Ag Paint Research Articles

Magnetocatalysis: The Interplay between the Magnetic Field and Electrocatalysis

Magnetocatalysis: The Interplay between the Magnetic Field and Electrocatalysis

Hydrothermally-Grown TiO2 Thin Film-Based Metal–Semiconductor–Metal UV Photodetector

A metal–semiconductor–metal (MSM) ultraviolet photodetector has been fabricated by using hydrothermally-grown TiO2 thin films. Ag paint was used as a contact electrode which showed the good ohmic contact between the metal–semiconductor junctions. The effect of deposition time on the structural, morphological and photodetector properties have been studied. The prepared TiO2 thin films are polycrystalline and show a rutile crystal structure with the preferred orientation along the (110) plane. The MSM UV photodetector was illuminated under a UV lamp with an intensity of 1.8 μW/cm2 and at 5-V bias. The photocurrent of the device increased linearly with the applied voltage. The maximum photocurrent of 3.96 μA was obtained for the film deposited at 5 h and maximum spectral photoresponsivity was 13.29 A/W. The device showed a fast optical switching behavior. The high responsivity and fast photoresponse shows that fabricated TiO2 detectors are good candidates for ultraviolet photodetectors.

Experimental conditions required for accurate measurements of electrical resistivity, thermal conductivity, and dimensionless figure of merit (ZT) using Harman and impedance spectroscopy methods

The Harman method is used extensively for the characterization of the dimensionless figure of merit ZT of thermoelectric (TE) materials and devices. However, its accuracy has often been questioned, since in many cases there are relatively high errors associated with the method. The impedance spectroscopy technique, which has recently been shown as a suitable tool to also characterize TE materials and devices, has some similarities with the Harman method and can also directly provide ZT. In order to obtain reliable measurements in both methods, there are some common critical points that must be taken into account, such as the requirement of fully adiabatic conditions and a negligible Joule effect. In this study, we have evaluated the effect of different experimental conditions in the accuracy of both methods using a sample with known TE properties. Our analysis has led to the identification of different sources of errors and other issues that have not been clearly identified to date that can lead to inaccurate results, namely, the need of a homogeneous Peltier effect at the junctions, problems arising from the use of Ag paint, and the selection of the right value for the current perturbation applied to the system. These problems and sources of errors need to be identified and carefully considered if accurate results are to be obtained.

DC-Driven, Sub-2 V Solid-State Electrochemiluminescent Devices by Incorporating Redox Coreactants into Emissive Ion Gels

We demonstrate a DC-driven solid-state electrochemiluminescent (ECL) device based on a solution-processable ion gel containing luminescent complexes and tetrabutylammonium oxalate (TBAOX) as a coreactant. The ECL gel, comprising a polystyrene-block-poly(methyl methacrylate)-block-polystyrene copolymer, 1-ethyl-3-methylimidazolium bis (trifluoromethylsulfonyl)imide ionic liquid, tris(2,2′-bipyridine)ruthenium(II) hexafluorophosphate (Ru(bpy)3(PF6)2) and TBAOX, was cast as a film on indium tin oxide-coated glass (anode) by spin-coating, and a top electrode (cathode) was prepared by brush-painting Ag paint. Application of 1.6 V DC bias across the device resulted in the onset of light emission. The maximum luminance was achieved at 1:5 mol ratio of Ru(bpy)3(PF6)2 and TBAOX, and the turn-on voltage was independent of the composition. The simplicity of the ECL device and its low voltage operation characteristics make it potentially attractive as a display element for printed electronic circuits.

Room temperature properties of electrical contacts to alumina composites containing silicon carbide whiskers

The electrical properties of contacts to hot-pressed alumina composites having variable volume fractions of SiC whiskers (Vw) were investigated with impedance spectroscopy and current-mode atomic force microscopy at room temperature. Three different contact materials were studied: sputtered Pt, sputtered Ag, and conductive Ag paint. Electrode properties were characterized while fresh due to instability over long times (∼100 h). For percolated samples with Vw≥0.10, the electrical response of the electrodes is manifested in the complex impedance plane by a semicircle whose properties are rooted in Schottky barrier blocking at metal contacts to surface whiskers participating in percolated linkages. This process was modeled with a parallel resistor-capacitor (RcCc) equivalent circuit having a relaxation frequency ωc. The dependences of the specific contact resistance (ρs) and specific capacitance (Cs) on Vw were in agreement with the microlevel interpretation above. The three contact materials exhibited significantly different properties, indicating sensitivities to metal work function and metal-whisker interfacing. Both Rc and ωc have exponential dependences on dc bias (Vdc) which are related through the equivalent circuit model. The strengths of these exponentials and the degree of nonlinearity in I-Vdc curves increase with the fraction of Vdc dropping at the electrodes. The dependence of Cs on Vdc also indicated symmetrical Schottky blocking and was used to estimate charge carrier concentration in the whiskers as 1017–1019 cm−3 and a barrier height of 0.2–1.6 eV for sputtered Ag.

Investigation of p-GaAsSb as a THz Emitter

Our purpose was to determine if GaAsSb might be made to emit THz-frequency electromagnetic radiation. Our result is that, with a suitable electric field imposed and under illumination by ultrashort pulses of near-infrared radiation, GaAsSb indeed emits THz radiation. To the best of our knowledge this is the first report of high-temperature-grown GaAsSb acting as a THz source. THz emission has been observed both by incoherent (pneumatic Golay cell) and by coherent (time-domain spectroscopy using electro-optic detection) experimental configurations. Both simple Ag paint and photolithographically formed Au on Ti antenna structures have been found to produce THz radiation. We compare our results with those from the better-known THz emitter, GaAs. In the case of GaAs, THz radiation is emitted even in the absence of applied bias. This is not the case for GaAsSb. We conclude that the photoconductive mechanism dominates in the emission of THz radiation from epitaxial single-crystal GaAsSb. A further proposal is made that such materials can be used with nanostructured surfaces for special THz-emission characteristics.

Point-contact spectroscopy in neutron-irradiatedMgB211

We report on recent results of point-contact spectroscopy measurements in Mg^{11}B_2 polycrystals irradiated at different neutron fluences up to 1.4 x 10^{20} cm^{-2}. The point contacts were made by putting a small drop of Ag paint -- acting as the counterelectrode -- on the cleaved surface of the samples. The gap amplitudes were extracted from the experimental conductance curves, showing Andreev-reflection features, through a two-band Blonder-Tinkham-Klapwijk fit and reported as a function of the Andreev critical temperature of the junctions, TcA. The resulting Delta_sigma(TcA) and Delta_pi(TcA) curves show a clear merging of the gaps when TcA ~ 9K that perfectly confirms the findings of specific-heat measurements in the same samples. Anomalous contacts with TcA > Tc (being Tc the bulk critical temperature) were often obtained, particularly in samples irradiated at very high fluences. Their fit gave a different dependence of Delta_pi on TcA. The possible origin of these contacts is discussed in terms of local current-induced annealing and/or nanoscale inhomogeneities observed by STM in the most irradiated samples.

Dependence of the Electrochemical Behavior of p-WSe2 Single Crystals on Ohmic Contacts

With the development of a wide variety of semiconductor devices (for instance injection lasers, light emitting diodes, microwave Schottky barriers, ®eld effect transistors, photovoltaic cells etc), the need for low resistance, reproducible, and stable ohmic contacts is increasingly felt. In fact, gradual degradation in many devices seems, to a large extent, to be related to the contact problems. A number of detailed investigations and reviews on the realization of ohmic contacts on different semiconductors have appeared [1]. However, experimental ®ndings indicate that achieving a good, reliable, low resistance ohmic contact is still an art. In the last two decades, electrochemical behavior of layered structure semiconductor=liquid junctions have been intensively investigated both in the dark and under illumination. Among the crystals that have a layered structure, semiconductor transition metal dichalcogenides (TMDC) electrodes used in solar cells, particularly MoSe2 and WSe2 have attracted much interest. Because the back ohmic contacts signi®cantly affect the photoresponse of a photoelectrochemical (PEC) solar cell, various investigators have tried several ohmic contact materials in the preparation of their photoelectrodes. In most of the cases, the electrical back ohmic contacts were made with Ag paint and Ag epoxy. In the present study, the authors tried various metal contacts to determine an appropriate ohmic contact for p-WSe2 layered single crystals. The effect of the metallic materials providing the best ohmic contact on photoconversion has then been compared with PEC solar cells prepared with usual silver paint back contacts. Single crystals used in the present work were grown by a direct vapor transport (DVT) technique. To prepare the ohmic contacts to p-WSe2 single crystals, the following procedure was adopted. Before starting the contact preparation, crystals were thoroughly cleaned: ®rst in trichloroethylene, then in acetone, and ®nally in methanol solution. Contact metals, usually Ag, Au, Ti-Ag, and In, were then coated individually at four different points on the crystal surface, maintaining a linear geometry in the vacuum coating unit at a pressure better than 10y3 Pa. To provide contacts to the deposited metal on the crystal specimen, a specially prepared alloy of silver was used. Copper wires were then ®xed to metal contacts using this alloy, with the help of a soldering gun. Current and voltage measurements were carried out using a Keithley electrometer. To evaluate speci®c contact resistance for different contacting materials, the current-voltage (I-V) characteristics obtained for p-WSe2 single crystals with usual Ag-paste and different metal contacts, In, Au, Ti-Ag, and Ag-metal, are given in Figs 1 to 4, respectively. The values of speci®c contact resistance obtained from these graphs for each of the metal contacts are listed in Table I. In each case, the value of contact resistance was determined by taking the slope near the origin.

Solar Cell Contacts Using Nano-Sized Dispersions

ABSTRACTNano-sized dispersions have been employed as precursor inks for the spray deposition of contacts to both Si and CdTe materials. In the case of Si, nano-sized Al particles (nano-Al) were dispersed and spray deposited onto p-type Si. Annealing above the eutectic temperature causes alloy formation yielding a p+ layer with p ∼ 10−4 Ω•cm. For CdTe, nano-sized Te particles (nano-Te) were dispersed and sprayed onto CdTe/CdS/SnO2/glass heterostructures. Contact to the CdTe layer occurred during a 30 min anneal in He (T = 215 to 255 °C). These solar cells were finished by spin-coating the Te layer with Ag paint and subsequently annealing in air (100 °C / 1 h). This approach produces solar cells with open circuit voltages (Voc) from 720 to 800 mV, short circuit current densities (Jsc) from 18 to 20 mA/cm2 and efficiencies up to 10.3%. The performance of these cells was similar to those produced using the standard NREL contact.

ChemInform Abstract: The Effect of Ohmic Contacts on the Electrochemical Behavior of Illuminated n‐WSe2 and n‐MoSe2

Abstractis studied using either Ag paint or a Ag/Ga alloy to prepare single‐crystal contacts.

The Effect of Ohmic Contacts on the Electrochemical Behavior of Illuminated n ‐ WSe2 and n ‐ MoSe2

A low resistance contact on single crystals is usually obtained simply through a drop of Ag paint. With single crystals a satisfactory ohmic contact is only possible with the use of Ag/Ga alloy. For the first time, a quantitative analysis of an appropriate ohmic contact on layered single crystals is given. Reproducible photoelectrochemical current‐potential characteristics and differential capacity measurements of interface are possible only when a low ohmic contact resistance is realized.

The lateral photovoltaic effect in CdS-Cu2S heterojunction solar cell

The lateral photovoltaic effect has been observed in CdS-Cu2S thin-film solar cells. The effect is more pronounced on the CdS side than on the Cu2S side of the cells. On the CdS side, where the contacts were formed by soldering Cu wire by indium and then applying Ag paint, the photovoltage developed were found to increase as the point of illumination was moved towards the contact. The spectral response of photovoltage for coevaporated cells shows a peak atλ=0.5μm (2.45 eV). But for topotaxial cells two peaks, one atλ=0.5μm and the other atλ=0.65μm (1.89eV) were observed. A band model has been proposed for the heat-treated optimized cells.

Preparation and Photovoltaic Properties of Screen Printed CdS/CuxS Solar Cells

CdS/CuxS solar cells were prepared by using a screen printing method. A low resistivity CdS film was obtained by screen printing CdS pasts on a glass substrate and then sintering it in N2 gas including a small amount of Cd vapor. A CuxS layer was formed on the surface of a CdS film by treating the surface electrochemically in an aqueous solution of CuSO4. An Ag paint electrode or Ni paint electrode was applied to the CuxS layer, which was then heat treated in N2 gas. The spectral responses of the cell suggest that the composition of the CuxS layer was changed to the Cu2S-rich side by this heat treatment. Fabrication of a low resistivity CdS film and heat treatment in N2 gas after applying electrodes were very important factors in obtaining a high efficiency cell. A maximum efficiency of 8.9% was attained for a cell with an active area of 0.90 cm2. The stability of the cell was found to be influenced by the electrode material on the CuxS layer.