Ion heat transport in electron cyclotron resonance heated L-mode plasma on the T-10 tokamak

Anomalous ion heat transport is analyzed in the T-10 tokamak plasma heated with electron cyclotron resonance heating(ECRH) in second-harmonic extra-ordinary mode. Predictive modeling with empirical scaling for Ohmical heat conductivity shows that in ECRH plasmas the calculated ion temperature could be overestimated, so an increase of anomalous ion heat transport is required. To study this effect two scans are presented: over the EC resonance position and over the ECRH power. The EC resonance position varies from the high-field side to the low-field side by variation of the toroidal magnetic field. The scan over the heating power is presented with on-axis and mixed ECRH regimes. Discharges with high anomalous ion heat transport are obtained in all considered regimes. In these discharges the power balance ion heat conductivity exceeds the neoclassical level by up to 10 times. The high ion heat transport regimes are distinguished by three parameters: the ratio Te/Ti, the normalized electron density gradient R/■, and the ion–ion collisionality νii~*. The combination of high Te/Ti, high νii~*, and R/■=6-10 results in values of normalized anomalous ion heat fluxes up to 10 times higher than in the low transport scenario.

Spin-dependent transport for a two-dimensional electron gas with magnetic barriers

The spin-dependent conductance and magnetoresistance ratio （MRR） for a semiconductor heterostructures consisting of two magnetic barriers with different height and space have been investigated by the transfer-matrix method. It is shown that the splitting of the conductance for parallel and antiparallel magnetization configurations results in tremendous spin-dependent MRR, and the maximal MRRs reach 5300% and 3800% for the magnetic barrier spaces W = 81.3 and 243.9 nm, respectively. The obtained spin-filtering transport property of nanostructures with magnetic barriers may be useful to magnetic-barrier-based spintronics.

Toward high-efficiency perovskite solar cells with one-dimensional oriented nanostructured electron transport materials

The unique advantages of one-dimensional(1D)oriented nanostructures in light-trapping and chargetransport make them competitive candidates in photovoltaic(PV)devices.Since the emergence of perovskite solar cells(PSCs),1D nanostructured electron transport materials(ETMs)have drawn tremendous interest.However,the power conversion efficiencies(PCEs)of these devices have always significantly lagged behind their mesoscopic and planar counterparts.High-efficiency PSCs with 1D ETMs showing efficiency over 22%were just realized in the most recent studies.It yet lacks a comprehensive review covering the development of 1D ETMs and their application in PSCs.We hence timely summarize the advances in 1D ETMs-based solar cells,emphasizing on the fundamental and optimization issues of charge separation and collection ability,and their influence on PV performance.After sketching the classification and requirements for high-efficiency 1D nanostructured solar cells,we highlight the applicability of 1D TiO_(2)nanostructures in PSCs,including nanotubes,nanorods,nanocones,and nanopyramids,and carefully analyze how the electrostatic field affects cell performance.Other kinds of oriented nanostructures,e.g.,ZnO and SnO_(2)ETMs,are also described.Finally,we discuss the challenges and propose some potential strategies to further boost device performance.This review provides a broad range of valuable work in this fast-developing field,which we hope will stimulate research enthusiasm to push PSCs to an unprecedented level.

Alleviating Interfacial Recombination of Heterojunction Electron Transport Layer via Oxygen Vacancy Engineering for Efficient Perovskite Solar Cells Over 23%

Electron transport layer(ETL)is pivotal to charge carrier transport for PSCs to reach the Shockley-Queisser limit.This study provides a fundamental understanding of heterojunction electron transport layers(ETLs)at the atomic level for stable and efficient perovskite solar cells(PSCs).The bilayer structure of an ETL composed of SnO_(2) on TiO_(2) was examined,revealing a critical factor limiting its potential to obtain efficient performance.Alteration of oxygen vacancies in the TiO_(2) underlayer via an annealing process is found to induce manipulated band offsets at the interface between the TiO_(2) and SnO_(2) layers.In-depth electronic investigations of the bilayer structure elucidate the importance of the electronic properties at the interface between the TiO_(2) and SnO_(2) layers.The apparent correlation in hysteresis phenomena,including current density-voltage(J-V)curves,appears as a function of the type of band alignment.Density functional theory calculations reveal the intimate relationship between oxygen vacancies,deep trap states,and charge transport efficiency at the interface between the TiO_(2) and SnO_(2) layers.The formation of cascade band alignment via control over the TiO_(2) underlayer enhances device performance and suppresses hysteresis.Optimal performance exhibits a power conversion efficiency(PCE)of 23.45%with an open-circuit voltage(V_(oc))of 1.184 V,showing better device stability under maximum power point tracking compared with a staggered bilayer under one-sun continuous illumination.

Transport properties of Hall-type quantum states in disordered bismuthene

Bismuthene,an inherently hexagonal structure characterized by a huge bulk gap,offers a versatile platform for investigating the electronic transport of various topological quantum states.Using nonequilibrium Green's function method and Landauer-Büttiker formula,we thoroughly investigate the transport properties of various Hall-type quantum states,including quantum spin Hall(QSH)edge states,quantum valley Hall kink(QVHK)states,and quantum spin-valley Hall kink(QSVHK)states,in the presence of various disorders.Based on the exotic transport features,a spin-valley filter,capable of generating a highly spin-and valley-polarized current,is proposed.The valley index and the spin index of the filtered QSVHK state are determined by the staggered potential and the intrinsic spin-orbit coupling,respectively.The efficiency of the spin-valley filter is supported by the spacial current distribution,the valley-resolved conductance,and the spin-resolved conductance.Compared with a sandwich structure for QSVHK,our proposed spin-valley filter can work with a much smaller size and is more accessible in the experiment.

Enhanced spin-dependent thermopower in a double-quantum-dot sandwiched between two-dimensional electron gases

We study the spin-dependent thermopower in a double-quantum-dot(DQD) embedded between the left and right two-dimensional electron gases(2DEGs) in doped quantum wells under an in-plane magnetic field. When the separation between the DQD is smaller than the Fermi wavelength in the 2DEGs, the asymmetry in the dots' energy levels leads to pronounced quantum interference effects characterized by the Dicke line-shape of the conductance, which are sensitive to the properties of the 2DEGs. The magnitude of the thermopower, which denotes the generated voltage in response to an infinitesimal temperature difference between the two 2DEGs under vanishing charge current, will be obviously enhanced by the Dicke effect. The application of the in-plane magnetic field results in the polarization of the spin-up and spin-down conductances and thermopowers, and enables an efficient spin-filter device in addition to a tunable pure spin thermopower in the absence of its charge counterpart.

Spin-dependent transport characteristics of nanostructures based on armchair arsenene nanoribbons

By employing non-equilibrium Green＇s function combined with the spin-polarized density-functional theory, we investigate the spin-dependent electronic transport properties of armchair arsenene nanoribbons（a As NRs）. Our results show that the spin-metal and spin-semiconductor properties can be observed in a As NRs with different widths. We also find that there is nearly 100% bipolar spin-filtering behavior in the a As NR-based device with antiparallel spin configuration. Moreover, rectifying behavior and giant magnetoresistance are found in the device. The corresponding physical analyses have been given.

Spin-Dependent Transport in Carbon Nanotubes with Chromium Atoms

Method is developed for self-consistent calculation of the energy spectrum of free energy and electrical disordered crystals. Processes of electron scattering on the ionic core potential of different sort, fluctuations of charge, spin density and lattice vibrations are taken into account. Electronic states of the system are described using tight binding multiband model. The nature of the spin-dependent electron transport of carbon nanotubes with chromium atoms adsorbed on the surface is explained. The value of the spin polarization of electron transport is determined by the difference of the partial densities of states of electrons with opposite spin projection at the Fermi level and the difference between the relaxation times of electron states. The value of the spin polarization of the electric current increases with increasing of Cr atoms concentration and magnitude of the external magnetic field.

Spin-Dependent Electron Properties of a Triple-Terminal Quantum Dot Structure

Electron transport properties of a triple-terminal Aharonov-Bohm interferometer are theoretically studied.By applying a Rashba spin-orbit coupling to a quantum dot locally, we find that remarkable spin polarization comesabout in the electron transport process with tuning the structure parameters, i.e., the magnetic flux or quantum dotlevels. When the quantum dot levels are aligned with the Fermi level, there only appear spin polarization in thisstructure by the presence of an appropriate magnetic flux. However, in absence of magnetic flux spin polarization andspin separation can be simultaneously realized with the adjustment of quantum dot levels, namely, an incident electronfrom one terminal can select a specific terminal to depart from the quantum dots according to its spin state.

SnO2-based electron transporting layer materials for perovskite solar cells: A review of recent progress

In recent years, due to their high photo-to-electric power conversion efficiency(PCE)(up to 23%(certified)) and low cost, perovskite solar cells(PSCs) have attracted a great deal of attention in photovoltaics field. The high PCE can be attributed to the excellent physical properties of organic–inorganic hybrid perovskite materials, such as a long charge diffusion length and a high absorption coefficient in the visible range. There are different diffusion lengths of holes in electrons in a PSC device, and thus the electron transporting layer(ETL) plays a critical role in the performance of PSCs. An alternative for TiO2, to the most common ETL material is SnO2, which has similar physical properties to TiO2 but with much higher electron mobility, which is beneficial for electron extraction. In addition, there are many facile methods to fabricate SnO2 nanomaterials with low cost and low energy consumption. In this review paper, we focus on recent developments in SnO2 as the ETL of PSCs. The fabrication methods of SnO2 materials are briefly introduced. The influence of multiple Sn O2 types in the ETL on the performance of PSCs is then reviewed. Different methods for improving the PCE and long-term stability of PSCs based on SnO2 ETL are also summarized. The review provides a systematic and comprehensive understanding of the influence of different Sn O2 ETL types on PSC performance and potentially motivates further development of PSCs with an extension to SnO2-based PSCs.

Blue light is more essential than red light for maintaining the activities of photosystem Ⅱ and Ⅰ and photosynthetic electron transport capacity in cucumber leaves

Blue and red lights differently regulate leaf photosynthesis. Previous studies indicated that plants under blue light generally exhibit better photosynthetic characteristics than those under red light. However, the regulation mechanism of related photosynthesis characteristics remains largely unclear. Here, four light qualities treatments （300 μmol m-2 s-1） including white fluorescent light （FL）, blue monochromatic light （B, 440 nm）, red monochromatic light （R, 660 nm）, and a combination of red and blue light （RB, R：B=8：1） were carried out to investigate their effects on the activity of photosystem II （PSII） and photosystem I （PSI）, and photosynthetic electron transport capacity in the leaves of cucumber （Cucumis sativus L.） seedlings. The results showed that compared to the FL treatment, the R treatment significantly limited electron transport rate in PSII （ETR11） and in PSI （ETR1） by 79.4 and 66.3%, respectively, increased non-light induced non-photochemical quenching in PSII （q^No） and limitation of donor side in PSI （φND） and reduced most JIP-test parameters, suggesting that the R treatment induced suboptimal activity of photosystems and inhibited electron transport from PSII donor side up to PSI. However, these suppressions were effectively alleviated by blue light addition （RB）. Compared with the R treatment, the RB treatment significantly increased ETR, and ETR1 by 176.9 and 127.0%, respectively, promoted photosystems activity and enhanced linear electron transport by elevating electron transport from QA to PSI. The B treatment plants exhibited normal photosystems activity and photosynthetic electron transport capacity similar to that of the FL treatment. It was concluded that blue light is more essential than red light for normal photosynthesis by mediating photosystems activity and photosynthetic electron transport capacity.

Numerical investigation of non-local electron transport in laser-produced plasmas

Non-local electron transport in laser-produced plasmas under inertial confinement fusion （ICF） conditions is studied based on Fokker-Planck （FP） and hydrodynamic simulations. A comparison between the classical Spitzer-Harm （SH） transport model and non-local transport models has been made. The result shows that among those non-local models the Epperlein and Short （ES） model of heat flux is in reasonable agreement with the FP simulation in overdense region. However, the non-local models are invalid in the hot underdense plasmas. Hydrodynamic simulation is performed with the flux limiting model and the non-local model, separately. The simulation results show that in the underdense region of the laser-produced plasmas the temperature given by the flux limiting model is significantly higher than that given with the non-local model.

PIC-MC Code to Model Fast Electron Beam Transport Through Dense Matter

A PIC （particle-in-cell）-MC （Monte Carlo） code to model electron beam transport into dense matter is developed. The background target is treated as a cold, stationary fluid and the fast electrons as particles with the relativistic motions. The process is described by a particle-in-cell method with consideration of the influence of both the self-generated electric and magnetic fields as well as collisions between the fast electrons and the target. The collisional part of the code is solved by the Monte Carlo-type method. Furthermore by assuming that the background current balances with the fast electron current, the electric field is given by the Ohm＇s law and the magnetic field is calculated from the Faraday＇s law. Both are solved in a two-dimensional cylindrical geometry. The algorithms implemented in the code are demonstrated and the numerical experiments are performed for monoenergy homogeneous fast electron beam transport in an aluminum target when the fields, collision and angular scattering are switched on and off independently.

Forward and reverse electron transport properties across a CdS/Si multi-interface nanoheterojunction

The electron transport behavior across the interface plays an important role in determining the performance of op- toelectronic devices based on heterojunctions. Here through growing CdS thin film on silicon nanoporous pillar array, an untraditional, nonplanar, and multi-interface CdS/Si nanoheterojunction is prepared. The current density versus voltage curve is measured and an obvious rectification effect is observed. Based on the fitting results and model analyses on the forward and reverse conduction characteristics, the electron transport mechanism under low forward bias, high forward bias, and reverse bias are attributed to the Ohmic regime, space-charge-limited current regime, and modified Poole-Frenkel regime respectively. The forward and reverse electrical behaviors are found to be highly related to the distribution of inter- facial trap states and the existence of localized electric field respectively. These results might be helpful for optimizing the preparing procedures to realize high-performance silicon-based CdS optoelectronic devices.

Manipulation and optimization of electron transport by nanopore array targets

The transport of sub-picosecond laser-driven fast electrons in nanopore array targets is studied.Attributed to the generation of micro-structured magnetic fields,most fast electron beams are proven to be effectively guided and restricted during the propagation.Different transport patterns of fast electrons in the targets are observed in experiments and reproduced by particle-in-cell simulations,representing two components:initially collimated low-energy electrons in the center and high-energy scattering electrons turning into surrounding annular beams.The critical energy for confined electrons is deduced theoretically.The electron guidance and confinement by the nano-structured targets offer a technological approach to manipulate and optimize the fast electron transport by properly modulating pulse parameters and target design,showing great potential in many applications including ion acceleration,microfocus x-ray sources and inertial confinement fusion.

Charging dynamics of a polymer due to electron irradiation:A simultaneous scattering-transport model and preliminary results

We present a novel numerical model and simulate preliminarily the charging process of a polymer subjected to electron irradiation of several 10 keV. The model includes the simultaneous processes of electron scattering and ambipolar transport and the influence of a self-consistent electric field on the scattering distribution of electrons. The dynamic spatial distribution of charges is obtained and validated by existing experimental data. Our simulations show that excess negative charges are concentrated near the edge of the electron range. However, the formed region of high charge density may extend to the surface and bottom of a kapton sample, due to the effects of the electric field on electron scattering and charge transport, respectively. Charge trapping is then demonstrated to significantly influence the charge motion. The charge distribution can be extended to the bottom as the trap density decreases. Charge accumulation is therefore balanced by the appearance and increase of leakage current. Accordingly, our model and numerical simulation provide a comprehensive insight into the charging dynamics of a polymer irradiated by electrons in the complex space environment.

Preparation and property of a novel soluble electron transport POSS-based hybrid material

A novel POSS-based organic/inorganic hybrid covalently attached at molecular level, 2-（4-（allyloxy）phenyl）-5-（4-（octyloxy）phenyl）-1,3,4-oxadiazole-POSS （6） （abbreviated as oxadiazole-POSS） was synthesized by Pt（dcp） catalyst. The hybrid was soluble in common organic solvents such as CHCl3, toluene, C2H4Cl2, and THF. Its structures and properties were characterized and evaluated with FTIR, 1^H NMR, 13^C NMR,29^Si NMR, EA, TGA, DSC, GPC, and CV, respectively. The results show that the novel hybrid possesses high thermal stability and good electron injection ability.

Contact effect in the dynamic electron transport of a two-probe mesoscopic conductor

Based on the self-consistent electron dynamic transport theory for multi-probe mesoscopic systems, we calculate the distribution of internal potential, charge density, and ac conductance of a two-probe mesoscopic conductor with wide trapezoid reservoirs, and study the contact effect. The results show that including the contact effect can make a significant difference to the frequency-dependent electron transport properties. In the nonzero frequency case, the internal potential and the charge density are complex with extremely small imaginary parts. Importantly, the imaginary part of the charge density gives rise to a real ac conductance （admittance）, which corresponds to the charge-relaxation resistance.

Electronic Structure and Transport Coefficients of the Thermoelectric Materials Bi_2Te_3 from First-principles Calculations

The electronic structures of bulk Bi_2Te_3 crystals were investigated by the first-principles calculations.The transport coefficients including Seeback coefficient and power factor were then calculated by the Boltzmann theory,and further evaluated as a function of chemical potential assuming a rigid band picture.The results suggest that p-type doping in the Bi_2Te_3 compound may be more favorable than n-type doping.From this analysis results,doping effects on a material will exhibit high ZT.Furthermore,we can also find the right doping concentration to produce more efficient materials,and present the ＂advantage filling element map＂ in detail.

Review of thermal transport and electronic properties of borophene

In recent years, two-dimensional boron sheets （borophene） have been experimentally synthesized and theoretically proposed as a promising conductor or transistor with novel thermal and electronic properties. We first give a general survey of some notable electronic properties of borophene, including the superconductivity and topological characters. We then mainly review the basic approaches, thermal transport, as well as the mechanical properties of borophene with different configurations. This review gives a general understanding of some of the crucial thermal transport and electronic properties of borophene, and also calls for further experimental investigations and applications on certain scientific community.