Ümit Demir

Formation of Bi2S3 thin films on Au(111) by electrochemical atomic layer epitaxy: kinetics of structural changes in the initial monolayers

Abstract The kinetics and growth mechanism of the first and second monolayers of Bi2S3 by electrochemical atomic layer epitaxy (ECALE) has been studied using voltammetry and chronoamperometry techniques. Scan rate dependent cyclic voltammetry experiments reveal that the peak current in the stripping of the S layer from a Bi modified Au(111) electrode is a linear function of a 2/3 power of the scan rate, ν2/3. Similar behavior is observed for the deposition of Bi on to one atomic layer of an S modified Au(111) electrode. The dissolution of the Bi atomic layer from the S modified Au(111) electrode involves an initial Langmuir-type adsorption–desorption accompanied by a nucleation and two-dimensional (2-D) growth process. When Bi atomic layers are used as a first layer, the nucleation and 2-D growth process was observed for both deposition and stripping. Analysis of the reduced variables demonstrates that the stripping of S from Au(111)Bi and stripping of Bi from Au(111)S fit the progressive model. Our results suggest that the nucleation and 2-D growth mechanism is the dominant process in the formation of Bi2S3 atomic layers if Bi is used as the first layer in the ECALE method.

Size-controlled electrochemical growth of PbS nanostructures into electrochemically patterned self-assembled monolayers.

1-Hexadecanethiol self-assembled monolayers (HDT SAMs) on Au(111) were used as a molecular resist to fabricate nanosized patterns by electrochemical reductive partial desorption for subsequent electrodeposition of PbS from the same solution simultaneously. The influences of potential steps of variable pulse width and amplitude on the size and the number of patterns were investigated. The kinetics of pattern formation by reductive desorption appears to be instantaneous according to chronoamperometric and morphological investigations. PbS structures were deposited electrochemically into the patterns on HDT SAMs by a combined electrochemical technique, based on the codeposition from the same saturated PbS solution at the underpotential deposition of Pb and S. Scanning tunneling microscopy measurements showed that all of the PbS deposits were disk shaped and uniformly distributed on Au(111) surfaces. Preliminary results indicated that the diameter and the density of PbS deposits can be controlled by controlling the pulse width and amplitude of potential applied at the reductive removal stage of HDT SAMs and the deposition time during the electrochemical deposition step.

Electrochemical synthesis and characterization of 2-amino-3-cyano-4-phenylthiophene dimer and oligomers

Abstract The electrochemical dimerization of 2-amino-3-cyano-4-phenylthiophene (ACPT) has been studied in acetonitrile solutions by using Pt electrodes. The resulting dimer obtained after a preparative electrolysis was characterized by using FAB mass, 13 C and 1 H nuclear magnetic resonance ( 13 C -NMR and 1 H -NMR) and fourier transform infrared spectroscopic techniques. Voltammetric measurements showed that the dimer formed by the coupling of two cation radicals (CR–CR) is stable and has a reversible electrochemical behavior. The fast scan voltammetric experiments using microelectrodes revealed that the dimer formed by the coupling of a cation radical with a parent molecule (CR–PM) has a quasi-reversible electrochemistry and undergoes to further couplings resulting in oligomers. On the basis of voltammetric and spectroscopic data, it was found that dimerization of ACPT occurs mainly by the coupling of a neutral ACPT molecule with the cation radicals, which is very important in the formation of regioregular oligomers and polymers.

Stoichiometry, Morphology, and Size-Controlled Electrochemical Fabrication of CuxO (x = 1, 2) at Underpotential

A new one-step electrochemical approach has been developed for the morphology, size, and stoichiometry-controlled synthesis of Cu2O, CuO, and Cu2O/CuO composite structures at room temperature without using surfactants, capping agents, or any other additives. The electrochemical deposition of a Cu monolayer using underpotential deposition (UPD) and the flow rate of oxygen gas bubbled through the deposition solution used for oxidation of the Cu layer are the key parameters for controlling the stoichiometry of the CuxO (x = 1, 2) structures. The morphologies, crystallinity, stoichiometries, optical properties, and photoelectrochemical properties of the as-electrodeposited Cu2O and CuO materials were analyzed using scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), energy dispersive spectroscopy (EDS), UV-vis absorption, and photoelectrochemical (PEC) techniques. The results indicated that the Cu2O and CuO materials electrodeposited on both indium tin oxide coated (ITO) quartz and gold electrodes using this new electrochemical technique exhibit high-quality single crystalline structures and high photoactivity with rapid photoelectrical response to light irradiation.

The electrochemical oxidation of 2-amino-3-cyano-4-phenylthiophene: evidence for a new class of photoluminescent material

Abstract The electrooxidation of 2-amino-3-cyano-4-phenylthiophene on platinum electrodes was investigated for the first time in acetonitrile by cyclic voltammetry, controlled potential electrolysis, and spectrometric methods. The voltammetric responses were similar to those of common aromatic amino compounds. Two types of dimers were observed as intermediates in the early stages of oxidation. Ethlyamine and phenol were added to an electrolytic solution in order to determine the electrochemical behavior of 2-amino-3-cyano-4-phenylthiophene under basic and acidic conditions. We propose an E(CE) n mechanism to account for this electrochemistry. 2-Amino-3-cyano-4-phenylthiophene is first oxidized to a cation radical, followed by chemical coupling to form dimers, which are electroactive. Controlled potential electrolysis gave a new class of π-conjugated oligoaminothiophenes exhibiting an absorbance at 432 nm and photoluminescence at 538 nm.

Fotovoltaik İnce Film Olarak Elektrokimyasal Depozit Edilmiş Cu-Grafen ve Cu2O-Grafen Nanokompozitler

Bu calismada, Au ve indiyum kalay oksit (ITO) elektrotlarda bakir iyonlarinin ve grafen oksitin sulu suspansiyonlarindan es zamanli olarak indirgemesine dayanan Cu-grafen ve Cu2O-grafen nanoyapilarinin elektrokimyasal buyumesine yeni bir yaklasim sunulmaktadir. Elde edilen kompozit nanoyapilar, taramali elektron mikroskobu (SEM), enerji dagilimli spektroskopi (EDS), X-isini kirinimi (XRD), fotoluminesans spektroskopi (PL) ve foto-akim olcumleri ile karakterize edildi. Deney sonuclari, Cu-grafen ve Cu2O-grafen kompozit film yapilarinin, uygulanan potansiyel ve deney ortami ile kolayca kontrol edilebildigini gostermektedir. Sentezlenen Cu-grafen ve Cu2O-grafen nanokompozit fotoelektrotlar; iyi fotovoltaik ozellikler sergilerler ve gunes enerjisi donusumundeki uygulamalar icin kullanilabilirler.