Table of contents

The formation of a hybridization state of Wannier Mott and Frenkel excitons is theoretically studied for different heterostructure configurations involving quantum dots. At the interfaces of the semiconductor quantum dots and the organic medium, the hybridization states are formed, having complimentary properties of both kinds of excitons as well as large optical nonlinearities. The coupling at resonance is very strong, depending on the parameters of the systems (dot radius, dot separation, generation of the organic dendrites and the materials of the systems, etc). The hybrid excitons are as sensitive to external perturbation as Wannier–Mott excitons. Upon the application of magnetic and electric fields, the coupling term between the two kinds of excitons increases. The most important feature of this system is that by adjusting the system parameters as well as the external fields and their orientation, one can tune the resonance between the two kinds of excitons to get different regions of mixing to obtain the expected high nonlinearity.

This brief overview demonstrates how the ion track-based technology for micro-structuring polymeric materials that has been practised for decades is shifting to the nanometre scale in research and development applications. We present selected results of studies that have focused on the development of new nanoporous materials, especially membranes, performed recently at the Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research (JINR).

^SnS₂ nanoparticles have been synthesized using a mild hydrothermal method in the presence of the surfactant sodium dodecyl sulfate (SDS) at 180 °^C for 12 h. Physical investigations were carried out to study their structure, size, morphology and optical properties. The x-ray diffraction (XRD) pattern of the as-prepared sample is indexed to the hexagonal phase of ^SnS₂ and the particle size is 100 nm, which is further confirmed by transmission electron microscopy (TEM). The UV-visible spectrum shows that the absorption edge is blue shifted, and the band gap of the prepared ^SnS₂ nanoparticles has been evaluated with UV-visible spectroscopy to be 3.54 eV, which is larger than the bulk ^SnS₂ (∼2.44 ^eV). The anionic surfactant SDS plays a key role in the formation of the 3D sphere like ^SnS₂ nanostructures. A probable reaction for the formation of nanocrystalline SnS₂ nanoparticles is proposed.

Randomly oriented polycrystalline ZnO nanowires with a mean diameter of 100–150 nm have been successfully synthesized on ^SiO₂/^Si substrates through the thermal oxidation of sputtered Zn nanowires in dry air at 400 °^C. Structural characterization by x-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed that each ZnO nanowire consisted of a chain of ZnO nanocrystallites. From gas sensing measurements for CO, ^H₂ and NO gases, the polycrystalline ZnO nanowires showed a highly sensitive and fast response to both reducing and oxidizing gases in dry air at relatively low concentrations and operating temperatures, indicating potential applications of polycrystalline ZnO nanowires as sensing materials for gas sensors.

Recent studies on the coupling effects between constituent elements of metamaterials have opened up a new gateway to many fascinating electromagnetic properties and functionalities that cannot be explained by the uncoupled point of view. In this work, we numerically investigated, in a THz regime, the coupling between a cut wire and a split-ring resonator, which gives rise to an interesting phenomenon—the so-called electromagnetically induced transparency-like effect. The trade-off between the maximum transmittance of the transmission window and the group index, which depends on the coupling strength between constituent elements, was systematically studied. Furthermore, by characterizing this trade-off by the transmittance-delay product (figure of merit), a criterion for slow-light applications was provided.

We present new results of a laser phenomenon that gives rise to a narrow green emission mode in a random photonic-crystal cavity based on an Er-doped glass–air gap–polymer with a 976 nm diode laser pump. Lasing occurs at 537 nm, which does not respond to the resonant radiative transition ^2H_11/2→^4I_15/2; ^4S_3/2→^4I_15/2 in Erbium ions. This effect can be seen as photon–atom coupling in the context of the interaction between a single atom and/or a few atoms and resonant optical media, such as cavities or photonic crystals. Experimental results show that the random lasing mode directly originates from the coupled photon–atom mode inside the random cavity. The measured Q-factor is of 2100–2800 for a random cavity with an air gap of 600–1700 nm between Er-doped glass fiber and a coated polymer layer.

This research presents the deposition and device fabrication of epitaxial ^Pb(^Zr,Ti)^O₃ (PZT) thin films for applications in microelectromechanical systems (MEMS). A piezoelectric micro-membrane is described as an example. Using the pulsed laser deposition (PLD) technique and the MEMS microfabrication process, the piezo-membranes with diameters ranging from 200 to 500 μ^m were obtained. The displacement of piezo-membranes increased from 5.1 to 17.5 ^nm V−1 with a piezoelectric-membrane diameter in the range of 200–500 μ^m. Furthermore, the effect of PZT film-thickness on the mechanical properties has been investigated. By using the conductive-oxide ^SrRuO₃ (SRO) layers as the electrodes, the degradation of both ferroelectric and piezoelectric properties is prevented up to 10¹⁰ switching cycles.

Metal matrix nanocomposites have become popular in industrial applications. Carbon nanotubes (CNTs), since theirs appearance, with their unique properties such as exceptionally small diameters and high Young's modulus, tensile strength and high chemical stability, are considered to be an attractive reinforcement material for lightweight and high-strength metallic matrix composites. The powder metallurgy method allows nanocomposite materials, notably metal–ceramic composites, to be produced by sintering a mixture of powders.

In this study, we have utilized the powder metallurgy method to fabricate a Cu/CNT nanocomposite. Sintering is the important process in this method; it is the process whereby powder compacts are heated so that adjacent particles fuse together. The aim of this paper is to investigate the effect of sintering temperature on the mechanical properties of the Cu/CNT nanocomposite. The sintering temperature was in the range of 850–950 °^C for 2 h. A correlation between the microstructure and mechanical properties, including the microstructure, density, hardness and compressive strength, is established. In this process, the density, and the physical and mechanical properties of the nanocomposites, can be changed, depending on the rate of sintering as well as the sintering temperature.

This study applied an in situ electric contact resistance technique to monitor delamination induced by indentation loads. A suddenly increasing indentation depth, together with a simultaneous drop in monitoring contact current, suggests that delamination occurred. During unloading processes, the rapid decrease in both contact depth and current imply that the delaminated film was suspended as long as the indentation load became sufficiently small. When delamination occurred during oscillating processes, the contact current was found to drop from an initial value to a steady value, which is related to a loss of interfacial contact.

In this paper, we present the experimental result as well as the theoretical calculation of the electronic band structures and the optical absorption spectra for N-doped and Fe-doped ^TiO₂ anatase. The main purpose is to provide evidence in the viewpoint of visible light photocatalytic activity of N-doped and weak ferromagnetism of Fe-doped in ^TiO₂ anatase. Accordingly, to evaluate the separate contributions of nitrogen doping and iron doping in anatase, we present the results of spin-polarized density functional theory (DFT) calculations that have been used to calculate the electronic band structures and optical absorption spectra that arise for a range of concentrations of (i) substitutional nitrogen and (ii) substitutional iron in anatase ^TiO₂. Our results show that absorption in the visible range is mainly due to nitrogen states located above the valence bands, whereas weak ferromagnetism of Fe-doped in ^TiO₂ anatase is mainly caused by spin polarization. These results have important implications for the understanding and further development of photocatalytic materials that are active under visible light. These findings agree favorably with our own experimental data and enable conclusions to be drawn about the nature of the practical catalyst in N-doped and the ferromagnetic origin in Fe-doped ^TiO₂ anatase.

Copper nanoparticles, due to their interesting properties, low cost preparation and many potential applications in catalysis, cooling fluid or conductive inks, have attracted a lot of interest in recent years. In this study, copper nanoparticles were synthesized through the chemical reduction of copper sulfate with sodium borohydride in water without inert gas protection. In our synthesis route, ascorbic acid (natural vitamin C) was employed as a protective agent to prevent the nascent Cu nanoparticles from oxidation during the synthesis process and in storage. Polyethylene glycol (PEG) was added and worked both as a size controller and as a capping agent. Cu nanoparticles were characterized by Fourier transform infrared (FT-IR) spectroscopy to investigate the coordination between Cu nanoparticles and PEG. Transmission electron microscopy (TEM) and UV–vis spectrometry contributed to the analysis of size and optical properties of the nanoparticles, respectively. The average crystal sizes of the particles at room temperature were less than 10 nm. It was observed that the surface plasmon resonance phenomenon can be controlled during synthesis by varying the reaction time, pH, and relative ratio of copper sulfate to the surfactant. The surface plasmon resonance peak shifts from 561 to 572 nm, while the apparent color changes from red to black, which is partly related to the change in particle size. Upon oxidation, the color of the solution changes from red to violet and ultimately a blue solution appears.

In this paper, we present the results of an investigation of the influence of fabrication conditions on the structure and magnetic properties of ^Nd_10.5−x^Fe_83.5−y^Co_x^Nb_y^B₆ (x=0–6; y=1.5–3) nanocomposites prepared by melt-spinning combined with annealing. By changing the quenching rate (by varying the tangential velocity of the copper wheel from 10 ^m s−1 to 40 ^m s−1), one can select a suitable velocity to obtain an alloy that has good, hard magnetic behavior without annealing. However, the hard magnetic behavior of the alloy is better and more stable when the alloy is quenched at a high rate to create an amorphous state and subsequently annealed in the range of 650–800 °^C for 10 min. The results also show that the Co concentration has an important effect on the structure and magnetic properties of the alloys.

Distorted cubane ^Mn4+Mn3+₃ single-molecule magnets (SMMs) have been studied by first-principles calculations, i.e. [^Mn₄^L₃^X(^OAc)₃(^dbm)₃] (^L=^O; ^X=^F, Cl, and Br; ^dbmH=^dibenzoyl-methane). It was shown in our previous paper (Tuan et al 2009 Phys. Chem. Chem. Phys.11 717) that the ferrimagnetic structure of ^Mn4+Mn3+₃ SMMs is dominated by π type hybridization between the d_^z2 orbitals at the three high-spin ^Mn3+ ions and the t_2^g orbitals at the ^Mn4+ ion. To design new ^Mn4+Mn3+₃ molecules having much more stable ferrimagnetic states, one approach is suggested. This involves controlling the ^Mn4+–L–^Mn3+ exchange pathways by rational variations in ligands to strengthen the hybridization between the Mn ions. Based on this method, we succeed in designing new distorted cubane ^Mn4+Mn3+₃ molecules having ^Mn4+–^Mn3+ exchange coupling of about 3 times stronger than that of the synthesized ^Mn4+Mn3+₃ molecules. These results give some hints regarding experimental efforts to synthesize new superior ^Mn4+Mn3+₃ SMMs.

In this paper, research on a CO catalytic gas sensor based on nano-crystalline perovskite oxide ^NdFeO₃ designed for exhaust gas measurement is presented. Nano-crystalline oxide ^NdFeO₃ was synthesized by a sol–gel citrate technique. The gas sensing characteristics of this sensor were investigated in the concentration range of CO between 0 and 5 vol.% in air. The influences of ^C₃^H₈, ^C₄^H₁₆ gases, relative humidity and air-flow rate on the cross-sensitivity of the CO sensor were also studied.

In this work, we present the design, fabrication and characterization of a novel micro-extractor that performs on-line extraction–concentration–detection (ECD) of target molecules flowing in a carrier liquid. The system comprises a primary microchannel containing a flowing aqueous carrier liquid and a secondary organic storage fluid circulating in an adjacent channel. The interfaces between the two immiscible fluids are stabilized by vertical micro-pillars. The system encompasses three functions: (i) extraction of the target molecules from the carrier fluid through the pillar-stabilized interfaces, (ii) concentration of the targets in the secondary organic solvent due to its very low—or zero—velocity and (iii) on-line detection via optical spectrometry. We successively present the analysis of the physics of the system, which has led us to a specific design, then the microfabrication of the chip, and finally we demonstrate the extraction, concentration and detection of lead ions (^Pb2+) from a water flow.

Bulk heterojunction organic solar cells were fabricated by sandwiching the active layer between indium tin oxide (ITO) and Al electrodes. The active layer used was a blend of poly(3-octylthiophene-2,5-diyl) (P3OT) as the electron donor and (6,6)-phenyl ^C₇₁ butyric acid methyl ester (^PC₇₁^BM) as the electron acceptor. The active layer thin films were deposited by an inkjet printing technique. Prior to deposition of the thin films, the active materials were blended in three different solvents. The printed films were annealed at three different temperatures. It was found that the selection of the appropriate solvent and annealing treatment significantly influences the printing process, the morphology of the printed film and subsequently the performance of the solar cell devices.

Recently, the electric field induced manipulation of magnetic properties has become one of the most interesting research topics because of its promising applications in magnetoelectronics, such as future logic elements and electric–magnetic memories. In this paper, the NiFe/CoFe ferromagnetic nanostructured thin films were directly deposited on the ferroelectric PZT substrate, which was polarized parallel to the thickness or along the surface. In these samples, the stress originating from the piezoelectric layer is transferred into the magnetostrictive layer, which induces an elastic strain and results in a change in magnetization, thanks to the converse magnetoelectric effect. By analyzing the magnetization of the nanocomposite under a fixed magnetic field up to 5×10^3 Oe at different voltages applied to the ferromagnetic substrate, we can investigate the voltage-controllable magnetization in this composite. The obtained results show that the magnetization of the NiFe/CoFe film changes around 6% at the low voltage of 60 V and up to two times larger at 800 V in an external magnetic field of 50 Oe. The use of voltage also allows the reversible adjustment of the magnetization orientation in ferromagnetic layers.

In the present work, silicon nanowires were prepared by a thermal evaporation method. The evaporating source was a mixture of silicon and carbon nanopowders. Surface morphology, structural characteristics and emission properties of the silicon nanowires were investigated by several techniques. The results showed that the obtained products have the shape of nanowires with diameters ranging from 30 to 120 nm and lengths from 300 to 400 nm. The x-ray diffraction (XRD) patterns confirmed the presence of crystalline silicon. Transmission electron microscope (TEM) images revealed the core-shell structure of the wires. In the photoluminescence (PL) spectra recorded at room temperature, only a broad emission band peaking at about 650 nm was observed. In addition to the red emission, two other bands centered at around 455 nm and 510 nm appeared when measured at low temperatures. The origin and emission mechanism of these bands are discussed.