Carbonyl mediated conductance through metal bound peptides: a computational study

Large increases in the conductance of peptides upon binding to metal ions have recently been reported experimentally. The mechanism of the conductance switching is examined computationally. It is suggested that oxidation of the metal ion occurs after binding to the peptide. This is caused by the bias potential placed across the metal-peptide complex. A combination of configurational changes, metal ion involvement and interactions between carbonyl group oxygen atoms and the gold leads are all shown to be necessary for the large improvement in the conductance seen experimentally. Differences in the molecular orbitals of the nickel and copper complexes are noted and serve to explain the variation of the improvement in conductance upon binding to either a nickel or copper ion.     

Mechanism of conductance switching: An optical investigation

Electronic conductance switching in devices based on thin films of an organic molecule has been studied. Switching between two conducting states has been induced by voltage pulse, while the states have been probed by optical and electrical measurements simultaneously. In situ optical measurements showed that electroreduction of molecules led to conductance switching and appearance of high-conducting state in the device. We could “write” or “erase” a state by applying electrical pulse and “read” it by measuring electronic absorbance and conductivity. The “write” and “read” processes have been carried out for many cycles to exhibit a correspondence between conductance switching and electrochromism.     

Redox switchable self-assembled monolayers of functional ruthenium(III/II) complexes on optically transparent platinum electrodes

Self-assembled monolayers (SAMs) of functional Ru^II complexes on optically transparent ultrathin Pt films (10-nm nominal thicknesses) have been prepared. We have demonstrated that reversible Ru^III/II redox switching of these SAMs can be achieved by using appropriate oxidizing or reducing agents. Such a switching in molecular properties has been simply detected by transmission spectroscopy with a conventional spectrophotometer following the appearance/disappearance of the optical absorption metal-to-ligand charge-transfer (MLCT) band in the visible region. In light of their potential multifunctional properties, these SAMs on an optically transparent metal electrode are appealing candidates in the perspective of integrated molecular switch nanodevices.     

Semiconductor/metal nanocomposites formed by in situ reduction method in multilayer thin films

A layer-by-layer adsorption and in situ reduction method was adopted for synthesizing semiconductor/metal nanocomposites in multilayer ultra-thin films. Alternate adsorption of ZnO nanoparticles modified with poly(ethyleneimine), hydrogentetrachloroaurate and poly(styrenesulfonate) sodium results in the formation of ZnO/AuCl₄⁻-loaded multilayer films. In situ reduction of the incorporated metal ions by heating yields ZnO/Au nanocomposites in the films. UV-vis absorption spectroscopy and X-ray photoelectron spectroscopy were used to characterize the components of the composite films. UV-vis spectra indicate regular growth of the films. The electrochemistry behavior of the multilayer films was studied in detail on indium tin oxide electrode. The combined results suggest that the layer-by-layer adsorption and subsequent reduction method used here provides an effective way to synthesize ZnO/Au nanocomposites in the polymer matrix.     

Mechanism of conductance switching: An optical investigation

Electronic conductance switching in devices based on thin films of an organic molecule has been studied. Switching between two conducting states has been induced by voltage pulse, while the states have been probed by optical and electrical measurements simultaneously. In situ optical measurements showed that electroreduction of molecules led to conductance switching and appearance of high-conducting state in the device. We could “write” or “erase” a state by applying electrical pulse and “read” it by measuring electronic absorbance and conductivity. The “write” and “read” processes have been carried out for many cycles to exhibit a correspondence between conductance switching and electrochromism.     

退火温度对TiO2基电阻开关器件性能的影响

采用直流磁控溅射法在n+-Si上制备了TiO2薄膜,采用电子束蒸发镀膜仪在TiO2薄膜上沉积Au电极,获得了Au/TiO2/n+-Si结构的器件.研究了退火温度对薄膜结晶性能及器件电阻开关特性的影响.Au/TiO2/n+-Si结构的器件具有单极性电阻开关特性,置位(set)电压,复位(reset)电压、reset电流及功率的大小随退火温度的不同而不同,并基于灯丝理论对器件的电阻开关效应的工作机理进行了探讨.研究结果表明,500℃退火的器件具有良好的非易失性.器件高低阻态的阻值比大于103,其信息保持特性可达10年之久.在读写次数为100次时,器件仍具有电阻开关效应.     

TbW10-Agarose柔性自支持绿光薄膜的制备及化学响应荧光开关性能研究

基于功能互补原理, 以稀土多酸Na₉TbW₁₀O₃₆(TbW₁₀)为发光功能组分、琼脂糖为成膜基质, 通过溶胶-凝胶及Casting技术制备了稀土多酸柔性自支持绿光薄膜TbW₁₀-Agarose, 利用FT-IR、Raman光谱对薄膜的组成及结构进行表征, 利用SEM、AFM和TEM对薄膜的厚度、表面粗糙度和微结构进行研究, 考察TbW₁₀掺杂量对薄膜透光率及发光性能的影响。在HCl/NH₃刺激下, 实现了TbW₁₀-Agarose绿光薄膜可逆的化学响应荧光开关性质, 利用荧光动力学方法对绿光薄膜化学响应荧光开关的响应时间及可逆性进行研究; 并拓展了该绿光薄膜对HCl气体的荧光光谱检测, 检出限为0.2731 mmol·L ^-1。     

Interface geometry and molecular junction conductance: geometric fluctuation and stochastic switching

Metal/molecule/metal transport junctions can transport charge in the elastic scattering (Landauer) regime if the injection gap is large and the molecule is relatively short. Stochastic switching and broad conduction peak distributions have been observed in such junctions. We examine the effect of altering interface geometry on transport, using density functional calculations. For most structures, variations in conductance of order 0-300% are found, but when an atomic wire of Au binds to the molecule, symmetry changes can modify currents by a factor of 10(3).     

Simultaneous observation of surface plasmons on both sides of thin silver films

Abstract

Both prism and grating coupling have been used to optically excite surface plasmons on the two sides of thin silver films. This allows the optical permittivity of the silver films to be determined simultaneously at the metal/air and the (protected) glass/metal interfaces. It is found that there is a significant difference between the permittivities for the two interfaces which depends upon the thickness of the metal film. This difference is tentatively attributed to the silver films being more porous at the air interface, although an alternative interpretation, based on possible changes in electron density through oxygen absorption by silver, is not excluded.     

Memristive switching mechanism for metal/oxide/metal nanodevices

Nanoscale metal/oxide/metal switches have the potential to transform the market for nonvolatile memory and could lead to novel forms of computing. However, progress has been delayed by difficulties in understanding and controlling the coupled electronic and ionic phenomena that dominate the behaviour of nanoscale oxide devices. An analytic theory of the 'memristor' (memory-resistor) was first developed from fundamental symmetry arguments in 1971, and we recently showed that memristor behaviour can naturally explain such coupled electron-ion dynamics. Here we provide experimental evidence to support this general model of memristive electrical switching in oxide systems. We have built micro- and nanoscale TiO2 junction devices with platinum electrodes that exhibit fast bipolar nonvolatile switching. We demonstrate that switching involves changes to the electronic barrier at the Pt/TiO2 interface due to the drift of positively charged oxygen vacancies under an applied electric field. Vacancy drift towards the interface creates conducting channels that shunt, or short-circuit, the electronic barrier to switch ON. The drift of vacancies away from the interface annilihilates such channels, recovering the electronic barrier to switch OFF. Using this model we have built TiO2 crosspoints with engineered oxygen vacancy profiles that predictively control the switching polarity and conductance.     

Highly conductive, printable and stretchable composite films of carbon nanotubes and silver

Conductive films that are both stretchable and flexible could have applications in electronic devices, sensors, actuators and speakers. A substantial amount of research has been carried out on conductive polymer composites, metal electrode-integrated rubber substrates and materials based on carbon nanotubes and graphene. Here we present highly conductive, printable and stretchable hybrid composites composed of micrometre-sized silver flakes and multiwalled carbon nanotubes decorated with self-assembled silver nanoparticles. The nanotubes were used as one-dimensional, flexible and conductive scaffolds to construct effective electrical networks among the silver flakes. The nanocomposites, which included polyvinylidenefluoride copolymer, were created with a hot-rolling technique, and the maximum conductivities of the hybrid silver-nanotube composites were 5,710 S cm?1 at 0% strain and 20 S cm?1 at 140% strain, at which point the film ruptured. Three-dimensional percolation theory reveals that Poisson's ratio for the composite is a key parameter in determining how the conductivity changes upon stretching.     

Bipolar injection as a cause of electrical switching phenomena in thin organic films

An investigation of electrical conductance switching phenomena in thin organic films has been carried out. For thin films of p-quaterphenyl and tetracene grown in high vacuum the electrical conductance, dynamic capacitance and temperature patterns corresponding to the distribution of electrical current density have been measured. The measurements were carried out in vacuum as well as in humid air. It is suggested that previously reported switching phenomena are caused by field-induced bipolar injection of charge carriers.     

Resistive switching memory properties of layer-by-layer assembled enzyme multilayers

The properties of enzymes, which can cause reversible changes in currents through redox reactions in solution, are of fundamental and practical importance in bio-electrochemical applications. These redox properties of enzymes are often associated with their charge-trap sites. Here, we demonstrate that reversible changes in resistance in dried lysozyme (LYS) films can be generated by an externally applied voltage as a result of charge trap/release. Based on such changes, LYS can be used as resistive switching active material for nonvolatile memory devices. In this study, cationic LYS and anionic poly(styrene sulfonate) (PSS) layers were alternately deposited onto Pt-coated silicon substrates using a layer-by-layer assembly method. Then, top electrodes were deposited onto the top of LYS/PSS multilayers to complete the fabrication of the memory-like device. The LYS/PSS multilayer devices exhibited typical resistive switching characteristics with an ON/OFF current ratio above 10(2), a fast switching speed of 100 ns and stable performance. Furthermore, the insertion of insulating polyelectrolytes (PEs) between the respective LYS layers significantly enhanced the memory performance of the devices showing a high ON/OFF current ratio of ~10(6) and low levels of power consumption.     

Ag／La0.67Sr0.33MnO3/Pt异质结构的电阻开关特性

采用脉冲激光沉积技术在Pt／Ti／SiO2／Si（100）衬底上制备出多晶La0.67Sr0.33MnO3（LSMO）薄膜,对其电脉冲致非挥发可逆电阻开关特性进行研究．结果表明,Ag/LSMO／Pt结构具有明显的室温电脉冲诱发电阻开关特性,且在宽电压脉冲作用下表现出较低的开关电压和较快的变阻饱和速度．由此可见,总脉冲能量或电荷（电流作用）为该结构的电阻开关效应提供驱动力．对Ag／LsMO／Pt结构进行了耐久性测试,表明该结构具有良好的疲劳特性与保持特性,可应用于新型不挥发存储器、传感器及可变电阻等电子元器件的研制     

Effect of nanophase concentration on the properties of metal-containing silicon–carbon nanocomposites

We have studied the effect of tungsten, molybdenum, and hafnium concentrations on the electrical conductivity, nanohardness, and elastic modulus of metal-containing silicon–carbon nanocomposite films. The results demonstrate that the addition of these metals to the films leads to the formation of metal carbide particles a few nanometers in size. At metal contents from 5 to 35 at %, the conductivity of the films varies over four orders of magnitude (from 10^–1 to 10³ S/cm). The composition dependences of the mechanical properties of the nanocomposites depend on the nature of the metal. We have analyzed the mechanisms underlying the effect of the metals on these properties.     

Synthesis,characterization and photoresponse study of undoped and transition metal (Co,Ni, Mn) doped ZnO thin films

The synthesis, characterization and photoresponse studies of undoped and transition metal doped zinc oxide thin films are carried out in this work, in prospect of visible light photo detection and sensor applications. The undoped and transition metal ions such as, Co, Ni and Mn doped ZnO films in this study were synthesized by chemical solution deposition, involving spin-coating. We have characterized the deposited films using X-ray diffraction, scanning electron microscopy, photoluminescence and UV–vis spectroscopy studies. The devices of the films for photoresponse study were fabricated by top Ag contacts on the film surface in metal–semiconductor–metal configuration. The current–voltage characteristics and switching measurements of these devices were studied under the illumination of an incandescent lamp. We found a high ON/OFF ratio of 8 and highest photocurrent density of 0.7 mA/cm² for Ni doped ZnO film.     

Optical switching of electric charge transfer pathways in porphyrin: a light-controlled nanoscale current router

We introduce a novel molecular junction based on a thiol-functionalized porphyrin derivative with two almost energetically degenerate equilibrium configurations. We show that each equilibrium structure defines a pathway of maximal electric charge transfer through the molecular junction and that these two conduction pathways are spatially orthogonal. We further demonstrate computationally how to switch between the two equilibrium structures of the compound by coherent light. The optical switching mechanism is presented in the relevant configuration subspace of the compound, and the corresponding potential and electric dipole surfaces are obtained by ab initio methods. The laser-induced isomerization takes place in two steps in tandem, while each step is induced by a two-photon process. The effect of metallic electrodes on the electromagnetic irradiation driving the optical switching is also investigated. Our study demonstrates the potential for using thiol-functionalized porphyrin derivatives for the development of a light-controlled nanoscale current router.     

Controlled fabrication of noble metal nanoparticles loaded on the surfaces of cyclotriphosphazene-containing polymer nanotubes

We report on the fabrication of noble metal nanoparticles loaded on the surfaces of cross-linked poly(cyclotriphosphazene-co-4,4′-sulfonyldiphenol) (PZS) nanotubes of high stability. PZS nanotubes were first synthesized by precipitation polymerization between hexachlorocyclotriphosphazene and 4,4′-sulfonyldiphenol based on in situ template mechanism. Then the PZS nanotubes were directly used as scafford to load metal Au, Ag, and Pd nanoparticles, respectively, through cation complexation followed by gentle reduction. The structure and morphology of the metal/PZS nanocomposites were determined by means of Fourier transform infrared spectra, energy dispersive X-ray spectroscopy, elemental analysis, X-ray diffraction, scanning electron microscope, transmission electron microscope, and thermogravimetric analysis (TGA). Results showed that the metal/PZS nanocomposites possessed 460 °C of initial thermal decomposition temperature under air atmosphere and the loading amount of metal nanoparticles on the PZS nanotube surfaces could be controlled easily. As-fabricated metal/PZS nanocomposites are expected to have potential applications in catalysis.     

Triggering the volume phase transition of core-shell Au nanorod-microgel nanocomposites with light

We have coated gold nanorods (NRs) with thermoresponsive microgel shells based on poly(N-isopropylacrylamide) (pNIPAM). We demonstrate by simultaneous laser-heating and optical extinction measurements that the Au NR cores can be simultaneously used as fast optothermal manipulators (switchers) and sensitive optical reporters of the microgel state in a fully externally controlled and reversible manner. We support our results with optical modeling based on the boundary element method and 3D numerical analysis on the temperature distribution. Briefly, we show that due to the sharp increase in refractive index resulting from the optothermally triggered microgel collapse, the longitudinal plasmon band of the coated Au NRs is significantly red-shifted. The optothermal control over the pNIPAM shell, and thereby over the optical response of the nanocomposite, is fully reversible and can be simply controlled by switching on and off a NIR heating laser. In contrast to bulk solution heating, we demonstrate that light-triggering does not compromise colloidal stability, which is of primary importance for the ultimate utilization of these types of nanocomposites as remotely controlled optomechanical actuators, for applications spanning from drug delivery to photonic crystals and nanoscale motion.     

Gasochromic switching of reactively sputtered molybdenumoxide films: A correlation between film properties and deposition pressure

Molybdenumoxide (MoO_x) thin films can change their optical properties upon exposure to hydrogen. Since the film properties strongly depend on process parameters we have studied how the films are affected by the total pressure during deposition. Stoichiometric and sub-stoichiometric MoO_x films were prepared by reactive direct current magnetron sputtering in an atmosphere of argon and oxygen. Substoichiometric films were coated with platinum as a catalyst and were colored in diluted hydrogen atmosphere and bleached in air. Optical spectroscopy, X-ray reectometry, spectroscopic ellipsometry and simulations of the measured spectra were used to characterize the films ex situ. In situ switching characteristics as revealed by optical spectroscopy and changes in stress were measured as well. We find that the total pressure during sputter deposition has a strong influence on the optical constants, the film density, and the sputter rate. The mechanical stresses and switching Preprint submitted to Elsevier Science 10 March 2006 cycles during the film coloration and bleaching also strongly depend on the total pressure. The influence of the sputter pressure on film properties is explained by the kinetics during the sputter process.