Study Of Electron Transport Research Articles

Acoustomagnetoelectric effect in two-dimensional materials: Geometric resonances and Weiss oscillations

We study electron transport in two-dimensional materials with parabolic and linear (graphene) dispersions of the carriers in the presence of surface acoustic waves and an external magnetic field using semiclassical Boltzmann equations approach. We observe an oscillatory behavior of both the longitudinal and Hall electric currents as functions of the surface acoustic wave frequency at a fixed magnetic field and as functions of the inverse magnetic field at a fixed frequency of the acoustic wave. We explain the former by the phenomenon of geometric resonances, while we relate the latter to the Weiss-like oscillations in the presence of the dynamic superlattice created by the acoustic wave. Thus we demonstrate the dual nature of the acoustomagnetoelectric effect in two-dimensional electron gas.

Characteristics of Electron Transport Study of Composited Graphene-Zinc Oxide Thin Film Photoanode for Dye-Sensitized Solar Cells

Graphene-Zinc Oxide (Gr-ZnO) nanocomposites films were successfully synthesized via facile electrodeposition method in an aqueous solution under Gr concentration conditions. Gr, as a highly conductive carbon, acts as an anchor for ZnO nanosheets and plays a substantial role in controlling the degree of dispersion of ZnO nanosheets onto indium-doped tin oxide (ITO) substrate to form Gr-ZnO nanocomposite. Atomic force microscopy (AFM) and field-emission scanning electron microscopy (FESEM) analysis of Gr-ZnO nanocomposite samples confirmed that the presence of ZnO nanosheets with a high degree of dispersity and crystallinity which is well linked to the thin layer of Gr nanoparticle on ITO substrate. The surface roughness of the films found increased to ~270 nm on Gr-ZnO as compared to Gr ~44 nm and ZnO ~3 nm. Further, the x-ray diffraction spectroscopy (XRD) analysis showed the result is in good agreement with Raman spectroscopy study. The cyclic voltammetry (CV) of Gr-ZnO nanocomposite revealed that the effect of electron-hole recombination process was increased and the presence of Gr in ZnO photoanode provides the fastest redox reaction and hence offers the fastest electron transfer in photoanode.

First principles study of electronic structure and thermoelectric transport in tin selenide and phase separated tin selenide–copper selenide alloy

The electronic structure and thermoelectric transport in SnSe and its alloy with Cu2Se have been studied using the first principles technique and semi classical Boltzmann transport theory. Our study reveals that SnSe is p-type with indirect band gap of 0.66 eV, while the alloy is phase separated and n-type with negligible indirect band gap of 0.064 eV. In both cases, two fold degeneracy in band extrema have been observed within the range of 25 meV. Delocalization of Se lone pair has been observed due to Cu substitution in Sn sites, which is supposed to lower its lattice thermal conductivity. A chemical potential map has been generated obeying thermodynamic restrictions to predict the possible existence of secondary phases. Our study shows the existence of SnSe2 as a secondary phase, while the possibility of Cu2Se as a secondary phase is negligible due to its higher formation energy. We calculated the transport coefficients as a function of carrier concentration and temperature to understand the range of optimized thermoelectric performance. The transport coefficients are similar along in plane direction whereas significant deviation is observed along the cross plane direction due to anisotropy in effective masses in SnSe. The effective masses are more isotropic in alloy than SnSe, thus transport properties show less anisotropy along three directions. Significant contribution of bipolar transport is observed in SnSe, while that is not noticed in the alloy. The behaviors of the Seebeck coefficients in both cases are discussed in terms of Mott’s theory and density of states modification near Fermi energy. Electron mobilities limited by acoustic phonon, ionized impurities, alloy scattering and inter carrier scattering have been examined relying on deformation potential approach and effective mass theory. The results indicate that acoustic phonon scattering is dominant scattering mechanism in SnSe over inter carrier scattering, whereas for the alloy the former contribute very weakly. Ionized impurity scattering and inter carrier scattering are most dominant in the alloy. Alloy scattering with U = 2 eV also contribute significantly.

Specific Features of Electron Transport in a Molecular Nanodevice Containing a Nitroamine Redox Center

Density functional theory in the local-density approximation and the method of nonequilibrium Green functions (DFT + NEGF) are used to study electron transport in a nanodevice consisting of the 2'-amino-4-ethynylphenyl-4'-ethynylphenyl-5'-nitro-1-benzenethiol molecule located between gold electrodes. The I–V and dI/dV characteristics, transmission spectrum, and electron density of the nanodevice are calculated. It is shown that the I–V characteristic of the nanodevice exhibits N shape in a voltage interval of –0.8–0.9 V and a fragment with a negative differential resistance related to the resonance tunneling of quasi-particles. The same changes are observed on the dI/dV characteristic. The results can be used for calculation of promising electronic switches.

Effect of Environment on the Scattering of Electrons by a Junction of Different Topological Materials

AbstractThe studies of electron transport through a junction of topological materials in the literature so far ignore the coupling of a topological material to its surrounding environment. Here, the dynamics of an open system through a stochastic Hamiltonian are simulated to investigate the influence of the environment on the scattering of electrons by a junction of different topological materials, such as a Dirac–Weyl magnetic junction and a topological insulator. It is found that, although the detrimental effect of the environment is inevitable, the Landauer conductance can be enhanced via adjusting the system–environment coupling strength. This result supplies the possibilty of changing the transport feature of topological materials by modulating the surrounded environment. It is also demonstrated that a non‐Hermitian Hamiltonian can be used to replace the stochastic Hamiltonian for this study, when the system and the environment coupling are weak.

Periodic energy decomposition analysis for electronic transport studies as a tool for atomic scale device manufacturing

Atomic scale manufacturing is a necessity of the future to develop atomic scale devices with high precision. A different perspective of the quantum realm, which includes the tunnelling effect, leakage current at the atomic-scale, Coulomb blockade and Kondo effect, is inevitable for the fabrication and hence, the mass production of these devices. For these atomic-scale device development, molecular level devices must be fabricated. Proper theoretical studies could be an aid towards the experimental realities. Electronic transport studies are the basis to realise and interpret the problems happening at this minute scale. Keeping these in mind, we present a periodic energy decomposition analysis (pEDA) of two potential candidates for moletronics: phthalocyanines and porphyrins, by placing them over gold substrate cleaved at the (111) plane to study the adsorption and interaction at the interface and then, to study their application as a channel between two electrodes, thereby, providing a link between pEDA and electronic transport studies. pEDA provides information regarding the bond strength and the contribution of electrostatic energy, Pauli’s energy, orbital energy and the orbital interactions. Combining this analysis with electronic transport studies can provide novel directions for atomic/close-to-atomic-scale manufacturing (ACSM). Literature survey shows that this is the first work which establishes a link between pEDA and electronic transport studies and a detailed pEDA study on the above stated molecules. The results show that among the molecules studied, porphyrins are more adsorbable over gold substrate and conducting across a molecular junction than phthalocyanines, even though both molecules show a similarity in adsorption and conduction when a terminal thiol linker is attached. A further observation establishes the importance of attractive terms, which includes interaction, orbital and electrostatic energies, in correlating the pEDA study with the transport properties. By progressing this research, further developments could be possible in atomic-scale manufacturing in the future.

Characterization of low-resistance ohmic contacts to a two-dimensional electron gas in a GaAs/AlGaAs heterostructure

The study of electron transport in low-dimensional systems is of importance, not only from a fundamental point of view, but also for future electronic and spintronic devices. In this context heterostructures containing a two-dimensional electron gas (2DEG) are a key technology. In particular GaAs/AlGaAs heterostructures, with a 2DEG at typically 100 nm below the surface, are widely studied. In order to explore electron transport in such systems, low-resistance ohmic contacts are required that connect the 2DEG to macroscopic measurement leads at the surface. Here we report on designing and measuring a dedicated device for unraveling the various resistance contributions in such contacts, which include pristine 2DEG series resistance, the 2DEG resistance under a contact, the contact resistance itself, and the influence of pressing a bonding wire onto a contact. We also report here a recipe for contacts with very low resistance values that remain below 10 Ω for annealing times between 20 and 350 s, hence providing the flexibility to use this method for materials with different 2DEG depths. The type of heating, temperature ramp rate and gas forming used for annealing is found to strongly influence the annealing process and hence the quality of the resulting contacts.

Characterization of an imploding cylindrical plasma for electron transport studies using x-ray emission spectroscopy

We report on the characterization of the conditions of an imploding cylindrical plasma by time-resolved x-ray emission spectroscopy. Knowledge about this implosion platform can be applied to studies of particle transport for inertial confinement fusion schemes or to astrophysical plasmas. A cylindrical Cl-doped CH foam within a tube of solid CH was irradiated by 36 beams (Itotal ∼ 5 × 1014 W/cm2, 1.5 ns square pulse, and Etotal ∼ 16.2 kJ) of the OMEGA-60 laser to radially compress the CH toward the axis. The analysis of the time-resolved spectra showed that the compression can be described by four distinct phases, each presenting different plasma conditions. First the ablation of the cylinder is dominant; second, the foam is heated and induces a significant jump in emission intensities; third, the temperature and density of the foam reaches a maximum; and finally, the plasma expands. Ranges for the plasma temperature were inferred with the atomic physics code SCRAM (Spectroscopic Collisional-Radiative Atomic Model) and the experimental data have been compared to hydrodynamic simulations performed with the 2D code FLASH, which showed a similar implosion dynamic over time.

Theoretical study of electronic transport through P-porphyrin and S-porphyrin nanoribbons

Electronic transport through P-porphyrin and S-porphyrin nanoribbons have been studied by using nonequilibrium Green’s function formalism (NEGF) combined with density functional theory (DFT) method. Band structure of both nanoribbons shows metallic behavior and bands near the Fermi level contain π character contributed by py orbital. Both nanoribbons exhibit metal-like conduction at extreme low bias. A remarkable negative differential resistance (NDR) effect is observed for both nanoribbons which is further explained with the evolution of transmission peak within energy bias window (EBW), and overlap of energy states of left and right electrodes. The low bias NDR phenomena of our proposed devices could be used in designing NDR devices including frequency multipliers, memory, and fast switches.

Electronic transport, Homo-Lumo and computational studies of CuS-ACT monowire for nano device fabrication by software approach

The electronic transport on these nanostructures is significant in the field of atomic gadgets since nano structures have diverse conduct contrasted with their mass partners. When all is said in done, atomic gadgets comprise of three districts specifically left anode, right cathode and the gadget sub-atomic locale or dissipating area. It is essential to break down the conduct of every area of the gadget hypothetically before manufacturing the gadget. The anode impacts are significant since they are the key parts in the atomic gadget. Numerous reports are accessible in the writing depicting the anode impacts of an atomic gadget. Then again, the commitment of the gadget district or dissipating locale in an atomic gadget for the gadget execution is extremely urgent. Various reports are accessible in the writing which respect the vehicle properties of the gadget atom and in that a large portion of them depend on the natural particles. Lesser number of reports is accessible portraying the gadget particle as inorganic. The present work is planned to consider the electronic vehicle properties of CuS sub-atomic gadget with the assistance of non-harmony Green's capacity (NEGF) strategy joined with thickness practical hypothesis (DFT). Likewise, the adsorption impact of acetylene and nitraso practical gatherings on the CuS monowire nano gadgets are additionally examined. The vehicle properties of CuS and natural utilitarian gathering adsorbed CuS-NIT monowire nano gadgets are attributed as far as their thickness of states, transmission range and the V-I qualities of the relating gadgets.

键合Si/Si p-n结电学输运特性及电场增强效应研究

键合Si/Si p-n结电学输运特性及电场增强效应研究

Development of a low energy small electron gun to study electron transport in hydrogen negative ion source plasmas.

We developed a small-size electron gun capable of producing electrons with kinetic energy less than few tens of eV to investigate the slowing down and transport mechanisms of electrons in hydrogen negative ion source plasmas. The maximum extractable beam current density reached 36 μA/cm2 for 1 eV beam energy in a preliminary experiment. Although the present electron current density is still insufficient compared with our target value, 1 mA/cm2, we have found some hints to realize larger beam current density from the electron gun through this study. The measured beam profile along the electron beam axis has shown that the electron beam could travel approximately 7 mm from the electron gun in vacuum. The Particle-In-Cell (PIC) simulation explained the measured beam profile well and indicated that the electron beam has an energy spread as small as 0.1 eV compared to the 1 eV mean energy. The PIC simulation showed a discrepancy from the measurement in the dependence of the electron beam current on the beam extraction voltage of the electron gun. It implies that we should introduce a more realistic filament structure inside the electron gun in the PIC simulation in order to study the transport of low energy electrons more precisely.

Influence of electric polarization on Coulomb blockade in a super-paraelectric clusters assembly

We study electron transport in an assembly of epitaxial Cr2O3 nanoparticles embedded in a MgO tunnel barrier: an unusual variation in the Coulomb blockade charging energy is observed as a function of the size of the clusters. In striking contrast to the expected increase in charging energy when decreasing the cluster size, an almost constant behavior is observed. We argue here that the spontaneous superparaelectric moment carried by the cluster core is the origin of this unusual behavior since it drives the dielectric constant in this cluster assembly. This phenomenon could be exploited to fabricate devices with single valued Coulomb blockade energy despite a statistical dispersion in the cluster size.

A Electron transport study on ultrathin armchair graphene nanoribbone

Using first-principles quantum transport simulations, this work examines changes in the total electronic currents within the plane of short ultrathin graphene nanoribbon with armchair edges (AGNR). A 5-AGNR-M (M = 4,12,20 and 28 zigzag line) junction was simulated and its transmission were analyzed. The I-V curves under external bias exhibit remarkable semiconducting characteristics. It further demonstrates that the length of the junction also showed significant effects in the determination of the semiconducting nature. More importantly, a significant increasing by double in bias voltage threshold of I–V characteristics have been observed for the positively charged nanoribbon in the family of 5-AGNRs.

Evidence for charge transfer and proximate magnetism in graphene– α−RuCl3 heterostructures

We report a study of electronic transport in van der Waals heterostructures composed of flakes of the antiferromagnetic Mott insulator a-RuCl_3 placed on top of monolayer graphene Hall bars. While the zero-field transport shows a strong resemblance to that of isolated graphene, we find a consistently $p$-type Hall effect suggestive of multiband conduction, along with a non-monotonic and gate-voltage-dependent excursion of the resistivity at low temperatures that is reminiscent of transport in the presence of a magnetic phase transition. We interpret these data as evidence for charge transfer from graphene to a-RuCl_3 in an inhomogeneous device yielding both highly- and lightly-doped regions of graphene, while the latter shows a particular sensitivity to magnetism in the a-RuCl_3. Thus proximity to graphene is a means to access magnetic properties of thin layers of magnetic insulators.

Nitrogen-doped NDR behavior of double gate graphene field effect transistor

Abstract This paper presents the negative differential resistance (NDR) behavior of double gate graphene field effect transistor. The channel length of the device is considered as 4 nm and source/drain regions are doped with nitrogen atoms. The carrier transport is assumed to be ballistic for the simulation. The semi-empirical Slater-Koster method is used to model the material and Nonequilibrium Green's Function (NEGF) is used for the electron transport study of the device. The NDR behavior of the device is discussed by using the transmission spectrum and device density of state (DDOS). The peak to valley current ratio (PVCR) of 105 is achieved with the peak current of -0.6 μA at room temperature. The other parameters like the NDR voltage window and the peak value of drain current are also discussed quantitatively. The simulation study shows the importance of graphene for negative differential resistance for future scaled electronic device applications.

The temperature dependence of electron transport in a composite film of graphene oxide with single-wall carbon nanotubes: an analysis and comparison with a nanotube film

The work describes the results of low-temperature studies (5–291 K) of electron transport in composite films of graphene oxide with single-wall nanotubes (GO-SWNTs) obtained by vacuum filtration of their aqueous suspension. The emergence of conductivity in such films is shown to be related to nanotubes, since the GO film, unlike the nanotube film, has no conductivity. For a comparative analysis, the electrical conductivity of the SWNT film was also considered. The GO-SWNT and SWNT films exhibit a semiconductor behavior with a negative temperature coefficient of electrical conductivity. The temperature dependences of film resistance have been analyzed using the 3D Mott model that describes the motion of electrons (due to thermally activated tunneling through barriers) with variable-range hopping (the VRH model) in an interval of 5–240 K. The analysis of the dependences yielded estimates for the parameters of electron transport in the composite GO-SWNT film and SWNT nanotube film: the average hopping range and energy of the electron; their temperature dependences have been plotted. A comparison of these parameters for different films showed that nanotube contact with the GO surface hinders electron transport in the composite film. To describe the temperature dependence of film resistance at Т > 240 K, the Arrhenius model is used from which the potential barrier value has been obtained.

Giant oscillations in a triangular network of one-dimensional states in marginally twisted graphene

At very small twist angles of ∼0.1°, bilayer graphene exhibits a strain-accompanied lattice reconstruction that results in submicron-size triangular domains with the standard, Bernal stacking. If the interlayer bias is applied to open an energy gap inside the domain regions making them insulating, such marginally twisted bilayer graphene is expected to remain conductive due to a triangular network of chiral one-dimensional states hosted by domain boundaries. Here we study electron transport through this helical network and report giant Aharonov-Bohm oscillations that reach in amplitude up to 50% of resistivity and persist to temperatures above 100 K. At liquid helium temperatures, the network exhibits another kind of oscillations that appear as a function of carrier density and are accompanied by a sign-changing Hall effect. The latter are attributed to consecutive population of the narrow minibands formed by the network of one-dimensional states inside the gap.

Structural, thermodynamic, thermal, and electron transport properties of single-crystalline LaPt2Si2

${\mathrm{LaPt}}_{2}{\mathrm{Si}}_{2}$ in a single-crystalline form was subjected to structure, thermodynamic, thermal, and electron transport studies with a special emphasis on the structure phase transition appearing at $T=85$ K. X-ray diffraction proves the noncentrosymmetric tetragonal structure of ${\mathrm{CaBe}}_{2}{\mathrm{Ge}}_{2}$-type (space group P4/nmm). The transition manifests as a small step of opposite sign in both lattice parameters, leaving almost no volume change. $c$ decreases and $a$ increases in the low-$T$ phase, but the change of the $c/a$ ratio does not exceed $0.1%$. Additional periodicity, related to the supposed charge density wave (CDW) state, can be related to satellites corresponding to the wave vector $q\ensuremath{\approx}(0.36,0,0)$, which start to grow with temperature decreasing below 175 K and almost vanish (or relocate from the investigated $ab$ plane) below the 85 K transition. Electrical resistivity reveals that the 85 K transition is hysteretic in temperature, with the difference between heating and cooling being almost 10 K, proving the first-order type of the transition. The transition dramatically enhances resistivity in the low-$T$ state, pointing to a formation of a pseudogap. This, however, does allow a superconducting state, arising below ${T}_{c}=1.6$ K. The temperature dependence up upper critical field is not compatible with the weak coupling BCS theory. Strong anisotropy of electronic structure and its dramatic changes at the structure transition are manifest also in thermal expansion and thermoelectric power. The Sommerfeld coefficient $\ensuremath{\gamma}=7.8\phantom{\rule{4pt}{0ex}}\mathrm{mJ}\phantom{\rule{0.16em}{0ex}}{\mathrm{mol}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{K}}^{\ensuremath{-}2}$ and Debye temperature of 205 K could be derived at low temperatures, but the specific heat has a strongly non-Debye like $T$ dependence, which can be ascribed to a low-energy Einstein mode.

Electrochemically Gated Long‐Distance Charge Transport in Photosystem I

AbstractThe transport of electrons along photosynthetic and respiratory chains involves a series of enzymatic reactions that are coupled through redox mediators, including proteins and small molecules. The use of native and synthetic redox probes is key to understanding charge transport mechanisms and to the design of bioelectronic sensors and solar energy conversion devices. However, redox probes have limited tunability to exchange charge at the desired electrochemical potentials (energy levels) and at different protein sites. Herein, we take advantage of electrochemical scanning tunneling microscopy (ECSTM) to control the Fermi level and nanometric position of the ECSTM probe in order to study electron transport in individual photosystem I (PSI) complexes. Current–distance measurements at different potentiostatic conditions indicate that PSI supports long‐distance transport that is electrochemically gated near the redox potential of P700, with current extending farther under hole injection conditions.