Scaling and the thermal conductivity of the Frenkel-Kontorova model

We have studied the dependence of the thermal conductivity kappa on the strength of the interparticle potential lambda and the strength of the external potential beta in the Frenkel-Kontorova model. We found that the functional relation can be expressed in a scaling form, kappa(proportional to) lambda 3/2/beta(2 center dot). This result is first obtained by nonequilibrium molecular dynamics. It is then confirmed by two analytical methods, the self-consistent phonon theory and the self-consistent stochastic reservoirs method. The thermal conductivity kappa is therefore a decreasing functon of beta and an increasing function of lambda.

Thermal rectifying effect in macroscopic size

We address the problem of the rectifying effect of heat conduction at macroscopic size. A design for a macroscopic thermal rectifier based on the macroscopic thermal conductivity of materials is introduced, and then realizations of the design are shown by numerical simulations and phenomenological estimations.

band Structure calculations on orthorhombic bulk and nanocrystalline SrY2O4

The electronic structure of SrY2O4 is calculated by using a density functional method, and the exchange and correlation have been treated by using a the generalized gradient approximation (GGA) within the scheme due to Perdew, Burke, and Ernzerhof (PBE). SrY2O4 is predicted to be a direct-gap material because the top of the valence band and the bottom of the conduction band are along the same direction at G. The bond length and the bond covalency are also calculated by using a chemical bond method.

Structural characterization, stability and electrical properties of strontium niobate ceramic

The double perovskite oxide Sr2CrNbO6 has a cubic structure according to powder X-ray diffraction. After reducing in CO, Sr2CrNbO6 still exhibited a cubic structure refined by Rietveld technique. The TG analysis indicated that Sr2CrNbO6 loses 0.127 oxygen per formula unit from 400 to 700 degrees C in H-2. The morphology and compositions of this ceramic did not significantly change on reduction

Charge transport in accumulation layers of organic heterojunctions

We studied the charge transport in organic heterojunction films consisting of copper phthalocyanine (CuPc) and copper hexadecafluorophthalocyanine (F16CuPc). The heterojunction effect between CuPc and F16CuPc induced high-density carriers at both sides of heterojunction. The Hall effect was observed at room temperature, which demonstrated the existence of free carriers and their delocalized transport under heterojunction effect. The Hall mobility of 1.2 cm(2)/V s for holes and 2.4 cm(2)/V s for electrons indicated that the transport capability of the heterojunction films is comparable to single crystals. The transport process was further explained by the multiple trap-and-release model according to the temperature dependence of conduction.

Origin of improvement in device performance via the modification role of cesium hydroxide doped tris(8-hydroxyquinoline) aluminum interfacial layer on ITO cathode in inverted bottom-emission organic light-emitting diodes

It has been found that cesium hydroxide (CsOH) doped tris(8-hydroxyquinoline) aluminum (Alq(3)) as an interfacial modification layer on indium-tin-oxide (ITO) is an effective cathode structure in inverted bottom-emission organic light-emitting diodes (IBOLEDs). The efficiency and high temperature stability of IBOLEDs with CsOH:Alq(3) interfacial layer are greatly improved with respect to the IBOLEDs with the case of Cs2CO3:Alq(3). Herein, we have studied the origin of the improvement in efficiency and high temperature stability via the modification role of CsOH:Alq(3) interfacial layer on ITO cathode in IBOLEDs by various characterization methods, including atomic force microscopy (AFM), ultraviolet photoemission spectroscopy (UPS), X-ray photoemission spectroscopy (XPS) and capacitance versus voltage (C-V). The results clearly demonstrate that the CsOH:Alq(3) interfacial modification layer on ITO cathode not only enhances the stability of the cathode interface and electron-transporting layer above it. which are in favor of the improvement in device stability, but also reduces the electron injection barrier and increases the carrier density for current conduction, leading to higher efficiency.

Realization of negative differential resistance and switching devices based on copper phthalocyanine by the control of evaporation rate

We have observed, respectively, a negative differential resistance (NDR) and switching conduction in current-voltage (I-V) characteristics of organic diodes based on copper phthalocyanine (CuPc) film sandwiched between indium-tin-oxide (ITO) and aluminum (Al) by controlling the evaporation rate. The NDR effect is repeatable which can be well, controlled by sweep rate and start voltage, and the switching exhibits write-once-read-many-times (WORM) memory characteristics. The traps in the organic layer and interfacial dipole have been used to explain the NDR effect and switching conduction. This opens up potential applications for CuPc organic semiconductor in low power memory and logic circuits.

Write-Once Read-Many-Times Memory Based on a Single Layer of Pentacene

We realized an organic electrical memory device with a simple structure based on single-layer pentacene film embedded between Al and ITO electrodes. The optimization of the thickness and deposition rate of pentacene resulted in a reliable device with an on/off current ratio as high as nearly 10(6), which was two orders of magnitude higher than previous results, and the storage time was more than 576 h. The current transition process is attributed to the formation and damage of the Interface dipole at different electric fields, in which the current conduction showed a transition from ohmic conductive current to Fowler-Nordheim tunneling current. After the transition from ON- to OFF-state, the device tended to remain in the OFF-State even when the applied voltage was removed, which indicated that the device was very promising for write-once read-many-times memory.

A novel alcohol dehydrogenase biosensor based on solid-state electrogenerated chemiluminescence by assembling dehydrogenase to Ru(bpy)(3)(2+)-Au nanoparticles aggregates

Based on electrogenerated chemiluminescence (ECL), a novel method for fabrication of alcohol dehydrogenase (ADH) biosensor by self-assembling ADH to Ru(bpy)(3)(2+) -AuNPs aggregates (Ru-AuNPs) on indium tin oxide (ITO) electrode surface has been developed. Positively charged Ru(bpy)(3)(2+) could be immobilized stably on the electrode surface with negatively charged AuNPs in the form of aggregate via electrostatic interaction. On the other hand, AuNPs are favourable candidates for the immobilization of enzymes because amine groups and cysteine residues in the enzymes are known to bind strongly with AuNPs. Moreover, AuNPs can act as tiny conduction centers to facilitate the transfer of electrons. Such biosensor combined enzymatic selectivity with the sensitivity of ECL detection for quantification of enzyme substrate, and it displayed wide linear range, high sensitivity and good stability.

Electroactive oligoaniline-containing self-assembled monolayers for tissue engineering applications

A novel electroactive silsesquioxane precursor, N-(4-aminophenyl)-M-(4'-(3-triethoxysilyl-propyl-ureido) phenyl-1,4-quinonenediimine) (ATQD), was successfully synthesized from the emeraldine form of amino-capped aniline trimers via a one-step coupling reaction and subsequent purification by column chromatography. The physicochemical properties of ATQD were characterized using mass spectrometry as well as by nuclear magnetic resonance and UV-vis spectroscopy. Analysis by cyclic voltammetry confirmed that the intrinsic electroactivity of ATQD was maintained upon protonic acid doping, exhibiting two distinct reversible oxidative states, similar to polyaniline. The aromatic amine terminals of self-assembled monolayers (SAMs) of ATQD on glass substrates were covalently modified with an adhesive oligopeptide, cyclic Arg-Gly-Asp (RGD) (ATQD-RGD). The mean height of the monolayer coating on the surfaces was similar to 3 nm, as measured by atomic force microscopy. The biocompatibility of the novel electroactive substrates was evaluated using PC12 pheochromocytoma cells, an established cell line of neural origin. The bioactive, derivatized electroactive scaffold material, ATQD-RGD, supported PC12 cell adhesion and proliferation, similar to control tissue-culture-treated polystyrene surfaces.

A single ionic conductor based on Nafion and its electrochemical properties used as lithium polymer electrolyte

In an attempt to raise the transport number of Li+ to nearly unity in solid polymer electrolytes, commercial perfluorinated sulfonate acid membrane Nafion 117 was lithiated and codissolved with copolymer poly(vinylidene fluoride)hexafluoropropylene. The effect of fumed silica on the physical and electrochemical properties of the single ion conduction polymer electrolyte was studied with atom force microscopy, fourier transform infrared spectroscopy, differential scanning calorimetry, and electrochemical impedance spectroscopy. It was confirmed that the fumed silica has an obvious effect on the morphology of polymer electrolyte membranes and ionic conductivity. The resulting materials exhibit good film formation, solvent-maintaining capability, and dimensional stability. The lithium polymer electrolyte after gelling with a plasticizer shows a high ionic conductivity of 3.18 x 10(-4) S/cm.

Conducting probe atomic force microscopy investigation of anisotropic charge transport in solution cast PBD single crystals induced by an external field

2-(4-Biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxdiazole (PBD) is a good electron-transporting material and can form single crystals from solution. In this work, solution cast PBD single crystals with different crystallographic axes (b, c) perpendicular to the Au/S substrates in large area are achieved by controlling the rate of solvent evaporation in the presence and absence of external electrostatic field, respectively. The orientation of these single crystals on Au/S substrate was characterized by transmission electron microscopy (TEM) and atomic force microscopy (AFM). Conducting probe atomic force microscopy (CP-AFM) was used to measure the charge transport characteristics of PBD single crystals grown on Au/S substrates. Transport was measured perpendicular to the substrate between the CP-AFM tip and the Au/S substrate. The electron mobility of 3 x 10(-3) cm(2)/(V s) for PBD single crystal along crystallographic b-axis is determined. And the electron mobility of PBD single crystal along the c-axis is about 2 orders of magnitude higher than that along the b-axis due to the anisotropic charge transport at the low voltage region.

Performance improvement by charge trapping of doping fluorescent dyes in organic memory devices

We studied the memory effect in the devices consisting of dye-doped N, N'-di(naphthalene-1-yl)-N, N'-diphenyl-benzidine sandwiched between indium-tin oxide and Ag electrodes. It was found that the on/off current ratio was greatly improved by the doped fluorescent dyes compared with nondoping devices. A mechanism of charge trapping was demonstrated to explain the improvement of the memory effect. For the off state, the conduction process is dominated by the trapping current, which is a characteristic of the space-charge limited current, whereas the on state is dominated by the detrapping current, and interpreted by Poole-Frenkel emission.

Investigation of charge-carrier injection characteristics in NPB/Alq3 heterojunction devices

The effect of copper phthalocyanine (CuPc) and LiF interfacial layers on the charge-carrier injection in NN'-di(naphthalene-l-yl)N,N'-diphenyl-benzidine (NPB)/tris(8-hydroxyquinoline) aluminium (Alq(3)) organic heterojunction devices have been studied through the analysis of current-voltage characteristics. The investigation clearly demonstrated that the hole injection into NPB from anode is Fowler-Nordheim (FN) tunneling and the electron injection into Alq3 from cathode is Richardson-Schottky (RS) thermionic emission. The barrier heights obtained from the FN and RS models proved that the band alignments for charge-carrier injection are greatly improved by the CuPc and LiF interfacial layers, which should fully clarify the role of the interfacial layer on the improvement of device performance.

Neodymium-cerium oxide as new thermal barrier coating material

Neodymium-cerium oxide (Nd2Ce2O7) was proposed as a new thermal barrier coating material in this work. Monolithic Nd2Ce2O7 powder was prepared by the solid-state reaction at 1400 degrees C. The phase composition, thermal stability and thermophysical properties of Nd2Ce2O7 were investigated. Nd2Ce2O7 with fluorite structure was thermally stable in the temperature range of interest for TBC applications. The results indicated that the thermal expansion coefficient (TEC) of Nd2Ce2O7 was higher than that of YSZ (6-8 Wt-% Y2O3 + ZrO2) and even more interesting was the TEC change as a function of temperature paralleling that of the superalloy bond coat. Moreover, the thermal conductivity of Nd2Ce2O7 is 30% lower than that of YSZ, which was discussed based on the theory of heat conduction. Thermal barrier coating of Nd2Ce2O7 was produced by atmospheric plasma spraying (APS) using the spray-dried powder. The thermal cycling was performed with a gas burner test facility to examine the thermal stability of the as-prepared coating.