Automated electrochemical deposition system

An automated electrochemical deposition system making use of a simple distribution valve is described. 

Define electros5mthetic routes amenable to the automated electrochemical deposition system for synthesizing for doped and mixed metal... 

Fig. 6.9 An automated electrochemical deposition system used for the production of metal oxides. The custom-made well plate shown has been designed fora 120-sample array, each sealed by 0-rings underneath a patterned Teflon block, and each containing a unique electrolyte composition. Reprinted with permission from [86], copyright 2005 American Chemical Society...

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. 

This paper describes ongoing studies of the electrodeposition thin films of the compound semiconductors CdTe and InAs, using the method of electrochemical atomic layer epitaxy (ALE). Surface limited electrochemical reactions are used to form the individual atomic layers of the component elements. An automated electrochemical flow deposition system is used to form the atomic layers in a cycle. Studies of the conditions needed to optimize the deposition processes are underway. The deposits were characterized using X-ray diffraction, scanning probe microscopy, electron probe microanalysis and optical/infrared absorption spectroscopy. 

Given the repetitive nature of compound formation using electrochemical ALE. an automated deposition system was constructed to form films of a reasonable thickness (Figure I) [24"). The cell is a... 

Colletti LP, Stickney JL (1998) Optimization of the growth of CdTe thin films formed by electrochemical atomic layer epitaxy in an automated deposition system. J Electrochem Soc 145 3594... 

The ellipsometer used in this study is described elsewhere(3). It consists of a Xenon light source, a monochromator, a polarizer, a sample holder, a rotating analyzer and a photomultiplier detector (Figure 1). An electrochemical cell with two windows is mounted at the center. The windows, being 120° apart, provide a 60° angle of incidence for the ellipsometer. A copper substrate and a platinum electrode function as anode and cathode respectively. Both are connected to a DC power supply. The system is automated with a personal computer to collect all experimental data during the deposition. Data analysis is carried out by a Fortran program run on a personal computer. 

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