Search

Very recently, half-hydrogenated germanene has been achieved in an experiment. In this paper, we investigate the effects of tetracyanoquinodimethane (TCNQ) molecular adsorption and strain on the electronic properties of half-hydrogenated germanene through first-principles. As an electron-acceptor molecule, TCNQ is exploited to non-covalently functionalize the half-hydrogenated germanene. However, this physical adsorption induces a ferromagnetic semiconductor–metal transition in half-hydrogenated germanene due to charge transfer from the substrate to the TCNQ molecule. More importantly, the superstructure of half-hydrogenated germanene/TCNQ is extremely sensitive to biaxial tensile strain. Under the biaxial tensile strain of 0.25%, the ferromagnetic semiconductor–metal transition induced by molecular adsorption can surprisingly be overturned. Meanwhile, a strong p-type doping is exhibited. Remarkably, it would return from a ferromagnetic semiconductor to a metal again when the biaxial tensile strain increases to 1.5%. Our analysis based on the structural and electronic properties of half-hydrogenated germanene/TCNQ indicates that such metal–semiconductor–metal transition in half-hydrogenated germanene/TCNQ under biaxial tensile strain may originate from the strong local deformation, resulting in the energy of the valence band maximum decreasing below or increasing above the Fermi level. [ABSTRACT FROM AUTHOR]

We analyze a phase-sensitive contribution to the oscillating magnetoresistance induced by the combined driving of two microwave fields having commensurate frequencies ω1 and ω2 (m1ω1+m2ω2=0 for at least a set of nonzero integers m1 and m2), based on the balance-equation approach to magnetotransport for high-density two-dimensional electron systems. This commensurate oscillating photoresistance not only depends on the frequencies and polarizations of both microwaves, but varies drastically when changing the relative phases of two incident radiation fields. It shows up most significantly in the case of ω2/ω1=3 and may lead to a phase-controllable change of more than a factor of two in the total magnetoresistivity in the vicinity of ω1/ωc=1.5 and 2.5 (ωc is the cyclotron frequency), when both radiation fields are linearly x-direction polarized. [ABSTRACT FROM AUTHOR]

This study is focused on the tribological properties of micro- and nano-crystalline diamond (MCD and NCD), non-hydrogenated and hydrogenated diamond-like carbon (DLC and DLC-H) and nitrogen-based (CrN, TiN and TiAlN) coatings sliding against the super alloy Inconel 718, in terms of the maximal and average coefficients of frictions (COFs), the worn morphologies and the specific wear rates, by the rotating ball-on-plate configuration under dry condition. The results show that the nitrogen-based films show comparable COFs and wear rates with the WC–Co substrates. The DLC and DLC-H show lower COFs compared with the nitrogen-based films. Furthermore, their wear resistance is limited due to their low thickness compared with MCD and NCD, which have the same elemental composition. The DLC-H coating exhibits much lower wear rate compared with the DLC coating, which may be derived from the passivation of dangling bonds by the linking of H to C atoms. The MCD and NCD films show the lowest average COFs and mild wear after tribotests, due to their high hardness and low adhesive strength between pure diamond and the super alloy. Among all the tested films, the NCD film-based tribopair presents the lowest maximal and average COFs, tiny wear debris particles, mild wear of ball and plate without scratching grooves, indicating that the NCD film may be suitable to be deposited on cutting tools for super alloy machining. [ABSTRACT FROM AUTHOR]

We analyze the effects of a distortion of the nuclear potential of a molecular quantum dot (QD) as well as a shift in its equilibrium position on nonequilibrium-vibration-assisted tunneling through the QD with a single level ([variant_greek_epsilon]d) coupled to the vibrational mode. For this purpose, we derive an explicit analytical expression for the Franck–Condon (FC) factor for a displaced-distorted oscillator surface of the molecule and establish rate equations in the joint electron-phonon representation to examine the current-voltage characteristics and zero-frequency shot noise and skewness as well. Our numerical analysis shows that the distortion has two important effects. The first one is that it breaks the symmetry between the excitation spectra of the charge states, leading to asymmetric tunneling properties with respect to [variant_greek_epsilon]d>0 and [variant_greek_epsilon]d<0. Second, distortion (frequency change in the oscillator) significantly changes the voltage-activated cascaded transition mechanism and consequently gives rise to a different nonequilibrium vibrational distribution from that of the case without distortion. Taken in conjunction with strongly modified FC factors due to distortion, this results in some new transport features: the appearance of strong negative differential conductance even for a single-level QD with symmetric tunnel couplings, a giant Fano factor even for a molecule with an extremely weak electron-phonon interaction, and enhanced skewness that can have a large negative value under certain conditions. [ABSTRACT FROM AUTHOR]

We present a kinetic equation approach to investigate dc transport properties of graphene in the diffusive regime considering long-range electron-impurity scattering. In our study, the effects of interband correlation (or polarization) on conductivity are taken into account. We find that the conductivity contains not only the usual term inversely proportional to impurity density Ni but also an anomalous term that is linear in Ni. This leads to a minimum in the density dependence of conductivity when the electron density Ne is equal to a finite critical value Nc. The effects of various scattering potentials on the conductivity minimum are also analyzed. Using typical experimental parameters, we find that for random-phase-approximation–screened electron-impurity scattering, the minimum conductivity is about 4.42e2/h when Ne≈0.11Ni, and the conductivity varies almost linearly with the electron density for Ne>Ni. [ABSTRACT FROM AUTHOR]

We examine the shot noise spectrum properties of coherent resonant tunneling in coupled quantum dots (CQDs) in both series and parallel arrangements by means of quantum rate equations and MacDonald’s formula. Our results show that for a series-CQD with a relatively high dot-dot hopping Ω and Ω/Γ>=1 (Γ denotes the dot-lead tunnel-coupling strength), the noise spectrum exhibits a dip at the Rabi frequency 2Ω in the case of noninteracting electrons, but the dip is supplanted by a peak in the case of strong Coulomb repulsion; furthermore, it becomes a dip again for a completely symmetric parallel-CQD by tuning the enclosed magnetic flux. [ABSTRACT FROM AUTHOR]

Reports on a study which analyzed the scattering for the intra- and intersubband transitions of electrons in a GaAs/AlAs quantum well with a central AlAs thin layer assisted by the emission and absorption of optical phonon modes. Application of transversal electric field through the structure; Frohlich interaction and electron mobility; Antisymmetric interface phonon modes.

Fully-hydrogenated germanene, named germanane, represents a new nanostructured material for a variety of potential applications, such as electronics and optoelectronics. However, a critical requirement for developing practical and reliable electronic devices based on germanane consists of achieving a flexibly controllable charge carrier and doping level. Different to the conventional doping methods such as ion implantation and diffusion, by first-principles calculations we demonstrate that tetracyanobenzene (TCNB) molecular adsorption could introduce effective p-type doping in germanane due to the combination of germanane with electroactive acceptor molecule TCNB. The corresponding energy difference between the empty band minimum of the dopant and the valence band maximum for electron excitation is 0.173 eV. More importantly, this nondestructive p-type doping could be linearly tuned under an external E-field. Analysis of charge transfer by means of the equivalent capacitor model and the shift of energy levels in the superstructure of germanane/TCNB further reveals that the superposition of the external E-field and molecular adsorption-induced internal E-field plays a key role in the charge transfer between TCNB and germanane, especially in achieving a controllable p-type molecular doping level in germanane. Such convenient and flexible E-field-engineering of p-type molecular doping in germanane would be very helpful for potential applications of germanane-based electronic and optoelectronic devices in the future. [ABSTRACT FROM AUTHOR]

Presents a study which developed a non-Boltzmann theory of a steady-state transport for two-dimensional systems in a strong electric field which includes a force- and an energy-balance equation. Method of the study; Results and discussion; Conclusion.

Proposes balance equations for high-field electron transport in nonparabolic multiband semiconductors. Relation between electron energy and lattice wave vector; Description of a balance equation for multiband systems; Findings of the study.

Deals with a study which investigated Bragg scattering and effective force-balance equations in superlattice miniband transport. Background to the study; Background on the Büttiker-Thomas momentum balance equation; Details on the acceleration and energy balance equations.

Investigates the linear and nonlinear miniband electron transport through a laterally confined superlattice using the balance-equation theory. Acceleration and energy-balance equations; Calculation of the linear and nonlinear properties of GaAs/AlAs superlattices; Linear mobilities.

Presents a study which examined linear and nonlinear characteristics of superconductor superlattice perpendicular conduction. Linear mobilities from the balance-equation theory; Comparisons between theories and experiments; Conclusions.

In this study, the effect of diamond interlayer on the tribological properties of titanium aluminum nitride (TiAlN) film sliding against medium carbon steel is investigated in dry rotary friction tests, by evaluating the coefficients of friction (COFs), wear rates, worn surfaces and element transitions of the contacted surfaces in the cemented carbide (WC-Co)-steel, TiAlN-steel, microcrystalline diamond (MCD)-steel, TiAlN/MCD-steel, micro- and nano-crystalline diamond (MNCD)-steel and TiAlN/MNCD-steel contacting pairs. It is found that compared with the TiAlN monolayer, the TiAlN/MCD bilayer film shows 57% higher COF, while the COF of TiAlN/MNCD multilayer inversely drops as much as 54%, due to the distinguished surface diamond grain morphologies of the MCD and MNCD interlayers as well as the copied effect of the TiAlN layer with relatively small thickness. Meanwhile, the diamond interlayer can provide robust load support for the top TiAlN layer, induce the wear mechanism transform from the abrasive wear to adhesive wear, and result in the mild wear of TiAlN/MCD and TiAlN/MNCD multilayers compared to the TiAlN monolayer. Moreover, the softer TiAlN top layer on MCD and MNCD interlayers can effectively improve the storage capacity of element oxygen and worn steel ball debris as well as accelerating the surface chemical reactions to form a smoother continuous ionic metal oxides tribofilm in the contacted zones due to its good self-lubricating property. Among all the hard coatings discussed when sliding against medium carbon steel, the TiAlN/MNCD coating shows the lowest COF and mild wear, due to the robust load support capacity of the beneath MNCD layer as well as the good self-lubricated and tribofilm formation capacity of the top TiAlN layer, which shows broad application potential in carbon steel machining. [ABSTRACT FROM AUTHOR]

The effects of both molecular adsorption and external electric field on the electronic properties of germanene are investigated through first-principles calculations in this work. The molecular adsorption-induced intrinsic electric field by small molecules (SMs) breaks the symmetry of two sublattices in germanene, leading to a band gap opening from zero to 3.2 meV, even up to 81.0 meV. Under an external electric field, a wide ranging linearly tunable band gap (0–69.39 meV for the germanene/methane system and 37.66–134.17 meV for the germanene/ammonia system) can be realized, which is merely determined by the strength of the composited electric field independent of its direction. More importantly, the band gap of germanene/SMs can be closed and reopened under a critical electric field. On the other hand, the mechanism of charge transfer between germanene and SMs under an external electric field is revealed by an equivalent capacitor model to explain the tunable charge transfer. The composited field-induced charge transfer could be promoted when an external electric field and a molecular adsorption-induced internal electric field have the same direction. Otherwise, the charge transfer will be inhibited. Particularly, the tunable electronic properties of germanene are sensitive to the concentration of molecular adsorption under an electric field, representing multiple-effects that would significantly enhance the performance of germanene for electronic devices in the future. [ABSTRACT FROM AUTHOR]

The demand for better tools for machining printed circuit boards (PCBs) is increasing due to the extensive usage of these boards in digital electronic products. This paper is aimed at optimizing coating type on micro drills in order to extend their lifetime in PCB machining. First, the tribotests involving micro crystalline diamond (MCD), nano crystalline diamond (NCD) and bare tungsten carbide (WC-Co) against PCBs show that NCD-PCB tribopair exhibits the lowest friction coefficient (0.35) due to the unique nano structure and low surface roughness of NCD films. Thereafter, the dry machining performance of the MCD- and NCD-coated micro drills on PCBs is systematically studied, using diamond-like coating (DLC) and TiAlN-coated micro drills as comparison. The experiments show that the working lives of these micro drills can be ranked as: NCDTiAlNDLCMCDbare WC-Co. The superior cutting performance of NCD-coated micro drills in terms of the lowest flank wear growth rate, no tool degradation (e.g. chipping, tool tipping) appearance, the best hole quality as well as the lowest feed force may come from the excellent wear resistance, lower friction coefficient against PCB as well as the high adhesive strength on the underneath substrate of NCD films. [ABSTRACT FROM AUTHOR]

A momentum balance equation is developed to investigate the magnetotransport properties in monolayer molybdenum disulphide when a strong perpendicular magnetic field and a weak in-plane electric field are applied simultaneously. At low temperature, in the presence of intravalley impurity scattering, Shubnikov–de Haas oscillation shows up accompanied by a beating pattern arising from large spin splitting and its period may halve due to the high-order oscillating term at large magnetic field for samples with ultrahigh mobility. In the case of intervalley disorders, there exists a magnetic-field range where the magnetoresistivity almost vanishes. For a low-mobility layer, a phase inversion of oscillating peaks is acquired in accordance with recent experiment. At high temperature when Shubnikov–de Haas oscillation is suppressed, the magnetophonon resonances induced by both optical phonons (mainly due to homopolar and Frohlich modes) and acoustic phonons (mainly due to intravalley transverse and longitudinal acoustic modes) emerge for a suspended system with high mobility. For the single layer on a substrate, another resonance due to surface optical phonons may occur, resulting in a complex behavior of the total magnetoresistance. The beating pattern of magnetophonon resonance due to optical phonons can also be observed. However, for a nonsuspended layer with low mobility, the magnetoresistance oscillation almost disappears and the resistivity increases with field monotonically. [ABSTRACT FROM AUTHOR]

In this paper, we studied the structural and electronic properties of core/shell nanocables composed of cubic silicon carbide nanowires (β-) and boron nitride nanotubes (BNNT) using first-principles pseudopotential plane wave method within density functional theory. Our results show that the β-/BNNT heterojunction structures are metallic, which primarily originates from the contributions of the BNNTs and the surfaces of s. The BNNTs exhibit metallic characters after the nanowires are inserted. The transition of the BNNTs is attributed to the charge transfer between BNNTs and s. [ABSTRACT FROM AUTHOR]

The platinum copper alloy nanocrystals(NCs) have generated muchinterest because of their wide applications in fuel cells due primarilyto their good catalytic performance and to decreasing sensitivitytoward CO poisoning. The exact atomic-level morphology of platinumcopper alloy NCs is still not clear in the literature, and researchto understanding the poisoning mechanism is still insufficient todate. In this article, we report on density functional calculationsof small PtnCu clusters and their adsorptionof a CO molecule that provide evidence for degrading adsorption ofthe CO molecule compared to pure platinum clusters. The lowest-energygeometries of PtnCu and PtnCuCO clusters have been identified. The CO moleculeprefers to be adsorbed on the nearest platinum atom by the C-end-onmode, forming linear or quasi-linear O–C–Pt structures.The adsorption energies indicate that the introduction of a copperatom decreases the adsorption ability of the CO molecule. The localdensity of states of the representative clusters is used to characterizethe adsorption properties of the CO molecule on the PtnCu clusters. Results from our theoretical calculationscan be helpful for understanding the poisoning mechanism of the COmolecule on the platinum copper alloy NCs. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents the effects of a planned CO2 injection on fault stability at Tomakomai offshore, Hokkaido, Japan. Using slip tendency scheme, the artesian reservoir is estimated to be naturally at moderate slip level around 0.5 at assumed faults optimally oriented for slip. The analysis results indicate that the planned injection has limited effects on fault stability at the site and the increased slip tendency is unlikely to be “ready-to-slip”. However, the attention is required at the vicinity of the injection point as well as the far pre-existing fault where would be the slippiest due to the high background value. [Copyright &y& Elsevier]

A balance-equation scheme is developed to investigate the magnetotransport in a dc current biased graphene. We examine the Shubnikov-de Haas oscillation under a nonzero bias current. With an increase in the current density, the oscillatory differential resistivity exhibits phase inversion, in agreement with recent experimental observation. In the presence of surface optical phonons, a second phase inversion may occur at higher dc bias due to the reduced influence of electron heating and the enhanced direct effect of current on differential magnetoresistivity. We also predict the appearance of current-induced magnetoresistance oscillation in suspended graphene at lower magnetic fields and larger current densities. For the graphene mobility currently available (≈20 m2/V s), the oscillatory behavior may be somewhat altered by magnetophonon resonance arising from intrinsic acoustic phonon under finite bias current conditions. [ABSTRACT FROM AUTHOR]

We examine the effect of changing the linear polarization angle θ of incident microwaves with respect to the dc current on radiation-induced magnetoresistance oscillations in a two-dimensional (2D) system within the balance-equation formulation of the photon-assisted magnetotransport model, considering the radiative decay as the sole damping mechanism. At an extremum the amplitude of oscillatory magnetoresistance Rxx exhibits a sinusoidal, up to a factor of 5, magnitude variation with rotating the polarization angle θ. The maximal amplitude shows up generally at a nonzero θ, which is dependent upon the extremum in question, the 2D electron setup, the radiation frequency, and the magnetic field orientation. These results provide a natural explanation for the experimental observations by Mani et al. [ Phys. Rev. B 84 085308 (2011)] and Ramanayaka et al. [ Phys. Rev. B 85 205315 (2012)]. [ABSTRACT FROM AUTHOR]

The low-lying candidates of hydrated divalent lead ion clusters [n]2+ with up to n = 17 have been extensively studied by using density functional theory (DFT) at B3LYP level. The optimized structures show that for n = 5-13 the lowest-energy structures prefer tetracoordinate with hemi-directed geometries, while the best candidates with n = 14-17 are hexacoordinate with holo-directed geometries, which is just consistent with the experimental observation. Furthermore, the origin of hemi-directed and holo-directed geometries has been revealed. It is found that in the hemi-directed geometries, the lone pair orbital has p character and fewer electrons are transferred from the water molecules to the ion. Contrarily, in the holo-directed geometries, the lone pair orbital has little or no p character and more electrons are transferred to the ion. On the other hand, the proton transfer reactions of the [n]2+(n = 2, 4, 8) complexes have been examined, from which the predicted products of these complexes are in good agreement with the experimental observation. [ABSTRACT FROM AUTHOR]

We examine the nonlinear magnetoresistance oscillations in a dc-biased high-mobility two-dimensional electron system irradiated by intense microwaves with a current-controlled balance-equation model for multi-photon-assisted magnetotransport. It is shown that the maxima/minima positions, particularly the oscillation period of the differential resistance as a function of the ratio of the microwave frequency ω to the cyclotron frequency ωc, strongly depend on the radiation intensity under a large bias dc current density. Theoretical predictions well reproduce the recent experimental findings by Khodas et al. Phys. Rev. Lett. 104 206801 (2010), and support the multiphoton origin of these unusual magnetoresistance oscillations. [ABSTRACT FROM AUTHOR]

The reservoir quality of Jurassic and Triassic fluvial and lacustrine-deltaic sandstones in the intracratonic Ordos Basin is strongly influenced by depositional facies and various types of diagenetic modifications. The fluvial sandstones have higher average He-porosity and permeability (14.8% and 12.7 mD, respectively) than the deltaic sandstones (9.8% and 5.8 mD, respectively). In addition to extensive mechanical compaction, eodiagenesis (220–97 Ma; depth < 2000 m; T < 70°C) has resulted in dissolution and kaolinitization of detrital silicates in the Jurassic fluvial sandstones, and in smectite infiltration and minor cementation by calcite and siderite in the Triassic fluvial and deltaic sandstones. Pervasive eogenetic carbonate cementation (> 20 vol.%) occurred in Triassic deltaic siltstones and very fine-grained sandstones which are closely associated with organic-rich mudstones. Mesodiagenesis (97–65 Ma), which occurred during rapid subsidence to depths of 3700–4400 m, resulted in the albitization of plagioclase, checmical compaction, the conversion of kaolinite into dickite, and cementation by quartz overgrowths, chlorite, illite, ankerite (δ13CVPDB=−2.4‰ to +2.6‰; δ18OVPDB=−21.5‰ to −10‰) and calcite (δ13CVPDB=−4.7‰ to +3.7‰; δ18OVPDB=−21.8‰ to −13.4‰). Oil emplacement (95 Ma) retarded cementation by mesogenetic quartz and carbonate but had little influence on dickite, illite and chlorite formation. Retardation of quartz cementation was also due to the presence of chlorite fringes around detrital quartz grains. Dickitization of eogenetic kaolinite together with the short residence time at maximum burial temperatures (105–124°C) has retarded the albitization of K-feldspars and illite formation and hence prevented severe permeability destruction. Telodiagenesis, which occurred after uplift (Eocene to end-Neogene), caused slight dissolution and kaolinitization of feldspars. This study demonstrates that despite complex patterns of diagenetic modifications in the Triassic and Jurassic successions, depositional porosity and permeability are better preserved in fluvial meandering channel sandstones than in deltaic sandstones. These results should be important for modelling of reservoir-quality distribution and exploration risk evaluation in the basin. [ABSTRACT FROM AUTHOR]

The spin Hall effect provides a new possible way to effectively inject spins into paramagnetic semiconductors. Here, we investigate the spin-Hall effect in a p-type Luttinger semiconductor employing a two-band kinetic equation analysis. The long-range disorder effect on spin-Hall current (SHC) is considered within the self-consistent Born approximation. We find that in addition to the intrinsic SHC proposed previously, there is a nonvanishing SHC that originates from long-range electron-impurity scattering, but which is independent of impurity density in the diffusive regime. This SHC has an opposite sign from the intrinsic one, leading to a significant reduction of the total SHC. We also carry out a numerical analysis of the hole density dependencies of SHC and spin mobility, finding that with increasing hole density, the SHC first increases and then falls, while the spin mobility monotonically decreases. [ABSTRACT FROM AUTHOR]

Presents a study that investigated the magnetic contribution and the charge density distribution in nickel-manganese-gallium alloys by using the first-principles discrete variational method. Interactions between central manganese atoms and the surrounding atoms; Interatomic energy difference between ferromagnetic (FM) and nonferromagnetic (NM) phases; Calculations on the electronic structure of the FM and NM phases in the Heusler alloy nickel-manganese-gallium.

: We study the localization properties of electrons in a two-dimensional model with on-site energies exhibiting long-range correlated disorder. The localization length and conductance of the system are calculated by using the finite size scaling method combined with transfer matrix technique. In the presence of long-range correlations, we find that there is a continuous line of fixed points indicating that the system undergoes a disorder driven Kosterlitz-Thouless-type metal-insulator transition. [ABSTRACT FROM AUTHOR]