Shyamal Chatterjee

Fast-electron impact ionization of molecular hydrogen: energy and angular distribution of double and single differential cross sections and Young-type interference

We report the energy and angular distribution of absolute double differential cross sections (DDCSs) of ejected electrons in collisions of 8 keV projectile electrons with molecular hydrogen. The ejected electrons with energy between 1 eV and 400 eV and ejection angles between 30° and 150° are detected. The measured data are compared with the theoretical calculations based on two-effective centre (TEC) model. The first-order interference is derived from the energy distribution of DDCS and the resulting ratio spectra (H2 to 2H) exhibit oscillating behaviour. The signature of first-order interference is also demonstrated in the DDCS spectra as a function of the ejection angle. We have shown that the constructive interference prevails in soft- and binary-collision regions. The single differential cross sections (SDCS) are deduced by integrating the DDCS over the solid angle as well as ejection energy. We demonstrate that the SDCS and corresponding ratio spectra also preserve the signature of interference.

Temporal wetting property of “Micro” versus “Nano” rods of ZnO grown using the pressure dependent aqueous solution method

We report the role of pressure dependent growth of micro and nanorod arrays of zinc oxide by an aqueous solution route. Initially, both micro- and nano-ZnO surfaces show hydrophobicity with water contact angles of 140° ± 3° and 130° ± 3°, respectively. We find that the temporal decay in water contact angle is faster in the case of the nanorod surface compared to that of the microrod surface. While for the microrod surface, the small change in contact angle happens due to water droplet evaporation, the significant change in the particular case of the nanorod surface is attributed to the capillary action.

Ionization of molecular hydrogen by 5 MeV/u bare fluorine ion and electron interference

Electrons emitted from H2 in collisions with 5 MeV/u F9 + ions were measured in the energy range from 1 to 300 eV and a wide range of emission angles between 20° and 160°. The measured energy and angular distributions of double-differential cross sections (DDCSs) of these electrons are compared with the molecular continuum distorted wave-eikonal initial state (CDW-EIS) calculation. The observed energy and angular distributions can be explained, in general, with the help of the two-centre effect which is included in the CDW-EIS model. In addition, the DDCS ratios of molecular-to-atomic hydrogen exhibit an oscillatory structure which is discussed in terms of Young-type electron interference. We have obtained the frequencies of such oscillations and studied their angular dependence. The single-differential cross sections (SDCSs) are deduced by integrating the DDCSs over solid angle and emission energy. We demonstrate that the SDCS ratio spectra also preserve the signature of interference to some extent. The asymmetry parameter, derived only from the molecular cross sections for forward and backward angles, shows an oscillatory behaviour as a function of electron velocity. This is understood in terms of the interference effect superimposed with the post-collisional two-centre effect.

Welding of copper oxide nanocolumns by ion irradiation: Transition from hydrophilic to hydrophobic surface

Crystalline nanocolumns of copper oxide has been fabricated through oblique angle sputter deposition technique. The columns are exposed to 15 keV Ar+ ion beam at a fluence of 2 × 1016 ions/cm2. Well-separated nanocolumns are welded upon ion irradiation. The tips of the nanocolumns show prominent joining. Furthermore, wetting property measurements are done for both pristine and irradiated sample, which reveals that a transition occurs from hydrophilic to hydrophobic surface upon ion irradiation.

Amorphization and recrystallization of single-crystalline hydrogen titanate nanowires by N+ ion irradiation

We report on the phase transformation of hydrogen titanate (H2Ti3O7) nanowires induced by 50 keV N+ ion irradiation at room temperature with fluences of 1 × 1015 ions/cm2 and 1 × 1016 ions/cm2, respectively. Using transmission electron microscopy, the internal structure of the ion irradiated nanowires is analyzed. At low fluence, a transformation from crystalline H2Ti3O7 to amorphous TiO2 is observed. However, at higher fluence, a remarkable crystalline-amorphous TiO2 core-shell structure is formed. At this higher fluence, the recrystallization occurs in the core of the nanowire and the outer layer remains amorphous. The phase transformation and formation of core-shell structure are explained using the thermal spike model, radiation enhanced diffusion, and classical theory of nucleation and growth under non-equilibrium thermodynamics. X-ray photoelectron spectroscopy and Raman scattering reveal further insight into the structure of the nanowires before and after ion irradiation.

Electron interference in fast ion collisions with H2 and the frequency parameter

The Young-type interference effect has been investigated in electron emission from molecular hydrogen in collision of 5 MeV u− 1 F9+ ions. The double differential cross section ratios of molecular-to-atomic hydrogen exhibits oscillatory structure, which is discussed in terms of the Young-type electron interference. We have obtained the frequencies of such oscillation for different angles. A comparative study of the frequency parameter is given with early measurements performed by other groups.

Tuning wettability of hydrogen titanate nanowire mesh by Na+ irradiation

Hydrogen titanate (HT) nanowires have been widely studied for remarkable properties and various potential applications. However, a handful studies are available related to ion beam induced structural changes and influence on wetting behavior of the HT nanowire surface. In this work, we exposed HT nanowires to 5 keV Na+ at an ion fluence of 1×1016 ions.cm-2. Scanning electron microscope shows that at this ion fluence nanowires are bent arbitrarily and they are welded to each other forming an interlinked network structure. Computer simulation shows that ion beam induces defect formation in the nanowires, which plays major role in such structural modifications. An interesting alteration of surface wetting property is observed due to ion irradiation. The hydrophilic pristine surface turns into hydrophobic after ion irradiation.Hydrogen titanate (HT) nanowires have been widely studied for remarkable properties and various potential applications. However, a handful studies are available related to ion beam induced structural changes and influence on wetting behavior of the HT nanowire surface. In this work, we exposed HT nanowires to 5 keV Na+ at an ion fluence of 1×1016 ions.cm-2. Scanning electron microscope shows that at this ion fluence nanowires are bent arbitrarily and they are welded to each other forming an interlinked network structure. Computer simulation shows that ion beam induces defect formation in the nanowires, which plays major role in such structural modifications. An interesting alteration of surface wetting property is observed due to ion irradiation. The hydrophilic pristine surface turns into hydrophobic after ion irradiation.

Superior electrical conduction of a water repelling 3D interconnected nano-network

A three-dimensional (3D) network of interconnected nanowires of functional materials possesses huge potential for device fabrication since it hinders sluggish interfacial charge carrier transport owing to reduced contact resistance. In the present work, the formation of a highly porous 3D interconnected nano-network by Na+ ion irradiation is demonstrated. The mechanism of solid junction formation at very low energy is established using the results obtained from TRI3DYN computer simulation studies. The formation of a 3D interconnected network resulted in a significant improvement in the electrical conduction as compared to that observed for the pristine nanotube mesh. Further, contact angle measurement shows a transition from “superhydrophilic” nature, as observed for pristine nanotubes, to “superhydrophobic” nature for the 3D nano-network. The superhydrophobicity of the 3D nano-network is expected to find application in miniaturized electronic devices, wherein water condensation and related effects such as short-circuits and erroneous signal output can be significantly minimized.

Effect of irradiation with argon ions on elastic scattering of spin-polarized electrons from W(110) surface

The energy and azimuthal angle dependencies of the asymmetry of spin-polarized low-energy electrons ((00) beam) elastically scattered from a W(110) surface, have been studied before and after irradiated with slow Ar+ ions with energies of 200 eV, 500 eV and 1 keV at a fluence of 5 × 1015 ions/cm2. The energy dependence of the scattered electron asymmetries and intensities (for a fixed azimuthal angle of 55°, which is determined by the angle between the normal to the scattering plane and the [] direction in the surface of the W(110) crystal) and the azimuthal angle dependence of the asymmetry for two different incident electron energies of 14 eV and 23 eV showed a significant change after irradiation. The low-energy ion irradiation influenced the spin-polarized electron scattering more than the higher energy ions. The reason for the change of spin-dependent electron scattering is a quenching of coherent elastic multiple scattering, mainly due to lattice defects induced by implanted ions. Thus, these modifications demonstrate a technological way to construct spin-active interface with required properties. The agreement between experimental results and theoretical ones with and without multiple scattering provides a consistent explanation of the observations.

Ionization of H2 and He in collision of 3 keV electrons and the Bethe binary-encounter peak

We have studied the energy distributions of double differential cross sections (DDCS) of electrons emitted in single-ionization of H2 and He induced by 3keVelectron impact in the Bethe binary-encounter (BE) region for wide range of ejection angles.We compare the absolute cross sections for these two isoelectronic systems at high ejection energies. We demonstrate that while Compton profile causes undulation in the BE peak, the constructive interference effect enhances the overall cross section of H2 compared to that of atomic targets.