Interface-dominated Growth of a Metastable Novel Alloy Phase

A new \textit{D0$_{23}$} metastable phase of Cu$_3$Au is found to grow at the interfaces of Au/Cu multilayers deposited by magnetron sputtering. The extent of formation of this novel alloy phase depends upon an optimal range of interfacial width primarily governed by the deposition wattage of the dc-magnetron used. Such interfacially confined growth is utilized to grow a $\sim$ 300 nm thick Au/Cu multilayer with thickness of each layer nearly equal to the optimal interfacial width which was obtained from secondary ion mass spectrometry (SIMS) data. This growth technique is observed to enhance the formation of the novel alloy phase to a considerable extent. SIMS depth profile also indicates that the mass fragment corresponding to Cu$_3$Au occupies the whole film while x-ray diffraction (XRD) shows almost all the strong peaks belonging to the \textit{D0$_{23}$} structure. High resolution cross-sectional transmission electron microscopy (HR-XTEM) shows the near perfect growth of the individual layers and also the lattice image of the alloy phase in the interfacial region. Vacuum annealing of the alloy film and XRD studies indicate stabilization of the \textit{D0$_{23}$} phase at $\sim$ 150$^{\circ}$C. The role of interfacial confinement, the interplay between interfacial strain and free energy and the hyperthermal species generated during the sputtering process are discussed.Comment: Accepted in Journal of Materials Researc

Phase Transitions In An Implicit Solvent Minimal Model Of Lipids: Role Of Head-Tail Size Ratio

We present Monte Carlo simulations under constant NVT conditions on a minimal three beads coarse grained implicit solvent model of lipid molecules, with the hydrophilic head represented by one bead and the hydrophobic tail represented by two beads. We consider two lipids, one with the head and tail bead sizes equal and the other with the tail beads smaller than the head. When cooled to the ambient temperature from an initial isotropic phase at high temperature, the first lipid transforms spontaneously to a lamellar phase while the second lipid transforms to a micellar phase, showing the crucial role of the head and tail size ratio on lipid phases.Comment: conference pape

Quasi-Stationary States in Ionic Liquid-Liquid Crystal Mixtures at the Nematic-Isotropic Phase Transition

An open system is a system driven away from equilibrium by a source that supplies an inflow of energy and a sink to maintain an outflow. A typical example of an open system is a system close to its phase transition temperature under irradiation by a laser. This provides a steady flow of energy through a photon flux. The sink in that case is the environment to which energy is lost in the form of heat dissipation. Creation of such a thermodynamically open state suggests that we can expect generation of exotic spatio-temporal structures length-scale independent correlation maintained under the global dissipative forces provided by the surroundings. Internal long-range forces can bring in additional spatio-temporal correlations, giving rise to states with a very long lifetime, the ``quasistationary states'' (QSS). In this communication, we report evolution of quasistationary states, in a mixture of the well-known liquid crystal (N-(4-methoxybenzylidene)-4-butylaniline, MBBA) and an iron-based room temperature ionic liquid (RTIL), namely, 1-ethyl-3-methylimidazolium tetrachloroferrate (EMIF) at the Nematic-Isotropic phase transition, when focused radiation with 532 nm wavelength from a Nd:YAG laser (200-300 mW optical power) is incident on the sample. We explain the QSS by invoking a sharp negative thermal gradient due to the laser photon flux and dipolar interactions. In our model, the dipoles are the charge transfer complexes (CTCs) formed in the RTIL by resonant laser pumping, which create an orientational ordering and balance the fluctuating force of the thermal gradient to create the QSS. In the absence of such CTCs in a mixture of MBBA and a Gallium-based RTIL (1-ethyl-3-methylimidazolium tetrachlorogallate, EMIG), the QSS was not observed

Preparation of serum capped silver nanoparticles for selective killing of microbial cells sparing host cells

Following access into the cell, colloidal silver nanoparticles exhibit generalized cytotoxic properties, thus appear as omnipotent microbicidal, but not suitable for systemic use unless are free of toxic effects on host cells. The AgNP-Serum-18 when prepared from silver nitrate, using dextrose as reducing and group-matched homologous serum as a stabilizing agent, selective endocytosis, and oxidative stress-dependent bio-functional damages to the host are mostly eliminated. For their bio-mimicking outer coat, there is the least possibility of internalization into host cells or liberation of excess oxidants in circulation following interaction with erythrocytes or vascular endothelial cells. The presence of infection-specific antibodies in the serum can make such nano-conjugates more selective. A potent antimicrobial action and a wide margin of safety for mammalian cells in comparison with very similar PVA-capped silver nanoparticles have been demonstrated by the in-vitro challenge of such nanoparticles on different microbes, human liver cell-line, and in-vivo study on mice model. This may open up wide-range therapeutic prospects of colloidal nanoparticles

Counterion Effects on Nano-confined Metal-Drug-DNA Complexes

We have explored morphology of DNA molecules bound with Cu-complexes of piroxicam molecules, a non-steroidal anti-inflammatory drug (NSAID), under one-dimensional confinement of thin films and have studied the effect of counterions present in a buffer. X-ray reflectivity at and away from the Cu K absorption edge and atomic force microscopy studies reveal that confinement segregates the drug molecules preferentially in a top layer of the DNA film, and counterions enhance this segregation