纳米颗粒在复杂生物介质中的反常扩散

由于生物微环境中存在各向异性等复杂物理因素影响,纳米颗粒在其中的扩散运动表现出反常的特征.反常扩散与生物微环境的功能实现有重要的关联,同时也是流体力学在微纳尺度方向的重要扩展.该综述系统介绍了近年来反常扩散研究的进展,从物理模型、数值模拟、测量方法及实验现象等方面揭示了纳米颗粒在复杂生物介质中的反常扩散机理及特征.该问题在微纳尺度流体力学、生物物理等领域是研究的热点,在理论上和实验时仍有重大挑战,有待进一步深入研究.

基于LAMMPS的含缺陷碳纳米管分子动力学研究

碳纳米管具有结构的均匀性、简单性和材料的稳定性特点,同时也拥有与生物通道相似的输运性质,因此碳纳米管成为观察受限水分子结构、研究受限水分子动力学特性的理想材料。完美的碳纳米管在实际制备中几乎无法获得,管壁中不可避免地存在缺陷,这些缺陷会对碳纳米管的物理特性造成一定程度的影响。本文基于LAMMPS,选用一种含缺陷的碳纳米管,采用分子动力学方法模拟研究了受限体系下水分子在这种含缺陷的碳纳米管中输运的微观行为。结果表明,当相同长度的缺陷出现在管内不同位置时,扩散系数最大可相差70%以上,因此缺陷的位置对水在碳纳米管中的输运有着至关重要的影响,这对碳纳米管的制备及应用具有一定的指导意义。

Fabrication of Polyaniline/Silver Nanocomposite Under Gamma-ray Irradiation

Polyaniline （PANI）/silver composite was one-step synthesized under γ-ray irradiation. The structure of the composite was characterized by Fourier transform infrared spectroscopy, UV-Visible, and X-ray diffraction, which indicated that PANI and face-centered-cubic silver were synthesized under γ-ray irradiation. The reaction mechanism were discussed, which revealed that the PANI was formed by the reaction of aniline cation radicals formed by the reaction of aniline cation and -OH, and Ag was formed by the reaction of Ag＋ and eaq. The morphology of the composite consisted of PANI nanofibers and Ag nanoparticles, and the mechanism of the morphology formation was discussed, which revealed that the rapid mixing like polymerization process might play an important role. It was revealed that the transport behavior of the composite well fitted with the variable-range-hopping model in 80-300 K and deviated from the model below 80 K.

MoO_3改善接触的薄层MoS_2 N-型场效应管的电输运性质研究

本文利用三氧化钼(MoO_3)/金(Au)作为二硫化钼(MoS2)场效应晶体管的电极,得到了接触改善的N型二硫化钼场效应晶体管,并对其输运性质进行了变温测量.研究发现,将氧化钼作为在二硫化钼与金属电极之间的过渡层,可以很好地改善二硫化钼场效应器件的肖特基接触:对于2nm厚度的二硫化钼,其室温迁移率可达25cm2V^(–1)s^(–1),与没有三氧化钼接触的器件相比,室温迁移率提高了近16倍;对于8nm厚度的二硫化钼,其低温迁移率最高可达100cm^2V^(–1)s^(–1).优化后的电接触使得我们可以提取出二硫化钼器件本征的低温输运特性,并发现缺陷杂质对载流子的散射是影响器件输运性质的主要原因;其中在少层二硫化钼中,缺陷杂质的散射作用随着载流子浓度的增加、屏蔽能力的增强而减少.这种改善接触的方法同样适用于其他过渡金属硫族化合物.

Nanoparticle Transport and Coagulation in Bends of Circular Cross Section via a New Moment Method

Transport of nanoparticles and coagulation is simulated with the combination of CFD in a circular bend. The Taylor-expansion moment method(TEMOM)is employed to study dynamics of nanoparticles with Brownian motion,based on the flow field from numerical simulation.A fully developed flow pattern in the present simulation is compared with previous numerical results for validating the model and computational code.It is found that for the simulated particulate flow system,the particle mass concentration,number concentration,particle polydispersity, mean particle diameter and geometric standard deviation over cross-section increase with time.The distribution of particle mass concentration at different time is independent of the initial particle size.More particles are concen-trated at outer edge of the bend.Coagulation plays more important role at initial stage than that in the subsequent period.The increase of Reynolds number and initial particle size leads to the increase of particle number concentration.The particle polydispersity,mean particle diameter and geometric standard deviation increase with decreasing Reynolds number and initial particle size.

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

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

Negative Differential Resistance and Spin-Filtering Effects in Zigzag Graphene Nanoribbons with Nitrogen-Vacancy Defects

We explore the electronic and transport properties of zigzag graphene nanoribbons （GNRs） with nitrogen-vacancy defects by performing fully self-consistent spin-polarized density functional theory calculations combined with non-equilibrium Green＇s function technique. We observe robust negative di erential resistance （NDR） effect in all examined molecular junctions. Through analyzing the calculated electronic structures and the bias-dependent transmission coefficients, we find that the narrow density of states of electrodes and the bias-dependent effective coupling between the central molecular orbitals and the electrode subbands are responsible for the observed NDR phenomenon. In addition, the obvious di erence of the transmission spectra of two spin channels is observed in some bias ranges, which leads to the near perfect spin-filtering effect. These theoretical findings imply that GNRs with nitrogenvacancy defects hold great potential for building molecular devices.

Response Characteristics of Strain Sensors Based on Closely Spaced Nanocluster Films with Controlled Coverage

Flexible strain sensor devices were fabricated by depositing Pd nanoclusters on PET membranes patterned with interdigital electrodes. The sensors responded to the deformation of the PET membranes with the conductance changes of the nanocluster films and were characterized by both high gauge factor and wide detection range. The response characteristics of the strain sensors were found to depend strongly on the nanocluster coverage, which was attributed to the percolative nature of the electron transport in the closely spaced nanocluster arrays. By controlling the nanocluster deposition process, a strain sensor composed of nanocluster arrays with a coverage close to the effective percolation threshold was fabricated. The sensor device showed a linear response with a stable gauge factor of 55 for the applied strains from the lower detection limit up to 0.3%. At higher applied strains, a gauge factor as high as 200 was shown. The nanocluster films also demonstrated the ability to response to large deformations up to 8% applied strain, with an extremely high gauge factor of 3500.

Nonlinear Diffusion and Transient Osmosis

We investigate both analytically and numerically the concentration dynamics of a solution in two containers connected by a narrow and short channel, in which diffusion obeys a porous medium equation. We also consider the variation of the pressure in the containers due to the flow of matter in the channel. In particular, we identify a phenomenon, which depends on the transport of matter across nano-porous membranes, which we call ＂transient osmosis＂. We find that nonlinear diffusion of the porous medium equation type allows numerous different osmotic-like phenomena, which are not present in the case of ordinary Fickian diffusion. Experimental results suggest one possible candidate for transiently osmotic processes.

Band Structure and Electron Transport of Bulk Based on an Ensemble Monte Carlo Calculation

The current demand growth of new components capable of operating at high power, high frequency, high temperatures and convergence towards miniaturization has lead to the development of new fields of nanotechnology based on II-VI semiconductor Interest in nanostructure：s based on II-VI semiconductor narrow gap containing mercury （such as super lattices HgTe/CdTe） was due to their advantages over alloys with cadmium telluride Mercury （MCT： HgCdTe）. The ternary alloy is a semiconductor band-gap direct, in that work the main interest is about the ternary compound. The results obtained are very satisfactory, they are compared with experimental results, and are in good agreement. These results are very promising and open new perspectives for the realization of solar cells and applications in the field of sensors.

A high-volumetric-capacity bismuth nanosheet/graphene electrode for potassium ion batteries

Potassium ion batteries(PIBs)with high-volumetric energy densities are promising for next-generation low-cost energy storage devices.Metallic bismuth(Bi)with a structure similar to graphite,is a promising anode material for PIBs due to its high theoretical volumetric capacity(3763 mA h cm^−3)and relatively low working potential(−2.93 V vs.standard hydrogen electrode).However,it experiences severe capacity decay caused by a huge volume expansion of Bi when alloying with potassium.This study reports a flexible and free-standing Bi nanosheet(BiNS)/reduced graphene oxide composite membrane with designed porosity close to the expansion ratio of BiNS after charging.The controlled pore structure improves the electron and ion transport during cycling,and strengthens the structural stability of the electrode during potassiation and depotassiation,leading to excellent electrochemical performance for potassium-ion storage.In particular,it delivers a high reversible volumetric capacity of 451 mA h cm^−3 at the current density of 0.5 A g^−1,which is much higher than the previously reported commercial graphite material.

Complete thermoelectric benchmarking of individual InSb nanowires using combined micro-Raman and electric transport analysis

Nanowires （NWs） are ideal nanostructures for exploring the effects of low dimensionality and thermal conductivity suppression on thermoelectric behavior. However, it is challenging to accurately measure temperature gradients and heat flow in such systems. Here, using a combination of spatially resolved Raman spectroscopy and transport measurements, we determine all the thermoelectric properties of single Se-doped InSb NWs and quantify the figure of merit ZT. The measured laser-induced heating in the NWs and associated electrical response are well described by a 1D heat equation model. Our method allows the determination of the thermal contact resistances at the source and drain electrodes of the NW, which are negligible in our system. The measured thermoelectric parameters of InSb NWs agree well with those obtained based on field-effect transistor Seebeck measurements.

Electron transport properties of magnetic granular films

In this paper,we present a review of electron transport properties of magnetic granular films.Magnetic granular films are nanocomposite materials which consist of magnetic nanoparticles embedded in a nonmagnetic matrix or assembling of magnetic nanoparticles.According to the style of the nonmagnetic matrix,microstructure and the electron transport mechanism of the films,the magnetic granular films were divided into three groups:(1) magnetic metal-metal granular films,(2) magnetic metal-insulator granular films and(3) magnetic nanocluster-assembled granular films.Moreover,we also systematically review the magnetic properties,transport properties and magnetoresistance effect of size-monodispersed Co and Fe nanocluster-assembled films.

Cotunneling transport in ultra-narrow gold nanowire bundles

We investigate the charge transport in close-packed ultra-narrow （1.5 nm diameter） gold nanowires stabilized by oleylamine ligands. We give evidence of charging effects in the weakly coupled one-dimensional （1D） nanowires, monitored by the temperature and the bias voltage. At low temperature, in the Coulomb blockade regime, the current flow reveals an original cooperative multi-hopping process between 1D-segments of Au-NWs, minimising the charging energy cost. Above the Coulomb blockade threshold voltage and at high temperature, the charge transport evolves into a sequential tunneling regime between the nearest- nanowires. Our analysis shows that the effective length of the Au-NWs inside the bundle is similar to the 1D localisation length of the electronic wave function （of the order of 120 nm _＋ 20 nm）, but almost two orders of magnitude larger than the diameter of the nanowire. This result confirms the high structural quality of the Au-NW segments.

Strain-tunable electronic and transport properties of MoS2 nanotubes

Using density functional theory calculations, we have investigated the mechanical properties and strain effects on the electronic structure and transport properties of molybdenum disulfide （MoS2） nanotubes. At a similar diameter, an armchair nanotube has a higher Young＇s modulus and Poisson ratio than its zigzag counterpart due to the different orientations of Mo-S bond topologies. An increase in axial tensile strain leads to a progressive decrease in the band gap for both armchair and zigzag nanotubes. For armchair nanotube, however, there is a semiconductor-to-metal transition at the tensile strain of about 8%. For both armchair and zigzag nanotubes, the effective mass of a hole is uniformly larger than its electron counterpart, and is more sensitive to strain. Based on deformation potential theory, we have calculated the carrier mobilities of MoS2 nanotubes. It is found that the hole mobility is higher than its electron counterpart for armchair （6, 6） nanotube while the electron mobility is higher than its hole counterpart for zigzag （10, 0） nanotube. Our results highlight the tunable electronic properties of MoS2 nanotubes, promising for interesting applications in nanodevices, such as opto-electronics, photoluminescence, electronic switch and nanoscale strain sensor.

Mg doping and native N vacancy effect on electronic and transport properties of AlN nanowires

The effects of Mg doping(MgAl) and native N vacancy(VN) on the electronic structures and transport properties of Al N nanowire(Al NNW) were theoretically investigated by using density functional theory. Either the MgAl defect or the VN defect prefers to be formed on the Al NNW surfaces. Both MgAl and VN defects could increase the conductivity owing to introducing a defect band inside the band gap of Al N and split the Al N band gap into two subgaps. The defect concentration has little influence on the magnitude of the subgaps. The MgAl serves as a shallow acceptor rendering the nanowire a p-type conductor. The VN introduces a deep donor state enabling the nanowire an n-type conductor. The MgAl systems exhibit higher conductivity than the VN ones owing to the narrow subgaps of MgAl systems. The conductivity is roughly proportional to the defect concentration in the MgAl and VN defect systems. When the MgAl and VN coexist, the hole state of the MgAl defect and the electron state of the VN defect will compensate each other and their coupling state appears just above the valence-band maximum leading to a little decrease of the band gap compared with the pure Al NNW, which is unfavorable for the enhancing of the conductivity.

Contactless probing of the intrinsic carrier transport single-walled carbon nanotubes

Intrinsic carrier transport properties of single-walled carbon nanotubes have been probed by two parallel methods on the same individual tubes： The contactless dielectric force microscopy （DFM） technique and the conventional field-effect transistor （FET） method. The dielectric responses of SWNTs are strongly correlated with electronic transport of the corresponding FETs. The DC bias voltage in DFM plays a role analogous to the gate voltage in FET. A microscopic model based on the general continuity equation and numerical simulation is built to reveal the link between intrinsic properties such as carrier concentration and mobility and the macroscopic observable, i.e. dielectric responses, in DFM experiments. Local transport barriers in nanotubes, which influence the device transport behaviors, are also detected with nanometer scale resolution.

Asymmetric transportation induced by thermal noise at the nanoscale

Based on a simple model, we theoretically show that asymmetric transportation is possible in nanoscale systems experiencing thermal noise without the presence of extemal fluctuations. The key to this theoretical advance is that the correlation lengths of the thermal fluctuations become significantly long for nanoscale systems. This differs from macroscopic systems in which the thermal noises are usually treated as white noise. Our observation does not violate the second law of thermodynamics, since at the nanoscale, extra energy is required to keep the asymmetric structure against thermal fluctuations.

Buildup of Sn@CNT nanorods by in-situ thermal plasma and the electronic transport behaviors

Monocrystal Sn nanorods encapsulated in the multi-walled carbon nanotubes(Sn@CNT NRs), were fabricated by a facile arc-discharge plasma process, using bulk Sn as the raw target and methane as the gaseous carbon source. The typical Sn@CNT NRs are 40–90 nm in diameter and400–500 nm in length. The CNTs protect the inner Sn nanorods from oxidation. Temperature dependent I–V curve and electronic resistance reveal that the dielectric behavior of Sn@CNT NRs is attributed to the multi-wall CNTs shell and follows Mott-David variable range hopping [ln R(T)∝T-1/4]model above the superconducting critical temperature of3.69 K, with semiconductor–superconductor transition(SST).Josephson junction of Sn/CNT/Sn layered structure is responsible for the superconducting behavior of Sn@CNT NRs.

Quantum Spin Transport in Rashba Spin-Orbit-Coupled Graphene Nanoflakes

We study the spin-resolved transport in a two-terminal graphene nanoflake device with a Rashba spinorbit coupling region in the center of the device. The Green's function method is applied to the system and the spin transmission probability and the spin polarization in x, y, and z directions are calculated. It is found that the components of the spin polarization are antisymmetric functions of Fermi energy, which oscillate and decay to the zero with increasing the energy for all values of the Rashba strength. It is shown that by tuning the Rashba strength via a gate voltage and/or changing the size of the system, it is possible to control the sign and magnitude of the spin polarization. The system represented here is a typical candidate for full electrical spintronic devices based on the carbon materials that are used for spin filtration.