Electrical and thermal conductivity of low temperature CVD graphene: the effect of disorder

In this paper we present a study of graphene produced by chemical vapor deposition (CVD) under different conditions with the main emphasis on correlating the thermal and electrical properties with the degree of disorder. Graphene grown by CVD on Cu and Ni catalysts demonstrates the increasing extent of disorder at low deposition temperatures as revealed by the Raman peak ratio, IG/ID. We relate this ratio to the characteristic domain size, La, and investigate the electrical and thermal conductivity of graphene as a function of La. The electrical resistivity, ρ, measured on graphene samples transferred onto SiO2/Si substrates shows linear correlation with La(-1). The thermal conductivity, K, measured on the same graphene samples suspended on silicon pillars, on the other hand, appears to have a much weaker dependence on La, close to K～La1/3. It results in an apparent ρ～K3 correlation between them. Despite the progressively increasing structural disorder in graphene grown at lower temperatures, it shows remarkably high thermal conductivity (10(2)-10(3) W K(-1) m(-1)) and low electrical (10(3)-3×10(5) Ω) resistivities suitable for various applications.     

Double-donor complex in vertically coupled quantum dots in a threading magnetic field

We consider a model of hydrogen-like artificial molecule formed by two vertically coupled quantum dots in the shape of axially symmetrical thin layers with on-axis single donor impurity in each of them and with the magnetic field directed along the symmetry axis. We present numerical results for energies of some low-lying levels as functions of the magnetic field applied along the symmetry axis for different quantum dot heights, radii, and separations between them. The evolution of the Aharonov-Bohm oscillations of the energy levels with the increase of the separation between dots is analyzed.     

Third-harmonic generation in air by use of femtosecond radiation in tight-focusing conditions

Third-harmonic generation (THG) in air in tight-focusing conditions is presented. Variation of the pulse duration supplied optimal conditions for THG by femtosecond pulses that varied in the range 110-1300 fs. We show that this third-harmonic generation was caused by Kerr-induced phase variations of fundamental and harmonic beams. Various characteristics (laser intensity, focusing conditions, pulse duration, air pressure, etc.) of THG in air were analyzed to optimize this process. The THG conversion efficiency of 795 nm, 300 fs radiation was 1 x 10(-3). The harmonic radiation did not show considerable disruption of its spectral and spatial distribution in tight focusing conditions for intensities as high as 5 x 10(14) W cm(-2).     

Polyphosphonates obtained by vapor-liquid interfacial polycondensation

Summary A series of polyphosphonates were synthesized by base promoted liquid-vapor interfacial polycondensation of various alkyl (aryl) phosphonic dichlorides (methylphosphonic dichloride (MPD), cyclohexylphosphonic dichloride (CPD) and phenylphosphonic dichloride (PPD)) with different bisphenols (hydroquinone (HQ), bisphenol A (BA), 4,4′ - biphenol (BP), 1,5-naphtalenediol (ND) and 4,4′ - sulfonyldiphenol (SD)). The polyphosphonates were characterized by infrared (IR) and proton magnetic resonance (¹H-NMR) spectroscopy. Yields in the range of 20–80% and Mn of ∼ 8500–35000 were obtained. DSC measurements show Tg in the range 95°–148°C. These polymers are soluble in solvents such as N,N-dimethylformamide, tetrahydrofuran and chloroform. Polyphosphonates were stable up 240°–300°C in air atmosphere. Received: 11 March 2002 / Revised version: 29 May 2002 / Accepted: 12 June 2002     

一种直列式6缸发动机主轴承盖的开发

将粉末冶金用于铝合金发动机汽缸体意味着对材料切削加工性能的一种挑战.除了要求静态与疲劳强度之外,为了能够对发动机汽缸体组件进行有效地镗孔,材料的切削加工性状还必须和铝合金相容.为了满足这项应用提出的要求,开发了含有六方氮化硼的粉末配方.这项重要发展包括材料选择、切削性评价,以及静态与动态强度试验.为确定轴承盖最关键的部位进行了有限元分析(FEA).轴承盖是在经过金相检验、尺寸变化测定、静态与疲劳试验之后,进行制造与鉴定的.对制造工艺提出并实行了一些改进.轴承盖顺利地进行了切削加工,并通过了用户的发动机试验.此后,这些轴承盖在数以百万件计地进行生产.     

Ion-specific isotopic fractionation of molybdenum during diffusion in aqueous solutions

Experiments modeling diffusion of Mo in aqueous solutions have been performed and, using multicollector ICP-MS, the ratios of the diffusivities of Mo isotopes, D97Mo/ D95Mo, in aqueous solutions have been determined. Diffusion of MoO42- ions in solution was concomitant with Mo isotopic fractionation with D97Md/D95Mo = 0.99988+/-0.00004 (2sigma for n = 3). In contrast, during diffusion of Mo polyanions, such as Mo70246- and Mo8O264-, no measurable isotope fractionation has been found with D97Mo/D95MO = 1.00000 +/- 0.00002 (2sigma for n = 3). These results indicate the need for due consideration to Mo speciation when attempting to interpret the role of diffusive fluxes in the formation of Mo isotopic signatures in nature. They also raise the possibility that the various chemical forms of other transition metals may be characterized by species-specific isotopic fractionation effects during physicochemical reactions.     

Heterogeneous catalysts obtained by incorporation of polymer-supported phosphonates into silica used in oxidation reactions

Summary The synthesis of copolymers functionalized with phosphonate groups, incorporation of them into ordered meso-macroporous silica, characterization and evaluation of the obtained materials as catalysts in oxidation of cyclohexene are presented. The catalysts obtained are very active and selective in epoxidation of cyclohexene using hydrogen peroxide as an environmentally friendly oxidant.     

Water-Soluble Chalcogenide W6-Clusters: On the Way to Biomedical Applications

Despite the great potential of octahedral tungsten cluster complexes in fields of biomedical applications such as X-ray computed tomography or angiography, there is only one example of a water-soluble W₆Q₈-cluster that has been reported in the literature. Herein we present the synthesis and a detailed characterization including X-ray structural analysis, NMR, IR, UV–Vis spectroscopies, HR-MS spectrometry, and the electrochemical behavior of two new cluster complexes of the general formula W₆Q₈L₆ with phosphine ligands containing a hydrophilic carboxylic group, which makes the complexes soluble in an aqueous medium. The hydrolytic stability of the clusters’ aqueous solutions allows us to investigate for the first time the influence of W₆-clusters on cell viability. The results obtained clearly demonstrate their very low cytotoxicity, comparable to the least-toxic clusters presented in the literature.     

Programmable Functionalization of Surfactant‐Stabilized Microfluidic Droplets via DNA‐Tags

Droplet‐based microfluidics has emerged as a powerful tool in synthetic biology. For many applications, chemical functionalization of the droplets is a key process. Therefore, a straightforward and broadly applicable approach is developed to functionalize the inner periphery of microfluidic droplets with diverse reactive groups and components. Instead of covalent modification of the droplet‐stabilizing surfactants, this method relies on cholesterol‐tagged DNA that self‐assembles at the droplet periphery. The cholesterol‐tagged DNA serves as an attachment handle for the recruitment of complementary DNA. The complementary DNA can carry diverse functional groups. We exemplify our method by demonstrating the attachment of amine groups, DNA nanostructures, microspheres, a minimal actin cortex, and leukemia cells to the droplet periphery. It is further shown that the DNA‐mediated attachment to the droplet periphery is temperature‐responsive and reversible. It is envisioned that droplet functionalization via DNA handles will help to tailor droplet interfaces for diverse applications—featuring programmable assembly, unique addressability, and stimuli‐responsiveness.     

Stiction-protected MEMS switch with low actuation voltage

Microsystem Technologies - Commercial success of microelectromechanical systems (MEMS) switches is limited by several issues. A high actuation voltage requires special circuitry solutions that...