No abstract

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.