Electrical and photoelectrical properties of Schottky barrier devices using the chloro aluminium phthalocyanines

Measurements of electrical and photoelectrical properties of Al/ClAlPc/ITO, In/ClAlPc/ITO and Au/ClAlPc/Au are presented. The devices Al/ClAlPc/ITO and In/ClAlPc/ITO show rectification properties, while device Au/ClAlPc/Au does not show rectification properties. These effects are explained in terms of p-type semiconducting behaviour of ClAlPc film and its formation of a Schottky barrier with Al and In electrodes and ohmic contact with ITO and Au electrodes. Under low forward bias (Al and In electrodes are negative with respect to ITO) Ohm's law is followed with a thermally activated hole concentration of p_o = 2.2 × 10¹⁷ m⁻³, a hole mobility μ_p = 1.2 × 10⁻⁶ m² V⁻¹ s⁻¹ and room temperature conductivity σ = 4.8 × 10⁻⁸ (Ω m)⁻¹. At high applied voltage there is a space charge limited conductivity (SCLC) controlled by a discrete trapping level above the valence band edge. The total trap concentration and depth of trap level are 1.4 × 10²⁴ m⁻³ and 0.78 eV, respectively. Under reverse bias, the conduction process is determined by Schottky emission over a potential barrier of height of 0.65 eV in the low voltage range and the Poole-Frenkel effect for higher voltage. On illumination through the ITO electrode with monochromatic light of 20 mW cm⁻² at 660 nm, the device parameters of the Al/ClAlPc/ITO and In/ClAlPc/ITO cells were determined. The experimental absorption and action spectra data are explained with the help of the comprehensive theoretical model proposed by Ghosh and Feng for organic solar cells.     

Characterization of graphene-based supercapacitors fabricated on Al foils using Au or Pd thin films as interlayers

We demonstrate that an Au or Pd interlayer between graphene and an Al-foil current collector plays an important role in enhancing supercapacitor performance. Graphene was prepared by scalable chemical exfoliation and mild thermal reduction (～150 °C) processes. Working electrodes were prepared by coating the graphene on Au/Al or Pd/Al by drop-dry method. The graphene deposited on the noble metals Au and Pd demonstrated excellent supercapacitor performance. Estimated specific energy and specific power of supercapacitors were ～40 Wh/kg and ～40 kW/kg at the current density of ～33 A/g, when operated in organic solution. Altogether, we demonstrate that employing noble metals in the fabrication of graphene-based supercapacitors can lead to excellent performance, and this could be a critical basis for further development of graphene-based supercapacitors.     

Investigation of electrical conductivity in Schottky-barrier devices based on nickel phthalocyanine thin films

Evaporated multilayer sandwich structure of Au/NiPc/Al was fabricated by thermal evaporation technique. The electrical conductivity of Au/NiPc/Al device has been measured both as prepared and after annealing at 623 K for 2 h. Under forward bias conditions, ohmic and SCLC conductions were identified at low and higher voltages respectively. After annealing, a strong rectifying effect was observed. The potential barrier height and the depletion region width for annealed sample were calculated as 0.96 eV and 70 nm, respectively. Hole and trap parameters for as prepared and after annealing devices, also, were evaluated.     

Current–voltage (I–V) characteristics of the molecular electronic devices using various organic molecules

Organic molecules have many properties that make them attractive for electronic applications. We have been examining the progress of memory cell by using molecular-scale switch to give an example of the application using both nano scale components and Si-technology. In this study, molecular electronic devices were fabricated with amino style derivatives as redox-active component. This molecule is amphiphilic to allow monolayer formation by the Langmuir–Blodgett (LB) method, and then this LB monolayer is inserted between two metal electrodes. According to the current–voltage (I–V) characteristics, it was found that the devices show remarkable hysteresis behavior and can be used as memory devices at ambient conditions, when aluminum oxide layer was existed on bottom electrode. The diode-like characteristics were measured only, when Pt layer was existed as bottom electrode. It was also found that this metal layer interacts with organic molecules and acts as a protecting layer, when thin Ti layer was inserted between the organic molecular layer and Al top electrode. These electrical properties of the devices may be applicable to active components for the memory and/or logic gates in the future.     

Current–voltage (I–V) characteristics of the molecular electronic devices using various organic molecules

Organic molecules have many properties that make them attractive for electronic applications. We have been examining the progress of memory cell by using molecular-scale switch to give an example of the application using both nano scale components and Si-technology. In this study, molecular electronic devices were fabricated with amino-style derivatives as redox-active component. This molecule is amphiphilic to allow monolayer formation by the Langmuir–Blodgett (LB) method, and then this LB monolayer is inserted between two metal electrodes. According to the current–voltage (I–V) characteristics, it was found that the devices show remarkable hysteresis behavior and can be used as memory devices at ambient conditions, when aluminum oxide layer was existed on bottom electrode. The diode-like characteristics were measured only, when Pt layer was existed as bottom electrode. It was also found that this metal layer interacts with organic molecules and acts as a protecting layer, when thin Ti layer was inserted between the organic molecular layer and Al top electrode. These electrical properties of the devices may be applicable to active components for the memory and/or logic gates in the future.     

Enhancement of the photoluminescence of porous silicon by sputter deposition of semitransparent metal films

Optoelectronic devices based on porous silicon (PS) undergo substantial degradation in luminescence with aging due to atmospheric oxidation. The passivation of PS has been reported with a transparent conducting material or a semi-transparent metal. In this paper, we report enhancement of the photoluminescence (PL) of PS by the passivation of PS with ultrathin metal films such as silver (Ag), aluminum (Al), and gold (Au). It has been found that Ag and Au are respectively most and least effective in enhancing the PL of PS among those three different metals. The highest PL enhancing effect of Ag is mostly attributed to the high electrical conductivity of Ag, whereas the lowest PL enhancing effect of Au is due to the lowest optical transmittance of Au. The details of the PL enhancing effect of metal passivation are discussed with the aid of FTIR analysis results.     

Photocurrent spectral responses in poly (2,5-dimethoxy-p-phenylenevinylene) devices

We report the spectral response of the photocurrent in the sandwich configuration of poly (2,5-dimethoxy-p-phenylenevinylene) (DMPPV) devices. The photocurrent spectral responses are dependent on the polarity of the illuminated surface and the electrodes. The polarity-dependent photocurrent is modeled on a basis where charge carrier drift plays a dominant mechanism and hole transport is predominant over electron transport. The model can explain the results for the Au/DMPPV/Au symmetric configuration. The model cannot however explain the results for the indium-tin oxide (ITO)/DMPPV/Al device. The response for the light incident on the Al side is also reported. The spectral dependence is also studied as a function of bias electric field. Mechanisms leading to the behavior of the photocurrent spectral dependence are speculated.     

Effect of Al in Ti－microalloyed Mn－Ni－Mo welding wire on microstructure and toughness of deposited metal

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Photoconductive properties of poly(2,3-di(p-tolyl)quinoxaline-5,8-diyl)

Photoconductive properties of poly(2,3-di(p-tolyl)quinoxaline-5,8-diyl), which has a high electron-accepting ability, are reported. The photocurrent spectra were observed using sandwich-type cells fabricated between transparent electrodes (ITO) and metal electrodes (Mg, Al and Au) under irradiation from each side of the electrodes. Two types of photocurrent spectra were observed depending on the experimental conditions, and the results are discussed from a viewpoint of carrier generation mechanisms. We conclude that the dissociation of photogenerated excitons occurs mainly in the depletion layer located near the Mg electrode and plays a major role in the generation of carriers. The dependences on light intensity, temperature and electric field were also measured. These experimental data were inspected based on both Poole-Frenkel theory and Bässler's model.     

Effect of Au deposition rate on the performance of top-contact pentacene organic field-effect transistors

A study of the influence of the deposition rate of top-contact Au source and drain electrodes deposited by electron-beam evaporation on the electrical performance of pentacene organic field-effect transistors (OFETs) is presented. By adjusting the deposition rate of the Au electrodes to minimize metal diffusion into the semiconductor pentacene layer, the source/drain contact resistance could be reduced. At a Au deposition rate of 10 Å/s, high-performance pentacene p-channel OFETs were obtained with a field-effect mobility of 0.9 cm²/Vs and a normalized channel width resistance of 23 kΩ cm in a device with a channel length of 25 μm.     

Polythiophene–polyoxyethylene copolymer in polyfluorene-based polymer blends for light-emitting devices

Polyfluorene (PFO) films doped with different amount of a polythiophene-co-polyoxyethylene (P1) polymer were studied with the aim to obtain white emission. The Förster resonant energy transfer (FRET) is the basic mechanism that takes place in the photoluminescence of these blends. The non-conducting poly(oxyethylene) behaves as a inert spacer leading to a larger donor–acceptor chromophores separation and then a better control of FRET efficiency. As result, the light-emitting device with the architecture Al/Ca/P1:PFO/PEDOT:PSS/ITO was found to be more efficient than either the devices using pure PFO or P1. Near white CIE coordinates of (0.26, 0.33) with a maximum luminance of 2500 cd/m² were found for 2 wt.% device.A maximum external quantum efficiency of 1% was obtained, hence, suggesting that the enhancement of the electronic and optoelectronic properties could be achieved by incorporating P1 into the PFO.     

Electrical bistability and memory applications of poly(p-phenylenevinylene) films

Devices based on oriented and unoriented poly(p-phenylenevinylene) films showed presence of electrical bistability. Depending on the voltage sweep direction, current through the device at any voltage had two values. Switching between a low- and a high-conducting state occurred when a suitable voltage pulse was applied. Impedance spectroscopy identified a change in bulk resistance of the device during the transition between the two states. Role of orientation of the polymer film on switching and electrical bistability has been studied. The bistability in these devices had an associated non-volatile memory. We have demonstrated read-only and random access memory applications in such devices using current–voltage and impedance characteristics.     

K424合金镀金膜后红外发射率变化

研究了表面镀金膜的K424合金在热处理前后红外发射率的变化和变化机制.XRD分析结果表明,在热处理后基体金属元素扩散到金膜中,并主要形成了Cr在Au中的固溶体-Au0.7Cr0.3.EDXS分析表明,粗糙表面镀金膜的试样在热处理后,表面主要形成了基体金属元素的氧化物;而抛光表面镀金膜的试样,其表面仍为金膜.通过SR5000光谱辐射计量仪测量合金的红外发射率,结果表明,合金的表面状态和热处理对红外发射率均有较大影响.     

Synthesis of Flexible Graphene/Polymer Composites for Supercapacitor Applications

In this paper, the graphene was synthesized using biocompatible cellulosic component from onions. Onion epidermal cells were chosen as raw material. During heating at high temperature, the bonding among atoms in material was rearranged and forms two-dimensional hexagonal carbon layer (graphene). The characterization of synthesized graphene was done by x-ray diffractometer, Raman spectrometer and field emission scanning electron microscopy, respectively. An attempt has been taken to form the capacitors with two different current collector electrodes, anticipating the performance of the supercapacitors. The observed capacitance values as-obtained for Al and Au current collector were 1.3 μF and 6.08 μF, respectively. However, when thermally exfoliated graphene was used as an electrode on Al and Au current collector, the capacitance value was drastically increased and found to be 1.6 and 41.25 μF, respectively.     

焊丝成分对SiCp/6061Al复合材料MIG焊焊缝组织及性能的影响

采用Al-Mg及Al—Si两种焊丝分别对SiCp／6061Al复合材料进行了MIG焊及脉冲MIG焊，利用光学显微镜、电子显微镜及MTS-810试验机对焊缝的组织及性能进行了分析。结果表明，采用Al—Mg焊丝焊接时，无论是MIG焊还是脉冲MIG焊，熔池中Al-SiC间的界面反应程度均较大，生成了较多的针状Al4C3，且Al4C3的尺寸较大。采用Al-Si焊丝时，MIG焊熔池中的界面反应程度显著降低，仅生成了少量尺寸较小的针状Al4C3；而采用Al—Si焊丝的脉冲MIG焊焊缝中没有发现针状Al4C3。同时，利用Al—Si焊丝可有效地防止焊缝熄弧处的宏观结晶裂纹。力学性能试验表明，采用同样焊丝时，脉冲MIG焊接头的强度及伸长率比MIG焊接头的高，而用Al-Si焊丝焊接的接头强度比用Al—Mg焊丝焊接的接头强度高。     

Impact of electrode metals on a pentacene-based write-once read-many memory device

We report a pentacene-based bistable memory device using Fe as the top electrode and compare it to the Al/pentacene/Al devices. The device displays stable switching from the low-current OFF state to the high-current ON state and long retention time. Our results suggest that Fe has the advantage over Al as the top electrode because it lowers the switching threshold voltage. The Fe devices exhibit similar temperature-dependent behaviors with the reported Al/pentacene/Al devices [D. Tondelier, K. Lmimouni, D. Vuillaume, Appl. Phys. Lett. 85 (2004) 5763]. The device is promising as a write-once read-many (WORM) memory.     

焊丝成分对SiCp/6061 Al复合材料MIG焊焊缝组织及性能的影响

采用Al-Mg及Al-Si两种焊丝分别对SiCp/6061Al复合材料进行了MIG焊及脉冲MIG焊,利用光学显微镜、电子显微镜及MTS-810试验机对焊缝的组织及性能进行了分析.结果表明,采用Al-Mg焊丝焊接时,无论是MIG焊还是脉冲MIG焊,熔池中Al-SiC间的界面反应程度均较大,生成了较多的针状Al4C3,且Al4C3的尺寸较大.采用Al-Si焊丝时,MIG焊熔池中的界面反应程度显著降低,仅生成了少量尺寸较小的针状Al4C3;而采用Al-Si焊丝的脉冲MIG焊焊缝中没有发现针状Al4C3.同时,利用Al-Si焊丝可有效地防止焊缝熄弧处的宏观结晶裂纹.力学性能试验表明,采用同样焊丝时,脉冲MIG焊接头的强度及伸长率比MIG焊接头的高,而用Al-Si焊丝焊接的接头强度比用Al-Mg焊丝焊接的接头强度高.     

Carrier injection from polypyrrole coated gold electrode in pentacene field effect transistors

Carrier injection characteristics of conjugated polymer coated gold (Au) electrode were investigated. Using pentacene field effect transistors (FETs) with Au electrodes covered with polypyrrole (PPy) film deposited electrochemically from an aqueous electrolyte solution of HCl or PTSA (1 M) containing pyrrole monomer, transient microscopic optical second harmonic generation (TRM-SHG) measurements were carried out. Transfer characteristics of the transistors suggested that the injection of holes was assisted by the deposited polymer film improving the hole injection efficiency. The TRM-SHG results well supported the results of the electrical measurements, and we anticipate that polypyrrole could be a potential candidate as an electrode material in polymer electronics.     

Electrodeposition of metals after cation-exchange on modified carbon fibre electrodes

Several metals, Ag, Cu, Pb, Hg and Au, have been electrodeposited on carbon fibre electrodes after cation exchange of their salts with the acidic functional groups of oxidized fibres.Oxidation of carbon fibres was performed by thermal, photochemical and electrochemical treatment. The uptake of the metal cations is greater in the case of anodically oxidized and partially re-reduced carbon fibres, since this procedure leads to the formation of functional groups not only on the carbon surface, as in the case of thermal or photochemical oxidation, but also in the bulk of the fibres.The above-mentioned metals are deposited on the carbon support in a highly dispersed state, which decreases the hydrogen overvoltage and catalyses the reduction of nitroalkanes. These reactions take place on the metal-modified carbon electrodes at much more positive potentials than on carbon and at slightly more positive potentials than on the respective plain metallic electrodes.