1,720,969 research outputs found
Initiated PECVD of organosilicon coatings: A new strategy to enhance monomer structure retention
No full textA 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 (0.07W·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. Herein we show a new deposition method, initiated-PECVD (iPECVD), as an alternative to iCVD and PECVD, for the monomers that are not easily polymerizable by iCVD (e.g., the organosilicon monomers) but where a certain structure retention is needed. The addition of a radical initiator allows to ignite a plasma discharge at plasma density as low as 0.07W·cm -2. In this condition the carbon content of the monomer molecule is completely retained and at reasonably high deposition rate. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
CVD of polymeric thin films: Applications in sensors, biotechnology, microelectronics/organic electronics, microfluidics, MEMS, composites and membranes
No full textPolymers with their tunable functionalities offer the ability to rationally design micro- and nano-engineered materials. Their synthesis as thin films have significant advantages due to the reduced amounts of materials used, faster processing times and the ability to modify the surface while preserving the structural properties of the bulk. Furthermore, their low cost, ease of fabrication and the ability to be easily integrated into processing lines, make them attractive alternatives to their inorganic thin film counterparts. Chemical vapor deposition (CVD) as a polymer thin-film deposition technique offers a versatile platform for fabrication of a wide range of polymer thin films preserving all the functionalities. Solventless, vapor-phase deposition enable the integration of polymer thin films or nanostructures into micro- and nanodevices for improved performance. In this review, CVD of functional polymer thin films and the polymerization mechanisms are introduced. The properties of the polymer thin films that determine their behavior are discussed and their technological advances and applications are reviewed. © 2012 IOP Publishing Ltd
Grafted crystalline poly-perfluoroacrylate structures for superhydrophobic and oleophobic functional coatings
No full textThis report describes the preparation of superhydrophobic and oleophobic surfaces by grafting of poly(perfluorodecylacrylate) chains with initiated chemical vapor deposition on silicon substrates. The grafting enhances the formation of a semicrystalline phase. The crystalline structures reduce the polymer chain mobility, resulting in nonwetting surfaces with both water and mineral oil. On the contrary, the same contacting liquid easily wets the amorphous ungrafted polymer. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Global and local planarization of surface roughness by chemical vapor deposition of organosilicon polymer for barrier applications
No full textParticulates and asperities on the surface of plastic substrates limit the performance of the current protective barrier coatings for flexible electronics. By applying a smoothing layer to the substrate, prior to barrier deposition, permeation is reduced. While application of smoothing layers from the liquid-phase application and curing of acrylate monomers is well known, reports of planarization achieved by vapor deposition are quite limited. In the current work, the chemical vapor deposition (CVD) of a flexible smoothing layer, requiring no curing, is implemented in the same reactor chamber and from the same organosilicon monomer used for depositing the multilayer barrier stack. The process similarity between the smoothing and barrier layer deposition steps has the potential to lower the overall cost of the process and to improve interfacial properties, such as adhesion between the smoothing layer and the barrier stack. The current methods adapts and combines features of two well established methods for CVD of organic layers, plasma enhancement (PECVD) and the specific use of an initiator species (iCVD). The novel, initiated plasma enhanced chemical vapor deposition (iPECVD) method achieves a far greater degree of planarization of flexible organic layer than either of its predecessors. Polystyrene microspheres serve as model defects and allow the degree of planarization to be quantitatively measured. Both cross-sectional scanning electron micrographs and atomic force micrographs demonstrate that when the iPECVD organic layer is 1.8 μm thick, the degree of global planarization is 99. A model demonstrates that the planarization is achieved as a result of the coating viscosity and the surface tension. Finally, the water vapor barrier performance of a 20-nm-thick SiOx layer is two orders of magnitude improved when it is deposited on a planarized substrate. © 2012 American Institute of Physics
Controlling the Degree of Crystallinity and Preferred Crystallographic Orientation in Poly‐Perfluorodecylacrylate Thin Films by Initiated Chemical Vapor Deposition
No full textPreferred crystallographic orientation (texture) in thin films of technologically important materials frequently has a strong effect on the properties of these films and is important for stable surface properties. The deposition of organized molecular films of a poly-perfluorodecylacrylate, poly-(1H,1H,2H,2H-perfluorodecyl acrylate) (p-PFDA), by initiated chemical vapor deposition (iCVD) is described. The tendency of p-PFDA to crystallize in a smectic B phase has been reported in films prepared from solution but not for those using a CVD technique. The degree of crystallinity and the preferred orientation of the perfluoro side chains, either parallel or perpendicular to the surface, are controlled by tuning the CVD process parameters (i.e., initiator to monomer flow rate ratio, filament temperature, and substrate temperature). Films with no observable X-ray diffraction patterns are also achieved. The observed differences in crystal texture strongly impact the observed water contact angles (150° to 130°, advancing) and corresponding hysteresis behavior. Low hysteresis (<7°) is associated with high crystallinity, particularly when the orientation of the crystallites resulted in the perfluoro side groups being oriented parallel to the surface. The latter texture resulted in smoother film than the texture with the chains oriented perpendicular to the surface and this can be very advantageous for applications in which relatively smooth but still crystalline films are needed. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Flexible cross-linked organosilicon thin films by initiated chemical vapor deposition
No full textHighly cross-linked but flexible polyhexavinyldisiloxane (p-HVDSO) thin films were deposited by initiated chemical vapor deposition (iCVD) for applications where smooth, adhesive, and flexible coatings are required, like biological implantations or thin film electronics. The substrate temperature and the initiator flow rate dependencies were investigated as routes to enhance the cross-linking degree of the network. The most cross-linked film was obtained at substrate temperature of 60°C and monomer/initiator ratio of ∼1. Kinetic analysis of the deposition process indicates that the film formation rate is limited by the saturation reactions of the vinyl groups, with an activation energy of 53.8 kJ/mol with respect to the substrate temperature. Atomic force microscopy showed microscopically flat surfaces, while tape test and bending cycles revealed high adhesion and flexibility. The possibility of obtaining a tunable cross-linking degree through methylene bridges by changing the substrate temperature makes the p-HVDSO films suitable for a wide range of applications. © 2009 American Chemical Society
Chemical vapor deposition for solvent-free polymerization at surfaces
No full textChemical vapor deposition (CVD) methods are a powerful technology for engineering surfaces. When CVD is combined with the richness of organic chemistry, the resulting polymeric coatings, deposited without solvents, represent an enabling technology in many different fields of application. This article focuses on initiated chemical vapor deposition (iCVD), a new technique that utilizes benign reaction conditions to yield conformal and functional polymer thin films. The latest achievements in coating surfaces and 3D substrates with functional materials, and the use of the technique for biotechnology and selective permeation applications are reviewed, and future directions for iCVD technology are discussed. Initiated chemical vapor deposition (iCVD) polymerization is a very elegant technique for designing new patterns and tuning the chemistry available on any kind of surface. These polymers attract considerable attention in many different fields of application. This trends article highlights the latest achievements in the fabrication of new surfaces and functional materials via iCVD and presents significant insights in its scale-up process. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Super-Hydrophobic and Oloephobic Crystalline Coatings by Initiated Chemical Vapor Deposition
Full text linkPreferred crystallographic orientation (texture) in thin films frequently has a strong effect on the properties of the materials and it is important for stable surface properties. Organized molecular films of poly-perfluorodecylacrylate p(PFDA) were deposited by initiated Chemical Vapor Deposition (iCVD). The high tendency of p(PFDA) to crystallize has been fully retained in the polymers prepared by iCVD. The degree of crystallinity and the preferred orientation of the perfluoro side chains, either parallel or perpendicular to the surface, were controlled by tuning the CVD process parameters (i.e. initiator to monomer flow rate ratio, filament temperature, and substrate temperature). Super- hydrophobicity (advancing water contact angle, WCA, of 160°, low hysteresis of 5°), and oleophobicity (advancing CA with mineral oil of 120°) were achieved. Low hysteresis was associated with high crystallinity, particularly when the orientation of the crystallites resulted in the perfluoro side groups being oriented parallel to the surface. The latter texture resulted in smoother film (RMS roughness < 30 nm) than the texture with the chains oriented perpendicularly to the surface. This can be very advantageous for applications that require smooth but still crystalline films.Massachusetts Institute of Technology. Institute for Soldier Nanotechnologies (Contract DAAD-19-02D-0002
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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