Is keV ion induced pattern formation on Si(001) caused by metal impurities?

We present ion beam erosion experiments performed in ultra high vacuum using a differentially pumped ion source and taking care that the ion beam hits the Si(001) sample only. Under these conditions no ion beam patterns form on Si for angles below 45 degrees with respect to the global surface normal using 2 keV Kr ions and fluences of 2 x 10^22 ions/m^2. In fact, the ion beam induces a smoothening of preformed patterns. Simultaneous sputter deposition of stainless steel in this angular range creates a variety of patterns, similar to those previously ascribed to clean ion beam induced destabilization of the surface profile. Only for grazing incidence with incident angles between 60 degrees and 83 degrees pronounced ion beam patterns form. It appears that the angular dependent stability of Si(001) against pattern formation under clean ion beam erosion conditions is related to the angular dependence of the sputtering yield, and not primarily to a curvature dependent yield as invoked frequently in continuum theory models.Comment: 15 pages, 7 figures. This is an author-created, un-copyedited version of an article published in Nanotechnology. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from i

CVD of polymeric thin films: Applications in sensors, biotechnology, microelectronics/organic electronics, microfluidics, MEMS, composites and membranes

Polymers 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

Flexible cross-linked organosilicon thin films by initiated chemical vapor deposition

Highly 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

Electrospun Nanofibers With pH-Responsive Coatings for Control of Release Kinetics

Functional and stimuli-responsive nanofibers with an enhanced surface area/volume ratio provide controlled and triggered drug release with higher efficacy. In this study, chemotherapeutic agent Rose Bengal (RB) (4,5,6,7-tetrachloro-2′, 4′,5′,7′-tetraiodofluoresceindisodium)-loaded water-soluble polyvinyl alcohol (PVA) nanofibers were synthesized by using the electrospinning method. A thin layer of poly(4-vinylpyridine-co-ethylene glycol dimethacrylate) p(4VP-co-EGDMA) was deposited on the RB-loaded nanofibers (PVA-RB) via initiated chemical vapor deposition (iCVD), coating the fiber surfaces to provide controllable solubility and pH response to the nanofibers. The uncoated and [p(4VP-co-EGDMA)-PVA] coated PVA-RB nanofiber mats were studied at different pH values to analyze their degradation and drug release profiles. The coated nanofibers demonstrated high stability at neutral and basic pH values for long incubation durations of 72 h, whereas the uncoated nanofibers dissolved in <2 h. The drug release studies showed that the RB release from coated PVA-RB nanofibers was higher at neutral and basic pH values, and proportional to the pH of the solution, whereas the degradation and RB release rates from the uncoated PVA-RB nanofibers were significantly higher and did not depend on the pH of environment. Further analysis of the release kinetics using the Peppas model showed that while polymer swelling and dissolution were the dominant mechanisms for the uncoated nanofibers, for the coated nanofibers, Fickian diffusion was the dominant release mechanism. The biocompatibility and therapeutic efficiency of the coated PVA-RB nanofibers against brain cancer was investigated on glioblastoma multiforme cancer cells (U87MG). The coated PVA nanofibers were observed to be highly biocompatible, and they significantly stimulated the ROS production in cells, increasing apoptosis. These promising results confirmed the therapeutic activity of the coated PVA-RB nanofibers on brain cancer cells, and encouraged their further evaluation as drug carrier structures in brain cancer treatment