ABSTRACT
A method for the surfactant-free coating of gold nanoparticles with thiols using sonochemistry is presented. The gold nanoparticles were prepared by a modified Zsigmondy method, affording good control over the particle-size distribution, and the thiol coating was performed by the sonication of a biphasic system consisting of a nanoparticle suspension in water and thiols in toluene. The effects of two important reaction parameters on the particle morphology, viz. sonication time and thiol concentration, were investigated in detail using transmission electron microscopy. The effect of the thiol chain length was also studied. We show that the morphology of the coated particles is determined through a competition between two opposing effects: particle fusion, due to the sonication conditions, and digestive ripening, due to the action of the thiols. Additionally, we illustrate the utility of our technique for various applications, including surface-enhanced Raman scattering from bound molecules, and further functionalization using a thiol-exchange reaction. Our technique paves the way for an efficient synthesis of thiol-coated AuNPs of different shapes and sizes, suitable for a range of diverse applications.
Subject(s)
Gold/chemistry , Metal Nanoparticles/chemistry , Metal Nanoparticles/radiation effects , Microtechnology/methods , Sulfhydryl Compounds/chemistry , Sulfhydryl Compounds/radiation effects , Ultrasonics/methods , Borohydrides , Indicators and Reagents , Particle Size , Spectrophotometry, Ultraviolet , Spectrum Analysis, RamanABSTRACT
The remarkable optical properties of metal nanoparticles are governed by the excitation of localized surface plasmon resonances (LSPRs). The sensitivity of each LSPR mode, whose spatial distribution and resonant energy depend on the nanoparticle structure, composition and environment, has given rise to many potential photonic, optoelectronic, catalytic, photovoltaic, and gas- and bio-sensing applications. However, the precise interplay between the three-dimensional (3D) nanoparticle structure and the LSPRs is not always fully understood and a spectrally sensitive 3D imaging technique is needed to visualize the excitation on the nanometre scale. Here we show that 3D images related to LSPRs of an individual silver nanocube can be reconstructed through the application of electron energy-loss spectrum imaging, mapping the excitation across a range of orientations, with a novel combination of non-negative matrix factorization, compressed sensing and electron tomography. Our results extend the idea of substrate-mediated hybridization of dipolar and quadrupolar modes predicted by theory, simulations, and electron and optical spectroscopy, and provide experimental evidence of higher-energy mode hybridization. This work represents an advance both in the understanding of the optical response of noble-metal nanoparticles and in the probing, analysis and visualization of LSPRs.
ABSTRACT
The straight-forward synthesis of Janus nanoparticles composed of Ag and AgBr is reported. For their formation, cucurbit[n]uril (CB)-stabilized AgBr nanoparticles are first generated in water by precipitation. Subsequent irradiation with an electron beam transforms a fraction of each AgBr nanoparticle into Ag(0) , leading to well-defined Janus particles, stabilized by the binding of CB to the surface of both AgBr and Ag(0) . With the silver ion reduction being triggered by the electron beam, the progress of the transformation can be directly monitored with a transmission electron microscope.
ABSTRACT
We present an electron energy loss study using energy filtered TEM of spatially resolved surface plasmon excitations on a silver nanorod of aspect ratio 14.2 resting on a 30 nm thick silicon nitride membrane. Our results show that the excitation is quantized as resonant modes whose intensity maxima vary along the nanorod's length and whose wavelength becomes compressed towards the ends of the nanorod. Theoretical calculations modelling the surface plasmon response of the silver nanorod-silicon nitride system show the importance of including retardation and substrate effects in order to describe accurately the energy dispersion of the resonant modes.
