Browsing by Author "Chattopadhyay, Surojit"

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Improved broadband and quasi-omnidirectional anti-reflection properties with biomimetic silicon nanostructures
(2007-12-01)
Huang, Yi-Fan
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Chattopadhyay, Surojit
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Jen, Yi-Jun
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Peng, Cheng-Yu
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Liu, Tze-An
Nature routinely produces nanostructured surfaces with useful properties, such as the self-cleaning lotus leaf, the colour of the butterfly wing, the photoreceptor in brittlestar and the anti-reflection observed in the moth eye. Scientists and engineers have been able to mimic some of these natural structures in the laboratory and in real-world applications. Here, we report a simple aperiodic array of silicon nanotips on a 6-inch wafer with a sub-wavelength structure that can suppress the reflection of light at a range of wavelengths from the ultraviolet, through the visible part of the spectrum, to the terahertz region. Reflection is suppressed for a wide range of angles of incidence and for both s- and p-polarized light. The antireflection properties of the silicon result from changes in the refractive index caused by variations in the height of the silicon nanotips, and can be simulated with models that have been used to explain the low reflection from moth eyes. The improved anti-reflection properties of the surfaces could have applications in renewable energy and electro-optical devices for the military.
Label free sub-picomole level DNA detection with Ag nanoparticle decorated Au nanotip arrays as surface enhanced Raman spectroscopy platform
(2011-01-15)
Lo, Hung-Chun
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Hsiung, Hsin-I
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Chattopadhyay, Surojit
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Han, Hsieh-Cheng
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Chen, Chia-Fu
Label free optical sensing of adenine and thymine oligonucleotides has been achieved at the sub-picomole level using self assembled silver nanoparticles (AgNPs) decorated gold nanotip (AuNT) arrays. The platform consisting of the AuNTs not only aids in efficient bio-immobilization, but also packs AgNPs in a three dimensional high surface area workspace, assisting in surface enhanced Raman scattering (SERS). The use of sub-10 nm AgNPs with optimum inter-particle distance ensures amplification of the chemically specific Raman signals of the adsorbed adenine, thymine, cytosine and guanine molecules in SERS experiments. High temporal stability of the Raman signals ensured reliable and repeatable DNA detection even after three weeks of ambient desk-top conservation. This facile architecture, being three dimensional and non-lithographic, differs from conventional SERS platforms. (C) 2010 Elsevier B.V. All rights reserved.
Luminescence properties of wurtzite AlN nanotips
(2006-10-16)
Shi, Shih-Chen
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Chen, Chia Fu
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Chattopadhyay, Surojit
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Chen, Kuei-Hsien
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Ke, Bo-Wen
The optical properties of aluminum nitride nanotips (AlNNTs) synthesized via vapor transport and condensation process have been studied by cathodoluminescence, photoluminescence (PL), thermoluminescence (TL), and UV absorption measurements. Two defect related transitions around 2.1 and 3.4 eV and an excitonic feature at 6.2 eV were identified. Compared to the AlN macropowders, the AlNNTs showed a blueshift (+0.2 eV) of the similar to 3.2 eV peak. Analysis of both PL and TL excitation measurements indicated the existence of subband gap multiple energy levels in AlNNTs. A significant TL intensity even at 145 degrees C suggests possible ultraviolet detector and dosimetric applications of these AlNNTs. (c) 2006 American Institute of Physics.