Ruthenium(II) trisbipyridine functionalized gold nanorods. Morphological changes and excited-state interactions

Gold nanorods synthesized using cetyltrimethylammonium bromide and tetraoctylammonium bromide as stabilizers are functionalized with a thiol derivative of ruthenium(II) trisbipyridyl complex [(Ru(bpy)3(2+)-C5-SH] in dodecanethiol using a place-exchange reaction. The changes in the plasmon absorption bands and transmission electron micrographs indicate significant changes in the gold rod morphology during the place-exchange reaction. The (Ru(bpy)(3)2+-C5-SH in its excited state undergoes quick deactivation when bound to gold nanorods. More than 60% of the emission was quenched when [(Ru(bpy)3(2+)-C5-SH] was bound to gold nanorods. Emission decay analysis indicates that the energy transfer rate constant is greater than 10(10) s(-1).     

Wavelength-dependent Coulomb explosion in carbon disulphide (CS2) clusters: generation of energetic multiply charged carbon and sulphur ions

A gigawatt laser-induced Coulomb explosion has been observed in carbon disulphide (CS(2)) clusters generating energetic, multiply charged [C](m+) (m = 1-4) and [S](n+) (n = 1-6) atomic ions of carbon and sulphur. The Coulomb explosion shows wavelength dependence. Comparison of these results with our earlier work shows that the polarizability and dipole moment might help in energy absorption from the laser field but they are not mandatory conditions for this low-intensity Coulomb explosion. The results show that in a field of 10(9) W/cm(2), absorption of 266 and 355 nm laser radiation by CS(2) clusters leads to multiphoton dissociation/ionization whereas at 532 nm the whole cluster explodes generating multiply charged atomic ions.     

Morphology of single-wall carbon nanotube aggregates generated by electrospray of aqueous suspensions

Airborne single-wall carbon nanotubes (SWCNTs) have a high tendency to agglomerate due to strong interparticle attractive forces. The SWCNT agglomerates generally have complex morphologies with an intricate network of bundles of nanotubes and nanoropes, which limits their usefulness in many applications. It is thus desirable to produce SWCNT aerosol particles that have well-defined, unagglomerated fibrous morphologies. We present a method to generate unagglomerated, fibrous particles of SWCNT aerosols using capillary electrospray of aqueous suspensions. The effects of the operating parameters of capillary electrospray such as strength of buffer solution, capillary diameter, flow rate, and colloidal particle concentration on the size distributions of SWCNT aerosols were investigated. Results showed that electrospray from a suspension of higher nanotube concentration produced a bimodal distribution of SWCNT aerosols. Monodisperse SWCNT aerosols below 100 nm were mostly non-agglomerated single fibers, while polydisperse aerosols larger than 100 nm had two distinct morphologies: a ribbon shape and the long, straight fiber. Possible mechanisms are suggested to explain the formation of the different shapes, which could be used to produce SWCNT aerosols with different morphologies.     

Bright,NIR‐Emitting Au23 from Au25: Characterization and Applications Including Biolabeling

A novel interfacial route has been developed for the synthesis of a bright‐red‐emitting new subnanocluster, Au₂₃, by the core etching of a widely explored and more stable cluster, Au₂₅SG₁₈ (in which SG is glutathione thiolate). A slight modification of this procedure results in the formation of two other known subnanoclusters, Au₂₂ and Au₃₃. Whereas Au₂₂ and Au₂₃ are water soluble and brightly fluorescent with quantum yields of 2.5 and 1.3 %, respectively, Au₃₃ is organic soluble and less fluorescent, with a quantum yield of 0.1 %. Au₂₃ exhibits quenching of fluorescence selectively in the presence of Cu²⁺ ions and it can therefore be used as a metal‐ion sensor. Aqueous‐ to organic‐phase transfer of Au₂₃ has been carried out with fluorescence enhancement. Solvent dependency on the fluorescence of Au₂₃ before and after phase transfer has been studied extensively and the quantum yield of the cluster varies with the solvent used. The temperature response of Au₂₃ emission has been demonstrated. The inherent fluorescence of Au₂₃ was used for imaging human hepatoma cells by employing the avidin–biotin interaction.     

Effect of pH on photoluminescence enhancement in Pb-doped ZnS nanoparticles

Narrowly dispersed Pb-doped zinc sulfide nanoparticles were synthesized at room temperature using a chemical method in which the nanoparticle surfaces were passivated using mercaptoethanol. The maximum intensity of the broad green luminescence (approximately 530 nm) from these nanoparticles was observed at an optimum dopant concentration of 0.104 Pb wt%. The emission intensity was found to depend on the synthesis pH conditions, thus yielding maximum intensity at 5.0 pH. Comparatively lower emission intensities were observed for the other pH values (2.5-9.0 pH range). This may be due to the pH-dependent Cl- (as well as Na+) incorporation into the ZnS matrix, which possibly helps in inducing required density of impurity (donor/co-activator) states in the energy gap of ZnS nanoparticles. X-ray diffraction analysis using Debye functional analysis showed that the particle size is 2.8+/-0.3 nm.     

Stokes flow past a porous spheroid embedded in another porous medium

A study is made with an analysis of an incompressible viscous fluid flow past a slightly deformed porous sphere embedded in another porous medium. The Brinkman equations for the flow inside and outside the deformed porous sphere in their stream function formulations are used. Explicit expressions are investigated for both the inside and outside flow fields to the first order in small parameter characterizing the deformation. The flow through the porous oblate spheroid embedded in another porous medium is considered as the particular example of the deformed porous sphere embedded in another porous medium. The drag experienced by porous oblate spheroid in another porous medium is also evaluated. The dependence of drag coefficient and dimensionless shearing stress on the permeability parameter, viscosity ratio and deformation parameter for the porous oblate spheroid is presented graphically and discussed. Previous well-known results are then also deduced from the present analysis.     

Electrical and structural properties enhancement in plasticized high Tg polymers using metal salts

Plasticized polymer electrolyte composite has been prepared in the form of a film by solution casting method. Poly (ethyl methacrylate) (PEMA) acts as a host polymer and is doped with Sodium Iodide (NaI). Ethylene carbonate (EC) added as a plasticizer and also enhances amorphicity of the polymer electrolyte. The electrical conductivity of the PEMA+NaI was evaluated using complex impedance spectroscopy. Maximum ionic conductivity obtained at room temperature was 8.75 × 10^?6 S/cm with the composition of PEMA: NaI (30%) + 60% EC. The conductivity further increased with increase in temperature and moved up to 5.8 × 10^?5 S/cm. Scanning electron microscopy was used to study the surface morphology of the composite film. Fourier transform infrared ray and X-ray diffraction data confirmed the complexation of material.     

Synthesis of α‐Benzylthiobenzimidazoleacetonitriles and Their Chemoselective Reduction of the Double Bond with NaBH4

Condensation of 2‐((1H‐benzimidazol‐2‐yl)thio)acetonitre 1 with aromatic aldehydes in methanol containing piperidine gave the corresponding 2‐((1H‐benzimidazol‐2‐yl)thio)‐3‐arylacrylonitrile 2 , which on treatment with NaBH₄ in ethanol unexpectedly and chemoselectively gave 2‐((1H‐benzimidazol‐2‐yl)thio)‐3‐arylpropanenitrile 3 by the reduction of the double bond of 2 . 3 on methylation with dimethyl sulfate containing K₂CO₃ as a base and tetrabutylammonium bromide as PTC gave 2‐((1‐methylbenzimidazol‐2‐yl)thio)‐3‐arylpropanenitrile 6 . The latter could also be prepared in an alternative way by reaction of 1 with dimethyl sulfate giving the intermediary 2‐((1‐methylbenzimidazol‐2‐yl)thio)acetonitrile 4 , followed by condensation with aromatic aldehydes yielding 5 and subsequent reduction of 5 with NaBH₄ in methanol. 6 could be directly synthesized by treatment of 4 with benzyl chloride in DMF and triethylamine as a base at 60°C for 5 h.     

A Quasi-3D Threshold Voltage Model for Dual-Metal Quadruple-Gate MOSFETs

Due to challenges with relentless scaling of conventional bulk complementary metal-oxide- semiconductor （CMOS） devices, non-conventional CMOS devices have been of great interest to scale metaboxide-semiconductor field effect transistors （MOSFETs） to the 32nm gate length and below effectively. Among non-conventional CMOS devices, quadruple-gate （QG） MOSFETs have been gaining interest because they are sup- posed to provide excellent electrostatic controllability for ultra-large-scale integration （ULSI） applications. A number of attempts have been made to analyze QG MOSFETs analytically with a great amount of success. Sharma et al. have presented an an- alytical threshold voltage model for QG MOSFETs using an isomorphic polynomial function for solv- ing the 3D Poisson equation. Chiang has presented a number of models of scaling length,threshold voltage and subthreshold current for QG MOS- FETs adopting a concept of the so-called equivalent number of gates （ENGs）.