Compesh Pannu

Radiation stability of graphene under extreme conditions

In this letter, we report radiation stability of graphene under extreme condition of high energy density generated by 150 MeV Au ion irradiation. The experiment reveals that graphene is radiation resistant for irradiation at 1014 ions/cm2 of 150 MeV Au ions. It is significant to note that annealing effects are observed at lower fluences whereas defect production occurs at higher fluences but significant crystallinity is retained. Our results demonstrate applicability of graphene based devices in radiation environment and space applications.

Large electronic sputtering yield of nanodimensional Au thin films: Dominant role of thermal conductivity and electron phonon coupling factor

Detailed experiments and theoretical calculations on electronic sputtering of Au thin films (5-200 nm) on a quartz substrate are performed, revealing unusually large electronic sputtering, dependent on the thickness of the films. The dependence of electronic thermal conductivity (κe), electron-phonon coupling factor (g), and lattice thermal conductivity (κa) on the effective electron mean free path is taken into account in the thermal spike calculation for nanodimensional systems to elucidate the combined effect of the thickness and grain size on the electronic sputtering yield. The thermal spike simulation with refined parameters for nanodimensional systems gives a better explanation of the electronic sputtering process with a very good correlation between the experimental and theoretical yields than that of the thermal spike model with bulk parameters.

Phase evolution and electrical properties of Co–Sb alloys fabricated from Co/Sb bilayers by thermal annealing and ion beam mixing

An investigation was carried out to understand the phase evolution and study the structural, morphological, optical and electrical properties of Co-Sb alloys fabricated by two different approaches: (a) thermal annealing and (b) ion-beam mixing followed by post annealing. The as-deposited and 100 MeV Ag ion beam irradiated Co/Sb bilayer thin films were subjected to thermal annealing from 200 to 400 °C for 1 hour. The Rutherford backscattering spectrometry (RBS) results showed partial mixing for the thermally annealed films and complete mixing for the irradiated and post annealed films at 400 °C. The XRD and RAMAN measurements indicated the formation of Co-Sb alloy, with ∼70% concentration of CoSb3 phase in the irradiated post annealed sample at 400 °C. The band gaps of the annealed and post irradiated annealed Co-Sb alloys were determined using UV-visible spectroscopy. Electrical and thermoelectric power measurements were performed in the temperature range of 300-420 K. It was observed that the alloys formed by ion-beam induced mixing exhibited higher electrical conductivity and thermoelectric power than the as-deposited and thermally annealed Co/Sb bilayer thin films.

A study on the consequence of swift heavy ion irradiation of Zn-silica nanocomposite thin films: electronic sputtering

Summary Zn–silica nanocomposite thin films with varying Zn metal content, deposited by atom beam sputtering technique were subjected to 100 MeV Ag ion irradiation. Rutherford backscattering spectrometry reveals the loss of Zn with irradiation, which is observed to be greater from thin films with lower Zn content. The sputtered species collected on carbon-coated transmission electron microscopy (TEM) grids consist of Zn nanoparticles of sizes comparable to those present in the nanocomposite thin film. The process of size-dependent electronic sputtering of Zn is explained on the basis of an inelastic thermal spike model. The possibility of direct cluster emission is explained by pressure spike built inside the track, initiated by a temperature spike.

Synthesis and characterization of Au–Fe alloy nanoparticles embedded in a silica matrix by atom beam sputtering

In the present study, we investigated the formation of AuFe alloy nanoparticles embedded in a silica matrix by the cosputtering of silica, Au and Fe with two different metal fractions using an atom beam source. The increase in the metal fraction in the thin film results in the formation of AuFe alloy nanoparticles. The absence of surface plasmon resonance peak for the Au nanoparticles in the optical spectra, structural studies and transmission electron microscopy results confirmed the existence of AuFe alloy nanoparticles. The nanocomposite is ferromagnetic at 2 K with a symmetric hysteresis loop. The formation of AuFe alloy nanoparticles in the thin film is explained on the basis of interatomic distance and diffusion during deposition.

Thermal stability of bimetallic Au/Fe nanoparticles in silica matrix

Thin silica film containing Au and Fe bimetallic nanoparticles were prepared by atom beam cosputtering. The samples were annealed at different temperatures from 400 to 800° C to study the thermal stability of bimetallic nanoparticles using X ray diffraction. It is observed that at 800° C strong structural rearrangement took place leading to thermal decomposition of bimetallic nanoparticles.