1,720,966 research outputs found
Initiated and oxidative chemical vapor deposition: a scalable method for conformal and functional polymer films on real substrates
No full textChemical vapor deposition (CVD) is a widely-used technology for the preparation of conformal and defect-free inorganic thin films with systematically tunable properties. Polymers are a desirable class of materials for surface modi. cation because of their low cost, wide array of chemical and physical functionality and mechanical flexibility. Initiated and oxidative chemical vapor deposition (iCVD and oCVD) are polymer CVD methods that combine the benefits of CVD processing with the possibilities of polymeric materials. Using these technologies, our laboratory has synthesized a number of functional, biocompatible and electrically conducting polymers as thin films on micro- and nano-structured surfaces. This Perspective will review recent advances in these areas and highlight devices and applications that utilize iCVD and oCVD polymers.This research was supported in part by the US Army through
the Institute for Soldier Nanotechnologies, Draper Laboratories
through their UiRAD program, and the DuPont-MIT
alliance
Systematic control of the electrical conductivity of poly (3,4-ethylenedioxythiophene) via oxidative chemical vapor deposition (oCVD)
No full textSystematic variation in the electrical conductivity of poly (3,4 ethylenedioxythiophene) (PEDOT) was achieved by oxidative chemical vapor deposition (oCVD). For oCVD, both the oxidant, Fe(III)Cl-3, and 3,4 ethylenedioxythiophene (EDOT) monomer are introduced in the vapor phase. A heated crucible allows for sublimation of the oxidant directly into the reactor chamber. Spontaneous reaction of the oxidant with the monomer results in the rapid (> 200 nm thick film in 30 min) formation of pi-conjugated PEDOT thin films directly onto a temperature controlled substrate. As the substrate temperature is increased from 15 degrees C to 100 degrees C, increasing conjugation length and doping level of the PEDOT chains are observed by Raman spectroscopy. The X-ray photoelectron spectroscopy (XPS) study showed that the surface consists of PEDOT polymer chains doped with Cl- ions in the absence of metallic impurities such as Fe. This contrasts to the surface composition of commonly used PEDOT:PSS films, where the PSS segregates to the surface. Scanning transmission electron microscopy (STEM) with energy dispersive X-ray analysis (EDX) study clearly demonstrates that the bulk composition is uniformly maintained throughout thickness of the film and is identical to the surface concentration. Both the substrate and air side interfaces were abrupt. The doping level could also be controlled by changing substrate temperature and accordingly, the work function was tuned from 5.1 to 5.4 eV, a range desirable for optimizing hole transport by lowering the charge injection barrier. The controllability of doping level and work function of oCVD PEDOT offers great potential advantages for optimization of the performance of organic devices. (C) 2007 Elsevier B.V. All rights reserved.This research was supported by, or supported in part by, the
U.S. Army through the Institute for Soldier Nanotechnologies,
under Contract DAAD-19-02-D-0002 with the U.S. Army
Research Office. The authors thank LG Chemicals Ltd. for the
measurement of work function. The content does not necessarily
reflect the position of the Government, and no official
endorsement should be inferred
Oxidative chemical vapor deposition of electrically conducting poly(3,4-ethylenedioxythiophene) films
No full textAn oxidative chemical vapor deposition (CVD) process is presented as an alternative to conventional solution-based processing of poly( 3,4-ethylenedioxythiophene) (PEDOT) thin films. This solventless technique yields PEDOT with higher conductivities and conformally coats fibers and other high area morphologies, important for enhancing efficiencies in some organic electronic devices. The CVD method eliminates corrosive poly(styrenesulfonate) that is used to disperse PEDOT in an aqueous suspension for solution-based processing. A mechanistic approach is presented that favors the deposition of the conjugated, conducting form of PEDOT. We achieved conductivities as high as 105 S/cm and demonstrated films about 100 nm thick that do not crack upon bending and are more than 84% transparent to visible light. The compatibility of oxidative CVD deposition of PEDOT is demonstrated on silicon, glass, plastic, and paper substrates.This research was supported by, or
supported in part by, the U.S. Army through the Institute for
Soldier Nanotechnologies, under Contract DAAD-19-02-D-0002
with the U.S. Army Research Office. The content does not
necessarily reflect the position of the Government, and no
official endorsement should be inferred
A conformal nano-adhesive via initiated chemical vapor deposition for microfluidic devices
No full textA novel high-strength nano-adhesive is demonstrated for fabricating nano-and microfluidic devices. While the traditional plasma sealing methods are specific for sealing glass to poly(dimethylsiloxane) (PDMS), the new method is compatible with a wide variety of polymeric and inorganic materials, including flexible substrates. Additionally, the traditional method requires that sealing occur within minutes after the plasma treatment. In contrast, the individual parts treated with the nano-adhesive could be aged for at least three months prior to joining with no measurable deterioration of post-cure adhesive strength. The nano-adhesive is comprised of a complementary pair of polymeric nanolayers. An epoxy-containing polymer, poly(glycidyl methacrylate) (PGMA) was grown via initiated chemical vapor deposition (iCVD) on the substrate containing the channels. A plasma polymerized polyallylamine (PAAm) layer was grown on the opposing flat surface. Both CVD monomers are commercially available. The PGMA nano-adhesive layer displayed conformal coverage over the channels and was firmly tethered to the substrate. Contacting the complementary PGMA and PAAm surfaces, followed by curing at 70 degrees C, resulted in nano-and micro-channel structures. The formation of the covalent tethers between the complementary surfaces produces no gaseous by-products which would need to outgas. The nano-adhesive layers did not flow significantly as a result of curing, allowing the cross-sectional profile of the channel to be maintained. This enabled fabrication of channels with widths as small as 200 nm. Seals able to withstand > 50 psia were fabricated employing many types of substrates, including silicon wafer, glass, quartz, PDMS, polystyrene petri dishes, poly(ethylene terephthalate) (PET), polycarbonate (PC), and poly(tetrafluoro ethylene) (PTFE).This research was supported by, or supported in part by, the US
Army through the Institute for Soldier Nanotechnologies, under
Contract DAAD-19-02-0002 with the US Army Research Office
Oxidative chemical vapor deposition (oCVD) of patterned and functional grafted conducting polymer nanostructures
No full textWe present a simple one-step process to simultaneously create patterned and amine functionalized biocompatible conducting polymer nanostructures, using grafting reactions between oxidative chemical vapor deposition (oCVD) PEDOT conducting polymers and amine functionalized polystyrene ( PS) colloidal templates. The functionality of the colloidal template is directly transferred to the surface of the grafted PEDOT, which is patterned as nanobowls, while preserving the advantageous electrical properties of the bulk conducting polymer. This surface functionality affords the ability to couple bioactive molecules or sensing elements for various applications, which we demonstrate by immobilizing fluorescent ligands onto the PEDOT nanopatterns. Nanoscale substructure is introduced into the patterned oCVD layer by replacing the FeCl(3) oxidizing agent with CuCl(2)
Doping level and work function control in oxidative chemical vapor deposited poly (3,4-ethylenedioxythiophene)
No full textControl over doping level and work function is achieved for poly(3,4-ethylenedioxythiophene) (PEDOT) films deposited by oxidative chemical vapor deposition (oCVD). Surface analysis reveals the equivalence of the surface and bulk compositions for the oCVD films. The oCVD PEDOT polymer chains doped solely with Cl- ions. By increasing the substrate temperature used for deposition, the doping level was monotonically increased from 17 to 33 at. %, resulting in a corresponding ability to tune the work function from 5.1 to 5.4 eV. The controllability of doping level and work function of oCVD PEDOT offers great potential advantages for organic devices. (c) 2007 American Institute of Physics.This research was supported by, or supported in part by,
the U.S. Army through the Institute for Soldier Nanotechnologies,
under Contract No. DAAD-19-02-D-0002 with the
U.S. Army Research Office. The authors thank Anthony
Garrett-Reed for the STEM measurement. The authors thank
LG Chemicals Ltd. for the measurement of work function
Electrochemical investigation of PEDOT films deposited via CVD for electrochromic applications
No full textA patterned solid-state electrochromic device on an ITO-coated plastic substrate was demonstrated that incorporates poly-3,4-ethylenedioxythiophene (PEDOT) deposited via a solventless oxidative chemical vapor deposition (oCVD) technique. In this paper, we present a thin-film electrochemical and optical analysis of oCVD PEDOT oCVD PEDOT films about 100 nm thick on ITO/glass had optical switching speeds of 0 and 8.5 s, for light-to-dark and dark-to-light transitions, respectively. The color contrast was 45% at 566 nm and is 85% stable over 150 redox cycles. An Anson plot indicates that oCVD PEDOT color transition speeds are limited by ion diffusion rates, rather than electron or hole conductivity. Dimensionless analysis predicts gains of up to in oCVD PEDOT redox switching speeds by reducing the film thickness an order of magnitude to 10 nm. oCVD is a temperature-controlled process capable of conformal conductive polymer depositions onto a range of substrates from the vapor phase. Compatible substrates include plastic, paper and fabric. Non-conductive dispersion additives are not needed with oCVD, eliminating a potential source of defect-causing corrosion. oCVD offers powerful capabilities that may overlap with key challenges for the designers and fabricators of organic thin-film electronics, including OLED lighting and displays, electrochromics, photovoltaics, and semiconductors. (c) 2007 Elsevier B.V. All rights reserved.This research was supported by, or supported in part by,
the U.S. Army through the Institute for Soldier Nanotechnologies,
under Contract DAAD-19-02-D-0002 with the U.S. Army
Research Office. The content does not necessarily reflect the
position of the Government, and no official endorsement should
be inferred
Patterning Nanodomains with Orthogonal Functionalities: Solventless Synthesis of Self-Sorting Surfaces
No full textA simple method to fabricate a multifunctional patterned platform on the nanometer scale is demonstrated. The platform contains two reactive functional groups on the surface: one is an acetylene group which can be functionalized via click chemistry, and the other is an amine group which can also be functionalized by classic carbodiimide chemistry with N-hydroxysuccinimide (NHS). The click-active and amine surface could be obtained from polymer coating of poly(propargyl methacrylate) (PPMA) via initiated chemical vapor deposition (iCVD) and poly(allylamine) (PAAm) via a plasma polymerization process, respectively, utilizing commercially available monomers. A capillary force lithography (CFL) process was applied on a stacked film of a PPMA layer on PAAm, and CFL could selectively pattern PPMA maintaining the bottom PAAm layer intact, which completes the multifunctional nanopatterns. The minimum feature size of this nanopattern was 110 nm. The entire fabrication process is solventless and low temperature which can minimize the loss of functionalities. The click and NHS reactions are highly orthogonal to each other so that nonspecific immobilization can be minimized. These advantageous characteristics enable the covalent functionalization of two independent components in a one-pot functionalization process in self-recognized way. The one-pot orthogonal functionalization was performed in an aqueous solution at room temperature, which is biocompatible. Considering the versatility and generality of the reactions used here, we believe this platform can be easily extended to various biodevice applications.This research was supported by the U.S.
Army through the Institute for Soldier Nanotechnologies, under
Contract DAAD-19-02-D-0002 with the U.S. Army Research
Office
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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