Nonstoichiometric films

From the optical transmission spectra, a bandgap of 1.50 eV was found for the most stoichiometric (in terms of Cu In 1 the S content was always found to be low) films. This value dropped slightly for nonstoichiometric films [39]. Resistivities varied with composition, from ca. 50 O-cm for In-rich films down to ca. 0.1 D-cm for very Cu-rich ones [36]. 

Multisource precursors tend to produce nonstoichiometric films... 

They reported that the fllms prepared at points B and P are almost stoichiometric and transparent independent of argon flow, whereas the nonstoichiometric films prepared at point A are nontransparent. 

The elements of Group 5 are in many ways similar to their predecessors in Group 4. They react with most non-metals, giving products which are frequently interstitial and nonstoichiometric, but they require high temperatures to do so. Their general resistance to corrosion is largely due to the formation of surface films of oxides which are particularly effective in the case of tantalum. Unless heated, tantalum is appreciably attacked only by oleum, hydrofluoric acid or, more particularly, a hydrofluoric/nitric acid mixture. Fused alkalis will also attack it. In addition to these reagents, vanadium and niobium are attacked by other hot concentrated mineral acids but are resistant to fused alkali. 

The monomer Ga(AsBut2)3 has been used in a number of deposition studies. In an initial study, films were grown at 480 °C under reduced pressure (5-10 torr) and gave epitaxial films with low carbon incorporation. The nonstoichiometric As Ga ratio (3 1) in the precursors gave rise to -type films, whereas the films are generally p-type when prepared using the dimers mentioned... 

Regarding the chemical nature of species in LB films, XPS has been used to identify mixed sulfide/polysulfides in nonstoichiometric sulfides of copper (9,19), elemental Se in CdAr films exposed to H2Se (75), and the nature of nitrogen-containing species in LB films made from ArH on subphases of amine-complexed metal ions of M2+ [M = Cu (9), Pt, Pd (74)1. The decomposition of PbS in StH acid films has also been investigated by XPS (68,70). Of two XPS studies of HgS formation in FA films (22,45), one was able to demonstrate that the p-HgS form (mefo-cinna-bar) was present. 

Kim YS, Ha SC, Kim K et al (2005) Room-temperature semiconductor gas sensor based on nonstoichiometric tungsten oxide nanorod film. Appl Phys Lett 86(21) 213105-1-213105-3... 

The mechanism of the scaling of iron is so complex as to require special mention. Above 570 °C, wiistite (Fei xO) is thermodynamically stable and forms the relatively thick basal layer in the oxide film. This is followed by a magnetite (FesCU) layer which is followed by a final layer of Fe2C>3. Magnetite itself tends to become nonstoichiometric under oxidizing conditions, with excess Fe3+, so that its composition and color can vary from Fe3.oooC>4 (black) toward cubic Fe2.667 04 (i.e., 7-Fe203, chocolate brown). Thus, as outlined in Section 4.6, the oxidation of iron above 570 °C involves mainly... 

By applying an outside potential, many metal oxide films are switchable to a nonstoichiometric redox state, creating an intervalence charge transfer with an... 

Spectral Photoresponses of Carbon-Doped Ti02 Film Electrodes. Raman spectra used to identify disordered carbon in the flame-formed samples in addition to lower nonstoichiometric titanium oxides identified by X-ray diffraction. 314... 

The reactivity of the actinide metals is in line with other electropositive highly reactive metals. In air, the actinides are rapidly covered with an oxide film. For Pu, the film has two distinct layers, Pu02 on the surface and PU2O3 on the subsurface. The relative quantity of each of these layers is dependent on the quantity of oxygen in the atmosphere. The metals also react with metalloids and nonmetals to form a number of solid-state stoichiometric and nonstoichiometric compounds. The following sections detail many of the products from direct interaction of the actinide metals with other elements. 

Zinc selenide (yellow) and telluride (brown) have similar stractures to those of the sulfide, both existing in both wurtzite and zinc blende modifications. The selenide is used with zinc sulfide as a phosphor. It has the interesting property that it can act as a bine-green solid state laser bine-green laser action in solids is rare (most solid-state lasers function towards the red end, 635 nm or more, of the spectrum). At room temperature, laser action with the selenide at a wavelength of 525 nm (green) is observed and at -196°C at 495 nm (bine). Unfortunately the laser is relatively short-lived. Zinc telluride is a wide band gap semicondnctor whose electron transport properties in the form of thin films of stoichiometric and nonstoichiometric forms have been mnch studied. Its applications in optoelectronics, for example, as an optical recording material, have been reviewed. ... 

The presence of KIO3 in W CMP slurry along with H2O2 was found to produce a nonstoichiometric duplex of WO2/WO3 leading to low removal rates due to the increasing hardness of the oxide film with the reduction in the oxygen content, and hence the presence of WO2 in the surface film leads to lower removal rates in case of KIO3 [29]. 

Since the reaction rate at potentials above Vp is limited by the dissolution of oxide and the dissolution rate depends on the nature of the oxides (see Chapter 4), the change of current with potential indicates that oxide composition/structure varies with the formation. The nonstoichiometric composition of an anodically formed oxide film can be expressed as SiO with a higher value of n close to the oxide/electrolyte interface and a lower value of n close to the Si/oxide interface.A thicker oxide film has a bulk composition closer to the stoichiometric SiOa. The dissolution rate of anodic oxide depends on the composition of the electrolyte as shown in Fig. 5.46. " (also Fig. 5.7 ). It depends little on the type of material and doping levels. ... 

On the other hand, according to Serre et the cnrrent transient at the end of etching of anodic oxide films in HF solutions is related to hydrogen termination. It is argned that because an anodic charge, equivalent to a nonstoichiometric oxide of 50 A, is also passed at the end of etching of a thermal oxide, the presence of a... 

Nonstoichiometric copper indium gallium diselenide [Cu(In,Ga) Se2—abbreviated as CIGS or CIS if the gallium is absent] is another promising thin-film PV material.f Large grains can be produced on foreign... 

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