No abstract

We report on the development of efficient infrared-active core-shell Er2O3-Si nanoparticle architecture. Sub 3-nm H-terminated Si nanoparticles are used to reduce/deposit Er3+ ions on the nanoparticles, which in an aqueous environment simultaneously oxidize to produce the core-shells. Our results show strong cathodoluminance at 1543 nm while being able to resolve the Stark splitting. The strong luminescence afforded by the core-shell architecture in which the Si-Er interspacing drops appreciably supports a sensitive interspacing-dependent dipole-dipole energy transfer interaction model, while the hydrogenated silicon-core allows increased loading and reduced segregation of Er as in amorphous silicon material. The room temperature-wet procedure, with pre-prepared and -sorted Si nanostructures affords promising applications in electronic and optical technologies.

We report on a wet none thermal integration of the binary silicon-gold nano system. Instead of thermally based gas-solid procedures, we use charge exchange/injection-based procedures in a chemical wet environment. SEM and TEM imaging and EDX show 0-D gold-silicon coreshell structures with diameters ranging from 6 to 500 nm in addition to a variety of silicon and gold nano structures. Optical and florescence spectroscopy show that colloids exhibit strong red luminescence and plasmonic resonance in the visible. Mie theory analysis of light scattering is in agreement with the optical observation. The results and procedures are discussed in terms of the relative electron/hole affinity, Schottky potential barrier, strength of the metal-silicon bond, as well as the surface diffusion of metal atoms or clusters on the interface of the constituent materials. Integration of gold and silicon, at the nanoscale in the form core-shell architecture affords the functionalities and attributes of plasmonic light scattering imaging and fluorescence imaging that would be useful for a wide variety of applications, including optical filters, sensing, therapeutics and tracking, and cancer therapy.

We use wet treatment to integrate red-luminescent Si nanoparticles with Mg-based wide-bandgap insulators Mg(OH) and MgO (5.7 and 7.3 eV respectively). In the process, Mg2+ is reduced on Si nanoparticle clusters, while suffering combustion in water, producing a spatially inhomogeneous Mg(OH)2/MgO-Si nanoparticle composite with an inner material predominantly made of Si, and a coating consisting predominantly of magnesium and oxygen (“core-shell” geometry). The nanocomposite exhibit luminescence covering nearly entire visible range. Results are consistent with formation of Mg(OH)2/MgO phase with direct 3.43-eV bandgap matching that of Si, with in-gap blue-green emitting states of charged Mg and O vacancies. Bandgap match with nanocomposite architecture affords strong enough coupling for the materials to nearly act as a single hybrid material with novel luminescence for photonic and photovoltaic applications.

We use silicon having multiple crystalline orientation domains and high metal doping in metal assisted chemical etching (MACEtch) in HF/H2O2. In device-quality silicon, MACEtch produces high-aspect ratio anisotropic (1-D) structures (wires, columns, pores or holes) and to a lesser degree non-high-aspect ratio luminescent (0-D) nano structures. While the 1-D structure symmetry is understood in terms of crystallography axis-dependent etching, predominantly along the <100> direction, the isotropic 0-D spherical symmetry etching is not understood. We observe in silicon having multiple crystalline orientation domains formation of metal tips (needles or whiskers) of diameters as small as 2-3 nm that bridge the metal to silicon and cause AFM/STM-like nanofabrication, producing 0-D mounds, indentations, or clusters. The formation of sharp needles can be understood in terms of charge injection/electric breakdown between metal clusters and silicon due to charge build-up. Silicon with high degree of impurities as well as with multiple crystalline orientation domains allow imaging these effects using electron spectroscopy without cross sectional cuts.