Wyatt E. Tenhaeff

Designing polymer surfaces via vapor deposition

Chemical Vapor Deposition (CVD) methods significantly augment the capabilities of traditional surface modification techniques for designing polymeric surfaces. In CVD polymerization, the monomer(s) are delivered to the surface through the vapor phase and then undergo simultaneous polymerization and thin film formation. By eliminating the need to dissolve macromolecules, CVD enables insoluble polymers to be coated and prevents solvent damage to the substrate. Since de-wetting and surface tension effects are absent, CVD coatings conform to the geometry of the underlying substrate. Hence, CVD polymers can be readily applied to virtually any substrate: organic, inorganic, rigid, flexible, planar, three-dimensional, dense, or porous. CVD methods integrate readily with other vacuum processes used to fabricate patterned surfaces and devices. CVD film growth proceeds from the substrate up, allowing for interfacial engineering, real-time monitoring, thickness control, and the synthesis of films with graded composition. This article focuses on two CVD polymerization methods that closely translate solution chemistry to vapor deposition; initiated CVD and oxidative CVD. The basic concepts underlying these methods and the resultant advantages over other thin film coating techniques are described, along with selected applications where CVD polymers are an enabling technology.

Integration of Reactive Polymeric Nanofilms Into a Low-Power Electromechanical Switch for Selective Chemical Sensing

This paper presents the fabrication and demonstration of an ultrathin microelectromechanical chemical sensing device. Microcantilevers are etched from 100-nm-thick silicon nitride, and a 75-nm-thick reactive copolymer film for sensing is deposited by initiated chemical vapor deposition. Cross-linking densities of the polymer films are controlled during the deposition process; it is shown that greater cross-linking densities yield greater cantilever deflections upon the polymers reaction with the analyte. Considering that chemical reactions are necessary for stress formation, the sensing is selective. Cantilever deflections of greater than 3 ¿m are easily attained, which allow a simple switch to be designed with resistance-based outputs. When exposed to a hexylamine vapor-phase concentration of 0.87 mol%, the resistance of the switch drops by over six orders of magnitude with a response time of less than 90 s.

Patterning nano-domains with orthogonal functionalities: Solventless synthesis of self-sorting surfaces

Vapor deposited functional polymer thin films can undergo rapid covalent functionalization. Patterning of two functional layers displaying orthogonal reactivity enables sorting of aqueous mixtures of dyes and nanoparticles, such as quantum dots, onto selective areas of nanopatterned surfaces.