SILAR process

The complete SILAR process was first described by Nicolau in 1985.1"3 Since then it has mostly been used to grow oxide and chalcogenide thin films. 

To allow the growth of another semiconducting material having the sulfide ion as the anion component, for example, CdS. The SILAR process has been proposed. For InP (n), the mechanism of sulfurization (the first step of CdS deposition) has been described [104] reversible adsorption of HS ions, followed by the irreversible expulsion of... 

Successive Ion-Layer Adsorption and Reaction (SILAR) Process... 

Fig. 2.7 Simplified schematic diagram of an automated SILAR process for CdS. 

SILAR-grown ZnO films have been tested for gas sensor applications.29 The ZnO films, doped with tin for this purpose, were grown from a mixture of dilute zinc sulfate, sodium hydroxide, and sodium tin(IV)oxide solutions. The final step, resulting in the oxide film, was treatment of the substrate and film in a nearly boiling water bath. The N02 gas sensing properties were tested for films doped with Al, Cu, Pd, and Sn, but only the film doped with tin exhibited sensitivity toward N02. The sensitivity of the ZnO Sn film was 5% /ppm after rapid photothermal processing (RPP). The best sensitivity was obtained when the tin concentration was 5-10%.29... 

Ranjith, R. John T. T. Kartha C. S. Vijayakumar K. P. Abe T. Kashiwaba Y. 2007. Post-deposition annealing effect on In2S3 thin films deposited using SILAR technique. Mater. Sci. Semicond. Process. 10 49-55. 

Electrodeposition is by its nature a condensed phase process, whereas most studies of ALE have been performed using gas phase or vacuum methodologies, CVD or MBE. A solution phase deposition methodology related to ALE has been developed in France by Nicolau et al. [27-32] (Fig. 2), in which adsorbed layers of elements are formed by rinsing a substrate in aqueous solutions containing ionic precursor for the desired elements, sequentially, in a cycle. After exposure to each precursor, the substrate is copiously rinsed and then transferred to a solution containing the precursor for the next element. The method is referred to as successive ionic layer adsorption and reaction (SILAR). Reactivity in SILAR appears to be controlled by the rinsing procedure, solution composition, pH, and specifically... 

Reference 92 describes not a normal CD process, but one closer to the SILAR technique described in Sec. 2.11.1. However, while the SILAR method involves dipping the substrate in a solution of one ion (e.g., sulphide), rinsing to remove all but (ideally) a monolayer of adsorbed ions and then dipping in a solution of the other ion (e.g., Ag ), the present technique omits the intermediate rinsing step. This means that a relatively large amount of solution can remain on the substrate between dips, and layer formation proceeds much more rapidly than for SILAR, albeit with less control. A typical rate was 4 nm/dip cycle. In this case, a visible layer of Ag2S formed after several dips. Since interference colors were ob-... 

CdS/Snj S PV cells have been fabricated where the CdS was deposited by CD and the SnS deposited by a variant of CD where the substrate is dipped first in a solution of one of the ions and then in the other without rinsing in between, as would be the procedure for SILAR (see Sec. 2.11.1) [41]. While the cells showed very low conversion efficiencies, the main emphasis was on Ag-doping of the CdS in order to increase the conductivity and the effect of this doping on the PV cells. An increase in efficiency from 0.03% to 0.08%, mainly as a result of an increase in short-circuit current, was obtained by doping the CdS with Ag. The doping was carried out by an ion exchange process whereby the undoped CdS film was immersed in a solution containing Ag complexed by thiosulphate. 

Cu induction of MT genes occurs efficiently in Drosophila and may be a direct effect. Drosophila melanogaster contains two distinct metallothio-neins, designated Mto and Mtn (Mokdad et al., 1987). The Mto gene is more efficiently induced by Cd salts than by Cu salts, whereas Mtn is more efficiently induced by Cu salts (Silar et al., 1990). The mechanism of Cu induction of Mtn remains unresolved, so a significant unresolved question is whether Cu induction of MT biosynthesis occurs through a direct transcriptional process as in yeast. 

The two processes are known as SILAR (successive ion layer adsorption and reaction) and ILGAR (ion layer gas reaction). Both methods work best when a metal salt is chosen in which the metal ion has the same valence state as in the desired final compound. Depending on concentration, temperature and duration, the thickness of the deposited metal can be varied from approximately monolayer thickness to more continuous single- or multi-layer coverage. 

Besides the sol-gel processing, there are many aqueous routes to synthesize ceramic powders, fibers, films and bulks. Niesen and DeGuire reviewed these low temperature and non-electrochemical processes (Niesen and DeGuire, 2001). According to them, the processes include a chemical-bath deposition (CBD), successive ionic-layer adsorption and reaction (SILAR), liquid-phase deposition (LPD), electroless deposition (ED), and film deposition on organic self-assembled monolayers (SAMs). Of course, an electrochemical route is an important process. Another non-sol-gel route is a spray pyrolysis of solution or sol, and is applied to the direct preparation of oxide powders and films. Since these processes do not form the gel phase, they are not described here. 

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