Underpotential

Chen C-FI, Washburn N and Gewirth A A 1993 In situ atomic force microscope study of Pb underpotential deposition on Au(111) Structural properties of the catalytically active phase J.Phys. Chem. 97 9754-60... 

Carnal D, Oden P I, Muller U, Schmidt E and Siegenthaler FI 1995 In situ STM investigation of T1 and Pb underpotential deposition on chemically polished Ag(111) electrodes E/ecfroc/r/m. Acta 40 1223-35... 

Li J and Abruna FI D 1997 Coadsorption of sulphate/bisulphate anions with Fig cations during Fig underpotential deposition on Au (111) An In situ x-ray diffraction study J. Phys. Chem. B 101 244-52... 

Blum L, Abruna FI D, White J, Gordon J G, Borges G L, Samant M G and Melroy 1986 Study of underpotentially deposited copper on gold by fluorescence detected surface EXAFS J. Chem. Phys. 85 6732-8... 

Huckaby D A and Blum L 1991 A model for sequential first-order phase transitions occuring in the underpotential deposition of metals J. Eiectroanai. Chem. 315 255-61... 

Zinc and tin The electrodeposition of Zn [52] has been investigated in acidic chloroaluminate liquids on gold, platinum, tungsten, and glassy carbon. On glassy carbon only three-dimensional bulk deposition was observed, due to the metal s underpotential deposition behavior. At higher overvoltages, codeposition with A1... 

Germanium In situ STM studies on Ge electrodeposition on gold from an ionic liquid have quite recently been started at our institute [59, 60]. In these studies we used dry [BMIM][PF<3] as a solvent and dissolved Gel4 at estimated concentrations of 0.1-1 mmol 1 the substrate being Au(lll). This ionic liquid has, in its dry state, an electrochemical window of a little more than 4 V on gold, and the bulk deposition of Ge started several hundreds of mV positive from the solvent decomposition. Furthermore, distinct underpotential phenomena were observed. Some insight into the nanoscale processes at the electrode surface is given in Section 6.2.2.3. 

Figure 6.2-4 Underpotential phenomena during Al reduction in acidic [BMIM] Cr/AICl3 on...

Copper electrodeposition on Au(111) Copper is an interesting metal and has been widely investigated in electrodeposition studies from aqueous solutions. There are numerous publications in the literature on this topic. Furthermore, technical processes to produce Cu interconnects on microchips have been established in aqueous solutions. In general, the quality of the deposits is strongly influenced by the bath composition. On the nanometer scale, one finds different superstmctures in the underpotential deposition regime if different counter-ions are used in the solutions. A co-adsorption between the metal atoms and the anions has been reported. In the underpotential regime, before the bulk deposition begins, one Cu mono-layer forms on Au(lll) [66]. 

Hydrogen adsorption from solution Oxygen adsorption from solution Underpotential deposition of metals Adsorption of probe molecules from solution ... 

Based on the experimental conditions the gold electrode is most likely covered with underpotential deposited (upd) silver. Consequently the value of iip c should be compared with the corresponding value for a silver electrode. 

Gregory WB, Norton ML, Stickney JL (1990) Thin-layer electrochemical studies of the underpotential deposition of cadmium and tellurium on polycrystalline Au, Pt and Cu electrodes. J Electroanal Chem 293 85-101... 

The authors [35] emphasize that their result regarding the first HgS monolayer, which involves reversible underpotential adsorption, suggests that nucleation cannot be considered as a universal mechanism for the formation of anodic films. Analogous conclusions have been inferred for cathodic HgSe films electrodeposited on mercury electrode by the reduction of selenous acid [37] the first monolayer appeared to be reversibly adsorbed, while formation of the following two layers was preceded by nucleation. 

Generally, the experimental results on electrodeposition of CdS in acidic solutions of thiosulfate have implied that CdS growth does not involve underpotential deposition of the less noble element (Cd), as would be required by the theoretical treatments of compound semiconductor electrodeposition. Hence, a fundamental difference exists between CdS and the other two cadmium chalcogenides, CdSe and CdTe, for which the UPD model has been fairly successful. Besides, in the present case, colloidal sulfur is generated in the bulk of solution, giving rise to homogeneous precipitation of CdS in the vessel, so that it is quite difficult to obtain a film with an ordered structure. The same is true for the common chemical bath CdS deposition methods. 

Cathodic electrodeposition of microcrystalline cadmium-zinc selenide (Cdi i Zn i Se CZS) films has been reported from selenite and selenosulfate baths [125, 126]. When applied for CZS, the typical electrocrystallization process from acidic solutions involves the underpotential reduction of at least one of the metal ion species (the less noble zinc). However, the direct formation of the alloy in this manner is problematic, basically due to a large difference between the redox potentials of and Cd " couples [127]. In solutions containing both zinc and cadmium ions, Cd will deposit preferentially because of its more positive potential, thus leading to free CdSe phase. This is true even if the cations are complexed since the stability constants of cadmium and zinc with various complexants are similar. Notwithstanding, films electrodeposited from typical solutions have been used to study the molar fraction dependence of the CZS band gap energy in the light of photoelectrochemical measurements, along with considerations within the virtual crystal approximation [128]. 

It appears that a way to efficient electrochemical growth of CdTe and other chalcogenides on silicon crystals is the utilization of light-assisted processes. Works in this direction will be discussed in a subsequent section regarding underpotential deposition studies. 

In a similar way, electrochemistry may provide an atomic level control over the deposit, using electric potential (rather than temperature) to restrict deposition of elements. A surface electrochemical reaction limited in this manner is merely underpotential deposition (UPD see Sect. 4.3 for a detailed discussion). In ECALE, thin films of chemical compounds are formed, an atomic layer at a time, by using UPD, in a cycle thus, the formation of a binary compound involves the oxidative UPD of one element and the reductive UPD of another. The potential for the former should be negative of that used for the latter in order for the deposit to remain stable while the other component elements are being deposited. Practically, this sequential deposition is implemented by using a dual bath system or a flow cell, so as to alternately expose an electrode surface to different electrolytes. When conditions are well defined, the electrolytic layers are prone to grow two dimensionally rather than three dimensionally. ECALE requires the definition of precise experimental conditions, such as potentials, reactants, concentration, pH, charge-time, which are strictly dependent on the particular compound one wants to form, and the substrate as well. The problems with this technique are that the electrode is required to be rinsed after each UPD deposition, which may result in loss of potential control, deposit reproducibility problems, and waste of time and solution. Automated deposition systems have been developed as an attempt to overcome these problems. 

Rajeshwar and co-workers performed photocatalytic underpotential deposition of Cd and Pb onto the surface of Se-modified Ti02 particles to prepare CdSe/Ti02 and PbSe/Ti02 composites [97, 98]. The Se-modified Ti02 particles were prepared themselves by UV illumination of titania particles in a Se(fV)-containing aqueous solution. The photocatalytic UPD of Cd and Pb on the bare Ti02 surface was found... 

Colletti LP, Teklay D, Stickney JL (1994) Thin-layer electrochemical studies of the oxidative underpotential deposition of sulfur and its application to the electrochemical atomic layer epitaxy deposition of CdS. J Electroanal Chem 369 145-152... 

Alois GD, CavaUini M, Innocent M, Foresti ML, Pezzatini G, GuideUi R (1997) In situ STM and electrochemical investigation of sulfur oxidative underpotential deposition on Ag(lll). J Phys Chem B 101 4774 780... 

Herrero E, Buller LJ, Abruna HD (2001) Underpotential deposition at single crystal surfaces of Au, Pt, Ag and other materials. Chem Rev 101 1897-1830... 

Michaelis R, Zei MS, Zhai RS, Kolb DM (1992) The effect of halides on the structure of copper underpotential-deposited onto Pt(lll) a low-energy electron diffraction and X-ray photoelectron spectroscopy study. J Electroanal Chem 339 299-310... 

Alanyahopu M, (Jakal H, Oztiirk AE, Demir U (2001) Electrochemical studies of the effects of pH and the surface stracture of gold substrates on the underpotential deposition of sulfur. J Phys Chem B 105 10588-10593... 

Santos MC, Machado SAS (2004) Microgravimetric, rotating ring-disc and voltammetric studies of the underpotential deposition of selenium on polycrystalline platinum electrodes. J Electroanal Chem 567 203-210... 

Santos MC, Machado SAS (2005) A voltammetric and nanogravimetric study of Te underpotential deposition on Pt in perchloric acid medium. Electrochim Acta 50 2289-2295... 

Osipovich NP, Streltsov EA, Susha AS (2000) Bismuth underpotential deposition on tellurium. Electrochem Commun 2 822-826... 

Chenthamarakshan CR, Ming Y, Rajeshwar K (2000) Underpotential photocatalytic deposition A new preparative route to composite semiconductors. Chem Mater 12 3538-3540... 

Ivanov DK, Osipovich NP, Poznyak SK, Streltsov EA (2003) Electrochemical preparation of lead-doped amorphous Se films and underpotential deposition of lead onto these films. Surf Sci 532-535 1092-1097... 

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