Patterning Inorganic (CaCO3) Thin Films via a Polymer-Induced Liquid-Precursor Process

Abstract

The biomimetic synthesis of patterned mineral thin films, based on a combination of the microcontact printing technique and a novel crystallization process called the polymer-induced liquid-precursor (PILP) process, is demonstrated. The PILP process enables the deposition of smooth and continuous calcitic mineral films (up to 1500 nm in thickness) under low-temperature and aqueous-based processing conditions. The films are formed by deposition of colloidal droplets composed of a liquid-phase mineral precursor that is induced by a polymeric process-directing agent (polyaspartate or polyacrylate salts). The droplets can be preferentially deposited onto patterned substrates templated with self-assembled monolayers (SAMs) of alkanethiolate on gold. The droplets coalesce to form an amorphous mineral film, which then transforms (solidifies and crystallizes) while retaining the shape of the patterned template, providing a means for patterning the location and morphology of two-dimensional calcite crystals. A vertical substrate experiment supports the premise that the calcite films are created by adsorption of colloidal droplets from solution, rather than heterogeneous nucleation and growth of an amorphous phase on the SAMs. Large single-crystalline domains, on the order of 50-100 microm, can be "molded" into nonequilibrium morphologies by constraining the mineral precursor to a chemically defined "compartment". Biominerals are well recognized for their elaborate nonequilibrium molded crystal morphologies, and increasing evidence suggests that many biominerals are formed from an amorphous precursor that is stabilized by polyanionic proteins. The biomimetic system examined here, which consists of a polyanionic process-directing agent in combination with a functionalized organic template, offers a practical tool for generating complex inorganic structures such as those found in biominerals.