Nanoscale control by chemically vapour-deposited polymers

Abstract

Chemical vapour deposition (CVD) enables nanoscale control for the synthesis of high-purity polymer thin films. Ultrathin (<20 nm) and ultrasmooth (<1 nm r.m.s. roughness) layers of CVD polymers can conform to the geometry of the growth surface. This Review focuses on CVD polymerization methods adapted from solution chemistry for selectively forming different classes of macromolecules. The mechanistically based CVD approaches provide full retention of the monomer’s organic functional groups and thus provide a rational basis for designing and optimizing film characteristics for a diverse array of applications. These include conjugated polymers for energy storage, thin dielectrics for low-power, flexible devices and responsive hydrogels for controlled drug release. Systematic variation in the CVD process parameters provides remarkable control of π–π stacking in conducting polymers, mesh sizes in hydrogels, crystallographic texture, surface energy, permeation rates of molecules and ions, optoelectronic properties and switchable smart behaviour. The initial research focus on process fundamentals, including adsorption, reaction kinetics, mass transport and conformality, formed a strong basis for the recent rapid expansion of materials, applications and scale-up activities in multiple laboratories. The materials and approaches used in CVD polymerization are also extending into hybrid inorganic/organic materials and devices. Chemical vapour deposition (CVD) enables the synthesis of high-purity, pinhole-free and conformal polymer thin films. This Review discusses the recent breakthroughs in mechanistically based CVD polymerization processes and designing CVD polymers for a diverse array of applications.