Ehsan U. Khan

Morphological evolution of au nanowires controlled by rayleigh instability

A sound knowledge and understanding of the thermal stability of nanowires is a prerequisite for the reliable implementation of nanowire-based devices. We investigate the morphology of Au nanowires annealed isothermally at different temperatures. During the processes, triggered by heating, the wires undergo various configurational changes to finally break up into chains of nanospheres at much lower than bulk melting temperatures due to capillary or so-called Rayleigh instability. The role of three parameters, namely, wire diameter, temperature, and annealing time, on the final morphology is investigated. Both the average sphere diameter and the mean spacing between adjacent spheres are larger than the values predicted for materials with isotropic surface energy. Possible reasons are discussed in the paper.

Influence of crystallinity on the Rayleigh instability of gold nanowires

The influence of the crystalline structure of nanowires on their thermal instability has been systematically investigated. Both poly- and single-crystalline (SC) cylindrical nanowires with diameters 87 and 132 nm transform into chains of spheres during annealing at 600–700 °C. SC nanowires oriented along the 1 1 0 direction are found to be more stable, i.e. longer annealing times are needed for their complete transformation into sphere chains. Sphere size and spacing between adjacent spheres formed after decay are controlled by the crystallinity of the wires and both are larger in the case of SC nanowires.

Etch Induction Time in CR-39 Detectors Etched in Na2CO3 Mixed NaOH Solution

Six different solutions of 6M NaOH, containing different amounts of Na2CO3 at 70°C were used for the revelation of latent damage trails in CR-39 plastic track detectors. These detectors were earlier exposed to fission fragments from 252Cf source for 30 min in vacuum and were then etched in the respective solutions for different etching time intervals of 5–20 min starting from 5min up to 160min. The etch induction time in each detector was obtained by extrapolating the intersection of resulting curves of track lengths and track diameters with the time axis.

Sequential and double sequential fission observed in heavy ion interaction Of (11.67 MeV/u)197Au projectile with 197Au target

The heavy ion interaction of 11.67 MeV/u 197Au + 197Au has been investigated using mica as a passive detector. By employing Solid State Nuclear Track Detection Technique the data of elastic scattering as well as inelastic reaction channel was collected. The off-line data analysis of multi-pronged events was performed by measuring the three-dimensional geometrical coordinates of correlated tracks on event-by-event basis. Multi-pronged events observed in this reaction were due to sequential and double sequential fission. Using a computer code PRONGY based on the procedure of internal calibration, it was possible to derive quantities like mass transfer, total kinetic energy loss and scattering angles.

Mass Transfer: a Deciding Factor for the Multiplicity of an Event in Deep Inelastic Collisions

Intermediate stage of the three and four-pronged events is investigated in the reaction 208Pb+ 197Au at beam energy 11.67 MeV/u. Multiprong events are analysed numerically using an empirical mass-dependent velocity-range relation. Using the measured three-dimensional coordinates of correlated tracks, it is possible to determine the quantities such as mass transfer and total kinetic energy loss. These quantities are then used to study the intermediate stage of the reaction. It has been observed that mass transfer and total kinetic energy loss at the first step of the reaction decides the multiplicity of an event at the second stage of the sequential fission process.