Tellurium, electrodeposition

SorensonT etal. (2001) Formation of and phase transitions in electrodeposited tellurium atomic layers on Au (111). SurfSci 470 197-214. 

Tellurium and cadmium Electrodeposition of Te has been reported [33] in basic chloroaluminates the element is formed from the [TeCl ] complex in one four-electron reduction step, furthermore, metallic Te can be reduced to Te species. Electrodeposition of the element on glassy carbon involves three-dimensional nucleation. A systematic study of the electrodeposition in different ionic liquids would be of interest because - as with InSb - a defined codeposition with cadmium could produce the direct semiconductor CdTe. Although this semiconductor can be deposited from aqueous solutions in a layer-by-layer process [34], variation of the temperature over a wide range would be interesting since the grain sizes and the kinetics of the reaction would be influenced. 

Traore M, Moddo R, Vittori O (1988) Electrochemical behaviour of tellurium and silver teUuride at rotating glassy carbon electrode. Hectrochim Acta 33 991-996 Ngac N, Vittori O, Quarin G (1984) Voltammetrie and chronoamperometric studies of tellurium electrodeposition of glassy carbon and gold electrodes. J Electroanal Chem 167 227-235... 

The induced co-deposition concept has been successfully exemplified in the formation of metal selenides and tellurides (sulfur has a different behavior) by a chalcogen ion diffusion-limited process, carried out typically in acidic aqueous solutions of oxochalcogenide species containing quadrivalent selenium or tellurium and metal salts with the metal normally in its highest valence state. This is rather the earliest and most studied method for electrodeposition of compound semiconductors [1]. For MX deposition, a simple (4H-2)e reduction process may be considered to describe the overall reaction at the cathode, as for example in... 

Telluro-cyanide (presumably TeCN ) has been explored as a source of tellurium for electrodeposition of CdTe [14], on account of the possible advantage that this species is less likely than tellurium dioxide to oxidize the cathodically produced telluride ion. Bath solutions were prepared by dissolving powdered Te in a concentrated aqueous solution of KCN and adding CdCb and EDTA. Stoichiometric CdTe deposits, free of excess Te, were reported. 

Darkowski and Cocivera [94] investigated trialkyl- or triarylphosphine tellurides, as low-valent tellurium sources, soluble in organic solvents. They reported the cathodic electrodeposition of thin film CdTe on titanium from a propylene carbonate solution of tri-n-butylphosphine telluride and Cd(II) salt, at about 100 °C. Amorphous, smooth gray films were obtained with thicknesses up to 5.4 p,m. The Te/Cd atomic ratio was seen to depend on applied potential and solution composition with values ranging between 0.63 and 1.1. Polycrystalline, cubic CdTe was obtained upon annealing at 400 C. The as-deposited films could be either p- or n-type, and heat treatment converts p to n (type conversion cf. Sect. 3.3.2). 

The electrodeposition of tellurium and silver has been investigated in dilute aqueous solutions of tellurous acid and Ag " ions (concentrations in the order of 10 to 10 " M) in 0.1 M HCIO4 [164], In particular, cyclic voltammetry experiments were conducted with rotating glassy carbon disk electrodes in baths with various concentration ratios of Ag(I) and Te(IV) precursors, and their outcome was discussed in terms of the voltammetric features. For a Ag(I)/Te(IV) ratio close to 0.8, formation of quasi pure silver telluride, Ag2Te, was reported. The authors, based on their measurements and on account of thermodynamic predictions, assumed that silver is deposited first on the electrode (Ag" + e Ag), and then Te(IV) is reduced on the previous silver deposit with formation of Ag2Te according to the reaction... 

Numerous works have been implemented on tellurium electrochemistry and its adsorption at metal surfaces. The morphological structures of electrodeposited Te layers at various stages of deposition (first UPD, second UPD, and bulk deposition) are now well known [88-93]. As discussed in the previous paragraphs, Stickney and co-workers have carried out detailed characterizations of the first Te monolayer on Au single-crystal surfaces in order to establish the method of electrochemical atomic layer epitaxy of CdTe. 

The UPD and anodic oxidation of Pb monolayers on tellurium was investigated also in acidic aqueous solutions of Pb(II) cations and various concentrations of halides (iodide, bromide, and chloride) [103]. The Te substrate was a 0.5 xm film electrodeposited in a previous step on polycrystalline Au from an acidic Te02 solution. Particular information on the time-frequency-potential variance of the electrochemical process was obtained by potentiodynamic electrochemical impedance spectroscopy (PDEIS), as it was difficult to apply stationary techniques for accurate characterization, due to a tendency to chemical interaction between the Pb adatoms and the substrate on a time scale of minutes. The impedance... 

Gregory BW, Suggs DW, Stickney JL (1991) Conditions for the deposition of CdTe by electrochemical atomic layer epitaxy. J Electrochem Soc 138 1279-1284 Suggs DW, Stickney JL (1991) Characterization of atomic layers of tellurium electrodeposited on the low-index planes of gold. J Phys Chem 95 10056-64 Suggs DW, Stickney JL (1993) Studies of the structures formed by the alternated electrodeposition of atomic layers of Cd and Te on the low-index planes of Au. 1. LEED and Auger studies. Surf Sci 290 362-374... 

Sorenson TA, Lister TE, Huang BM, Stickney JL (1999) A comparison of atomic layers formed by electrodeposition of selenium and tellurium Scanning tunneling microscopy studies on Au(lOO) and Au(lll). J Electrochem Soc 146 1019-1027... 

The irreversibility of Te electrodeposition is increased by changing the tellurite solution to pH 10, Figure 9C. At pH 10, the potential difference between deposition and stripping for the 1/1 couple is 600 mV. The origin of peak 0 is still unclear, but appears to be due to changes in an adsorbed layer of tellurium oxide. 

CdTe The mechanism of CdTe electrodeposition was studied intensively [194-197]. Electrodeposition of CdTe semiconductor thin films was carried out in acidic aqueous solutions at pH 1-3 [195-197]. To prevent accumulation of tellurium in CdTe film, the concentration of Te(IV) ions in acidic electrolyte must be much lower than the concentration of Cd(II). 

Electrodeposition and stripping of tellurium and CdTe in sulfate electrolyte was studied by voltammetric and electrogravi-metric experiments [206]. 

Cathodic electrodeposition of CdTe in acidic solutions with higher tellurium... 

Sorenson etal. [449] have carried out similar studies on electrodeposition of atomic Te layers on Au(lll) surfaces from aqueous solutions. Similarly as in earher works, in this study also, the following techniques were utilized voltammetry, in situ STM, low-energy electron diffraction, and Auger electron spectroscopy. Prior to the deposition, tellurium oxide species coated the surface. Two steps were distinguished in the UPD process. Deposition process was Idnetically slow. 

Much of the early literature of polonium describes methods for separating it from these mixtures many of these have subsequently been adapted to the separation of milligram amounts of polonium from irradiated bismuth and to its purification. The methods range from a simple chemical separation of the element with a tellurium carrier to its electrodeposition on to a more noble metal or its spontaneous electrochemical replacement on the surface of a less noble metal. 

Electrodeposition of metals is very often evolving under mixed kinetic conditions which deeply influence the resulting structure and aspect of the surface. The following example shows how the EHD technique gives an in-situ information about some geometrical characteristics of the growing electrodeposit in the case of tellurium. 

Tellurium is a constituent common to several definite compounds having semiconducting properties which can be obtained by electrolytic deposition (e.g. CdTe, ZnTe,...). The low solubility of tellurium oxide in acidic aqueous solutions explains why its kinetics of electrodeposition, in the binary of tertiary alloys involved, is mainly controlled by mass transport. 

The electrodeposition of tellurium, Te, has been reported in a basic EMICl-AICI3 ionic liquid [31]. Tellurium tetrachloride, TeCLi, is soluble in the basic ionic liquid to form a tetravalent tellurium chlorocomplex anion, TeClg , which can be reduced to metallic Te by four electron transfer reaction ... 

Solutions containing the metal, most commonly in nitric acid, will deposit the metal on a platinnm electrode by electrodeposition. Polonium metal is deposited spontaneously from such solutions on to metals such as silver or nickel. The metal can be sublimed off such support metals at low pressures. Thermal decomposition of polonium sulfide also yields the metal. In much the same way as tellurium, the metal can be obtained from its solutions by the action of reducing agents such as hydrazine, tin(II) ion, titanium(III) ion, and dithionite. Such metal precipitates appear as gray-black powders. Thin foils, silvery in color, have been prepared by vacuum sublimation of the metal. 

The effect of ultrasound on the process of tellurium anodic dissolution in alkaline solutions was studied by the method of plotting polarization and galvanostatic curves [148]. Tests were made in NaOH solutions (concentrations of 0—20 g/L), subjected to the action of ultrasound at a frequency 17.5 kHz and using Te electrodeposited under ultrasound. The anodic polarization curves plotted without ultrasound and in its presence shifted with increased NaOH concentration towards negative values as a result of the increasing rate of Te anodic dissolution. The presence of ultrasound inhibited the process of Te anodic dissolution, probably due to the desorption of OFT anions from the anode surface. This sonoelectrodeposited Te thus showed greater corrosion resistance in alkaline solution than that deposited... 

In a very recent paper various oxides and oxyanions of tellurium were reinvestigated with a source of electrodeposited on to platinum [45]. 

Cadmium atomic layer electrodeposition above reversible Cd2+/Cd potential (underpotential deposition, upd) on bulk tellurium and Te atomic layer predeposited on gold has been characterised with potentiodynamic electrochemical impedance spectroscopy (PDEIS) by variations, with the electrode potential E, of double layer pseudocapacitance Q,u, charge transfer resistance Rrt and Warburg coefficient Aw of diffusion impedance. 

The goal of this work was the characterization with PDEIS of Cd atomic layer electrodeposition on bulk tellurium and Te monolayer predeposited on gold. Cd upd on Te is an important stage of electrodeposition of CdTe nanostructures. Atomic level control of CdTe electrosynthesis is expected to enable wider application of electrochemical assembling of various micro- and nanodevices that use CdTe as an active semiconductor component. 

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