A. Fernandez

Bio: A. Fernandez is an academic researcher from National Autonomous University of Mexico. The author has contributed to research in topics: Thin film & Glazing. The author has an hindex of 3, co-authored 3 publications receiving 273 citations.

Prospects of chemically deposited metal chalcogenide thin films for solar control applications

Abstract: Solar control coatings, required for architectural glazing applications in warm climates, must provide controlled optical transmission ( approximately 10-50%) of the solar radiation in the visible region and should reflect efficiently in the infrared (>0.7 mu m) region to create a cool interior in the buildings. Thin films of PbS and CuxS on glass substrates, deposited from chemical baths, are shown to possess excellent solar control characteristics-superior or comparable to the metallic solar control coatings. For example, for an acceptable range of integrated optical transmittance ( approximately 10-20%) in the visible region, the integrated infrared reflectance for AM2 solar spectrum for the different glazings are: PbS coated glass, 50%; CuxS coated glass, 14%; stainless steel/Cu coated glass, 25% and tinted glass, 4%. The CuxS and PbS coatings also have the advantage of giving pleasant reflected colours (golden, purple, blue, etc), which improves the cosmetic appearance. This paper presents the basic requirements of solar control coatings and provides a comparison of the characteristics of PbS and CuxS coatings against commercially available coatings.

Optimization of chemically deposited CuxS solar control coatings

Abstract: CuxS thin films appropriate for use as solar control coatings for architectural glazing applications have been deposited from chemical baths constituted from copper(II) nitrate or chloride, NH3(aq), NaOH, triethanolamine and thiourea. At ambient temperature (25 degrees C), the duration of deposition ranges from 2 to 12 h, but at 50 degrees C, deposition can be considerably faster, from 1 h to 2 h 50 min. CuxS films deposited in this manner require air annealing at 150 degrees C for about 10 min, to reduce the integrated infrared transmittance, T*(IR), to about 10%. The corresponding integrated transmittance in the visible region, T*(vis), is about 30% and the integrated transmittance for AM2 solar spectra is about 20%. The optical transmittance spectra of the annealed films are peaked in the 0.55-0.575 mu m wavelength range, which provides a greenish yellow illumination inside the building under daylight, that corresponds to the peak in the spectral sensitivity curve of the human eye for photopic (daylight) vision. The reduction in sheet resistance of the CuxS films with the air annealing, from about M Omega Square Operator -1 to about 10-100 Omega Square Operator -1, ensures a low thermal emittance which is a requirement for high-efficiency solar control coatings. The issues involved in the optimization of the deposition conditions for large-area production of the coatings and the choice of protective polymer coatings are also discussed.

Solar control characteristics of chemically deposited lead sulfide coatings

Abstract: Chemically deposited lead sulfide thin films on glass substrates are found to satisfy the basic requirements for solar control coatings for window glazing applications in warm climates, where a low transmittance ( ∼10%–30% ) in the visible region is to be coupled with an appreciable reflectance for infrared radiation The depositions were made on glass substrates from alkaline/ ammoniacal baths of lead acetate, thiourea and small amounts of triethanolamine The coating can produce a gray, purple or bluish appearance in reflected daylight with near normal specular reflectance (visible region) of ∼15%–25% These coatings appear yellowish in transmitted daylight with 7%–25% transmittance, depending on the duration of deposition The integrated infrared (070 to 25 μm) reflectance for air mass (AM) 2 solar spectrum of typical PbS coated glass is ∼37% as compared to ∼7% for the uncoated glass The advantages of chemical deposition for large area coatings, the desirable features of PbS as a solar control coating, and toxicity considerations are discussed

Chemical deposition method for metal chalcogenide thin films

Abstract: Metal chalcogenide thin films preparation by chemical methods are currently attracting considerable attention as it is relatively inexpensive, simple and convenient for large area deposition. A variety of substrates such as insulators, semiconductors or metals can be used since these are low temperature processes which avoid oxidation and corrosion of substrate. These are slow processes which facilitates better orientation of crystallites with improved grain structure. Depending upon deposition conditions, film growth can take place by ion-by-ion condensation of the materials on the substrates or by adsorption of colloidal particles from the solution on the substrate. Using these methods, thin films of group II–VI, V–VI, III–VI etc. have been deposited. Solar selective coatings, solar control, photoconductors, solid state and photoelectrochemical solar cells, optical imaging, hologram recording, optical mass memories etc. are some of the applications of metal chalcogenide films. In the present review article, we have described in detail, chemical bath deposition method of metal chalcogenide thin films, it is capable of yielding good quality thin films. Their preparative parameters, structural, optical, electrical properties etc. are described. Theoretical background necessary for the chemical deposition of thin films is also discussed.

Atmospheric Pressure Chemical Vapor Deposition of Tin Sulfides (SnS, Sn2S3, and SnS2) on Glass

Abstract: Atmospheric pressure chemical vapor deposition of SnS2, Sn2S3, and SnS has been achieved onto glass substrates from the reaction of SnCl4 with H2S at 300−545 °C. The films show good uniformity and surface coverage, adherence, and a variety of colors (black, yellow, brown, and gray) dependent on deposition temperature and film thickness. Growth rates were on the order of 1−2 μm min-1. All the films were crystalline. For substrate temperatures of up to 500 °C single phase films with the hexagonal SnS2 structure (a = 3.65(1) A, c = 5.88(1) A) were formed. At 525 °C a film of mixed composition containing predominantly orthorhombic Sn2S3 (a = 8.83(1) A, b = 3.76(1) A, c = 14.03(1) A) was formed together with some SnS2. At 545 °C films with orthorhombic SnS structure (a = 4.30(1) A, b = 11.20(1) A, c = 3.99(1) A) were formed. Scanning electron microscopy (SEM) revealed a variety of different film thicknesses and morphologies, including needles, plates, and ovoids, dependent on the deposition temperature and tim...

Semiconductor thin films by chemical bath deposition for solar energy related applications

Abstract: In this paper we present the basic concepts underlying the chemical bath deposition technique and the recipes developed in our laboratory during the past ten years for the deposition of good-quality thin films of CdS, CdSe, ZnS, ZnSe, PbS, SnS, Bi2S3, Bi2Se3, Sb2S3, CuS, CuSe, etc. Typical growth curves, and optical and electrical properties of these films are presented. The effect of annealing the films in air on their structure and composition and on the electrical properties is notable: CdS and ZnS films become conductive through a partial conversion to oxide phase; CdSe becomes photosensitive, SnS converts to SnO2, etc. The use of precipitates formed during deposition for screen printing and sintering, in polymer composites and as a source for vapor-phase deposition is presented. Some examples of the application of the films in solar energy related work are presented.

Review: Deposition of ceramic thin films at low temperatures from aqueous solutions

Abstract: Many techniques for the synthesis of ceramic thin films from aqueous solutions at low temperatures (25–100°C) have been reported. This paper reviews non-electrochemical, non-hydrothermal, low-temperature aqueous deposition routes, with an emphasis on oxide materials for electronic applications. Originally used for sulfide and selenide thin films, such techniques have also been applied to oxides since the 1970's. Films of single oxides (e.g., transition metal oxides, In2O3, SiO2, SnO2) and multicomponent films (doped ZnO, Cd2SnO4, ZrTiO4, ZrO2-Y2O3, Li-Co-O spinel, ferrites, perovskites) have been produced. The maximum thicknesses of the films obtained have ranged from 100 to 1000 nm, and deposition rates have ranged from 2 to 20,000 nm/h. Compared to vapor-deposition techniques, liquid-deposition routes offer lower capital equipment costs, lower processing temperatures, and flexibility in the choice of substrates with respect to topography and thermal stability. Compared to sol-gel techniques, the routes reviewed here offer lower processing temperatures, lower shrinkage, and (being based on aqueous precursors) lower costs and the potential for reduced environmental impact. This review emphasizes the influence of solution chemistry and process design on the microstructures and growth rates of the films. The current understanding of the mechanisms of film formation is presented, and the advantages and limitations of these techniques are discussed.

Synthesis and Characterization of Copper Sulfide Nanoparticles in Triton-X 100 Water-in-Oil Microemulsions

Abstract: Nanoparticles of copper sulfide have been synthesized by reacting a copper ammonia complex with an equimolar thiourea solution in Triton-X 100/cyclohexane water-in-oil microemulsions. The presence of an exceptionally sharp and blue-shifted peak at 475 ± 2 nm in the UV−vis spectrum reveals the formation of quasi-monodispersed, size-quantized particles. Using absorption spectroscopy, the formation of a chalchocite (Cu2S) phase is inferred. The peak position in the absorption spectra was found to be independent of net micellar water content as well as aging effect. It is attributed to the formation of a Cu(I) thiourea complex on the surface of the particles, which are hydrogen bonded to the polyoxyethylene (POE) chain of Triton-X 100 (TX-100). The role of thiourea in the tailoring of particles to the micellar periphery was confirmed by synthesizing the nanoparticles using other S2- agents like H2S, and Na2S. The role of the POE chain in mediating the adsorption was brought out by carrying out the reaction in...