Initiated chemical vapor deposition (iCVD) enables the fabrication of chemically well-defined polymeric nanofilms on both planar and three-dimensional substrates. In iCVD, a variant of hot filament chemical vapor deposition, monomer and initiator vapors are introduced into a vacuum chamber, and polymerization occurs on the substrate surface. By including divinyl monomers in the reactor feed, films with controlled crosslinker densities can be deposited. Reactive copolymeric thin films containing maleic anhydride (MA) have been deposited, and many applications have been developed that utilize the chemical versatility of the anhydride functional group.

Copolymerization was necessary for MA since the monomer does not hompolymerize readily. By flowing styrene and MA simultaneously into the iCVD reactor along with tert-butyl peroxide initiator, the deposition rate was 75 nm/min. When MA and styrene were introduced separately, the deposition rates were 5.5 and 0 nm/min, respectively. X-ray photoelectron spectroscopy and ¹³C nuclear magnetic resonance conclusively show that the films were composed of alternating copolymers, as expected from solution-phase copolymerizations.

By substituting N,N-dimethylacrylamide (DMAA), a monomer that does not form alternating copolymers with MA, for styrene, highly swellable hydrogel nanofilms were created. Before the iCVD process, substrates were primed with 3-aminopropyldimethylethoxysilane, imparting the surfaces with free amine functional groups. Three monomers vapors were introduced into the reactor along with tert-butyl peroxide initiator: 0.6 sccm of MA, 6 sccm of DMAA, and 0.4 sccm of di(ethylene glycol) divinyl ether crosslinker (DEVE). The composition of the polymer was 76% DMAA, 14% MA, and 10% DEVE, as determined by X-ray photoelectron spectroscopy (XPS). The DEVE crosslinker created a network by linking all of the polymer chains together, while MA groups formed covalent bonds with amine groups at the interface between the substrate and hydrogel film. Hydrolysis of the anhydride functionality imparted anionic character to the film. In pH = 8 buffer solution, the film's swelling ratio was 14, while in pH = 1 buffer, the ratio was 7.

Reactive copolymeric nanofilms have also been integrated into ultrathin microelectromechanical switches for chemical sensing. 75 nm of crosslinked copolymer films were applied to 100 nm-thick silicon nitride microcantilevers. Two crosslinking densities were compared; it was shown that higher crosslinking densities yielded greater cantilever deflection upon the reaction of the polymer with analytes. Upon exposure to a hexylamine vapor-phase concentration of 0.9 mol%, the resistance dropped by over six orders of magnitude in less than 90 seconds. The sensor did not respond to nitrogen vapor saturated with heptane or 2-propanol, showing that chemical reaction is necessary for signal transduction. Multiple polymer chemistries have been investigated, and potential defense applications for the sensor will be discussed. Furthermore, alternative device designs will be described.