Archita Patnaik

The room-temperature electrical conductivity of High Density Polyethylene-Carbon Black (HDPE-CB) switching composites as a function of the conductive filler (CB) content was studied by Positron Annihilation Lifetime Spectroscopy (PALS). The CB, highly structured and porous, imparted high conductivity to its composite, starting at a low level of loading. Deconvolution of the lifetime spectra into 4 components reflected upon 3 different morphologies of the composite structure. The free volume was probed using o-Ps pick-off annihilation lifetime parameter τ4 as a measure of electron density and the mean free volume cavity radius. The probability of o-Ps formation and the concentration of free volume cavities were probed by the o-Ps pick-off intensity I4. In the blended composite of 29 phr (parts per hundred parts of resin), the mean free volume size increased to 3.56 Å from 3.27 Å in the pristine polymer with the corresponding increase in the free volume to 204.5 Å3 from 146.8 Å3. The relative number of free volume cavities (I4) in the composite remained fewer than the host polymer over the CB concentration studied. The changes in the cavity size and concentration, particularly a decrease in the relative intensity I4 by 10.5% resulted in the introduction of enhanced crystallinity into the composite structure which was evidenced from a variation in crystallinity from %75% in the pristine to 85% in the 29 phr CB-HDPE composite in the X-ray diffraction profiles.

A stack of polyimide (PI) thin foils was irradiated with 900 MeV 40Ar15+ ions up to a fluence of 8 × 1011 ions/cm2. Subsequently, the electrical conductivity and UV-VIS absorption spectra of specimens were measured for the selected foils from the irradiated stack. Two well defined characteristic absorption peaks at wavelengths 482 and 501 nm appeared after irradiation and their absorption peak intensities progressively increased with increasing electronic energy loss in the substrate. Over a range of deposited electronic energy density from 8 to 23 eV/nm3, the depth profile of the chemical yields closely pursued the electronic energy transfer profile. The integrated optical absorption bands at 482 and 501 nm were used to evaluate the normalized damage fraction, the damage production cross-section and the track radii in the irradiated PI matrix as a function of deposited electronic energy density. The measured enhanced electrical conductivity substantiated by the optical band gap values was attributed to the formation of condensed polycyclic aromatic ring compounds and clusters with greater degree of conjugation in the multiple overlapping ion track in the PI matrix. The critical energy loss rate (track etch threshold) for 40Ar ion in PI was obtained from the optical absorbance and electrical conductivity measurements. © 1998 Elsevier Science B.V.

The effect of energy charged particles in the enhancement of conductivity laser ablated poly(phenylene sulfide) (PPS) is described. Based on the results, it is shown that the FTIR spectrum of the as-deposited film showed characteristic vibrational frequencies at 1560 and 1470 cm-1, these being attributed to aromatic structural vibrations, 1090 cm-1 to thioether linkage and 1008 cm-1 to p-aromatic substitution. XPS analysis of the as-deposited thin films showed formation of oxygen free PPS. The integrated area under the peaks corresponding to C1s and S2p profiles with proper sensitive factors for the as-deposited film amounted to the original stoichiometry of pristine PPS having C:S as 6:1.

N+ ion beam induced effects on the spin coated amorphous poly(2,6-dimethyl phenylene oxide) (PPO) films in terms of chemical structure and electronic and vibrational properties were investigated using Fourier Transform Infrared spectroscopy (FTIR) and Ultraviolet-Visible (UV-VIS) spectroscopy. Both techniques revealed that the stability of PPO was very weak towards 100 keV N+ ions revealing the threshold fluence to be 1014 ions/cm2 for fragmentation of the polymer. FTIR analysis showed disappearance of all characteristic IR bands at a total fluence of 1014 ions/cm2 except for the band CC at 1608 cm-1 which was found to shift to a lower wave number along with an enhancement in the full width half maximum (FWHM) value with increasing fluence. A new bond appeared due to oxidation as a shoulder at 1680 cm-1 in FTIR spectra indicating the presence of CO type bond as a result of N+ implantation on PPO films. The optical band gap (Eg) deduced from absorption spectra, was observed to decrease from 4.4 to 0.5 eV with fluence. The implantation induced carbonaceous clusters, determined using Robertson's formula for the optical band gap, were found to consist of ~160 fused hexagonal aromatic rings at the maximum energy fluence. An enhanced absorption coefficient as a function of fluence indicated incorporation of either much larger concentration of charge carriers or their mobility than that of the pristine sample. Calculated band tail width from Urbach band tail region for the implanted samples pointed the band edge sharpness to be strongly dependent on fluence indicating an increased disorder with increasing fluence. © 1999 Elsevier Science B.V.

We report the energetic N+ (100 keV) implantation effect on the spin cast film of poly(2,6-dimethyl phenylene oxide) [PPO] and formation of ion beam induced crystalline nano-clusters, for the first time. Evidence for the formation of highly oriented clusters of ∼ 22 nm size is obtained from grazing incidence XRD (GIXRD) analysis of the implanted PPO films with a fluence of 6 × 1016 ions/cm2 whereas the as-deposited film is found amorphous. All the characteristic Raman peaks of PPO film disappears and subsequently a broad peak at 1500 cm-1 in the FT-Raman spectrum appears implying the presence of graphite like carbon (GLC) in the implanted polymer. DC conductivity behaviour in the implanted sample has shown the dominant role of three dimensional (3-D) variable range hopping (VRH) mechanism in the temperature range of 303-500 K. The role of clusters is discussed in analysing the current transport mechanism in the implanted polymer. © 1999 Elsevier Science B.V. All rights reserved.

Binary and ternary gas mixtures of H2O, CO2, NH3 and CH4 were condensed at 10-6 mbar onto a KBr cold finger at 10 K. The composition of the few micrometre thick layers has been determined by infrared spectroscopy in transmission mode. The condensation dynamics together with the predominant matrix effect studied as a function of gas composition, deposition time and ice layer thickness reveal a lower condensation probability for the more volatile components CH4 and CO2 in mixtures of H2O-NH3-CH4 and H2O-NH3-CO2, respectively, with varying composition. The phenomena explain representative cases of early condensation and accretion processes of icy layers on interstellar grains.

The single comparator method for achieving multielement analysis of airborne particulates is adopted after being modified with the incorporation of infinite resonance integrals and the ratio of thermal to epithermal neutron flux at the activation site. Dust samples from ferro alloy and lime kiln emission sources upon analysis indicated the major elements to be Fe, Cr, Cu, Zn, Ba, Sr, Rb, Ag, Hg, Th, amongst others. Inorganic soluble sulphates, nitrates and ammonium and the organics extractable in benzene were estimated. Most of the aerosol mass seems to comprise organic carbon.

Thin films of poly(p-phenylene sulfide) [PPS], were deposited by pulsed laser deposition with a doubled Nd: YAG laser (λ = 532 nm) on Si (100) and quartz substrates at temperatures above and below the glass transition temperature (T g ) of the polymer. SEM micrographs of the films showed a decrease of particulate size with increasing substrate temperature. An absorption band edge at 3.4 eV in the UV-VIS spectrum of the deposited film indicated that they were polymeric as well as insulating. FTIR spectra of films deposited at various substrate temperatures mimicked all characteristic vibrational frequencies observed in pristine bulk samples. Low-angle X-ray diffraction patterns and FTIR spectral analysis of the deposited PPS films confirmed that the crystallinity was enhanced when the substrate temperature during deposition exceeded T g . X-ray photoelectron spectroscopic (XPS) investigations of the C 1s spectra of the as-deposited film on Si (100) revealed oxidation of the surface with the formation of sulfone, sulfoxide, C-O and C=O. Ar + ion sputtering with a 4 keV beam at 1 μA beam current removed ∼ 2 nm of the surface film and completely eliminated the sulfone peak from the XPS spectra, retaining a very negligible oxide component. © 1998 Elsevier Science B.V. All rights reserved.

The formation, configuration and the interactions at the gold/polycarbonate (Au/PC) interface formed by thermally evaporated Au on PC film, a technologically important polymer, is studied by X-ray photoelectron spectroscopy (XPS) at an Au thickness of 35.4 Å. XPS depth profiling with 3 keV Ar + ion sputtering at 1 μA revealed the interface between the as-deposited 35.4 Å Au film and the PC substrate to be sharp covering a few monolayers. A substantial Au atomic concentration of ~3% in the bulk PC indicated that Ar + ion assisted diffusion of the metal into the bulk. Existence of weak Au→C charge transfer interactions with Au as the electron injector distributing a net charge density at the C=O as the primary interaction site was deduced from the appearance of the 282.6 eV C 1s feature, thus resulting in the formation of Au-CO π back bond. The sputtering experiments revealed the growth-mode of Au on PC to proceed by metal monolayer deposition followed by cluster growth on the already weakly bonded Au onto the C=O carbon of the polymeric backbone.

Structural and chemical investigation for the laser ablated Poly (Phenylene Sulfide) (PPS) films upon 100 keV H+ implantation is reported here for the first time. PPS thin films were fabricated by laser ablation with a Nd: YAG laser as a source of visible photons (532 nm). The laser ablated thin films showed strong polymer breakdown resistance upto a total fluence of 1015 ions/cm2. Bulk properties of the as-deposited and the implanted samples were investigated using FTIR and UV-VIS spectroscopy. Drastic reduction in the intensity of all characteristic vibrational frequencies in the FTIR spectrum at higher doses revealed the transformation of the polymer to a conjugated carbonaceous material. UV-VIS studies showed a positive shift in the absorption edge value for the as-deposited polymer towards higher wavelengths and destruction of phenyl ring due to the H+ bombardment. X-ray Photoelectron Spectroscopic (XPS) investigation indicated the sulfur depletion as a prominent phenomenon whereas carbon content remained almost the same. XPS studies of the implanted sample also revealed a minor change in the oxidized species of carbon and more prominent change in oxidized species of sulfur which were present in the as-deposited samples. A peak at 283.4 eV attributed to 'surface reconstruction' in the XPS analysis for the as-deposited PPS film disappeared after proton implantation. © 1998 Elsevier Science B.V.