Surface morphology, metallic films

Thin films of metals, alloys and compounds of a few micrometres diickness, which play an important part in microelectronics, can be prepared by die condensation of atomic species on an inert substrate from a gaseous phase. The source of die atoms is, in die simplest circumstances, a sample of die collision-free evaporated beam originating from an elemental 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 die crystallographic form of die condensate. If diis surface is at room teiiiperamre, a polycrystalline film is usually formed. As die temperature of die surface is increased die 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 odier properties such as surface morphology and dislocation sttiicmre can be established by electron microscopy. 

For iron oxides, IR spectroscopy is useful as a means of identification. Hematite crystals in films that were too thin (<70nm) to be characterized by XRD were shown by IR to be oriented with the c-axis perpendicular to the surface of the film (Yubero et al. 2000). This technique also provides information about crystal morphology, degree of crystallinity and the extent of metal (especially Al) substitution because these properties can induce shifts in some of the IR absorption bands. It is also widely used both to obtain information about the vibrational state of adsorbed molecules (particularly anions) and hence the nature of surface complexes (see Chap. 11) and to investigate the nature of surface hydroxyl groups and adsorbed water (see Chap. 10). Typical IR spectra of the various iron oxides are depicted in Figure 7.1. Impurities arising either from the method of preparation or from adsorption of atmospheric compounds can produce distinct bands in the spectra of these oxides -namely at 1700 cm (oxalate), 1400 cm (nitrate) and 1300 and 1500 cm (carbonate). 

The microstructure and morphology of thick single-phase films have been extensively studied for a wide variety of metals, alloys, and refractory compounds. Structural models have been proposed (12,13). Three zones with different microstructure and surface morphology were described for thick (tens of micrometers) deposits of pure metal. At low temperature (< 0.3 Tm ), where Tm is the melting point (K) of the deposit metal, the surface mobility of the adatoms is reduced, and the deposit was reported to grow as tapered crystallites. The surface is not full density (Zone 1). At higher substrate temperature (0.3-0.45 Tm ), the surface mobility increases. The surface... 

To realize second-order anisotropy, the atomic environment of the transition-metal atoms must have a sufficiently low symmetry [49, 62-65]. Figure 6 illustrates that this is often, but not always, the case for surface atoms. Magnetic surface anisotropy, first analyzed by Neel [62], is important in complicated structures and morphologies such as ultrathin transition-metal films [66], multilayers [67], rough surfaces [65], small... 

The surface morphology of the PLD grown ZnO-based films is important for the interface quality of multilayer structures, including quantum wells with thickness of a few nanometer only, for the formation of metal-semiconductor Schottky contacts and for the optical emission properties. Therefore, the control and optimization of surface properties is essential for the successful application of ZnO thin films in related device configurations. 

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