Electrochemical Quartz Crystal Microgravimetry Research Articles

Ionic charge transfer in films of polymeric complexes of transition metals with Schiff

Transport of charge-compensating ions in redox transformations in films of polymeric complexes of nickel, copper, and palladium with tetradentate Schiff bases was studied by electrochemical quartz crystal microgravimetry.

Compositional Analysis of Electrodeposited Bismuth Telluride Thermoelectric Thin Films Using Combined Electrochemical Quartz Crystal Microgravimetry−Stripping Voltammetry

Bismuth telluride (Bi 2Te 3 ) is a benchmark material for thermoelectric power generation and cooling applications. Electrodeposition is a versatile technique for preparing thin films of this material; however, it affords films of variable composition depending on the preparation history. A simple and rapid assay of electrodeposited films, therefore, has both fundamental and practical importance. In this study, a new protocol for the electroanalysis of Bi 2Te 3 thin films is presented by combining the two powerful and complementary techniques of electrochemical quartz crystal microgravimetry (EQCM) and stripping voltammetry. First, any free (and excess) tellurium in the electrodeposited film was reduced to soluble Te ( 2- ) species by scanning to negative potentials in a 0.1 M Na 2SO 4 electrolyte, and the accompanying frequency increase (mass loss) was used to determine the content of free tellurium. The film was again subjected to cathodic stripping in the same medium (to generate Bi (0) and soluble Te (2-) from the Bi 2 Te 3 film component of interest), and the EQCM frequency change was used to determine the content of chemically bound Te in the Bi 2Te 3 thin film and thereby the compound stoichiometry. Finally, the EQCM frequency change during Bi oxidation to Bi (3+) and the difference between total Bi and Bi in Bi 2Te 3 resulted in the assay of free (excess) Bi in the electrodeposited film. Problems associated with the chemical/electrochemical stability of the free Bi species were circumvented by a flow electroanalysis approach. Data are also presented on the sensitivity of electrodeposited Bi 2Te 3 film composition to the electrodeposition potential. This newly developed method can be used for the compositional analysis of other thermoelectric thin-film material candidates in general.

Photoelectrochemical Deposition of CdZnSe Thin Films on the Se-Modified Au Electrode

Photoelectrochemical deposition of CdZnSe thin films on the Se-modified Au electrode using electrochemical quartz crystal microgravimetry (EQCM) and voltammetry is described. Corrosion of pre-deposited Se electrodes by illumination at a fixed potential resulted in <TEX>$Se^{2-}$</TEX> species, which was manifest from the EQCM frequency changes. <TEX>$Se^{2-}$</TEX> species generated from the photocorrosion reacted with <TEX>$Cd^{2+}$</TEX> and <TEX>$Zn^{2+}$</TEX> ions in the electrolyte to form CdZnSe films on the Au electrode. The effect of electrolyte composition on the composition and band gap of CdZnSe films was studied in detail. Also, photoelectrochemistry, EDX, Raman spectroscopy were used for the characterization of CdZnSe thin films.

Electrodeposition of Ternary CdZnS Semiconductor Thin Films Using a S-Modified Polycrystalline Au Electrode

This paper describes a two-step approach for the electrochemical deposition of CdZnS thin films on the polycrystalline Au electrode. Initially, an Au substrate is electrochemically modified with a sulfur layer. In the second step, the layer is electroreduced to <TEX>$S^{2-}$</TEX> in the electrolyte dosed with the requisite amount of <TEX>$Cd^{2+}$</TEX> and <TEX>$Zn^{2+}$</TEX> ions to generate CdZnS films in situ. This approach was validated using a combination of linear sweep voltammetry and electrochemical quartz crystal microgravimetry. Thus synthesized CdZnS thin films have different composition depending on the composition of electrolytes. CdZnS thin films are characterized by energy-dispersive X-ray analysis and Raman spectroscopy.

Photoinduced synthesis of CdTe nanoparticles using Te-modified gold electrode in poly(vinyl pyrrolidone)-containing electrolyte

Photocathodic stripping of a pre-deposited tellurium film on a gold electrode in 0.1 M Na2SO4 electrolyte containing Cd2+ ions and poly(vinyl pyrrolidone) (PVP) was used as a route to the photoelectrosynthesis of CdTe nanoparticles. Thus illumination of a Te-modified gold surface generated Te2− species, which were removed from the surface into the bulk electrolyte containing Cd2+and PVP by vigorous stirring. The reaction of Te2−and Cd2+ produced PVP-protected nanosized CdTe particles dispersed in solution in the size range 20–40 nm. In this approach, PVP played a critical role as a stabilizer to form discrete CdTe particles instead of larger (agglomerated) ones. Electrochemical quartz crystal microgravimetry was used to monitor stripping of Te films during the light illumination and the synthesized CdTe nanoparticles were characterized by scanning electron microscopy, energy dispersive X-ray analyses and laser Raman spectroscopy.

PH dependence of the composition of electrodeposited Co films in aqueous sulfate solutions

The electrodeposition of cobalt onto gold is studied as a function of the pH of the electrolyte. Electrochemical quartz crystal microgravimetry is used to identify the material deposited. Using a Co sulfate solution without additives, it is found that for pH 3.2 and at sufficiently negative applied potential, first Co hydroxide deposits and then Co metal. The addition of boric acid, H3BO3 to cobalt sulfate solutions leads to different results: measurements done up to pH 5.5 indicate that only Co metal deposits, showing that boric acid prevents the formation of cobalt hydroxide.

Photoinduced cathodic deposition of CdTe nanoparticles on polycrystalline gold substrate

A combination of photocathodic stripping and precipitation was used to prepare CdTe nanoparticles (size range: 30–60 nm) that were immobilized on a polycrystalline Au substrate. Thus visible light irradiation of a Te modified Au surface generated Te 2− species in situ followed by interfacial reaction with added Cd 2+ ions in 0.1 M Na 2SO 4 electrolyte. The resultant CdTe compound semiconductor deposited as nanosized particles uniformly dispersed on the Au substrate surface. This approach to CdTe nanoparticle deposition was monitored by a combination of electrochemical methods (voltammetry, chronoamperometry) and quartz crystal microgravimetry in the “dark” and under illumination. The synthesized CdTe nanoparticles were characterized by scanning electron microscopy and energy dispersive X-ray analyses and laser Raman spectroscopy.

Electrochemical, microscopic, and EQCM studies of cathodic electrodeposition of ZnO/FAD and anodic polymerization of FAD films modified electrodes and their electrocatalytic properties

Two kinds of chemically modified electrodes were prepared. In the first type of electrodes, zinc oxide (ZnO) and flavin adenine dinucleotide (FAD) molecules were deposited onto the glassy carbon-, gold-, and SnO2-coated glass electrodes by using cyclic voltammetry from the bath solution containing aqueous 0.1 M zinc nitrate, 0.1 M sodium nitrate, and 1 × 10−4 M FAD. It was called as ZnO/FAD modified electrodes. The second type of modified electrode was prepared by the electropolymerization method. Electrochemical polymerization of FAD was carried out from the acidic solution containing 1 × 10−4 M FAD monomers onto electrode surfaces. This poly(FAD)-modified electrode yields a new redox couple in addition to the monomers redox couple. The influence of the concentrations, pH, and electrocatalytic properties of the ZnO/FAD- and poly(FAD)-modified electrodes are investigated by means of the in situ technique electrochemical quartz–crystal microgravimetry (EQCM) combined with cyclic voltammetry and the ex situ technique scanning electron microscopy. From these studies, it appears that the cathodic deposition of ZnO/FAD-modified electrodes gives only one redox couple, and the anodically polymerized FAD film-modified electrodes gives two reversible redox couples. The pH dependence of the redox responses were investigated and the kinetics of electron transfer was evaluated. In addition, the EQCM technique was employed to follow the deposition process of both kinds of modified electrodes in real time as well as the characteristics of the charge transfer associated with the surface-confined redox-active couples. The electrocatalytic activity of the poly(FAD)-modified electrode towards the reduction of hydrogen peroxide and the oxidation of dopamine and ascorbic acid was explored. The important electrocatalytic properties of poly(FAD)-modified electrode were observed for simultaneous separation of dopamine and ascorbic acid in neutral solution. This poly(FAD)-modified electrode has several advantages than the previously reported FAD-modified electrodes.

Electrodeposition of CdTe thin films on Te-modified polycrystalline gold substrates

Abstract A novel two-step approach for the cathodic electrodeposition of CdTe films, based on the initial electrochemical modification of polycrystalline gold substrates with elemental tellurium, is described. This Te-modified Au electrode is subjected to electroreduction (to generate Te 2− species) in a separate, Te-free medium containing Cd 2+ species. In situ precipitation results in the formation of a CdTe semiconductor film. For this two-step approach to work, the electroreduction of Cd 2+ species will have to be shifted to more negative potentials past the Te 0 → Te 2− conversion regime. This was accomplished in the present study by complexation of Cd 2+ species with ethylenediaminetetraacetic acid (EDTA). The CdTe films thus obtained were characterized by linear sweep voltammetry, electrochemical quartz crystal microgravimetry, energy-dispersive X-ray analysis, X-ray photoelectron spectroscopy, and photoelectrochemical experiments.

Underpotential Deposition and Stripping of Lead at Disorganized Monolayer‐Modified Gold Electrodes

AbstractUnderpotential deposition (UPD) and stripping of Pb2+ at thiol‐based disorganized monolayer‐modified gold electrodes was studied by cyclic voltammetry (CV) and electrochemical quartz crystal microgravimetry (EQCM). Electrodes modified with mercaptoacetic acid or mercaptoethane sulfonic acid were studied. Due to the proximity of the potentials for the Pb UPD and thiol reductive desorption, achievement of a UPD‐stripping voltammetry methodology for determination of low concentrations of Pb2+ was not successful. However by comparison of the CV and EQCM data and consideration of the possible mass changes per mole electrons transferred in light of the other species present in solution, possible mechanisms are put forward for the deposition and stripping of Pb2+ at thiol‐modified electrodes.

EQCM Study of Iridium Anodic Oxidation in H2SO4 and KOH Solutions

AbstractIn the present study anodic oxidation of iridium layer formed thermally on a gold‐sputtered quartz crystal electrode has been investigated by electrochemical quartz crystal microgravimetry (EQCM) in the solutions of 0.5 M H2SO4 and 0.1 M KOH. The emphasis here has been put on the microgravimetric behavior of iridium as a metal, because a few previous EQCM studies reported in literature have been devoted to iridium oxide films (IROFs). The objective pursued here has been to elucidate the nature of the main voltammetric peaks, which occur at different ranges of potential in the solutions investigated. It has been found that anodic oxidation of iridium electrode in 0.5 M H2SO4 and 0.1 M KOH solutions is accompanied by irregular fluctuations of the electrode mass at 0.4 V&lt;E&lt;0.8 V followed by regular increase in mass at 0.8 V&lt;E&lt;1.2 V. The cathodic process initially, at 1.2 V&gt;E&gt;0.9 V, proceeds without any or with slight increase in electrode mass, whereas at E&lt;0.8 V a regular decrease in mass is observed. It has been found that mass to charge ratio characterizing the processes of interest is 2 to 3 g F−1in acidic medium, whereas in the case of alkaline one it is 4 to 6 g F−1. The main pair of peaks seen in the voltammograms of Ir electrode in alkaline medium at E&lt;0.8 V is attributable to redox transition Ir(0)→Ir(III), whereas those observed in the case of acidic medium at E&gt;0.8 V should be related to the redox process Ir(0)→Ir(IV) going via intermediate stage of Ir(III) formation. As a consequence of these redox transitions, the gel‐like surface layer consisting of Ir(III) or Ir(IV) hydrous oxides forms on the electrode surface.

Elucidation of the electrodeposition mechanism of molybdenum oxide from iso- and peroxo-polymolybdate solutions

The cathodic electrodeposition of molybdenum oxide thin films prepared from aqueous solutions containing iso-polymolybdates and peroxo-polymolybdates is described. Chronocoulometry, x-ray photoelectron spectroscopy, spectroelectrochemistry, and electrochemical quartz crystal microgravimetry were used to establish corresponding reaction mechanisms for films grown at different deposition potentials. Electrodeposition from acidified iso-polymolybdate solutions proceeds by the reduction of molybdic acid, whereas deposition from aqueous peroxo-based solutions involves the graded reduction of several solution components, primarily comprising molybdic acid and peroxo-polymolybdates. Careful regulation of the deposition potential allows for controlled growth of distinct molybdenum oxide compositions producing films with varied water content and valency.

Open circuit potential transients and electrochemical quartz crystal microgravimetry measurements of dissolution of copper in acidic sulfate solutions

It is demonstrated that open circuit potential transients measurements are able to give the realistic and fast information on the rate of metal corrosion. The results of the studies of the rate of copper corrosion in naturally aerated unstirred acidic sulfate solutions obtained by this method are close to the results of electrochemical quartz crystal microgravimetry measurements. It was found that within the concentration range CuSO 4: 0.001–0.01 M, H 2SO 4: 0.005–0.5 M, independently of whether 0.1 M K 2SO 4 is present in the solution or not, the rate of corrosion of thin (about several tens monolayers) and fresh deposits of copper does not depend on the solution composition and is limited by the transport of the dissolved oxygen. The rate of corrosion of such deposits sometimes exceeds the rate of corrosion of compact copper samples.

Cd underpotential deposition (upd) from a sulfate electrolyte on Au(1 1 1): studies by in situ STM and UHV-EC

Cd underpotential deposition (upd) on Au(111), from a sulfate electrolyte, has been investigated using electrochemical scanning tunneling microscopy (EC-STM), ultra-high-vacuum emersion techniques and electrochemical quartz crystal microgravimetry (EQCM). A number of atomically resolved adlattices were imaged with EC-STM and structures are proposed. Low energy electron diffraction (LEED) patterns observed after Cd upd consistently indicated a (√3×√3)R30° unit cell, which is closely related to those observed with in situ STM. Comparisons of the EC-STM structures with the LEED results suggest that some change occurred upon emersion of the crystal from solution. EC-STM suggests that the Au(111)-(1×23) reconstruction was not lifted by Cd upd. Additionally, the morphology of the reconstruction dictated the structures formed by the adlayer on the surface. Specially, two structures were observed on the reconstructed surface, while others were observed in its absence. EQCM results suggest a large increase in mass upon Cd upd, which appears to result from co-adsorbed anions and possibly the formation of a CdSO4 bilayer. There was evidence that Cd upd results in a surface alloy. Near −0.5 V, small alloy nanoclusters appeared, distributed randomly across the surface in the absences of the reconstruction, and at domain walls in the presences of the reconstruction.

Electrical frequency dependent characterization of DNA hybridization

The hybridization of oligomeric DNA was investigated using the frequency dependent techniques of electrochemical impedance spectroscopy (EIS) and quartz crystal microgravimetry (QCM). Synthetic 5′-amino terminated single stranded oligonucleotides (ssDNA) were attached to the exposed glass surface between the digits of microlithographically fabricated interdigitated microsensor electrodes using 3-glycidoxypropyl-trimethoxysilane. Similar ssDNA immobilization was achieved to the surface of the gold driving electrodes of AT-cut quartz QCM crystals using 3-mercaptopropyl-trimethoxysilane. Significant changes in electrochemical impedance values (both real and imaginary components) (11% increase in impedance modulus at 120 Hz) and resonant frequency values (0.004% decrease) were detected as a consequence of hybridization of the bound ssDNA upon exposure to its complement under hybridization conditions. Non-complementary (random) sequence sowed a modest decrease in impedance and a non-detectable change in resonant frequency. The possibility to detect the binding state of DNA in the vicinity of an electrode, without a direct connection between the measurement electrode and the DNA, has been demonstrated. The potential for development of label-free, low density DNA microarrays is demonstrated and is being pursued.

Pd Nanoparticles as a New Activator for Electroless Copper Deposition

Pd nanoparticles were synthesized and finely controlled by the proper choice of surfactants with different carbon chain lengths. The feasibility of using this newly synthesized Pd nanoparticles as an activator for electroless copper deposition was examined. In this study, copper was successfully deposited on a wafer with a 0.25 μm microtrench. In addition, the effects of the surrounding functional group and the particle size on the kinetics of electroless copper deposition were studied by electrochemical quartz crystal microgravimetry. The performance of Pd nanoparticles was also compared with the traditional Pd/Sn colloid-type activator. © 2003 The Electrochemical Society. All rights reserved.

Electrochemical Synthesis of Molybdenum Oxide Thin Films: Deposition Mechanism and Template-Directed Assembly of Nanostructured Materials and Components

AbstractWe describe the electrochemical deposition of molybdenum oxide thin films prepared from aqueous solutions containing peroxo-poly and oxometallate complexes of molybdenum(VI). Electrochemical quartz crystal microgravimetry (EQCM) was used to establish corresponding reaction mechanisms for films grown at different deposition potentials. Electrodeposition from acidified sodium molybdate solutions proceeds by the reduction of molybdic acid; whilst deposition from aqueous peroxo-based solutions involves the graded reduction of several solution components, primarily comprising molybdic acid and peroxopolymolybdates. Films grown from acidified sodium molybdate solutions are weakly adherent and easily rinsed off, while those grown from peroxo-polymolybdate solutions are strongly attached and stable. Careful regulation of the deposition potential allows for controlled growth of distinct molybdenum oxide compositions to produce films with varied water content and valency. Electrochemical deposition through sacrificial colloidal-crystal templates is also demonstrated to prepare macroporous thin films comprising hexagonally close-packed arrays of spherical pores.

Anodic Electrosynthesis of a Thin Film of Cu2S on a Gold Electrode. A Voltammetric, Nanoelectrogravimetric, and I/t Transient Study

The electroformation of a Cu2S phase, obtained by sulfidization of a thin film of copper placed by the spin-coating technique onto the gold surface of a gold/quartz crystal that is part of an electrochemical quartz crystal microbalance (EQCM), was studied by cyclic voltammetry (CV) and electrochemical quartz crystal microgravimetry. The electrolytic medium employed was a bisulfide-containing aqueous buffered solution (pH 9.2). CV parameters showed that the formation of the Cu2S phase occurred by means of an irreversible diffusion-controlled mechanism, where a first uncomplicated electron transfer was the rate-determining step. The EQCM data showed that the initially formed phase was Cu2S, which was later oxidized to nonstoichiometric compounds (Cu(2-x)S) and CuS. Furthermore ΔQ/Δm data analysis established that the electron reaction valence (n) was close to 2 for all electrochemical processes where Cu/S compounds were involved. The nucleation and growth mechanism (NGM) of the Cu2S phase corresponded to a bidimensional instantaneous mechanism containing two contributions, one controlled by diffusion and the other controlled by charge transfer. Atomic force microscopy (AFM) revealed that the Cu2S phase electroformed on the gold/crystal quartz electrode was deposited as hemispherical particles (sized between 40 and 130 nm) on the terraces and in the cavities present in the gold film.

Cobalt(II) anodic oxidation on silver in ammonia and ethylenediamine solutions studied by rotating disc electrode and EQCM techniques

The electrochemical oxidation of cobalt(II) (Co(II)) on Ag, a partial reaction of the electroless silver plating process, was studied in ammonia, ammonia+ethylenediamine (En) and En solutions (pH 9–12) by voltammetry using a rotating disc electrode and electrochemical quartz crystal microgravimetry (EQCM). In NH 3+(NH 4) 2SO 4 solutions Co(II) (0.01 mol l −1) oxidation takes place simultaneously with Ag dissolution. The Co(II) oxidation on a non-dissolving Ag electrode is observed only at higher concentration (0.1 mol l −1) at pH 10–11. The addition of En does not accelerate Ag dissolution but enhances Co(II) oxidation and shifts its region to more negative potential values by ca. 0.3 V. The En effect is explained by the formation of more easily oxidized and more active Co(II) complexes with En. The Co(II) oxidation current was found to be proportional to CoEn m 2+ ( m=2, 3) concentration and to depend on solution pH. The Co(II) oxidation rate in the presence of En is higher compared to that in ammonia solutions by a factor of 10–40.

Electrochemical and microgravimetric characterization of magnetron-sputtered Fe–Cr–Ni–Ta and Fe–Cr–Ni alloy films in neutral and strongly acidic media

The Fe–Cr–Ni and Fe–Cr–Ni–Ta alloy films were deposited on quartz substrates by magnetron-sputtering using targets of AISI 316 stainless steel and in combination with pure tantalum. The conventional melting of the Fe–Cr–Ni–Ta alloy formed is virtually impossible because the melting point of tantalum is higher than the boiling points of the other components. Elemental content of the films was determined by XPS analysis. Corrosion behaviour of both alloy films was studied in 5% NaCl and 10 M HCl by electrochemical quartz crystal microgravimetry (EQCM), electrochemical impedance spectroscopy (EIS) and dc-voltammetry. The corrosion resistance of Fe–Cr–Ni–Ta appeared to be significantly higher than that of Fe–Cr–Ni in both neutral (5% NaCl) and strongly acidic (10 M HCl) media. The Fe–Cr–Ni–Ta specimen exhibited an extremely high corrosion resistance in 10 M HCl, where the corrosion rates were about one order of magnitude lower than those of Fe–Cr–Ni in neutral solution. EQCM measurements in NaCl solution indicated accumulation of corrosion products on the Fe–Cr–Ni–Ta surface, which was evident from a distinctive increase in electrode mass. By contrast, the mass of the tantalum-free alloy film decreased with a constant rate, which indicated alloy dissolution to prevail. The corrosion current calculated from the mass decrease was in good agreement with that derived from voltammetric measurements. The EQCM data showed that the corrosion resistance of the Fe–Cr–Ni–Ta alloy film in 10 M HCl was about two orders of magnitude higher than that of the Fe–Cr–Ni.