Amorphous annealing

In Refs. 10 and 11, aqueous NaiSiOs was added to SbCls in glacial acetic acid (SbCls hydrolyzes in water unless complexed or the solution is moderately acidic or strongly alkaline). A pH of ca. 3 was optimum below 2.5, adhesion was poor above 4, basic antimony salts precipitated. The solution was kept below room temperature to prevent rapid bulk precipitation. No XRD pattern was found for the as-deposited film, which was presumed to be amorphous. Annealing at 170°C crystallized the film, at least partly. The bandgap of the as-deposited film was reported to be 2.48 eV and that of the annealed film 1.76 eV. Photoconductivity was exhibited by the annealed film but not by the as-deposited one. 

In Ref 59, no XRD pattern was observed for the as-deposited films, which were thus assumed to be amorphous. Annealing at 200°C was enough to give an XRD pattern (of hexagonal HgSe), although no crystal size details were given. 

Figure Bl.24.11. The backscattering yield from an Si sample tiiat has been implanted with Si atoms to fonn an amorphous layer. Upon annealing this amorphous layer reerystallizes epitaxially leading to a shift in the amorphous/single-erystal interfaee towards the surfaee. The aligned speetra have a step between the amorphous and erystal substrate whieh shifts towards the surfaee as the amorphous layer epitaxially reerystallizes on the Si.

This is a fairly reasonable way to describe man-made amorphous polymers, which had not been given time to anneal. For polymers that form very quickly, a quick Monte Carlo search on addition can insert an amount of nonoptimal randomness, as is expected in the physical system. 

Writing by Phase Change. In an amorphous layer, crystalline marks are generated by local annealing with a focused laser beam. 

To erase information by the transition amorphous — crystalline, the amorphous phase of the selected area must be crystallized by annealing. This is effected by illumination with a low power laser beam (6—15 mW, compared to 15—50 mW for writing/melting), thus crystallizing the area. This crystallization temperature is above the glass-transition point, but below the melting point of the material concerned (Eig. 15, Erase). 

The stmcture of the polysihcon depends on the dopants, impurities, deposition temperature, and post-deposition heat annealing. Deposition at less than 575°C produces an amorphous stmcture deposition higher than 625°C results in a polycrystalline, columnar stmcture. Heating after deposition induces crystallization and grain growth. Deposition between 600 and 650°C yields a columnar stmcture having reasonable grain size and (llO)-preferred orientation. 

Figure 6 Backscattering spectra for a thin fiim of Ni deposited on an amorphous SiOj fiim grown on top of Si (111) for three different annealing temperatures.

The commercial poly-(4-methypent-1-ene) (P4MP1) is an essentially isotactic material which shows 65% crystallinity when annealed but under more normal conditions about 40%. For reasons given later the material is believed to be a copolymer. In the crystalline state P4MP1 molecules take up a helical disposition and in order to accommodate the side chains require seven monomer units per two turns of the helix (c.f. three monomers per turn with polypropylene and polybut-I-ene). Because of the space required for this arrangement the density of the crystalline zone is slightly less than that of the amorphous zone at room temperature. 

This approach is an alternative to quantitative metallography and in the hands of a master gives even more accurate results than the rival method. A more recent development (Chen and Spaepen 1991) is the analysis of the isothermal curve when a material which may be properly amorphous or else nanocrystalline (e.g., a bismuth film vapour-deposited at low temperature) is annealed. The form of the isotherm allows one to distinguish nucleation and growth of a crystalline phase, from the growth of a preexisting nanocrystalline structure. 

In one of the most significant observations, small amounts of recrystallized material were observed in rutile at shock pressure of 16 GPa and 500 °C. Earlier studies in which shock-modified rutile were annealed showed that recovery was preferred to recrystallization. Such recrystallization is characteristic of heavily deformed ceramics. There has been speculation that, as the dislocation density increases, amorphous materials would be produced by shock deformation. Apparently, the behavior actually observed is that of recrystallization there is no evidence in any of the work for the formation of amorphous materials due to shock modification. Similar recrystallization behavior has also been observed in shock-modified zirconia. 

After the thermal oxidation opening, an amorphous carbon (a-C) residue is frequently left on/over the tip or even inside the cavity close to the tube extrema [29,32] (see Fig. 3) this a-C actually plugs the CNT. To eliminate this plug, we have performed an additional high temperature annealing (2000-2100"C, 10" Torr) [22]. The furnace used for this steps was very simple the CNTs were... 

PTEB-Q) to the annealed ones, owing to the presence of the crystalline phase. Moreover, the temperature of the peak increases with the annealing, as well as the broadness of the relaxation. These results suggest that the liquid crystalline phase gives raise to an a relaxation similar to that of amorphous polymers despite the existence of the two-dimensional order characteristic of smectic mesophases, and it changes following the same trend than that of semicrystalline polymers. 

Contrary to widespread opinion, the value of Ea is not a constant quantity. As was proved previously [52], the value of E is variable, since it depends on the ordering of macromolecules in the amorphous material of the fiber. At the same time, one can suppose that this ordering will be affected by the specificity of the fine structure of the fiber, and particularly by the type of substructure of the fiber. The relationship determining the modulus Ea appropriate for a definite type of fiber substructure can be derived from Eq. (11) when appropriate values of A are assumed. In the case of the microfibrillar substructure, i.e., for A < I, typical of PET fibers stretched, but not subjected to annealing, this equation has the form [52] ... 

Annealing temperature (°C) Density of the amorphous material (da) (g/cm ) Amorphous orientation function (fa) Crystallite length (Ic) (nm) Long period (L) (nm) Degree of crystallinity (X ) Substructure parameter (A) Axial elastic modulus ... 

Annealing temperature rc) Annealing time (min) Birefringence (An) Anid Volume crystallinity (%) TTM fraction Critical dissolve time (s) Amorphous orientation function (/ )... 

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