Showing papers on "Variable-range hopping published in 2017"
TL;DR: The structural, optical, magnetic, and electrical properties of sol-gel-derived Ti1−xFexO2 (0.00 ≤ x ≤ 0.05) nanoparticles were investigated in this paper.
Abstract: The structural, optical, magnetic, and electrical properties of sol–gel-derived Ti1−xFexO2 (0.00 ≤ x ≤ 0.05) nanoparticles were investigated. Rietveld refinement of the X-ray diffraction data and TEM measurements were carried out to analyze the crystalline structure and quality of all the samples. Raman spectroscopy revealed a decrease in intensity and broadening of the characteristics peaks of Fe-doped TiO2 with respect to those of the pristine sample, which signifies a structural distortion of the lattices. FT-IR, UV-vis, and PL spectroscopy were used to investigate the optical properties. Magnetic measurements showed a weak ferromagnetism at room temperature in both the pristine and Fe-doped TiO2 (x = 0, 0.02, and 0.05) nanoparticles. Temperature-dependent resistivity measurements showed the semiconducting nature of the samples and revealed that the thermally activated conduction (Arrhenius) mechanism is valid in the high-temperature region, whereas Mott variable range hopping (VRH) mechanism is valid in the low-temperature region. Dielectric properties of the samples were studied as a function of temperature in the frequency range of 1 kHz to 1 MHz.
68 citations
TL;DR: In this paper, the thermoelectric properties of CuCr2-xSbxS4 (0.22 ≤ x ≤ 0.5) were reported for the first time.
Abstract: We report for the first time the thermoelectric properties of CuCr2–xSbxS4 (0.22 ≤ x ≤ 0.5). Although CuCr2S4 has been reported to be a metallic compound, addition of Sb shifts the material toward the semiconductor side. This is confirmed by band structure calculations of CuCr2–xSbxS4 (x = 0, 0.25, 0.5) models. Increasing Sb content enhances the power factor. However, beyond x = 0.3, further Sb addition lowers the electrical conductivity and power factor. A very interesting point is the simultaneous increase of the Seebeck coefficient as well as the electrical conductivity with increasing temperature, which acts like a variable range hopping (VRH) compounds but possesses much better properties than those having VRH. Samples were annealed for 48 h prior to thermoelectric properties measurements to have a reliable dimensionless figure of merit (ZT). An attractive ZT of 0.43 is obtained at ∼650 °C. The attractive thermoelectric properties we discovered by driving a metal compound into a semiconductor make th...
61 citations
TL;DR: The perovskite La2CrMnO6 has a Griffith-like phase with the occurrence of ferromagnetic short range correlations above TC and the system ultimately turns into paramagnetic at the Griffiths temperature 180 K as discussed by the authors.
Abstract: DC and AC magnetic measurements indicate the presence of multiple magnetic transitions arising from the competing magnetic interaction between Cr and Mn in the perovskite La2CrMnO6. Ferromagnetic and spin glass transitions are observed in La2CrMnO6. The material also has a Griffith-like phase with the occurrence of ferromagnetic short range correlations above TC. The system ultimately turns into paramagnetic at the Griffiths temperature 180 K. A combination of variable range hopping, and the nearest neighbor small polaron hopping governs the conduction mechanism in the material. A negative magnetoresistance of 22% at 105 K is observed for the material at 90 kOe which increases to 29% near 110 K and reduces gradually to zero on further increase in the temperature.
44 citations
TL;DR: In this paper, a three-dimensional variable range hopping model is adopted to analyze the abnormal temperature dependency of electrical conductivity and Seebeck coefficient in the basal plane of black phosphorus (BP) nanoribbons.
Abstract: Black phosphorus (BP) is a layered semiconductor with a high mobility of up to ∼1000 cm2 V−1 s−1 and a narrow bandgap of ∼0.3 eV, and shows potential applications in thermoelectrics. In stark contrast to most other layered materials, electrical and thermoelectric properties in the basal plane of BP are highly anisotropic. To elucidate the mechanism for such anisotropy, we fabricated BP nanoribbons (∼100 nm thick) along the armchair and zigzag directions, and measured the transport properties. It is found that both the electrical conductivity and Seebeck coefficient increase with temperature, a behavior contradictory to that of traditional semiconductors. The three-dimensional variable range hopping model is adopted to analyze this abnormal temperature dependency of electrical conductivity and Seebeck coefficient. The hopping transport of the BP nanoribbons, attributed to high density of trap states in the samples, provides a fundamental understanding of the anisotropic BP for potential thermoelectric appl...
39 citations
TL;DR: The structural, magnetic, electrical and dielectric properties of an Ir-based double perovskite compound, La2CoIrO6, have been investigated and it is shown that a clear magnetodielectric coupling effect exists in La2 coirO6 at low temperatures.
Abstract: The structural, magnetic, electrical and dielectric properties of an Ir-based double perovskite compound, La2CoIrO6, have been investigated. The sample undergoes a paramagnetic-ferromagnetic transition at TC, followed by a reentrant spin-glass transition at lower temperatures. The reentrant spin glass state in La2CoIrO6 is associated with the competitions of the antiferromagnetic coupling between Ir4+ and Co2+ ions and the ferromagnetic clusters. La2CoIrO6 shows a semiconducting transport behavior in the temperature range 65 to 360 K and the transport behavior can be well described by the three-dimensional Mott variable range hopping conduction mechanism. Moreover, a strong frequency dependence of dielectric constant behavior for La2CoIrO6 is observed and the dielectric relaxation can be ascribed to the electron hopping between different transition metal ions. In addition, the isothermal magnetic field dependent dielectric constant measurements show that a clear magnetodielectric coupling effect exists in La2CoIrO6 at low temperatures.
35 citations
TL;DR: In this article, the effect of the sputtering atmosphere on the electron transport in nanocomposites is explained by reduction of concentration of the defects in matrix when oxygen is added to the ion-beam sputtering chamber.
32 citations
TL;DR: A generalized non-Hermitian equation of motion to go beyond standard trajectory surface hopping dynamics and applications to model Hamiltonians demonstrate improved performance over the standard FSSH approach, through comparison to exact quantum results.
Abstract: We present a generalized non-Hermitian equation of motion (nH-EOM) to go beyond standard trajectory surface hopping dynamics. The derivation is based on the Born-Huang expansion of the total wave function and the polar representation of the nuclear factor. The nH-EOM contains two additional terms, a skew symmetry term iΓ with dissipation operator Γ to account for decoherence, and a kinetic-energy renormalization term to account for phase shifts, without destroying the invariance to the choice of representation. Numerically, the nH-EOM can still be solved efficiently using a semiclassical approximation in the framework of Tully's fewest-switches surface hopping (FSSH) algorithm. Applications to model Hamiltonians demonstrate improved performance over the standard FSSH approach, through comparison to exact quantum results.
32 citations
TL;DR: Zhang et al. as mentioned in this paper showed that the layered MoSe2 grows in a scalable manner on the substrate and reveals characteristics of a stoichiometric 2H-phase with polycrystalline features.
Abstract: Molecular beam epitaxy technique has been used to deposit a single layer and a bilayer of MoSe2 on sapphire. Extensive characterizations including in-situ and ex-situ measurements show that the layered MoSe2 grows in a scalable manner on the substrate and reveals characteristics of a stoichiometric 2H-phase. The layered MoSe2 exhibits polycrystalline features with domains separated by defects and boundaries. Temperature and magnetic field dependent resistivity measurements unveil a carrier hopping character described within two-dimensional variable range hopping mechanism. Moreover, a negative magnetoresistance was observed, stressing a fascinating feature of the charge transport under the application of a magnetic field in the layered MoSe2 system. This negative magnetoresistance observed at millimeter-scale is similar to that observed recently at room temperature in WS2 flakes at a micrometer scale [Zhang et al., Appl. Phys. Lett. 108, 153114 (2016)]. This scalability highlights the fact that the underl...
29 citations
TL;DR: In this article, the effect of sintering temperature, pressure and atmosphere on the thermoelectric power factor of STN ceramics were investigated in order to optimize the SPS condition.
28 citations
TL;DR: The unified microscopic theory of current-induced spin orientation, spin-galvanic, and spin-Hall effects for the two-dimensional hopping regime is developed and it is shown that the corresponding susceptibilities are proportional to each other and determined by the interplay between the drift and the diffusion spin currents.
Abstract: In disordered systems, the hopping conductivity regime is usually realized at low temperatures where spin-related phenomena differ strongly from the cases of delocalized carriers. We develop the unified microscopic theory of current-induced spin orientation, spin-galvanic, and spin-Hall effects for the two-dimensional hopping regime. We show that the corresponding susceptibilities are proportional to each other and determined by the interplay between the drift and the diffusion spin currents. Estimations are made for realistic semiconductor heterostructures using the percolation theory. We show that the electrical spin polarization in the hopping regime increases exponentially with the increase of the concentration of localization sites and may reach a few percent at the crossover from the hopping to the diffusion conductivity regime.
27 citations
TL;DR: In this article, the authors investigated the transport properties of single-layer reduced graphene oxides (rGOs) and showed that the crossover of the transport mechanism from Efros-Shklovskii (ES) variable range hopping (VRH) between the localized states to Mott-VRH was observed near 70 K using the temperature-dependent conductance.
Abstract: This study investigated the transport properties of single-layer reduced graphene oxides (rGOs). The rGOs were prepared by the bubble deposition method followed by thermal reduction. The crossover of the transport mechanism from Efros-Shklovskii (ES) variable range hopping (VRH) between the localized states to Mott-VRH was observed near 70 K using the temperature-dependent conductance. The ES-VRH conduction below 70 K is apparent in the electric field dependence of the field-driven hopping transport in the high-electric field regime. We also figure out that the thermoelectric power is consistent with the 2D Mott VRH above 70 K. We argue that the VRH conduction results from the topological disorders of rGO as confirmed by Raman spectroscopy. This infers that the average distance between defects is approximately 2.0 nm.
TL;DR: In this paper, the electrical conductance of fixed-gap and variable-gap junctions with spacers at the boundaries is investigated. And the authors show that the electrical properties of such junctions are dominated by two (rather than three) mechanisms: phase-coherent resonant conduction and multi-step thermally induced hopping.
Abstract: The electrical conductance of molecular junctions may depend strongly on the temperature and weakly on molecular length, under two distinct mechanisms: phase-coherent resonant conduction, with charges proceeding via delocalized molecular orbitals, and incoherent thermally assisted multi-step hopping. While in the case of coherent conduction, the temperature dependence arises from the broadening of the Fermi distribution in the metal electrodes, in the latter case it corresponds to electron-vibration interaction effects on the junction. With the objective to distill the thermally activated hopping component, thus exposing intrinsic electron-vibration interaction phenomena on the junction, we suggest the design of molecular junctions with "spacers," extended anchoring groups that act to filter out phase-coherent resonant electrons. Specifically, we study the electrical conductance of fixed-gap and variable-gap junctions that include a tunneling block, with spacers at the boundaries. Using numerical simulations and analytical considerations, we demonstrate that in our design, resonant conduction is suppressed. As a result, the electrical conductance is dominated by two (rather than three) mechanisms: superexchange (deep tunneling) and multi-step thermally induced hopping. We further exemplify our analysis on DNA junctions with an A:T block serving as a tunneling barrier. Here, we show that the electrical conductance is insensitive to the number of G:C base-pairs at the boundaries. This indicates that the tunneling-to-hopping crossover revealed in such sequences truly corresponds to the properties of the A:T barrier.
TL;DR: In this paper, the structural, magnetotransport and thermopower properties of a series of polycrystalline La 0.7−x Sm x Ba 0.3 MnO 3 (0≤x≤0.2) compounds were studied.
TL;DR: In this paper, the authors used the variational cluster approximation to study the isotropic triangular lattice Hubbard model at half filling, taking into account the nearest-neighbor $(t) and next-nearest-nighbor hopping parameters for magnetic frustrations.
Abstract: The variational cluster approximation is used to study the isotropic triangular-lattice Hubbard model at half filling, taking into account the nearest-neighbor $({t}_{1})$ and next-nearest-neighbor $({t}_{2})$ hopping parameters for magnetic frustrations. We determine the ground-state phase diagram of the model. In the strong-correlation regime, the ${120}^{\ensuremath{\circ}}$ N\'eel- and stripe-ordered phases appear, and a nonmagnetic insulating phase emerges in between. In the intermediate correlation regime, the nonmagnetic insulating phase expands to a wider parameter region, which goes into a paramagnetic metallic phase in the weak-correlation regime. The critical phase boundary of the Mott metal-insulator transition is discussed in terms of the van Hove singularity evident in the calculated density of states and single-particle spectral function.
TL;DR: Around the Mott transition region of this material under pressure, nuclear magnetic resonance experiments capture the emergence of slow electronic fluctuations of the order of kilohertz or lower, which is not expected in the conventional Mott Transition that appears as a clear first-order transition at low temperatures.
Abstract: The Mott transition-a metal-insulator transition caused by repulsive Coulomb interactions between electrons-is a central issue in condensed matter physics because it is the mother earth of various attractive phenomena. Outstanding examples are high-Tc (critical temperature) cuprates and manganites exhibiting colossal magnetoresistance. Furthermore, spin liquid states, which are quantum-fluctuation-driven disordered ground states in antiferromagnets, have recently been found in magnetic systems very near the Mott transition. To date, intensive studies on the Mott transition have been conducted and appear to have established a nearly complete framework for understanding the Mott transition. We found an unknown type of Mott transition in an organic spin liquid material with a slightly disordered lattice. Around the Mott transition region of this material under pressure, nuclear magnetic resonance experiments capture the emergence of slow electronic fluctuations of the order of kilohertz or lower, which is not expected in the conventional Mott transition that appears as a clear first-order transition at low temperatures. We suggest that they are due to the unconventional metal-insulator fluctuations emerging around the disordered Mott transition in analogy to the slowly fluctuating spin phase, or Griffiths phase, realized in Ising spin systems with disordered lattices.
TL;DR: Zhang et al. as mentioned in this paper showed that the layered MoSe 2 grows in a scalable manner on the substrate and reveals characteristics of a stoichiometric 2H-phase with polycrystalline features with domains separated by defects and boundaries.
Abstract: Molecular beam epitaxy technique has been used to deposit a single layer and a bilayer of MoSe 2 on sapphire. Extensive characterizations including in-situ and ex-situ measurements show that the layered MoSe 2 grows in a scalable manner on the substrate and reveals characteristics of a stoichiometric 2H-phase. The layered MoSe 2 exhibits polycrystalline features with domains separated by defects and boundaries. Temperature and magnetic field dependent resistivity measurements unveil a carrier hopping character described within two-dimensional variable range hopping mechanism. Moreover, a negative magnetoresistance was observed, stressing a fascinating feature of the charge transport under the application of a magnetic field in the layered MoSe 2 system. This negative magnetoresistance observed at millimeter-scale is similar to that observed recently at room temperature inWS2 flakes at a micrometer scale [Zhang et al., Appl. Phys. Lett. 108, 153114 (2016)]. This scalability highlights the fact that the underlying physical mechanism is intrinsic to these two-dimensional materials and occurs at very short scale.
TL;DR: In this article, a universal scaling factor for grain and grain boundary responses has been explored in the ac conductivity domain for polycrystalline double perovskite oxides A2HoRuO6 (AHR; A = Ba, Sr, Ca).
Abstract: The pursuit for a universal scaling factor to satisfy the time–temperature superposition principle for grain and grain boundary responses has been explored in the ac conductivity domain for polycrystalline double perovskite oxides A2HoRuO6 (AHR; A = Ba, Sr, Ca). The samples show different structural phases, from cubic to monoclinic, with decreasing ionic radii. The degree of distortion in the materials is correlated to the strength of the bonding through the bond valence sum (BVS) formalism. The conductivity spectra for all of the samples obey the power law variation. The contribution of different microstructural domains to the conduction process is established. Thermal variation of the dc resistivity points towards a gradual crossover from nearest neighbour to variable range hopping. The activation energies obtained from the dc conductivity, hopping frequency and relaxation frequency show close correlation between the conduction and relaxation mechanisms. The scaled conductivity curves for AHR display the presence of two different conduction processes with dissimilar activation energies in the grain boundary and the grain response regimes. It is thus concluded that a single scaling parameter is insufficient to satisfy the time temperature superposition principle universally when two different thermally activated regions are present simultaneously in the materials.
TL;DR: In this article, a magnetic exchange bias was observed that reproducibly occurs in both (111)- and (001)-oriented superlattices with the thin single layers of 5 and 7 unit cells, respectively.
Abstract: High-quality lattice-matched LaNiO3/LaMnO3 superlattices with monolayer terrace structure have been grown on both (111)- and (001)-oriented SrTiO3 substrates by pulsed laser deposition. In contrast to the previously reported experiments, a magnetic exchange bias is observed that reproducibly occurs in both (111)- and (001)-oriented superlattices with the thin single layers of 5 and 7 unit cells, respectively. The exchange bias is theoretically explained by charge transfer-induced magnetic moments at Ni atoms. Furthermore, magnetization data at low temperature suggest two magnetic phases in the superlattices, with Neel temperature around 10 K. Electrical transport measurements reveal a metal-insulator transition with strong localization of electrons in the superlattices with the thin LaNiO3 layers of 4 unit cells, in which the electrical transport is dominated by two-dimensional variable range hopping.
TL;DR: In this article, the authors investigated the electrical conductivity of single wall and multi-walled carbon nanotubes (SWCNT and MWCNT) thin films deposited on a polymeric substrate by Langmuir-Schaefer technique.
TL;DR: In this article, the structural, magnetic and transport properties using X-ray diffraction, dc magnetization, ac susceptibility, exchange bias and dc resistivity measurements were reported for single-phase polycrystalline La 1.5 Ca 0.5 CoMnO 6 double perovskite nanoparticles.
TL;DR: In this paper, the structural, optical and electrical properties of Niobium pentoxide (Nb2O5) thin films have been investigated using XRD and AFM techniques.
Abstract: We report on the structural, optical and electrical properties of RF sputtered Niobium pentoxide (Nb2O5) thin films. The structural studies have been carried out using XRD, and AFM techniques. Optical constants such as optical band gap energy, absorption coefficient, refractive index, complex dielectric constant and optical conductivity have been estimated for as-deposited and annealed Nb2O5 thin films. The estimated direct optical band gap energy values were found to be E g d = 3.62 e V for the as deposited which decreases to E g d = 3.07 e V for the annealed films at 973 K. The dispersion curves of the refractive index of Nb2O5 thin films in the optical transparency region are explained by using single oscillator and Drude models. The correlations between optical parameters and the annealing temperature of the Nb2O5 thin films are discussed. The DC activation energy has been estimated by using two probe technique.Mott’s variable range hopping conduction process (VRH) and small-polaron hopping have been used to understand DC electrical conductivity.
TL;DR: In this article, the authors show that the dependence of the electric field on the hopping mobility in regular grids can drastically differ from that in systems with spatial disorder, which makes lattice models inappropriate for studying the field dependence of hopping mobility.
Abstract: The theoretical description of the effect of the electric field $F$ on the hopping mobility $\ensuremath{\mu}$ belongs to the not-yet-resolved problems related to charge transport in disordered materials. An often proposed solution is to simulate hopping transport via sites placed on regular grids and to fit the results by phenomenological equations. This approach currently dominates the theoretical research of hopping transport in organic disordered semiconductors. We show that the dependence $\ensuremath{\mu}(F)$ in the case of regular grids can drastically differ from that in systems with spatial disorder. While $\ensuremath{\mu}$ increases with $F$ on lattices, it can decrease in random systems with the same material parameters. Moreover, the material parameters responsible for the dependence $\ensuremath{\mu}(F)$ on lattices differ from those responsible for $\ensuremath{\mu}(F)$ in spatially disordered systems, which makes lattice models inappropriate for studying the field dependence of the hopping mobility.
TL;DR: In this paper, the electrical conductivity of 0.5V2O5-0.5[B2O3-(1−−x) P2O4] glasses has been investigated.
Abstract: In this paper, we have studied structure and electrical conductivity of 0.5V2O5-0.5[xB2O3-(1 − x) P2O5] glasses. The reduced vanadium ion ratio V4 +/(V4 + + V5 +) and the ratio of bridging oxygens to non-bridging oxygens have been determined from analysis of V2p3/2 and O1s X-ray photoelectron spectra respectively. It is observed that the reduced vanadium ion ratio V4 +/(V4 + + V5 +) decreases continuously with the substitution of P2O5 by B2O3. The dc conductivity shows a minimum for composition x = 0.4. The electrical conductivity data has been analyzed with various models existing in literature. It is observed that at high temperatures Mott's nearest neighbor hopping model can explain the dc conductivity data, while at low temperatures dc conductivity data is consistent with Mott's variable range hopping model. Schnakenberg's polaron hopping model is valid for the entire temperature range of measurement. The parameters obtained from these models are reasonable.
TL;DR: In this paper, a template-free polyaniline nanofibres (NF) with controlled diameters was synthesized using a template free method, with ammonium peroxidisulfate (APS) or ferric chloride (FeCl3) as oxidants.
Abstract: Polyaniline nanofibres (NFs) with controlled diameters were synthesized using a template-free method, with ammonium peroxidisulfate (APS) or ferric chloride (FeCl3) as oxidants. Porosity studies reveal that NFs prepared with FeCl3 possess higher effective surface area and larger pore volume compared to NFs prepared with APS. The FeCl3-assisted NFs show around twofold enhanced sensing response (ca 4.5%) towards 5 ppm of SO2 at room temperature compared to APS-assisted NFs (ca 2%). The enhancement can be attributed to the lower diameter, higher effective surface area and larger porosity of FeCl3-assisted NFs. To further explain this enhanced sensing response, the conduction mechanism was studied. NFs possessing a smaller diameter (ca 10 nm) are found to follow the one-dimensional variable range hopping (VRH) model, whereas NFs with larger diameter (ca 100 nm) follow the conventional three-dimensional VRH model. This can be due to the restriction of charge carrier transport into only one direction due to quantum size effects. Furthermore, the calculated Mott parameters suggest that the NFs prepared using FeCl3 provide a better pathway for charge transport of charge carriers as compared to NFs prepared using APS in terms of shorter hopping distance, lower activation energy and lower hopping energy, and weaker localization of charge carriers.
TL;DR: The experimental observation of variable range hopping conduction in focused-ion-beam (FIB) fabricated ultra-narrow nanowires of topological insulator (Bi2Se3) indicates the presence of 2D topological surface states and the surface state contribution to the conductance was found very close to one conductance quantum.
Abstract: We report the experimental observation of variable range hopping conduction in focused-ion-beam (FIB) fabricated ultra-narrow nanowires of topological insulator (Bi2Se3). The value of the exponent (d + 1)−1 in the hopping equation was extracted as $$ \sim \frac{1}{2}\,\,$$
for different widths of nanowires, which is the proof of the presence of Efros-Shklovskii hopping transport mechanism in a strongly disordered system. High localization lengths (0.5 nm, 20 nm) were calculated for the devices. A careful analysis of the temperature dependent fluctuations present in the magnetoresistance curves, using the standard Universal Conductance Fluctuation theory, indicates the presence of 2D topological surface states. Also, the surface state contribution to the conductance was found very close to one conductance quantum. We believe that our experimental findings shed light on the understanding of quantum transport in disordered topological insulator based nanostructures.
TL;DR: In this article, the effect of physisorbed vs. chemiscorbed oxygen on highly organized single walled carbon nanotube (SWCNT) ultrathin films is investigated by correlating the thermoelectric properties measured by a suspended micro-device to the SWCNT structure characterized by Raman spectroscopy and transmission electron microscopy.
Abstract: The effect of physisorbed vs. chemisorbed oxygen on highly organized single walled carbon nanotube (SWCNT) ultrathin films is investigated by correlating the thermoelectric properties measured by a suspended micro-device to the SWCNT structure characterized by Raman spectroscopy and transmission electron microscopy. The results show that SWCNTs with weakly bonded oxygen molecules on the surface were determined to be initially p-type with metallic behavior and after annealing in vacuum they transition to n-type with semiconducting behavior where the charge transport is dominated by a 2D Mott variable range hopping mechanism due to molecular desorption. The structural characterization reveals that there is no change in the structure of the SWCNT network, indicating that the source of the drastic change in electrical properties is due to the molecule interaction with the surface of the SWCNT. Even though there is a significant change in the electrical properties, the thermal conductivity remains unchanged. On the other hand, the oxidized SWCNT sample with stronger C–O bonds exhibits purely p-type metallic behavior that is insensitive to annealing conditions and shows lower thermal conductivity values because of the enhanced phonon scattering due to the absorbed oxygen molecules and residual poly-methyl-methacrylate (PMMA).
TL;DR: In this paper, the electrical conductivity of the as-sintered samples was found to increase with Ag 2 O addition as a result of increases in the carrier density, which can be attributed to thermally activated transitions from the acceptor state to the valence band.
TL;DR: In this article, variable range hopping (VRH) conduction of Mott type for a constant and nonvanishing density of states at the Fermi level is observed over a wide range of temperature between 45 and 210
Abstract: Variable range hopping (VRH) conduction of Mott type for a constant and non-vanishing density of states at the Fermi level is observed over a wide range of temperature between 45 and 210 K in the ordered defect compound CuIn3Te5 (CIT135). For this type of electrical conduction at a very high temperature, not reported before in elemental, II-VI, and I-III-VI2 compound semiconductors, we employed three different methods to analyze the data and to confirm this behavior. The occurrence of VRH at very high temperatures is explained as due to the presence of the electrically inactive ( In Cu + 2 + 2 V Cu − 1 ) donor-acceptor defect pairs in CIT135. This defect-pair partially annihilates the shallow acceptor defect state Cu vacancy, which is responsible for the activated electrical conductivity observed in p-type ternary I-III-VI2 chalcopyrite compounds in the temperature range of liquid nitrogen. In such conditions, the only acceptor level available for electrical conduction in CIT135 is a deep acceptor state whose activation energy is about 200 meV and cannot be activated below about 200 K. Hence, the VRH conduction mechanism dominates the electrical properties of this material up to about 200 K. The study of the temperature and magnetic field dependence of the magnetoresistance (MR) up to 27 T is made by taking into consideration different theoretical models. To explain the negative MR at lower fields, the theory based on quantum interference is used. At higher magnetic fields, the MR becomes positive and is explained with the model based on the shrinkage of the wave function.
TL;DR: In this article, the electrical current of high density polystyrene/carbon nanotube nano-composite, over the extensive range of absorbed dose in different nanotubes weight percentages were simulated as the dosimetry response of this material.
Abstract: In this research work, the electrical current of high density polystyrene/carbon nanotube nano-composite, over the extensive range of absorbed dose in different nanotube weight percentages were simulated as the dosimetry response of this material. The adiabatic temperature rise (Δ T) from absorption of ionizing energy is given by Δ T=D/C, where D is the average dose and C is heat capacity. The heat capacity was calculated for the nano-composite in different concentration of inclusions. For assessment of electrical conductivity of the nano-composite over the extensive range of absorbed dose, two models were considered as thermally activated hopping (TAH) and variable range hopping (VRH), for polymer and nanotube respectively. In this simulation, finite element method was used to investigate electrical currents of the nano-composite in different doses, voltages and nanotube weight percentages. The results showed a linear dose response over the extensive dose range, especially in the diagnostic and therapy dosimetry levels.
TL;DR: In this paper, the electrical transport properties of polycrystalline germanium thin films which are grown by the DC magnetron sputtering method are reported. But the authors focus on the high temperature regime and the low temperature electron transport is governed by the variable range hopping (VRH) mechanism.
Abstract: We report on the electrical transport properties of polycrystalline germanium thin films which are grown by the DC magnetron sputtering method. The temperature dependent resistance of seven devices are measured from 290 K down to 10 K. The thermal excitation model dominating the transport properties at the high temperature regime (above ~60 K) is demonstrated and the low temperature electron transport is governed by the variable-range hopping (VRH) mechanism. Moreover, we observed a transition from Efros–Shklovskii to Mott VRH at ~25 K over the entire VRH conduction regime, which is well described by a universal scaling law.