The Electric Double Layer at the Semiconductor/Electrolyte Interface

Studies of the structure of the semiconductor/electrolyte solution interface are of interest both for the physics of semiconductors - inasmuch as they throw light on some fundamental characteristics of solids ..:_ and for electrochemistry - since the structure of the interface is in many respects the decisive factor in determining the rate of electrochemical reactions on semiconductor electrodes. The object of this review is to give a general idea of recent results obtained in those sections of the electrochemistry of semiconductors which treat the semiconductor electrodes in the equilibrium state. The problems considered are: 1. The electric double layer structure at semiconductor electrodes (potential distribution, charge, relaxation). 2. Methods of investigation. The characteristic features and limits of applicability of basic methods (»field effect«, differential capacity, fast and slow charging curves, electrooptical). 3. Review of experimental results on the electric double layer structure on germanium, silicon and binary compounds

The Li Insertion/Extraction Characteristics of Amorphous Silicon Thin Films

Amorphous hydrogenated silicon (a-Si:H) is known to be a perspective material for negative electrodes of modern lithium-ion batteries. The electrochemical lithium insertion into thin-film a-Si:H electrodes is studied using chronopotentiometry, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The electrodes were grown on stainless-steel substrates by glow discharge at the temperature of T = 100 and 250 oC. The insertion capacity of the films deposited at 250 oC is higher than that of the equally thick films deposited at 100 oC. The increase in the film thickness involves the drastic decrease of the insertion capacity during the potential cycling. An equivalent circuit is suggested for the lithium insertion to the electrodes, which comprises electrolyte resistance and three RC-chains in series, each chain being a parallel connection of a resistance and a constant-phase element, which relate to charge transfer at the silicon/electrolyte interface, charge transport in the passive film on silicon, and the lithium diffusion into the silicon bulk. With the potential cycling in progress, the most significant changes are observed in the chain relating to the passive film. The Li diffusion coefficient in a-Si:H is estimated from data of CV and EIS. It equals D = 4 ·10–13 and 10–13 cm2 s–1 for electrodes synthesized at a temperature of 100 and 250 oC, respectively

Light Activated Electrochemistry: Light Intensity and pH Dependence on Electrochemical Performance of Anthraquinone Derivatized Silicon

We seek to understand how the thermodynamics and kinetics of anthraquinone-containing self-assembled monolayer on silicon electrodes are affected by two key experimental variables: the intensity of the light assisting the anthraquinone/anthrahydroquinone redox process and the local solution environment. The substrates are chemically passivated poorly doped p-type silicon electrodes. The study presents a strategy for the selective modulation of either the anodic or the cathodic process occurring at the interface. Cyclic voltammetry studies showed that unlike for a proton-coupled electron transfer process performed at metallic electrodes, for the redox reaction of the anthraquinone unit on a silicon electrode it becomes possible to (i) selectively facilitate only the oxidation process by increasing the electrolyte pH or (ii) at a given pH value to increase the illumination intensity to anodically shift the onset of the reduction step only but leave the oxidation process thermodynamic unchanged. A model concerning the proton coupled electron transfer mechanism was proposed, where the electron transfer is the rate-determining step for the anthraquinone reduction while a deprotonation step is the rate-determining event for the anthrahydroquinone oxidation on poorly doped illuminated p-type silicon

Light-Activated Electrochemistry for the Two-Dimensional Interrogation of Electroactive Regions on a Monolithic Surface with Dramatically Improved Spatial Resolution

The concept of light-activated electrochemistry (LAE) was recently presented where faradaic electrochemistry could be spatially resolved on a monolithic silicon electrode by illuminating the specific region with light. A major implication from the previous study using illumination from the nonsolution side, or backside, is that the spatial resolution is limited by the finite thickness of silicon wafer. To overcome this restriction, and enable the further application of LAE, in combination with optical imaging for example, herein the spatial resolution of LAE using topside illumination (illumination from the solution side) is explored. The applied potential and irradiated light intensity are found to have significant effects on the spatial resolution. A spatial resolution of ~30 µm was achieved with optimal parameters, which is a 20 times improvement compared with the previously reported backside illumination design, demonstrating the potential application of the strategy including microarray patterning of silicon or for single cell analysis

The Li Insertion/Extraction Characteristics of Amorphous Silicon Thin Films

Amorphous hydrogenated silicon (a-Si:H) is known to be a perspective material for negative electrodes of modern lithium-ion batteries. The electrochemical lithium insertion into thin-film a-Si:H electrodes is studied using chronopotentiometry, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The electrodes were grown on stainless-steel substrates by glow discharge at the temperature of T = 100 and 250 oC. The insertion capacity of the films deposited at 250 oC is higher than that of the equally thick films deposited at 100 oC. The increase in the film thickness involves the drastic decrease of the insertion capacity during the potential cycling. An equivalent circuit is suggested for the lithium insertion to the electrodes, which comprises electrolyte resistance and three RC-chains in series, each chain being a parallel connection of a resistance and a constant-phase element, which relate to charge transfer at the silicon/electrolyte interface, charge transport in the passive film on silicon, and the lithium diffusion into the silicon bulk. With the potential cycling in progress, the most significant changes are observed in the chain relating to the passive film. The Li diffusion coefficient in a-Si:H is estimated from data of CV and EIS. It equals D = 4 ·10–13 and 10–13 cm2 s–1 for electrodes synthesized at a temperature of 100 and 250 oC, respectively

In situ detection of dopamine using nitrogen incorporated diamond nanowire electrode

[[abstract]]Significant difference was observed for the simultaneous detection of dopamine (DA), ascorbic acid (AA), and uric acid (UA) mixture using nitrogen incorporated diamond nanowire (DNW) film electrodes grown by microwave plasma enhanced chemical vapor deposition. For the simultaneous sensing of ternary mixtures of DA, AA, and UA, well-separated voltammetric peaks are obtained using DNW film electrodes in differential pulse voltammetry (DPV) measurements. Remarkable signals in cyclic voltammetry responses to DA, AA and UA (three well defined voltammetric peaks at potentials around 235, 30, 367 mV for DA, AA and UA respectively) and prominent enhancement of the voltammetric sensitivity are observed at the DNW electrodes. In comparison to the DPV results of graphite, glassy carbon and boron doped diamond electrodes, the high electrochemical potential difference is achieved via the use of the DNW film electrodes which is essential for distinguishing the aforementioned analytes. The enhancement in EC properties is accounted for by increase in sp2 content, new C–N bonds at the diamond grains, and increase in the electrical conductivity at the grain boundary, as revealed by X-ray photoelectron spectroscopy and near edge X-ray absorption fine structure measurements. Consequently, the DNW film electrodes provide a clear and efficient way for the selective detection of DA in the presence of AA and UA.[[booktype]]紙

Superhard Phases of Simple Substances and Binary Compounds of the B-C-N-O System: from Diamond to the Latest Results (a Review)

The basic known and hypothetic one- and two-element phases of the B-C-N-O system (both superhard phases having diamond and boron structures and precursors to synthesize them) are described. The attention has been given to the structure, basic mechanical properties, and methods to identify and characterize the materials. For some phases that have been recently described in the literature the synthesis conditions at high pressures and temperatures are indicated.Comment: Review on superhard B-C-N-O phase