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Basics of Growth Techniques Used for Bulk Single Crystals of Transparent Semiconducting Oxides
Published in Zbigniew Galazka, Transparent Semiconducting Oxides, 2020
This class of techniques first utilizes sublimation at a combustion zone, i.e., a direct solid → gas phase transition of a source (starting) material to be grown. Then the gas phase is transported to a growth zone, where it deposits in a reverse process, i.e., in a gas → solid phase transition. The deposition takes place on a crystal seed surface, or on another, typically amorphous surface, e.g., on an ampoule wall. The transport of the gas phase can be direct (in the case of volatile materials) or indirect by using a CATA (in the case of less or non-volatile materials at operating temperatures). The former technique is called the physical vapor transport (PVT) method. In the latter case, there is a chemical reaction between the source material and the transport agent, and additionally with oxygen in the growth zone. This technique is referred to the chemical vapor transport (CVT) method. There are different arrangements in setups and environments for the growth from the gas phase that are described in Chapters 3–8 for TSOs, and in general, e.g., by Wilke [1].
Influence of tin precursor concentration on physical properties of nebulized spray deposited tin disulfide thin films
Published in Journal of Asian Ceramic Societies, 2018
N. Anitha, M. Anitha, J. Raj Mohamed, S. Valanarasu, L. Amalraj
Thin films of SnS2 were fabricated by various techniques like close-spaced sublimation [11], sulphurization of metallic precursors [12], atmospheric pressure chemical vapor deposition [13], chemical vapor transport [14], chemical deposition [15], vacuum evaporation [16,17], dip coating [18,19], solvothermal process [20], chemical spray pyrolysis [21,22] and each method has its own characteristic advantages and drawbacks in producing homogeneous and defect-free thin film. Among them, nebulized spray pyrolysis method is principal to prepare tin disulfide thin film, which is a low-cost method that can be used to coat uniform deposition on large surface area [23] with less solution wastage. Since this new nebulized spray pyrolysis method is capable of producing mist-like sprayed particles of the precursor solution, nanostructured morphological surface with distinct semiconductor properties were anticipated. In the present study, it is desired to prepare and characterize tin disulfide thin films on amorphous glass substrates at different Tin (MSn) precursor concentrations using the precursor solutions of Tin tetra chloride penta hydrate and thiourea by nebulized spray pyrolysis technique. As the substrate temperature was optimized earlier, these films of SnS2 were prepared at that substrate temperature by changing the concentration of both cation and anion precursor solutions, keeping the ratio of precursors of cation and anion species as 1:2 always.
Photocatalyst ZnO nanorod arrays on glass substrates: the critical role of seed layer in nanorod alignment and photocatalytic efficiencies
Published in Chemical Engineering Communications, 2020
ZnO nanostructures can be prepared as powders or immobilized thin film coatings onto supports. There are many different methods of producing a wide variety of ZnO nanostructures, such as sol-gel (Xian et al., 2012), spray pyrolysis (Patil et al., 2011), pulsed laser deposition (Mannam et al., 2017), chemical vapor transport (2015), chemical vapor deposition (Chu et al., 2012), chemical bath deposition (CBD; Poornajar et al., 2016), and hydrothermal synthesis (Baruah and Dutta, 2009). CBD is the most cost-effective and convenient one among the other ways to deposit a thin film coating as can operate at the low processing temperatures (<100 °C) using simple, inexpensive equipment and allow a uniform coverage of the entire substrate surface (Ibupoto et al., 2013). By using this technique, ordered arrays of vertical ZnO nanorods with minimal defects can easily be generated through the controlled growth parameters, such as CBD duration time, pH, and concentration of precursor and temperature. The surface preparation and the resulting nature of the substrates prior to CBD also play a significant role in producing ordered nanostructures (Rezabeigy et al., 2015). With careful design of the ZnO seeds on the glass substrate, the desired morphology and alignment of the nanorod arrays can be achieved by a seed-mediated growth. They eliminate any mismatch between the substrate and the nanorods and provide nucleation centers that support the growth of nanorods (Greene et al., 2005). Dip coating offers one of the simplest ways to coat the substrate with a seed layer by immersion in a suitable precursor solution that contains zinc ions. The thickness of the seed layer can be adjusted by the number of dipping cycles. After the dipping procedure, the freshly coated and dried substrates typically need calcination at temperatures usually higher than 150 °C for the crystallization (Bobowska et al., 2017). The chemistry of the seed precursor solution and the annealing temperature significantly affect the seed properties, such as roughness, crystallinity, and seed density, which in turn affect the morphology of the ZnO nanorod arrays (Ghayour et al., 2011; Holi et al., 2016). For example, zinc acetate has been reported in the literature as a widely used zinc source in the formation of especially a seed layer or a thin film rather than a nanorod array (Semenova et al., 2017). Other zinc salts, such as zinc nitrate and zinc chloride, have also been studied in many investigations of coating processes to evaluate their effect on the structural properties of ZnO nano features. Interestingly, in the absence of a proper ZnO seed layer, among the acetate, nitrate and chloride salts only the zinc chloride containing precursor solutions were reported to be successful in direct growth of ZnO nanorods on the bare substrate surfaces (Bacaksiz et al., 2008; Aslan et al., 2016). On the other hand, the polarity of the solvent in which the zinc salts are dissolved is also extremely effective in the shape of the growing ZnO nanostructure features. The polar solvent molecules attach selectively to the crystal facets and may act as a surfactant that contributes the crystal growth mechanism (Davis et al., 2019).