Fiber textures

The film is fibrillated mechanically by mbbing or bmshing. Immiscible polymers, such as polyethylene or polystyrene (PS), may be added to polypropylene to promote fibrillation. Many common fiber-texturing techniques such as stuffer-box, false-twist, or knife-edge treatments improve the textile characteristics of slit-film fibers. 

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. 

The properties of mesophase pitch-based carbon fibers can vary significantly with fiber texture. Inspection of the cross-section of a circular mesophase fiber usually shows that the graphitic structure converges toward the center of the fiber. This radial texture develops when flow is fully developed during extrusion through the spinnerette. Endo [48] has shown that this texture of mesophase pitch-based carbon fibers is a direct reflection of their underlying molecular structure. 

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

The ordering of crystallites in the fiber texture is best and univocally described in the quantitative manner... 

Steps, or growth layers, are structure components for construction of a variety of growth forms in the electrodeposition of metals (e.g., columnar crystals, whiskers, fiber textures). We can distinguish between monoatomic steps, polyatomic microsteps, and polyatomic macrosteps. Only the propagation of polyatomic steps can be observed directly, in situ. 

The required degree of understanding of the physical properties of metal thin films used for interconnects on chips is illustrated by the following example. It was found that the performance of conductors on chips, A1 or Cu, depends on the structure of the conductor metal. For example, Vaidya and Sinha (10) reported that the measured median time to failure (MTF) of Al-0.5% Cu thin films is a function of three microstructural variables (attributes) median grain size, statistical variance (cr ) of the grain size distribution, and degree of [111] fiber texture in the film. 

The diagrams thus show, on the scale of the anisotropic areas, a fiber texture similar to that described by Kuroda (2, 13) for petroleum cokes and Kakinoki (12) for thin films of carbon. The presence of the arcs 002, when the electron beam is not perpendicular to the C-axis, is caused by the fact that the texture axis shows some dispersion. This, however, does not prevent each area from having an average direction of the axis 002 different from that of the adjacent ones. 

Figure 6.3 Stability of various fiber textures of nickel electrodeposits vs. pH of a Watts bath and partial current density of nickel deposition [6.61].

The epitaxy of nickel electrodeposits has been studied by electron microscopy using a new method for the preparation of sections [6.67, 6.68]. It was demonstrated that the electrodeposit structure results from competition between a simple epitaxial growth process maintaining substrate orientation and the formation of new randomly oriented nuclei which are rapidly submitted to the selection process, giving a fiber texture. TTiis competition depends on both the substrate orientation and the nucleation and growth processes leading to the final texture. 

The classification of asbestos fibers is carried out on the basis of type and deposits, important classification criteria are also, however, fiber length, degree of decomposition and fiber texture. This leads to a grouping according to industrial application (Table 5.2-, i). 

Carrageenans i, K, y, p, v Red seaweed Gel-forming agent stabilizer protein fiber texturizer milk fat anticoagulant milk clarifying agent... 

The individual crystals in wire are so oriented that the same crystallographic direction [m w] in most of the grains is parallel or nearly parallel to the wire axis. Because a similar texture occurs in natural and artificial fibers, it is called 3i fiber texture and the axis of the wire is called the fiber axis. Materials having a fiber texture have rotational symmetry about an axis in the sense that all crystal orientations about this axis are equally probable, like those of beads on a string. A fiber texture is therefore to be expected in any material formed by forces that have... 

Fiber textures vary in perfection, i.e., in the scatter of the direction about the fiber axis, and both single and double fiber textures have been observed. Thus, cold-drawn aluminum wire has almost a single [ill] texture, but copper, also FCC, has a double [111] + [100] texture i.e., in drawn copper wire there are two sets of grains, the fiber axis of one set being [111] and that of the other set [100]. 

In its simplest, most highly developed form, the texture of sheet is such that most of the grains are oriented with a certain crystallographic plane hkl) roughly parallel to the sheet surface, and a certain direction [wnv] in that plane roughly parallel to the direction in which the sheet was rolled. Such a texture is described by the shorthand notation hkl) uvw. In an ideal texture of this kind, the grain orientations in the sheet are fixed with respect to axes in the sheet there is none of the rotational freedom of grain orientation possessed by a fiber texture. 

The pole figure of a fiber texture necessarily has rotational symmetry about the fiber axis (Fig. 9-8). The degree of scatter of this texture is given by the angular... 

Fig. 9-8 (111) pole figure for an imperfect [100] fiber texture. F.A. = fiber axis. Cross-hatched areas are areas of high (111) pole density. 

Because of its rotational symmetry a pole figure of a fiber texture displays redundant information, in the sense that the pole density along any longitude line (meridian) is the same as along any other. Thus a plot of pole density vs. angle between 0 and 90° is a simpler description of the texture for the texture shown in Fig. 9-8, such a plot would show a single maximum at 54.7°. 

The chief problem presented by a fiber texture is the identification of the fiber axis uvw This can be done fairly easily with a single diffraction photograph, and the procedure is described in this section. If, in addition, we wish to determine the amount of scatter in the texture, a diffractometer method is preferable (Sec. 9-9). 

The wire is examined in a transmission pinhole camera with filtered radiation and with the wire axis vertical, parallel to one edge of the flat film. The problem of finding the indices uv v of the fiber axis is best approached by considering the diffraction effects associated with an ideal case, for example, that of a wire of a cubic material having a perfect [100] fiber texture. Suppose we consider only the 111 reflection. In Fig. 9-9, the wire specimen is at C with its axis along NS, normal to the incident beam IC. CP is the normal to a set of (111) planes. Diffraction from these planes can occur only when they are inclined to the incident beam at an angle 6 which satisfies the Bragg law, and this requires that the (111) pole lie somewhere... 

---