Oriented Growth of Calcite Controlled by Self-Assembled Monolayers of Functionalized Alkanethiols Supported on Gold and Silver

Abstract

This paper describes the oriented nucleation of calcite controlled by self-assembled monolayers (SAMs) of ω-terminated alkanethiols (HS(CH2)nX) supported on metal films. The effect of the chemistry and geometry of the organic surfaces was surveyed by using different functional groups (X = CO2-, SO3-, PO32-, OH, N(CH3)3+, CH3) and different supporting metals (Au and Ag). Optical microscopy, SEM with image analysis, and XRD were employed to characterize density and orientation of the crystals. Compared to the control surfaces of bare metal films, SAMs terminated in CO2-, SO3-, PO32-, and OH groups were more active in inducing nucleation, whereas SAMs terminated in N(CH3)3+ and CH3 inhibited nucleation. The crystallographic orientations of the crystals were distinct and highly homogeneous for each surface, but different on different surfaces. SAMs of CO2-/Au, CO2-/Ag, OH/Au, OH/Ag, SO3-/Au, and SO3-/Ag induced the face-selective nucleation of calcite from the (015), (012), (104), (103), (1 0 12), and (107) crystallographic planes, respectively. SAMs of PO32-/Au and PO32-/Ag were specific for a family of planes that form an angle of 24° and 40° with the c-axis, respectively. The high degree of orientational uniformity of the overgrown crystals (97−100% oriented crystals for well-ordered SAMs) and the decrease of uniformity as the defect density in the SAMs increased imply that nucleation takes place from the oriented, homogeneous SAM and that the specific interfacial structure is controlling orientation of crystal growth. The possible correlation between the differences in the structure of SAMs supported on Au and Ag and the orientation of the incipient crystals is discussed. Varying the geometry, chemistry, and pattern of the functional groups on SAMs provides, therefore, a tool for a fine-tuning of the orientation of crystal growth and for the formation of high-resolution patterns of oriented crystals.