Oriented growth

In addition, it is of interest to note that investigations of the microscopic processes leading to nucleation, growth, oriented growth by the surfactant monolayer, and growth inhibition of nanoparticles in reversed micelles and of confinement and adsorption effects on such phenomena represent an intriguing and quite unexplored research field [218]. 

N Tanigaki, K Yase, and A Kaito, Oriented films of poly(p-phenylene) by friction-deposition and oriented growth in polymerization, Mol. Cryst. Liq. Cryst., 267 335-340, 1995. 

JC Wittmann and P Smith, Highly oriented thin films of poly(tetrafluoroethylene) as a substrate for oriented growth of materials, Nature, 352 414—418, 1991. 

Fibrous. This type of grain is the result of oriented growth of grains that cover the substrate only incompletely. 

Oriented growths. Observed enclosing pyroaurite, with brucite 0001 [1010] 11 pyroaurite [0001) [1010]. ... 

By means of magnetic measurements, Selwood (82) observed that the concentration of electron holes (here identical with Ni + ions) in NiO films can be increased, if these NiO films are prepared on y-alumina supports. Obviously the chemisorption or the incorporation of oxygen into the lattice of NiO is favored by the effect of the epitaxy (oriented growth) of NiO on 7-AI2O3. 

Acidic amino acids seem to play a key role in (1) the fixation of calcium, (2) the nucleation of CaC03 crystals, and (3) the oriented growth of the mineral phase. There appears to be no essential difference between biochemical or geochemical template-induced mineral formation. The only requirement is the presence of a calcium-specific template and an environment suitable for the deposition of calcite or aragonite. 

The orientated growth of A(3 fibrils and peptide nanofibers on HPOG is due to the underlying six-fold symmetry of the graphite surface. This directs fiber formation in the three observed directions, each orientated at 120°, as illustrated in the schematic in Figure 3. Kowalewski suggested such growth is driven by hydrophobic forces (Kowalewski and Holtzman, 1999), where... 

Figure 4 Schematic illustrating the orientated growth of Api-40 fibrils along the hydrophilic step edges of highly orientated pyrolytic graphite (HOPG) in preference to assembly on the hydrophobic basal plane surface. Copyright (Losic, Martin et al., 2006). Reprinted with permission of John Wiley Sons, inc.

Figure 5 The orientated growth of AP25-35 fibrils from an aqueous solution on a mica surface. The fibrils grow along three main directions, each orientated at 120°. The images were collected by in situ time lapse Atomic Force Microscopy (Karsai, Grama et al. 2007). Copyright IOP Publishing Ltd. Reproduced with permission.

First sputtering processes for ZnO deposition were developed in the late 1960s for manufacturing surface acoustic wave devices [2]. The piezoelectric properties of ZnO films are crucial for that application and major efforts were made to develop ZnO sputtering processes which enabled c-axis oriented growth, high resistivity and unique termination of the ZnO crystallites [3,4]. 

For ZnO films with good piezoelectric properties, it is crucial to achieve c-axis oriented growth as well as a unique termination of the wurtzite phase ZnO crystallites [3]. 

Boron-doped LP-CVD ZnO, as developed by Fay et al. [17] the corresponding XRD graph for an LP-CVD ZnO B layer is shown in Fig. 6.6. A strong preferentially oriented growth is observed here also, but it is, in this case, perpendicular to the (1120) crystallographic planes. This means that the c-axis is parallel to the substrate, in contrast with the orientation more commonly observed for AP-CVD and sputtered ZnO layers [15,25,26]. 

Oriented growth of lanthanide oxide thin films of Sm, Eu, Gd, Er and Yb on different substrates is possible by the low-pressure MOCVD technology from the corresponding phenanthroline adducts of rare earth metal enolates Ln(acac)3(phen) as described by Shiv-ashankar and coworkers (Table As expected, the films grown at lower... 

Reactivity in the solid-state is always connected with specific motions which allow the necessary contact between the reacting groups. In most cases solid-state reactions proceed by diffusion of reactions to centers of reactivity or by nucleation of the product phase at certain centers of disorder. This leads to the total destruction of the parent lattice. If the product is able to crystallize it is highly probable that nucleation of the crystalline product phase at the surface of the parent lattice will lead to oriented growth under the influence of surface tension. In such topotactic reactions certain crystallographic directions of parent and daughter phases will coincide. Typical examples for this behaviour are the solid-state polymerizations of oxacyclic compounds such as trioxane, tetroxane or 3-propiolactone... 

It has been widely demonstrated that the preparation of oriented, and in some cases epitaxial films by CSD is possible, despite the relatively large thickness of the films that is deposited in a single step. Lange ° reviewed the various mechanisms that lead to oriented growth, and a variety of factors including reactions at the electrode interface, - organic content within the film," " and the use of seed layers" to promote homoepitaxy have been discussed. The ability to control film properties (remanent polarization, dielectric constant, etc.) through manipulation of film orientation has also been shown. 

Jansen JC and van Rosmalen GM. Oriented growth of silica molecular-sieve crystals as supported films. J Crystal Growth 1993 128(1 ) 1150-1156. 

Heterogeneous nucleation mechanisms can significantly affect the dissolution of metastable solid phases, because this form of nucleation can occur at low driving forces. While the choice of a metastable solid phase with solubility higher than other crystalline modifications is motivated by the expectation of faster dissolution rates, achievement of faster dissolution rates and higher concentrations in solutions is jeopardized by surface-mediated nucleation. We have reported that the surface of the metastable phase of theophylline promoted the nucleation of the stable monohydrate crystals. The observed oriented growth of monohydrate crystals on the anhydrous surface is consistent with a close lattice match between the b and c... 

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