In this paper, we describe a method for the growth of gold nanowires and nanoplates starting from a bilayer array of gold seeds, anchored on electrically conducting indium tin oxide (ITO) substrates. This is based on a seed-mediated growth approach, where the nanoparticles attached on the substrate through molecular linkages are converted to nanowires and nanoplates at certain cetyltrimethylammonium bromide (CTAB) concentration. Our modified approach can be used to make nanowires of several tens of micrometers length at a lower CTAB concentration of 0.1 M. The length of the nanowires can be varied by adjusting the time of the reaction. As the concentration of CTAB was increased to 0.25 M, the nanoparticles got converted to nanoplates. These Au nanoplates are (111) oriented and are aligned parallel to the substrate. © Indian Academy of Sciences.

Pradeep Thalappil

Department Of Chemistry

Panikkanvalappil Ravindranathan Sajanlal

ANISOTROPIC GOLD NANOSTRUCTURES

INDIUM TIN OXIDE (ITO) SUBSTRATES

nanoplates

SEED-MEDIATED GROWTH

Anisotropy

Concentration (process)

Conductive materials

growth rate

Substrates

Nanowires

Fulltext

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 Chemical Sciences

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 comparative study of the surface-enhanced Raman scattering (SERS) effect of the spherical gold nanoparticles (NPs) and highly uniform and oriented gold nanotriangles (NTs), anchored on indium tin oxide (ITO) coated conducting glass surfaces is reported. Contact and non-contact mode atomic force microscopic (AFM) analyses confirmed that all the triangles observed are equilateral and uniformly stacked. The NTs-coated ITO exhibited intense near-infrared (NIR) absorption and showed an extremely strong SERS activity than the spherical NPs. The NTs showed a very good SERS enhancement factor on the order of 4 × 10 8. The results are interpreted in terms of the increased density of hot spots on the NTs-coated surface. © 2009 American Scientific Publishers.

Journal of Nanoscience and Nanotechnology

Electric field assisted growth of highly surface enhanced Raman active gold nanotriangles

International Conference on Advanced Nanomaterials & Emerging Engineering Technologies

Growth and study of gold microplates for electrodes application

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 report the shape transformation of gold nanorods to spherical nanoparticles, assisted by cupric ions. The reaction proceeds through a series of structures and could be arrested at any stage to produce particles of desired shape. In the presence of a larger concentration of cetyltrimethylammonium bromide (CTAB), selective etching of the tips of the nanorods occurs to a greater extent. The subsequent transformation is driven by the surface reconstruction of nanorods to generate more stable surfaces. As the stability of various surfaces depends on the protecting agent used, the reactivity is modified by controlling its presence at the surface. We show that the body of the rods is more susceptible for reaction at reduced CTAB concentrations. During the conversion to particles, several anisotropic transient structures were observed and were imaged using high-resolution transmission electron microscopy (HRTEM). The transformation occurs due to the hydroxyl radicals produced by Cu21 in the presence of ascorbic acid (AA). A mechanism has been proposed and several control experiments were conducted to test it. The cupric ion induced shape transformations can be extended to other ions, and knowing the mechanism allows the control of the process to stabilize various anisotropic structures. © 2007 American Chemical Society.

Langmuir

Body- or tip-controlled reactivity of gold nanorods and their conversion to particles through other anisotropic structures

We observe the transverse electrokinetic effect (TEK), namely, the generation of a transverse potential difference due to the flow of liquids over a surface on which self-assembled arrays of metallic nanoparticles are immobilized. This paper covers the recent experimental findings and improvements to the theoretical model described in ref 1 [Subramaniam, C.; Pradeep, T.; Chakrabarti, J. Phys. Rev. Lett. 2005, 95, 0164501], leading to a better understanding of the phenomenon. Issues critical for the comprehension and applicability of this effect as a potential flow sensor such as the need for a critical dipole moment, optimum surface coverage, nature of the flow rate dependence, and generalization of the phenomenon for several metallic nanostructures have been addressed in detail from both experimental and theoretical perspectives. This complete work stresses the uniqueness of this new phenomenon which could find applications in emerging areas of science, like microfluidics. © 2007 American Chemical Society.

Journal of Physical Chemistry C

Transverse electrokinetic effect: Experiments and theory

Hexagonal patterns of gold nanorods were made by assembling gold nanorod-coated poly(N-isopropyl acrylamide) microgels. The required population of nanorods on the microgels was achieved by attaching nanoparticle seeds on the latter and growing them to nanorods. The various materials prepared were characterized by UV-vis spectroscopy and transmission electron microscopy. Similar experiments with nanoparticle-coated or prefabricated nanorod-coated microgels did not give such hexagonal patterns. We suggest that the interlocking of nanorods leads to these regular structures. This is the first report of a solution phase method for assembling nanorods into a hexagonal pattern. © 2007 American Chemical Society.

Gold nanorods grown on microgels leading to hexagonal nanostructures

We report the generation of a potential difference, of the order of tens of millivolts, induced by the flow of polar liquids over an assembly of gold nanoparticles. The device consisted of two conducting glass plates, one of which contained the gold nanoparticle multilayer assembly. The potential generated is in transverse direction to the flow and is dependent on the nature of the flowing liquid. We propose a simple theoretical model to account qualitatively for the generation of the flow-induced transverse potential. © 2005 The American Physical Society.

Journal	Journal of Chemical Sciences
ISSN	02534134
Open Access	No