Electrochemical bath technique

Lead sulfide films have been prepared by various deposition processes like vacuum evaporation and chemical bath deposition. Electrochemical preparation techniques have been used in a few instances. Pourbaix diagrams for all three aqueous lead-chalcogen Pb-S, Pb-Se, and Pb-Te systems, along with experimental results and cited discussion on the chemical etching and electrolytic polishing of lead chalcogenide crystals and films, have been presented by Robozerov et al. [201]. 

Lincot D, Ortega-Borges R (1992) Chemical bath deposition of cadmium sulfide thin films. In situ growth and structural studies by Combined Quartz Crystal Microbalance and Electrochemical Impedance techniques. J Electrochem Soc 139 1880-1889... 

In Figure 12.17A a simple double pulse program is shown. In Figure 12.17B a third pulse that has zero current or even reversed current is added between the two deposition pulses. This pulse is applied to stop the non-noble metal deposition. In the low current pulse only the noble component will be deposited at higher currents and at more cathodic potential the non-noble component will be deposited together with the noble component. The concentration of the noble component must be so low that the amount of noble metal co-deposited with the non-noble component is negligible. This shows that the plating conditions are very restrictive. For this reason the dual bath technique could be an alternative for electrochemical deposition of a special metal combination. 

In the practical application of electrochemical decontamination procedures, different electrode arrangements are possible, depending on the geometric form of the component to be treated. Two basic possibilities, namely the bath (or immersion) technique and the in-situ technique, are schematically shown in Fig. 4.53. When the bath technique is used, which is mainly applicable for disassembled parts with... 

These results are quite interesting. The initial stages of Al deposition result in nanosized deposits. Indeed, from the STM studies we recently succeeded in making bulk deposits of nanosized Al with special bath compositions and special electrochemical techniques [10]. Moreover, the preliminary results on tip-induced nanostructuring show that nanosized modifications of electrodes by less noble elements are possible in ionic liquids, thus opening access to new structures that cannot be made in aqueous media. 

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. 

Recovery of process chemicals in coil coating plants is applicable to chromating baths and sealing rinses. Recovery techniques currently in use include ion exchange and electrochemical chromium regeneration.8-9... 

Particularly desirable among film deposition processes are solution-based techniques, because of the relative simplicity and potential economy of these approaches. However, the covalent character of the metal chalcogenides, which provides the benefit of the desired electronic properties (e.g., high electrical mobility), represents an important barrier for solution processing. Several methods have been developed to overcome the solubility problem, including spray deposition, bath-based techniques, and electrochemical routes, each of which will be discussed in later chapters. In this chapter, a very simple dimensional reduction approach will be considered as a means of achieving a convenient solution-based route to film deposition. 

If an actinide metal is available in sufficient quantity to form a rod or an electrode, very efficient methods of purification are applicable electrorefining, zone melting, and electrotransport. Thorium, uranium, neptunium, and plutonium metals have been refined by electrolysis in molten salts (84). An electrode of impure metal is dissolved anodically in a molten salt bath (e.g., in LiCl/KCl eutectic) the metal is deposited electrochemically on the cathode as a solid or a liquid (19, 24). To date, the purest Np and Pu metals have been produced by this technique. 

The simplest way to assist electrochemical techniques with US is by using a bath to immerse the electrochemical cell, as proposed by Lorimer et al. [154] (see Fig. 8.15A). These authors used a three-compartment thermostated voltammetric cell consisting of a platinum flag (the counter electrode), a saturated calomel electrode (the reference electrode) and a rotating disc (the working electrode). Although an ultrasonic bath affords less accurate control of US irradiation, it affords a tenfold current increase in sonovoltammetry [167]. 

Schrebler et al. studied the nucleation and growth mechanisms for Re deposition on polyerystalline Au electrodes, from a bath containing 0.75 mM perrhenic acid and 0.1 M sodium sulfate at pH = 2. The potentiostatic step technique was simultaneously employed with measurements of mass changes in an electrochemical quartz-crystal microbalance. The mass vs. time transients were fitted with equations deduced from the current versus time relationships of the conventional nucleation and growth models. It was concluded that electrodeposition of Re started with progressive nucleation and two-dimensional growth, followed by two other contributions ... 

All experiments were performed on 200mm wafers using Semitool s plating tool. Trenches with various geometries and aspect-ratios were patterned in silicon oxide coated wafers. Titanium Nitride (TiN) or Tantalum (Ta) diffusion barriers with nominal thickness of 300 A were deposited on the trenches by vacuum techniques such as PVD or CVD. Unless specified differently, a PVD copper adhesion layer with a nominal thickness of 200A was deposited on top of the barrier by PVD techniques. This thin PVD copper adhesion layer was electrochemically enhanced in Semitool s proprietary ECD seed plating solution prior to the full deposition from an acid copper sulfate bath. 

Electrochemical studies of the electrocatalysts were carried out using the thin porous coating technique [12,13]. An amormt of 20 mg of the eletrocatalyst was added to a solution of 50 mL of water containing 3 drops of a 6% polytetrafluoroethylene (PTFE) suspension. The resulting mixture was treated in an ultrasound bath for 10 min, filtered and transferred to the cavity (0.30 mm deep and 0.36 cm area) of the working electrode. The quantity of electrocatalyst in the working electrode was determined with a precision of... 

Monometallic systems based on Pt, Pd, Rh, Co, Cu, and also some bimetallic systems, Pt-Ag, Pt-Sn, Pd-Rh, Pt-Pb, have been developed, using a similar electrochemical deposition process [48-55]. Due to its important electrocatalytic behaviour, particles of platinum were mainly considered [48,54-66], but also bimetallic Pt-based systems, such as Pt-Ag [46], Pt-Ru [67-69] and Pt-Sn [53,68-70]. Dispersion of palladium particles was also carried out [47,71-73] and bimetallic Pd-Rh and Pd-Pt particles were also obtained [74], Deposition of nickel and copper into polypyrrole films from standard plating baths was considered recently, and observed by the Electrochemical Quartz Crystal Microbalance technique [75,76]. 

M.A.V. Devanathan, Z. Stachurski, W. Beck, A technique for the evaluation of hydrogen embritde-ment characteristics of electroplating baths, J. Electrochem. Soc. Ill (1963) 886—890. 

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