Initiated chemical vapor deposition and light-responsive cross-linking of poly(vinyl cinnamate) thin films.

The first vapor-phase deposition of poly(vinyl cinnamate) (PVCin) is reported. Initiated chemical vapor deposition (iCVD) is used to synthesize PVCin thin films with an average thickness of 100 nm. Free radical polymerization and cyclization reactions compete during the deposition process, with approximately 45% of the repeat units undergoing cyclization. Exposure to UV light (λ = 254 nm) induces dimerization (cross-linking) of the PVCin, which is quantified using spectroscopic techniques. Approximately 90% of the free cinnamate moieties are dimerized at a UV dose of 300 mJ cm(-2) . PVCin is also incorporated into a copolymer with N-isopropylacrylamide, which exhibits a characteristic change in hydrophilicity with temperature. The copolymer is selectively cross-linked through a mask, and reversible swelling of patterns with 30 µm resolution is demonstrated by submerging the film in water.

Closed batch initiated chemical vapor deposition of ultrathin, functional, and conformal polymer films.

A modified fabrication process based on initiated chemical vapor deposition (iCVD) has been developed for producing ultrathin and uniform polymer films. This so-called "closed batch" (CB) iCVD process provides fine-tuning of the thickness and deposition rate of polymeric materials while using significantly less reactant material than the conventional continuous flow (CF) iCVD process. Four different polymers, poly(N-isopropylacrylamide), poly(trivinyltrimethylcyclotrisiloxane), poly(1H,1H,2H,2H-perfluorodecyl acrylate), and poly(ε-caprolactone), were synthesized by both CB and traditional CF iCVD. The resulting CB iCVD polymers are functionally identical to CF iCVD and solution-polymerized materials. Additionally, the new CB process retains the desirable ability to achieve conformal coverage over microstructures. Ultrathin (<30 nm) films can be controllably and reproducibly deposited; no prior optimization process is required to obtain excellent film thickness uniformity. The CB iCVD films are also extremely smooth, exhibiting RMS roughness values between 0.4 and 0.7 nm. Use of the CB process improves reaction yield by factors of 10-200 for the four different film chemistries and decreases material cost per 100 nm of film by 1-2 orders of magnitude.

25th anniversary article: CVD polymers: a new paradigm for surface modification and device fabrication.

Well-adhered, conformal, thin (<100 nm) coatings can easily be obtained by chemical vapor deposition (CVD) for a variety of technological applications. Room temperature modification with functional polymers can be achieved on virtually any substrate: organic, inorganic, rigid, flexible, planar, three-dimensional, dense, or porous. 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. CVD film growth proceeds from the substrate up, allowing for interfacial engineering, real-time monitoring, and thickness control. Initiated-CVD shows successful results in terms of rationally designed micro- and nanoengineered materials to control molecular interactions at material surfaces. The success of oxidative-CVD is mainly demonstrated for the deposition of organic conducting and semiconducting polymers.

Initiated chemical vapor deposition-based method for patterning polymer and metal microstructures on curved substrates.

A simple, efficient, and scalable method for patterning microstructures on curved substrates is demonstrated. Initiated chemical vapor deposition is used to synthesize a thin film that crosslinks upon UV exposure. Polymeric features are defined on glass rods with high curvature and used as masks for metal patterning. Additionally, vapor-deposited polymer layers are selectively patterned to produce bifunctional surfaces.

Chemical vapor deposition of conformal, functional, and responsive polymer films.

Chemical vapor deposition (CVD) polymerization utilizes the delivery of vapor-phase monomers to form chemically well-defined polymeric films directly on the surface of a substrate. CVD polymers are desirable as conformal surface modification layers exhibiting strong retention of organic functional groups, and, in some cases, are responsive to external stimuli. Traditional wet-chemical chain- and step-growth mechanisms guide the development of new heterogeneous CVD polymerization techniques. Commonality with inorganic CVD methods facilitates the fabrication of hybrid devices. CVD polymers bridge microfabrication technology with chemical, biological, and nanoparticle systems and assembly. Robust interfaces can be achieved through covalent grafting enabling high-resolution (60 nm) patterning, even on flexible substrates. Utilizing only low-energy input to drive selective chemistry, modest vacuum, and room-temperature substrates, CVD polymerization is compatible with thermally sensitive substrates, such as paper, textiles, and plastics. CVD methods are particularly valuable for insoluble and infusible films, including fluoropolymers, electrically conductive polymers, and controllably crosslinked networks and for the potential to reduce environmental, health, and safety impacts associated with solvents. Quantitative models aid the development of large-area and roll-to-roll CVD polymer reactors. Relevant background, fundamental principles, and selected applications are reviewed.