Sensing technologies based on metallic nanoparticles, known as Ag, Au, and so on, have raised enormous interest for their extraordinary sensing resolution and sensitivity to analytes of chemical or biological importance under optical detection have received wide attention in recent decades. Currently, a discrete nanoparticle in a free-standing form, either being organically or biologically modified on the nanoparticle surface, on a given substrate surface region has been employed for photosensing purpose. However, metallic nanoparticles suffering from physical and chemical instability such as oxidation, interparticle coupling, agglomeration, and so on during the processing stages may render undesirable outcomes, which further results in poorer performance than the theoretical expectation. Here we propose a facile and elegant concept to prepare an Ag-decorated silica nanoparticle (hereinafter termed core-shell SiO 2 @Ag nanosphere) based on the modified Sto ¨ber method. The Ag nanoparticles with an average size controlled at about 1, 3, and 5 nm deposited over the surface of the silica nanocarrier were well separated, making the resulting SiO 2 @Ag nanospheres. The nanospheres showed physically and optically stable surface plasmon resonance spectra and also demonstrated a relatively high Ag-sized dependent sensitivity to ppb level for the detection of analyte molecule, that is, melamine. Theoretical model fitting has been well managed to correlate the optical behavior of the nanosensors, and the outcomes strongly indicated a promising potential of the Ag-decorated SiO 2 core-shell nanospheres for sensory applications.

Electrical conductivities of various mullite/zirconia composites, as well as monolithic mullite and zirconia, were measured using AC impedance spectroscopy from 100 Hz to 10 MHz at temperatures ranging from 150 to 1300 °C. The impedance spectra of monolithic zirconia and mullite/zirconia composites showed two semicircles because of the contributions from grains and grain boundaries, while those of monolithic mullite had one semicircle due to the predominant contribution from grains. This indicates that the conductivities of the mullite/zirconia composites increased with zirconia content. The activation energies of electrical conduction in mullite and zirconia were about 65 and 79 kJ/mol, respectively, and those of mullite/zirconia composites were between 65 and 79 kJ/mol. While the conductivities of various composites at 1 MHz were fitted by Lichtenecker’s rule, the general mixing equation could be applied to the conductivities measured at 1 kHz.

We discovered a promising sensing capability of SiO2@Ag core-satellite nanoparticles with respect to organic melamine when they were consolidated into a solid-type thin-film entity. A series of theoretical models were proposed which provided calculation outcomes superior to those of existing models for the localized surface plasmon resonance spectra of the solid-state assemblies. We envisioned not only that such a SiO2@Ag film is a potential candidate for a transparent solid-state optical nanosensor for the detection of organic molecules but also that the resulting plasmonic resonance model facilitates a better understanding of such a solid-state nanosensor used for a number of sensory applications.

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Impedance spectroscopy technique was employed to characterize the LixZn1-xO2 (x=0.001~0.008) polycrystalline thin film. IS is shown to be an efficient method capable of detecting the contributions of the resistances of grains and grain boundaries resistance to the complex impedance of a compound, accurately estimating its electrical conductivity as well as its corresponding activation energies and conclude on its structural properties. This is demonstrated for the case of lithium segregation in the grain/grain boundary of LixZn1-xO2., we found that the activation energy decrease associated with grain-boundary conductivity reflects the onset of the segregation of excessive Li in the grain boundaries when the Li-content exceeds 0.5 mol%. For Li-content below 0.5mol% is the detection of a transition from p-type conductivity. It might be due to that the Li+ doped mainly in grains and no precipitation observed on the grain boundaries. So we could be process stable p type thin film for Li content below 0.5mol%.