Electrodeposition of Al in 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide ionic liquids: in situ STM and EQCM studies

In the present paper, the electrodeposition of Al on flame-annealed Au(111) and polycrystalline Au substrates in two air- and water-stable ionic liquids namely, 1-butyl-1-methyl-pyrrolidinium bis(trifluoromethylsulfonyl)amide, [Py(1,4)]Tf(2)N, and 1-ethyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)amide, [EMIm]Tf(2)N, has been investigated by in situ scanning tunneling microscopy (STM), electrochemical quartz crystal microbalance (EQCM), and cyclic voltammetry. The cyclic voltammogram of aluminum deposition and stripping on Au(111) in the upper phase of the biphasic mixture of AlCl(3)/[EMIm]Tf(2)N at room temperature (25 degrees C) shows that the electrodeposition process is completely reversible as also evidenced by in situ STM and EQCM studies. Additionally, a cathodic peak at an electrode potential of about 0.55 V vs Al/Al(III) is correlated to the aluminum UPD process that was evidenced by in situ STM. A surface alloying of Al with Au at the early stage of deposition occurs. It has been found that the Au(111) surface is subject to a restructuring/reconstruction in the upper phase of the biphasic mixture of AlCl(3)/[Py(1,4)]Tf(2)N at room temperature (25 degrees C) and that the deposition is not fully reversible. Furthermore, the underpotential deposition of Al in [Py(1,4)]Tf(2)N is not as clear as in [EMIm]Tf(2)N. The frequency shift in the EQCM experiments in [Py(1,4)]Tf(2)N shows a surprising result as an increase in frequency and a decrease in damping with bulk aluminum deposition at potentials more negative than -1.8 V was observed at room temperature. However, at 100 degrees C there is a frequency decrease with ongoing Al deposition. At -2.0 V vs Al/Al(III), a bulk aluminum deposition sets in.     

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.     

Underpotential deposition studies of copper on glassy carbon

Studies on the deposition and dissolution of copper from 0·5 M sulphuric acid solutions onto glassy carbon (GC) using potential sweep techniques indicated that an additional peak occurs at higher positive potentials than the bulk stripping peak. This peak is identified as due to the stripping of underpotential deposited (UPD) copper. Results of investigations on the effect of sweep rate, deposition potential and time of deposition on the peak characteristics of UPD and bulk deposited copper are also reported.     

Electrochemical characterization of gold stepped surfaces modified with Pd

Three different single crystals, Au(111), Au(332), and Au(331), were used as the substrate for palladium deposition in the underpotential deposition (UPD) regime. The Au(111) single crystal was used for control experiments to compare the behavior of the vicinal surfaces. Cyclic voltammetry in 0.1 M sulfuric acid solution, as well as electrochemical impedance spectroscopy (EIS) were used to study the hydrogen adsorption on the Pd thin films. Our results suggest that the voltammetric peaks at approximately 0.3 V versus the reversible hydrogen electrode (RHE) are related to the adsorption of hydrogen at large palladium terraces, and that at least two adjacent Pd rows are needed in order for the adsorption to take place. Further cycling to more positive potentials leads to the oxidation and slow dissolution of the Pd film. The behavior of the oxidation cycles is explained in terms of a higher stability of Pd at the steps.     

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…     

Electrochemical atomic layer epitaxy (ECALE)

Electrodeposition holds promise as a low cost, flexible room temperature technique for the production of II-VI compound semiconductors. Previous studies, however, have resulted in the production of polycrystalline deposits in every case. This paper describes a new method, developed in this laboratory, for depositing these materials epitaxially. The method involves the alternate deposition of the component elements a monolayer at a time. To limit deposition to a monolayer, underpotential deposition (UPD) is employed. UPD occurs because of the enhanced stability provided by bond formation between the II and VI elements, relative to formation of bulk elemental deposits. This method is the electrochemical equivalent of atomic layer epitaxy (ALE), and is thus referred to as “electrochemical atomic layer epitaxy” (ECALE). This paper describes the first example of the ECALE method, involving the thin-layer electrodeposition of CdTe on a Au polycrystalline electrode.     

Underpotential Deposition and Stripping of Lead at Disorganized Monolayer‐Modified Gold Electrodes

Underpotential deposition (UPD) and stripping of Pb²⁺ at thiol‐based disorganized monolayer‐modified gold electrodes was studied by cyclic voltammetry (CV) and electrochemical quartz crystal microgravimetry (EQCM). Electrodes modified with mercaptoacetic acid or mercaptoethane sulfonic acid were studied. Due to the proximity of the potentials for the Pb UPD and thiol reductive desorption, achievement of a UPD‐stripping voltammetry methodology for determination of low concentrations of Pb²⁺ was not successful. However by comparison of the CV and EQCM data and consideration of the possible mass changes per mole electrons transferred in light of the other species present in solution, possible mechanisms are put forward for the deposition and stripping of Pb²⁺ at thiol‐modified electrodes.     

Underpotential deposition of thallium, lead, and cadmium at silver electrodes modified with self-assembled monolayers of (3-mercaptopropyl)trimethoxysilane

Investigation of the underpotential deposition (UPD) of three metals-Tl, Pb, and Cd-on Ag surfaces modified with self-assembled monolayers (SAMs) of (3-mercaptopropyl)trimethoxysilane (3MPT) is reported. On the basis of the observation of negative potential shifts for their UPD processes, Tl and Pb undergo UPD directly on the underlying Ag surface by insertion between the Ag-S bond. This process is proposed to occur by penetration of the 3MPT monolayer by hydrated metal ions through spaces in six-membered siloxane rings that form at the terminus of the 3MPT layer after hydrolysis and condensation. In contrast, Cd does not undergo similarly facile UPD at 3MPT-modified Ag electrodes due to a hydrated ion size too large to fit through these openings. The voltammetric evidence that suggests that the hydrated metal cation size, as described by the Stokes diameter, is the primary determinant of Ag electrode accessibility for UPD through the cross-linked 3MPT layer is further supported by molecular mechanics energy minimization computations of six-membered siloxane rings on each of the three low-index faces of Ag. Finally, the 3MPT monolayer is shown to be exceptionally stable to repeated UPD/stripping cycles of Tl and Pb in contrast to SAMs of similar thickness formed from normal alkanethiols.     

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.     

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.     

Double deposition/accumulation and double stripping steps system as a new way of decreasing the detection limit and elimination of interferences in stripping voltammetry of inorganic ions: A review

The article reviews an application of double deposition/accumulation and stripping steps as a new and beneficial manner of decreasing a detection limit and/or interferences elimination in stripping voltammetric determination of inorganic ions: Pb(II), Cd(II), Tl(I), U(VI), Au(III), As(III), Se(IV), In(III), Co(II), Cu(II), Bi(III) and Ga(III). A simple design of four-electrodes system, containing two working electrodes differing in their surface area, allows for conducting two preconcentration and two stripping steps in one measurement cycle and in one voltammetric cell. Considerable analytes preconcentration and, consequently, an increase of sensitivity of determinations was obtained by conducting the first stripping step in a small volume of a solution near the microelectrode surface. An appropriate selection of the conditions of the first deposition/accumulation and the first stripping steps allowed for a minimization/elimination of interference effects. The proposed procedures allows for ultra-trace levels determinations of mentioned inorganic ions (often impossible to determine by means of traditional three-electrodes systems) without additional preconcentration outside the electrochemical cell and with the use of mercury-free electrodes.     

Determination of iodide ions at poly(3-methylthiophene)-modified electrode by differential pulse stripping voltammetry

A voltammetric electrode based on a poly(3-methylthiophene) (PMT) film for the differential pulse stripping voltammetric (DPSV) determination of iodide was developed. Gold electrodes were first coated with PMT, and iodide was then doped into the polymer film by electrochemical oxidation of iodide at 0.75 V. The effects of various electrochemical parameters, such as electroyte type and its pH, deposition potential, deposition time, and precipitation time, were examined. Using DPSV, the PMT electrode was found to be suitable for the measurement of iodide concentrations above 1 × 10⁻⁹ M. The text was submitted by the authors in English.     

Determination of the electronic structure of self-assembled L-cysteine/Au interfaces using photoemission spectroscopy

The electronic and chemical structure of the interface between the amino acid L-cysteine and Au was determined by photoemission spectroscopy (PES). L-cysteine was deposited by repeatedly dipping Au substrates into solutions of L-cysteine in methanol with various concentrations. To enable repeat deposition without significant contamination, the dipping procedure was performed in a glovebox directly connected to the ultrahigh vacuum (UHV) chamber in a N2 atmosphere. X-ray photoemission spectroscopy (XPS) measurements between deposition steps allowed to characterize the chemical interaction at the interface to be characterized. Ultraviolet photoemission spectroscopy (UPS) measurements yielded the orbital line-up at the interface as well as the highest occupied molecular orbital (HOMO) structure of L-cysteine. The charge injection barrier between the L-cysteine HOMO and the Au Fermi level was found to be 3.0 eV. The interface dipole between the Au substrate and the L-cysteine overlayer was determined to be 1.03 eV. The results also indicate the formation of an interface state approximately 1.5 eV above the HOMO of the L-cysteine.     

Lead underpotential deposition on Au(110)

The electrochemical underpotential deposition (UPD) of lead on Au(110) was investigated by XPS using a custom‐built ultrahigh vacuum apparatus containing a chamber for electrochemical studies. A two‐step deposition process for lead UPD was confirmed. A large increase in the surface concentration of oxygen was found in solutions containing lead. The presence of lead was detected on the gold surface at all potentials within the range investigated (?500 mV to 1500 mV vs. Ag/AgCl). Degradation of chlorine by x‐rays was observed. The change in surface components with potential was investigated and linked to models of UPD and oxidation. The initial random deposition of lead from solution led to surface disordering. Copyright © 2003 John Wiley & Sons, Ltd.     

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.     

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.     

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.     

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”.     

Scanning tunneling microscopy of template-stripped Au surfaces and highly ordered self-assembled monolayers

Template stripping of Au films in ultrahigh vacuum (UHV) produces atomically flat and pristine surfaces that serve as substrates for highly ordered self-assembled monolayer (SAM) formation. Atomic resolution scanning tunneling microscopy of template-stripped (TS) Au stripped in UHV confirms that the stripping process produces a flat, predominantly 111 textured, atomically clean surface. Octanethiol SAMs vapor deposited in situ onto UHV TS Au show a c(4 x 2) superlattice with (square root 3 x square root 3) R30 degrees basic molecular structure having an ordered domain size up to 100 nm wide. These UHV results validate the TS Au surface as a simple, clean and high-quality surface preparation method for SAMs deposited from both vapor phase and solution phase.