Polycrystalline morphology

These model compounds can also be used in device fabrication, since thin films of appropriate thickness can be obtained by sublimation and subsequent deposition onto a substrate in vacuum. Electrical as well as optical properties of such devices have turned out to be strongly dependent on both the molecular packing within the crystallites and the polycrystalline morphology. Understanding and control of this aspect is one of the current scientific challenges. 

Polycrystalline morphology of double habit consisting offibrous crystals overgrown epitaxially by lamellar crystals, the stems of which are parallel to the fibre axis. 

Figure 6.9. TMAFM image taken at ambient conditions of a TTF-TCNQ thin film (thickness um) grown on KCl(lOO), revealing its polycrystalline morphology. Reprinted from Surface Science, Vol. 482 85, C. Rojas, J. Caro, M. Gri-oni and J. Fraxedas, Surface characterization of metallic molecular organic thin films tetrathiafulvalene tetracyanoquinodimetane, 546-551, Copyright (2001), with permission from Elsevier.

LiCo02 films obtained by PLD with polycrystalline morphology were successfully used as cathode materials in lithium microbatteries. Typical charge and discharge curves of a Li//LiCo02 cell using pulsed-laser deposited film grown at... 

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. 

In summary, large (>lpm) single crystal platelets of aurichalcite produced highly dispersed Cu and ZnO particles with dimensions on the order of 5 nm, as a result of standard catalyst preparation procedures used in the treatment of the precipitate precursors. The overall platelet dimensions were maintained throughout the preparation treatments, but the platelets became porous and polycrystalline to accommodate the changing chemical structure and density of the Cu and Zn components. The morphology of ZnO and Cu in the reduced catalysts appear to be completely determined by the crystallography of aurichalcite. 

The catalytic tests show that, over the Pt(l 0 0)/Al2O3 catalyst, the formation of CO and NH3 is largely prevented, whereas the yield of N2O increases compared with the Pt(polycrystalline)/Al203 catalyst. These main differences observed should be ascribed to the morphological differences between two catalysts, i.e., the dominant orientation of the crystallographic facets and the average size... 

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