Graded SiO2-TiO2 binary composite films were prepd. by a unique electro-assist deposition approach from a mixt. of sol-gel precursors contg. tetramethoxysilane (TMOS) and Ti tetraisopropoxide (TTIP). A neg. potential applied to either stainless steel or ITO substrates causes the redn. of the solvent, thus increasing the concn. of hydroxyl ions, which enhances the precursor condensation and film deposition. The Ti:Si ratio in the films depends on the deposition potential, time and compn. of the precursor soln. This ratio decreases as the films grow thicker due to the more facile kinetics of SiO2 deposition. Nevertheless, the Ti:Si ratio in the films is always lower than in the corresponding precursor soln. As the Ti:Si ratio in the deposition soln. increases, the thickness of the electro-assist deposited films at the same conditions gradually decreases. SIMS and cross-section EDX anal. show that the Ti:Si ratio in the films increases from the surface to the substrate, suggesting electro-assist deposition as a potential method for 1-step prepn. of graded sol-gel films. [on SciFinder(R)]

Conductive polymers, such as polypyrrole (ppy), have been the subject of numerous studies due to their promising applications in organic solar cells, flexible electronics, electrochromic devices, super capacitors, etc. Yet, their application is still limited as a result of poor processability. Silica has been reported to improve the mechanical strength and adhesion of conductive polymer films. In this work, we propose a controllable electrochemical approach for preparing ppy-silica hybrid thin films from a solution containing both pyrrole and silane monomers. It is known that pyrrole can be electropolymerised using anodic potentials, while silica can be electrodeposited under cathodic potentials. Thus, we studied the formation of ppy-silica hybrid thin films on a stainless steel surface by applying alternating potentials, i.e. cathodic followed by anodic pulses (denoted C + A) or anodic followed by cathodic pulses (denoted A + C). We show that by controlling the deposition potential and time for the cathodic and anodic pulses, the film thickness and composition can be manipulated well as analysed using profilometry and EDX. The element depth profile of the films was characterized using secondary ion mass spectroscopy (SIMS). In essence, for the C + A process, pyrrole diffuses through the cathodically electrodeposited wet silica gel layer and undergoes anodic polymerisation on the substrate, while for the A + C process, silane can be electrodeposited both on top of the anodically electrodeposited conductive ppy films as well as on the stainless steel through the pinholes in the ppy film. This offers a simple approach for tuning the structure of conductive polymer-sol-gel composite films.[on SciFinder (R)]

Conductive polymers, such as polypyrrole (ppy), were the subject of numerous studies due to their promising applications in org. solar cells, flexible electronics, electrochromic devices, super capacitors, etc. Yet, their application is still limited as a result of poor processability. SiO2 is reported to improve the mech. strength and adhesion of conductive polymer films. The authors propose a controllable electrochem. approach for prepg. ppy-SiO2 hybrid thin films from a soln. contg. both pyrrole and silane monomers. Pyrrole can be electropolymd. using anodic potentials, while SiO2 can be electrodeposited under cathodic potentials. Thus, the authors studied the formation of ppy-SiO2 hybrid thin films on a stainless steel surface by applying alternating potentials, i.e. cathodic followed by anodic pulses (denoted C + A) or anodic followed by cathodic pulses (denoted A + C). By controlling the deposition potential and time for the cathodic and anodic pulses, the film thickness and compn. can be manipulated well as analyzed using profilometry and EDX. The element depth profile of the films was characterized using secondary ion mass spectroscopy (SIMS). In essence, for the C + A process, pyrrole diffuses through the cathodically electrodeposited wet silica gel layer and undergoes anodic polymn. on the substrate, while for the A + C process, silane can be electrodeposited both on top of the anodically electrodeposited conductive ppy films as well as on the stainless steel through the pinholes in the ppy film. This offers a simple approach for tuning the structure of conductive polymer-sol-gel composite films. [on SciFinder(R)]

Measuring the oxidation-reduction potential (Eh) requires an interface that is not selective toward specific species but exchanges electrons with all redox couples in the solution. Sluggish electron transfer (ET) kinetics with the species will not reflect the "true" Eh of the solution. Here, we present a novel approach by which adsorbed metal nanoparticles (NPs) are used for enhancing ET exchange rates between redox species and electrode surface and therefore affect significantly the measurement of the open circuit potential (OCP) and cyclic voltammetry (CV). The OCP and CV of various organic and inorganic species such as l-dopa, dopac, iron(II), and iodide are measured by bare stainless steel and by stainless steel modified by either Pt or Au NPs. We study the effect of the surface coverage of the stainless steel surface by NPs on the electrochemical response. Moreover, the stainless steel electrode was modified simultaneously by Au and Pt nanoparticles. This improved concurrently the stainless steel response (CV and potentiometry) toward two different species; l-dopa, which shows fast electron transfer on Pt, and catechol, which exhibits fast electron transfer on Au. We believe that this approach could be a first step toward developing a superior electrode for measuring the "true" Eh of complex aquatic systems.[on SciFinder (R)]

Measuring the oxidn.-redn. potential (Eh) requires an interface that is not selective toward specific species but exchanges electrons with all redox couples in the soln. Sluggish electron transfer (ET) kinetics with the species will not reflect the true Eh of the soln. Here, the authors present a novel approach by which adsorbed metal nanoparticles (NPs) were used for enhancing ET exchange rates between redox species and electrode surface and therefore affect significantly the measurement of the open circuit potential (OCP) and cyclic voltammetry (CV). The OCP and CV of various org. and inorg. species such as l-dopa, dopac, Fe(II), and iodide are measured by bare stainless steel and by stainless steel modified by either Pt or Au NPs. The authors study the effect of the surface coverage of the stainless steel surface by NPs on the electrochem. response. Also, the stainless steel electrode was modified simultaneously by Au and Pt nanoparticles. This improved concurrently the stainless steel response (CV and potentiometry) toward two different species; l-dopa, which shows fast electron transfer on Pt, and catechol, which exhibits fast electron transfer on Au. Probably this approach is a 1st step toward developing a superior electrode for measuring the true Eh of complex aquatic systems. [on SciFinder(R)]

Vanadium dioxide is an intriguing candidate for use in intelligent devices such as sensors, magnetic refrigeration and particularly as solar modulating smart window materials. A facile sol-gel route is developed to produce pure VO2 with different nanostructures in a CO2 atmosphere. It was found that the nanoporous structures demonstrated a 16% increase in the luminous transmittance (Tlum) (from 20% to 36%) compared with the vacuum results, while large supercooling effects of up to 30 °C have been obsd. in zero-dimensional structures. [on SciFinder(R)]

Ti-doped V oxide thin films were fabricated by electrochem. deposition on linear polyethylenimine (LPEI)-modified In Sn oxide-coated glass from mixed V oxide and Ti oxide solns. with different Ti concns. The as-prepd. films were studied by XRD, at. force microscopy (AFM), and XPS. The electrochem. behavior of the films was studied using cyclic voltammetry (CV) in 1.0 M LiClO4/propylene carbonate soln. Electrochromism of the oxide films upon Li-ion intercalation/deintercalation was studied by transmittance measurements during the CV process. The charge transfer resistance of the Ti-doped V oxide film was systematically analyzed with electrochem. impedance spectroscopy (EIS). The amorphous Ti-doped V oxide film contg. 4 mol% Ti exhibited the highest transmittance contrast (Δ%T = Tmax - Tmin) of \~51.1%T, and coloration efficiency of 95.7 cm2 C-1 at 415 nm. By increasing the Ti content to 10 mol%, the Ti-doped V oxide film exhibited high switching speed and good cycling reversibility reaching 80% of coloring and bleaching time of 5 and 6 s, resp. Also, the transmittance contrast drops by only 10% after 600 cycles in a two-electrode system. [on SciFinder(R)]

We demonstrate localized electrodeposition of anisotropic metal nanoobjects, namely Au nanorods (GNR), on indium tin oxide (ITO) using scanning electrochemical microscopy (SECM). A gold microelectrode was the source of the gold ions whereby double pulse chronoamperometry was employed to generate initially Au seeds which were further grown under controlled conditions. The distance between the microelectrode and the ITO surface as well as the different experimental parameters (electrodeposition regime, solution composition and temperature) were optimized to produce faceted gold seeds with the required characteristics (size and distribution). Colloidal chemical synthesis was successfully exploited for better understanding the role of the surfactant and different additives in breaking the crystallographic symmetry and anisotropic growth of GNR. Experiments performed in a conventional three-electrode cell revealed the most appropriate electrochemical conditions allowing high yield synthesis of nanorods with well-defined shape as well as nanocubes and bipyramids.[on SciFinder (R)]

We demonstrate localized electrodeposition of anisotropic metal nanoobjects, namely Au nanorods (GNR), on indium tin oxide (ITO) using scanning electrochem. microscopy (SECM). A gold microelectrode was the source of the gold ions whereby double pulse chronoamperometry was employed to generate initially Au seeds which were further grown under controlled conditions. The distance between the microelectrode and the ITO surface as well as the different exptl. parameters (electrodeposition regime, soln. compn. and temp.) were optimized to produce faceted gold seeds with the required characteristics (size and distribution). Colloidal chem. synthesis was successfully exploited for better understanding the role of the surfactant and different additives in breaking the crystallog. symmetry and anisotropic growth of GNR. Expts. performed in a conventional three-electrode cell revealed the most appropriate electrochem. conditions allowing high yield synthesis of nanorods with well-defined shape as well as nanocubes and bipyramids. [on SciFinder(R)]

An approach for patterning surfaces with prepd. nanoparticles is described. Chitosan-stabilized gold nanoparticles (Au/chitosan NPs) were locally deposited on stainless steel (StSt), indium tin oxide (ITO), and highly-ordered pyrolytic graphite (HOPG). Deposition was driven by local pH gradient formed between a surface and a scanning electrochem. microscopy tip set in the direct mode. The pH at the substrate was increased upon biasing the surface by neg. potentials, which caused the redn. of water. As the pH on the surface exceeded that of pKchitosanH+\~6.3 deprotonation of the amino groups of chitosan caused the irreversible deposition of the chitosan/AuNPs. The effect of different parameters, such as tip-surface distance and time, on deposition was studied. While the potential duration showed no clear influence, smaller tip-substrate distance and more neg. potentials applied to the surface caused larger deposits. The overpotential needed for the deposition of nanoparticles on HOPG was the highest while that for StSt was the lowest. On the former, the sluggish kinetics caused the deposition of ring-shaped structures while disk-shaped deposits were formed on the other surfaces. [on SciFinder(R)]

A review. The following topics are discussed: Patterning by the Direct and Feedback modes of the SECM (Semiconductor, metal, and inorg. material etching and deposition; deposition of conducting polymers; self-assembled monolayers, polymers, and biomol. patterning); Speed of patterning, resoln., and scope of materials and approaches. [on SciFinder(R)]