Current-time Curves Research Articles

Direct Observation of Sn Adatoms Dynamical Fluctuations at theSn/Ge(111)Surface

The well-known low-temperature phase transition sqrt[3]xsqrt[3] to 3x3 for the 1/3 monolayer of Sn adatoms on the Ge(111) surface has been studied by scanning tunneling microscopy. The STM tip was used as a probe to record the tunneling current as a function of time on top of the Sn adatoms. The presence of steps on the current-time curves allowed the detection of fluctuating Sn atoms along the direction vertical to the substrate. We discuss the effect of temperature and surface defects on the frequency of the motion, finding consistency with the dynamical fluctuations model.

Electrochemical Characteristics of Poly(o-Aminobenzoic Acid) Modified Glassy-Carbon Electrode and Its Electrocatalytic Activity towards Oxidation of Epinephrine

Poly(o-aminobenzoic acid) (o-ABA) film is deposited on glassy-carbon electrode (GCE) by electropolymerization in pH 7.0 phosphate buffer solution (PBS). Electrochemical behavior of modified electrode is investigated by electrochemical impedance spectroscopy (EIS), different pulse voltammetry (DPV), and cyclic voltammetry (CV). The results indicate that there is a greater resistance during the electron transfer process in poly(o-ABA) film than in bare GCE for the redox of [Fe(CN)6]3−/[Fe(CN)6]4−. Further research indicates that epinephrine (EP) can be strongly absorbed on the surface of the poly(o-ABA) film-modified electrode. The modified electrode shows an excellent electrocatalytical activity on EP oxidation. The EP cathodic peak potential shifts negatively with a slope of −53.5 mV/pH, indicating that equal amounts of proton and electron are involved in the electrode reaction process. In pH 7.0 PBS, the peak current of EP and the concentration has a linear relationship from 0 to 65 µM by amperometric current-time curve.

V color centers in electrolytically colored hydroxyl-doped sodium chloride crystals

Hydroxyl-doped sodium chloride crystals were successfully colored electrolytically by using pointed anode and flat cathode at various temperatures and under various electric field strengths. V 2 and V 3 color centers were produced in the colored crystals. Current–time curves for the electrolytic colorations were given, and activation energy for the V 2 and V 3 color center migration was determined. Production of the V 2 and V 3 color centers and formation of current zones for the electrolytic colorations of the hydroxyl-doped sodium chloride crystals are explained.

Evaluation of the Li insertion/extraction reaction rate at a vacuum-deposited silicon film anode

We have recognized that a vacuum-deposited silicon film shows very attractive Li insertion/extraction reaction performance, but the reaction rate in view of Li diffusion in the silicon film has not been determined yet. In this study, we performed analysis of the reaction rate by the means of potential-step chronoamperometry (PSCA) method. Samples of the silicon films of several different thicknesses ranging from 500 to 14000 Å were prepared by depositing silicon in vacuum on an etched Ni foil. The current–time curves were recorded under PSCA condition and offered to evaluate the apparent diffusion coefficient D app of Li in the silicon films. The obtained D app values were as low as 10 −10 to 10 −13 cm 2 s −1, which were dependent on the film thickness.

Synthesis of barium titanate films by plasma electrolytic oxidation at room electrolyte temperature

Crystalline barium titanate films were directly synthesized onto Ti plates by plasma electrolytic oxidation at room temperature using barium acetate and 2 M NaOH as electrolytes. The effect of the concentration of barium acetate ranging from 0.05 M to 0.5 M on the synthesis of BaTiO 3 was investigated. XRD results showed that the formation of BaTiO 3 required a minimum of 0.1 M barium acetate. The electrolytic voltage was controlled at voltages below 85 V to avoid film deterioration by the intense arcing. The current–time curves indicated that intermittent spark discharges were initiated at about 60 V and continued to above 80 V. SEM results revealed the crater-shaped and grained cubic phase barium titanate films formed by plasma electrolytic oxidation. Surface roughness could be greatly reduced by about one order of magnitude by decreasing electrolytic temperature from 55 °C to room temperature. The thickness of the films could reach 20 μm and the dielectric constant could reach 1240 at frequency of 100 Hz.

Study of nano-Au-assembled amperometric CO gas sensor

A novel electrochemical sensor based on nano-Au colloid modified on Pt disk microelectrode was developed for determination of carbon monoxide (CO). The catalytic activation of nano-Au colloid modified on Pt disk microelectrode as substrate was investigated in different supporting electrolyte solutions by cyclic voltammetry and constant potential transient method. The result shows that nano-Au colloid modified on Pt disk microelectrode exhibited strong catalytic effect toward the electrochemical oxidation of CO in 0.5 mol l −1 HClO 4. As compared with the bare Pt disk microelectrode, the nano-Au colloid modified on Pt disk microelectrode can greatly decrease the overpotential and obviously increase the current of CO oxidation. The current–time curve recorded under conditions of constant potential and various CO concentrations suggests that current response depends linearly on CO concentration. A linear equation I (μA) = 0.00917 (μg ml −1) + 0.151 with a correlation coefficient of 0.9938 is obtained over the concentration range 0.756 μg ml −1 at potential +800 mV relative to Ag/AgCl reference electrode. The detection limit is 0.65 μg ml −1 and the relative standard deviation is 5.3% ( n = 5) at room temperature.

Electrolytic coloration of hydroxyl-doped sodium chloride crystals

Hydroxyl-doped sodium chloride crystals were successfully colored electrolytically, which should mainly benefit the appropriate coloration temperatures and electric field strengths. The V, F, colloid, R, M and N centers were produced in the colored crystals, corresponding absorption bands of the centers were reasonably resolved from the absorption spectra of the colored crystals. The current–time curves for the electrolytic colorations were given, and the activation energy for the V center migration was determined, by which the mechanism of electrolytic coloration was well understood.

Effect of electrolysis potential on reduction of solid silicon dioxide in molten CaCl 2

Electrochemical reduction of solid SiO 2 by using a contacting electrode method was investigated in molten CaCl 2 at 1123 K. The samples were prepared by potentiostatic electrolysis at 0.35–1.30 V (vs. Ca 2+/Ca) for 1 h. From the results of XRD, SEM and EPMA, it was confirmed that SiO 2 was electrochemically reduced to Si at 1.25 V or more negative potential, which agreed with the thermodynamic calculation. The current–time curves during electrolysis and the cross-sectional SEM measurements of the samples clearly showed that reduction rate is higher at more negative potential. In addition, Si–Ca alloy formation was confirmed at 0.35 V.

Current–time and current–potential profiles in electrochemical film production. (I) Current–time curves

This is the first article of a series concerning the theoretical description of the current–potential and current–time profiles verified during electrochemical deposition of metals on n -silicon. Our goal is to derive an analytical expression that relates the deposition current to temperature, potential, concentration and potential scan rate – the macroscopic parameters, commonly used to control deposition experiments. In this paper we introduce a model that assumes the existence of two mechanisms to describe the nucleation and growth of the material deposited: the diffusion of ions and the catalytic reaction on the electrode. Analyzing the diffusion of ions into a finite electrochemical system and introducing the reaction kinetics through a time-dependent boundary condition, the model avoids the need for the depletion zone concept. A theoretical expression for current transients under diffusion-controlled growth, I ( c , k , t ), is obtained as a function of the ion concentration c , the parameter that regulates the surface activity and the time t . An analytical expression for the current is particularly convenient to investigate the connection between k , the theoretical parameter that regulates the reaction kinetics, and the potential, which plays the same role in real experiments. This relationship is obtained through a comparison between theoretical and experimental results.

Current–time and current–potential profiles in electrochemical film production. (I) Current–time curves

This is the first article of a series concerning the theoretical description of the current–potential and current–time profiles verified during electrochemical deposition of metals on n-silicon. Our goal is to derive an analytical expression that relates the deposition current to temperature, potential, concentration and potential scan rate – the macroscopic parameters, commonly used to control deposition experiments. In this paper we introduce a model that assumes the existence of two mechanisms to describe the nucleation and growth of the material deposited: the diffusion of ions and the catalytic reaction on the electrode. Analyzing the diffusion of ions into a finite electrochemical system and introducing the reaction kinetics through a time-dependent boundary condition, the model avoids the need for the depletion zone concept. A theoretical expression for current transients under diffusion-controlled growth, I( c, k, t), is obtained as a function of the ion concentration c, the parameter that regulates the surface activity and the time t. An analytical expression for the current is particularly convenient to investigate the connection between k, the theoretical parameter that regulates the reaction kinetics, and the potential, which plays the same role in real experiments. This relationship is obtained through a comparison between theoretical and experimental results.

The influence of platinum on the performance of silver–platinum anti-bacterial coatings

Abstract Anti-bacterial silver coatings were deposited on thermally sensitive polymeric substrates using a combination of magnetron sputtering and neutral atom beam (Saddle Field) plasma sources. The anti-bacterial activity of silver is dependent on the release of Ag+ ions, which act by displacing other essential metal ions such as Ca2+ or Zn2+. This study reports some initial electrochemical experiments intended to evaluate the use of platinum to enhance the release of silver ions from the silver coating. In the galvanic series in seawater silver is more active than platinum and therefore probably enhances Ag+ ion formation through galvanic action when the two metals are in electrical contact. In order to evaluate this several electrochemical methods were employed using magnetron target samples as working electrodes. Cyclic voltammetric, open circuit potential measurements and potential step (chronoamperometric) experiments were performed on several silver–platinum alloys containing from 0.5% to 3.0% Pt and on a pure silver target electrode. In the case of the chronoamperometric measurements, the resulting current–time curves demonstrated that Ag+ formation was enhanced with platinum addition by up to 100%. Results of this preliminary work are discussed with reference to various reactions that can occur on the surface of silver in chloride-containing environments.

Determination of Gold, Silver, and Copper in Gold-Base Alloys by Potentiostatic Coulometry

The working conditions for the simultaneous coulometric determination of 0.5 to 3 mg of gold, silver, and copper with a relative standard deviation of at most ≤0.5% were found in the study of the voltammetric behavior of Au(III), Ag(I), and Cu(II) at a platinum electrode in a 2 M HCl + 0.1 M KCNS solution. Fivefold mass amounts of gold with respect to silver and copper did not interfere with their determination. The three elements can be triply determined in a single portion of a solution using the alternate cathodic and anodic polarization of the electrode ensuring the complete deposition and stripping of Au(0) and Ag(0) and the complete reduction and oxidation of Cu(II) ⇄ Cu(I). The mechanism of current formation due to the chemical reaction of Au(I) disproportionation and its effect on the results of gold determination were studied using the current–time curves. Experimental conditions were proposed to eliminate this reaction. The procedure was used for determining the composition of ternary jewelry alloys containing different amounts of gold, silver, and copper without their preliminary separation.

Study of multi-wall carbon nanotubes self-assembled electrode and its application to the determination of carbon monoxide

A novel electrochemical sensor based on multi-wall carbon nanotubes (MWCNTs) has been developed for the determination of carbon monoxide (CO). The catalytic activation of multi-wall carbon nanotubes microelectrode (MWCNTME) with Pt micro-disk as substrate was investigated in different supporting electrolyte solutions by cyclic voltammetry and constant potential transient method. The result shows that MWCNTME exhibited strong catalytic effect toward the electrochemical oxidation of carbon monoxide in 0.5 mol l −1 HClO 4. As compared with the bare Pt disk electrode, MWCNTME can greatly decrease the overpotential and obviously increase the current of CO oxidation. The current–time curve recorded under conditions of constant potential and various CO concentrations suggests that current response depend linearly on CO concentration. A linear equation I ( μA)=0.00624c ( μg ml −1)+0.2299 with a correlation coefficient of 0.9957 was obtained over the concentration range 0.72–52 μg ml −1 at potential +700 mV relative to Ag/AgCl reference electrode. The detection limit was 0.60 μg ml −1 and the relative standard deviation was 4.8% ( n=5) at room temperature.

Dielectric property and structure of anodic alumina template and their effects on the electrophoretic deposition characteristics of ZnO nanowire arrays

The template-mediated preparation for ZnO nanowire arrays was conducted by electrophoretic deposition (EPD) within the channel of anodic alumina membrane (AAM) template in this study. The influence of annealing temperature on the structure and dielectric properties of AAM template is investigated, and the related deposition mechanisms and morphologies of ZnO nanowire arrays at different AAM annealing temperatures and applied voltages are also discussed. The results show that heat treatment strongly affects the microstructure and dielectric properties of AAM templates, which in turn determines the deposition characteristics of ZnO nanoparticles within template during EPD process. The phase of AAM is changed from amorphous to crystalline structure after annealing. In addition, the grain size and dielectric constant of AAM increase as annealing temperature increases. The breakdown characteristic of AAM is closely related to the oxygen vacancy and grain size of AAM itself, and the applied voltages. The morphologies of ZnO nanowire arrays and current-time curve during EPD are determined by the breakdown behaviors of AAM templates and the applied voltages.

Faradaic current detection during anodic oxidation of the H-passivated p-Si(001) surfacewith controlled relative humidity

Faradaic current during anodic oxidation is measured over a relative humidityrange of 40–70% using an atomic force microscope with humidity control. Thelevel of detected current during the fabrication of oxide dots on H-passivatedSi(001) is in the picoampere (pA) level. Current flow began immediately (within afew milliseconds) after applying an oxidation voltage above a threshold valueand decreased with time according to oxide growth. The total charge resultingfrom the current flow was calculated by integrating the current–time curve andwas found to agree well with an estimation of expected current from the volumeof the fabricated oxide dots. Actual monitoring of the oxidation process by theFaradaic current is demonstrated during the fabrication of a two-dimensionallattice.

Transient current distribution in a cylindrical solid conductor placed in a semiclosed slot

An analytical description which permits arbitrary initial values and an arbitrary current–time curve is presented for the two-dimensional transient current distribution in a cylindrical solid conductor placed in a semi-closed slot. The solution is verified based on characteristic applications. It is then demonstrated how the method developed for individual bars can be incorporated into the analytical integration of the non-linear systems equations of electrical machines using cylindrical conductors.

Superconductive joint on Bi2223/Ag multifilamentary tape

The joining methods between two Bi2223/Ag powder-in-tube–multifilamentary tapes were investigated in this paper. Several kinds of joining process––lap, butt and direct joint were used for green and reacted Bi-tapes. The experimental results and analyses of different methods show that the biggest critical current ratio (CCR) could be obtained by direct connection on green tapes. Meanwhile, on reacted tapes, the biggest CCR (about 77%) was also gained by direct connection with precursor powder adopted 10% Ag. It was found that the sinter time of jointed tape for retaining the better critical current should be shorter than that of unjoined (original) tapes. The critical current versus sinter time curve of jointed tape is much difference comparing with original tape. The microstructure and properties of jointed tape were studied.

Anti-bacterial silver coatings exhibiting enhanced activity through the addition of platinum

Anti-bacterial silver coatings were deposited on thermally sensitive polymeric substrates using a combination of magnetron sputtering and neutral atom beam (Saddle Field) plasma sources. The anti-bacterial activity of silver is dependent on the release of Ag+ ions, which act by displacing other essential metal ions such as Ca2+ or Zn+. This study evaluates the use of platinum to enhance the release of silver ions from the silver coating. In the galvanic series platinum is more active than silver and therefore Pt enhances Ag+ ion formation through galvanic action. In order to evaluate this, potential step (chronoamperometric) experiments were performed on silver/platinum alloys containing 0.5 and 3.0% Pt. The resulting current–time curves demonstrated that Ag+ formation increased with platinum addition by up to 100%. A magnetron sputtering target was fabricated consisting of 1% Pt in a Ag matrix. This was used to sputter Pt/Ag coatings with thicknesses in the range 5–12 nm onto silicone and polyurethane substrates. The bacterial adhesion and bactericidal effects of the coated polymers was assessed using Straphylococcus epidermidis and the cytotoxicity using fibroblast cells. The addition of 1% Pt was found to significantly enhance the anti-bacterial effectiveness of the Ag coatings. Up to a 2 log reduction in bacterial adhesion was achieved for 5 nm thick Ag/1% Pt coatings on silicone, which did not exhibit cytotoxicity.

Similarities between electrochromic windows and thin film batteries

One of the most important type of electrochromic devices (smart windows) is essentially a transparent rechargeable thin film battery (rocking-chair type battery) consisting of a pair of complementary intercalation layers, separated by an ion-conducting polymer electrolyte and contacted by transparent conducting oxide electrodes on glass. At least one of that intercalation electrodes must show colouration by anodic oxidation or cathodic reduction. The similar features of electrochromics and rechargeable thin film batteries concern the material properties, structure of the layers, kinetics of switching (charge/discharge cycles), energy and power density and electrical parameters but also differences between them will be comprehensively discussed. Additionally, we have studied electrochromic devices containing WO 3 as cathodic and Prussian white (PW) as anodic electrochromic layers (glass/FTO/WO 3/K +-Polymer/PW/FTO/glass). Such device configurations reaching high colouration efficiencies, especially in the near IR-range, with a long-term cycle stability >10 5 cycles. The optical response properties in relation to the current–time curves of the charge/discharge processes are discussed.

Modified electrodes for probing the metal-reductase activity of metalloproteins: the reduction of iron(III) catalyzed by Desulfovibrio vulgaris Hildenborough cytochrome c3

Cytochromes c 3 are polyheme c-type cytochromes characterized by low redox potentials, that have been shown to develop metal-reductase activity. In this paper, different strategies are explored to immobilize one of them, Desulfovibrio vulgaris Hildenborough cytochrome c 3, a highly basic tetraheme cytochrome, including adsorption, covalent bonding, imprisonment in a layer-by-layer assembly, and entrapment within cast films or a dialysis membrane. The performance and efficiency of modified (carbon or gold) electrodes have been evaluated using electrochemical (cyclic and square-wave voltammetry, current–time curves) techniques in the presence of a soluble Fe(III) complex, ammonium Fe(III) citrate acting as the soluble substrate, and chosen as a model system. The advantages and drawbacks of each strategy are discussed with the view of further extension of environmental interest to more toxic metal contaminants.