Consequence of the Pulling Solution Ageing on the Properties of Tin Oxide Layers Elaborated by the Sol-Gel Dip-Coating Technique

In the sol-gel technology, either for bulk or thin films, the stability in time of the solutions is a major factor to control. An evolution of the solution may influence strongly the properties of the elaborated material (thickness, cracks, refractive index, conductivity, etc.), and cases have been reported where solutions had to be stored in a dry and cold place to prevent any hydrolysis-condensation reaction, and so any consequent gelation.This paper evaluates the influence of the solution aging on the properties of undoped SnO₂ layers obtained by sol-gel dip-coating (SGDC). Results are given in relation with storage conditions and for experiences conducted over several months.The evolution of the solution viscosity is first followed, and the corresponding properties for the layers are presented: optical reflection and transmission, optical gap, conductivity, morphology... The importance of the interaction with water is discussed.     

Influence of Elaboration Parameters on the Properties of Tin Oxide Films Obtained by the Sol-Gel Process

The influence of elaboration parameters during the sol-gel process is studied for tin oxide films deposition. The Dip Coating Sol-Gel route can be divided into three elaboration stages: the pulling phase and the drying and densification steps. During the pulling phase, the relative humidity ratio and the withdrawal speed are found to influence the film morphology and the film thickness respectively. Then, we show how a correct control of the sample drying is able to eliminate cracks. The densification step (temperature and duration), leading to the final network, is considered in details, and resulting effects on physical properties are presented: crytallinity, optical behaviour, atomic density, stoichiometry, electrical conductivity etc... We show through these results the specificity of the tin oxide elaborated with our procedure     

Frequency characterization of thin soft magnetic material layers used in spiral inductors

The paper details the characterization of thin magnetic materials layers, particularly soft materials, with respect to their behaviour in frequency (from 10 MHz to 1 GHz). The proposed method is suitable for any soft but insulating magnetic material; Yttrium Iron Garnet (YIG) is used as an example. The principle is based on a comparison between simulations for different values of the permeability and measurement values versus frequency of planar inductor structures; an experimental validation is proposed as well. Thin magnetic material is first deposited on an alumina substrate using RF sputtering technique; a planar spiral winding of copper is then deposited on the magnetic material by the same technique. The effective permeability versus frequency is obtained by comparing two samples of spiral windings with and without magnetic material. Network analyser measurements on samples of various geometrical dimensions and of different thicknesses are necessary to determine the effective magnetic permeability; we have obtained a relative effective permeability of about 30 for seven turns spiral inductor of a 17 μm YIG film.     

A subgradient algorithm for certain minimax and minisum problems

We present a subgradient algorithm for minimizing the maximum of a finite collection of functions. It is assumed that each function is the sum of a finite collection of basic convex functions and that the number of different subgradient sets associated with nondifferentiable points of each basic function is finite on any bounded set. Problems belonging to this class include the linear approximation problem and both the minimax and minisum problems of location theory. Convergence of the algorithm to an epsilon-optimal solution is proven and its effectiveness is demonstrated by solving a number of location problems and linear approximation problems.This research was partially supported by the Army Research Office, Triangle Park, NC, under contract number DAH-CO4-75-G-0150, and by NSF grants ENG 16-24294 and ENG 75-10225.     

Analysis of Antimony Doping in Tin Oxide Thin Films Obtained by the Sol-Gel Method

The antimony doping in SnO₂ thin films prepared by the sol-gel dip-coating method has been studied using two characterization techniques. In order to determine the actual doping level directly in the deposited layers, X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS) have been used. We found that this doping level is systematically lower than expected from the starting solutions composition, and that two oxidation states are present: Sb³⁺ and Sb⁵⁺. As the antimony content increases, there is a competition between Sb⁵⁺ and Sb³⁺ species.The SnO₂: Sb thin films have also been observed by transmission electron microscopy (TEM), showing that the measured mean size of crystallites decreases as the Sb content increases in the oxide. No precipitates of either Sn or Sb oxides (other than SnO₂) could be detected.