Single-Layer Films

The first step towards the fabrication of thin-film devices is the growth of a single-layer film. The anisotropic layered structure and short superconducting coherence lengths of most high Tc superconductors introduce aspects of film growth that need not to be considered for conventional low-temperature superconductors. 

The detailed behavior of an individual grain boundary depends on its geometry, see Fig. 14.2, and the presence of doping elements. Epitaxial growth where the crystal structure unit cell of the deposited material has a fixed orientation relationship with respect to the unit cell of the substrate is most often desired when depositing thin films where a high Jc is required. 

1 Epitaxial growth of c-axis-oriented films on planar surfaces 

One of the most investigated high Tc superconductors is YBa2Cu307 t (YBCO). The discovery of this superconductor initiated a worldwide effort to optimize the quality of thin films on different types of planar substrate using various deposition techniques, for example pulsed laser deposition, magnetron sputter deposition, co-evaporation and molecular beam epitaxy. It should be 

The vast majority of the reported work on YBCO thin films concerns c-axis films since the growth kinetics and surface energies usually promote this orientation [14.8-14.10]. This is illustrated in Fig. 14.3 where the surface is assumed not to interact with the YBCO film. The YBCO spontaneously forms platelets with the c-axis along the short axis of the plates. The a- and Z -axes are the rapid growth directions and the low-energy surfaces are (001), (100) and (010). The preferred orientation with respect to the substrate can be manipulated by the interaction between the film and the surface on which it is growing. 

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The principle application of XRF thin-film analysis is in the simultaneous determination of composition and thickness. The technique has been used for the routine analysis of single-layer films since 1977 and multiple-layer films since 1986. Two main sources of publications in the fields are the annual volumes of Advances in X-Ray Analysis by Plenum Press, New York, and the Journal of X-Ray Spectrometry by Heyden and Sons, London. Typical examples on the analysis of single-layer films and multiple-layer films are used to illustrate the capabilities of the technique. 

In multiple-layer thin films, it is possible that some of the elements may be present simultaneously in two or more layers. XRF analysis of this type of film can be complicated and cannot be made solely from their observed intensities. Additional information, such as the compositions or thickness of some of the layers is needed. The amount of addidonal non-XRF information required depends on the complexity of the film. For example, in the analysis of a FeMn/NiFe double-layer film, the additional information needed can be the composition or thickness of either the FeMn or NiFe layer. Using the composition or thickness of one of the film predetermined from a single-layer film deposited under identical condidons, XRF analysis of the FeMn/NiFe film was successfiil. ... 

Fig. 10 a-c SFM micrographs demonstrate wetting of HOPG by carbosilane dendrimers [72] a initially, droplets with a contact angle of 8° were observed b after 1 month at 23 °C, the droplets spread and formed islands with a spherical cap providing a reservoir for spreading c after 20 min at 150°C, lamellae, mostly bilayers with a thickness of about 4.5 nm, were formed. Within small areas single layer films are also observed with a thickness of 2.4 nm... 

Fig. 66. Magnetostriction hysteresis loops of a TbFeCo single-layer film and a Fe/TbFeCo/Fe sandwich films.

Enteric film coatings are usually applied as a simple single-layer film coat, although in some instances it may be necessary to apply multiple-layer film coatings. 

Dmytrenko O.P., Kulish M.P., Shpilevskiy E.M., Poperenko L.V., Yurgelevych I.V., Shulze S., Hietschold M., Prylutskyy Yu.I., Matveeva L.A. The connection between optical properties and electron structure of Cu-C60 single-layer films. Funct. Mat. 2003 10 521-524. 

The blown film process involves extruding a relatively thick tube that is then expanded or blown by the usual internal air pressure or the water quench process to produce a relatively thin film (Figure 5.6). The tube can be collapsed to form double-layer layflat film or can be slit to make one or two single-layer film webs. The water quench process is the generally preferred method of producing blown PP type film. 

If the Schottky barrier cells are by far the most extensively studied, the limited absorption spectra of single-layer films, combined with the narrow widths of their depletion layer, restrict the ultimate sunlight conversion to about 4% [55]. An organic p-n junction, in contrast, should have a higher efficiency because of improved matching of absorption and solar spectra by the use of more than one absorber in the depletion layer. The p-n junction, in fact, is composed of two layers, constituted of a p-type and an n-type organic conductor. 

This system s pattern identification fimction can automatically metisure the film thickness with very fine test patterns (as small as 40 square microns). When used with Si02 single layer films, the experimental prototype s measurements proved reliably reproducible (showing a deviation of less than 4 nm at 3 o over repeated trials), and required thirty seconds or less per wafer (including time for pre-alignment and five-point measurement). The system s theoretical basis and actual operations are described below. 

Film thickness measurement reproducibility (for SiO, single layer films at 3E) < 4 nm... 

Ethylene vinyl alcohol barrier resins are never used as single layer films in packaging but rather are utilized in coextruded structures combined with less expensive structural polymers. 

The next step in the development of high thin-film devices after the optimization of single layer films is the introduction of defects in precisely defined positions in order locally to alter the properties of the superconductor. The use of grain boundaries as Josephson junctions in SQUlDs (Superconducting Quantum Interference Devices) is an example of how defects can be utilized. 

To protect metal ware from external effects and mechanical damages they undergo preservation by packing into inhibited film materials inside which an atmosphere is created that averts corrosion. The requirements imposed on the preservation material depend upon the product to be protected therefore to create a single-layer film meeting all the requirements is in fact impossible. 

Liquid Cl can be contained in a specific carrier layer (Fig. 2.3, c, d) or in the space between layers of a multilayered film (Fig. 2.3e), as well as in a jelly-like polymer of a single-layered film. 

More perfect and ecologically safe techniques for manufacturing the jelly layer as a Cl carrier on the inner surface of hose single-layer films have since been elaborated [51, 52]. Furthermore, the means of fixing this layer to the barrier base surface have been developed [3]. 

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