Preparation of amorphous films

Preparation of Amorphous Films Essential Results and Interpretation 103... 

Several physical properties of amorphous poly-DSP films have been measured64). For the preparation of amorphous films, a trifluoroacetic acid solution containing 10% poly-DSP is cast on a glass plate and dried in vacuo. The resulting film is extracted with triethylamine to remove the last traces of the acid and then extracted with ethanol. 

Acetate and triacetate polymers are white amorphous soHds produced in granular, flake, powder, or fibrous form. They are used as raw materials in the preparation of fibers, films, and plastics. Polymer density varies and ranges from 100 kg/m for the fibrous form to 500 kg/m for granules. Acetate polymer is shipped by trailer tmck, railroad freight car, or multiwaH bags. 

Germanium difluoride can be prepared by reduction (2,4) of GeF by metallic germanium, by reaction (1) of stoichiometric amounts of Ge and HF in a sealed vessel at 225°C, by Ge powder and HgF2 (5), and by GeS and PbF2 (6). Gep2 has been used in plasma chemical vapor deposition of amorphous film (see Plasma TECHNOLOGY Thin films) (7). 

Fabrication techniques, especially the preparation of thin films of functional materials, have made major progress in recent years. Thin-film solid electrolytes in the range of several nanometers up to several micrometers have been prepared successfully. The most important reason for the development of thin-film electrolytes is the reduction in the ionic resistance, but there is also the advantage of the formation of amorphous materials with stoichiometries which cannot be achieved by conventional techniques of forming crystalline compounds. It has often been observed that thin-film electrolytes produced by vacuum evaporation or sputtering provide a struc-... 

The relatively high volatility of Tg[CH = CH2]8 has enabled it to be used as a CVD precursor for the preparation of thin films that can be converted by either argon or nitrogen plasma into amorphous siloxane polymer films having useful dielectric propertiesThe high volatility also allows deposition of Tg[CH = CH2]g onto surfaces for use as an electron resist and the thin solid films formed by evaporation may also be converted into amorphous siloxane dielectric films via plasma treatment. ... 

Another type of Chi interfacial layer employed on a metal electrode was a film consisting of ordered molecules. Villar (79) studied short circuit cathodic photocurrents at multilayers of Chi a and b built up on semi-transparent platinum electrodes in an electrolyte consisting of 96% glycerol and 4% KCl-saturated aqueous solution. Photocurrent quantum efficiencies of multilayers and of amorphous films prepared by solvent evaporation were compared. The highest efficiency (about 10 electrons/ absorbed photon, calculated from the paper) was obtained with Chi a multilayers, and the amorphous films of Chi a proved to be less efficient than Chi b multilayers. 

High speed of cooling of the deposit material during the process of film formation, sufficient for the preparation of metal films in metastable or amorphous state (usually these states appeared when the kinetic energy of the depositing atoms was higher than 10 eV). 

Amorphous carbons, carbon black, soot, charcoals, and so on, are forms of graphite or fullerenes. The physical properties depend on the nature and magnitude of the surface area. They show electrical conductivity, have high chemical reactivity due to oxygenated groups on the surface, and readily intercalate other molecules (see later). Graphite and amorphous carbons as supports for Pd, Pt, and other metals are widely used in catalysis and for the preparation of diamond films.18... 

FIG. 17.7 Changes in refractive index of amorphous film of diarylethene 2 at 817 nm (squares) and 632.8 nm (circles) upon irradiation with (a) visible light and (b) UV light-The sample films (film thickness = 4 pm) were prepared from (a) closed-ring and (b) open-ring form isomers. 

Both crystalline [168] and amorphous [169] alloys are considered as precursors in the preparation of HTSC films. Atomic-level uniformity of the component distribution in metallurgical alloys can be achieved. One more type of metal precursor, the oxidation of which gives good results under relatively mild conditions, are multilayer polymetallic coatings with nanometer-thick layers [170], Similar compositions are also the most frequently used type of precursors in the technology of semiconductors [171]. 

In 1979, White [3.2] observed that, by milling elemental Nb and Sn powders, the distinct X-ray diffraction peaks of the elements disappeared and typical diffuse peaks of an amorphous pattern showed up. But these samples did not show the superconducting transition temperature of vapor-quenched amorphous Nb-Sn alloys. In 1983, Koch et al. reported on the Preparation of amorphous Ni60Nb40 by mechanical alloying [3.3]. After the detection of amorphization by solid-state reaction in evaporated multilayer films by Schwarz and Johnson [3.4] (see also Chap. 2), Schwarz et al. [3.5] proposed after investigating glass formation in Ni-Ti alloys, that amorphization by mechanical alloying is also based on the solid-state reaction process. Within the last couple... 

The equipment needed in flash evaporation is comparatively modest, and this method is also suitable for the preparation of amorphous alloy films whose constituents have different vapour pressures. It consists of a single heated filament usually made of molybdenum. Powder of the alloy is fed continuously onto the filament, the temperature of which is sufficiently high for evaporation. No shifts in composition of the alloy occur since all the material is evaporated to completion. Devices for monitoring the vapour flux and the source temperature are not needed. The method is restricted to materials that can be obtained in powdered form. 

IR and Raman spectra of PH3 and PD3 films (see Table 17, p. 194) were recorded, and their splitting pattern was analyzed in terms of the phosphane modifications being present see the chapter on the crystal structure on p. 176. The films were prepared by distilling phosphane onto a substrate precooled to the desired temperature [3 to 7]. Deposition of PH3 at 40 K [4] or 35 K [3] resulted in the formation of amorphous films, indicated by the broad and structureless appearance of the V2 band. One or more annealing cycles yielded the crystalline phase [3, 4]. Deposition between 65 and 74 K gave films that revealed the fine structure of the 6 phase on first cooling [4]. 

Preparation of Various Mixed Metal Oxides. In order to deposit the mixed metal oxide, Pb(Zro.5Tio.5)03 a 2 1 1 stoichiometric solution of the lead, zirconium and titanium precursors was prepared. An amorphous film of these precursors was prepared by spin coating on silicon. 

Preparation of Amorphous Precursor Films. A solution of Mn(02CC7Hi5)2 in CH2CI2 was spin coated onto a Si chip. The solvent evaporated leaving an amorphous film of Mn(02CC7Hi5)2. Other films were prepared in an analogous way. 

Some physical properties of PTMSN are presented in Table 3.2. This is an amorphous glassy polymer with very high Tg. Its glass transition is very close to the decomposition temperature and can be discerned only by accurate analysis of the TGA curves. Its mechanical properties are rather modest, though sufficient for preparation of stable films if the molecular mass of the sample is 400 000 Da or higher. 

The parameters of amorphous films vary considerably with the conditions of preparation and annealing as discussed in the text. 

Stuke and Zimmerer (1972). Density and no of amorphous films depend on sample preparation but this point has not been studied in III—V compounds in so much detail as in Ge and Si films (cf. Connell and Paul (1972)). 

In the last section we considered the synthesis of carbon fibers. In this section we are interested in the details of preparation of amorphous carbon films by different techniques, e.g., pyrolysis, thermal evaporation, plasma deposition, chemical methods, ion beam deposition, and high pressure. 

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