Determination of preferential rare earth adatom adsorption geometries on Si(001)

The adsorption patterns of rare earth atoms on Si(001) were investigated using scanning tunneling microscopy measurements and density functional calculations. Stable configurations were systematically determined via calculation of binding energies of various adatom coverage and adsorption geometry. Competition between inter-adatom hybridization and Coulomb repulsion is the mechanism contributing to binding energy minima associated with commonly observed rare earth adsorption geometries. Comparison of stable configurations with experimental scanning tunneling microscopy images demonstrated accuracy of the theoretical models. This paves a way for the understanding of self-assembly of rare earth disilicide nanowires on vicinal Si(001) substrates.     

Dy3+ emission in M5(PO4)3F (M = Ca, Ba) phosphor

Ultrafine M₅(PO₄)₃F:Dy³⁺ (M = Ca, Ba) phosphors were prepared via combustion process using metal nitrates as precursors. The formation of crystalline phosphate was confirmed by X-ray diffraction pattern. The PL excitation spectra show the excitation peaks observed at 250 to 400 nm due to f → f transition of Dy³⁺ ion, which are useful for solid-state lighting purpose (mercury free excitation). The PL emission of Dy³⁺ ion by 348 nm excitation gave an emission at 489 nm (blue), 582 nm (yellow) and 675 nm (red). All the characteristics of BYR emissions like BGR indicate that Dy doped Ca₅(PO₄)₃F and Ba₅(PO₄)₃F phosphors are good candidates that can be applied in solid-state lighting phosphor (mercury free excited lamp phosphor) and white light LED.      

Potentiation of the cytotoxicity of the anticancer agent tirapazamine by benzotriazine N-oxides: the role of redox equilibria

Tirapazamine (3-amino-1,2,4-benzotriazine 1,4-dioxide), the lead bioreductive drug with selective toxicity for hypoxic cells in tumors, is thought to act by forming an active oxidizing radical of high one-electron reduction potential, E(1), when reduced by reductases. It has a dual mechanism of action, both generating DNA radicals, following its one-electron reduction and subsequently oxidizing these DNA radicals to form labile cations or hydrolyzable lactones through transferring an O atom, resulting in DNA strand breaks. These parallel secondary reactions have been proposed to be also initiated by its two-electron reduced metabolite, the 1-oxide. We have used pulse radiolysis to show that the benzotriazinyl radical of a highly soluble analogue of tirapazamine, the 3-(N,N-dimethyl-1,2-ethanediamine) analogue, is able to oxidize tirapazamine itself. We have found that both tirapazamine and the 1-oxides are in equilibrium with their respective benzotriazinyl radicals, with high concentrations of the more soluble 1-oxide maintaining a high concentration of the more reactive oxidizing radical of tirapazamine. The one-electron reduction potentials, E(1), of the 1-oxides and related compounds have been measured and, together with the E(1) values of tirapazamine and the 2-nitroimidazole radiosensitizer, misonidazole, are shown to predict the published percentages of electron transfer. This radical chemistry study gives an insight into the mechanisms of the potentiation of radical damage, reported for DNA, that underlies the hypoxic cytotoxicity of electron affinic compounds. The E(1) values of the benzotriazinyl radicals of the benzotriazine compounds govern the position of the redox equilibria, which determine the amount of initial radical damage. The E(1) values of the 1,4-dioxides and 1-oxide compounds govern the degree of potentiation of the initial radical damage once formed.     

Releasable luciferin-transporter conjugates: tools for the real-time analysis of cellular uptake and release

The design, synthesis, and evaluation of conjugates of arginine-rich transporters and luciferin are described that release luciferin only after entry into cells that are stably transfected with luciferase. Each molecule of free luciferin that is released after entry generates a photon that can be measured allowing for real-time quantification of uptake and release in cells. The process provides a method to assay uptake and release of free luciferin as a function of variations in the releasable linker and in the transporter.     

Structural,optical, and photoelectrochemical properties of nanosphere-like CdXZn1-XS synthesized by electrochemical route

Here, we present the effect of different Zn contents on the structural, morphological, and optical properties of Cd_XZn_1-XS thin films deposited by electrodeposition method on stainless steel and indium-doped tin oxide (ITO) glass substrates. Electrosynthesized Cd_XZn_1-XS thin films are characterized by using X-ray diffraction (XRD), UV-Vis spectrophotometer, field emission scanning electron microscope (FE-SEM), and surface wettability analysis. XRD pattern reveals that the Cd_XZn_1-XS thin films are polycrystalline in nature with hexagonal crystal structure. FE-SEM micrograph displays that these Cd_XZn_1-XS thin films exhibit the different sizes of sphere-like nanostructures by varying the X value. The optical absorption study indicates that drastic variation in band gap energy of Cd_XZn_1-XS thin films. In advance photovoltaic measurements, Cd_XZn_1-XS thin films are to be studied by forming the photoelectrochemical (PEC) cell having Cd_XZn_1-XS/0.5 M (Na₂SO₃)/C configuration. The efficiency values of Cd_XZn_1-XS are found to be 0.2, 0.35, 0.32, 0.25, and 0.23 % respectively at X content.

     

Electrochemical preparation of luminescent graphene quantum dots from multiwalled carbon nanotubes

Green luminescent, graphene quantum dots (GQDs) with a uniform size of 3, 5, and 8.2(±0.3)?nm in diameter were prepared electrochemically from MWCNTs in propylene carbonate by using LiClO(4) at 90?°C, whereas similar particles of 23(±2)?nm were obtained at 30?°C under identical conditions. Both these sets of GQDs displayed a remarkable quantum efficiency of 6.3 and 5.1?%, respectively. This method offers a novel strategy to synthesise size-tunable GQDs as evidenced by multiple characterisation techniques like transmission and scanning electron microscopy, atomic force microscopy, Raman spectroscopy and X-ray diffraction (XRD). Photoluminescence of these GQDs can be tailored by size variation through a systematic change in key process parameters, like diameter of carbon nanotube, electric field, concentration of supporting electrolyte and temperature. GQDs are promising candidates for a variety of applications, such as biomarkers, nanoelectronic devices and chemosensors due to their unique features, like high photostability, biocompatibility, nontoxicity and tunable solubility in water.     

Nanocrystalline gadolinium iron garnet for circulator applications

Due to high resistivity and low microwave losses, gadolinium iron garnets (GdIG) are useful materials for non-reciprocal devices such as circulators or isolators. Keeping the miniaturization and cost reduction in mind, the trend is to modify the conventional methods of preparation of samples. In this connection we have synthesized nanocystalline GdIG by using the Microwave Hydrothermal method at 160 °C/45 min. As synthesized powders were characterized by using X-ray diffraction (XRD), transmission electron microscopy and Fourier Transform Infrared Spectroscopy. XRD patterns show the formation of a garnet phase with crystallite size varying between 19 nm and 40 nm. Differential Thermal Analysis studies were also carried out on the nanopowders. The powders were densified at a lower sintering temperature of 1100 °C/45 min using a microwave sintering method. The sintered samples were characterized by XRD and atomic force microscopy. The frequency dependence of complex permittivity and ferromagnetic resonance were measured in the K_a band frequency (27–40 GHz). Magnetic properties were also measured at room temperature.     

A one-pot catalysis: the strategic classification with some recent examples

In this "Emerging Area", the strategic classification of one-pot catalysis, i.e. cooperative, relay and sequential catalysis, is described. In order to illustrate this classification, we take the readers through a series of recent examples which utilize either metal-metal, metal-organo and organo-organo catalysts. The compilation clearly demonstrates the explosive growth and power of this field, which has become, in the last few years, an important technique particularly in the case of enantioselective catalysis.