Development of a reversible machining method for fabrication of microstructures by using micro-EDM

A new micromachining method for the fabrication of micro-metal structures by using micro-reversible electrical discharge machining (EDM) was investigated. The reversible machining combines the micro-EDM deposition process with the selective removal process, which provides the ability of depositing or removing metal material using the same micro-EDM machining system. From the discharge mechanism of micro-EDM, the process conditions of micro-EDM deposition were analyzed firstly. Using the brass and steel materials as a tool electrode, the micro-cylinders with 200 μm in diameter and height-to-diameter ratio of more than 5 were deposited on a high-speed steel surface. Then the machining procedure was transformed easily from deposition to selective removal process by switching the process conditions. Different removal strategies including micro-EDM drilling and micro-EDM milling were used in the machining. Micro-holes with 80 μm in diameter are drilled successfully in the radial direction of the deposited micro-steel cylinder. Also, a brass square column with 70 μm in side length and 750 μm in height, and a micro-cylinder with 135 μm in diameter and 1445 μm in height are obtained by using micro-EDM milling. Finally, the characteristics of the deposited material were analyzed. The results show that the material components of a deposited micro-cylinder are almost the same as those of the tool electrode, and the metallurgical bonding has been formed on the interface. In addition, the Vickers-hardness of 454Hv of the steel deposited material is higher when compared to the hardness of 200Hv of the raw steel electrode.     

Electrophoretic deposition of manganese dioxide–carbon nanotube composites

Nanofibers of manganese dioxide have been prepared by a chemical precipitation technique. Electron microscopy studies of the nanofibers showed a large aspect ratio with a length ranged from 0.1 to 1 μm and a diameter of about 2–4 nm. Electrophoretic deposition (EPD) method has been developed for the fabrication of composite films containing manganese dioxide nanofibers and multiwalled carbon nanotubes (MWCNT) for application in electrochemical supercapacitors (ES). Film thickness was varied in the range of 1–20 μm by variation in deposition time and voltage. The method enabled the formation of porous nanostructured composite films with pore size of 10–100 nm. Cyclic voltammetry (CV) data for the films tested in the 0.1 M Na₂SO₄ solutions showed ideal capacitive behavior and high-specific capacitance (SC) in the voltage window of 0–1.0 V versus standard calomel electrode (SCE). Composite films showed higher SC compared to the films without MWCNT. The SC decreased with increasing film thickness and increasing scan rate. Obtained results indicate that EPD is a promising method for the fabrication of manganese dioxide electrodes for ES.     

Study on the characteristics of metal–organic interface for organic thin-film transistors

In this study, the interfacial characteristics between pentacene and Au layers were investigated with varying of the deposition rate of Au layer from 1.0 to 15.0 Å/s. For the devices with the structure of bottom-Au/pentacene/top-Au, it was observed that the electrical characteristics could be improved by increasing the deposition rate of top-Au, and the highest electrical conductivity value, 1.5 × 10⁻⁶ S/cm, was obtained for the device with the top-Au-deposited at 15.0 Å/s. AES results showed that the integrated atomic content of Au in top-Au layer is substantially increased with the deposition rate of top-Au, but there was no critical difference in the depth profile of Au atoms regardless of the deposition rate of top-Au. And also, we fabricated pentacene-based Schottky diodes and measured the hole injection barrier heights from Au electrode into pentacene layer using Fowler-Nordheim theory. Upon the investigations, it was observed that the hole injection barrier was reduced with increasing the deposition rate of Au electrode and the lowest value of 0.12 eV was obtained for the device with the Au electrode deposited at 15.0 Å/s. As a result, the performance of top-contact OTFT could be improved with increasing the deposition rate of Au electrodes (source and drain).     

Semitransparent organic photovoltaic cell with carbon nanotube-sheet anodes and Ga-doped ZnO cathodes

We demonstrate a semitransparent organic photovoltaic (OPV) cell with two transparent electrodes: a multi-wall carbon nanotube (MWCNT) sheet and a Ga-doped ZnO (GZO) are used as a transparent anode and cathode, respectively. As an active layer, we used a bulk heterojunction structure with poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61 butyric acid methyl ester (PCBM). The photovoltaic cell has a GZO/P3HT:PCBM/poly(3,4-ethylene-dioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS)/MWCNT/PEDOT:PSS structure. For comparison, an OPV cell with a MWCNT-sheet anode and an indium tin oxide (ITO) cathode were also fabricated. The OPV cell with the GZO cathode showed better performance than that with the ITO cathode, owing to the lower work function of the former. The semitransparent OPV cell with GZO cathode demonstrated a short-circuit current of 3.4 mA/cm², open-circuit voltage of 0.51 V, and efficiency of 0.45%.     

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.     

Polysilane based ultraviolet light-emitting diodes with improved turn-on voltage,stability and color purity

We demonstrate ultraviolet organic light-emitting diodes (OLEDs) with improved stability, low turn-on voltage and color purity by changing the cathode and annealing temperature of the polymer film. The electron injection process, which limits the electroluminescent performance of organic devices, has been enhanced tremendously by inserting a layer of LiF with appropriate thickness between the cathode and a poly(n-butylphenylsilane) (PS-4) layer, whose device structure is ITO/PEDOT:PSS/polysilane (PS-4)/LiF/Al. Devices with a LiF (6 Å) have the turn-on voltage of 4 V, which is lower than 7 V of devices made with Ca/Al layer. By inserting LiF as the anode interfacial layer, there is increase in the injection of electrons from Al (cathode) side due to tunneling effect and also act as hole blocking layer which enhance the recombination of electron and hole in the emissive layer. PS-4 is spin coated and annealed in vacuum for 1 h at different temperatures (90–120 °C). EL Spectra from these devices consists of white emission along with the UV peak. White emission is significantly suppressed when PS-4 is annealed at higher temperature and threshold voltage is lowest at 110 °C annealing temperature.     

Preparation and characterization of tungsten nanopowders from WC scrap in molten salts

Tungsten carbide (WC) scrap was used as a consumable anode to prepare tungsten powder in NaCl–KCl melt at 1023 K for the first time. The electrolysis process was investigated. Results showed that the tungsten component in WC anode was dissolved as W^2 + into the NaCl–KCl melt. The cathode reaction was controlled by the diffusion of tungsten ions. The effect of electrolysis parameters, including the anode–cathode distance, cathode current density and different electrolysis ways (galvanostatic and potentiostatic electrolysis), on the purity and grain size of the cathode deposits was studied. It showed that a large anode–cathode distance was beneficial to the formation of pure tungsten powder at the cathode. With increasing the cathode current density, the tungsten grain size first decreased and then increased. When the cathode current density was 0.125 A cm^− 2, tungsten powder with a diameter of smaller than 100 nm was obtained. Deposits prepared through galvanostatic and potentiostatic electrolysis was compared in the end.     

Process of mass transfer of amorphous alloys under low-voltage electric spark treatment

Theoretical and experimental studies revealing the physical essence of electric spark deposition (ESD) are presented. The mathematical model is developed for mass transfer during low-voltage ESD of the electrode material, which makes it possible to calculate the mass of material being transferred from the anode to the cathode and control this parameter by changing the initial voltage, the capacitance of the capacitor unit, and the amplitude and vibration frequency of electrode. The mathematical model is confirmed by an experimental study of erosion traces left by electrodes made of amorphous alloys based on cobalt (84KKhSR) and iron (2NSR). The regression exponential dependences of the mass of the material deposited on the cathode on the initial voltage are plotted. The discrepancy between the calculated and experimental values of the mass of material deposited on the cathode does not exceed 5%.     

MoOx interlayer to enhance performance of pentacene-TFTs with low-cost copper electrodes

We demonstrated that the electrical properties of pentacene-thin film transistors with low-cost Cu electrodes can be enhanced by inserting a thin MoO_x interlayer layer between pentacene and Cu source/drain (S/D) electrodes. In comparison with the device having Cu-only electrodes, the performance of the device with MoO_x/Cu electrodes was significantly improved. The saturation mobility increased from 0.13 to 0.61 cm²/V s, threshold voltage reduced from ?14.5 to ?7.3 V, on/off ratio shifted from 8.9 × 10⁵ to 1.6 × 10⁶ and threshold swing varied from 1.92 to 1.33 V/decade. The improvement was attributed to the reduction of contact resistance and the enhancement of hole-injection efficiency. The results suggest modification of Cu S/D electrodes is a simple and effective way to improve device performance and reduce the fabrication cost.     

Development of micro-plasma transferred arc (μ-PTA) wire deposition process for additive layer manufacturing applications

Micro-plasma transferred arc (μ-PTA) deposition process has potential to meet requirements of the meso-sized fabrication and repair of the high value components. This paper reports on the development of μ-PTA as cost effective and energy efficient alternative process for small sized deposition with an overall objective to repair and/or remanufacture the defective dies and molds. An experimental setup was developed to deposit 300 μm diameter wire of AISI P20 tool steel on the substrate of the same material which is one of the most commonly used materials for making the dies and molds used for various applications. Two stage experiments were conducted to indentify the important process parameters generating regular and smooth single bead geometry. The process was further explored for highest possible deposition rate for fabrication of straight walls through multi-layer deposition. The μ-PTA deposition process was found to be capable of fabricating straight walls having total wall width of 2.45 mm and effective wall width of 2.11 mm. The deposition efficiency was found to be 87% for the maximum deposition rate of 42 g/h. The microscopic examination and micro-hardness measurements revealed that the deposited wall is free from cracks, porosity, and inclusions. This study confirms the capability of μ-PTA for ALM in comparison to the existing high energy deposition processes used for meso-scale fabrication and repair applications of the dies and molds. This work confirms that μ-PTA wire deposition process offers the advantages of the laser based processes at much lower cost and more energy efficiency thus making it potential alternative process for repair and remanufacturing of the defective dies and molds. Use of finer wire can further reduce the deposition size enabling μ-PTA wire deposition process to fabricate the miniaturized parts.     

Electrophoretic deposition of conjugated polymer: Deposition from dilute solution and PEDOT coating effect

It has been shown that the films of a soluble conjugated polymer poly[(9,9-dioctyl-2,7-divinylene fluorenylene)-alt-{2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene}] for electronic devices can be prepared by the electrophoretic deposition with polymer suspensions derived from dilute polymer solutions which are so dilute that the conventional spin-coating technique is not applicable. For example, a 100 nm-thick film can be prepared on an indium-tin-oxide (ITO) electrode from a suspension from solution containing 0.1 g/l of the polymer. The thickness of the polymer film deposited is found to be almost proportional to the concentration of the polymer, and the linearity down to 5.0 × 10^?3 g/l is confirmed. On the other hand, it has been found that coating the ITO electrode with poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) salt results in low and nonlinear deposition rate.     

Direct emissive pattern formation in PPV-type polymer with built-in photoresist properties and the application to light emitting devices

The principle of photobleaching in the conjugated polymer material didodecylstilbenevinylene (didodecyl-PSV) was used as a built-in photoresist property to control the extent of the emissive layer in polymer light emitting devices (PLEDs). Illumination of thin films of the conjugated polymer material on optically transparent conducting substrates through a positive mask with short exposure times (20–60 s) using a 150 W Xenon lamp and subsequent application of the and the second electrode enabled the formation of an electroluminescent image of the mask. We demonstrate a direct method where no photoresist, intermediate steps or mechanical manipulation is required to generate a complex emissive pattern employing a homogenous film and homogenous electrodes. The fluorescence of the film showed complex lifetime decays. We found that the lifetime increased with emission wavelength indicating the presence of energetically disordered excitons. The fine structure observed in the solution emission is absent in the film emission. However, after photobleaching the film emission becomes very similar to the solution emission. The appearance of fine structure could indicate that only one state became responsible for the photoluminescence spectrum. Infrared spectroscopy was used to confirm the presence of a degradation route similar to that reported for dialkoxypolyphenylenevinylene materials where the vinylene bonds are react with molecular oxygen and form carboxylic acid groups. Finally the effect of using different electrode metals was established and a comparison made between the photoluminescence and electroluminescence properties. The electroluminescence emission maximum (580 nm) of didodecyl-PSV light emitting devices was found to be redshifted by 20 nm compared to the photoluminescence, exhibited turn-on voltages below 3 V and reached a luminance of 100 cd m⁻² at current densities below 10 mA cm⁻².     

Electrochemical polymerization of acetylene with copper catalyst on platinum and copper electrodes

Acetylene was electrochemically polymerized cathodically at −0.60 V (versus Ag/AgCl) in the presence of copper(I)perchlorate catalyst in acetonitrile containing tetrabutylammonium perchlorate (TBAP) at room temperature under nitrogen atmosphere. An insoluble, black film was deposited on platinum (Pt) and copper (Cu) working electrodes. The dry electrical conductivity of the fresh film was about 550 S cm⁻¹. The chemical structure of the product was investigated by cyclic voltammetry, infrared spectroscopy (IR) and atomic absorption spectroscopy (AAS). Based on the IR data the product consists of a cis-rich form of polyacetylene.     

The characteristics of organic light emitting diodes with Al doped zinc oxide grown by atomic layer deposition as a transparent conductive anode

Al doped zinc oxide (AZO) films, deposited by atomic layer deposition (ALD) were investigated for applying a transparent conductive oxide (TCO) layer as an anode for organic light emitting diode (OLED) devices. AZO films with a thickness of 100 nm were deposited at various Al atomic ratios ranging from 0 to 5% at a deposition temperature (250 °C). The optimum electrical properties: the carrier mobility, the resistivity, and the sheet resistance for the 2% AZO film were found to be 16.2 cm² V^?1 s^?1, 1.5 × 10^?3 cm^?3, and 217 Ω/sq, respectively. The red OLED devices were fabricated using AZO anodes utilizing the various Al atomic ratios; the electrical and optical characteristics were then investigated. The best luminance, quantum efficiency, and current efficiency were found in the OLED device using the 2% AZO TCO; the results were 16599 cd/m², 8.2%, and 7.5 cd/A, respectively.     

Chemical synthesis of cobalt oxide thin film electrode for supercapacitor application

Cobalt oxide thin film electrode was grown on copper substrate from an aqueous alkaline bath containing cobalt chloride as a cobalt source by adopting simple and inexpensive chemical deposition method and characterized for structural and morphological studies. The supercapacitive properties of cobalt oxide electrode were studied in aqueous KOH electrolyte solution. The effect of electrolyte concentration on specific capacitance and the stability of cobalt oxide electrode were studied. The highest specific capacitance achieved with cobalt oxide films was 118 F g^?1. The specific energy (E), specific power (P) and coulomb efficiency (η%) were 5.8 Wh kg^?1, 0.33 kW kg^?1 and 93.44%, respectively.     

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.     

Electrochemical synthesis and characterization of conducting polyparaphenylene using room-temperature melt as the electrolyte

Freestanding polyparaphenylene films were obtained on polymerization of benzene at potential of 1.2 V versus Al wire on substrates like platinum/transparent conducting glass as an anode. The electrolyte used was chloroaluminate room-temperature melt, which was prepared by intimate mixing of a 1:2 ratio of cetyl pyridinium chloride and anhydrous aluminum chloride to yield a viscous liquid. This liquid was miscible in all proportions with benzene and other aromatic hydrocarbons in all proportions at room temperature. The polyparaphenylene films deposited on platinum anode exhibited a prominent cyclic voltammetric peak at 0.7 V versus Al wire as reference electrode in chloroaluminate medium. The impedance spectra gave low charge transfer resistance. The diffused reflectance electronic spectra of the film gave the peaks at 386 nm and 886 nm. The PPP films showed electronic conductivity around 3–4 × 10⁴ S/cm by four probe method under nitrogen atmosphere. The polymer was also characterized by IR spectra, thermal studies, and SEM studies.     

Spatially resolved Langmuir probe measurements of a magnetically enhanced hollow cathode arc plasma

Hollow cathode arc discharges are efficient plasma sources and are applied in substrate pretreatment or plasma-activated deposition processes. In order to generate large volume homogeneous plasmas to guarantee uniformity of plasma activation and coating properties, in the presented configuration a ring-shaped anode is positioned coaxially around the hollow cathode tube. A magnetic field is applied, which is axial within the cathode tube and spreads out in the deposition chamber. In order to characterize the hollow cathode plasma, spatially resolved Langmuir probe measurements have been carried out. The charge carrier density maximum on the cathode tube axis reaches values up to 10¹³ cm^? 3. With increasing distance from the plasma source, the plasma density decreases and shows a smoother lateral profile. Maxwellian electron energy distribution functions are observed with spatially homogeneous electron temperatures in the range 1–4 eV. Increasing the chamber pressure leads to higher plasma densities and lower electron temperatures. Reduction of the gas flow through the hollow cathode tube results in a strong rise of the plasma density over two orders of magnitude. The magnetic field supports the low gas flow mode and leads to higher plasma densities, too. The results of the Langmuir probe measurements are discussed by means of the active zone model and are further related to optical emission measurements performed in the vicinity of the hollow cathode orifice.     

A new symmetric solid-oxide fuel cell with La0.8Sr0.2Sc0.2Mn0.8O3-δ perovskite oxide as both the anode and cathode

A novel perovskite-type La_0.8Sr_0.2Sc_0.2Mn_0.8O₃ (LSSM) oxide was synthesized and evaluated as the electrode material of a symmetric solid-oxide fuel cell. Characterization was done by electrical conductivity, crystal structure stability, redox stability, catalytic activity for methane oxidation and oxygen electro-reduction. LSSM shows greater electrical conductivity than the typical La_0.8Sr_0.2Cr_0.5Mn_0.5O₃ (LSCM) perovskite oxide under both anode and cathode operating conditions. It also shows excellent chemical and structural stability due to the backbone effect of Sc³⁺ for the perovskite lattice structure. A symmetric electrolyte-supported cell with 0.3 mm thick scandium-stabilized zirconia electrolyte and LSSM as cathode and anode shows peak power densities of 310 and 130 mW cm² at 900 °C, respectively, when operating on wet H₂ and wet CH₄. Stable performance is demonstrated.     

Potentiodynamic deposition of polyaniline on non-platinum metals and characterization

Polyaniline (PANI) was potentiodynamically deposited on stainless steel (SS), Ni, Ti, Al and Pb electrodes from aqueous solutions of NaClO₄, oxalic acid and H₂SO₄ of different concentrations. Platinum was also used as a substrate for the purpose of comparison. Although, the non-platinum metals showed reactivity in the electrolytes, the adsorption of aniline monomer occurred leading to initiation and growth of PANI during repeated potential sweeps. The nature of voltammograms of the non-platinum metals during PANI deposition differed from that of the Pt electrode. Subsequent to potentiodynamic deposition, the electrodes were studied for their electrochemical activity in 0.5 M H₂SO₄ without and with dissolved redox species. On all metals, the PANI exhibited the potentiodynamic peak at about 0.2 V corresponding to transition from leucoemaraldine (LE) state to emeraldine (EM) state at low scan rates. However, this peak disappeared on repetition of potential scan and also at high scan rates. The PANI deposited on non-platinum metals showed response to dissolved redox species, viz. hydroquinone/quinone, ferrous/ferric, ferrocyanide/ferricyanide, as reflected in the potentiodynamic and ac impedance measurements. However, the peak potential separation of cyclic voltammograms was very large.