The structural properties which are different from those in the corresponding bulk materials appear in nanoparticles, since the free energy changes extremely by the solute concentrations or atomic arrangements. The chemical free energy by the interaction between the different atoms, the strain energy due to the different atomic sizes and the interface energy play important roles in the structural properties of multicomponent nanoparticles, and their artificial control will make it possible to form specific structures. The spontaneous alloying, phase equilibrium and electronic- excitation- induced phase separation in nanoparticles are reviewed based on the results obtained by in-situ TEM.
Energy transfer (ET) of fluorescence is a key process for organic based photonic devices and also a powerful tool for biosensors detecting conformational changes and measuring intermolecular distances of biomolecules. In recent years, ET using semiconductor quantum dots (QDs) is getting increased attention. However, it has been postulated that ET between QDs is based on the Förster model, which is a well-established model of ET mechanism in organic dye systems, without verification. In this work, we have investigated ET mechanism in colloidal CdS QDs measuring photoluminescence dynamics of a bilayer structure consisting of differently-sized CdS QDs. In the bilayer structure, the distance between the monolayer of donor QDs and that of acceptor QDs was controlled precisely by a spacer layer that is layer-by-layer assembly of polyelectrolytes. The bilayer structure enabled us to systematically measure the spacer layer dependence of photoluminescence dynamics reflecting the ET process between QDs. It is demonstrated that ET between the donor and acceptor QDs is conclusively dominated by the dipole-dipole interaction, which verifies the appropriateness of the Förster model.
Carrying out a first-principles time-dependent molecular dynamics simulation of light-harvesting dendrimers, star-shaped stilbenoid phthalocyanine (SSS1Pc) having oligo (π-phenylenevinylene) peripheries and phenylenebased dendrimer (phDG2), we found that electron and hole transfer takes place from periphery to core when an electron is excited in periphery selectively. Moreover, we investigated the charge separation dyanamics of a system composed of C60 and zinc phthalocyanine (ZnPc) and found that when an electron is selectively excited in ZnPc, the one-way electron transfer occurs from ZnPc to C60
We have developed a transport simulator for four-probe resistance measurements in nanoscale based on density functional tight-binding method and Green's function method. To achieve fast and reliable simulations applicable to large systems, we adopted the extended Anderson method for accelerating the self-consistent convergence, the residue theorem for integrating Green’s function, and MPI parallelization. We applied the simulator to four-probe carbon nanotube systems and analyzed how current and potential probes affect four-probe resistance in the coherent regime. The results show that 1) contact resistance does not affect the four-probe resistance seriously even in the coherent regime, while 2) negative values, peaks and dips appear in four-probe resistance spectra.
Recently, the research of fabricating magnetic nanparticles is studied for the coming future usage for
biochemistry, recording media, and spintronics. We have suggestested the
novel method for facile preparation of magnetic nanoparticles using metal
coordination nano-polymers as precursors. In this study, we have presented
the synthesis and the film formation of graphitic carbon (GC)-coated FeCo
nanoparticles with ferromagnetism at room temperature using reductive calcination
of nanometric Prrusian blue analogues stabilized by oleylamine (OA). The
obtained GC-coated FeCo nanoparticles (Fe/Co = 1-2.5) with the average
diameter of 12-19 nm possessed an onion like structure protected by 5~10
GC layers with high saturation magnetization. This method can be developed
for the facile fabrication of an FeCo NP film with GC shells that displays
magneto-optical properties.
Density gradient ultracentrifugation (DGU) is considered one of the most effective, affordable, and scalable
methods to sort single-walled carbon nanotubes (SWNTs). Here we present
a protocol using different surfactant agents to selectively isolate SWNTs
with a chirality of (6,5) from pristine SWNTs synthesized by various methods:
CoMoCAT (Co-Mo catalytic process), HiPCO (high pressure CO disproportionation),
and ACCVD (alcohol catalytic chemical vapor deposition). Although different
starting materials were used, highly-enriched (6,5) was obtained in each
case. Furthermore, a colorful expansion of the dispersed SWNTs revealed
selective enrichment of (6,5), (7,5) and (7,6) SWNTs in the topmost three
layers. To explain these results we propose a possible wrapping morphology
of surfactant around the SWNTs, and we believe that by further refinement
and improvement of this process, more chiralities can be isolated through
iterations or optimizing the experimental parameters.
Single-walled carbon nanotubes (SWNTs) are promising materials for high-performance stationary phases of gas chromatographic (GC) columns. High-performance stationary phases are expected to play a major role in the development of microfabricated columns, for which much shorter column lengths than conventional columns should be used. So far, the reported SWNT stationary phase columns suffer from problems of elution of compounds having high boiling points and of relatively low separation efficiency. The lack of performance of the reported SWNT columns is very likely caused by the use of relatively thick layers of SWNTs having a low degree of crystallinity. Here, we report the microfabrication of a gas chromatographic column with a stationary phase consisting of a thin layer of high-quality SWNTs synthesized by the alcohol catalytic chemical vapor deposition method. The separation efficiency was evaluated by determining the minimum of the height equivalent to an effective theoretical plate (HEETP), which was found to be 0.4 cm for the microfabricated column, a much smaller value than those estimated from literature reports of SWNT microfabricated columns. Moreover, the microfabricated column was able to separate n-alkanes having high boiling points under temperature-programmed conditions in spite of the low final column temperature of 105˚C. The microfabricated column coated with SWNTs offered good separation efficiency even for high-boiling-point n-alkanes at low temperature and, thus, it is thought that the microfabrication of thin layer of high-quality SWNT columns will contribute to open up new opportunities in the miniaturization of GC systems.