Swe Zin Oo

Disposable gold coated pyramidal SERS sensor on the plastic platform.

In this paper we investigate suitability of arrays of gold coated pyramids for surface-enhanced Raman scattering (SERS) sensing applications. Pyramidarrays composed of 1000 nm pit size with 1250 nm pitch lengthwerereplicated on a plastic substrate by roll-to-roll (R2R) ultraviolet (UV) embossing. The level of SERS enhancement, and qualitative performance provided by the new substrate is investigated by comparing Raman spectrum of benzenethiol (BTh) test molecules to the benchmark Klarite SERS substrate which comprises inverted pyramid arrays(1500 nm pit size with 2000 nm pitch length) fabricated on a silicon substrate. The new substrate is found to provide upto 11 times increase in signal in comparison to the inverted pyramid (IV-pyramid) arrays fabricated on an identical plastic substrate. Numerical simulation and experimental evidence suggest that strongly confined electromagnetic fields close to the base of the pyramids, are mainly responsible for the Raman enhancement factor, instead of the fields localized around the tip. Unusually strong plasmon fields are projected upto 200nm from the sidewalls at the base of the pyramid increasing the cross sectional sensing volume.

3D analysis of surface plasmon dispersion for SERS sensor based on inverted pyramid nanostructures

Surface enhanced Raman scattering (SERS) can be used to amplify the Raman cross-section of signals by several orders of magnitude, when a mixed photon-Plasmon mode (surface Plasmon polaritons) couples to molecules on a nano textured metallo-dielectric substrate. In this paper we demonstrate a comprehensive 3D computational model based on Rigorous coupled wave analysis (RCWA) for the purpose of analysing propagating and localised surface Plasmon polaritons supported by planar SERS substrates based on periodic array of metal coated inverted pyramidal nanostructures. Although studies [1, 2] have explored the optical properties of inverted square pyramidal pits using simulation and experimentation, there has yet been no investigation performed on rectangular inverted pyramidal pits. Here we perform 3D modelling and simulation on rectangular pit arrays with aspect ratio 1:1.2 over 400nm thick gold. We investigate the effect of incident polarisation and electric-field density within the pits and show that inverted rectangular pyramidal pit array can be used as highly effective SERS and Plasmonic substrates.

Experimental measurement of photonic/plasmonic crystal dispersion, applied to the investigation of surface plasmon dispersion for SERS sensing applications

In this paper we describe an experimental measurement procedure and automated system for analysis of angle dependent dispersion associated with dielectric photonic crystals or surface Plasmon polariton dispersion associated with nanostructured metallo-dielectric surfaces. This fully automated system utilizes a broadband spectroscopic reflectometry method to acquire polarization resolved data. Angular dispersion is mapped by illuminating a sample with a white light laser ranging from 450nm to 1800nm. A movable fiber probe then collects the reflected signal. Dips in reflectivity then correspond to partially coupled Bloch modes. The measurement system was applied to the investigation of Plasmon dispersion of periodic arrays of metal coated square pyramids SERS sensors. Comparisons are then made to computational simulations derived using RSOFT DiffractMOD based on Rigorous Coupled Wave Analysis (RCWA). Measured experimental dispersion patterns are found to closely match simulation in the exact frame of wavelength (400nm to 900nm).

Low-Loss Slot Waveguides with Silicon (111) Surfaces Realized Using Anisotropic Wet Etching

We demonstrate low-loss slot waveguides on silicon-on-insulator (SOI) platform. Waveguides oriented along the (11-2) direction on the Si (110) plane were first fabricated by a standard e-beam lithography and dry etching process. A TMAH based anisotropic wet etching technique was then used to remove any residual side wall roughness. Using this fabrication technique propagation loss as low as 3.7dB/cm was realized in silicon slot waveguide for wavelengths near 1550nm. We also realized low propagation loss of 1dB/cm for silicon strip waveguides.

A nanoporous gold membrane for sensing applications

Design and fabrication of three-dimensionally structured, gold membranes containing hexagonally close-packed microcavities with nanopores in the base, are described. Our aim is to create a nanoporous structure with localized enhancement of the fluorescence or Raman scattering at, and in the nanopore when excited with light of approximately 600 nm, with a view to provide sensitive detection of biomolecules. A range of geometries of the nanopore integrated into hexagonally close-packed assemblies of gold micro-cavities was first evaluated theoretically. The optimal size and shape of the nanopore in a single microcavity were then considered to provide the highest localized plasmon enhancement (of fluorescence or Raman scattering) at the very center of the nanopore for a bioanalyte traversing through. The optimized design was established to be a 1200 nm diameter cavity of 600 nm depth with a 50 nm square nanopore with rounded corners in the base. A gold 3D-structured membrane containing these sized microcavities with the integrated nanopore was successfully fabricated and ‘proof of concept’ Raman scattering experiments are described.

Design and fabrication of a 3D-structured gold film with nanopores for local electric field enhancement in the pore.

Three-dimensionally structured gold membrane films with nanopores of defined, periodic geometries are designed and fabricated to provide the spatially localised enhancement of electric fields by manipulation of the plasmons inside nanopores. Square nanopores of different size and orientation relative to the pyramid are considered for films in aqueous and air environments, which allow for control of the position of electric fields within the structure. Designs suitable for use with 780 nm light were created. Here, periodic pyramidal cavities produced by potassium hydroxide etching to the {111} planes of (100) silicon substrates are used as templates for creating a periodic, pyramidal structured, free-standing thin gold film. Consistent with the findings from the theoretical studies, a nano-sized hole of 50 nm square was milled through the gold film at a specific location in the cavity to provide electric field control which can subsequently used for enhancement of fluorescence or Raman scattering of molecules in the nanopore.

Laser annealing of low temperature deposited silicon waveguides

We report the fabrication of low temperature deposited polysilicon waveguides using a laser annealing process. Micro-Raman and XRD measurements reveal the quasi-single crystal-like quality of the material, which exhibits low optical losses of 5.13 dB/cm.

Laser annealed low temperature deposited polysilicon waveguides for nonlinear photonics

The intrinsic properties of silicon (Si) make it an excellent material for integrated photonics devices with small footprints [1]. To date, most of the reported devices have been based on crystalline silicon (c-Si), but this material suffers from difficult integration with electronic layers due to fabrication constraints. Subsequently, there has been growing interest in alternative forms of Si, such as hydrogenated amorphous silicon (a-Si:H), silicon nitride (SiN) and polysilicon (poly-Si) [2]. Among these materials, only poly-Si has the potential to exhibit both optical and electronic properties that are equivalent to c-Si. However, to achieve good material quality, poly-Si is typically deposited at temperatures higher than 900°C, rendering it incompatible with most CMOS fabrication processes. Thus there is a growing drive to develop new techniques to deposit poly-Si at low temperatures (<450°C) [2], but so far the optical losses in these materials have been high, limiting its use in all-optical systems employing nonlinear optical processing. In this work, we report the fabrication and characterisation of laser annealed, low temperature deposited silicon waveguides with low optical losses. Our results represent the first demonstration of nonlinear propagation in a poly-Si waveguide suitable for integration.

Laser writing of polycrystalline Si ridge waveguides

Polycrystalline silicon (poly-Si) has attracted significant interest in the area of silicon photonics because of its potential for combining good optical transmission, electronic functionality and low fabrication cost, which makes it an attractive material for commercial applications [1]. In addition, it was shown recently that by laser processing of amorphous Si (a-Si) it is possible to obtain very large grain poly-Si [2] resulting in a material with superior optical and electronic performance.

Raw data for paper 2D Photonic Crystal Structures in Silicon Rich Nitride Platform

The excel file contains experimental data for the paper “2D Photonic Crystal Structures in Silicon Rich Nitride Platform”. In particular: Figure 1b: Measured transmission and the trend in transmission of a 400 μm long W0.7 PhC waveguides in a hexagonal photonic crystal of air holes in a silicon rich nitride substrate for lattice period of a = 580 nm and r = 0.3a. Figure 2b: Measured RS intensity from a PhC cavity in a hexagonal photonic crystal of air holes in a silicon rich nitride substrate for lattice period of a = 570 nm and r = 0.3a.