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CONTENTS
Volume 1, Number 3, September 2013
 

Abstract
This study is aimed to calculate the radiative lifetime of Wannier-Mott excitons in nanoclusters of a narrow-bandgap semiconductor embedded in a wide-bandgap one. The nanocluster linear dimensions are assumed to be much larger than the radius of the exciton so that the latter is not destructed by the confinement potential as it takes place in small quantum dots. The calculations were carried out for an example of InAs nanoclusters put into the GaAs matrix. It is shown that the radiative lifetime of Wannier-Mott excitons in such clusters increases with the decrease of the cluster dimensions, this tendency being more pronounced at low temperatures. So, the creation of excitons in nanoclusters of a narrow-bandgap material embedded in a wide-bandgap one can be used to significantly prolong their radiative lifetime in comparison with that of excitons in a bulk semiconductor.

Key Words
exciton radiative lifetime; nanoclusters; Wannier-Mott excitons

Address
Vladimir A. Kukushkin : Department of Plasma Physics and High-Power Electronics, Institute of Applied Physics of the Russian Academy of Science, 46 Ulyanov st., 603950 Nizhny Novgorod, Russia; Advanced School of General and Applied Physics, Nizhny Novgorod State University named after N.I. Lobachevsky, 23 Gagarina pr., 603950 Nizhny Novgorod, Russia

Abstract
The availability of advanced nanotechnological methodologies (experimental and theoretical) has widened the investigation of biological/organic matter in interaction with substrates. Minerals are good candidates as substrates because they may present a wide variety of physico-chemical properties and surface nanostructures that can be used to actively condense and manipulate the biomolecules. Scanning Probe Microscopy (SPM) is one of the best suited techniques used to investigate at a single molecule level the surface interactions. In addition, the recent availability of high performance computing has increased the possibility to study quantum mechanically the interaction phenomena extending the number of atoms involved in the simulation. In the present paper, firstly we will briefly introduce new SPM technological developments and applications to investigate mineral surfaces and mineral-biomolecule interaction, then we will present results on the specific RNA-mineral interaction and recent basics and applicative achievements in the field of the interactions between other fundamental biological molecules and mineral surfaces from both an experimental and theoretical point of view.

Key Words
minerals; nucleic acids; amino acids; SPM; ab initio simulations; molecular dynamics

Address
Giovanni Valdre, Daniele Moro and Gianfranco Ulian : Interdisciplinary Research Centre of Biomineralogy, Crystallography and Biomaterials, Department of Biological, Geological and Environmental Sciences, Alma Mater Studiorum University of Bologna, Piazza di Porta San Donato 1, I-40126 Bologna, Italy

Abstract
An approach to achieving of spatially homogeneous, ordered ensemble of semiconductor quantum rods in polymer film of polyvinyl butyral is reported. The CdSe/ZnS quantum rods are embedded to the polymer film. Obtained film is stretched up to four times to its initial length. A concentration of quantum rods in the samples is around 2x10-5 M. The absorption spectra, obtained in the light with orthogonal polarization, confirm the occurrence of spatial ordering in a quantum rod ensemble. Anisotropy of the optical properties in the ordered quantum rod ensemble is examined. The presented method can be used as a low-cost solution for preparing the nanostructured materials with anisotropic properties and high concentration of nanocrystals.

Key Words
semiconductor quantum rod, nanostructured material, ordering, anisotropy of absorption

Address
Maria V. Mukhina, Vladimir G. Maslov, Alexander V. Baranov and Anatoly V. Fedorov : National Research University of Information Technologies, Mechanics and Optics, 197101 St-Petersburg, Russia
Mikhail V. Artemyev : Institute for Physico-Chemical Problems, Belarusian State University, 220030 Minsk, Belarus

Abstract
A preparation method for gadolinium compound (GdC) nanoparticles coated with silica (GdC/SiO2) is proposed. GdC nanoparticles were prepared with a homogeneous precipitation method at 80oC using 1.0x10-3 M Gd(NO3)3, 0.5 M urea and 0-3.0x10-4 M ethylenediaminetetraaceticacid disodium salt dihydrate (ETDA) in water. As a result of preparation at various EDTA concentrations, GdC nanoparticles with a size as small as 40.5+-6.2 nm, which were colloidally stable, were prepared at an EDTA concentration of 2.0x10-4 M. Silica-coating of the GdC nanoparticles was performed by a Stober method at 35oC using 1.0-10.0x10-3 M tetraethylorthosilicate (TEOS), 11 M H2O and 1.5x10-3 M NaOH in ethanol in the presence of 1.0x10-3 M GdC nanoparticles. Performance of preparation at various TEOS concentrations resulted in production of GdC/SiO2 particles with an average size of 106.1+-11.2 nm at a TEOS concentration of 5.0x10-3 M. The gadolinium (Gd) concentration of 1.0x10-3M in the as-prepared GdC/SiO2 particle colloid solution was increased up to a Gd concentration of 0.2 M by concentrating with centrifugation. The core-shell structure of GdC/SiO2 particles was undamaged, and the colloid solution was still colloidally stable, even after the concentrating process. The concentrated GdC/SiO2 colloid solution showed images of X-ray and magnetic resonance with contrast as high as commercial Gd complex contrast agents.

Key Words
core-shell; gadolinium; homogeneous precipitation method; Stober method; X-ray imaging; MRI

Address
Yoshio Kobayashi, Hikaru Morimoto : Department of Biomolecular Functional Engineering, College of Engineering, Ibaraki University, 4-12-1 Naka-narusawa-cho, Hitachi, Ibaraki 316-8511, Japan
Tomohiko Nakagawa, Kohsuke Gonda and Noriaki Ohuchi : Department of Nano-Medical Science, Graduate School of Medicine, Tohoku University, 2-1 Seiryo-machi, Aoba-ku, Sendai, Miyagi 980-8575, Japan
Noriaki Ohuchi : Department of Surgical Oncology, Graduate School of Medicine, Tohoku University, 2-1 Seiryo-machi, Aoba-ku, Sendai, Miyagi 980-8574, Japan

Abstract
The alternating current (AC) conductivity in semiconductor crystals with an open-core screw dislocation is studied in the current work. The screw dislocation in crystalline media results in an effective potential field which affects the electronic transport properties of the system. Therefore, from a technological view point, it is interesting to investigate properties of AC conductivity at frequencies of a few terahertz. To quantify the screw-induced potential effect, we calculated the AC conductivity of dislocated crystals using the Kubo formula. The conductivity showed peaks within the terahertz frequency region, where the amplitude of the AC conductivity was large enough to be measured in experiments. The measurable conductivity peaks did not arise in dislocation-free crystals threaded by a magnetic flux tube. These results imply different conductivity mechanisms in crystals with a screw dislocation than those threaded by a magnetic flux tube, despite the apparent similarity in their electronic eigenstates.

Key Words
alternating conductivity; screw dislocation; electronic structure; quantum phase; numerical calculation

Address
Hisao Taira and Motohiro Sato : Division of Engineering and Policy for Sustainable Environment, Faculty of Engineering, Hokkaido University, Kita 13 Nishi 8, Kita-ku, Sapporo 060-8628, Japan


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