Polyciystalline films

An experimental illustration of the study of such objects, made of several polyciystalline films, is shown in Figure 7.7. We reahzed a sample comprised of a titaniirm oxide film placed on top of a zirconia film, all of this deposited on a sapphire substrate. The titaniirm oxide film is roughly 20 run wide and the zirconia film about 50 run wide. Two diffraction patterns obtained with the incidence angles... 

Subsequent X-ray structure analysis of specimens cross-section showed that resulting polyciystalline film had MnP type orthorhombic structure with the following constants a = 0.592 nm, h = 0.558 nm, c = 0.360 nm, which corresponds to the lattice parameters of PtSi compound (Suprun et al., 1995). 

Ullal, H.S., K. Zweibel, and B. von Roedem. 2002. Polyciystalline Thin Film Photovoltaics Research, Development, and Technologies. Paper presented at 29th Institute of Electrical and Electronics Engineers Photovoltaic Specialists Conference (IEEE PVSC), New Orleans, La., May... 

Kontani et al. (1995, 1996) measured hole mobilities of vapor-deposited TiOPc. The transit times were derived from photocurrent transients in double logarithmic representation. In agreement with the work of Ioannidis and cowoikers with ClAlPc, the results showed that the mobilities were strongly dependent on the substrate temperature during the vapor deposition. For substrate temperatures between -160 to 160 C, the room temperature mobility increased from 6.0 x 10-6 to 8.0 x 10-5 cn /Vs. The authors attributed this to an increase in film crystallinity. Films prepared at low temperatures were largely amorphous while those prepared at high temperatures were mainly polyciystalline. 

First, a polyciystalline sample usually has a size that ranges in millimeters and the beam irradiating this sample is partially absoibed. This means that a crystal located in a given area of the sample sees an incident intensity 1 that is different from the initial beam s intensity lo. Furthermore, the diffracted beams are also partially absoibed. As a result, the actual intensity that is measured is attenuated by an absorption factor which we will denote by A. The form of this factor depends on the geometric characteristics of the diffractometer used for the experiment. This point will be detailed later on, in particular when describing the diffractometers designed for the study of thin films. 

Ohashi M, lida Y, Wada S (2000) MuUite-based substrates for polyciystalline silicon thin-film solar cells. J Ceram Soc Jpn 108 105-107... 

Electrochemical atomic layer epitaxy (EC-ALE) is the combination of underpotential deposition (UPD) and ALE. UPD is the formation of an atomic layer of one element on a second element at a potential under, or prior to, that needed to deposit the element on itself [5, 6]. The shift in potential results from the free energy of the surface compound formation. Early UPD studies were carried out mostly on polycrystalline electrode surfaces [7], This was due, at least in part, to the difficulty of preparing and maintaining single-crystal electrodes under well-defined conditions of surface structure and cleanliness [8]. The definition of epitaxy is variable but focuses on the formation of single crystal films on single crystal substrates. This is different from other thin film deposition methods where polyciystalline or amorphous film deposits are formed even on single crystal substrates. Homoepitaxy is the formation of a compound on itself. Heteroepitaxy is the formation of a compound on a different compound or element and is much... 

Electrochemical methods for the preparation of anode electrocatalysts for DAFCs involve either the electrodeposition of one metal at a time, eventually followed by the electrodeposition of other metals, or the contemporaneons electrodeposition of two or more metals. Highly ordered Pd nanowires arrays (Fig. 5) have been prepared by template-electrodeposition on glassy carbon electrodes, while cyclic potential sweep techniqnes have been used to prepare Pd thin films on polyciystalline Pt or An substrates. Ni-Pd electrodes for methanol oxidation have been prepared by electrodeposition onto titaninm discs nsing a PdCl2/NiS04-7H20 bath." ... 

The highest bulk mobility of liquid crystal materials reported so far are 0.3 cm A s [ 14], for both hole and electron crmduction in calamitic liquid crystals, and 0.3 cm A s for electron crmduction and 0.2 cm A s [15] for hole cOTiductirm in discotic liquid crystals. These values are comparable to the mobility in polyciystalline thin films of organic semicrmductor materials. 

Since no synthetic chemistiy infrastructure was available at the Department (or, indeed, the Institute) before 2008, polyciystalline samples of catalysts had to be obtained from external, often industrial, partners. In order to produce model systems in house, researchers in the Department of Inorganic Chemistry developed a suite of instruments allowing the synthesis of metal oxides by physical vapor deposition of elements and by annealing procedures at ambient pressure. They chose the dehydrogenation of ethylbenzene to styrene on iron oxides as the subject of their first major study. Figure 6.6 summarizes the main results. The technical catalyst (A) is a complex convolution of phases, with the active sites located at the solid-solid interface. It was possible to synthesize well-ordered thin films (D) of the relevant ternary potassium iron oxide and to determine their chemical structure and reactivity. In parallel. Department members developed a micro-reactor device (B) allowing them to measure kinetic data (C) on such thin films. In this way, they were able to obtain experimental data needed for kinetic modeling under well-defined reaction conditions, which they could use to prove that the model reaction occurs in the same way as the reaction in the real-life system. Thin oxide... 

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