Enhanced Magnetization of Cobalt Defect Clusters Embedded in TiO2-δ Films.

High magnetizations are desirable for spintronic devices that operate by manipulating electronic states using built-in magnetic fields. However, the magnetic moment in promising dilute magnetic oxide nanocomposites is very low, typically corresponding to only fractions of a Bohr magneton for each dopant atom. In this study, we report a large magnetization formed by ion implantation of Co into amorphous TiO2-δ films, producing an inhomogeneous magnetic moment, with certain regions producing over 2.5 µB per Co, depending on the local dopant concentration. Polarized neutron reflectometry was used to depth-profile the magnetization in the Co:TiO2-δ nanocomposites, thus confirming the pivotal role of the cobalt dopant profile inside the titania layer. X-ray photoemission spectra demonstrate the dominant electronic state of the implanted species is Co0, with a minor fraction of Co2+. The detected magnetizations have seldom been reported before and lie near the upper limit set by Hund's rules for Co0, which is unusual because the transition metal's magnetic moment is usually reduced in a symmetric 3D crystal-field environment. Low-energy positron annihilation lifetime spectroscopy indicates that defect structures within the titania layer are strongly modified by the implanted Co. We propose that a clustering motif is promoted by the affinity of the positively charged implanted species to occupy microvoids native to the amorphous host. This provides a seed for subsequent doping and nucleation of nanoclusters within an unusual local environment.

Novel chemical synthesis and characterization of CeTi(2)O(6) brannerite.

Cerium titanate CeTi2O6 was prepared by a new soft chemistry route in aqueous solution. A suite of characterization techniques, including X-ray diffraction, thermal analysis, vibrational spectroscopy, and scanning and transmission electron spectroscopy, were employed to investigate the brannerite structure formation and its bulk properties. The synthesized powder formed the brannerite crystal structure upon calcination at temperatures as low as 800 °C. Samples sintered at 1350 °C possess a high level of crystallinity. X-ray absorption near-edge structure results indicate the presence of six-coordinated Ce(4+) in the brannerite samples.

Optimizing radiolabeling amine-functionalized silica nanoparticles using SarAr-NCS for applications in imaging and radiotherapy.

Silica nanoparticles functionalized with amine groups and in the size range of approximately 60-94 nm were produced by combining sol-gel processing and emulsion technology. Hexa-aza cage ligand SarAr-NCS was conjugated to the silica nanoparticles and subsequently radiolabeled with a solution of (57)Co(2+)-doped carrier Co(2+). The number of Co(2+) ions bound to the silica particles at pH 7 was used to determine the average number of available SarAr-NCS ligands conjugated to a silica particle. For organically modified silica particles of 94.0 and 59.5 nm diameter, the maximum number of metal binding sites was determined to be 11700 and 3270 sites per particle, respectively. For silica particles (63.5 nm peak diameter) produced using an water-in-oil emulsion, the calculated average was 4480 on the particle surface. The number of SarAr-NCS conjugated on the particles was easily controlled, potentially providing for a range of products for applications in the risk assessment of particles and theranostic imaging or radiotherapy when radiolabeled with a suitable radioisotope such as (64)Cu or (67)Cu.

Determining the orientation and molecular packing of organic dyes on a TiO2 surface using X-ray reflectometry.

The determination of the orientation and molecular density for several porphyrin dyes adsorbed on planar TiO(2) surfaces using X-ray reflectometry (XRR) is reported. Adsorption of nanoscale water layers occurred rapidly upon exposure of freshly prepared TiO(2) surfaces to ambient conditions; however, this was successfully eliminated, resulting in clearly discernible adsorbed dye layers for sensitized surfaces. Adsorbed dye orientations, determined from computations constrained by the measured dye layer thickness, were calculated to have a binding tilt angle of 35°-40°. Combining the XXR data with the orientation models indicates that the porphyrins form densely packed surfaces with an intermolecular spacing of 3-4 Å, consistent with π-π stacking interactions. Changes in the molecular size of probe dyes were reflected in corresponding changes in the measured dye layer thickness, confirming the ability of this technique to resolve small variations in dye layer thickness and consequently adsorption orientation. Application of these results to understanding the behavior of dye-sensitized devices is discussed.

CO2 triggering and controlling orthogonally multiresponsive photochromic systems.

We report a new generic method of reversibly controlling the photochromism of spiropyrans. It was found that the photochromic effect of spiropyrans can be reversibly switched on and off by addition and removal of carbon dioxide (CO(2)) to spiropyran in alcohol solutions containing an amidine (i.e., DBU) that acts as a CO(2) sensitizer. Spiropyrans are not photochromic in the presence of DBU but photochromic when CO(2) is subsequently added to the solution. The CO(2) is readily removed by inert gas bubbling, thus allowing facile activation and deactivation of the photochromic effect. Carbon dioxide, without the presence of the sensitizing amidine, had no effect on photochromism of the spiropyrans. Other photochromic dyes classes such as spirooxazines and chromenes are not affected by this CO(2)/DBU stimulus. As a result, orthogonal activation of mixtures of spirooxazines and spiropyrans was achieved to provide four color states (clear, yellow, green, and blue) by varying the combinations of the stimuli of UV, visible light, CO(2), and CO(2) depleted. This finding now permits the many applications using spiropyrans to be CO(2) responsive.