No abstract

No abstract

The preparation from vapor and the structure of filamentary crystals of silicon have been studied in detail. It was found by chemical etching, by examination for a twist associated with a screw dislocation, and by observations in the electron microscope, that both ribbons and needles of small dimensions are free of dislocations and imperfections. Certain impurities such as gold, nickel, or platinum, however, are essential for the growth of filamentary crystals. The growth of micron size and larger whisker crystals from the vapor takes place in two stages. The first is a rapid extension in length of a leader-like crystal of small cross section; the second, a slow thickening of the leader through deposition on lateral faces. Initial growth is associated with impurities and does not require an axial screw dislocation. Subsequent growth may be explained by classical nucleation at a step and lateral translation of the step.

From darkness came light: Incorporation of urea‐based fluorescent dyes in an anion‐imprinted thin polymer shell coated onto silica microparticles leads to a unique and highly enantioselective fluorescent “light‐up” response to analytes (see scheme, MIP molecularly imprinted polymer).

The morphology of the solid‐liquid interface and the contact angle configuration of the liquid alloy droplet determine the direction of growth of crystals prepared by the vapor‐liquid‐solid (VLS) technique. There are four different processes by which both growth kinks and branches can be formed. A change in solid‐liquid interface shape during VLS caused by a lateral temperature gradient results in the formation of growth kinks. Branches are formed if the alloy droplet ruptures during the kinking sequence. A sudden increase in temperature can cause an unstable contact angle configuration. The alloy droplet may run down the side faces of the growing crystal, leading to the formation of growth kinks or branches. A sudden decrease in temperature may cause “pinching off” of small droplets from the main droplet, giving rise to branches. Finally, the codeposition of liquid‐forming impurities may also lead to branch and kink formation. The proposed models have been verified experimentally for VLS growth of silicon and germanium. Crystalline defects, such as dislocations, are not essential for the branching and kinking process. It is shown that “growth shaping” during the VLS process is possible.

J. DiPiazza for their assistance, and J. White for the use of his gallium arsenide curves. ABSTRACTThe experimental procedure for controlled vapor-liquid-solid, or VLS, crystal growth is discussed for silicon. The hydrogen reduction of SIC14 was used as transport reaction, and gold as the liquid-forming impurity. The stability of the liquid droplet, which is the main criterion for controlled VLS growth, is discussed in detail. It is shown that an adverse temperature gradient or an oversupply of silicon from the vapor may render the liquid droplet unstable, thereby terminating controlled VLS growth. Silicon crystals can be grown epitaxially on perfect or imperfect silicon substrates. The control of both location of crystal growth and of diameter and length of the crystals is demonstrated.) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 130.15.241.167 Downloaded on 2015-03-08 to IP

Crystalline defects have been studied in silicon crystals grown by the vapor-liquid-solid (VLS) technique. Most of these crystals are highly perfect. However, some crystals contain defects such as dislocations, stacking faults, and second-phase regions. An elastic stress field, resulting from differential thermal contraction was found near the tip of every crystal. The formation and prevention of these defects and their relation to the VLS growth mechanism are discussed in detail. The morphology of the prismatic side faces of the crystals depends on deposition temperature, and is primarily due to vapor-solid deposit. This deposit is perfect even at deposition temperatures as low as 700°C.

A naphthalimide-based fluorescent indicator monomer 1 for the integration into chromo- and fluorogenic molecularly imprinted polymers (MIPs) was synthesized and characterized. The monomer was equipped with a urea binding site to respond to carboxylate-containing guests with absorption and fluorescence changes, namely a bathochromic shift in absorption and fluorescence quenching. Detailed spectroscopic analyses of the title compound and various models revealed the signaling mechanism. Titration studies employing benzoate and Z-L-phenylalanine (Z-L-Phe) suggest that indicator monomers such as the title compound undergo a mixture of deprotonation and complex formation in the presence of benzoate but yield hydrogen-bonded complexes, which are desirable for the molecular imprinting process, with weakly basic guests like Z-l-Phe. Compound 1 could be successfully employed in the synthesis of monolithic and thin-film MIPs against Z-L-Phe, Z-L-glutamic acid, and penicillin G. Chromatographic assessment of the selectivity features of the monoliths revealed enantioselective discrimination and clear imprinting effects. Immobilized on glass coverslips, the thin-film MIPs of 1 displayed a clear signaling behavior with a pronounced enantioselective fluorescence quenching dependence and a promising discrimination against cross-analytes.