25 research outputs found
Preparation of small silicon carbide quantum dots by wet chemical etching
Fabrication of nanosized silicon carbide (SiC) crystals is a crucial step in many biomedical
applications. Here we report an effective fabrication method of SiC nanocrystals based on
simple electroless wet chemical etching of crystalline cubic SiC. Comparing an open reaction
system with a closed reaction chamber, we found that the latter produces smaller nanoparticles
(less than 8 nm diameter) with higher yield. Our samples show strong violet-blue emission in the
410â450 nm region depending on the solvents used and the size. Infrared measurements unraveled
that the surface of the fabricated nanoparticles is rich in oxidized carbon. This may open an
opportunity to use standard chemistry methods for further biological functionalization of such
nanoparticles
On the formation of blisters in annealed hydrogenated a-Si layers
Differently hydrogenated radio frequency-sputtered a-Si layers have been studied by infrared (IR) spectroscopy as a
function of the annealing time at 350 Celsius with the aim to get a deeper understanding of the origin of blisters previously
observed by us in a-Si/a-Ge multilayers prepared under the same conditions as the ones applied to the present a-Si
layers. The H content varied between 10.8 and 17.6 at.% as measured by elastic recoil detection analysis. IR
spectroscopy showed that the concentration of the clustered (Si-H)n groups and of the (Si-H2)n (n â„ 1) polymers
increased at the expense of the Si-H mono-hydrides with increasing annealing time, suggesting that there is a
corresponding increase of the volume of micro-voids whose walls are assumed from literature to be decorated by the
clustered mono-hydride groups and polymers. At the same time, an increase in the size of surface blisters was
observed. Also, with increasing annealing time, the total concentration of bonded H of any type decreases, indicating
that H is partially released from its bonds to Si. It is argued that the H released from the (Si-H)n complexes and
polymers at the microvoid surfaces form molecular H2 inside the voids, whose size increases upon annealing because
of the thermal expansion of the H2 gas, eventually producing plastic surface deformation in the shape of blisters
Nanowires of lead-methylamine iodide (CH3NH3PbI3) prepared by low temperature solution-mediated crystallization
We report the synthesis of lead-methylamine iodide (CH3NH3PbI3) nanowires by a low temperature solution processed crystallization using a simple slip-coating method. The anisotropic particle shape exhibits advantages over nanoparticles in terms of charge transport under illumination. These results provide a basis for solvent-mediated tailoring of structural properties like the crystallite size and orientation in trihalide perovskite thin films, which once implemented into a device, may ultimately result in an enhanced charge carrier extraction
Chemical Transformation of Carboxyl Groups on the Surface of Silicon Carbide Quantum Dots
Silicon carbide quantum dots in the size range of 1â10 nm are in the center of interest with unique properties that makes them very promising biomarkers. A central requirement for this application is the control over the complex structure of the surface to enable further surface functionalization processes, which are crucial for drug delivery. In this paper, a temperature dependent infrared and photoluminescence spectroscopy study, combined with ab initio modeling, is presented in order to reveal the chemical transformations of the surface termination groups. We found that at temperatures above 370 K, acid anhydride groups form by condensation of water between neighboring carboxyl groups. The presence of the anhydride groups reveals the proximity of the carboxyl groups and represents a new possibility of selective engineering of
new hybrid materials involving silicon carbide quantum dots
Chemical Interface Damping as an Indicator for Hexadecyltrimethylammonium Bromide Replacement by Short-Chain Thiols on Gold Nanorods
From nano voids to blisters in hydrogenated amorphous silicon
AFM and FTIR spectroscopy were applied to study thĂš relationship between surface
blisters and nanovoids in annealed hydrogenated a-Si. The influence of thĂš H bonding
configuration on thĂš way thĂš nanovoids give rise to thĂš blisters is discussed. Annealing
causes an increase of thĂš polymers density. As they reside on thĂš voids walls their density
increase causes an increase of thĂš voids volume. The polymers may release H inside thĂš
voids with creation of H2 gas, whose expansion, upon annealing, further contributes to thĂš
volume increase of thĂš voids till thĂš formation of surface blisters
Interactions and Chemical Transformations of Coronene Inside and Outside Carbon Nanotubes
By exposing flat and curved carbon surfaces to coronene, a variety of van der Waals hybrid heterostructures were prepared, including coronene encapsulated in carbon nanotubes, and coronene and dicoronylene adsorbed on nanotubes or graphite via Ï â Ï interactions. The structure of the final product is determined by the temperature of the experiment and the curvature of the carbon surface. While at temperatures below and close to the sublimation point of coronene, nanotubes with suitable diameters are filled with single coronene molecules, at higher temperatures additional dimerization and oligomerization of coronene occurs on the surface of carbon nanotubes. The fact that dicoronylene and possible higher oligomers are formed at lower temperatures than expected for vapor-phase polymerization indicates the active role of the carbon surface used primarily as template. Removal of adsorbed species from the nanotube surface is of utmost importance for reliable characterization of encapsulated molecules: it is demonstrated that the green fluorescence attributed previously to encapsulated coronene is instead caused by dicoronylene adsorbed on the surface which can be solubilized and removed using surfactants. After removing most of the adsorbed layer, a combination of Raman spectroscopy and transmission electron microscopy was employed to follow the transformation dynamics of coronene molecules inside nanotubes
Dominant luminescence is not due to quantum confinement in molecular-sized silicon carbide nanocrystals
Molecular-sized colloid silicon carbide (SiC) nanoparticles are very promising candidates to realize bioinert non-perturbative fluorescent nanoparticles for in vivo bioimaging. Furthermore, SiC nanoparticles with engineered vacancy-related emission centres may realize magneto-optical probes operating at nanoscale resolution. Understanding the nature of molecular-sized SiC nanoparticle emission is essential for further applications. Here we report an efficient and simple method to produce a relatively narrow size distribution of water soluble molecular-sized SiC nanoparticles. The tight control of their size distribution makes it possible to demonstrate a switching mechanism in the luminescence correlated with particle size. We show that molecular-sized SiC nanoparticles of 1-3 nm show a relatively strong and broad surface related luminescence whilst the larger ones exhibit a relatively weak band edge and structural defect luminescence with no evidence of quantum confinement effect