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Buyukkose S.,MESA Institute for Nanotechnology | Hernandez-Minguez A.,Paul Drude Institute For Festkorkperelektronik | Vratzov B.,NTandD Nanotechnology and Devices | Somaschini C.,Paul Drude Institute For Festkorkperelektronik | And 4 more authors.
Nanotechnology | Year: 2014

The oscillating piezoelectric fields accompanying surface acoustic waves are able to transport charge carriers in semiconductor heterostructures. Here, we demonstrate high-frequency (above 1 GHz) acoustic charge transport in GaAs-based nanowires deposited on a piezoelectric substrate. The short wavelength of the acoustic modulation, smaller than the length of the nanowire, allows the trapping of photo-generated electrons and holes at the spatially separated energy minima and maxima of conduction and valence bands, respectively, and their transport along the nanowire with a well defined acoustic velocity towards indium-doped recombination centers. © 2014 IOP Publishing Ltd. Source


Moonen P.F.,MESA Institute for Nanotechnology | Vratzov B.,NTandD Nanotechnology and Devices | Smaal W.T.T.,Holst Center | Kjellander B.K.C.,Holst Center | And 3 more authors.
Organic Electronics: physics, materials, applications | Year: 2012

A multistep imprinting process is presented for the fabrication of a bottom-contact, bottom-gate thin-film transistor (TFT) on poly(ethylene naphthalate) (PEN) foil by patterning all layers of the metal-insulator-metal stack by UV nanoimprint lithography (UV NIL). The flexible TFTs were fabricated on a planarization layer, patterned in a novel way by UV NIL, on a foil reversibly glued to a Si carrier. This planarization step enhances the dimensional stability and flatness of the foil and thus results in a thinner and more homogeneous residual layer. The fabricated TFTs have been electrically characterized as demonstrators of the here developed fully UV NIL-based patterning process on PEN foil, and compared to TFTs made on Si with the same process. TFTs with channel lengths from 5 μm down to 250 nm have been fabricated on Si and PEN foil, showing channel length-dependent charge carrier mobilities, μ, in the range of 0.06-0.92 cm2 V-1 s -1 on Si and of 0.16-0.56 cm2 V-1 s -1 on PEN foil. © 2012 Elsevier B.V. All rights reserved. Source


Buyukkose S.,MESA Institute for Nanotechnology | Vratzov B.,NTandD Nanotechnology and Devices | Van Der Wiel W.G.,MESA Institute for Nanotechnology
Journal of Vacuum Science and Technology B:Nanotechnology and Microelectronics | Year: 2011

The authors present a novel global contact planarization technique based on the spin-on-glass material hydrogen silsequioxane (HSQ) and demonstrate its excellent performance on patterns of 70 nm up to several microns generated by UV-based nanoimprint lithography. The HSQ layer (∼165 nm) is spin coated on the imprinted organic layer and planarized by pressing it with a flat wafer at room temperature. Before retracting the planarization wafer, the HSQ is hardened by baking at 120 or 70 °C, depending on the underlying material. Fluorine-based reactive ion etching (RIE) is used to etch the HSQ (etch-back) down to the top of the features in the organic imprint layer. Subsequently, oxygen-based RIE is used to etch the organic imprint layer in the exposed regions, thereby transferring the imprinted pattern down to the substrate. The etch selectivity between the HSQ and the underlying layers is found to be more than 1:100, enabling very accurate pattern transfer with excellent critical dimension control and well-defined undercut profile suitable for further metal liftoff processes. The dependence of the contact planarization quality on the HSQ spinning speed and pressure is investigated, achieving a global planarization degree as good as 93%, an improvement of 45% compared to standard spin-coating planarization. © 2011 American Vacuum Society. Source


Benetti E.M.,ETH Zurich | Acikgoz C.,MESA Institute for Nanotechnology | Sui X.,MESA Institute for Nanotechnology | Vratzov B.,NTandD Nanotechnology and Devices | And 3 more authors.
Advanced Functional Materials | Year: 2011

Functional polymer brush nanostructures are obtained by combining step-and-flash imprint lithography (SFIL) with controlled, surface-initiated polymerization (CSIP). Patterning is achieved at length scales such that the smallest elements have dimensions in the sub-100 nm range. The patterns exhibit different shapes, including lines and pillars, over large surface areas. The platforms obtained are used to selectively immobilize functional biomacromolecules. Acrylate-based polymer resist films patterned by SFIL are first used for the selective immobilization of ATRP silane-based initiators, which are coupled to unprotected domains of silicon substrates. These selectively deposited initiators are then utilized in the controlled radical SIP of poly(ethylene glycol)methacrylates (PEGMA). Nanostructured brush surfaces are then obtained by removal of the resist material. The areas previously protected by the SFIL resist are passivated by inert, PEG-based silane monolayers following resist removal. PEGMA brush nanostructures are finally functionalized with biotin units in order to provide selective attachment points for streptavidin proteins. Atomic force microscopy and fluorescence spectroscopy confirm the successful immobilization of streptavidin molecules on the polymer grafts. Finally, it is demontrated that this fabrication method allows the immobilization of a few tens of protein chains attached selectively to brush nanostructures, which are surrounded by nonfouling PEG-functionalized areas. Step-and-flash imprint lithography and controlled, surface-initiated polymerization in aqueous media are combined to prepare patterned functional brush nanostructures. The immobilization of a few tens of protein chains that are selectively attached through biotin ligands onto brush nanostructures and surrounded by a nonfouling surface is achieved. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

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