Synthesis of oxocarbon-encapsulated gold nanoparticles with blue-shifted localized surface plasmon resonance by pulsed laser ablation in water with CO2 absorbers.

Colloidal suspensions of oxocarbon-encapsulated gold nanoparticles have been synthesized in a one-step procedure by pulsed-laser ablation (PLA) at 532 nm of a solid gold target placed in aqueous solution containing CO2 absorbers, but without any stabilizing agent. Multi-wavelength surface enhanced Raman spectroscopy allows the identification of adsorbed amorphous carbon and graphite, Au-carbonyl, Au coordinated CO2-derived bicarbonates/carbonates and hydroxyl groups around the AuNPs core. Scanning electron microscopy, energy dispersive x-ray analysis and high resolution transmission electron microscopy highlight the organic shell structure around the crystalline metal core. The stability of the colloidal solution of nanocomposites (NCs) seems to be driven by solvation forces and is achieved only in neutral or basic pH using monovalent hydroxide counter-ions (NaOH, KOH). The NCs are characterized by a blue shift of the localized surface plasmon resonance (LSPR) band typical of metal-ligand stabilization by terminal π-back bonding, attributed to a core charging effect caused by Au-carbonyls. Total organic carbon measurements detect the final content of organic carbon in the colloidal solution of NCs that is about six times higher than the value of the water solution used to perform PLA. The colloidal dispersions of NCs are stable for months and are applied as analytical probes in amino glycoside antibiotic LSPR based sensing.

Accurate and simultaneous measurement of thickness and refractive index of thermally evaporated thin organic films by surface plasmon resonance spectroscopy.

We demonstrate that Surface Plasmon Resonance spectroscopy can be used for the accurate and simultaneous determination of the thickness and refractive index of transparent thin thermally deposited organic films. The experimental approach is based on a two-metal deposition or a two-thickness method. These methods have been applied to an encapsulated sample containing a thin film of commercial tris(8-hydroxyquinoline) (Alq3). The accuracy of the measurement depends on the control of the film deposition process and suggests the use of SPR spectroscopy as inexpensive and valuable metrology tool for small molecule organic thin films.