Electrochemical Growth Process Research Articles

Growth of poly(2,5-dimethoxyaniline) coatings on low carbon steel

Poly(2,5-dimethoxyaniline) (PDMA) coatings on low carbon steel (LCS) substrates have been grown by the electrochemical polymerization (ECP) of 2,5-dimethoxyaniline (DMA). The ECP was carried out in an aqueous solution of oxalic acid at room temperature under galvanostatic conditions. Uniform, strongly adherent dark green PDMA coatings were obtained on LCS substrates. These coatings were characterized by potential–time ( E– t) curves, UV-visible absorption spectroscopy, Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). It has been found that the oxalic acid is a suitable medium for the ECP of DMA on the LCS substrate and the electrochemical growth process is characterized by three distinct stages-induction time for ECP of DMA, complete passivation of LCS electrode surface and decomposition of the interphase followed by the ECP of DMA. The induction time is observed to decrease with increase in the applied current density. The optical absorption spectroscopy study reveals the exclusive formation of emeraldine salt (ES) phase of PDMA at lower current density whereas at higher current density coating constitutes the mixed phase of emeraldine base (EB) and ES. The FTIR spectroscopy indicates that the formation of PDMA coating. The surface morphology of PDMA coating is observed to depend on the applied current density and it improves with the increase in the current density.

Electrocopolymerization of Indole and Thiophene: Conductivity-Peak Current Relationship and In Situ Spectroelectrochemical Investigation of Soluble Co-Oligomers

Electropolymerization of indole (IN) in the presence of thiophene (Th) was followed by in situ and ex situ spectroelectrochemical studies. A correlation between absorbance (390 nm) and charge (at 600 mV) values indicated that oligomeric species were formed in solution, and similar results were found with in situ measurements. The increase in conductivity by the incorporation of Th into polyindole was about 60 times for a feed ratio n IN / n Th =1: 10 and 19 times for n IN / n Th =1: 1. Similar effects were also observed during in situ spectroelectrochemical measurements of copolymer formation. It was also found that the cyclic voltametry peak potentials for the electrogrowth of copolymer films were closely correlated to the conductivities of the corresponding films (measured separately by four-point probe method), thereby allowing us to use the peak potential currents to predict the final copolymer film conductivities during the electrochemical growth process. The T g value of the polymer also increased with the incorporation of Th. The results strongly suggest that IN and Th copolymerize on the electrode surface as well as in solution.

Structural study of anodic films formed on aluminum in nitric acid electrolyte

The paper presents the results of investigations of porous Al anodic films formed in HNO 3 electrolytes carried out by means of electrochemical techniques and X-ray diffraction as well as scanning electron microscopy (SEM). It was assumed that both electrochemical formation of a porous oxide and anodic dissolution of metal take place at Al/oxide interface at the same time. The analysis of short-range order (SRO) parameters for relatively high current density, 1×10 3 A/m 2, and anodizing time, 10 min, leads to the conclusion that films mainly consist of amorphous alumina with γ′-Al 2O 3-like SRO and a small amount (∼10%) of amorphous aluminum oxyhydroxide. SEM investigation of the films revealed strong dependence of the surface relief on different applied forming conditions. This marked change in the surface relief is discussed taking into account the relatively complex behavior of Al during anodization in HNO 3 electrolytes, that involves both electrochemical growth and dissolution processes of anodic film associated with an electrochemical dissolution of aluminum substrate.

Doping level change of polythiophene film during its electrochemical growth process

Polythiophene (Pth) films have been electrochemically deposited on mirror-like stainless steel (SS) (or gold) electrode surfaces by direct oxidation of thiophene in boron trifluoride diethyl etherate (BFEE) solutions at a constant applied potential of 1.3 V (vs. Ag/AgCl). The Raman spectra of Pth films have been investigated by excitation with a 514, 633 or 785 nm laser beam. The 633 nm laser beam was found to be the best among the three excitation lights tried for studying the doping level change of Pth film. The overall features of 633 nm excited resonance Raman spectra of as-grown Pth films depend strongly on film thickness. Raman and X-ray photoelectron energy spectroscopic (XPS) results and electrochemical studies demonstrated that the doping level of the Pth film increased with the increase of film thickness. Furthermore, successive cyclic voltammetric scanning was found to be a more effective approach than applying a constant positive potential for doping a thin compact conducting polymer film.

Thermoelectric Nanowires By Template Synthesis: Fabrication, Contacts and Properties

ABSTRACTUsing the technique we have developed to grow porous anodic alumina (PAA) templates on the surface of silicon wafers, we have fabricated arrays of nanowires of thermoelectric materials. By this method we can control both (1) the in-plane geometry by the design of the template and the substrate, and (2) the out-of-plane dimension by control over the electrochemical nanowire growth process. We use several straightforward methods to make electrical contacts to the nanowires. Our transport studies show that both the structure of the nanowire and the contact region have a strong influence on the observed properties of the arrays.

Raman Spectroscopic and Electrochemical Studies on the Doping Level Changes of Polythiophene Films during Their Electrochemical Growth Processes

Polythiophene (PT), poly(3-chlorothiophene) (PCT), and poly(3-methylthiophene) (PMeT) have been electrochemically deposited on mirrorlike stainless steel (SS) electrode surfaces by direct oxidative polymerization of corresponding monomers in boron trifluoride diethyl etherate (BFEE) solution. The doping levels of as-grown thin films have been determined electrochemically. The results demonstrated that PTs were formed nearly in neutral state initially and their doping levels increased during electrochemical growth processes. Monomer structure and electrolyte have strong effects on the doping levels of PTs with a given thickness. Raman spectroscopic studies also confirmed these findings. Furthermore, it is found that the oxidized species of polythiophene and poly(3-chlorothiophene) are mainly presented in radical cations, while dications are favored to be formed in poly(3-methylthiophene) with a doping level higher than ca. 5%.

The Hardness and Wear of Electrochemically Grown Tantalum Oxide

ABSTRACTFor several metallic systems, including tantalum, barrier (non-porous) oxide layers up to 200 nm thick can be grown quickly and efficiently using electrochemical techniques. The thickness of the oxide layer has been found to be linearly proportional to the voltage applied during the electrochemical growth process. These oxides can cause a substantial increase in both the hardness and wear-resistance of the surface. Ex-situ Micro and Nano indentation testing of the Ta/ Ta2O5 system has clearly shown that the indentation hardness increases with oxide thickness, even for indentation depths much greater than the oxide thickness. AFM imaging of indentations and analysis of nanoindentation curves suggests this increased hardness is due to the oxide impeding the pile-up of material at the edges of the indentation, which changes the geometry of the contact. Tribometer testing of various oxide thicknesses has shown that the oxide plays a similar role in preventing wear, specifically by preventing the transfer of material between the two contacting bodies and spreading the load over a greater area. Thus, the electrochemical growth of Ta2O5 provides a convenient method for providing protective hard coatings.

Amperometric biosensors based on the immobilization of oxidases in a Prussian blue film by electrochemical codeposition

Prussian blue has been formed by cyclic voltammetry onto the basal pyrolytic graphite surface to prepare a chemically modified electrode which provides excellent electrocatalysis for both oxidation and reduction of hydrogen peroxide. It is found for the first time that glucose oxidase or D-amino oxidase can be incorporated into a Prussian blue film during its electrochemical growth process. Two amperometric biosensors were fabricated by electrochemical codeposition, and the resulting sensors were protected by coverage with a thin film of Nafion. The influence of various experimental conditions was examined for optimum analytical performance. The glucose sensor responds rapidly to substrates with a detection limit of 2 × 10 −6 M and a linear concentration range of 0.01–3 mM. There was no interference from 2 mM ascorbic acid or uric acid. Another ( D-amino acid) sensor gave a detection limit of 3 × 10 −5 M D-alanine, injected with a linear concentration range of 7.0 × 10 −5-1.4 × 10 −2 M. Glucose and D-amino acid sensors remain relatively stable for 20 and 15 days, respectively. There is no obvious interference from anion electroactive species due to a low operating potential and excellent permselectivity of Nafion.

Experimental evidence for homoclinic chaos in an electrochemical growth process

Experimental investigations of galvanostatic electrochemical growth processes in steady thin layer electrolytes are reported. For some control parameter values, the measurement of the cell potential versus time provides periodic and aperiodic oscillations. The deterministic character of these potential signals is demonstrated using standard dynamical systems theory tools such as time-delay phase portrait reconstructions, Poincaré maps and one-dimensional maps. A transient period-doubling transition is described. The homoclinic nature of the chaotic behavior is emphasized. The origin of the spatio-temporal behavior is discussed in terms of the competition between the electrochemical process (reduction of metallic ions) and the transport processes (migration, diffusion and convection). Analysis of video images shows that the oscillations in growth rate are in phase across the entire cell width (up to 40 mm) and are in phase with the oscillations in the cell potential.

Advanced Dielectrics for Passivation of INSB

ABSTRACTA combination of Electron Cyclotron Resonance (ECR) plasma, electrochemical, and chemical growth process were examined to synthesize dielectric surface passivation layers on InSb. The material properties of ECR-grown SiOxNyon InSb at temperatures from 30°C to 250°C were investigated. Composition analysis was done using Rutherford backscattering spectrometry (RBS) and elastic recoil detection (ERD). The electrical quality of the passivation layer was characterized with capacitance-voltage (C-V) measurements on metal-insulator-semiconductor structures over the frequency range from 1 kHz to 1 MHz. Sulfided layers, Si3ON2on InSb, and sulfided layers capped with S3ON2all exhibited good C-V properties consistent with interface state densities on the order of 1011/cm2-eV, and flatband voltages of magnitude less than 1 V. The difference in adhesion of Si3N4on InSb and the adhesion of Si3ON2on InSb was described in terms of the strength of the bonding at the dielectric-InSb interface. This work is the first to demonstrate passivation of an InSb surface with high-quality ECR silicon oxynitrides grown at room temperature.