We report a comparative study of a single plasma and a colliding laser produced plasma, investigated using a Faraday cup. An enhancement in ion emission and stagnation is observed in colliding plasma ...plume compared to single plasma plume. We observed that fast ion generation in laser ablated plasma can be achieved at large laser intensity on to the target. As laser intensity increases ionic yield increases for both colliding and single plume and at a fixed laser intensity ionic yield decreases with increase in ambient pressure. The double peak structure is observed in the ion signal at large fluence where the peaks correspond to fast and slow species. A Faraday cup composed of nine collectors is used to measure the spatial/angular distribution of ion of expanding plasma plume. Ionic yield is found to be larger in the colliding plasma plume than the single plasma plume at all spatial/angular positions.
Faraday cup; Laser-produced plasma; Colliding plasma; Carbon plasma.
We report crater formation due to interaction of the high power laser pulse with the brass and aluminum in water and air ambient. The deposited nanostructures on brass near and away from the crater ...periphery are distinctly different with larger particle size (3.5 mu m) and broader particle size distribution with full width half maximum (FWHM) 2.9 mu m close to the crater compared to relatively smaller particle size (2.5 mu m) and narrower size distribution (FWHM 1.7 mu m) near the periphery of the crater in air ambient. The morphology of brass in water ambient shows nanosize particles (55nm) and narrow distribution (FWHM 7.5nm) away from the crater with nanorod shaped structures at crater periphery.
The formation of CuTiO
2
nanocomposites has been observed in an experiment in which laser plasma plumes of Cu and Ti collide and stagnate in an oxygen atmosphere. The inherent advantage of this ...technique lies in its simplicity and flexibility where laser, target composition and geometry along with ambient atmosphere are all controllable parameters through which the stoichiometry of the deposited nanocomposites may be selected. The experiment has been performed at three oxygen ambient pressures 10
−4
, 10
−2
, 10
0
mbar and we observe its effect on stoichiometry, and morphology of the deposited nanocomposites. Here, we show how the stoichiometry of deposited nanocomposites can be readily controlled by changing just one parameter, namely the ambient oxygen pressure. The different peaks of photoluminescence spectra
λ
=
390
nm
E
=
3.18
eV
corresponding to the anatase phase of TiO
2
, along with the peaks at
λ
= 483 nm (
E
= 2.56 eV) and 582 nm (
E
= 2.13 eV) of deposited nanocomposites, shows the doping/blending effect on the band gaps which may potentially be of value in solar cell technology. The technique can, in principle, be extended to include nanocomposites of other materials making it potentially more widely applicable.
Catalyst free ZnO nanowires are grown by thermal evaporation, and are characterized by scanning electron microscopy (SEM), x-ray diffraction (XRD) and photoluminescence (PL). The ultra-violet (UV) ...emission band observed in the PL of ZnO nanowires grown on ZnO buffer layer is investigated at different temperatures and excitation intensities. The prominently observed transitions at low temperatures are bound exciton (BX), first longitudinal optical (LO) phonon replica of free exciton ( ) and donor-acceptor pair (DAP). Electron-hole plasma (EHP) emission is observed above 175 K of temperature and above 1.27 MW cm−2 of excitation intensity which is associated with the thermal ionization of bound excitons. The observed intensity and temperature dependent EHP emission is attributed to spontaneous emission.
We report on the pulsed laser ablation of aluminum (Al) plasma in
presence of ambient nitrogen to understand the formation of aluminum
nitride (AlN). Formation of carbon nitride (CN) and titanium ...oxide (TiO)
by pulsed laser-ablation of graphite and titanium targets in presence of
ambient nitrogen and oxygen is also compared. We discuss the dynamics of
plasma expansion based on existing models, shock and drag models, and the
plasma gas interface distortion, Rayleigh-Taylor instability at various
ambient pressures of nitrogen. Since Rayleigh-Taylor instability may give
rise to self-generated magnetic field in the plasma, an attempt is made to
understand the mechanism of generation as well as the estimation of this
field near the focal spot using the information from the images of the
expanding plasma. This is the first time images of the expanding plume are
used to estimate self generated magnetic fields. At the irradiance level
used in the experiment the field is high very close to the target surface
therefore we expect splitting of the energy levels thus giving rise to
emissions that may be anisotropic in nature. We discuss the extent of
anisotropy by measuring the degree of polarization using emission
intensity in optical emission spectrum of selected Al III transition 4s
2S1/2–4p
2P3/2o at 569.6 nm using both
nanosecond and picosecond pulses.
We report the synthesis of various nanostructures of ZnO using thermal evaporation technique. Morphology and stoichiometry of the prepared samples show a strong dependence on their synthesis ...temperatures. The photoluminescence of various nanostructures using fourth harmonic of Nd:YAG laser at 266 nm with pulse width of 4 ns is reported at low temperature in the range ∼ 6-300 K. The observed photoluminescence spectra show dependence on morphological properties of the nanostructures. ZnO nanostructures grown at low temperature are observed to be defect free.
Preparation of N-doped ZnO thin films was attempted using various co-doping methods. A ZnO:Ga (Ga
2O
3 of 5 wt.%) target was ablated in NO gas by pulsed laser deposition (PLD). In addition, a ...nitrogen ion gun and an ECR nitrogen plasma source were used as post-N-doping treatment of undoped ZnO films. Optical emission from elemental Zn I, Ga I and O I, as well as from N
2 molecules, was identified in the plasma plume. The structural, optical and electrical properties of these synthesized films were investigated. All films show n-type conduction, with resistivity in the range 10
−3–10
−2 Ω cm and carrier density from 10
17 to 10
20 cm
−3.
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