Electrical structure of the surface of crystalline substrates and its influence on nucleation and growth processes

Abstract

The electrical structure of crystalline substrates has been studied by a new technique based on selective crystallization of decorating material and selective deposition of charged colloidal particles. Silver chloride was found to be a very effective indicator of the electrical relief of crystal surfaces. At early stages of thermal condensation, it crystallizes orientedly on negatively charged regions of the surface and randomly on those charged positively. The method has been applied to the study of triglycine sulphate, LiF, and NaCl crystals. It has been found that the surface of real crystals consists as a rule of positive and negative regions, representing assemblies of charged point defects. Near the cleavage steps certain "dead zones" arise, in which a local compensation of charges takes place. Nucleation occurs mainly a t charged point defects and oriented coalescence of islands proceeds with different velocity on surface local regions of different signs. The selectivity of crystallization depends on the relation of the sign and magnitude of potential between different smooth areas of the surfaces of crystalline substrates, on the one hand, and between steps and smooth areas, on the other. The charged point defects and their assemblies which are present on the surface of crystalline substrates induce polarization structures of the electret type in amorphous interfacial layers. These structures are "frozen" in interfacial layers in so stable a manner that the layers turn out to be electrical copies of crystal surfaces, thus reflecting the distribution of potential of the surface. Such copies preserve t h e "electrical memory" even after they are detached from the surfaces of crystals and can hence be used as active substrates for various heterogeneous processes, in particular, for epitaxy.

Extended structural defects in ?-Hgl2 single crystals

“…The formation of cellular structures as a result of accumulation of electrically charged vacancies, interstitials and/or impurities in boundaries has also been observed in LiF, AgCI, NaC1 [200,201], AgBr [202], A1 [187,203,204] and ZnO crystals [205]. The cellular boundaries in ~-HgI 2 have been accidentally revealed with a bright contrast by surface decoration with impurities inside the microscope enclosure during the SEM examination of crystals grown from the vapour, indicating the electrostatic origin of the observed topographic contrast (see Fig.…”

Growth Control and Optics of Organic Nanoaggregates

“…Among the lightemitting organic molecules studied are thiophenes, [6] perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA), [7] pentacene, [8] phenyls, [9] and anthraquinone. [10] Among those, para-phenyls have been found to provide the most promising nanoaggregates, and therefore we will concentrate here on this class of molecules.…”

Triboelectricity in insulating polymers: evidence for a mechanochemical mechanism

“…For this reason, simply contacting polymer surfaces or applying different types of mechanical action at different speeds should be expected to produce different chemical, structural, morphological and electrostatic results analogous to those described by Distler in ionic solids. 49 To sum up, mechanochemical reactions triggered by friction produce ionic polymer chain fragments, especially at the surface of particles pulled away from the rubbing surfaces that can be transferred from one rubbing body surface to another. Amphiphilic species are thus formed, containing charged end-groups that are excluded from the polymer-air interface, since their contribution to the material surface tension is more positive than the contribution of other, less polar groups.…”