Size-dependent chemical transformation,structural phase change,and optical properties of nanowires

Nanowires offer a unique approach for the bottom-up assembly of electronic and photonic devices with the potential of integrating photonics with existing technologies. The anisotropic geometry and mesoscopic length scales of nanowires also make them very interesting systems to study a variety of size-dependent phenomenon where finite-size effects become important. We will discuss the intriguing size-dependent properties of nanowire systems with diameters in the 5–300?nm range, where finite-size and interfacial phenomena become more important than quantum mechanical effects. The ability to synthesize and manipulate nanostructures by chemical methods allows tremendous versatility in creating new systems with well-controlled geometries, dimensions, and functionality, which can then be used for understanding novel processes in finite-sized systems and devices.     

In-situ and ex-situ study of crystallization behaviour of magnetron sputtered Ni63Zr37 amorphous thin film

ABSTRACT

The stages of crystallization of magnetron sputter-deposited Ni₆₃Zr₃₇ film with mostly amorphous structure have been investigated by differential scanning calorimetry (DSC) and in-situ annealing at 300°C by use of heating stage on a high-resolution transmission electron microscope (HRTEM). These results have been further confirmed by grazing incidence X-ray diffraction analyses of thin film specimens annealed ex-situ at 300°C for various durations. The temperature for crystallization found by DSC has been found to increase from 371°C to 434°C with an increase in heating rate from 3°C/min to 10°C/min, and the apparent activation energy for amorphous to crystalline transformation has been found as ～260.2?kJ/mol from the Kissinger plot. Studies on HRTEM using in-situ heating stage have shown the crystallization to occur on annealing at 300°C for ～10?min. Crystallization at a temperature lower than that found by DSC is attributed to structural relaxation with reduction of free volume due to thermal activation. It has been observed that Ni₃Zr forms first due to its large negative enthalpy of formation, and is followed by the formation of Ni-rich solid solution (Ni_ss) grains. HRTEM studies have shown grain rotation with the formation of partial dislocations at Ni₃Zr-Ni_ss interfaces as well as twinning followed by detwinning with dislocation formation in the Ni_ss matrix possibly to reduce the interfacial energy.     

Electrical transport characteristics of ZnO–Bi2O3–B2O3 glasses

Optically clear glasses in the ZnO–Bi₂O₃–B₂O₃ (ZBBO) system were fabricated via the conventional melt-quenching technique. Dielectric constant and loss measurements carried out on ZBBO glasses unraveled nearly frequency (1 kHz–10 MHz)-independent dielectric characteristics associated with significantly low loss (D?=?0.004). However, weak temperature response was found with temperature coefficient of dielectric constant 18?±?4 ppm °C^?1 in the 35–250 °C temperature range. The conduction and relaxation phenomena were rationalized using universal AC conductivity power law and modulus formalism respectively. The activation energy for relaxation determined using imaginary parts of modulus peaks was 2.54 eV which was close to that of the DC conduction implying the involvement of similar energy barriers in both the processes. Stretched and power exponents were temperature dependent. The relaxation and conduction in these glasses were attributed to the hoping and migration of Bi³⁺ cations in their own and different local environment.     

Contrasting friction and diffusion in molecularly thin confined films

We study, using fluorescence correlation spectroscopy, translational diffusion in molecularly thin liquids confined within a surface forces apparatus. The diffusion coefficient decreases exponentially from the edges towards the center of the Hertzian contact and further suggests the presence of a small number of distinct diffusion processes. This holds alike a crystallizable fluid (OMCTS) and a glass-former (1,2-propane diol), both of which displayed static friction. We conclude that friction, the average of an ensemble of molecules, masked massively heterogeneous molecular mobility.     

Effect of absorbed pump power on the quality of output beam from monolithic microchip lasers

The dependence of the beam propagation factor (M ² parameter) with the absorbed pump power in the case of monolithic microchip laser under face-cooled configuration is extensively studied. Our investigations show that the M ₂ parameter is related to the absorbed pump power through two parameters (α and β) whose values depend on the laser material properties and laser configuration. We have shown that one parameter arises due to the oscillation of higher order modes in the microchip cavity and the other parameter accounts for the spherical aberration associated with the thermal lens induced by the pump beam. Such dependency of M ² parameter with the absorbed pump power is experimentally verified for a face-cooled monolithic microchip laser based on Nd³⁺ -doped GdVO₄ crystal and the values of α and β parameters were estimated from the experimentally measured data points.     

Quark mass corrections to the perturbative thrust and its effect on the determination of αs

We consider the effects of quark masses to the perturbative thrust in e ⁺ e ⁻ annihilation. In particular we show that perturbative power corrections resulting from non-zero quark masses considerably alters the size of the non-perturbative power corrections and consequently, significantly changes the fitted value of α_s.     

Reactivity studies of carbon,phosphorus and sulfur‐based acyl sites with tertiary oximes in gemini surfactants

Kinetic studies of the reactions of tertiary oximes (monoisonitroso acetone; MINA and butane 2,3 dione monooxime; BDMO) with some carboxylate (p‐nitrophenyl acetate and p‐nitrophenyl benzoate), phosphate (p‐nitrophenyl diphenyl phosphate and bis (2,4‐dinitrophenyl) phosphate) and sulfonate (p‐nitrophenyl p‐toluene sulphonate) esters in gemini surfactants have been conducted. The observed first‐order rate constant versus surfactant profiles show micelle‐assisted bimolecular reactions involving interfacial ion exchange between bulk aqueous media and micellar pseudophase. Experimental results showed that MINA exhibited better nucleophilic activity towards ester cleavage than BDMO. Pseudophase model has been applied in order to determine micellar second‐order rate constants and binding constants. Copyright © 2013 John Wiley & Sons, Ltd.     

Surface Coating Rescues Proteins from Magnetite Nanoparticle Induced Damage

The presence of magnetic nanoparticles (NPs) in physiological systems induces toxicity through its effects on mitochondrial function and reactive oxygen species (ROS) imbalance. Magnetic NP induced cytotoxicity has been elaborately evaluated for impending threats, however, a detailed investigation is lacking. It is shown that the interaction of Fe₃O₄ NPs with cytochrome c can lead to different events based on the NPs to protein ratio, the solution conditions, and the type of surface protection. At low NPs concentration, rapid binding and subsequent electron transfer are the preferred events while at higher concentration slow oxidative modification of the protein is initiated. The slow event of protein modification yields conformational disorientation, loss of stability, and formation of amyloid‐like structures with cytochrome c. The possibility that the NP induced oxidative stress and age can work in concert to compromise different aspects of cellular quality control processes is discussed. Suitable surface modifications of the NPs inhibit their direct binding to the protein molecules and minimize NP induced toxicity.     

Casson fluid flow and heat transfer over a nonlinearly stretching surface

A boundary layer analysis is presented for non-Newtonian fluid flow and heat transfer over a nonlinearly stretching surface. The Casson fluid model is used to characterize the non-Newtonian fluid behavior. By using suitable transformations, the governing partial differential equations corresponding to the momentum and energy equations are converted into non-linear ordinary differential equations. Numerical solutions of these equations are obtained with the shooting method. The effect of increasing Casson parameter is to suppress the velocity field. However the temperature is enhanced with the increasing Casson parameter.