A general model of metal underpotential deposition in the presence of thiol-based additives based on an in situ STM study

Bis(3-sulfopropyl)disulfide (SPS) is a common additive in commercial copper electroplating baths. We have studied the influence of SPS on Cu underpotential deposition (UPD) on a Au(111) single crystal surface by means of cyclic voltammetry (CV) and electrochemical scanning tunneling microscopy (EC-STM). By combining our results with the results from the literature we propose a model that describes different stages of Cu UPD in the presence of SPS. Further analysis shows that our model is also applicable to a more general case of UPD of different metals, e.g. Cu and Ag, on a thiol-modified single-crystal surface, where the bond between the substrate and the thiol is adatom mediated. In addition, we have verified our model by in situ observation of the lifting of the Herringbone reconstruction on the Au(111) surface by Cu UPD.     

Hydration processes of electrolyte anions and cations on pt(111), Ir(111), Ru(001) and Au(111) surfaces: coadsorption of water molecules with electrolyte ions

Water adsorption on Pt( 111) and Ru(001) treated with oxygen, hydrogen chloride and sodium atom at 20 K has been studied by Fourier transform infrared spectroscopy, scanning tunneling microscopy and surface X-ray diffraction. Water molecules chemisorb predominantly on the sites of the electronegative additives, forming hydrogen bonds. Three types of hydration water molecules coordinate to an adsorbed Na atom through an oxygen lone pair. In contrast, water molecules adsorb on electrode surfaces in a simple way in solution. In 1 mM CuSO4 + 0.5 M H2SO4 solution on an Au(111) electrode surface, water molecules coadsorb not only with sulfuric acid anions through hydrogen bonding but also with copper, over wide potential ranges. In the first stage of underpotential deposition (UPD), each anion is accommodated by six copper hexagon (honeycomb) atoms on which water molecules dominate. At any UPD stage water molecules interact with both the copper atom and sulfuric acid anions on the Au(111) surface. Water molecules also coadsorb with CO molecules on the surface of 2 x 2-2CO-Ru(001). All of the hydration water molecules chemisorb weakly on the surfaces. There appears to be a correlation between the orientation of hydrogen bonding water molecules and the electrode potential.     

Understanding the copper underpotential deposition process at strained gold surface

Copper underpotential deposition (UPD) on a gold surface is investigated by cyclic voltammetry coupled with in situ cyclic strain to understand the strain-modulated electrodeposition. Our work emphasizes quantification of an electrocapillary coupling coefficient ς, which relates the response of Cu electrodeposition potential, E, to applied strain, ε. The different responses to the strain are observed at two Cu UPD stages. The data indicate that tensile strain could enhance the formation of a Cu monolayer on the Au surface. The typical electrodeposition process could be modulated by an external mechanical strain.     

离子液体中Au(111)和Pt(111)表面Ge欠电位沉积的现场STM研究

本文研究BMIPF₆离子液体中Au(111)和Pt(111)表面Ge的电沉积行为. 循环伏安法测试结果表明,在含0.1 mol·L^-1 GeCl₄的BMIPF₆溶液Au(111)和Pt(111)表面均有两个与Ge沉积过程相关的还原峰. 第一个还原峰包含了Ge⁴⁺还原成Ge²⁺及Ge的欠电位沉积,第二个还原峰对应Ge的本体沉积. 现场扫描隧道显微镜研究结果表明,Ge在Au(111)和Pt(111)表面均有两层欠电位沉积. 第一层欠电位沉积厚度约为0.25 nm、形貌平整、带有缝隙的亚单层结构. 第二层欠电位沉积形貌相对粗糙的点状团簇结构. 该欠电位沉积过程伴随表面合金化.     

Investigation of nucleation processes under the influence of magnetic fields

The present work demonstrates the possibilities and the limits of the in situ electrochemical scanning tunneling microscopy for investigation of nucleation processes in magnetic fields on the examples of Cu and Co electrodeposition onto Au(111) electrodes from sulfate electrolytes with pH 3. Cyclic voltammograms of Cu in the underpotential range (UPD) exhibit no significant change in the cathodic and anodic peaks recorded in magnetic fields parallel to the surface. In magnetic fields of a permanent magnet, the reconstruction of Au has been annihilated during UPD of Cu. In the overpotential range, the dissolution of Cu is inhibited. This triggers the formation of a Cu–Au surface alloy. The UPD deposition of Co onto Au(111) could be proven without magnetic field, which leads to the formation of two monolayers. The nucleation in an applied field could not be observed due to higher induced fluctuations and microconvective effects. Contribution to special issue “Magnetic field effects in Electrochemistry”.     

铅在铜上电沉积的原位椭圆偏振法

采用循环伏安法(CV)和原位椭圆偏振法(SE)研究铅在铜电极上的电沉积行为。 原位椭圆偏振参数Ψ和Δ值的变化率在CV图峰电位处同时出现极值。 通过建立单层膜模型描述“电极-溶液”界面的结构并对椭圆偏振光谱数据进行拟合得到铅沉积层厚度随电位的变化规律。 拟合结果显示,铅在铜电极上的电沉积有3个不同的沉积速率,-0.20～-0.35 V之间沉积速率为0.003 nm/mV,-0.35～-0.48 V之间沉积速率为0.025 nm/mV,-0.48～-0.60 V之间沉积速率为0.116 nm/mV,由此表明铅的电沉积分为3个不同阶段：欠电位沉积阶段、欠电位沉积向本体沉积的过渡阶段和本体沉积阶段。     

锰欠电位沉积的密度泛函计算与循环伏安实验的研究

用密度泛函计算和循环伏安法研究了锰在金和铅表面的欠电位沉积(UPD)行为. 理论计算, 假设生成紧密的二维相(2D)欠电位沉积层, 用基于密度泛函理论的DMol3软件计算在金与铅表面生成2D相锰层的欠电位偏移值∆fE2DMe, 证明锰在金表面可发生欠电位沉积, 而在铅表面不能发生欠电位沉积. 循环伏安实验结果与理论计算不一致: 金电极析氢电位高不利于研究锰的还原沉积反应, 没有发现锰的欠电位沉积现象; 铅电极在MnCl2溶液中有锰的欠电位沉积现象. 这种理论计算与电化学实验结果的差异, 主要是因为理论计算没有考虑溶剂与阴离子特性吸附作用的影响, 理论计算模型是电化学实验体系的一种理想模型.     

Silver UPD ultra-thin film modified nanoporous gold electrode with applications in the electrochemical detection of chloride

Nanoporous noble metals are usually expected to exhibit much higher surface areas than smooth ones, making them of particular importance in many electrochemical applications. This paper describes a simple electrochemical method to modify a nanoporous Au (NPG) surface by using an under potentially deposited (UPD) Ag adlayer. The NPG electrode was obtained by the dealloying of Zn from Au_xZn_1−x in a 40-60 mol% zinc chloride-1-ethyl-3-methylimidazolium chloride (ZnCl₂-EMIC) ionic liquid. The Ag UPD modified nanoporous gold (NPG/Ag(UPD)) electrode possessed dual properties, including an intrinsic high surface area from the nanoporous structure and the characteristics of the Ag UPD adlayer. The potential utility of using NPG/Ag(UPD) for sensors was demonstrated by its excellent sensitivity and selectivity in the electrochemical determination of chloride ions. An atomic scale metal monolayer obtained in the UPD process was selected as a sensing agent. The long-term storability and operational stability of the electrode were strongly demonstrated. Specifically, two couples of redox waves at ∼552 mV and ∼272 mV, respectively, were observed in the cyclic voltammograms (CVs) of the NPG/Ag(UPD) after the adsorption of chloride ions. The first couple of redox waves was related to the UPD and silver stripping and the second couple of redox waves was induced by the adsorption of Cl⁻. The Cl⁻ adsorption process on the NPG/Ag(UPD) electrode followed the transient Langmuir adsorption kinetic model. The ratio of the integrated charges for these two anodic stripping peaks was selectively used to determine dilute chloride ion levels. The calibration curve was linear in the Cl⁻ concentration range of 0.5-30.0 μM.     

锌在金电极上的欠电位沉积

采用循环伏安法和计时电流法,研究了强碱溶液中锌在金电极上的欠电位沉积。 通过改变锌离子浓度和扫描速率等实验参数,在约-0.935 V（vs.SCE）开始出现锌的欠电位沉积,并且金属离子浓度的变化可能会影响到欠电位沉积过程的动力学机制;计时电流实验证实,锌欠电位沉积于金衬底上遵循的是受掺入吸附原子控制的二维瞬时成核和生长机制;且OH-离子的吸附对锌欠电位沉积具有重要的影响。     

电极/反相微乳液体系电沉积制备纳米金镀层

将含有氯化金的强酸性水溶液作为水相与Triton X-100、正己醇、正己烷组成反相微乳液体系, 并以该微乳液构成电极/反相微乳液电极系统, 利用电沉积方法成功地制备出纳米Au镀层. 循环伏安和交流阻抗对反相微乳液体系电沉积过程的研究发现, 微乳液中Au(III)的还原为完全不可逆过程, 其电化学反应的阻抗值约为具有相同表观浓度氯化金水溶液体系的5.5倍. SEM研究结果表明, 利用微乳液体系电沉积获得的金镀层由纳米Au颗粒组成, 直径为50 nm左右. 所制备的纳米Au修饰电极由于具有较大的比表面积, 其电化学性能优于纯Au电极, 该电极在酸性条件下有较好的析氢性能, 在碱性条件对丙三醇有较好的电催化氧化性能.     

Pb deposition on I-coated Au(111). UHV-EC and EC-STM studies

This article concerns the growth of an atomic layer of Pb on the Au(111)( radical3 x radical3)R30 degrees -I structure. The importance of this study lies in the use of Pb underpotential deposition (UPD) as a sacrificial layer in surface-limited redox replacement (SLRR). SLRR reactions are being applied in the formation of metal nanofilms via electrochemical atomic layer deposition (ALD). Pb UPD is a surface-limited reaction, and if it is placed in a solution of ions of a more noble metal, redox replacement can occur, but limited by the amount of Pb present. Pb UPD is a candidate for use as a sacrificial layer for replacement by any more noble element. It has been used by this group for both Cu and Pt nanofilm formation using electrochemical ALD. The I atom layer was intended to facilitate electrochemical annealing during nanofilm growth. Two distinctly different Pb atomic layer structures are reported, studied using in situ scanning tunneling microscopy (STM) with an electrochemical flow cell and ultrahigh vacuum surface analysis combined directly with electrochemical reactions (UHV-EC). Starting with the initial Au(111)( radical3 x radical3)R30 degrees -I, 1/3 monolayer of I on the Au(111) surface, Pb deposition began at approximately 0.1 V. The first Pb UPD structure was observed just below -0.2 V and displayed a (2 x radical3)-rect unit cell, for a structure composed of 1/4 monolayer each of Pb and I. The I atoms fit in Pb 4-fold sites, on the Au(111) surface. The structure was present in domains rotated by 120 degrees. Deposition to -0.4 V resulted in complete loss of the I atoms and formation of a Pb monolayer on the Au(111), which produced a Moiré pattern, due to the Pb and Au lattice mismatch. These structures represent two well-defined starting points for the growth of nanofilms of other more noble elements. It is apparent from these studies that the adsorption of I- on Pb is weak, and it will rinse away. If Pb is used as a sacrificial metal in an electrochemical ALD cycle and adsorbed I atoms are employed for electrochemical annealing, I atoms will need to be applied each cycle.     

(110)晶面全择优取向Cu镀层的制备及其条件优化

研究了添加剂聚乙二醇(PEG)、氯离子(Cl－)和电流密度对Cu的电沉积过程的影响, 着重探讨了制备(110)晶面全择优取向Cu镀层的电沉积条件及其形成机理. 循环伏安(CV)结果表明, PEG阻化Cu的电沉积, Cl－加快Cu的电沉积速率. XRD实验结果表明, PEG和Cl－在一定浓度范围有利于(110)晶面择优取向; 这两种不同特性的添加剂的协同作用可以制得(110)晶面全择优取向的较薄的Cu镀层; 所制备的全择优Cu镀层较稳定. 全择优取向Cu镀层形成的机理在于PEG和Cl－吸附过程联合起作用, 在不同晶粒的不同晶面进行选择吸附, 改变了晶面的生长速率及晶粒的快生长方向.     

Comparative investigation of underpotential deposition of Ag from aqueous and ionic electrolytes: An electrochemical and in situ STM study

Underpotential deposition (UPD) of Ag on Au(111) has been studied with two different electrolytes: aqueous 0.1 M H2SO4 solution in comparison with the ionic liquid 1-butyl-3-methylimidazolium chloride BMICl + AlCl3. Of particular interest is the distinct behavior of 2D phase formation at both interfaces, which has been investigated by cyclic and linear sweep voltammetry in combination with in situ electrochemical scanning tunneling microscopy (STM). It is found that one monolayer (ML) of Ag is formed in the UPD region in both electrolytes. In aqueous solution, atomically resolved STM images at 500 mV versus Ag/Ag+ show a (3 x 3) adlayer of Ag, whereas after sweeping the potential just before the commencement of the bulk Ag deposition, a transition from expanded (3 x 3) to pseudomorphic ML of Ag on Au(111) occurs. In BMICl-AlCl3, the first UPD process of Ag exhibits two peaks at 410 and 230 mV indicating that two distinct processes on the surface take place. For the first time, STM images with atomic resolution reveal a transition from an inhomogeneous to an ordered phase with a (square root of 3 x square root of 3)R30 degrees structure and an adsorption of AlCl4- anions having a superlattice of (1.65 x square root of 3)R30 degrees preceding the deposition of Ag.     

Sb在Au单晶电极上结构敏感吸附行为的比较

本文研究比较Sb(III)在Au(111)和Au(100)电极上的不可逆吸附与还原和Sb的欠电位沉积行为及其相互影响.现场扫描隧道显微镜和循环伏安法测试结果表明,基底表面结构不仅影响阴离子的吸附行为和Sb的吸附结构,而且还影响其自身结构的稳定性.在Au(111)表面,致密无序膜的SbO+不可逆吸附层还原后基本保持原有的无序结构;而在Au(100)表面,由于SO42-的共吸附,不可逆吸附物种还原后形成(2×2)有序结构.在Au(111)表面上,Sb的欠电位沉积伴随显著的合金化,且因表面有序结构的破坏而形成沟道状二维结构;但对Au(100)表面,由于其晶格和尺寸与稳定的AuSb2合金之(100)面有较好的匹配性,使Au与Sb得以形成有序的表面化合物,从而避免了欠电位沉积过程中的表面合金化问题,进一步体现基底结构的敏感性和重要性.     

Lightweight ITO Electrodes Decorated with Gold Nanostructures for Electrochemical Applications

Gold nanostructures were fabricated on a transparent indium tin oxide (ITO) coated PET substrate by an electrodeposition technique from a potassium gold (III) chloride solution for two different types of applications. It was found that the optical transparency of lightweight ITO electrodes could be maintained by depositing isolated gold nanostructures while opening up the use of these electrodes for inner sphere electron reactions, such as hydroquinone oxidation, which are not possible at ITO electrodes. For practical applications the adhesion of gold to the ITO electrode was improved by modifying the ITO surface with 3‐mercaptopropyl‐trimethoxysilane (MPS). Compared to Au/ITO, the Au/MPS/ITO electrode showed vastly improved electrochemical activity toward various electron transfer reactions when subjected to mechanical stress. The biosensing properties of the Au/MPS/ITO electrode was also investigated by studying the detection of immobilized DNA on the Au/MPS/ITO electrode via electrochemical impedance spectroscopy (EIS).     

A Modulation QCM Applied to Copper Electrodeposition and Stripping

A fast electrochemical quartz crystal microbalance with dissipation monitoring (EQCM−D) was applied to copper electrodeposition and subsequent stripping. Accumulation brings the frequency noise down to the mHz range, corresponding to 0.1 % of a monolayer. With this precision, the apparent mass transfer rate as determined from the time-derivative of the frequency shift can be directly compared to the current. Small but systematic deviations between the two can be attributed to nanoscale roughness. In the voltage range of underpotential deposition (UPD), the apparent mass transfer rate shows peaks and shoulders. The plating additive benzotriazole (BTA) leaves the magnitude of electrogravimetric signals unchanged, but shifts the UPD onset potential. The additive thiourea (TU) promotes UPD and strongly increases the bandwidth.     

Self-assembling Process of Alkanethiol Monolayers on Gold Surface via Underpotential Deposition

IntroductionThe measurement of the effective surface area(i.e.unoccupied area) of a given substrate is of fun-damental importance in the characterization of interfa-cial modification processes. Several methods, such asiodine chemisorption[1], cyclic volta…     

Construction of mixed mercaptopropionic acid/alkanethiol monolayers of controlled composition by structural control of a gold substrate with underpotentially deposited lead atoms.

Mixed monolayers of 3-mercaptopropionic acid (MPA) and alkanethiols of various chain lengths have been constructed on Au based on a novel concept, namely, control of the composition of the component thiols in mixed monolayers by controlling the surface structure of the substrate. The Au substrate surface was first modified with underpotentially deposited Pb (UPD Pb) atoms, followed by the formation of a self-assembled monolayer (SAM) of alkanethiol. The UPD Pb atoms were then oxidatively stripped from the surface to create vacant site, on which MPA was adsorbed to finally form the mixed monolayers. The surface coverages of Pb, alkanethiol and MPA, and the total numbers of thiols were determined using an electrochemical quartz crystal microbalance, X-ray photoelectron spectroscopy, and reductive desorption voltammetry. These results demonstrate that the surface coverage of MPA in the mixed monolayers is determined by the initial coverage of UPD Pb. Fourier transform infrared spectra also support this conclusion. The observed single peak in the cyclic voltammogram for the reductive desorption shows that MPA and alkanethiol do not form their single-component domains. Scanning tunneling microscopy revealed the single-row pinstripe structure for all the thiol adlayers formed during each step of the preparation. This shows that the surface structure of the mixed monolayers is determined by the structure of the initially formed SAM on Au partially covered with UPD Pb.     

Influence of Substrate Steps on the Catalytic Properties of Pt Layers: The Ethanol Electrooxidation Reaction

The ethanol oxidation reaction (EOR) is investigated on Pt/Au(hkl) electrodes. The Au(hkl) single crystals used belong to the [n(111)x(110)] family of planes. Pt is deposited following the galvanic exchange of a previously deposited Cu monolayer using a Pt²⁺ solution. Deposition is not epitaxial and the defects on the underlying Au(hkl) substrates are partially transferred to the Pt films. Moreover, an additional (100)‐step‐like defect is formed, probably as a result of the strain resulting from the Pt and Au lattice mismatch. Regarding the EOR, both vicinal Pt/Au(hkl) surfaces exhibit a behavior that differs from that expected for stepped Pt; for instance, the smaller the step density on the underlying Au substrate, the greater the ability to break the C?C bond in the ethanol molecule, as determined by in situ Fourier transform infrared spectroscopy measurements. Also, we found that the acetic acid production is favored as the terrace width decreases, thus reflecting the inefficiency of the surface array to cleave the ethanol molecule.     

Methodical aspects of studying the electroreduction of nitrate on modified single crystal Pt(hkl) + Cu electrodes

Technique of modification of basal faces Pt(hkl) by adatoms and epitaxial copper deposits is developed. Analysis of potentiostatic current transients of copper deposition/dissolution and atomic force microscopy showed that the activity of Pt(hkl) faces regarding the processes of copper nucleation and epitaxial growth increases in the sequence of Pt(111) < Pt(110) < Pt(100). The reaction of nitrate anion reduction is sensitive towards the surface structure, not only in the case of platinum, but also in the case of copper deposits (including a monolayer of adatoms). The highest process rate is observed for the Pt(100) electrode modified by a monolayer of adatoms or islands of bulk copper; nitrate reduction at the lowest rate occurs at Pt(111) + Cu electrodes. Structure-sensitive competitive adsorption of background electrolyte and nitrate anions is the factor that largely determines the kinetics of nitrate reduction on different faces of platinum single crystal and copper deposits.