density dependence of the characteristic temperature Θ(BG) defining the crossover between the two distinct regimes, and show that, for all n, ρ(T) scales as a universal function of the normalized temperature T/Θ(BG).

Temperature and Electric Field Dependent Electron Transport in Cationic and Anionic Conjugated Polyelectrolytes

The temperature and electric field dependence of electron mobilities in conjugated polyelectrolytes (CPEs) with structure variations of the ionic functionality and counterions were investigated to gain insight into the influence of these parameters on charge transport. Electron mobilities were determined by using electron-only diodes, and the temperature and electric field dependence were modeled with the Gaussian disorder model, the correlated Gaussian disorder model, and the polaronic correlated Gaussian disorder model for comparison. The transport characteristics were found to be dependent on the type of charge, as well as the choice of counterion, with the former baring a stronger influence on transport. Anionic CPEs are more susceptible to differences in the calculated energetic disorder than their cationic counterparts. Examination of cationic CPEs with different counterions show that, although the energetic disorder is similar, large differences in electron mobilities can be obtained. These observa...

Monte Carlo simulation of carrier dynamics in terahertz quantum cascade lasers

We employ a Monte Carlo method to investigate the carrier dynamics in the terahertz quantum cascade lasers with vertical and diagonal radiative transition designs. Electron-electron and electron-phonon scattering are included in the calculations and their effects on the temperature dependence of electron transport are evaluated. The simulation shows that the degradation of temperature performance is mainly due to the rapid electron relaxation from upper to lower laser levels, in which the electron-phonon interaction is the dominant scattering mechanism. The parasitic coupling between laser levels is weakened in the diagonal design, resulting in better device performance such as lower current density, higher operating temperature, and less hot electron effects. The calculations are in good agreement with experimental results.

Wave-Vector and Temperature-Dependent Electron Transport in a Magnetic Nanostructure Modulated by Bias

We theoretically investigate the wave-vector and temperature-dependent electron transport in a magnetic nanostructure modulated by an applied bias. The large spin-polarization can be achieved in such a device, and the degree of spin-polarization strongly depends on the transverse wave-vector and the temperature. These interesting properties may be helpful to spin-polarize electrons into semiconductors, and this device may be used as a spin filter.

Field, temperature and thickness dependent electron transport in 5,5′-(2,6-di-tert-butylanthracene-9,10-diyl)bis(2-p-tolyl-1,3,4-oxadiazole)

Charge transport in 5,5′-(2,6-di-tert-butylanthracene-9,10-diyl)bis(2-p-tolyl-1,3,4-oxadiazole) is investigated as a function of temperature and organic layer thickness. The thickness dependence of the current indicates towards the trap charge limited conduction (TCLC) with a field and temperature dependent mobility. The density of trap states has been found to be dependent on sample thickness. As the thickness has increased from 80 nm to 120 nm, trap energy has correspondingly increased from 78 meV to 130 meV. TCLC model with Poole Frenkel type field dependent mobility has been fitted into the data and has been found in excellent agreement. Temperature dependency of zero field mobility ( μ 0) and β has been estimated from the model.

Temperature-dependent electron and hole transport in disordered semiconducting polymers: Analysis of energetic disorder

We have used space-charge limited current measurements to study the mobility of holes and electrons in two fluorene-based copolymers for temperatures from 100 to 300 K. Interpreting the results using the standard analytical model produced an Arrhenius-type temperature dependence for a limited temperature range only and mobility was found to be apparently dependent on the thickness of the polymer film. To improve on this, we have interpreted our data using a numerical model that takes into account the effects of the carrier concentration and energetic disorder on transport. This accounted for the thickness dependence and gave a more consistent temperature dependence across the full range of temperatures, giving support to the ex-tended Gaussian disorder model for transport in disordered polymers. Furthermore, we find that the same model adequately describes both electron and hole transport without the need to explicitly include a distribution of electron traps. Room-temperature mobilities were found to be in the region of $4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}$ and $2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}\text{ }{\text{cm}}^{2}\text{ }{\text{V}}^{\ensuremath{-}1}\text{ }{\text{s}}^{\ensuremath{-}1}$ in the limit of zero field and zero carrier density with disorders of $110\ifmmode\pm\else\textpm\fi{}10$ and $100\ifmmode\pm\else\textpm\fi{}10\text{ }\text{meV}$ for polymers $\text{poly}{9,9\text{-dioctylfluorene-co-bis}[N,{N}^{\ensuremath{'}}\text{\ensuremath{-}}(4\ensuremath{-}\text{butylphenyl})]\text{bis}(N,{N}^{\ensuremath{'}}\text{-phenyl-}1,4\text{-phenylene})\text{diamine}}$ and poly(9,9-dioctylfluorene-co-benzothiadiazole), respectively.

Temperature Dependence of Oxygen Evolution in the Thylakoid Membrane: Thermal Transitions above 273 K in Steady-State Conditions

The temperature dependence of electron transport through photosystem II (PSII), measured as oxygen evolution, was investigated in thylakoid membranes irradiated with white light of 450 micromol of photons/(m(2) x s). The experiments were performed in steady-state conditions at temperatures between 273 and 303 K. The results show discontinuities, or thermal transitions, in the temperature-response curves of oxygen evolution. The experimental data was examined with the Marcus theory of electron transfer modified to take into account the oxygen evolution discontinuities. For this purpose, the Gibbs free energy of activation of the electron transfer reaction, DeltaG(o), is replaced in the classical Marcus equation with the expression DeltaH(o) - TDeltaS(o), where H(o) and DeltaS(o) are respectively the enthalpy and entropy of activation, and T is the temperature in kelvin. The result of the derivation is a summation of j Gaussian functions, or states, OE = 69 250 summation operator(j){(V(DA)(4)/lambdaT)(1/2) exp[-(T(max) - T)(2)/2Tsigma(o)(2)]}(j) (eq 1), where OE is expressed in micromol oxygen evolution.(mg Chl x h)(-1), and V(DA) is the electronic coupling matrix element between electron donor (D) and acceptor (A) wave functions, lambda the reorganization free energy, k(B) the Boltzmann constant, T(max) = (DeltaH(o) + lambda)/DeltaS(o), sigma(o) = (2k(B)lambda/DeltaS(o2))(1/2), and sigma = T(1/2)sigma(o) is the standard deviation of the Gaussian band. The mathematical simulations revealed the presence of six thermal transitions, or Gaussian bands with maxima at 275.3, 281.2, 286.4, 291.4, 297.1, and 302.4 K. The resolution of the Gaussian bands is about 0.55 owing to multiple band superpositions. The theoretical analyses showed that (i) the oxygen evolution in PSII is essentially dependent on V(DA)(2)/(lambdaT)(1/2) in the pre-exponential term of the modified Marcus equation (eq 1), and (ii) the reorganization energy, lambda, decreases exponentially with increasing temperature, and is also dependent on the electron donor-acceptor distance. It is concluded that the temperature dependence of the large enhancement of oxygen evolution observed in this work originates, at least partly, in heat-induced structural rearrangements in the photosystem II reaction center.

Temperature-dependent current–voltage characteristics of the Au/n-InP diodes with inhomogeneous Schottky barrier height

Abstract The current–voltage (I–V) characteristics of Au/n-InP Schottky contacts have been measured in the temperature range of 70–300 K by steps of 10 K. Our data of the Au/n-InP Schottky contact strongly suggest that the temperature-dependent electron transport at the metal–semiconductor interface is significantly affected by the barrier inhomogeneity. The distribution of local effective SBHs has been modeled by a summation of existence of double Gaussian barrier heights which represents the high- and low-barrier of the full distribution in 170–300 and 70–170 K ranges.

Temperature-dependent transport and spin accumulation in a quantum wire with Rashba spin-orbit interaction

We study the theory of temperature-dependent electron transport, spin polarization, and spin accumulation in a Rashba spin-orbit interaction (RSOI) quantum wire connected nonadiabatically to two normal conductor electrode leads. The influence of both the wire-lead connection and the RSOI on the electron transport is treated analytically by means of a scattering matrix technique and by using an effective free-electron approximation. Through analytical analysis and numerical examples, we demonstrate a simple way to design a sensitive spin-transfer switch that operates without applying any external magnetic fields or attaching ferromagnetic contacts. We also demonstrate that the antisymmetry of the spin accumulation can be destroyed slightly by the coupling between the leads and the wire. Moreover, temperature can weaken the polarization and smear out the oscillations in the spin accumulation.

Temperature-Dependent Electronic Transport through Alkyl Chain Monolayers: Evidence for a Molecular Signature

Temperature-dependent transport measurements through alkyl chain monolayers that are directly chemically bound to Si, show that the currents decrease as the temperature increases. We relate this te...

Spatial variations in biomarkers of Mytilus edulis mussels at four polluted regions spanning the Northern Hemisphere

Economic and social developments have taken place at the expense of the health of the environment, both locally and on a global scale. In an attempt to better understand the large-scale effects of pollution and other stressors like climate change on the health status of Mytilus edulis, mussels were collected during the first two weeks of June 2005 at three sites (one pristine and two affected by pollution) located in each of the regions of the Canadian West Coast, the St. Lawrence estuary, the Atlantic East Coast and the northwestern coast of France, covering a total distance of some 11 000 km. The mussels were analyzed for morphologic integrity (condition factor), gametogenic activity (gonado-somatic and gonad maturation index, vitellogenin(Vtg)-like proteins), energy status (temperature-dependent mitochondrial electron transport activity and gonad lipid stores), defense mechanisms (glutathione S-transferase, metallothioneins, cytochrome P4503A activity and xanthine oxidoreductase-XOR), and tissue damage (lipid peroxidation-LPO and DNA strand breaks). The results showed that data from the reference sites in each region were usually not normally distributed, with discriminant factors reaching the number of regions (i.e. four), except for the biomarkers gonadal lipids, XOR and LPO in digestive gland. The integrated responses of the biomarkers revealed that biomarkers of stress were significantly more pronounced in mussels from the Seine estuary, suggesting that the impacts of pollution are more generalized in this area. Mussels from the Seine estuary and the Atlantic East Coast (Halifax Harbor) responded more strongly for Vtg-like proteins, but was not related to gonad maturation and gonado-somatic indexes, suggesting the presence of environmental estrogens. Moreover, these mussels displayed reduced DNA repair activity and increased LPO. Factorial analyses revealed that energy status, cytochrome P4503A activity and Vtg-like proteins were the most important biomarkers. Adaptation to warmer temperatures was reflected at the energy status levels, mussels from both the polluted and warmer sites displaying increased ratios of mitochondrial activity to lipid stores. Regional observations of biomarkers of energy status, gametogenesis and pollutant-related effects were influenced by nutrition, oxygen availability (eutrophication), and thermal history.

Electron-Phonon Interaction and Localization of Surface-State Carriers in a Metallic Monolayer

Temperature-dependent electron transport in a metallic surface superstructure, Si(111)sqrt[3] x sqrt[3]-Ag, was studied by a micro-four-point probe method and photoemission spectroscopy. The surface-state conductivity exhibits a sharp transition from metallic conduction to strong localization at approximately 150 K. The metallic regime is due to electron-phonon interaction while the localization seemingly originates from coherency of electron waves. Random potential variations, caused by Friedel oscillations of surface electrons around defects, likely induce strong carrier localization.

Relationships between intertidal clam population and health status of the soft-shell clam Mya arenaria in the St. Lawrence Estuary and Saguenay Fjord (Québec, Canada)

The purpose of this study was to examine the impacts of anthropogenic activity on the health status of intertidal clam populations of the Saguenay Fjord and the St. Lawrence Estuary (Québec, Canada). Clams were collected during low tide at sites subject to direct contamination and at sites far from human activity. Clams were analyzed for tributyltin and dibutyltin total levels and toxic stress (glutathione S-transferase, gonadal lipid peroxidation and DNA strand breaks), immunocompetence (phagocytic activity, hemocyte count and viability), reproduction (gonado-somatic index, gamete maturation, and vitellogenin-like proteins), energy status (temperature-dependent mitochondrial electron transport, and gonad lipids), and individual status (age, condition factor, and growth index). These responses were compared against population characteristics such as live clam density, number of empty shells, and sex ratio. The results show that clam density decreased with distance from the estuary (high salinity level) to upstream of the fjord (low salinity). There was no clear relationship between the number of empty shells and distance or site quality. Clam density values corrected against distance were significantly correlated with hemocyte viability, phagocytic activity, mitochondrial electron transport (MET), DNA damage in gonad, and temperature-dependent mitochondrial electron transport activity. A canonical analysis of the various groups of biomarkers revealed that population metrics were more strongly related with immunocompetence, followed by energy status and temperature-dependent mitochondrial electron transport activity. However, toxic stress biomarkers were strongly associated with energy status and reproduction. This was further confirmed by non-linear modeling using adaptive artificial neural networks (genetic selection and back propagation learning paradigms), where the following parameters were able to predict population parameters with <20% error: gonad maturation and somatic index, MET (at 4 °C), gonad LPO, DNA damage, and phagocytic capacity. Intertidal clam populations were influenced by a distance gradient effect (salinity), where immunocompetence, in addition to energy status, was the strongest physiological parameter related to clam population metrics.

Temperature dependent electron transport in graphene

We have investigated the electron transport in graphene at different carrier densities. Single layer graphene was fabricated into Hall bar shaped devices by mechanical extraction onto a silicon oxide/silicon substrate followed by standard microfabrication techniques. From magnetoresistance and Hall measurements, we measure the carrier density and mobility at different gate voltages. Different temperature dependent resistivity behaviors are found in samples with high and low mobilities.

Implication of site quality on mitochondrial electron transport activity and its interaction with temperature in feral Mya arenaria clams from the Saguenay Fjord

The advent of global warming has given rise to questions about the impact of temperature/pollution interactions on the integrity of certain benthic organisms like bivalves. This interaction was examined in intertidal Mya arenaria clams from the Saguenay Fjord using the concepts of cellular energy allocation and temperature-dependent mitochondrial electron transport (MET T) activity. Clams were collected at low tide from six sites (two clean, four polluted) for determinations of condition factor (weight/shell length), growth index (age-to-length ratio), gonadal lipids and maturation index, gonad MET at various habitat temperatures, MET T, gill xanthine oxidase and gill DNA damage. Condition factor was generally lower at the four polluted sites, with growth index being severely affected at two of them. Gonadal maturation was also significantly dampened at two of the four pollution-impacted sites. Gill xanthine oxidase (purine bases salvage pathway) and DNA strand breaks were significantly increased at most of the polluted sites, confirming pollution-mediated damage in clams. Moreover, MET at 20 °C, MET T and gonad lipids were significantly induced at the polluted sites. Clam condition factor was negatively correlated with most of the biomarkers for cellular energy allocation (gonadal lipids, MET and MET T), but not with gonadal maturation. DNA damage and xanthine oxidase were positively correlated with MET at 20 °C and MET T. This is the first report of electron transport in mitochondria being more sensitive to incremental temperature increases in clams under pollution stress. The gradual warming of clam habitats would likely worsen the impacts of pollution in feral clam populations.