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Lee K.H.,Nanyang Technological University | Romanato F.,University of Padua | Romanato F.,Laboratory for Nanofabrication of Nanodevices | Kang H.K.,Nanyang Technological University | Wong C.C.,Nanyang Technological University
Sensors and Actuators, B: Chemical | Year: 2010

We present a method to explore the full sensitivity of grating coupled surface plasmon resonance (GCSPR) sensors on an azimuthally rotatable grating by optimizing the polarization angle of the incident light. This is the condition where double surface plasmons polaritons (SPPs) can be excited by a single wavelength [1]. This configuration provides a sensitivity up to 950°/RIU compared to a system without azimuthal control [2]. We show here that the sensitivity of this configuration is only achievable when the polarization angle of the incident light is optimized. This is due to the excitation of a fully coupled SPP (as can be observed as a deeper dip in the reflectivity spectra) which is only possible using the optimized polarization angle in an azimuthally rotated grating. This result in a well-defined, sharper spectrum and the positions of the minima are more obvious. The figure of merit (FOM) increases by 50-100% compared to spectra collected using p-polarized light. We demonstrate this sensitivity using a dodecanethiol (C12) self-assembled monolayer (SAM) on a Au grating surface, representing a thickness difference of 1.5 nm compared to the uncoated grating. Using the new configuration with optimized polarization angle, a shift in resonance angle as large as 3.6° can be observed. In principle, we expect the refractive index resolution of this method to be on the order of 5 × 10-7 RIU. © 2010 Elsevier B.V. All rights reserved.

Lee K.H.,Nanyang Technological University | Lim X.Y.,Nanyang Technological University | Wai K.W.,Nanyang Technological University | Romanato F.,Nanyang Technological University | And 3 more authors.
Journal of Nanoscience and Nanotechnology | Year: 2011

In order to form tapered nanocapillaries, we investigated a method to vary the nanopore diameter along the porous anodic alumina (PAA) channels using multi-step anodization. By anodizing the aluminum in either single acid (H 3PO 4) or multi-acid (H 2SO 4, oxalic acid and H 3PO 4) with increasing or decreasing voltage, the diameter of the nanopore along the PAA channel can be varied systematically corresponding to the applied voltages. The pore size along the channel can be enlarged or shrunken in the range of 20 nm to 200 nm. Structural engineering of the template along the film growth direction can be achieved by deliberately designing a suitable voltage and electrolyte together with anodization time. Copyright © 2011 American Scientific Publishers All rights reserved.

Ruffato G.,University of Padua | Romanato F.,Laboratory for Nanofabrication of Nanodevices | Romanato F.,CNR Institute of Neuroscience
COMPEL - The International Journal for Computation and Mathematics in Electrical and Electronic Engineering | Year: 2013

Purpose - The purpose of this paper is to simulate and analyze the excitation and propagation of surface plasmon polaritons (SPPs) on sinusoidal metallic gratings in conical mounting. Design/methodology/approach - Chandezon's method has been implemented in MATLAB environment in order to compute the optical response of metallic gratings illuminated under azimuthal rotation. The code allows describing the full optical features both in far- and near-field terms, and the performed analyses highlight the fundamental role of incident polarization on SPP excitation in the conical configuration. Findings - Results of far-field polarization conversion and plasmonic near-field computation clearly show that azimuthally rotated metallic gratings can support propagating surface plasmon with generic polarization. Originality/value - The recent papers experimentally demonstrated the benefits in sensitivity and the polarization phenomenology that are originated by an azimuthal rotation of the grating. In this work, numerical simulations confirm these experimental results and complete the analysis with a study of the excited SPP near-field on the metal surface. Copyright © 2013 Emerald Group Publishing Limited. All rights reserved.

Brigo L.,University of Padua | Pistore A.,University of Padua | Grenci G.,CNR Institute of Neuroscience | Carpentiero A.,CNR Institute of Neuroscience | And 4 more authors.
Microelectronic Engineering | Year: 2010

The direct nanopatterning of a novel hybrid organic-inorganic sol-gel film based on bridged polysilsesquioxanes (BPS) using X-ray synchrotron radiation is reported. The main advantages of a direct fabrication technique with respect to conventional photolithography are represented by the possibility to bypass some typical post-exposure lithographic steps and to avoid the use of a sacrificial layer. The distinctive features rendering hybrid BPS-based material innovative for photolithographic applications are: the patternability as resist, the positive tone behaviour exhibited under X-ray irradiation, the porous structure demonstrated at low temperature, and the possibility to widely tailor material electro-optical and structural properties to experimental needs. A systematic investigation of the interactions between sol-gel BPS films based on the bis(triethoxysilyl)benzene precursor and soft X-rays is conducted. Under X-ray exposure, BPS-based films suffer structural changes attributed to the organic bridge breaking, and become soluble in suitable acidic aqueous solutions, producing final lithographies of sub-micron resolution, high contrast and good edge definition. © 2009 Elsevier B.V. All rights reserved.

Brigo L.,University of Padua | Grenci G.,CNR Institute of Materials | Ba L.,University of Padua | Carpentiero A.,CNR Institute of Materials | And 7 more authors.
Microelectronic Engineering | Year: 2011

Natively porous hybrid organic-inorganic sol-gel systems have been engineered to be used as functional positive photoresists, aimed to the realization of microsensors in a single-step process. Interesting results have been obtained combing three main sol-gel system features: the direct patternability through X-ray lithography, being processable without the addition of a photocatalyst; the functionalizability, properly designing the organic component of the hybrid network or incorporating active species; the open micro or mesoporosity, tailored by the synthesis process and precursor choice. The photoprocessable porous films have been synthesized starting from a Bridged Polysilsesquioxane (BPS) precursor, 1,4-bis(triethoxysilyl)benzene. The correlation between chemical properties of the sol-gel material and its patternability is described in detail. X-ray exposure leads to a progressive alkyl and aromatic compound elimination and promotes inorganic condensation in the system, allowing the selective dissolution of irradiated cross-linked films in suitable etchants. Patterns of final resolution lower than 100 nm have been realized on BPS-based films synthesized in acid conditions, a procedure that allows to take advantage of a straightforward embedding protocol for active species in the sol-gel matrix. The BPS-based system has been doped with a covalently linked quinolinium dye, obtaining thin sensing films patternable by X-ray lithography. A feasibility test for the fabrication of optical microdevices, where fluorescence properties are obtained directly on the patterned coatings, has been provided. © 2011 Elsevier B.V. All rights reserved.

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