将三角形六边硼氮碳(h-BNC)和三角形石墨烯(TG)夹在两个扶手椅型石墨烯纳米带电极之间,构建了三明治异质结.第一性原理计算表明,当顶点原子由氮和碳(硼和碳)连接时,出现了正向(反向)整流特性.对于特定的连接方式,h-BNC中元素比例p越大,正向(反向)整流比越大.提出的整流机制为控制基于TG的纳米器件整流特性提供了理论参考.

构建了由扶手椅型石墨烯和六方氮化硼(石墨烯/h-BN)杂化纳米带组成的异质结,利用密度泛函理论结合非平衡格林函数方法研究了异质结的电流整流特性.计算结果表明,具有较小(大)带宽的异质结出现了新奇的反向(正向)整流行为,而整流方向与异质结的界面类型无关.研究表明,可通过控制石墨烯/h-BN异质结的宽度设计出具有反转整流特性的纳米器件.

We fused zigzag graphene to boron nitride nanoribbons by gradually doping C atoms at only one edge of the ribbons to design a hybridized ZBxNyCz (x + y + z = 12) structure. To create asymmetric edge hydrogenation, the ZBxNyCz ribbons were monohydrogenated (N–H) at one edge and dihydrogenated (C–H2) at the opposite edge, and the structure was subsequently labeled as H-ZBxNyCz-H2. On the basis of density functional theory and non-equilibrium Green’s function, our simulation revealed that H-ZBxNyCz-H2-based devices present a variety of abnormal spin-polarized transport properties. When the value of x and y in the H-ZBxNyCz-H2 structure is not equal (i.e., z is an odd number), the spin-polarized currents are restricted, regardless of their ferromagnetic (FM) or anti-ferromagnetic (AFM) state. When x is equal to y (i.e., z is an even number), the H-ZBxNyCz-H2 structure exhibits negative differential resistance and spin-filtering features in the FM state. Conversely, in the AFM state, the spin-polarized currents of the structure exhibit an exceptional oscillation effect with spin polarization as high as 100% at certain bias voltages. By adjusting the width of graphene and the spin states, the resulting hybridized H-ZBxNyCz-H2 structure can be potentially applied to the fabrication of spin nanodevices with exotic functionalities.

The hetero-junctions composed of armchair graphene and hexagonal boron nitride (graphene/ h -BN) hybridized nano-ribbons are constructed, and their current rectification characteristics are investigated by using the density functional theory in combination with the non-equilibrium Green’s function method. The calculation results indicate that the hetero-structures with a minor (large) ribbon width appear a novel forward (reverse) rectification behavior, but the rectifying directions are independent of the interface types of graphene/ h -BN hybridized nano-ribbons. This interesting width-dependent inverse rectification behavior is further tested by increasing the length in scattering region. The findings in this work demonstrate that graphene/ h -BN-based nano-devices with an inversion of rectification behavior can be fabricated by selecting the appropriate nano-ribbon widths.

In this study, we investigated the spin-resolved transport aspects of step-like zigzag graphene ribbons (ZGNRs) with single or double edge-saturated hydrogen using a method that combined the density functional theory with the nonequilibrium Green’s function method under the local spin density approximation. We found that, when the ZGNR-based heterojunctions were in a parallel or antiparallel layout, negative differential resistance, the maximum bipolar spin-filtering, and spin-rectifying effects occurred synchronously except for the case of spin-down electrons in the parallel magnetic layouts. Interestingly, these spin-resolved transport properties were almost unaffected by altering the widths of the two component ribbons. Therefore, step-like ZGNR heterojunctions are promising for use in designing high-performance multifunctional spintronic devices.

Calculations of electronic structures and transport properties of zigzag graphene nanoribbons (ZGNRs) by ordered doping of a column of boron (B) or nitrogen (N) atoms were conducted using density functional theory combined with the non-equilibrium Green’s function. Introducing B or N impurity atoms into ZGNRs with an odd number of zigzag chains can suppress currents compared with the intrinsic ZGNR device. The ZGNRs with an even number of zigzag chains across their width show that B or N atom doping can increase currents compared with the intrinsic ZGNR nanojunction. Notably, B or N doping can induce a significant negative differential resistance behavior for ZGNRs with an even number of zigzag chains across their width. These findings provide avenues to modify the electronic transport of ZGNR-based systems. The findings also suggest that ZGNRs are potential materials for future nanoscale negative differential resistance device.

In this work, nanojunctions consisting of two combined similar right triangle graphenes (SRTGs) bonded covalently with zigzag-edged graphene nanoribbon electrodes are designed, and their electron transport properties are investigated using density functional theory and non-equilibrium Green’s function method. Results reveal that the SRTG-based devices exhibit an interesting negative differential resistance (NDR) effect and present a rule indicating that the NDR effect increases with the increasing sizes of both SRTGs. The electron transport properties are further tested using two combined SRTGs with different sizes. Overall, this study suggests that the SRTG-based structures are promising candidates in the design of nanoscale NDR devices.

Ag-SnO2 coating on copper substrate has been prepared by an atmospheric plasma spraying method using high energy ball milled Ag-12wt%SnO2 composite powder as raw material. The microstructures of the Ag-SnO2 coating were characterized by XRD and SEM. The mechanical properties and arc erosion performance of the as sprayed coating have been determined by tensile test, microhardness and arc erosion tests, respectively. The results show that the Ag-SnO2 coating presents a compact microstructure, and the nanosized SnO2 particles are uniformly dispersed in the Ag matrix of the coating. The mechanical properties and the arc erosion performance of the Ag-SnO2 coating are close to those of Ag-SnO2 bulk. After arcing test, the surface of the coating presents the dispersion of cathode spots and a little erosion, indicating that the Ag-SnO2 coating has excellent arc-erosion resistance. Plasma spray technique is an effective approach to manufacture Ag-SnO2 contact coating with good mechanical properties and arc erosion resistance.

First-principles calculations have shown dramatically unexpected rectifying regularities in particular heterojunction configurations with triangular hexagonal boron-nitride-carbon (h-BNC) and triangular graphene (TG) sandwiched between two armchair graphene nanoribbon electrodes. When the triangular h-BNC and TG are linked by vertex atoms of nitrogen and carbon (boron and carbon), forward (reverse) rectifying performance can be observed. Moreover, for a certain linking mode, the larger the elemental proportion p (where p = Nboron+nitrogen/Nboron+nitrogen+carbon) in the h-BNC, the larger the ratio for forward (reverse) rectification. A mechanism for these rectification behaviors is suggested. The findings provide insights into control of rectification behaviors in TG-based nanodevices.

Hybridized Z-BexSyCz (x+y+z=16) systems connected by zigzag beryllium-sulfide (BeS) and graphene nanoribbons are theoretically designed, and their electronic transport characteristics are explored by first-principles approach. For the hybridized systems with unequal number of x and y, i.e. z is an odd number, an exceptional negative differential resistance (NDR) property occurs. However, for the hybridized systems including an even number of zigzag carbon chains, namely x equal to y, an interesting current-limited behavior happens. Meanwhile, the NDR phenomenon disappears. The spin transport properties of these hybridized Z-BexSyCz systems with parallel magnetism configuration also reveal the above odd–even dependence conductance behavior.

The spin transport properties of zigzag graphene nanoribbon (ZGNR) hetero-junctions, in which ZGNR electrodes are doped with B or N atoms, are investigated based on spin-polarized density functional theory and non-equilibrium Green's function. ZGNRs are C–H2 bonded at one edge and C–H bonded at the other edge to form asymmetric edge hydrogenation. The spin-polarized currents of ZGNR-based nano-devices with an odd or even number of the zigzag-shaped chains show a perfect bipolar spin-filtering effect on parallel and anti-parallel magnetic configurations. This study provides insights into the design of high-performance graphene-based spin filters.

We develop a facile method for preparing the porous gold nanoparticles (Au-NPs)/2H-form MoS2 nanocomposite that forms a unique 3-dimensional structure and shows a high surface enhanced Raman spectroscopy effect.

This paper aims to improve the anti-oxidation and thermal cycling life of thermal barrier coating system (TBCs) by tailoring the microstructure of MCrAlYbond coat. The cobalt-based and nickel-basedbond coats were deposited byhigh efficiency supersonic atmospheric plasma spraying (SAPS) system. The microstructures of bond coats were optimized by ahigh-temperature oxidation test. A comparative study between SAPS-coating and HVOF-coating (high velocity oxygen fuel spraying, HVOF) was conducted in order to analyze the microstructure-property differences between them. The results showed that the SAPS-coatings that remained 35%± 5%(cobalt-based) and 10%± 3%(nickel-based) unmelted particles exhibited the best oxidation resistance. For the same composition of bond coat and microstructure of top coat, the thermal cycling life of SAPS-coating was two times as much as that of HVOF-coating, however, the average growth rate of thermally grown oxides (TGOs) was reduced by more than 20%. The SAPS can“one-step” deposit the bond coat and top coat , whicheffectively avoids the pollution resulted from the so-called “two-step”process method. With the advantages of simple process, high deposition efficiency and low production cost, the SAPS method shows a good industrial prospect.

A nanocomposite Mo-4wt% La2O3 cathode was prepared by a high-energy ball-milling and hot pressing technique. The sizes of lanthana particles in the nanocomposite Mo-La2O3 cathode are less than 100 nm; in contrast, the sizes of thoria particles are about 1∼2 μm in a commercial W-4wt% ThO2 cathode. The average vacuum arc-starting field intensity of the nanocomposite Mo-La2O3 cathode is 2.97×107 V/m, which is 62.7% lower than that of the commercial W-ThO2. The nanocomposite Mo-La2O3 cathode exhibits superior electron emission performances, and its distribution area and thickness of electron emission spots are remarkably larger, as compared to those of the commercial W-ThO2 cathode. The size of oxide particles has a great effect on the electron emission performances and vacuum arc characteristics of cathode. The electron emission performance of Mo-La2O3 cathode will be improved with decreasing of the lanthana particles size. When La2O3 particle size decreases to less than 100 nm, the electron emission area and ability of the Mo-La2O3 cathode significantly increase. The much enhanced electron emission performance of the nanocomposite Mo-La2O3 cathode is attributed to the formation of a higher inter electric field and space-charge regions at the interphase boundaries between Mo and La2O3 phases.

The magnetic and spin transport properties of asymmetric edge-hydrogenated zigzag graphene nanoribbons (ZGNRs) selectively doped with nitrogen atoms were investigated using spin-polarized density functional theory and non-equilibrium Green's function. Results show that the rectifying performance of spin-polarized current with a ratio higher than 10 5 can be modulated by changing the positions of the nitrogen dopant. Complete spin filtering (100%) and excellent negative differential resistance behaviors were observed in the ZGNR junctions. These doping position-dependent spin transport characteristics were further tested by shifting from the odd-numbered zigzag-shaped C chains (N-Z) to the even-numbered N-Z in ZGNRs. This study suggests that adopting a suitable nitrogen doping position could be an effective approach to significantly enhance the rectifying behavior of asymmetric edge-hydrogenated ZGNRs, which are promising materials for multifunctional spintronic devices.

In this work, an effective approach to control the thickness and porosity of porous gold nanonetworks (PGNs) was demonstrated. The 3-dimensional (3-D) PGNs were accomplished by repeated overlaying of two-dimensional (2-D) monolayer gold nanonetworks which assembled at the pentanol/water interface. The porosity of the PGNs can be improved by increasing the number of layers, which greatly enhances the intralayer and interlayer plasmon coupling and the mass diffusion of the analyte molecules, resulting in an improved sensitivity for SERS and glucose detection. In addition, the current approach also offered an effect method to produce 3-D porous nanostructures through the self-assembly of the isolated nanoparticles (NPs).

We investigate electronic transport properties of molecular device models constructed by a dipyrimidinyl–dimethyl molecule embedding in a carbon chain, which are then coupled to the gold electrodes through thiol or isocyanide group. Using the density functional theory combined with the nonequilibrium Green’s function method, negative differential resistance behaviors are observed in such molecular junctions. Most importantly, system with the isocyanide group can achieve a larger negative differential resistance at lower bias voltage (0.1V).

The microstructures of surface melt layers for W–Cu contact materials after vacuum breakdown were analyzed in detail and the arc motion characteristic was investigated with a digital high-speed video camera. The experimental results revealed that cathode spots probably occurred on the Cu phase during the first breakdown. The Cu-rich melts were sprayed out of the cathode spots due to the high plasma pressure and great volume expansion resulting from the partial boiling of Cu. The spraying of the droplets was clearly observed by a digital high-speed video camera. The calculated work function of the close-packed plane of Cu (111) was smaller than that of W (110) and the arc would firstly appear on the Cu phase of the W–Cu alloys during the breakdown. The theoretical calculations were in exact accordance with the experimental results. The experiment also indicated that liquid phase separation was involved in the microstructure evolution of W–Cu alloys.

Rectification performances of rhombic graphene nanoribbons coupled to gold electrodes through thiolate bonds with left and right vertical carbon atoms substituted by one nitrogen or boron atom are analyzed by performing theoretical calculations using a self-consistent ab initio approach that combines the density functional theory with the non-equilibrium Green's function formalism. Increasing the size of graphene nanoribbon markedly improves the rectification effect because of the asymmetric potential profile distribution in rhombic graphene for polarization near the boron and nitrogen atoms.