Bismuth underpotential deposition on tellurium

Electroless underpotential deposition (UPD) of Bi adatoms (Bi_ad) on Te by Bi^III reduction with Ti^III in aqua solution has been investigated. Comparison studies of electroless Bi UPD on Te and of a corresponding electrochemical process have been performed. Bi_ad stability on Te under the open-circuit conditions has been investigated.     

欠电势沉积Bi-Te基体系热电材料的平衡热力学分析

基于普通的能斯特方程, 建立了单原子层平衡电势的热力学模型. 据此, 分析了单原子层覆盖度以及电吸附价与欠电势之间的相互关系, 获得了沉积物与衬底之间干涉特性. 并且分析了Bi-Te基体系欠电势沉积热力学特性. 通过对Bi欠电势沉积在几个不同的金属衬底体系的分析阐明了功函数随覆盖度的变化机制. 研究了铋离子的浓度变化对铋的欠电势及覆盖度的影响关系, 结果表明, 铋在铂上欠电势沉积的体系在整个欠电势范围内具有恒定的电吸附价, 而铋在覆盖了一层碲的铂衬底上欠电势沉积的体系其电吸附价随覆盖度的增加而降低, 从热力学理论角度对铋在碲覆盖的衬底上导致欠电势负移的特性给予了解释.     

Bond energies in alloys determined from underpotential deposition potentials

A procedure is presented to determine bond energies between the metal (Me) and substrate (S) components of binary alloys from characteristic underpotential deposition (UPD) potentials. The bond energy between Me and S atoms is one of the factors governing the deposition kinetics and structure of Me-S alloy deposits. The proposed procedure is based on the determination of the UPD potential for formation of a condensed two-dimensional (2D) phase of the less noble metal Me (the UPD metal) on the more noble metal S (the substrate). Making reasonable approximations, the sublimation enthalpy of the condensed 2D Me phase is obtained from the corresponding formation underpotential. From this sublimation enthalpy the bond energy of an atom of the UPD metal in a kink site position of the 2D Me phase is calculated. This value is used to calculate the bond energy (_Me-S) between an Me atom and an S atom. The method is demonstrated using experimental data obtained in selected electrochemical UPD systems.     

Cadmium atomic layers on tellurium electrodes

The process of electrodeposition of atomic layers of cadmium Cd_ad at order of magnitude polycrystalline tellurium electrodes at potentials in excess of equilibrium potential E _Cd ²⁺/_Cd (underpotential deposition, UPD) is studied. In acid sulfate solutions (0.1 M H₂SO₄ + 0.05 M CdSO₄), the magnitude of underpotential (underpotential shift) ΔE ^UPD = 0.41 V. In cyclic voltammograms, the anodic oxidation of Cd_ad is recorded in the form of two peaks of anodic current that are displaced relative to one another in the potential scale (weakly and strongly bound adatoms). The cadmium UPD process on tellurium is accompanied by the diffusion of cadmium into the bulk of tellurium and a transition from a 2D structure Cd_ad/Te to 3D CdTe nanostructures, which are distributed in the tellurium matrix. In contrast with tellurium, the Te/CdTe_nano heterostructure exhibits photoelectrochemical activity, i.e. it generates a cathodic photocurrent.     

Underpotential deposition and involved alloy formation of cadmium on silver particles modified HOPG substrates

Cadmium underpotential deposition (UPD) on Ag particles modified highly ordered pyrolytic graphite (HOPG) surfaces, and the involved alloy formation were studied by conventional electrochemical techniques. Voltammetric results indicated that the Cd UPD followed an adsorption behavior different from that observed for massive Ag electrodes and Ag particles supported on vitreous carbon. Nanometer-sized bimetallic Cd–Ag particles were characterized by ex situ atomic force microscopy (AFM). Initially, AFM images show Ag deposits of similar size distributed preferably on HOPG step edges. No remarkable morphological changes are observed on the surface after the subsequent Cd deposition, suggesting that the Cd particles are deposited selectively over the Ag crystals. From the analysis of desorption spectra, employing different polarization times, and density functional theory (DFT) calculations, the formation of a Cd–Ag surface alloy could be inferred.     

Electrochemical deposition of Bi<Subscript>2</Subscript>Te<Subscript>3</Subscript> for thermoelectric microdevices

The electrolyses of solutions of bismuth oxide and tellurium oxide in nitric acid with molar ratios of Bi:Te=3:3–4:3 lead to cathodic deposits of films of bismuth telluride (Bi₂Te₃), an n-type semiconductor. Current densities of 2–5 mA/cm² were applied. Voltammetric investigations showed that Bi₂Te₃ deposition occurred at potentials more negative than −0.125 V (Ag/AgCl, 3 M KCl). The deposit was identified as bismuth telluride (γ-phase) by X-ray analysis. Hall-effect measurements verified the n-type semiconducting behaviour. The films can be deposited in microstructures for thermoelectric microdevices like thermoelectric batteries or thermoelectric sensors.     

Underpotential Deposition Study and Determination of Bismuth on Gold Electrode by Using Voltammetry

ＴｈｅｃｏｍｂｉｎａｔｉｏｎｏｆｓｔｒｉｐｐｉｎｇｖｏｌｔａｍｍｅｔｒｙｗｉｔｈＵＰＤｃａｎｌｅａｄｔｏｔｈｅｉｍｐｒｏｖｅｍｅｎｔｏｆｓｅｎｓｉｔｉｖｉｔｙ ,ｓｅｌｅｃｔｉｖｉ ｔｙａｎｄｒｅｖｅｒｓｉｂｉｌｉｔｙｆｏｒｅｌｅｃｔｒｏａｎａｌｙｔｉｃａｌｐｕｒｐｏｓｅａｎｄａｖｏｉｄｔｈｅｕｓｅｏｆｔｏｘｉｃｍｅｒｃｕｒｙａｓｔｈｅｗｏｒｋｅｌｅｃｔｒｏｄｅ1ａｎｄｔｈｅｎａｎａｌｙｔｉｃａｌａｐｐｌｉｃａｔｉｏｎｓｈａｖｅｂｅｅｎｄｅｓｃｒｉｂｅｄ .2 4 Ｉｎｔｈｉｓｗｏｒｋ ,ｗｅｄｅｖｅｌｏ…     

Silver overlayer-modified surface-enhanced Raman scattering-active gold substrates for potential applications in trace detection of biochemical species

Because Ag and Au nanoparticles (NPs) possess well-defined localized surface plasmon resonance (LSPR) they are popularly employed in the studies of surface-enhanced Raman scattering (SERS). As shown in the literature and in our previous studies, the advantage of SERS-active Ag NPs is their higher SERS enhancement over Au NPs. On the other hand, the disadvantage of SERS-active Ag NPs compared to Au NPs is their serious decay of SERS enhancement in ambient laboratory air. In this work, we develop a new strategy for preparing highly SERS-active Ag NPs deposited on a roughened Au substrate. This strategy is derived from the modification of electrochemical underpotential deposition (UPD) of metals. The coverage of Ag NPs on the roughened Au substrate can be as high as 0.95. Experimental results indicate that the SERS of Rhodamine 6G (R6G) observed on this developed substrate exhibits a higher intensity by ca. 50-fold of magnitude, as compared with that of R6G observed on the substrate without the deposition of Ag NPs. The limit of detection (LOD) for R6G measured on this substrate is markedly reduced to 2 × 10⁻¹⁵ M. Moreover, aging of SERS effect observed on this developed substrate is significantly depressed, as compared with that observed on a generally prepared SERS-active Ag substrate. These aging tests were performed in an atmosphere of 50% relative humidity (RH) and 20% (v/v) O₂ at 30 °C for 60 day. Also, the developed SERS-active substrate enables it practically applicable in the trace detection of monosodium urate (MSU)-containing solution in gouty arthritis without a further purification process.     

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.     

Intermetallic phase formation in electrochemical alloy deposition

Three examples of the electrochemical deposition of intermetallic phases are shown. Electrodeposition of the single-phase -brass superlattice at underpotentials of Zn in Cu-Zn alloy plating is explained by an accumulative underpotential deposition (UPD) mechanism. Growth of the Cu-Sn intermetallic phase layer in the contact immersion deposition of Sn onto Cu is accounted for by a UPD/vertical solid-state diffusion mechanism. Ag₃Sn formation in the Sn/Ag-nanoparticle composite plating is illustrated by atomic site exchange at the interface between the deposited Sn matrix and the occluded Ag nanoparticles.     

碲在金衬底上的不可逆吸附行为及其欠电位沉积机制的研究

研究了碲在金衬底上的不可逆吸附行为特征及其对碲原子欠电位沉积行为的影响. 同时也探讨了碲原子于金衬底上的欠电位沉积机制. 结果显示在开路条件下碲原子在金衬底表面具有不可逆的吸附行为, 证实了在金的双电层范围内很难将这种碲的吸附物移走. 为了完全移走碲的吸附物, 需要采用特定的电化学清洗程序. 发现碲的吸附物移走发生在电位循环至金的氧化区域, 且在该区域这种碲的吸附物移走与金的表面氧化同时发生. 扫描速率分析结果证实碲欠电位沉积在金表面符合Sanchez-Maestre模型的三个标准, 说明碲原子于金衬底上欠电位沉积符合二维形核和生长机制.     

Kinetic studies of underpotential deposition of antimony on Se-modified Au electrode

Atomic layers of antimony can be electrodeposited onto the Se monolayer covered Au electrode in the underpotential region. In this paper, the formation and dissolution kinetics of antimony monolayer on the Se monolayer covered Au electrode are investigated using cyclic voltammetry (CV) and chronoamperometry (CA) techniques. Scanning-rate-dependent CV experiments reveal that the peak current of underpotential deposition (UPD) wave of antimony is not a linear function of the scanning rate, υ, but scales as υ ^2/3. Similar behavior is observed when the Antimony monolayer is stripped from the modified substrate. These results indicate the character of monolayer formation and dissolution by a two-dimensional nucleation and growth mechanism. Additionally, current density−time transient obtained through CA experiments also reveal that both the deposition and stripping of the antimony monolayer involve an instantaneous nucleation and two-dimensional growth process.     

New insights into the Sn underpotential deposition on Au(100)

The underpotential deposition (UPD) of Sn in the system Au(100)/Sn²⁺, SO₄^2? has been studied by classical electrochemical techniques and in situ scanning tunneling microscopy. The results show that the Sn UPD initiates at relatively high potentials with the formation of a quasi‐hexagonal structure characterized as Au(100) ? (√2 × 7)R45°. This expanded overlayer contributes to the modification of the surface morphology which exhibits flat terraces with step edges showing angles of 60 or 120°. At lower potentials two‐dimensional (2D) islands are formed which tend to grow, causing a coverage increase. In the underpotential region close to the formation of the 3D bulk phase the long time polarization experiments indicate the formation of different Au–Sn alloy phases. Copyright © 2011 John Wiley & Sons, Ltd.     

Fabrication of nanocables by electrochemical deposition inside metal nanotubes

We report a novel route for fabricating Au-Te nanocables. Using nanoporous polycarbonate tract-etching (PCTE) membrane as the template, Au nanotubes were fabricated by electroless Au deposition inside the nanopores of the PCTE membrane. Using the Au nanotube membrane as a second template, Te was deposited on the surfaces of the Au nanotubes by slow electrochemical deposition, taking advantage of underpotential deposition (UPD). The deposition rate was sufficiently slow to radially grow Te nanotubes coaxially within the Au nanotubes to form nanocables.     

Underpotential deposition of tin(II) on a gold disc electrode and determination of tin in a tin plate sample

This work describes a study of the underpotential deposition (UPD) of Sn²⁺ on a polycrystalline gold disc electrode using cyclic voltammetry (CV) and chronocoulometry (CC). Sn²⁺ ions showed well-defined peaks from UPD and UPD stripping (UPD-S) in 1 mol/L HCl solutions, while bulk deposition (BD) and BD stripping (BD-S) of the ions were also observed. The measured UPD shifts, E_UPD, between the UPD-S and the BD-S peaks were more than 200 mV. The UPD charge and the surface coverage of tin were measured by CC. A new method for determining Sn²⁺ was therefore developed, based on the excellent electrochemical properties of the Au/Sn UPD system. A plot of the UPD-DPASV (differential pulse anodic stripping voltammetry) signal versus the Sn(II) concentration was obtained for [Sn(II)] of 1.98×10^–7 to 3.64×10^–5 M. The method developed here has been applied to determine the tin in a tin plate sample.     

固/液界面电化学体系与XPS联用系统对Pt/Sb和Pt/Bi电极表面化学状态的比较研究

利用巳建立的固/液界面电化学体系Electrochemistry(EC)与超高真空电子能谱Ultra-High Vacaum X-ray Photoelectron Spectroscopy(UHV-XPS)联用系统详细研究了Pt电极表面欠电位沉积Underpotential deposition(UPD)Sb、Bi的表面化学状态特征，结果表明Sb、Bi虽同为VA族元素，但二者在Pt电极表面的UPD特征却有很大差异。     

Electrochemical aspects and structure characterization of VA-VIA compound semiconductor Bi2Te3/Sb2Te3 superlattice thin films via electrochemical atomic layer epitaxy

This paper concerns the electrochemical atom-by-atom growth of VA-VIA compound semiconductor thin film superlattice structures using electrochemical atomic layer epitaxy. The combination of the Bi2Te3 and Sb2Te3 programs and Bi2Te3/Sb2Te3 thin film superlattice with 18 periods, where each period involved 21 cycles of Bi2Te3 followed by 21 cycles of Sb2Te3, is reported here. According to the angular distance between the satellite and the Bragg peak, a period of 23 nm for the superlattice was indicated from the X-ray diffraction (XRD) spectrum. An overall composition of Bi 0.25Sb0.16Te0.58, suggesting the 2:3 stoichiometric ratio of total content of Bi and Sb to Te, as expected for the format of the Bi2Te3/Sb2Te3 compound, was further verified by energy dispersive X-ray quantitative analysis. Both field-emission scanning electron microscopy and XRD data indicated the deposit grows by a complex mechanism involving some 3D nucleation and growth in parallel with underpotential deposition. The optical band gap of the deposited superlattice film was determined as 0.15 eV by Fourier transform infrared spectroscopy and depicts an allowed direct type of transition. Raman spectrum observation with annealed and unannealed superlattice sample showed that the LIF mode has presented, suggesting a perfect AB/CB bonding in the superlattice interface.     

Cu + Au alloy particles formed in the underpotential deposition region of copper in acid solutions

Cu + Au alloy particles electrodeposited on an amorphous carbon electrode at the underpotential region of Cu in both perchloric acid and sulfuric acid solutions were investigated by means of transmission electron microscopy. The fraction of Cu in the Cu + Au alloy particles grown in both acid solutions with a concentration of 1 mM Au ion increased while the underpotential deposition (UPD) potential was decreased. However, it was independent of the concentration of Cu ion in solution. It is inferred that the composition of the Cu + Au alloy particles is dependent on the UPD potential. The fraction of Cu in the Cu + Au alloy particles grown at around the reversible Nernst potential of Cu in 0.1 mM HAuCl₄ + 50 mM Cu(ClO₄)₂ containing perchloric acid solution was 505. This result suggests a layer-by-layer formation of the Cu + Au alloy particles. The fraction of Cu in the Cu + Au alloy particles formed in the presence of sulfate was lower than that in the perchloric acid solution as the UPD potential and the concentration of Cu ion were the same. This is attributed to an influence of coadsorbed sulfate ions.     

The effects of the underpotential and overpotential deposition of lead and thallium on silver on the Raman spectra of adsorbates

It is shown that the underpotential deposition (UPD) and dissolution of monolayers of Pb and Tl onto Ag surfaces roughened in a controlled oxidation-reduction cycle produces a Ag surface which shows diminished surface enhanced Raman scattering (DSERS). Significantly enhanced Raman spectra can still be obtained from electrodes covered by complete UPD and overpotential deposited (OPD) layers of the metals. Correct choice of electrolytes for the UPD of the metal reduces the loss of enhanced Raman scattering; chloride ions, constituents of many electrolytes used in the investigation of surface enhanced Raman scattering (SERS), are shown to be especially active in causing the loss of SERS.     

CdTe electrodeposition on InP(100) via electrochemical atomic layer epitaxy (EC-ALE): studies using UHV-EC

The II-VI compound semiconductor CdTe was electrodeposited on InP(100) surfaces using electrochemical atomic layer epitaxy (EC-ALE). CdTe was deposited on a Te-modified InP(100) surface using this atomic layer by atomic layer methodology. The deposit started with formation of an atomic layer of Te on the InP(100) surface, as Cd was observed not to form an underpotential deposition (UPD) layer on InP(100), although it was found to UPD on Te atomic layers. On the In-terminated 'clean' InP(100) surface, Te was deposited at -0.80 V from a 0.1 mM solution of TeO2, resulting in formation of a Te atomic layer and some small amount of bulk Te. The excess bulk Te was then removed by reduction in blank solution at -0.90 V, leaving a Te atomic layer. Given the presences of the Te atomic layer, it was then possible to form an atomic layer of Cd by UPD at -0.58 V to complete the formation of a CdTe monolayer by EC-ALE. That cycle was then repeated to demonstrate the applicability of the cycle to the formation of CdTe nanofilms. Auger spectra recorded after the first three cycles of CdTe deposition on InP(100) were consistent with the layer-by-layer CdTe growth. It is interesting to note that Cd did not form a UPD deposit on the In-terminated InP(100) surface and only formed Cd clusters at an overpotential. This issue is probably related to the inability of the Cd and In to form a stable surface compound.