The local electric field enhancement at various regions of an individual nanometre-thin gold mesotriangle has been demonstrated both numerically and experimentally. This work provides, for the first time, direct experimental evidence of localized enhancement of Raman signals at three edges of nanometre-thin gold mesotriangles at single particle level, using Raman microscopy. Raman images were collected from mesotriangles of ∼11 μm edge length and ∼30 nm thickness, using adsorbed crystal violet as the probe molecule. Spatial distribution and the extent of electric field enhancement around a single mesotriangle are investigated theoretically by finite-difference time-domain (FDTD) simulations. Confocal Raman studies provided direct proof for the substantial electrical field enhancement at the edges and corners compared to the face of the mesotriangle. The simulated electric field enhancement was in the order, corner > edge > surface, which is in complete agreement with the experimental results. © 2010 The Royal Society of Chemistry.

Pradeep Thalappil

Department Of Chemistry

Panikkanvalappil Ravindranathan Sajanlal

Confocal Raman

Crystal violet

Edge length

Electric field enhancement

Electrical field

Experimental evidence

FINITE-DIFFERENCE TIME-DOMAIN SIMULATION

Local electric field

NANOMETRES

Probe molecules

RAMAN IMAGES

Raman microscopy

RAMAN SIGNAL

Single particle

spatial distribution

SPECTRAL EFFECTS

ELECTRIC FIELD MEASUREMENT

finite difference time domain method

Gold

Raman spectroscopy

Electric fields

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Journal of Materials Chemistry

We present the synthesis of highly anisotropic nickel nanowires (NWs) and large area, free-standing carpets extending over cm 2 area by simple solution phase chemistry. The materials can be post-synthetically manipulated to produce hybrid tubes, wires, and carpets by galvanic exchange reactions with Au 3+, Ag +, Pt 2+, and Pd 2+. All of these structures, especially the hybrid carpets and tubes, have been prepared in bulk and are surface enhanced Raman scattering (SERS) active substrates. Molecules of relevance such as dipicolinic acid (constituting 5-15% of the dry weight of bacterial spores of Bacillus anthracis), dinitrotoluene, hexahydro-1,3,5-triazine (RDX), and trinitrotoluene at nanomolar concentrations have been detected. An enhancement factor of ∼10 10 was observed for the Ni-Au nanocarpet. The reusability of the Ni-Au nanocarpet for SERS applications was tested 5 times without affecting the sensitivity. The reusability and sensitivity over large area have been demonstrated by Raman microscopy. Our method provides an easy and cost effective way to produce recyclable, large area, SERS active substrates with high sensitivity and reproducibility which can overcome the limitation of one-time use of traditional SERS substrates. © 2012 The Royal Society of Chemistry.

Nanoscale

Functional hybrid nickel nanostructures as recyclable SERS substrates: Detection of explosives and biowarfare agents

Five natural faceted diamond samples, considered to have inherent submicroscopic and nanometric inclusions, were studied using various techniques such as Raman spectroscopy, Raman microscopy, scanning electron microscopy (SEM), and energy dispersive analysis of X-rays (EDAX). The principal focus was to find out the chemical nature of the inclusions and their distribution. As a confirmative tool, laser desorption ionization mass spectrometry (LDI MS) was used for the characterization of the inclusions. Our study suggests that the inclusions in diamond belong to the pyroxene group of silicate minerals with Fe, Mg, Ca, Ru, and Cr as the major elements. As evidenced by the absence of alkali, aluminum, and rare earth elements in the inclusion, the diamond can be of peridotitic origin. Interestingly, we found that chromium scavenges Ru, a platinum group element (PGE), and other metals such as Nb, Co, and Ni, entrained into the pyroxene inclusions. We established that the diamond sample in which inclusions are found is of Kimberlitic origin. © 2011 Elsevier B.V. All rights reserved.

Diamond and Related Materials

Nano and sub-micro inclusions as probes into the origin and history of natural diamonds

This article describes the high yield synthesis of a range of anisotropic gold mesostructures such as flowers, cubes, plates, and quasispherical mesostructures using a seed-mediated approach. These structures were formed from precursor seed nanoparticles of gold stabilized by the template, 1,2-phenylenediamine (1,2-PDA). We demonstrated that control of the morphologies from mesoflowers to quasispherical structures is possible with the molecular precursors used in the synthesis of seeds. It was found that concentration of the template, 1,2-PDA added during seed preparation played an important role in the conversion of mesoflowers to quasispherical and cube-like structures. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV-vis spectroscopy and energy dispersive analysis of X-rays (EDAX) were used for the determination of physical and chemical composition of the nano/mesostructures formed. The seed nanoparticles responsible for the formation of these various anisotropic structures were further characterized and analyzed using laser desorption ionization mass spectrometry (LDI MS) and TEM. We demonstrated high surface-enhanced resonance Raman scattering (SERRS) activity of the mesoflowers using crystal violet (CV) as the analyte molecule. The shape-dependent SERRS activity of various meso/nanostructures was also studied. A ∼0.8×102 decrease in the SERRS intensity was observed in quasispherical structures compared to mesoflowers. The increased SERRS activity is attributed to the unique shape and nanofeatures present on the mesoflowers, which were absent in the quasispherical mesostructures. We believe that the high SERRS activity exhibited by the mesoflowers may be utilized for developing novel sensors. © 2009 Elsevier B.V. All rights reserved.

Journal of Crystal Growth

Molecular precursor-mediated tuning of gold mesostructures: Synthesis and SERRS studies

A reply to the comments by Diao and coworkers on electric-field-assisted growth of highly uniform and oriented gold nanotriangles on conducting glass substrates, is presented. The authors say that SEM, AFM, and optical images are presented, which suggest that nanotriangles (NTs) are indeed formed. In order to confirm the formation of the NTs, samples were imaged using dynamic force microscopy (DFM), and the results were confirmed for both the parent and the NT surfaces. The non-contact-mode topographic and phase AFM images of NTs that were synthesized under optimized condition showed that most of the NTs observed had an edge length of 400-450 nm. In the UV-vis absorption spectra, the feature at 520nm can be attributed to the transverse plasmon absorption, as is the case for other anisotropic structures. The authors are convinced that the results indicate the electric-field-assisted formation of NTs and were not caused by artifacts of AFM.

Advanced Materials

Reply to "Comments on electric-field-assisted growth of highly uniform and oriented gold nanotriangles on conducting glass substrates"

We developed a cheap and rapid method for the fabrication of 3D nanoparticle superlattices (SLs) of Au@SGAN and Au@MSA (N-acetyl glutathione (SGAN) and mercaptosuccinic acid (MSA) protected gold nanoparticles, respectively) in gram scale, at a liquid-liquid interfaces under flowing nitrogen gas. While available methods take several weeks to make crystalline SLs, the present route makes them in a day. Morphology of these crystals was examined with scanning electron microscopy (SEM), and their structures were probed using transmission electron microscopy (TEM). The surface enhanced Raman scattering (SERS) studies of these crystals were done using crystal violet (CV) molecules as the analyte which exhibited a detection limit of 10-8 M. The SERS spectrum was used to map the Raman images of the superlattce crystals. SERS from the edges of the crystal showed more enhancement than from the flat surfaces, which is in good agreement with theoretical reports of such anisotropic structures. The sides of the crystals are not sharp, and they show corrugations at the nanometer scale. This helps to produce more "hot spots" at the edges, which result in larger electric field enhancement from these locations. The enhancement factors (EF) for Au@MSA and Au@SGAN SLs were calculated to be around 1.47 x 106 and 3.60 x 105, respectively. More enhancements from Au@MSA SL compared to that of Au@SGAN could be attributed to the smaller chain length of the MSA molecule, which allows closer analyte approach to the nanoparticle surface. © 2009 American Chemical Society.

Chemistry of Materials

Gold nanoparticle superlattices: Novel surface enhanced raman scattering active substrates

Applied Physics Letters

Single gold nanostars enhance Raman scattering

Nano Letters

Optical Near-Field Mapping of Plasmonic Nanoprisms

Electric field enhancement and concomitant Raman spectral effects at the edges of a nanometre-thin gold mesotriangle

Journal	Journal of Materials Chemistry
ISSN	09599428
Open Access	No