Selective Homoepitaxial Growth of ZnO Layers on c(+)-Surface by Solvothermal Reaction in Water-Ethylene Glycol Solvent.

Solvothermal deposition of ZnO layers on the c(±)-surfaces of ZnO single crystal substrates in a water-ethylene glycol solvent was investigated. Homoepitaxial growth of nanoparticulate layers was observed on the c(+)-surface. The manner of nanoparticle deposition on the c(+)-surface was similar to that of spherical particles precipitated in the solution, in that both grew through the oriented attachment of small particles during the early growth stage. The growth of the nanoparticulate film on the c(-)-surface was much slower than that on the c(+)-surface. After aging, the top surface of the film on the c(+)-surface transformed into a layer of pyramid-like particles so that the base of the pyramids was directed toward the surface. In contrast, randomly oriented pyramidal particles covered the c(-)-surface. Ostwald ripening through dissolution-recrystallization transformed the nanoparticles into pyramid-shaped particles in the latter stage when they were in contact with the solution. The faster growth on the c(+)-surface than on the c(-)-surface and the pyramidal shape of the particles with c(+)-basal plane deposited on the c(±)-surfaces after aging confirmed that the growth of the c(+)-plane was promoted, whereas the growth of {101̅0} and c(-)-planes was inhibited in this solution.

Time-gated luminescence bioimaging with new luminescent nanocolloids based on [Mo6I8(C2F5COO)6]2- metal atom clusters.

Bioimaging and cell labeling using red or near infrared phosphors emitting in the "therapeutic window" of biological tissues have recently become some of the most active research fields in modern medical diagnostics. However, because organic and inorganic autofluorophores are omnipresent in nature, very often the background signal from fluorochromes other than targeted probes has to be eliminated. This discrimination could be available using a time-gated luminescence microscopy (TGLM) technique associated with long lifetime phosphorescent nanocomposites. Here, we report new SiO2 nanostructured particle (50 nm in diameter) embedded luminescent nanosized [Mo6I8(C2F5COO)6]2- metal atom clusters (1 nm in diameter), successfully prepared by the microemulsion technique. This combination provides new physical insight and displays red emission in biological based solution under UV-Vis excitation with long lifetimes of around 17 and 84 µs. Moreover, the nanoparticles can be internalized by cancer cells after surface functionalization by transferrin protein and clearly imaged by TGLM under excitation at 365 nm. The nanocomposites have been mainly characterized by scanning and transmission electron microscopies (SEM and HAADF-STEM), UV-Vis and photoluminescence (PL) spectroscopies.

The effect of n- and p-type doping on coherent phonons in GaN.

The effect of doping on the carrier-phonon interaction in wurtzite GaN is investigated by pump-probe reflectivity measurements using 3.1 eV light in near resonance with the fundamental band gap of 3.39 eV. Coherent modulations of the reflectivity due to the E2 and A1(LO) modes, as well as the 2A1(LO) overtone are observed. Doping of acceptor and donor atoms enhances the dephasing of the polar A1(LO) phonon via coupling with plasmons, with the effect of donors being stronger. Doping also enhances the relative amplitude of the coherent A1(LO) phonon with respect to that of the high-frequency E2 phonon, though it does not affect the relative intensity in Raman spectroscopic measurements. We attribute this enhanced coherent amplitude to the transient depletion field screening (TDFS) excitation mechanism, which, in addition to impulsive stimulated Raman scattering (ISRS), contributes to the generation of coherent polar phonons even for sub-band gap excitation. Because the TDFS mechanism requires photoexcitation of carriers, we argue that the interband transition is made possible at a surface with photon energies below the bulk band gap through the Franz-Keldysh effect.

Fabrication of dielectric nanocubes in ordered structure by capillary force assisted self-assembly method and their piezoresponse properties.

Ordered structures of barium titanate (BT) nanocubes, strontium titanate (ST) nanocubes and BT/ST nanocubes mixture were directly fabricated on Si and Pt-coated Si substrates using a capillary force assisted assembly method. The morphology of self-assembled structures was observed using field emission scanning electron microscopy (FE-SEM) and scanning probe microscopy (SPM). It was revealed that nanocubes were arranged with various degrees of ordering to develop multilayer and monolayer regions at the surface of substrates. The elemental mapping of the structure consisting of the nanocubes mixture was also investigated by transmission electron microscopy (TEM) with an energy dispersive X-ray spectroscopy (EDX). It was revealed that BT and ST nanocubes coexisted homogeneously in the structure and had possibility to be arranged in order to each other. The piezoresponse properties obtained by scanning probe microscopy (SPM) indicated that the hetero-interface between BT and ST nanocubes would introduce anomaly in piezoelectric properties.

In situ growth BaTiO3 nanocubes and their superlattice from an aqueous process.

Ordered aggregated BaTiO(3) nanocubes with a narrow size distribution were obtained in an aqueous process by using bis(ammonium lactate) titanium dihydroxide (TALH) as Ti source in the presence of oleic acid and tert-butylamine. Kinetics of the formation of BaTiO(3) nanocubes indicated that an in situ growth mechanism was dominant and the superlattice of nanocubes formed in situ through the growth of BaTiO(3) nanoparticles in Ti-based hydrous gel. The size and morphology of nanocubes were controlled by tuning the concentration and molar ratio of surfactants. A novel growth model dependant on the structure of Ti precursor for the formation and morphology control of BaTiO(3) nanocubes and their superlattice was demonstrated.

Hierarchical structures of ZnO spherical particles synthesized solvothermally.

We review the solvothermal synthesis, using a mixture of ethylene glycol (EG) and water as the solvent, of zinc oxide (ZnO) particles having spherical and flower-like shapes and hierarchical nanostructures. The preparation conditions of the ZnO particles and the microscopic characterization of the morphology are summarized. We found the following three effects of the ratio of EG to water on the formation of hierarchical structures: (i) EG restricts the growth of ZnO microcrystals, (ii) EG promotes the self-assembly of small crystallites into spheroidal particles and (iii) the high water content of EG results in hollow spheres.

Synthesis and characterization of A4[Re6Q8L6]@SiO2 red-emitting silica nanoparticles based on Re6 metal atom clusters (A = Cs or K, Q = S or Se, and L = OH or CN).

Metal atom clusters constitute very promising candidates as luminophores for applications in biotechnology because they are nanosized entities offering robust luminescence in the near-infrared field (NIR). However, they cannot be used as prepared for biological applications because of potential toxic effects and quenching of the clusters' luminescence in aqueous media, and they therefore need to be dispersed in a biocompatible matrix. We describe herein the encapsulation of octahedral rhenium clusters, denoted as A(4)[Re(6)Q(8)L(6)] (A = Cs or K, Q = S or Se, and L = OH or CN), in silica nanoparticles by a water-in-oil microemulsion process, paying particular attention to the clusters' stability. The obtained A(4)[Re(6)Q(8)L(6)]@SiO(2) nanoparticles are 30 nm in size with good monodispersity and a perfectly spherical shape, as shown by scanning electron microscopy (SEM). The presence of cluster units inside the silica matrix was evidenced by scanning transmission electron microscopy in annular dark-field mode (ADF-STEM). From the point of view of their optical properties, the A(4)[Re(6)Q(8)L(6)]@SiO(2) nanoparticles show red and NIR emission under UV excitation, even when dispersed in water. The evolution of the structural and luminescence properties of clusters before and after encapsulation was followed by Raman and photoluminescence spectroscopy.

A new effect of ultrasonication on the formation of BaTiO(3) nanoparticles.

A new effect of ultrasonic irradiation on the formation of BaTiO(3) particles was identified. Ultrasonication caused the aggregation of the original 5-10nm BaTiO(3) particles in the same crystal axis and accelerated the formation of BaTiO(3) particles significantly. Furthermore, narrow size distribution was obtained for the aggregated particles under ultrasonic irradiation.

Functional silica nanoparticles synthesized by water-in-oil microemulsion processes.

Water-in-oil (W/O) microemulsion is a well-suitable confined reacting medium for the synthesis of structured functional nanoparticles of controlled size and shape. During the last decade, it allowed the synthesis of multi-functional silica nanoparticles with morphologies as various as core-shell, homogenous dispersion or both together. The morphology and properties of the different intermediates and final materials obtained through this route are discussed in the light of UV-Vis-NIR spectroscopy, dynamic light scattering (DLS) and X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and magnetometer SQUID analysis.

Synthesis and characterization of Eu3+, Ti4+ @ ZnO organosols and nanocrystalline c-ZnTiO3 thin films aiming at high transparency and luminescence.

By exploiting colloidal properties, such as transparency, rheology and versatile chemistry, we propose to synthesize new photonic nanomaterials based on colloidal solutions and thin films. This contribution highlights our efforts to elaborate and to characterize nanostructures based on the ZnO-TiO2 system. Using a recently developed sol-gel route to synthesize new Ti4+@ZnO organosols, we were able to prepare, at relatively low temperature (400 °C) and short annealing time (15 min), highly transparent, luminescent, nanocrystalline Eu3+ doped c-ZnTiO3 thin films. The organosols and thin films were characterized with UV-visible-near infrared absorption, ellipsometry, photoluminescence spectroscopy, dynamic light scattering, x-ray diffraction and scanning electron microscopy.

One-pot synthesis and characterizations of bi-functional phosphor-magnetic @SiO(2) nanoparticles: controlled and structured association of Mo(6) cluster units and gamma-Fe(2)O(3) nanocrystals.

Nanostructured silica coated bifunctional nanoparticles based on [Mo(6)Br(14)](2-) units as phosphorescent dye and magnetic gamma-Fe(2)O(3) nanocrystals were synthesized and characterized.

Diffusion properties of point defects in barium strontium titanate thin films.

The relationship between the diffusion behavior of hydrogen and the electrical properties of (Ba, Sr)TiO3 (BST) thin-film capacitors was investigated using thermal desorption spectroscopy and secondary ion mass spectroscopy analyses. It has been clearly shown that the frequency dependence of the complex impedance profile of the BST thin-film capacitors could be successfully represented by two parallel resistor-capacitor (RC) electrical equivalent networks in series correlated with the distribution of the hydrogen, namely, the Pt/BST interface region with the influence of hydrogen and the BST bulk region without the influence of hydrogen. However, the I-V properties of the BST thin-film capacitors could be determined almost from the hydrogen atoms existing at the Pt/BST interface.

AFM and TEM observations of alpha-helix to beta-sheet conformational change occurring on carbon nanotubes.

Bacteriorhodopsin (BR), which is rich in alpha-helical structure, was spread onto water with single-wall carbon nanotubes (SCNTs). After a Langmuir trough was used to apply compressive surface pressure to maintain the alpha-helices monolayer of denatured BR, the composite films comprising alpha-helices and SCNTs were transferred horizontally onto substrates. Atomic force microscopy (AFM) and fluorescence microscopy observation suggested that alpha-helices in contact with SCNTs changed into beta-sheets. High-resolution transmission electron microscopy (HR-TEM) showed 0.54 nm periodicity characteristic of the turn of alpha-helical structure in the SCNTs-free alpha-helix monolayer region and showed the 0.70 nm periodicity of beta-sheet pleated structure in the region where SCNTs were covered with unfolded BR. Unique features of carbon nanotubes that trigger conformational changes of a protein were revealed.

Enhancement of photocatalytic activity of sprayed nitrogen-containing ZnO powders by coupling with metal oxides during the acetaldehyde decomposition.

Colored N-containing MOx-ZnO (M = W, V) composite powders with high surface area were synthesized by spray pyrolysis. The nitrogen content was controlled from 600 to 3000 ppm by changing the powder ingredients and the spray pyrolysis temperature. Ultraviolet-visible spectra indicated that the N-containing MOx-ZnO powders absorbed not only ultraviolet light like pure ZnO powder, but also some visible-light. Acetaldehyde decomposition was used as a probe reaction to evaluate the photocatalysis of these MOx-ZnO powders. The photocatalytic activity of the N-containing ZnO powder was pronouncedly enhanced by the WO3 or V2O5 addition under both UV and visible-light irradiation. This enhancement was ascribed to the MOx acting as a sink for photogenerated electrons in the UV case, and to a synergistic effect of N-doping and MOx-ZnO coupling in the case of visible-light.

Morphologies of zinc oxide particles and their effects on photocatalysis.

ZnO powders with different morphologies were synthesized by alkali precipitation, organo-zinc hydrolysis, and spray pyrolysis. Acetaldehyde decomposition was used as a probe reaction to evaluate the photocatalysis of these ZnO powders. We investigated the relationship between photocatalytic activity and crystallinity, surface area, or morphology. Results indicate that the photocatalytic activity of ZnO powder depends on crystallinity rather than surface area for the same original ZnO powders prepared by equal conditions other than the difference in calcination temperature. However, no direct relationship between photocatalytic activity and crystallinity or surface area was found for the differently original ZnO powders prepared by different methods, or the same method with different conditions. Instead, we find that the particle morphology significantly affects its photocatalysis.

Highly Porous (TiO2-SiO2-TeO2)/Al2O3/TiO2 Composite Nanostructures on Glass with Enhanced Photocatalysis Fabricated by Anodization and Sol-Gel Process.

Three-dimensional highly porous TiO2-4%SiO2-1%TeO2/Al2O3/TiO2 composite nanostructures (φ30-120 nm) directly fixed on glass substrates were fabricated by anodization of a superimposed Al/Ti layer sputter-deposited on glass and a sol-gel process. The porous composite nanostructures exhibited enhanced photocatalytic performances in decomposing acetaldehyde gas under UV illumination, which can be mainly ascribed to the combination of their large surface areas (7750-14770 m(2)/m(2)), high porosities (34.2-45.6%), and transparency. Specially, the composite nanostructure with ∼φ120 nm pores calcined at 500 °C showed the highest photocatalytic activity that is 6-10 times higher than commercial P-25 TiO2 under the experimental conditions.