Shape, Size and Morphology Control of Inorganic Crystals With Self-Assembled Monolayers
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Shape, Size and Morphology Control of Inorganic Crystals With Self-Assembled Monolayers Yong-Jin Han and Joanna Aizenberg Materials Research Department Bell Laboratories, Lucent Technologies 600 Mountain Ave, Murray Hill, NJ 07974, USA ABSTRACT Self-assembled monolayers (SAMs) provide simple, yet sophisticated surfaces to mimic the effect of proteins associated with the process of biomineralization. A careful selection of organic molecules with an appropriate surface chemistry (i.e. HS-(CH2)n-X- supported on a metal surface) allows the nucleation and growth of oriented calcite crystals and provides opportunities to study the formation of inorganic crystals assisted by organic molecules. We have successfully crystallized calcite crystals on different SAMs in the presence of additives such as proteins and/or ions in solution, and found correlations between the orientations of crystals to their final shapes, sizes and morphologies. We report here our experimental results demonstrating how underlying organic molecules along with inorganic additives can control and mold the final shape, size and morphology of calcium carbonate crystals.
INTRODUCTION Sophisticated structures created by nature have always fascinated and inspired scientists. Namely, biominerals including calcium carbonates, silica, and iron oxides can be observed in biology with multitude of morphologies, which can vary dramatically depending on their function.[1, 2] Many attempts have been made to control various parameters of crystals, including their orientation, size, shape and morphology to elucidate the formation and morphogenesis of biominerals.[3-10] We have reported previously the effectiveness of magnesium ions in controlling the size, shape and morphology of oriented calcite crystals when used in conjunction with carboxylic acid functionalized self-assembled monolayers on silver surface.[11] Here, we extend the studies to include SAMs terminated in different functional groups supported on gold surfaces to analyze the generality of the effect of Mg ions on the morphology and size of oriented calcite crystals nucleated from various crystallographic planes.
EXPERIMENTAL Substrates were prepared by e-beam evaporation of Au (500 nm) on Si(100) wafer primed with Ti (2nm). The substrates were quickly removed and immediately immersed in 5mM solutions of alkanethiols in ethanol at RT. The following thiols were used: HS-(CH2)11-OH, HS(CH2)10-COOH, HS-(CH2)15-COOH, and HS-(CH2)11-SO3- Na+. The adsorption of alkanethiols to the metal thin films were allowed to take place for 24 hours, after which the substrates were exhaustively rinsed with EtOH, followed by H2O wash. Crystallization of calcite crystals on SAMs took place in a reaction vessel containing 20 mM CaCl2. Various amounts of MgCl2 were
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also added to the reaction vessel. The crystallization was initiated with an addition of ammonium carbonate to a separate reaction vessel placed along side the reaction vessel containing SAMs. The crystallization was allowed to take place for 2
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