iCVD Process Research Articles

Site-specific immobilization of proteins on non-conventional substrates via solvent-free initiated chemical vapour deposition (iCVD) process

Currently, the development of protein chips faces new requirements of improved environmental stability, disposability, and cost-effectiveness for their wide applicability in our daily life. Here, we demonstrate a new protein detection platform on low-cost plastic and paper substrates. To achieve this platform, a highly selective thiol–ene photochemical reaction between vinyl functionality on the surface and cysteine-linked protein was utilized to immobilize the relevant proteins on the disposable substrates. First, the surface of the flexible substrates was modified with a vinyl-containing polymer, poly(2,4,6,8-tetravinyl-2,4,6,8-tetramethyl cyclotetrasiloxane) (pV4D4), via a solvent-free initiated chemical vapour deposition (iCVD) process. Next, on the vinyl functionalized surface, cysteine-linked proteins were covalently immobilized by a UV-assisted thiol–ene click reaction. The solvent-free characteristic of iCVD enabled us to directly pattern the functionality on the substrate via shadow mask patterning. On the patterned substrate, selective immobilization of the proteins was possible. With four model proteins, including two fluorescent proteins, single-chain variable fragment (scFv), and non-immunoglobulin protein scaffold (human kringle domain), we successfully demonstrated the immobilization of proteins on various substrates including polyethylene (PE) film and chromatography paper.

Reliable Synthesis of Monodisperse Microparticles: Prevention of Oxygen Diffusion and Organic Solvents Using Conformal Polymeric Coating onto Poly(dimethylsiloxane) Micromold

An effective polymeric thin film deposited by initiated chemical vapor deposition (iCVD) process was presented and its application as a barrier film on the PDMS micromold blocking the penetration of oxygen and organic solvents was investigated. With this barrier film, we were able to synthesize monodisperse polymeric particles of sizes down to 3 μm, which has been reported to be extremely challenging with bare PDMS micromold. The polymeric barrier film on the PDMS micromold enabled this successful synthesis of microparticles by effectively blocking the diffusion of oxygen, which is a well-known radical quencher in radical polymerization, through the PDMS micromold. Furthermore, the iCVD barrier film substantially decreased the penetration of various organic solvents such as acetone, tert-butanol, PDMS oil, and decane as well as organic substances including fluorescent molecules like rhodamine B and fluorescein isothiocyanate (FITC). Therefore, the polymeric barrier film coated on PDMS micromold via iCVD process will broaden the application of PDMS to microfluidic area for the synthesis of smaller microparticles with various organic substances.

A stacked polymer film for robust superhydrophobic fabrics

A robust superhydrophobic fabric was achieved by depositing a stacked polymer film composed of a poly(1,3,5,7-tetravinyl-1,3,5,7-tetramethylcyclotetrasiloxane) (p(V4D4)) layer and a poly(1H,1H,2H,2H-perfluorodecylacrylate) (p(PFDA)) layer. The polymer film was deposited by initiated chemical vapor deposition (iCVD), a solventless process that allows conformal coating of the stacked polymer film on various micro-structured substrates. The two polymeric layers most likely formed a covalent bonding at their interface, and thus the stacked polymer film was characterized by both strong hydrophobicity and enhanced mechanical robustness originated from highly cross-linked p(V4D4) and p(PFDA). The surface topography of superhydrophobic coating was systematically tunable by controlling the operating parameters of iCVD process and a hierarchical structure was obtained by a simple one-step iCVD process. The film was also highly transparent in the wavelength range from 380 nm to 780 nm. Fabrics coated with this stacked polymer film displayed chemical robustness even after exposure to different chemicals including acetone, toluene, H2SO4, and KOH. The fabric also maintained its water repellency even after 20 000 cycles of the abrasion test and after 75 cycles of the laundry test.

Self-supporting superhydrophobic thin polymer sheets that mimic the nature's petal effect

The high adhesive force between the red rose petal and the water droplet on its surface is termed as the ‘petal effect’, which is caused by the hierarchical array of micro papilla on the surfaces together with the nano-folds existing on top of each papilla. Because of that special surface topography, the surface is superhydrophobic, but at the same time highly adherent to the water droplet such that the droplet cannot move even if the surface is turned upside down. In this work, we produced a thin (thickness below 1μm) self-supporting polymer sheet that mimics the surface of a red rose petal. The product is a two-layer polymer sheet made from poly(glycidyl methacrylate) (PGMA) as the supporting layer and a hydrophobic poly(1H,1H,2H,2H-perfluorodecyl acrylate) (PPFDA) on top of it as the functional layer, both of which were deposited by initiated chemical vapor deposition (iCVD) process. The integration of conformal and solvent-free iCVD process into the classical two-step molding procedure allowed exact transfer of surface topography of the petal surface, which was verified by SEM analysis. The static contact angle of water droplet on the surface of the polymer replica was found to be 152±3°, and the water droplet did not roll-off even the polymer sheet is tilted or turned upside down.

Conformal coating of poly-glycidyl methacrylate as lithographic polymer via initiated chemical vapor deposition

This study reports on the investigation of the potential applicability of poly-glycidyl methacrylate (PGMA) films deposited via initiated chemical vapor deposition (i-CVD) as lithographic resists in the microfabrication of non-planar structures. We investigate the appropriate deposition conditions of i-CVD required to form PGMA films with smooth surfaces. As a result, under the optimal conditions determined by us, we fabricate films with nanometer-scale flat surfaces. Subsequently, we demonstrate that i-CVD is effective for conformally coating a high-aspect-ratio Si trench with PGMA film via our deposition experiments. In our deep-ultraviolet lithography experiment, we successfully fabricate a fine 20-μm line-and-space (L/S) pattern with a height of approximately 1 μm. Furthermore, in our electron-beam (EB) lithography experiment, we define a fine 350-nm L/S pattern with a height of 120 nm. In addition, the i-CVD process can be used to form highly-sensitive EB resist films; the lowest dose amount for patterning these films is evaluated to be less than 0.01 μC/cm2. Our results demonstrate that i-CVD is a potentially powerful method to conformally coat lithographic resist films on three-dimensional structures.

Initiated PECVD of Organosilicon Coatings: A New Strategy to Enhance Monomer Structure Retention

AbstractA new deposition method, initiated PECVD (iPECVD), is proposed for the formation of organosilicon polymers with enhanced monomer structure retention compared to conventional PECVD. The quasi‐selective fragmentation of an initiator is driven by a low power plasma discharge, as opposed to using a hot filament for initiator decomposition as in a standard, plasma‐free initiated CVD (iCVD). The weak peroxide bond (OO) in the initiator permits the formation of radical species at very low plasma power density (0.07 W · cm−2). Kinetic analysis of the deposition process indicates that the film formation rate follows the Arrhenius law, similarly to other iCVD process from organosilicon monomers. magnified image

Integration of polymer electrolytes in dye sensitized solar cells by initiated chemical vapor deposition

The mesoporous titanium dioxide electrode of dye sensitized solar cells (DSSC) has been successfully filled with polymer electrolyte to replace the conventional liquid electrolyte. Polymer electrolyte was directly synthesized and deposited using the initiated chemical vapor deposition (iCVD) process, and an iodide–triiodide redox couple in different redox solvents was then incorporated into the polymer. We have investigated different candidate polymer electrolytes, including poly(2-hydroxyethyl methacrylate) (PHEMA). The open circuit voltage of cells fabricated with iCVD PHEMA was found to be higher when compared with a liquid electrolyte that is attributed to a lower rate of electron recombination.

A directly patternable click-active polymer film via initiated chemical vapor deposition (iCVD)

A new “click chemistry” active functional polymer film was directly obtained from a commercially available monomer of propargyl acrylate (PA) via easy, one-step process of initiated chemical vapor deposition (iCVD). Fourier transform infrared (FTIR) spectra confirmed that significant amount of the click-active acetylene functional group was retained after the iCVD process. The degree of crosslinking could be controlled by intentionally adding crosslinker, such as ethylene glycol diacrylate (EGDA) that was polymerized with PA to form click-active, completely insoluble copolymer. The formed iCVD polymers could also be grafted on various inorganic substrates with silane coupling agents. These crosslinking and grafting techniques give iCVD polymers chemical and mechanical stability, which allows iCVD polymers applicable to various click chemistry without any modification of reaction conditions. Pre-patterned iCVD polymer could be obtained via photolithography and an azido-functionalized dye molecule was also successfully attached on iCVD polymer via click chemistry. Moreover, pPA film demonstrated sensitivity to e-beam irradiation, which enabled clickable substrates having nanometer scale patterns without requiring the use of an additional e-beam resist. Direct e-beam exposure of this multifunctional iCVD layer, a 200 nm pattern, and QD particles were selectively conjugated on the substrates via click chemistry. Thus, iCVD pPA has shown dual functionality as of “clickable” e-beam sensitive material.

Surface modification of high aspect ratio structures with fluoropolymer coatings using chemical vapor deposition

Initiated chemical vapor deposition (iCVD) was used to coat the internal surfaces of high aspect ratio capillary pore membranes and silicon trenches with poly(1H,1H,2H,2H-perfluorodecyl acrylate) (PPFDA). The presence of the fluoropolymer coating along the pore walls of the membranes was confirmed using X-ray photoelectron microscopy, electron microprobe analysis, and contact angle measurements. The results of this study demonstrate that the iCVD process can be used to conformally coat high aspect ratio microstructures (up to 80:1) with organic polymers.

Heat transfer model of an iCVD reactor

Contrary to conventional HWCVD, the power consumption in the iCVD process is dominated by heat conduction rather than radiation. This is due to the fact that while the typical wire temperature for HWCVD is about 1750–2200 °C, for iCVD the temperature is only 250–500 °C. Typical deposition pressures are in the transition regime between the collision free regime, where the conduction is pressure dependent, and the collision mediated regime, where the conduction is pressure independent. The power loss due to heat conductivities of molecular nitrogen, glycidyl methacrylate (GMA) and tert-butylperoxide (TBPO) gases have been determined experimentally for these pressure regimes. The necessary power input to the filaments can be explained to be due to mainly heat dissipation by radiation and by gas conduction. This means that the dissociation process requires only very little power, about 2% of the total power consumption in a typical iCVD process.

Initiated Chemical Vapor Deposition of Poly(1H,1H,2H,2H-perfluorodecyl Acrylate) Thin Films

A solvent-free initiated chemical vapor deposition (iCVD) process was used to create low surface energy poly(1H,1H,2H,2H-perfluorodecyl acrylate) (PPFDA) thin films at deposition rates as high as 375 nm/min. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy showed full retention of the fluorine moieties, and no measurable cross-linking was detected. Additionally, the FTIR studies support the hypothesis that film deposition results from vinyl polymerization. For all iCVD PPFDA films, the static contact angle was found to be 120.8 +/- 1.2 degrees. The roughness of the films was found to be between 14.9 and 19.8 nm RMS, and the refractive index of the films was found to be between 1.36 and 1.37. The deposition rate was studied as a function of the substrate temperature and the partial pressure of the monomer. It was found that the deposition rate increases with decreasing substrate temperature and increasing monomer partial pressure. It was also found that the molecular weight increases with decreasing substrate temperature and increases with increasing monomer partial pressure. The highest molecular weight measured was 177 300 with a polydispersity of 2.27. Quartz crystal microbalance (QCM) measurements showed that these effects correlated with an increased monomer concentration at the surface. The deposition rate data and the QCM data were quantitatively analyzed to find the rate constants of the process using a previously published model for the iCVD process involving nonfluorinated monomers. The determined values of the rate constants of the surface polymerization were found to be similar to the rate constants measured in liquid-phase free radical polymerization. The kinetic data found in this paper can now be used to study iCVD deposition onto substrates with more complex geometries.

Large-scale initiated chemical vapor deposition of poly(glycidyl methacrylate) thin films

The initiated chemical vapor deposition (iCVD) of poly(glycidyl methacrylate) (PGMA) was scaled up using dimensionless analysis. In the first stage, PGMA was deposited onto a large stationary substrate and a deposition rate as high as 85 nm/min was achieved. It was found that the deposition rate increases with increasing filament temperature, whereas the deposition rate and the number-average molecular weight decrease with increasing substrate temperature. In the second stage, PGMA was deposited onto a moving substrate. At speeds between 20 mm/min and 60 mm/min, the deposition rate on the moving substrate was found to be equal to the deposition rate on the stationary substrate. Fourier transform infrared spectroscopy showed that the epoxide functionality of the PGMA films was retained during the iCVD process. Since the iCVD polymerization of different vinyl monomers all use similar parameters, this scale up can be applied to the scale up of other vinyl monomers such as 2-hydroxyethyl methacrylate and perfluoroalkyl ethyl methacrylate.

Vapor-Deposited Fluorinated Glycidyl Copolymer Thin Films with Low Surface Energy and Improved Mechanical Properties

Copolymer films of glycidyl methacrylate (GMA) with 2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoroheptyl acrylate (DFHA) and with (perfluoroalkyl)ethyl methacrylate (PFEMA) were synthesized using initiated chemical vapor deposition (iCVD). By varying the inlet monomer feed ratios during iCVD process, the mole percentage of fluorinated acrylics in the P(GMA-co-DFHA) and P(GMA-co-PFEMA) copolymers was systematically varied between 19% and 65%. Vacuum annealing of the as-deposited copolymer films induced cross linking between epoxy functionalities of the GMA units. Both the hardness and the modulus of the annealed copolymers films were observed to increase with increasing GMA fraction, providing an order of magnitude improvement in these mechanical properties. The dispersive surface energy of the annealed copolymers showed a limited dependence on GMA fraction, with the range of values being 17.5−18.6 mN/m and 9.9−14.7 mN/m for the P(GMA-co-DHFA) and P(GMA-co-PFEMA) films, respectively. These data are as low as or lowe...

Initiated Chemical Vapor Deposition of Linear and Cross-linked Poly(2-hydroxyethyl methacrylate) for Use as Thin-Film Hydrogels

Initiated chemical vapor deposition (iCVD) is able to synthesize linear and cross-linked poly(2-hydroxyethyl methacrylate) (PHEMA) thin films, in one step, from vapors of 2-hydroxyethyl methacrylate (HEMA), ethylene glycol diacrylate (EGDA), and tert-butyl peroxide (TBPO) without using any solvents. This all-dry technique also allows control of the cross-link density by adjusting the partial pressure of the cross-linking agent EGDA in the vapor phase. Films with specific cross-link densities and hence thermal, wetting, and swelling properties can be created in one single vacuum processing step. Through selective thermal decomposition of the initiator TBPO, films with well-defined chemical structures and full functionality retention can be deposited, which is evident in the Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) analyses. These spectroscopic methods also facilitate determination of EGDA incorporation in the cross-linked films based on the fact that HEMA contains a hydroxyl group but EGDA does not. For the linear PHEMA depositions, the growth rate was found to be nonlinear in the partial pressure of HEMA, possibly due to nonlinear multilayer adsorption and/or primary termination. The EGDA/HEMA ratio in the films systematically increased from 0.00 to 0.46 as the EGDA partial pressure was raised. The onset temperatures of decomposition were between 270 and 302 degrees C for the linear and the most cross-linked films, respectively. Thermal annealing at approximately 430 degrees C resulted in minuscule amounts of residue for all films, linear or cross-linked. The most cross-linked film had approximately 99.50% thickness removed after annealing. The contact angle was found to increase with increasing cross-link density. Significant contact-angle hysteresis was observed, indicating surface reconfiguration, and the lowest receding angle was 17 degrees for the linear film. Swelling measurements using spectroscopic ellipsometry showed that the degree of swelling decreased with increasing EGDA incorporation. The water content decreased from 35% (v/v) for the linear film to below 10% (v/v) for the most cross-linked film. These results show that iCVD is able to produce PHEMA thin films that function as hydrogels when soaked in water. The spectroscopic results, the contact-angle results, and the swelling analysis altogether prove the retention of the hydrophilic pendant groups in the iCVD process.