Synthesis and characterization of heteroleptic titanium MOCVD precursors for TiO2 thin films.

Heteroleptic titanium alkoxides with three different ligands, i.e., [Ti(OiPr)(X)(Y)] (X = tridentate, Y = bidentate ligands), were synthesized to find efficient metal organic chemical vapor deposition (MOCVD) precursors for TiO2 thin films. Acetylacetone (acacH) or 2,2,6,6-tetramethyl-3,5-heptanedione (thdH) was employed as a bidentate ligand, while N-methyldiethanolamine (MDEA) was employed as a tridentate ligand. It was expected that the oxygen and moisture susceptibility of titanium alkoxides, as well as their tendency to form oligomers, would be greatly reduced by placing multidentate and bulky ligands around the center Ti atom. The synthesized heteroleptic titanium alkoxides were characterized both physicochemically and crystallographically, and their thermal behaviors were also investigated. [Ti(OiPr)(MDEA)(thd)] was found to be monomeric and stable against moisture; it also showed good volatility in the temperature window between volatilization and decomposition. This material was used as a single-source precursor during MOCVD to generate TiO2 thin films on silicon wafers. The high thermal stability of [Ti(OiPr)(MDEA)(thd)] enabled the fabrication of TiO2 films over a wide temperature range, with steady growth rates between 500 and 800 °C.

Wafer-scale single-domain-like graphene by defect-selective atomic layer deposition of hexagonal ZnO.

Large-area graphene films produced by means of chemical vapor deposition (CVD) are polycrystalline and thus contain numerous grain boundaries that can greatly degrade their performance and produce inhomogeneous properties. A better grain boundary engineering in CVD graphene is essential to realize the full potential of graphene in large-scale applications. Here, we report a defect-selective atomic layer deposition (ALD) for stitching grain boundaries of CVD graphene with ZnO so as to increase the connectivity between grains. In the present ALD process, ZnO with a hexagonal wurtzite structure was selectively grown mainly on the defect-rich grain boundaries to produce ZnO-stitched CVD graphene with well-connected grains. For the CVD graphene film after ZnO stitching, the inter-grain mobility is notably improved with only a little change in the free carrier density. We also demonstrate how ZnO-stitched CVD graphene can be successfully integrated into wafer-scale arrays of top-gated field-effect transistors on 4-inch Si and polymer substrates, revealing remarkable device-to-device uniformity.

Improvement of the Cycling Performance and Thermal Stability of Lithium-Ion Cells by Double-Layer Coating of Cathode Materials with Al2O3 Nanoparticles and Conductive Polymer.

We demonstrate the effectiveness of dual-layer coating of cathode active materials for improving the cycling performance and thermal stability of lithium-ion cells. Layered nickel-rich LiNi0.6Co0.2Mn0.2O2 cathode material was synthesized and double-layer coated with alumina nanoparticles and poly(3,4-ethylenedioxythiophene)-co-poly(ethylene glycol). The lithium-ion cells assembled with a graphite negative electrode and a double-layer-coated LiNi0.6Co0.2Mn0.2O2 positive electrode exhibited high discharge capacity, good cycling stability, and improved rate capability. The protective double layer formed on the surface of LiNi0.6Co0.2Mn0.2O2 materials effectively inhibited the dissolution of Ni, Co, and Mn metals from cathode active materials and improved thermal stability by suppressing direct contact between electrolyte solution and delithiated Li(1-x)Ni0.6Co0.2Mn0.2O2 materials. This effective design strategy can be adopted to enhance the cycling performance and thermal stability of other layered nickel-rich cathode materials used in lithium-ion batteries.

Facile synthesis of tailored nanostructured ORMOSIL particles by a selective dissolution process.

Tailored nanostructured ORMOSIL particles, of raspberry shaped, hollow, and rattle type structures, were prepared by a selective dissolution of siloxane networks in composite ORMOSIL particles with a multi-layered structure. The synthesis of monodisperse ORMOSIL particles involved a one-pot process in an aqueous solution using a binary or ternary mixture from three organosilanes, (3-aminopropyl)trimethoxysilane (APTMS), vinyltrimethoxysilane (VTMS), and/or phenyltrimethoxysilane (PTMS). In the following step, ORMOSIL particles were treated with a mixture of water and alcohol with mild heating. This mild etching process was efficient to selectively dissolve some of organosilane functional groups within the ORMOSIL particles but not their main silica frameworks, leading to formation of mesoporous particles. The strategy developed in this study is not only very facile, economical, and less time-consuming, but also more environmentally friendly by avoiding the use of corrosive etching chemicals and harsh reaction conditions. Surface roughness, core diameter, and shell thickness of the resultant mesoporous ORMOSIL particles were controlled by manipulating synthetic parameters such as the relative ratios of the silane monomers as well as the dissolution parameters such as temperature and type of solvent.

One-pot synthesis and surface modifications of organically modified silica (ORMOSIL) particles having multiple functional groups.

Here we report a facile one-pot synthetic method for organically modified silica (ORMOSIL) particles having multiple functional groups and demonstrate the homogeneous distribution of functional groups in ORMOSIL particles by chemical reactions of each surface functional group with fluorescent dyes such as fluroescamine and rhodamine B isothiocyanate. Dye-tagged ORMOSIL particles having tri-functional groups are exhibited two fluorescent emission peaks at 475 (blue) and 570 nm (red), indicating the positions of functional groups. The surface reaction of these functionalized ORMOSIL particles with various organic or inorganic materials not only endowed additional functionalities and physical properties, but also produced metallic hybrid composite particles. Chemical and physical properties of functionalized ORMOSIL particles were characterized by FT-IR, solid state (13)C and (29)Si NMR, thermogravimetric analysis (TGA), electron microscopy (SEM and TEM), and X-ray diffraction (XRD) analysis.

Selective surface reactions for Janus ORMOSIL particles with multiple functional groups using an ordered monolayer film at liquid-liquid interface.

Monodispersed, submicron-sized Janus ORMOSIL particles with multiple functional groups were prepared by the selective surface reaction of a monolayer film formed at a hexane-water interface. A well-ordered monolayer film was obtained by self-assembly of ORMOSIL particles with multiple functional groups at hexane-water interface. The photopolymerization of an ordered monolayer containing ORMOSIL particles yields a rigid film strong enough to maintain its integrity for transfer and further chemical reaction. The chemical reaction of this ordered film with organic and inorganic functional groups produced Janus ORMOSIL particles with multiple functional groups. The morphologies, structures, and chemical compositions of monolayer films and Janus ORMOSIL particles were characterized by FT-IR, solid state NMR, X-ray diffraction (XRD), optical microscopy (OM), electron microscopies (SEM and TEM), and confocal laser scanning microscopy.

One-step synthesis of structurally controlled silicate particles from sodium silicates using a simple precipitation process.

Silicate particles with various types of internal structures were prepared via one-pot synthesis. Spherical particles with sizes of 50-100 nm could be obtained by a simple precipitation process with the addition of alcohol to an aqueous sodium silicate solution. By controlling the reaction conditions such as the precipitating solvent (different types of alcohols), reaction time, temperature, and addition rate, spherical silicate particles with hollow, porous, dense internal structures were synthesized without using an external template. In addition, the amount of Na in the silicate particles was effectively reduced by washing with hot water, acid, or ion-exchange resins. Spherical particles maintained their morphologies after heat treatment at 500 degrees C. Electron microscopy, N(2) adsorption/desorption measurements, ICP-OES, XRD analysis, and IR and (29)Si NMR spectrometry were performed to elucidate the chemical and physical properties of the obtained silicate particles. This method of synthesis could provide a commercial route to the simple, economical mass production of silica particles.

Self-assembly growth process for polyhedral oligomeric silsesquioxane cubic crystals.

The colloidal self-assembly process for the formation of polyhedral oligomeric silsesquioxane cubic crystals is described; the growth process consists of the formation of spherical particles, one-dimensional particle chains, bundles of chains, and finally, the formation of cubic crystals.

Ratiometric singlet oxygen nano-optodes and their use for monitoring photodynamic therapy nanoplatforms.

Ratiometric photonic explorers for bioanalysis with biologically localized embedding (PEBBLE) nanoprobes have been developed for singlet oxygen, using organically modified silicate (ORMOSIL) nanoparticles as the matrix. A crucial aspect of these ratiometric singlet-oxygen fluorescent probes is their minute size. The ORMOSIL nanoparticles are prepared via a sol-gel-based process and the average diameter of the resultant particles is about 160 nm. These sensors incorporate the singlet-oxygen-sensitive 9,10-dimethyl anthracene as an indicator dye and a singlet-oxygen-insensitive dye, octaethylporphine, as a reference dye for ratiometric fluorescence-based analysis. We have found experimentally that these nanoprobes have much better sensitivity than does the conventional singlet-oxygen-free dye probe, anthracene-9,10-dipropionic acid disodium salt. The much longer lifetime of singlet oxygen in the ORMOSIL matrix, compared to aqueous solutions, in addition to the relatively high singlet oxygen solubility because of the highly permeable structure and the hydrophobic nature of the outer shell of the ORMOSIL nanoparticles, results in an excellent overall response to singlet oxygen. These nanoprobes have been used to monitor the singlet oxygen produced by "dynamic nanoplatforms" that were developed for photodynamic therapy. The singlet oxygen nanoprobes could potentially be used to quantify the singlet oxygen produced by macrophages.

Real-time measurements of dissolved oxygen inside live cells by organically modified silicate fluorescent nanosensors.

Optical PEBBLE (probes encapsulated by biologically localized embedding) nanosensors have been developed for dissolved oxygen using organically modified silicate (ormosil) nanoparticles as a matrix. The ormosil nanoparticles are prepared via a sol-gel-based process, which includes the formation of core particles with phenyltrimethoxysilane as a precursor followed by the formation of a coating layer with methyltrimethoxysilane as a precursor. The average diameter of the resultant particles is 120 nm. These sensors incorporate the oxygen-sensitive platinum porphyrin dye as an indicator and an oxygen-insensitive dye as a reference for ratiometric intensity measurement. Two pairs of indicator dye and reference dye, respectively, platinum(II) octaethylporphine and 3,3'-dioctadecyloxacarbocyanine perchlorate, and platinum(II) octaethylporphine ketone and octaethylporphine, were used. The sensors have excellent sensitivity with an overall quenching response of 97%, as well as excellent linearity of the Stern-Volmer plot (r(2) = 0.999) over the whole range of dissolved oxygen concentrations (0-43 ppm). In vitro intracellular changes of dissolved oxygen due to cell respiration were monitored, with gene gun injected PEBBLEs, in rat C6 glioma cells. A significant change was observed with a fluorescence ratio increase of up to 500% after 1 h, for nine different sets of cells, which corresponds to a 90% reduction in terms of dissolved oxygen concentration. These results clearly show the validity of the delivery method for intracellular studies of PEBBLE sensors, as well as the high sensitivity, which is needed to achieve real-time measurements of intracellular dissolved oxygen concentration.

New synthetic route for preparing rattle-type silica particles with metal cores.

Rattle-type silica particles with metal cores, applicable to catalysts and metal/inorganic composite coating materials, were prepared by the pre-shell/post-core method that can control the size of metal cores inside silica capsules and exchange from metal cores into different ones with a metal displacement reaction.