发光多孔硅的光谱及电化学研究

单晶硅是E_g为1.1eV的间接带隙半导体材料,在可见光区不发光,不能应用于光电子领域.但是,Canham 1990年首次发现^[1],适当条件下形成的多孔硅在室温下就可发出强度能与Ⅲ-Ⅴ族半导体发光二极管相媲美的可见光。     

硅在HF溶液中阳极溶解的研究

Uhlir及Turner早在50年代就已发现^[1,2],硅在HF溶液中阳极极化时,阳极电流大于某一特定值硅表面会发生电抛光反应,而低于这个值硅表面则会形成一层不同颜色的多孔硅层.1990年Canham发现多孔硅层在室温下有光致发光现象^[3],受到科学界的高度重视,在世界范围内掀起了研究多孔硅的热潮^[4].众多的研究表明,多孔硅的发光性能与其微孔的多少、大小和分布密切相关.但多孔硅要发展成为可实用的光电子材料,首先必须制备出微孔分布均匀,孔径及孔深可控的多孔硅材料.这就有必要弄清多孔硅的形成机理^[5],了解硅在HF溶液中的溶解过程及机理.为此,本文对不同掺杂浓度不同导电类型的(111)晶面单晶硅在HF溶液中的电流-电压(I-V)、电容-电压(C-V)特性进行了研究,并对这些特性进行了分析.     

Influence of the electrolyte composition and pH on the anodic dissolution of p-type Si in aqueous HF solutions

The influence of the electrolyte composition and pH on the anodic currents obtained during electrochemical etching of p-type silicon in aqueous HF solutions has been investigated. Original and accurate pH measurements were performed to characterize the exact composition of the HF + H₂O electrolytes commonly used. It is shown that for these very acid solutions (pH < 2) almost all fluoride is in the form of the non-dissociated HF species which appears to play a preponderant role in the silicon dissolution reaction kinetics. The effect of pH can be restricted to its influence on the modification of the different concentrations by shifting the equilibria.     

Electrochemical reactions at a copper electrode in copper-conducting solid electrolytes

Potentiostatic measurements are used to show that, depending on the overvoltage sign, either electrochemical deposition or dissolution of copper occurs at the Cu/Cu₄RbCl₃I₂ interface at overvoltages η > 8–10 mV. At η = 10–100 mV, the reaction rate is limited by the formation and expansion of dissolution centers at the copper surface during anodic polarization and crystallization centers, during cathodic polarization. At η > 120 mV, the reaction rate is limited by charge transfer; the exchange current density is 2.7 mA cm^?2 and the anodic transfer coefficient is ～0.45. Under anodic polarization, formation of electron holes in the electrolyte occurs in parallel with the copper anodic dissolution. Therefore, nonstoichiometry of the electrolyte emerges in the near-electrode layer and divalent copper accumulates there.     

Kinetics of Active Dissolution of Hydrophilic Metals Allowing for Anodic Activation

The anodic activation of dissolution of the iron metals is due to the accelerated formation of excess sources of steps during an activating anodic pulse. This is shown on the basis of a model of spatial separation of dissolution and passivation, with allowance made for the formation of pairs of kinks on stationary steps. The formation of pairs of kinks is also the reason for the emergence of a nonpolarizability portion in steady-state current–voltage curves pertaining to anodic dissolution of iron in acid chloride solutions.     

Electrochemical Memory Cells*

Principles of writing and reading the data in a binary code in memory cells based on electrochemical cells are considered. The realization of a multibit cell with a liquid electrolyte, where the data are written by a successive cathodic deposition of alternating metallic layers with different electrochemical properties and thicknesses on the working electrode, is shown. The layer deposition can be controlled by current or voltage pulses of different amplitudes and lengths. The written data are read on the basis of a successive controlled anodic dissolution of the multilayer structures. Attainable parameters of the electrochemical memory of an integral design combining a multicell memory and a controller on the same crystal are estimated.     

Kinetic effects of alcohol addition on the anodic behavior of silicon in acid fluoride media

The anodic dissolution of silicon in acid solutions of ammonium fluoride is investigated in aqueous and water-alcohol media by rotating disk voltammetry and impedance spectroscopy. The voltammograms recorded in water-alcohol media show, in comparison to water, the following effects: an increase of the dissolution currents measured at pH>2 and an opposite effect at pH<2; a distortion of the curve, with a relative increase of the characteristic currents in the region of low applied potentials, indicating easier dissolution of the "wet" oxide forming under those conditions; a shift of the maximum of the current-pH curves from about pH 3 in water to about pH 4 in 50% ethanol v/v. Analysis of impedance data at pH values 4-5 in water and water-ethanol media show similar dependence on potential for the parameters Chf (high-frequency capacitance) and RhfI (Rhf is a high-frequency resistance and I is the steady state current), suggesting the formation of oxide films with similar properties. The marked differences of anodic behavior in the two types of media are discussed and explained in terms of the effects of alcohol addition on the speciation equilibria of hydrofluoric acid and on the kinetic rate constants of dissolution of the surface oxide layer.     

Electrochemical interferometry of a carbon steel in 5–20 ppm KGR-134 inhibited seawater

In the present investigation, holographic interferometry was utilized for the first time to determine the rate change of the number of the fringe evolutions during the corrosion test of a carbon steel in blank seawater and with seawater with different concentrations of a corrosion inhibitor. In other words, the anodic dissolution behaviors (corrosion) of the carbon steel were determined simultaneously by holographic interferometry, an electromagnetic method, and by the electrochemical impedance spectroscopy (EIS), an electronic method. So, the abrupt rate change in the number of the fringe evolutions during corrosion test, EIS, of the carbon steel is called electrochemical interferometry. The corrosion process of the steel samples was carried out in blank seawater and seawater with different concentrations, 5–20 ppm, of KGR-134 corrosion inhibitor using the EIS method, at room temperature. The electrochemical interferograms of the carbon steel in different solutions represent a detail picture of the rate change of the anodic dissolution of the steel throughout the corrosion processes. Furthermore, the optical interferometry data of the carbon steel were compared to the data which were obtained from the EIS tests. Consequently, holographic interferometry is found to be very useful as an electrochemical interferometer for monitoring the anodic dissolution behaviors of metals in aqueous solutions, in which the number of the fringe evolutions of the steel samples can be determined in situ.     

Influence de la distribution de potentiel électrochimique sur l'interprétation de la courbe courant-tension anodique d'une électrode tournante d'alliage Fe-31 % Ni en milieu sulfurique

Influence of the electrochemical potential distribution on the interpretation of the anodic current-voltage curve of a rotating electrode of a Fe-31 % Ni alloy in normal sulfuric acid solution. The anodic steady-state polarization curve of a Fe-31 % Ni rotating-ring electrode in normal sulfuric acid was studied, and the dissolution profiles obtained at different points of the curve were surveyed. We showed that the use of a rotating-ring electrode allowed to obtain the entire J(E) relationship between the current density J and the electrochemical potential E, whereas this relationship cannot be obtained from the polarization curve of the classical rotating-disk electrode because of the non-uniform potential distribution over the disk surface. With the ring electrode, additional information on the transitions between three different states of the metal (homogeneous dissolution, intergranular dissolution and passivity) could be obtained.     

Influence of laser microfabrication on silicon electrochemical behavior in HF solution

Influence of direct laser writing with femtosecond pulses on electrochemical etching of n-type low conductivity (>1,000 Ωcm) silicon is demonstrated. It has been shown that thermal 1-μm-thick SiO₂ layer on silicon surface can be used as a protective layer in the electrochemical etching process. It has been found that laser ablation changes not only the surface morphology and structure of silicon samples but also the character of their anodic etching in aqueous solution of hydrofluoric acid. Formation of microvoids and caverns of irregular shape has been observed at the laser-ablated sites. It is proposed that the change of silicon conductivity from n- to p-type takes place at the laser fabricated regions. Processes of Si anodic oxidation and electrochemical etching are discussed.     

Enhancement and stabilization of the photoluminescence from porous silicon prepared by Ag‐assisted electrochemical etching

In this paper, we present the results of studies on the photoluminescence (PL) of porous silicon (PSi) samples obtained by etching with the assistance of silver metal in different ways. If the Si sample, after being coated with a layer of silver nanoparticles, is electrochemically etched, its PL intensity becomes hundreds of times stronger than the PL intensity when it is chemically etched in the similar conditions. The difference in the PL intensities is explained partly by the anodic oxidation of silicon which occurs during the electrochemical etching process. The most obvious evidence that silicon had been oxidized anodically in the electrochemical etching process is the disappearance of the PSi layer and the appearance of the silicon oxide layer with mosaic structure when the anodization current density is large enough. The anodic oxidation has the effect of PSi surface passivation. Because of that, the PL of obtained PSi becomes stronger and more stable with time. Copyright © 2012 John Wiley & Sons, Ltd.     

Effect of Cl~-ion on Anodic Iron Dissolution in H_2S-Containing Sulfuric Acid Solutions

ResearchershavestudiedtheeffectofCI-onthestructureandpropertiesofthecorrosionproductsinchloridesolutionscontainingH,S"'.IthasbeenfoundthattherearenocorrosioneffectsonironsurfaceswhicharesubmergedinconcentratedacidicchloridesolutionswithlowHZSlevel.Inthepast,theinteractionbetweentheCI-ionandFehasnotbeenstudiedcompletelyandintensively.TheanodicreactionofironinacidicsolutionscontainingHZSwastheironoxidationcatalyzedbyHS-3.WhenCI-ispresentinHZS-containingacidicsolutions,theeffectofCI-onir…     

An environment-friendly electrochemical detachment method for porous anodic alumina

This paper describes an improved one-step voltage pulse detachment method by using perchloric acid and ethanol mixture as detaching solution for the preparation of through-hole porous anodic alumina (PAA) membranes. The detachment of PAA from aluminum substrate and the dissolution of the barrier layer can be completed simultaneously in the detachment solution by applying a pulse voltage in situ after the anodization process. The influence of voltage pulse height and nature of the detachment solution on the efficiency of detachment have been systematically investigated. The present procedure is more environmental friendly and efficient as compared to the conventional electrochemical detachment methods and is promising for the preparation of freestanding PAA films with through-hole morphology which are important for nanomaterials synthesis and nanoscale separation.     

锌电极在氢氧化钾溶液中阳极惰化时的表面相变的研究

本文试图进一步从动力学方面证明恒电位下的锌电极在KOH溶液中阳极惰化时,阳极溶解电流随时间而缓慢下降是由于“表面相变”所引起。用恒电位法测取了锌电极在不同浓度的KOH溶液中电流对时间的曲线。实验结果与推导的动力学方程式相符,表明在恒电位惰化条件下,锌电极表面上最初形成的[Zn(OH)_2]_(ad)在OH~-参预下徐缓地转变为较不易溶的[ZnO]_(ad),因而导致阳极溶解电流的下降。这一表面相变过程可表示如下:     

The determination of copper in silicon by anodic stripping and differential pulse voltammetry

A critical comparison of the application of differential pulse voltammetry and anodic stripping voltammetry to the determination of micro amounts of copper in silicon is described. The anodic stripping technique offers advantages when a dropping mercury capillary with a long drop time is used. The method recommended allows the determination of copper in silicon with a precision of ± 5 %; the limit of determination is about 1μg g^-1. Calibration graphs are linear in the range 0–0.2 μg Cu ml^-1. Methods for the dissolution of silicon are also compared.     

人工体液中TiNiCu形状记忆合金的电化学行为

在Hank’s人工模拟体液中对TiNiCu形状记忆合金的电化学行为进行了研究 .结果表明 ,TiNiCu合金阳极极化时 ,于酸性条件下合金的钝化区较窄、在 10 0～ 150mV电位区间出现了阳极活性溶解 ,钝化膜受到破坏 .pH的降低和Cl- 浓度的升高 ,使孔蚀电位负移 .在Hank’s人工模拟体液中TiNiCu合金的电化学性能比TiNi形状记忆合金劣 ,其原因是TiNiCu合金的晶体结构不单一 ,造成电化学性质不均一 ,构成腐蚀原电池 ,加之晶界析出富Ti的Ti2 Ni析出物成为孔蚀诱发的敏感位置     

Individual Detection and Electrochemically Assisted Identification of Adsorbed Nanoparticles by Using Surface Plasmon Microscopy

The increasing production and application of nanoparticles necessitates a highly sensitive analytical method for the quantification and identification of these potentially hazardous materials. We describe here an application of surface plasmon microscopy for the individual detection of each adsorbed nanoparticle and for visualization of its electrochemical conversion. Whereas the adsorption rate characterizes the number concentration of nanoparticles, the potential at which the adsorbed nanoparticles disappear during an anodic potential sweep characterizes the type of material. All the adsorbed nanoparticles are subjected to the potential sweep simultaneously; nevertheless, each of the up to a million adsorbed nanoparticles is identified individually by its electrochemical dissolution potential. The technique has been tested with silver and copper nanoparticles, but can be extended to many other electrochemically active nanomaterials.     

Recovery of Metals from Anodic Dissolution Slime of Waste from Electric and Electronic Equipment(WEEE) by Extraction in Ionic Liquids

The recovery of metals from a multi-component alloy obtained by crushing, melting and anodic dissolution of waste from electric and electronic equipment(WEEE) was investigated. The anodic dissolution of the alloy was carried out in an electrolysis cell with one copper cathode and a central cast anode, immersed in the electrolyte formed by choline chloride-ethylene glycol-iodine. The temperature of the electrolyte during the process was 343 K. Depending on the electrolysis parameters(current density and cell voltage), cathodic deposits of Sn, Pb and Zn of >99% purity were obtained. Cyclic voltammetry was used in order to determine the deposition potentials of the studied metals. The obtained metallic deposits were subject of determination of XRD, SEM/EDX and AFM in order to evidence the deposits structure and morphology. The experiments performed demonstrated the possibility of separating/selective recovery of metals from the multi-component alloy resulted from the waste from electrical and electronic equipment by anodic dissolution in ionic liquids.     

Anodic behavior of iron, cobalt, and nickel silicides in alkaline electrolytes

Anodic behavior of iron, cobalt, and nickel silicides with different silicon-to-metal ratios and that of pure silicon are studied in NaOH and NaOH + KCl electrolytes using cyclic voltammetry and x-ray photo-electron spectroscopy. Basic silicide dissolution regularities are revealed and compositions of the surface films are examined. Despite a high silicon solubility in alkaline electrolytes, due to protective properties of the surface oxide film of a complex composition, the silicides exhibit good anodic stability.     

Use of the photoluminescence intensity variation as an in-situ probe for electrochemical copper deposition on a p-type GaAs electrode

Photoluminescence was used as an in-situ method for following the electrodeposition of copper on p-type GaAs electrodes from a 0.5 M H₂SO₄ solution containing Cu(II) sulphate. The method appeared to be very sensitive to copper coating and to be able to detect a copper amount of the monolayer range. Moreover, during anodic polarisation of the metallised electrode, photoluminescence measurements showed the complete dissolution of the copper layer. In-situ photoluminescence measurements were confirmed by ex-situ analyses at different stages of the electrochemical treatment of the GaAs electrode.