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The bad adherence to the substrate of chemical-solutiondeposited chalcogenide films in alkaline solution is a current technological problem. However, this issue is belittled since is commonly solved by employing pre-sensitized substrates or by empirically changing the deposition parameters until "finding" the "proper" chemical formulation. For these reasons, the issue of the adherence has not been previously studied. The present research aims to properly discuss the issue of adherence by taking as example CdS. As a substrate, we used float glass sheets to take advantage of the surface duality of this interesting flat glass (different tin content). It was found that both the surface chemical composition of the substrate and the concentration of Cd 2 + in the reaction solution play important roles in the adherence of the CdS thin films; an important effect of temperature was also found. The results were also consistent for indium tin oxide and silicon wafer surfaces. We propose a general surface reaction scheme which considers both the surface reactive sites and the hidroxocadmium-thiourea complexes of the reaction solution, as well as the formation of a surface intermediate entity which dissociates into a CdS molecule bonded to the surface and byproducts. The adherence depends on the quantity of surface intermediate entities formed, and therefore, the conditions that promote their formation contribute to the adherence: high reagent concentration, high-reactive surface sites, and low reaction temperature.

The development of an electrochemical sensor for the analysis of formaldehyde, based on the use of a screen printed carbon electrode modified with gold clusters, is reported in this work.

In a previous paper, we reported that thin films of ZnO:Al [aluminum-zinc oxide (AZO)] deposited after achieving a very low base pressure [from 4.0×10–7 Torr (5.6×10–5 Pa) to 5.7×10–7 Torr (7.6×10–5 Pa)] result dark yellow in color and are resistive. These are undesirable characteristics for the application of AZO thin films as front electrodes in solar cells. However, given the increasingly tendency in the acquisition of equipment that allow us to reach excellent vacuum levels, it is necessary to find the deposition conditions that lead to an improving of transmittance without greatly impacting the electrical properties of materials deposited after achieving these levels of vacuum. In this way, the present work is focused on AZO thin films deposited after achieving a very low base pressure value: 4.2×10–7 Torr (5.6×10–5 Pa). For this, we studied the effect of the variation of the oxygen volume percent in the argon/oxygen mixture (by maintaining the deposition pressure constant) and the effect of deposition pressure with only argon gas on the main properties of AZO thin films. The depositions were done at room temperature on glass substrates by direct-current magnetron sputtering with a power of 120 W (corresponding to a power density of 2.63 W/cm2). As results, we found that the variation of deposition pressure with only argon gas is a good option for the control of optical and electrical properties, since the addition of oxygen, although improves transmittance, greatly impacts on the electrical properties. Furthermore, an interesting correlation was found between the optical and electrical properties and the chemical composition of the AZO films, the latter depending on the argon pressure (for this, a careful X-ray photoelectron spectroscopy analysis was performed). Also, the inverse relationship between crystallinity and deposition rate was confirmed, in which deposition rate inversely depends on argon pressure.

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Five studies were conducted in order to produce less waste and economize the application of a CdCl 2 -Na 3 C 6 H 5 O 7 -KOH-H 3 BO 3 /NaOH/KCl-(NH 2 ) 2 CS definite aqueous system in the chemical bath deposition of CdS thin films, as well as to generate supporting information helpful to explain the effects of varying certain parameters established for the use of this formulation. These studies are related to the utility of the pH 10 borate buffer, to the selection of the appropriate OH -concentration, commercial alkali, and reaction temperature, and to the reusing of the residual solution. These studies were conducted by means of optical characterization, pH measurements, energy consumption tests, and chemical analysis; and all possible implications were analyzed in detail and widely supported by the literature. It is observed that the addition of 5.0 mL of pH 10 borate buffer in the reaction solutions only causes a slight reduction in the pH value and, therefore, in the thickness of the resulted films. It is observed that a decrease in CdCl 2 concentration causes an increase in the pH values, and when such reagent concentration is varied it is necessary to determine the pH value at which the best CdS films can be obtained; this indicates the existence of an optimum pH of deposition, depending on the used reagent concentrations. It is demonstrated that the use of KOH and NaOH is interchangeable, and the advantages of NaOH are evaluated in the context of hygroscopicity, CO 2 absorption, purity, and price. It is observed that the energy consumption when depositing a determined film is lower at high temperatures, and it is concluded that the time and energy savings at high temperatures are undoubtedly advantages in the deposition process of CdS thin films. A formulation to recycle the residual solution is presented, which is very important for the reducing of residual volume, and, therefore, in the minimizing of the environmental impact. An indirect objective of this work is to generate interest in identifying those points that could be modified in other chemical formulations to minimize costs and waste.

A novel, very simple, and environmentally friendly chemical procedure is presented for solving the problem of adhesion of chemical-solution-deposited CdS thin films to tin-free glass sheets and silicon wafers: the addition of a single drop (0.05 mL) of 0.05 M Al2(SO4)3 solution for every 100 mL of reaction solution. The issue of film adhesion is fully explained, and the in situ effect of the added Al3+ ions, which occurs through modification of the substrate surface by adsorption of the Al(OH)4− ions formed in the alkaline reaction solution, is explained in detail. With this chemical procedure, the addition of more toxic cadmium salt is not required, and no tedious sensitization procedures or slow reactions at low temperatures are needed. Also, it is demonstrated that the addition of one drop of 0.05 M Al2(SO4)3 into the reaction solution does not affect the growth rate, the chemical composition, or the optical and electrical properties of the resulting CdS thin films.

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