Thin films transparent

One example of a very low band gap material is polyisothianaphthalene (Figure 17.13). This material has been synthesized. Because of the low band gap, the material is blue in the undoped state. Doping, as usual, moves the absorption to longer wavelengths, but in this case that means out of the visible range. Doped polyisothianaphthalene is a transparent material, and there are many uses for thin film, transparent, conducting materials. You are asked in the Exercises to rationalize the low Eg of polyisothianaphthalene. 

K. Itoh, M. Nakao, and K. Honda, Preparation of ZnO thin-film transparent electrodes and their application to electrochemical spectral sensitization, Denki Kagaku Oyobi Butsuri Kagaku, vol. 52, 382 pages, 1984. 

Grids with carbon films are widely used, and among the advantages is the high thermal and electrical conductivity. This feature helps to reduce the thermal expansion and loading effects during exposure of the sample to the electron beam [10]. It is important that the material is deposited on a thin film transparent to electrons the thickness may vary from about 10 to 30 nm, depending on the manufacturer. 

Polyaniline (PANI) can be formed by electrochemical oxidation of aniline in aqueous acid, or by polymerization of aniline using an aqueous solution of ammonium thiosulfate and hydrochloric acid. This polymer is finding increasing use as a "transparent electrode" in semiconducting devices. To improve processibiHty, a large number of substituted polyanilines have been prepared. The sulfonated form of PANI is water soluble, and can be prepared by treatment of PANI with fuming sulfuric acid (31). A variety of other soluble substituted AJ-alkylsulfonic acid self-doped derivatives have been synthesized that possess moderate conductivity and allow facile preparation of spincoated thin films (32). 

Tetrathiafulvalene (TTE) has also been used in electrochromic devices. TTE-based polymers spin-coated onto transparent electrode surfaces form stable thin films with reproducible electrochromic properties (100). The slow response of these devices has been attributed to the rate of ion movement through the polymer matrix. 

Atr—ftir can be readily performed on most commercial ftir spectrometers through the use of an attachment for atr spectroscopy. These devices provide ir-transparent internal reflection elements that are typically made of Ge, KRS-5, ZnSe, or ZnS. These internal reflection elements are made of materials that are of extremely high purity to avoid losses from absorption by impurities in these devices. Coupling of a thin film or surface sample to one of these reflection elements is accompHshed by pressing the sample against the element while acquiring the spectmm. 

Thin films (qv) of lithium metal are opaque to visible light but are transparent to uv radiation. Lithium is the hardest of all the alkaH metals and has a Mohs scale hardness of 0.6. Its ductiHty is about the same as that of lead. Lithium has a bcc crystalline stmcture which is stable from about —195 to — 180°C. Two allotropic transformations exist at low temperatures bcc to fee at — 133°C and bcc to hexagonal close-packed at — 199°C (36). Physical properties of lithium are Hsted ia Table 3. 

Space-based solar ceUs are covered with a very thin layer of vitreous siHca to protect against the damaging environment of space such as atomic oxygen, micrometeorites, and radiation effects. Because the siHca is transparent to damaging uv radiation, it is normally coated with a uv-reflective thin film... 

Some polymers, although transparent, may have a cloudy or milky appearance, generally known as haze. It is often measured quantitatively as the amount of light deviating by more than 2.5 degrees from the transmitted beam direction. Haze is often the result of surface imperfections, particularly with thin films of low-density polyethylene. 

Polyethylene is a wax-like thermoplastic softening at about 80-130°C with a density less than that of water. It is tough but has moderate tensile strength, is an excellent electrical insulator and has very good chemical resistance. In the mass it is translucent or opaque but thin films may be transparent. 

For an electron-transparent specimen the absorption and fluorescence correction parts can often be neglected, this is the so-called thin-film criterion introduced by Cliff and Lorimer [4.118]. Thus, for a thin specimen containing two elements A and B yielding the net X-ray intensities I a and 1b, the concentration ratio reduces to ... 

Tarnish dulling, staining or discoloration. of ttietals due to the formation of thin films of corrosion products. (The, term.can also be applied to thin transparent film which may give rise to interference colours.) ... 

Electronic conductivity of thin-film solid electrolytes. Besides having low electronic transference numbers, it is essential for thin films of the order of 1 jim that the magnitude of the electronic resistance is low in order to prevent self-discharge of the battery. For this reason, specific electronic resistances in the range of 1012-1014 Qcm are required for thin-film solid electrolytes. Often the color may be a valuable indication of the electronic conductivity. In this regard, solid electrolytes should preferably be transparent white [20]. 

The simplicity mentioned above exists for various kinds of samples that meet the fundamental requirements laid down in Chapters 6 and 7. Examples are a thin film on a suitable substrate, a sample dissolved at low concentration in a solvent transparent to x-rays, or a sample uniformly dispersed in a similarly transparent medium. In all cases, scattered x-rays should be at a minimum to keep the background low. From the point of view taken here, a trace is thus regarded as a major constituent in a sample if sensible absorption and enhancement effects are absent—if, that is, Equation 7-3 is valid. 

Absorption. Absorption, the attenuation of a beam through a transparent medium, can be characterized by an absorption coefficient. For thin films, such as those of optical oxides, absorption is very small and can usually be ignored. In metallic or semiconductor coatings however, absorption is a major factor. 

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