Textured thin films

The film thickness of epitaxial and highly textured thin films can be measured with XRD. Close to the usual or primary difftaction peaks there are secondary or subsidiary maxima in the difftacted intensity (see Figure 6), which are due to the finite film thickness. The film thickness is inversely proportional to the spacing between these maxima and is easily calculated. X-ray reflectivity is another accurate method for measuring a film s thickness. 

I Schnitzer, E Yablonovitch, C Caneau, TJ Gmitter, and A Scherer, 30% External quantum efficiency from surface textured, thin-film light-emitting diodes, Appl. Phys. Lett., 63 2174—2176, 1993. 

Atomically resolved STM studies require preparation of a flat surface with well-defined crystallography. Studies to date have focused on either singlethin film noble metal electrodes. The haditional approach to single-crystal preparation involves growing an ingot or boule by solidification from a melt using a seed crystal to control the orientation. Alternatively, a remarkably simple and inexpensive technique has been developed whereby a H2-O2 flame is used to melt the end of a polycrystalline... 

Oba, F., Ohta, H., Sato, Y, Hosono, H., Yamamoto, T, and Ikuhara, Y (2004) Atomic structure of [OOOlj-tilt grain boundaries in ZnO A high-resolution TEM study of fiber- textured thin films. Phys. Rev. B, 70, 125415-125420. 

Both, piezoelectric and pyroelectric behavior is possible only in ferroelectric ceramics, or in otherwise polar materials that are deposited as textured thin films. 

The results for characterizing stress in elastically anisotropic cubic single crystal films presented in Section 3.5 and in this section can also be adapted, under appropriate conditions, for textured polycrystalline films. An equi-biaxial mismatch strain in the (001) or (111) textured thin film of a cubic crystal results in an equi-biaxial mismatch stress. Because the response is transversely isotropic, the biaxial moduli derived for cubic crystals of these orientations can also be used to characterize polycrystalline thin... 

Clemens, B. M. and Bain, J. A. (1992), Stress determination in textured thin films using x-ray diffraction, MRS Bulletin 17, 46-51. 

The rather weak response of 5T and 6T [174] is due to the unfavorable orientation of the long molecular axis with respect to the normal of the textured thin films. Since the long molecular axis makes an angle of 32° with respect to the normal [12,133] (section 7.4.3.1), the lowest Bu state contributes accidentally very little to the actual three-photon resonance enhancement (vide infra). A marked increase of the three-photon resonance would be observed if the long axis would lie in the substrate plane. 

Coercivity of Thin-Film Media. The coercivity ia a magnetic material is an important parameter for appHcations but it is difficult to understand its physical background. It can be varied from nearly zero to more than 2000 kA/m ia a variety of materials. For thin-film recording media, values of more than 250 kA / m have been reported. First of all the coercivity is an extrinsic parameter and is strongly iafluenced by the microstmctural properties of the layer such as crystal size and shape, composition, and texture. These properties are directly related to the preparation conditions. Material choice and chemical inborn ogeneties are responsible for the Af of a material and this is also an influencing parameter of the final In crystalline material, the crystalline anisotropy field plays an important role. It is difficult to discriminate between all these parameters and to understand the coercivity origin ia the different thin-film materials ia detail. 

The determination of particle size and stmctural iaformation for fibers and polymers, and the study of stress, texture, and thin films are appHcations that are growing ia importance and can be examined with x-ray iastmments. 

X-ray diffraction consists of the measurement of the coherent scattering of x-rays (phenomenon 4 above). X-ray diffraction is used to determine the identity of crystalline phases in a multiphase powder sample and the atomic and molecular stmctures of single crystals. It can also be used to determine stmctural details of polymers, fibers, thin films, and amorphous soflds and to study stress, texture, and particle size. 

As we have seen, the orientation of crystallites in a thin film can vary from epitaxial (or single crystalline), to complete fiber texture, to preferred orientation (incomplete fiber texture), to randomly distributed (or powder). The degree of orientation not only influences the thin-film properties but also has important consequences on the method of measurement and on the difficulty of identifying the phases present in films having multiple phases. 

Other excellent methods of phase identification include TEM and electron diffraction. These may be more useful for low-Z materials, ultrathin films, and for characterizing small areas, including individual grains. For multiphase films with incomplete texture, these methods and XRD are complementary, since in commonly used geometries, they probe atomic planes perpendicular and parallel to the thin film surface, respectively. 

Strained set of lattice parameters and calculating the stress from the peak shifts, taking into account the angle of the detected sets of planes relative to the surface (see discussion above). If the assumed unstrained lattice parameters are incorrect not all peaks will give the same values. It should be borne in mind that, because of stoichiometry or impurity effects, modified surface films often have unstrained lattice parameters that are different from the same materials in the bulk form. In addition, thin film mechanical properties (Young s modulus and Poisson ratio) can differ from those of bulk materials. Where pronounced texture and stress are present simultaneously analysis can be particularly difficult. 

R. W. Smith. A kinetic Monte Carlo simulation of fiber texture formation during thin-film deposition. J Appl Physics 57 1196, 1997. 

Textured Tin Oxide Films Produced by Atmospheric Pressure Chemical Vapor Deposition from Tetramethyltin and Their Usefulness in Producing Light Trapping in Thin-Film Amorphous Silicon Solar Energy Mater., 18 263-281 (1989)... 

A thin film of tin oxide with a rough texture, produced by MOCVD from tetramethyl tin, (CH3)4Sn, deposited on an amorphous silicon cell provides a light-trapping surface, which enhances the efficiency of the device. 

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