Small aromatic organothiol derivatives, with the structure HS±C 6 H 4 ±X, have been used to stabilise gold nanoparticles. The nature of the functional group, X, is important for controlling the relative strength of the particle±particle and particle±solvent interactions and hence in determining the physical properties of these systems (e.g. solubility). Particles were stabilised with different ligands for which X~OH, ±COOH, ±NH 2 , and ±CH 3 and thin ®lms of the particles were formed, by solution evaporation, on microelectrode patterned surfaces. The electronic behaviour indicates that conduction can be understood in terms of an activated electron tunnelling model. Finally, preliminary studies were carried out on the effect of exposure to different chemical vapours on the electronic transport properties.

The electrical and optical response of thin films of surface functionalized nanoparticles upon exposure to various chemical vapours has been studied. It was found that the electrical response to chemical vapours adsorbed on the various nanoparticle films varied markedly and was determined by the surface functional groups. Ellipsometric studies revealed that the film thickness increased during exposure to the chemical vapours. These thickness changes of the films correlate with the changes in electrical conductivity. Two physical effects are believed to play a role in determining these conductivity changes. Under high partial pressure, the change in nanoparticle core-core separation is the main contribution to the change in conductivity and generally leads to a reduction in the conductivity. However, for relatively low partial pressures the adsorption of vapour molecules leads to permittivity changes that tend to increase the conductivity.

The application of three-dimensional (3D) plasmonic nanostructures as metamaterials (MMs), nano-antennas, and other devices faces challenges in producing metallic nanostructures with easily definable orientations, sophisticated shapes, and smooth surfaces that are operational in the optical regime and beyond. Here, we demonstrate that complex 3D nanostructures can be readily achieved with focused-ion-beam irradiation-induced folding and examine the optical characteristics of plasmonic ''nanograter'' structures that are composed of free-standing Au films. These 3D nanostructures exhibit interesting 3D hybridization in current flows and exhibit unusual and well-scalable Fano resonances at wavelengths ranging from 1.6 to 6.4 mm. Upon the introduction of liquids of various refractive indices to the structures, a strong dependence of the Fano resonance is observed, with spectral sensitivities of 1400 nm and 2040 nm per refractive index unit under figures of merit of 35.0 and 12.5, respectively, for low-order and high-order resonance in the near-infrared region. This work indicates the exciting, increasing relevance of similarly constructed 3D free-standing nanostructures in the research and development of photonics and MMs.

A series of gold nanoparticles stabilized by the adsorption of heterocyclic mercaptan derivatives, including 2-mercaptopyridine (2MPy), 2-mercaptopyrimidine (2MPm) and 4-mercaptopyridine (4MPy), were synthesized and characterized by TEM, FTIR, UV-vis, and XPS. The adsorption of 2MPy molecules led to the most stable and uniform nanoparticles. In contrast, the 4MPy-coated nanoparticles showed a strong tendency to form 3D aggregates, which is attributed to cross linking between sulfur groups on neighboring particles. FTIR and UV-vis spectroscopy were employed to study the chemical conformation of the heterocyclic molecules on the gold surface. Significant differences between the IR spectra of the functionalized nanoparticles and the free mercaptan molecules were observed. Interpretations of these IR spectra were achieved with the aid of ab initio calculations. We found that the "thione form" is predominant when the molecules are either in a polycrystalline state or in methanol solution; however, they are stabilized in the "thiol-like form" when adsorbed on the particles. The XPS spectra of the 2MPy nanoparticles showed narrow peaks with the expected peak position. In contrast, the peaks in the spectra of the 2MPm-and 4MPy-passivated nanoparticles were strongly shifted. Oxidization of the sulfur group was detected in the 4MPy-modified nanoparticles, indicating that some molecules were adsorbed onto the gold surface via their nitrogen groups.