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[en] Low energy ions beam often develop periodic patterns on surfaces under normal or off-normal incidence. Formation of such periodic patterns depends on the substrate material, the ion beam parameters, and the processing conditions. Processing conditions introduce unwanted contaminant atoms, which also play strong role in pattern formation by changing the effective sputtering yield of the material. In this work we have analysed the effect of Cu, Fe and Al impurities introduced during low energy Ar"+ ion irradiation on HOPG substrate. It is observed that by changing the species of foreign atoms the surface topography changes drastically. The observed surface topography is co-related with the modified sputtering yield of HOPG. Presence of Cu and Fe amplify the effective sputtering yield of HOPG, so that the required threshold for the pattern formation is achieved with the given fluence, whereas Al does not lead to any significant change in the effective yield and hence no pattern formation occurs.
[en] Plasmonic coupling is observed in the self-aligned arrays of silver nanoparticles grown on ripple-patterned substrate. Large differences observed in the plasmon resonance wavelength, measured and calculated using Mie–Gans theory, predict that strong plasmonic coupling exists in the nanoparticles arrays. Even though plasmonic coupling exists both along and across the arrays, but it is found to be much stronger along the arrays due to shorter interparticle gap and particle elongation. This effect is responsible for observed optical anisotropy in such arrays. Measured red-shift even in the transverse plasmon resonance mode with the increasing nanoparticles aspect ratio in the arrays, deviate from the prediction of Mie–Gans theory. This essentially means that plasmonic coupling is dominating over the shape anisotropy. Plasmon resonance tuning is presented by varying the plasmonic coupling systematically with nanoparticles aspect ratio and ripple wavelength. Plasmon resonance red-shifts with the increasing aspect ratio along the ripple, and blue-shifts with the increasing ripple wavelength across the ripple. Therefore, reported bottom-up approach for fabricating large area-coupled nanoparticle arrays can be used for various field enhancement-based plasmonic applications
[en] Magnetron is being widely used in thin film deposition and other industrial manufacturing processes. Using special geometry of magnetic field on the cathode surface the ionization can be enhanced many fold, resulting in plasma density enhancement by few orders of magnitude. Recently use of magnetron in reverse polarity as ion source has been reported. The concept is also reported for better plasma polymerization process. In present study plasma property of the discharge is being investigated in reverse polarity, the usual E × B region of electron trap is now disappeared. The characteristic ring of the normal magnetron now becomes donut shaped anode dark space, and plasma takes shape of an inverted funnel. A measurement of spatial variation of electron temperature and density has been done, in plume region across magnetron with the help of single and double Langmuir probe. The potential structure is mapped in transverse direction. Electron temperature was measured with respect to changing discharge voltage i.e. input power and background pressure. Density found to increases with both input power and pressure while temperature falls in the central region of the plume. (author)
[en] In plasma source ion implantation, the sample is immersed in a plasma and biased negative with high voltage pulses. In the present investigation, the back ground plasma is not used; rather the pulse bias on the sample and the pressure is adjusted in such a way so that it generates the plasma for implantation. Using the present technique one can eliminate the high hardware costs incurred for external plasma source and also it is possible to avoid the etching and oxidation as the plasma exists for very short duration in comparison to traditional PSII. (author)
[en] The combined effect of magnetic field (B), gas pressure (P), and the corresponding discharge voltage on the discharge properties of argon in inverted cylindrical magnetron has been investigated. In the experiment, anode is biased with continuous 10 ms sinusoidal half wave. It is observed that at a comparatively higher magnetic field (i.e., >200 gauss) and lower operating pressure (i.e., <1 × 10"−"3 mbar), the discharge extinguishes and demands a high voltage to reignite. Discharge current increases with increase in magnetic field and starts reducing at sufficiently higher magnetic field for a particular discharge voltage due to restricted electron diffusion towards the anode. It is observed that B/P ratio plays an important role in sustaining the discharge and is constant for a discharge voltage. The discharge is transformed to negative space charge regime from positive space charge regime at certain B/P ratio and this ratio varies linearly with the discharge voltage. The space charge reversal is indicated by the radial profile of the floating potential and plasma potential in between two electrodes for different magnetic fields. At a particular higher magnetic field (beyond 100 gauss), the floating potential increases gradually with the radial distance from cathode, whereas it remains almost constant at lower magnetic field
[en] On ripple patterned substrates produced by ion beam sputtering, silver nanoparticles are successfully produced by using angular varied PVD electron beam evaporation method. Nanoparticle self-assembly is observed even in a non-shadow deposition region, though ripple pattern has a shallow modulation of ∼2 nm. Therefore, the contribution of the surface adatom diffusion kinetics and the local flux variation seems to be important for this self-assembly process. Due to lower incident flux and lower adatom energy PVD e-beam evaporation deposition method is proven to be superior to sputter deposition for the nanoparticles self-assembly. The self-assembly of nanoparticles is largely dependent on angle of incidence θ, rate of deposition, and deposition direction with respect to the surface topography. We propose the local flux variation model based on the ripple asymmetric tilt and the local incident angle which explains the self-assembly process nicely in terms of the nanoparticle size distribution. The optimum incident angles are calculated to be θ = ± 70° with respect to surface normal by using an analytical rippled surface model for the best alignment of nanoparticles as well as nanowires that are indeed obtained experimentally even though these angles are out of the shadow deposition regime. (papers)
[en] Highlights: • O2/Ar feed ratio is varied in reactive sputter coating of erbia. • Higher O2/Ar feed ratio gives higher roughness and superior crystallization • Er pre-layer deposition induces film growth in cubic phase at 500 °C temperature. • In absence of Er pre-layer, only monoclinic phase grows, even at 600 °C temperature • Ellipsometry gives encouraging result for non-destructive characterization of film - Abstract: Erbium oxide (erbia/Er2O3) is one of the leading candidate coating types to address the issues of tritium permeation reduction and Magnetohydrodynamic (MHD) drag reduction in fusion reactor with liquid Lead–Lithium (Pb–Li) or molten salt Flibe (2LiF + BeF2) as the coolant and breeder materials. The electrical resistivity, hydrogen/deuterium permeation reduction property, liquid metal corrosion, radiation effects and deposition techniques are major areas of research on erbia coating. Though it is having a single stable phase of cubic structure up to 2300 °C, it is known to develop metastable monoclinic phase especially in sputter coating methods. We grow erbia by reactive magnetron sputter coating method and study the phase formation, electrical, microstructural and optical dielectric properties. The effects of erbium metal pre-layer deposition, post annealing in oxygen rich vacuum and oxygen to argon gas feed ratio are studied keeping other parameters constant. The film grows in mixed phase of cubic and monoclinic structures when erbium metal pre-layer is deposited on the P91 steel substrate and in pure monoclinic phase in absence of the pre-layer. Post annealing seems to partially convert monoclinic into cubic phase in the mixed phase coating. Better crystallization and slightly more surface roughness is observed in the sample processed with higher oxygen to argon ratio. DC resistivity is found in 1015 Ω*cm range and it is marginally more in the sample processed with more oxygen. The spectroscopic ellipsometry on these films to obtain optical dielectric properties gives encouraging results in terms of close match of the thickness and roughness values with those obtained from SEM and AFM respectively. Systematic study of optical dielectric property suggests a trend consistent with DC resistivity.
[en] The high voltage dc pulsed glow discharge can be ignited earlier by putting an electron emitting filament in the plasma chamber. The electrons emitted from the filament act as a seed and can cause earlier ignition. The potential of the hot filament shows some periodic positive perturbations (electron loss signals) when it is kept floating in the plasma chamber. It is observed that the positive perturbations disappear as potential difference between the plasma and the filament is made smaller by directly connecting the filament to the grounded chamber
[en] The increased requirements of payload capacity of the satellites have resulted in much higher power requirements of the satellites. In order to minimize the energy loss during power transmission due to cable loss, use of high voltage solar panels becomes necessary. When a satellite encounters space plasma it floats negatively with respect to the surrounding space plasma environment. At high voltage, charging and discharging on solar panels causes the power system breakdown. Once a solar panel surface is charged and potential difference between surface insulator and conductor exceeds certain value, electrostatic discharge (ESD) may occur. This ESD may trigger a secondary arc that can destroy the solar panel circuit. ESD is also called as primary or minor arc and secondary is called major arc. The energy of minor arc is supplied by the charge stored in the coverglass of solar array and is a pulse of typically several 100 ns to several 100 μs duration. The damage caused by minor arc is less compared to major arcs, but it is observed that the minor arc is cause of major arc. Therefore it is important to develop an understanding of minor arc and mitigation techniques. In this paper we present a linear circuit analysis for minor arcs on solar panels. To study arcing event, a ground experimental facility to simulate space plasma environment has been developed at Facilitation Centre for Industrial Plasma Technologies (Institute for Plasma Research) in collaboration with Indian Space Research Organization's ISRO Satellite Technology Centre (ISAC). A linear circuit model has been developed to explain the experimental results by representing the coverglass, solar cell interconnect and wiring by an LCR circuit and the primary arc by an equivalent LR circuit. The aim of the circuit analysis is to predict the arc current which flows through the arc plasma. It is established from the model that the current depends on various parameters like potential difference between insulator and conductor, arc resistance, stored charge in the solar cell coverglass and the external capacitor that simulates wire harness. A close correlation between the experiments and circuit model results has been observed.
[en] Highlights: • Used an ingenious helium ion source to produce self-organized carbon nanostructure on graphite surface. • FESEM results confirm the formation of multi-modal spherical and elongated agglomerated structures. • AFM micrographs display rounded structures with the evidence of an increase in surface roughness with the increase in ion pulses. • The Raman study reads a decrease in the value after ion irradiation and suggests a loss in crystallinity of the irradiated samples. - Abstract: The effects of helium ion irradiation on the graphite surface are studied by employing a plasma focus device. The device emits helium ion pulse having energies in the range of a few keV to a few MeV and flux on the order of 1025 m−2 s−1 at 60 mm axial position from the anode tip. The field emission scanning electron microscopy confirms the formation of multi-modal spherical and elongated agglomerated structures on irradiated samples surface with increase in agglomerate size with increasing number of irradiation shots. The transient annealing in each irradiation was not enough to cause the Oswald ripening or sintering of particles into bigger particle or crystal size but only resulted in clustering. The atomic force micrographs reveal an increase in average surface roughness with increasing ion irradiation. The Raman study demonstrates increase in disordered D peak along with reduced crystallite size () with increasing number of irradiation shots.