Polycrystalline thin films structure

Cathodic deposition of lead sulfide from acidic aqueous solutions of Pb(II) ions (nitrate salts mainly) and Na2S203 on various metallic substrates at room temperature has been reported. Stoichiometric PbS films composed of small crystallites (estimated XRD diameter 13 nm) of RS structure were obtained at constant potential on Ti [204]. Also, single-phase, polycrystalline thin films of RS PbS were electrode-posited potentiostatically on Ti, Al, and stainless steel (SS) [205]. It was found that the Al and Ti substrates promoted growth of PbS with prominent (200) and (111)... 

Each organic layer should have uniform and pinhole-free thin films at a thickness of about 50 nm. Amorphous morphology was found to satisfy this requirement. Sometimes, polycrystalline thin films are also acceptable, when their grain sizes are less than 50 nm and they form dense pinhole-free films. The previous systematic studies proposed a molecular design for the formation of uniform thin films. It was reported that the introduction of bulky substituents and steric hindrance into molecular structures, as well as an appropriate three-dimensional steric configuration resulted in amorphous morphology.35,58,61... 

Fair and Forsyth [96] investigated the optical absorption in polycrystalline thin films prepared by the novel technique of exposing thin films of vacuum-deposited lead to gaseous HN3 in the presence of water vapor. The optical absorption spectrum taken at 15°K shows considerable structure (Figure 15). 

Spray pyrolysis technique has been used to deposit polycrystalline thin films comprising of CuInSa nanocrystals onto glass substrates. p-XRD studies demonstrate that the films have a chalcopyrite structure with preferred orientation along (112) lattice plane. Average diameter of the nanocrystals, as determined by SEM and TEM images, was found to be about 40-60 nm while band gap calculated through optical absorption studies was found to be 1.55 eV. A solar device fabricated by using these films demonstrated a power conversion efficiency of 7.60%. 

In much of the research on boron-doped diamond (BDD) electrodes published thus far, for both fundamental and appHed aspects, polycrystalline thin films have been used, because continuous BDD thin films of high quality and purity can be obtained easily and useful research results can be obtained. However, in order to understand the electrochemical properties of diamond electrodes in greater detail, especially concerning the relationships between the crystal structure and the electrode properties, it is becoming essential to carry out studies with single-crystal diamond electrodes. 

It was reported recently [216] that optical-quality PbTe thin films can be directly electrodeposited onto n-type Si(lOO) substrates, without an intermediate buffer layer, from an acidic (pH 1) lead acetate, tellurite, stirred solution at 20 °C. SEM, EDX, and XRD analyses showed that in optimal deposition conditions the films were uniform, compact, and stoichiometric, made of fine, 50-100 nm in size, crystallites of a polycrystalline cubic structure, with a composition of 51.2 at.% Pb and 48.8 at.% Te. According to optical measurements, the band gap of the films was 0.31 eV and of a direct transition. Cyclic voltammetry indicated that the electrodeposition occurred via an induced co-deposition mechanism. 

Thin films of metals, alloys and compounds of a few micrometres thickness, which play an important part in microelectronics, can be prepared by the condensation of atomic species on an inert substrate from a gaseous phase. The source of the atoms is, in the simplest circumstances, a sample of the collision-free evaporated beam originating from an elementary substance, or a number of elementary substances, which is formed in vacuum. The condensing surface is selected and held at a pre-determined temperature, so as to affect the crystallographic form of the condensate. If this surface is at room temperature, a polycrystalline film is usually formed. As the temperature of the surface is increased the deposit crystal size increases, and can be made practically monocrystalline at elevated temperatures. The degree of crystallinity which has been achieved can be determined by electron diffraction, while other properties such as surface morphology and dislocation structure can be established by electron microscopy. 

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