Synthesis of nanostructured Cd–Se–Te films through periodic voltammetry for photoelectrochemical applications

In the present investigation, polycrystalline semiconductor Cd–Se–Te films have been electrodeposited at room temperature on conducting glass substrates using cyclic voltammetric technique under controlled periodic scans. The successive anodic and cathodic scans were recorded within the potential range, from 0 to −1.0 V, and over the range of periodic cycles, from 250 to 2,000, in an acidic bath containing respective reducible precursor ions like Cd²⁺, Se⁴⁺, Te⁴⁺, and 1 vol.% Triton X-100 as the surface-active reagent. Thin composite films were produced having variable thickness and composition and grain size of the order of 80–100 nm. The film properties were determined by focused ion beam analysis, energy dispersive analysis of x-rays, x-ray diffraction studies, atomic force microscopy, and scanning electron microscopy. Thickness of the semiconductor films was found to increase linearly with the number of voltammetric cycles. Band gap energies of the films as derived from the reflectance spectra were found to lie between 1.4 and 1.7 eV. The composite films of the Cd–Se–Te ternary system when electrochemically characterized in aqueous polysulfide solution exhibited n-type semiconducting properties and photoconversion efficiency more than 0.4%.     

Surface modification of a reactive metal or alloy by polyaniline for electrooxidation of iodide

Generally, an inert metal such as platinum is used for studying electrooxidation reactions. As a non-platinum metal or alloy undergoes corrosion and oxidation, it is not useful for this purpose. In the present study, surface modification of non-platinum metals by coating electronically conducting polymers for electrooxidation reactions was investigated. Polyaniline (PANI) was electrochemically deposited on stainless steel (SS) substrate by potentiodynamic method. The oxidation of I⁻ was studied by cyclic voltammetry and amperometry experiments. The I⁻/I₂ reaction couple was found to be quasireversible on the PANI/SS electrode. The amperometry study, conducted under fast mass transport conditions, has provided linear relationship between current and concentration of I⁻. The data were analyzed and rate constant of the reaction was evaluated. Thus the oxidation of I⁻, which does not occur on bare SS electrode, was shown to occur through electron transfer mediated by polyaniline.     

Amperometric enzyme electrode for glucose determination based on poly(pyrrole-2-aminobenzoic acid)

Polymerization of pyrrole and 2-aminobenzoic acid has been investigated, and a functionalized stable film of poly(pyrrole-2-aminobenzoic acid) (PP2ABA) has been obtained electrochemically onto platinum electrode. Different cyclic voltammetric behavior is obtained for polypyrrole and PP2ABA during electrosynthesis. Fourier-transformed infrared spectrometry and surface-enhanced Raman spectrometry measurements on the two films have confirmed the presence of carboxylate group in the films. The enzyme, glucose oxidase, was covalently immobilized on a conducting PP2ABA film, and amperometric response was measured as a function of concentration of glucose at a potential of 0.7 V vs Ag/AgCl in 0.1 M phosphate buffer at pH 6.2. The effect of polymeric film thickness, pH, and possible interferents were investigated. The linear range of the calibration curve is from 3 to 40 mM with a sensitivity of 0.058 μA mM⁻¹ cm⁻² and a limit of detection of 0.5 mM. The apperent Mishaelis–Menten constant K _M is calculated to be 1 × 10⁻² mM, and the response time is 5 s.     

Electrochemical Treatment for Effectively Tuning Thermoelectric Properties of Free‐Standing Poly(3‐methylthiophene) Films

The degree of oxidation of conducting polymers has great influence on their thermoelectric properties. Free‐standing poly(3‐methylthiophene) (P3MeT) films were prepared by electrochemical polymerization in boron trifluoride diethyl etherate, and the fresh films were treated electrochemically with a solution of propylene carbonate/lithium perchlorate as mediator. The conductivity of the resultant P3MeT films depends on the doping level, which is controlled by a constant potential from ?0.5 to 1.4 V. The optimum electrical conductivity (78.9 S cm^?1 at 0.5 V) and a significant increase in the Seebeck coefficient (64.3 μV K^?1 at ?0.5 V) are important for achieving an optimum power factor at an optimal potential. The power factor of electrochemically treated P3MeT films reached its maximum value of 4.03 μW m^?1 K^?2 at 0.5 V. Moreover, after two months, it still exhibited a value of 3.75 μW m^?1 K^?2, and thus was more stable than pristine P3MeT due to exchange of doping ions in films under ambient conditions. This electrochemical treatment is a significant alternative method for optimizing the thermoelectric power factor of conducting polymer films.     

Electrochemically formed fullerene-based polymeric films

The recent results of investigations involving the electrochemical formation of polymers containing fullerenes and studies of their properties and applications are critically reviewed. From a structural point of view, these polymers can be divided into four main categories including (1) polymers with fullerenes physically incorporated into the foreign polymeric network without forming covalent bonds, (2) fullerene homopolymers formed via [2+2] cycloaddition, (3) “pearl necklace” polymers with fullerenes mutually linked covalently to form polymer chains, and (4) “charm bracelet” polymers containing pendant fullerene substituents. The methods of electrochemical polymerization of these systems are described and assessed. The structural features and properties of the electrochemically prepared polymers and their chemically synthesized analogs are compared. Polymer films containing fullerenes are electroactive in the negative potential range due to electroreduction of the fullerene moieties. Related films made with fullerenes derivatized with electron-donating moieties as building blocks are electroactive in both the negative and positive potential range. These can be regarded as “double cables” as they exhibit both p- and n-doping properties. Fullerene-based polymers may find numerous applications. For instance, they can be used as charge-storage and energy-converting materials for batteries and photoactive units of photovoltaic cell devices, respectively. They can be also used as substrates for electrochemical sensors and biosensors. Films of the C₆₀/Pt and C₆₀/Pd polymers containing metallic nano-particles of platinum and palladium, respectively, effectively catalyze the hydrogenation of olefins and acetylenes. Laser ablation of electrochemically formed C₆₀/M and C₇₀/M polymer films (M=Pt or Ir) results in fragmentation of the fullerenes leading to the formation of hetero-fullerenes, such as [C₅₉M]⁺ and [C₆₉M]⁺.Dedicated to Professor Dr. Alan M. Bond on the occasion of his 60th birthday.     

Electrical characterization of poly(3-methylthiophene) electrosynthesized onto a tin-oxide substrate

We have investigated poly(3-methylthiophene) (PMeT) thin films electrochemically synthesized directly onto a tin-oxide (TO) electrode. We find that the PMeT film thickness depends linearly on the charge density used during the electropolymerization. We have demonstrated that the current transport in PMeT films (solid phase) is space-charge limited or controlled by thermionic emission, depending on the electrode material. Using TO/PMeT/Ni devices we estimate the positive charge carrier mobility in PMeT to be around 4 × 10⁻⁴ cm² V⁻¹ s⁻¹, and the potential barrier height for positive charge carrier injection at the Al/PMeT interface to be 0.17 eV. Received: 6 December 1999 / Accepted: 24 February 2000     

Ag clusters electrochemically reduced in stearic acid Langmuir-Blodgett films and their structural characterizations

Silver ions confined in the silver stearate Langmuir-Blodgett (L-B) films of 8-14 layers were elec-trochernically reduced into Ag clusters,which made the observation of well-ordered scanning tunneling microscope (STM) images of the films with molecular resolution.A hexagonal packing of the hydrophobic chains was obtained,which was superimposed on the two-dimensional Ag clusters of 2-3 nm m diameter.Furthermore,a (2×1) struc-time of the hexagonal packing was observed.It was attributed to a self-assembled structure of the hydrophilic surface of the L-B films through hydrogen bonding.The strong surface enhanced Raman scattering (SERS) effect of Ag clusters made it possible to record Raman spectra of two-layer steanc acid L-B films in the region of C-C stretching vibration frequencies The appearance of the bands at 1 128 0 and 1 100.7 cm-1,which correspond to the antisymmetric C-C stretching model of the acyl chains m the all-trans conformation and the C-C stretching model of the acyl chains in the gauche     

Light sensitivity and potential stability of electrically conducting polymers commonly used in solid contact ion-selective electrodes

The results of a systematic study of the light sensitivity and long-term potential stability (30 days) of poly(pyrrole) (PPy), poly(3-octylthiophene) (POT), poly(3,4-ethylenedioxythiophene) (PEDOT), poly(aniline) (PANI) and plasticised poly(vinyl chloride) (PVC) containing 20% (m/m) PANI are reported. Thin films were prepared either electrochemically or by the solution casting technique. This fundamental study is of importance because conducting polymers (CP) are commonly used as ion-to-electron transduction materials in all-solid-state solid contact ion-selective electrodes. The potential stability test done in 0.1 M KCl (pH 7.5) simulates the extreme situation when the CP-based SC becomes in direct contact with water. Films prepared of a nanodispersion of PANI showed both good potential stability and insensitivity to light even under illumination with very intensive light (>10⁵ lx). In contrary, it was observed that POT is very light-sensitive. Upon illumination with intensive light, the potential responses of POT films prepared by solution casting and electropolymerisation were 315 and 590 mV, respectively. A room light sensitivity of approximately −10 to −15 mV was observed for these films. The other CPs in this study were insensitive to room light (∼150 lx), but were light-sensitive under illumination with intensive light. The potential drift of PPy(Cl) is below −10 μV/h (3–30 days), whereas the other most stable CPs in this study had a slightly higher potential drift.     

Synthesis, characterization, and thermoelectric properties of a conducting copolymer of 1,12-bis(carbazolyl)dodecane and thieno[3,2-b]thiophene

Poly(1,12-bis(carbazolyl)dodecane-co-thieno[3,2-b]thiophene) (P(2Cz-D-co-TT)), a conducting copolymer was synthesized electrochemically by direct anodic oxidation of 1,12-bis(carbazolyl)dodecane (2Cz-D) and thieno[3,2-b]thiophene (TT) in boron trifluoride diethyl ethrate containing 30% (vol) dichloromethane. As-formed copolymers exhibited high redox activity and reversibility and good conductive properties. The emitting property of as-formed copolymer was different from those of respective homopolymers, and could be tuned by changing the initiate monomer feed ratios. Thermoelectric investigations revealed that the electrical conductivities of as-obtained copolymer films were between 0.1 and 0.3 S cm⁻¹ at ambient temperature, lower than that of polythieno[3,2-b]thiophene (PTT) (0.42 S cm⁻¹) but two orders of magnitude higher than that of poly(1,12-bis(carbazolyl)dodecane) (P2Cz-D) (10⁻³ S cm⁻¹). The Seebeck coefficients and the power factors of the copolymers were improved with different degrees compared with those of PTT and P2Cz-D. As expected, the thermoelectric performance of PTT and P2Cz-D were both improved through copolymerization, which may be beneficial to the exploration and investigation of novel organic thermoelectric materials.     

Capacitive characteristics of nanocomposites of conducting polypyrrole and functionalized carbon nanotubes: effects of in situ dopant and film thickness

The nanocomposites of functionalized single-walled carbon nanotubes (FSWNTs) and conducting polypyrrole (PPy) doped by FSWNTs, Cl⁻, toluenesulfonate (TOS⁻), and dodecylbenzenesulfonate (DBS⁻), respectively, were electrochemically co-deposited to evaluate their applicability in supercapacitors. The effects of the dopants, with focus on their mass, size and surfactivity, and film thickness on the capacitive characteristics were investigated in 3 M KCl aqueous solution. Although the nanostructure of composites can admittedly improve the capacitive properties, dopant anion was demonstrated to be a more essential factor. The specific capacitance of PPy-TOS/FSWNT nanocomposites was greater than that of pristine PPy/FSWNT nanocomposites and PPy-DBS/FSWNT nanocomposites by ten and 100 times, respectively. Furthermore, PPy-TOS/FSWNT nanocomposites exhibited the lowest dependence of capacitance on the charging–discharging rate and composite thickness due to its high electronic and ionic conductivity resulting from the appropriate doping level and size of TOS^- as well as the synergic effect of PPy-TOS and FSWNTs. In addition, PPy-TOS/FSWNT nanocomposites presented a remarkably stable cycling performance.     

Electrochemistry of conductive polymers 39. Contacts between conducting polymers and noble metal nanoparticles studied by current-sensing atomic force microscopy

Electrical properties of contacts formed between conducting polymers and noble metal nanoparticles have been examined using current-sensing atomic force microscopy (CS-AFM). Contacts formed between electrochemically prepared pi-conjugated polymer films such as polypyrrole (PPy), poly(3-methylthiophene) (P3MeT), as well as poly(3,4-ethylenedioxythiophene) (PEDOT) and noble metal nanoparticles including platinum (Pt), gold (Au), and silver (Ag) have been examined. The Pt nanoparticles were electrochemically deposited on a pre-coated PPy film surface by reducing a platinum precursor (PtCl62-) at a constant potential. Both current and scanning electron microscopic images of the film showed the presence of Pt islands. The Au and Ag nanoparticles were dispersed on the P3MeT and PEDOT film surfaces simply by dipping the polymer films into colloid solutions containing Au or Ag particles for specified periods (5 to approximately 10 min). The deposition of Au or Ag particles resulted from either their physical adsorption or chemical bonding between particles and the polymer surface depending on the polymer. When compared with PPy, P3MeT and PEDOT showed a stronger binding to Au or Ag nanoparticles when dipped in their colloidal solutions for the same period. This indicates that Au and Ag particles are predominantly linked with the sulfur atoms via chemical bonding. Of the two, PEDOT was more conductive at the sites where the particles are connected to the polymer. It appears that PEDOT has better aligned sulfur atoms on the surface and is strongly bonded to Au and Ag nanoparticles due to their strong affinity to gold and silver. The current-voltage curves obtained at the metal islands demonstrate that the contacts between these metal islands and polymers are ohmic.     

Electrochemical behavior of lead(II) at poly(phenol red) modified glassy carbon electrode, and its trace determination by differential pulse anodic stripping voltammetry

Poly(phenol red) (denoted as PPR) films were electrochemically synthesized on the surface of a glassy carbon electrode (GCE) by cyclic voltammetry to obtain a chemically modified electrode (denoted as PPR-GCE). The growth mechanism of PPR films was studied by attenuated total reflection spectroscopy. This PPR-GCE was used to develop a novel and reliable method for the determination of trace Pb²⁺ by anodic stripping differential pulse voltammetry. At optimum conditions, the anodic peak exhibits a good linear concentration dependence in the range from 5.0 × 10⁻⁹ to 5.0 × 10⁻⁷ mol L⁻¹ (r = 0.9989). The detection limit is 2.0 × 10⁻⁹ mol L⁻¹ (S/N = 3). The method was employed to determine trace levels of Pb²⁺ in industrial waste water samples. Correspondence: Gongjun Yang, Ming Shen, College of Chemistry and Chemical Engineering, Yangzhou University, Yangzhou 225002, P.R. China     

Sol-gel derived Li+-doped poly(ε-caprolactone)/siloxane biohybrid electrolytes

Electrolytes based on a poly(ε-caprolactone) (PCL)/siloxane organic/inorganic host framework doped with lithium triflate (LiCF₃SO₃) were synthesised through the sol-gel process. In this biohybrid matrix short PCL chains are covalently bonded via urethane linkages to the siliceous network. Samples with salt composition n (molar ratio of PCL repeat units per Li⁺ ion) ranging from ∞ to 0.5 were investigated. All the ormolyte materials analyzed are amorphous. Xerogels with n > 0.5 are thermally stable up to about 300°C. The most conducting ormolyte of the series is that with n = 0.5 (1.6×10⁻⁷ and 3.2×10⁻⁵ Ω⁻¹ cm⁻¹ at 25 and 100°C, respectively). This sample is electrochemically stable between −1 and 6 V versus Li⁺.     

Silver containing sol–gel derived silica thin films: effect of aluminum incorporation on optical,microstructural and bactericidal properties

Silver containing silica (Ag–SiO₂) thin films with and without aluminum (Al) were prepared on soda-lime-silica glass by spin coating of aqueous sols. The coating sol was formed through mixing tetraethyl orthosilicate [Si(OC₂H₅)₄]/ethanol solution with aqueous silver nitrate (AgNO₃) and aluminum nitrate nonahydrate [(AlNO₃)₃·9H₂O] solutions. The deposited films were calcined in air at 100, 300 and 500 °C for 2 h and characterized using x-ray diffraction, UV-visible and x-ray photoelectron spectroscopy. The effect of Al incorporation and calcination treatment on microstructure and durability of the films, and chemical/physical state of silver in the silica thin film have been reported. The bactericidal activity of the films was also determined against Staphylococcus aureus via disk diffusion assay studies before and after chemical durability tests. The investigations revealed that the optical, bactericidal properties and chemical durability of Ag–SiO₂ films can be improved by Al addition. The Al-modified Ag–SiO₂ thin films do not exhibit any coloring after calcination in the range of 100–500 °C, illustrating that silver is incorporated within the silica gel network in ionic form (Ag⁺). Al incorporation also improved the overall durability and antibacterial endurance of Ag–SiO₂ thin films.     

Poly(vinylferrocenium) perchlorate–polyaniline composite film-coated electrode for amperometric determination of hydroquinone

Poly(vinylferrocenium) perchlorate–polyaniline (PVF⁺–PANI) composite film was synthesized electrochemically on Pt electrode in a methylene chloride solution containing a mixture of poly(vinylferrocene) (PVF) polymer and aniline monomer. PVF⁺ polymer in the composite film was used as an electron transfer mediator. The composite coating showed significant electrochemical activity towards hydroquinone (HQ) at pH 4, with high sensitivity and a wide linearity range. The interaction of HQ with PVF⁺ and PANI homopolymer films was investigated electrochemically and spectroscopically. HQ molecules are accumulated on the electrode surface due to trapping by both polymers in the composite film and then oxidized catalytically by PANI. The most significant contribution of PVF⁺ polymer is that it facilitates electron transfer in the composite film. The linear response range was found to be between 1.60 × 10⁻⁴ mM and 115 mM (R ² = 0.999) at 0.45 V vs saturated calomel electrode. The limit of detection (LOD) was 4.94 × 10⁻⁵ mM.     

Structural and Optical Properties of Sol-Gel Deposited Proton Conducting Ta2O5 Films

Proton conducting tantalum oxide films were deposited on ITO (Indium Tin Oxide) coated glass, fused silica and soda-lime glass substrates by spin coating using a sol-gel process. The coating solutions were prepared using Ta(OC₂H₅)₅ as a precursor. X-ray diffraction studies determined that the sol-gel films, heat treated at temperatures below 400°C, were amorphous. Films heat treated at higher temperatures were crystalline with the hexagonal δ-Ta₂O₅ structure. The solar transmission values (T _s ) of tantala films on glass generally range from 0.8–0.9, depending on thickness. The refractive index and the extinction coefficient were evaluated from transmittance characteristics in the UV-VIS-NIR regions. The refractive index values calculated at λ=550 nm increased fromn=1.78 to 1.97 with increasing heat treatment from 150 to 450°C. The films heat treated at different temperatures showed low absorption, with extinction coefficients of smaller thank=1×10⁻³ in the visible range. Impedance spectroscopic investigations performed on Ta₂O₅ films revealed that these films have a protonic conductivity of 3.2×10⁻⁴S/m. The films are suitable for proton conducting layers in electrochromic (EC) devices.     

Stripping chronopotentiometric analysis of cysteine on nano-silver coat polyquercetin–MWCNT modified platinum electrode

Silver nanoparticles coat polyquercetin (Qu) and multi-walled carbon nanotube (MWCNT) complex films were prepared using an electrochemical coupling strategy on platinum electrode (Ag/Qu/MWCNT/Ch/Pt). The new composite material was characterized by means of field emission scanning electron microscopy, X-ray photoelectron spectroscopy spectra, X-ray diffraction, and electrochemical techniques, which confirmed that polyquercetin plays an important role to obtain a great deal of uniformly dispersed silver nanoparticles and MWCNT complex film with a diameter of 10 ± 6 nm. The resulting Ag/Qu/MWCNT/Ch/Pt electrode shows a significant electrocatalysis for the redox of cysteine (CysH). The stripping chronopotentiometric analysis of CysH has been successfully used with a satisfying effect. A linear range of 1 × 10⁻¹⁰ to 9 × 10⁻⁸ M was obtained with a detection limit of 3 × 10⁻¹¹ M (3σ) and sensitivity of 35 μA/nM. The films were also robust, surviving up to 100 consecutive cyclic voltammograms and sonication.     

Electrochemical storage properties of polyaniline-, poly(N-methylaniline)-, and poly(N-ethylaniline)-coated pencil graphite electrodes

Three types of conducting polymers, polyaniline (PANI), poly(N-methylaniline) (PNMA), poly(N-ethylaniline) (PNEA) were electrochemically deposited on pencil graphite electrode (PGE) surfaces characterized as electrode active materials for supercapacitor applications. The obtained films were electrochemically characterized using different electrochemical methods. Redox parameters, electro-active characteristics, and electrostability of the polymer films were investigated via cyclic voltammetry (CV). Doping types of the polymer films were determined by the Mott-Schottky method. Electrochemical capacitance properties of the polymer film coating PGE (PGE/PANI, PGE/PNMA, and PGE/PNEA) were investigated by the CV and potentiostatic electrochemical impedance spectroscopy (EIS) methods in a 0.1 M H₂SO₄ aqueous solution. Thus, capacitance values of the electrodes were calculated. Results show that PGE/PANI, PGE/PNMA, and PGE/PNEA exhibit maximum specific capacitances of 131.78 F g^?1 (≈ 436.50 mF cm^?2), 38.00 F g^?1 (≈ 130.70 mF cm^?2), and 16.50 F g^?1 (≈ 57.83 mF cm^?2), respectively. Moreover, charge-discharge capacities of the electrodes are reported and the specific power (SP) and specific energy (SE) values of the electrodes as supercapacitor materials were calculated using repeating chronopotentiometry.     

Surface modification of neural probes with conducting polymer poly(hydroxymethylated-3,4-ethylenedioxythiophene) and its biocompatibility

A novel conducting polymer, poly(hydroxymethylated-3,4-ethylenedioxy-thiophene) (PEDOT-MeOH), was electrochemically deposited onto the electrodes of micromachined neural probes. Uniformly distributed film was obtained from aqueous solution when doped with polystyrenesulfonate. The surface morphology was rough and had good cellular adhesion. Impedance spectroscopy showed that the magnitude of coated electrode was lower than that of the bare gold over a range of frequencies from 10⁰ to 10⁵ Hz. Since the biocompatibility of the interface between the neural probes and brain tissue plays an important role when the probes are implanted in the central nervous system for long-term application, biomolecules were incorporated into the coating. Nonapeptide CDPGYIGSR was codeposited as the counterion in the conducting films. The surface morphology of the coating was fuzzy, providing many bioactive sites for interaction with neural cells. The magnitude of impedance was as low as 53 kω at the biologically relevant frequency of 1 kHz. An in vitro experiment demonstrated that the neuroblastoma cells grew preferentially on the PEDOT-MeOH/CDPGYIGSR-coated electrode sites and spread beyond the electrode area.     

Nano silver coated patterned silica thin film by sol–gel based soft lithography technique

We report the fabrication of nano silver coated patterned silica thin film by sol–gel based soft lithography technique. Initially, silica gel film on soda lime silica glass was prepared by dipping technique from a silica sol of moderate silica concentration. A PolydimethylSiloxane elastomeric stamp containing the negative replica of the patterns of commercially available compact disc was used for embossing the film and the embossed film was cured up to 450 °C in pure oxygen atmosphere for oxide film. Finally, a precursor solution of AgNO₃ in water containing polyvinyl alcohol as an organic binder was made and used for coating on the patterned silica film by dipping technique and cured the sample up to 450 °C in reducing gas atmosphere to obtain nano silver layer. The formation of only cubic silver (~4.0 nm) and both cubic silver (~5.2 nm) and silver oxide (~3.6 nm) crystallites at 350 and 450 °C film curing temperatures respectively were confirmed by XRD measurements. The % of nano silver metal and silver oxide were 75.4 and 24.6 respectively. The nano-structured surface feature was visualized by FESEM whereas AFM revealed the high fidelity grating structure of the films. Presence of both spherical and rectangular structure (aspect ratio, 2.37) of nano silver/silver oxide was confirmed by TEM. The films were also characterized by UV–Vis spectral study. The patterned film may find application in chemical sensor devices.