Shikuan Yang

Ultra-fine β-SiC quantum dots fabricated by laser ablation in reactive liquid at room temperature and their violet emission

A simple and flexible route is presented for the fabrication of ultrafine β-SiC quantum dots (QDs) based on laser ablation of silicon wafers immersed in ethanol and subsequent etching. The obtained β-SiC QDs are nearly monodispersed and about 3.5 nm in size. The relative content of β-SiC after laser ablation depends on the liquid phases ability to supply carbon atoms at a certain laser fluence. Proper liquid media with appropriate carbon atoms supply capacity can lead to nearly pure β-SiC in the as-prepared sample. The obtained β-SiC QDs exhibit strong and stable emission in the violet region, significantly blue-shifting relative to that of bulk SiC. This big blue shift of emission is attributed to the significant quantum confinement effect induced by their ultrafine size. This method can be extended to produce some other ultrafine Si compounds which are usually formed at high temperature and/or high pressure. This study could present the building blocks of nanostructured devices as violet light sources and new materials in biological molecular labels.

Luminescent hollow carbon shells and fullerene-like carbon spheres produced by laser ablation with toluene

Hollow carbon shells and fullerene-like carbon spheres are prepared by laser ablation with toluene molecules as a carbon precursor. The liquid carbon precursor is superior to the gaseous carbon precursors conventionally used, such as C2H2, due to its safety and ease of handling. The formation mechanism of these carbon nanostructures is discussed. The laser irradiation-induced high temperature results in the decomposition of toluene molecules to carbon atoms. Consequently, these carbon atoms nucleate and grow to novel carbon nanostructures as the temperature drops. The graphene-like hollow carbon shells show strong and excitation wavelength-dependent light emission, which has potential optical applications.

Polycrystalline Si nanoparticles and their strong aging enhancement of blue photoluminescence

Nearly spherical polycrystalline Si nanoparticles with 20 nm diameter were fabricated based on laser ablation of silicon wafer immersed in sodium dodecyl sulfate aqueous solution. Such Si nanoparticles consist of disordered areas and ultrafine grains of 3 nm in mean size and exhibit significant photoluminescence in blue region. Importantly, aging at ambient air leads to continuing enhancement of the emission (more than 130 times higher in 16 weeks) showing stable and strong blue emission. This aging enhancement is attributed to progressive passivation of nonradiative Pb centers corresponding to silicon dangling bonds on the particles’ surface. This study could be helpful in pushing Si into optoelectronic field and Si-based full color display, biomedical tagging, and flash memories.

Dramatic excitation dependence of strong and stable blue luminescence of ZnO hollow nanoparticles

Strong and stable blue luminescence was obtained from ZnO hollow nanoparticles. Significantly, dramatic excitation dependence was observed for blue emissions of ZnO: (1) band-gap energy (Eg) is the optimal excitation energy but smaller energies are still effective; (2) there exist several fixed emitting wavelengths in blue wave band, such as 412, 439, and 458 nm. These phenomena, combined with previously reported defect levels and formation thermodynamics, point out that the initial states of corresponding transitions to blue emissions could be zinc interstitials-related defect states, which were further verified by subsequent electron paramagnetic resonance examinations.

Janus particle arrays with multiple structural controlling abilities synthesized by seed-directed deposition

Janus particle arrays have attracted much investigation interest in recent years due to their wide application potentialities. Here, we introduce a new protocol to synthesize Janus particle arrays depending on seed-directed eletrophoretic deposition on monolayer colloidal crystal (MCC) templates. The size and feature of the Janus particles can be conveniently tailored by selecting different sized polystyrene spheres and deposition current densities and/or times, respectively. Non-close-packed Janus particle arrays can be prepared by adopting plasma treated monolayer colloidal crystal templates. The spacing between neighbouring Janus particles in the ordered array is determined by the plasma etching time of the MCC template. Due to the symmetry breaking and the plasmon hybridization, the Janus particle arrays show interesting plasmonic properties. They have multiple plasmonic peaks and have infrared absorption, making them have applications in sensing and bio-related areas.

Template-directed dewetting of a gold membrane to fabricate highly SERS-active substrates

Highly SERS-active substrates can be prepared by heating a discontinuous gold film (thickness about 5 nm) on ordered bowl templates. Nanoparticles (about 20 nm) will uniformly locate on the inner surface of the bowls with an interparticle distance of about 5 nm after heating the discontinuous gold membrane, which is quite different from the morphology of annealing a continuous gold film (>10 nm) (a nanodot array will be obtained in this case). The dewetting process for continuous and discontinuous gold films is discussed. The main difference between the dewetting processes of continuous and discontinuous gold membranes on bowl templates are the hole nucleation sites. For a continuous gold membrane, hole nucleation first takes place at the edge of the bowl. However, hole nucleation emerges uniformly in the discontinuous gold film. This study deepens our understanding of the influence of film thickness on the dewetting process.