David Beke

Room temperature quantum emission from cubic silicon carbide nanoparticles

The photoluminescence (PL) arising from silicon carbide nanoparticles has so far been associated with the quantum confinement effect or to radiative transitions between electronically active surface states. In this work we show that cubic phase silicon carbide nanoparticles with diameters in the range 45-500 nm can host other point defects responsible for photoinduced intrabandgap PL. We demonstrate that these nanoparticles exhibit single photon emission at room temperature with record saturation count rates of 7 × 10(6) counts/s. The realization of nonclassical emission from SiC nanoparticles extends their potential use from fluorescence biomarker beads to optically active quantum elements for next generation quantum sensing and nanophotonics. The single photon emission is related to single isolated SiC defects that give rise to states within the bandgap.

Characterization of luminescent silicon carbide nanocrystals prepared by reactive bonding and subsequent wet chemical etching

Fabrication of nanosized silicon carbide crystals is a crucial aspect for many biomedical applications. Here, we report an effective fabrication method of silicon carbide nanocrystals based on the reactive bonding method followed by electroless wet chemical etching. Our samples show strong violet-blue emission in the 410–450 nm region depending on the used solvents. Raman and infrared measurements unraveled the surface bonding structure of the fabricated nanoparticles being different from silicon carbide microcrystals. This might give an opportunity to use standard chemistry methods for biological functionalization of such nanoparticles.

Effect of low hydrostatic pressures on the solid state reactions in multilayers

Abstract In amorphous SiGe multilayers annealing at 858 K under 180 bar led to the depression of porosity formation. In crystalline Ni-Zr multilayers a small enhancement of the growth of amorphous phase was observed under 200 bar. In CoSn bilayers the kinetics of electrical resistivity at 298 K showed a characteristic cross-over as the pressure increased above 150 bar.

Determination of silicon and aluminum in silicon carbide nanocrystals by high-resolution continuum source graphite furnace atomic absorption spectrometry

The determination of Al contaminant and the main component Si in silicon carbide (SiC) nanocrystals with the size-distribution of 1-8nm dispersed in an aqueous solution was developed using high-resolution continuum source graphite furnace atomic absorption spectrometry (HR-CS-GFAAS). The vaporization/atomization processes were investigated in a transversally heated graphite atomizer by evaporating solution samples of Al and Si preserved in various media (HCl, HNO3). For Si, the best results were obtained by applying a mixture of 5µg Pd plus 5µg Mg, whereas for Al, 10µg Mg (each as nitrate solution) was dispensed with the samples, but the results obtained without modifier were found to be better. This way a maximum pyrolysis temperature of 1200°C for Si and 1300°C for Al could be used, and the optimum (compromise) atomization temperature was 2400°C for both analytes. The Si and Al contents of different sized SiC nanocrystals, dispersed in aqueous solutions, were determined against aqueous (external) calibration standards. The correlation coefficients (R values) of the calibrations were found to be 0.9963 for Si and 0.9991 for Al. The upper limit of the linear calibration range was 2mg/l Si and 0.25mg/l Al. The limit of detection was 3µg/l for Si and 0.5µg/l for Al. The characteristic mass (m0) was calculated to be 389pg Si and 6.4pg Al. The Si and Al content in the solution samples were found to be in the range of 1.0-1.7mg/l and 0.1-0.25mg/l, respectively.

Harnessing no-photon exciton generation chemistry to engineer semiconductor nanostructures

Production of semiconductor nanostructures with high yield and tight control of shape and size distribution is an immediate quest in diverse areas of science and technology. Electroless wet chemical etching or stain etching can produce semiconductor nanoparticles with high yield but is limited to a few materials because of the lack of understanding the physical-chemical processes behind. Here we report a no-photon exciton generation chemistry (NPEGEC) process, playing a key role in stain etching of semiconductors. We demonstrate NPEGEC on silicon carbide polymorphs as model materials. Specifically, size control of cubic silicon carbide nanoparticles of diameter below ten nanometers was achieved by engineering hexagonal inclusions in microcrystalline cubic silicon carbide. Our finding provides a recipe to engineer patterned semiconductor nanostructures for a broad class of materials.

Surface-Mediated Energy Transfer and Subsequent Photocatalytic Behavior in Silicon Carbide Colloid Solutions

We demonstrate that particle-particle interaction affects the photocatalytic efficiency of colloids. Colloid silicon carbide nanoparticles were examined by varying their size, size distribution, and surface chemistry, and we found that surface moieties show no effect on the individual particles but dramatically affect the collective photocatalytic efficiency of the system.