Au nanoparticle based localized surface plasmon resonance substrates fabricated by dynamic shadowing growth

Au nanoparticle (NP) substrates, Au NP/TiO2/Au NP sandwich structures, and Ti coated Au NP substrates are fabricated by glancing angle deposition (GLAD) and oblique angle deposition (OAD) methods. Under the same deposition condition, the Au NP substrates produced by GLAD are more uniform and reproducible compared to those fabricated by OAD. The localized surface plasmon resonance (LSPR) wavelength of Au NP substrates can be easily tuned by changing the film thickness, the deposition angle, and the coating of the dielectric layer (TiO2) and metallic layer (Ti). In addition, the thickness and the deposition angle of the Ti coating on Au NP also affect the LSPR wavelength. Our results demonstrate that GLAD is a very versatile fabrication technique to produce reproducible and fine-tuned LSPR substrates

Localized oblique-angle deposition: Ag nanorods on microstructured surfaces and their SERS characteristics

In this paper, we demonstrate a simple and convenient method of depositing Ag nanorods on a substrate inside a standard evaporation chamber with the substrate resting on a leveled stage. Microstructuring the substrate prior to the deposition imparts a large incidence angle (>70°) between the collimated vapor atoms and the local surface normal, which is essential to induce the shadowing effect. Thereby, a localized oblique-angle deposition (LOAD) is realized, forming nanorods selectively on the steep sidewalls of surface microcavities patterned via standard photolithography and silicon dry etching. We also demonstrate that these nanorods can boost SERS activity of the underlying substrate and thus perform comparable to those fabricated via advanced patterning techniques or conventional OAD whereby the entire substrate has to be tilted with respect to the incident vapor atoms. Our results suggest the viability of decorating microchannel sidewalls with SERS-active nanorods for integrated sample processing and SERS detection. © 2011 IOP Publishing Ltd

UV-illuminated dielectrophoresis by two-dimensional electron gas (2DEG) in AlGaN/GaN heterojunction

Dielectrophoresis (DEP) induced by activating a patterned two-dimensional electron gas (2DEG) at the interface of compound semiconductor AlGaN/GaN heterojunction has been demonstrated for the first time in our previous work. Briefly, with a peak voltage of +/-10Vand a frequency from 100 kHz to 1 MHz, characteristics of both positive and negative DEP have been observed successfully manipulating 2 mm polystyrene microspheres in a drop of deionized (DI) water (pH similar to 7 and conductivity 1 x 10(-4) Sm-1) over castellated 2DEG electrodes separated by critical dimensions 50 and 150 mu m. This study reports a peculiar observation encountered when performing the DEP experiments under ultraviolet (UV) radiation: The microspheres have been repelled from the 2DEG electrodes yet remained on the surface during pDEP and then levitated upon switching to nDEP. This behavior is not observed in DEP with conventional microelectrodes and explained here by the UV-induced electron-hole generation and the subsequent charge redistribution in the AlGaN/GaN heterostructure. (C) 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinhei

Porosification-reduced optical trapping of silicon nanostructures

Metal-assisted chemical etching (MACE) was carried out to fabricate solid silicon nanowires (s-SiNWs) and mesoporous silicon nanowires (mp-SiNWs). Total reflection and transmission were measured using an integrated sphere to study optical properties of the MACE-generated silicon nanostructures. Without NW aggregation, mp-SiNWs vertically standing on a mesoporous silicon layer trap less light than s-SiNWs over a wavelength range of 400–800 nm, owing to porosification-enhanced optical scattering from the rough inner surfaces of the mesoporous silicon skeletons. Porosification substantially weakens the NW mechanical strength; hence the elongated mp-SiNWs aggregate after 30 min etching and deteriorate optical trapping

MICROFLUIDIC INTEGRATION OF PLASMONIC APPLICATIONS FOR HIGHLY SENSITIVE BIOANALYSIS

We integrate plasmonic applications such as surface enhanced Raman spectroscopy (SERS) and metal enhanced fluorescence (MEF) with micro-patterned substrates and microfluidic device using localized oblique angle deposition. Plasmonic nanostructures such as Ag nanorods in microcavities and microwells exhibit high sensitivity for SERS and MEF, respectively. Further, a MEF enhancement factor of 6 is observed for the optical detection of amino acid peaks in capillary electrophoresis (CE)