This paper shows that an introduction of thiosulfate anions in place of bromide anions greatly improves both chemical and thermal stability of tetraoctylammonium-protected gold nanoparticles. Tetraoctylammonium thiosulfate [(Oct)4N+-O3SS]-protected gold nanoparticles are synthesized by the reduction of (Oct)4N+-AuCl4 to Au(I)-SSO3-, followed by the addition of sodium borohydride. The presence of thiosulfate anions instead of bromide anions on the surface of gold nanoparticles results in a significant dampening of the surface plasmon band of gold at 526 nm due to the strong interaction between thiosulfate and the gold nanoparticle surface. Cyanide decomposition and heating treatment studies suggest that (Oct)4N+-O3SS-protected nanoparticles have much higher overall stability compared to (Oct)4N+-Br-protected gold nanoparticles.
Sum
frequency generation (SFG) images of microcontact patterned
self-assembled alkanethiol monolayers on metal surfaces were analyzed
by factor analysis (FA) to determine the spatial distribution of the
patterned monolayers over the images. Additionally, each significant
abstract factor produced by FA was assessed to determine the information
contained within it. These results indicate that FA of the SFG spectra
is a promising method to determine the composition and identities
of mixed alkanethiol systems that show different vibrational spectra
and image contrast. Factor analysis has successfully been applied
to SFG images obtained with low signals, which reduces the time required
for full spectral SFG imaging.
We have successfully utilized the newly developed near-infrared multispectral imaging (NIR-MSI) microscope to observe and measure directly the localized surface plasmon absorption (LSPR) of individual gold nanoshells. The NIR-MSI is suited for this task because it can simultaneously record spectral and spatial information of a sample with high sensitivity (single pixel resolution) and high spatial resolution (approximately 0.9 microm/pixel). Importantly, the LSPR of individual nanoshells measured by the NIR-MSI microscope agrees well with the spectra calculated theoretically using Mie scattering for the nanoshells (i.e., nanoshells with silica cores approximately 800 nm in diameter and gold shell thicknesses of approximately 35 nm). Additionally, the NIR-MSI microscope enables measurement of LSPR at different positions within a single nanoshell. LSPR spectra were found to be distinct at various positions within a single nanoshell. Since LSPR spectra are known to depend on the shape and morphology of the nanoshells, these results seem to suggest that the individual nanoshells are not smooth and well-defined, but are rather rough and inhomogeneous. The LSPR spectra of single nanoshells in several different solvents were also examined using NIR-MSI and were found to depend on the dielectric constant of the medium. However, the relationship was discovered to be more complex than simply following the Drude equation. Specifically, when (lambda(max)/fwhm)(2) values of LSPR for single gold nanoshells were plotted as a function of 2n(2) (or 2epsilon) for nanoshells in six different solvents, a linear relationship was found for only three solvents: D(2)O, acetonitrile-d(3), and ethyl acetate. Acetone-d(6) showed a slight deviation, whereas formamide and pyridine-d(5) exhibited distinctly different correlations.
Although the current array of nanomachines mostly comprises simple devices (at least from a mechanical viewpoint), the underlying physical and chemical interactions that play key roles in the 'assembly' of these machines have required decades of research to ascertain a fundamental understanding of how such processes can be manipulated at the nanoscale. In this review, we wish to convey a realistic picture of the current developments in the design and implementation of nanomachines, with an emphasis on how these developments are leading to practical applications in medicine, including a sense of how such simple devices are rapidly becoming the building blocks for assembling the nanorobots of tomorrow.
ABSTRACT(Co/Pd)N multilayers with Co and Pd layer thicknesses of only a few monolayers exhibit high vertical magnetic anisotropy and have been extensively explored as recording medium candidates for high density magnetic recording applications. In the work reported here, the magnetic properties of (Co/Pd)N multilayers deposited by magnetron sputtering and designed for bit-patterned medium applications are correlated with X-Ray Photoelectron Spectroscopy (XPS) data – an approach commonly used to probe the binding energies and valence band positions. Although the XPS probing depth is limited to ˜2–3 nm, it is sufficient for the evaluation of the 1–2 topmost bilayers in a multilayer stack, and allows us to infer the relevant details of the bandstructure of the entire film. Confirming theoretical predictions, we demonstrate that the degree of d-shell hybridization at Co/Pd interfaces directly correlates with the magnitude of the magnetic anisotropy. Significantly, the highest hybridization of Pd atoms is observed for about one monolayer thick Co layers in the bilayer stack. Variation of the deposition conditions (e.g., deposition pressure) shows a measurable influence on d-electron hybridization, multilayer microstructure, and magnetic anisotropy.
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