Formation of amorphous xenon nanoclusters and microstructure evolution in pulsed laser deposited Ti62.5Si37.5 thin films during Xe ion irradiation

As deposited amorphous and crystallized thin films of Ti 37.5% Si alloy deposited by pulsed laser ablation technique were irradiated with 100 keV Xe+ ion beam to an ion fluence of about 1016 ions-cm−2. Transmission electron microscopy revealed that the implanted Xe formed amorphous nanosized clusters in both cases. The Xe ion-irradiation favors nucleation of a fcc-Ti(Si) phase in amorphous films. However, in crystalline films, irradiation leads to dissolution of the Ti5Si3 intermetallic phase. In both cases, Xe irradiation leads to the evolution of similar microstructures. Our results point to the pivotal role of nucleation in the evolution of the microstructure under the condition of ion implantation.

A Study of Nanostructures of Thin Films in B–C–N System Produced by Pulsed Laser Deposition and Nitrogen Ion-Beam-Assisted Pulsed Laser Deposition

We report the synthesis of thin films of B–C–N and C–N deposited by N+ ion-beam-assisted pulsed laser deposition (IBPLD) technique on glass substrates at different temperatures. We compare these films with the thin films of boron carbide synthesized by pulsed laser deposition without the assistance of ion-beam. Electron diffraction experiments in the transmission electron microscope shows that the vapor quenched regions of all films deposited at room temperature are amorphous. In addition, shown for the first time is the evidence of laser melting and subsequent rapid solidification of B4C melt in the form of micrometer- and submicrometer-size round particulates on the respective films. It is possible to amorphize B4C melt droplets of submicrometer sizes. Solidification morphologies of micrometer-size droplets show dispersion of nanocrystallites of B4C in amorphous matrix within the droplets. We were unable to synthesize cubic carbon nitride using the current technique. However, the formation of nanocrystalline turbostratic carbo- and boron carbo-nitrides were possible by IBPLD on substrate at elevated temperature and not at room temperature. Turbostraticity relaxes the lattice spacings locally in the nanometric hexagonal graphite in C–N film deposited at 600 °C leading to large broadening of diffraction rings.

Microwave preparation and sintering of industrially important perovskite oxides: LaMO3 (M = Cr, Co, Ni)

Perovskite oxides LaMO3 (M = Cr, Co, Ni), have been successfully prepared using microwaves of 2.45 GHz. Microwave preparation is rapid, clean and energy efficient. Preparation of LaCrO3, LaCoO3 and LaNiO3 has been achieved in 3 min, 5 min and 10 min respectively. Direct reaction between component oxides is used for the preparation of LaCrO3 and LaCoO3, whereas nitrates are used as starting materials for LaNiO3 preparation. Products have been characterized using XRD, IR spectroscopy and SEM. Their dc electrical conductivity has also been studied and their fracture behaviour has been examined. All three microwave prepared oxide powders are of submicron size. These perovskite oxides have been sintered to very high densities using microwaves. Possible mechanisms of the microwave-material interaction both during preparation and during sintering have been discussed.

Role of La0.5Sr0.5COO3 template layers on dielectric and electrical properties of pulsed-laser ablated Pb(Nb2/3Mg1/3)O-3-PbTiO3 thin films

Relaxor ferroelectric thin films of 0.7Pb(Mg1/3Nb2/3)O-3-0.3PbTiO(3) (PMN-PT) deposited on platinized silicon substrates with and without template layers were studied. Perovskite phase (80% by volume) was obtained through proper selection of the processing conditions on bare Pt/Ti/SiO2/Si substrates. The films were initially grown at 300 degreesC using pulsed-laser ablation and subsequently annealed in a rapid thermal annealing furnace in the temperature range of 750-850 degreesC to induce crystallization. Comparison of microstructure of the films annealed at different temperatures showed change in perovskite phase formation and grain size etc. Results from compositional analysis of the films revealed that the films initially possessed high content of lead percentage, which subsequently decreased after annealing at temperature 750-850 degreesC. Films with highest perovskite content were found to form at 820-840 degreesC on Pt substrates where the Pb content was near stoichiometric. Further improvement in the formation of perovskite PMN-PT phase was obtained by using buffer layers of La0.5Sr0.5CoO3 (LSCO) on the Pt substrate. This resulted 100% perovskite phase formation in the films deposited at 650 degreesC. Dielectric studies on the PMN-PT films with LSCO template layers showed high values of relative dielectric constant (3800) with a loss factor (tan delta) of 0.035 at a frequency of 1 kHz at room temperature. (C) 2002 Elsevier Science B.V. All rights reserved.

Transient analysis in Al-doped barium strontium titanate thin films grown by pulsed laser deposition

Thin films of (Ba0.5Sr0.5)TiO3 (BST) with different concentrations of Al doping were grown using a pulsed laser deposition technique. dc leakage properties were studied as a function of Al doping level and compared to that of undoped BST films. With an initial Al doping level of 0.1 at. % which substitutes Ti in the lattice site, the films showed a decrease in the leakage current, however, for 1 at. % Al doping level the leakage current was found to be relatively higher. Current time measurements at elevated temperatures on 1 at. % Al doped BST films revealed space-charge transient type characteristics. A complete analysis of the transient characteristics was carried out to identify the charge transport process through variation of applied electric field and ambient temperature. The result revealed a very low mobility process comparable to ionic motion, and was found responsible for the observed feature. Calculation from ionic diffusivity and charge transport revealed a conduction process associated with an activation energy of around 1 eV. The low mobility charge carriers were identified as oxygen vacancies in motion under the application of electric field. Thus a comprehensive understanding of the charge transport process in highly acceptor doped BST was developed and it was conclusive that the excess of oxygen vacancies created by intentional Al doping give rise to space-charge transient type characteristics. © 2001 American Institute of Physics.

Synthesis of new (Bi, La)(3)MSb(2)O(11) phases (M = Cr, Mn, Fe) with KSbO(3)-type structure and their magnetic and photocatalytic properties

Synthesis and structure of new (Bi, La)(3)MSb(2)O(11) phases (M = Cr, Mn, Fe) are reported in conjunction with their magnetic and photocatalytic properties. XRD refinements reflect that Bi(3)CrSb(2)O(11), Bi(2)LaCrSb(2)O(11), Bi(2)LaMnSb(2)O(11) and Bi(2)LaFeSb(2)O(11) adopt KSbO(3)-type structure (space group, Pn (3) over bar). The structure can be described through three interpenetrating networks where the first is the (M/Sb)O(6) octahedral network and other two are the identical networks having Bi(6)O(4) composition. The magnetic measurements on Bi(2)LaCrSb(2)O(11) and Bi(2)LaMnSb(2)O(11) show paramagnetic behaviour with magnetic moments close to the expected spin only magnetic moments of Cr(+3) and Mn(+3). The UV-Visible diffuse reflectance spectra are broad and indicate that these materials possess a bandgap of similar to 2 eV. The photocatalytic activity of these materials has been investigated by degrading Malachite Green (MG) under exposure to UV light.

CFD Based Design Optimizations of the Diffuser of a Gas Dynamically Driver Laser Cavity

Based on the an earlier CFD analysis of the performance of the gas-dynamically controlled laser cavity [1]it was found that there is possibility of optimizing the geometry of the diffuser that can bring about reductions in both size and cost of the system by examining the critical dimensional requirements of the diffuser. Consequently,an extensive CFD analysis has been carried out for a range of diffuser configurations by simulating the supersonic flow through the arrangement including the laser cavity driven by a bank of converging – diverging nozzles and the diffuser. The numerical investigations with 3D-RANS code are carried out to capture the flow patterns through diffusers past the cavity that has multiple supersonic jet interactions with shocks leading to complex flow pattern. Varying length of the diffuser plates is made to be the basic parameter of the study. The analysis reveals that the pressure recovery pattern during the flow through the diffuser from the simulation, being critical for the performance of the laser device shows its dependence on the diffuser length is weaker beyond a critical lower limit and this evaluation of this limit would provide a design guideline for a more efficient system configuration.The observation based on the parametric study shows that the pressure recovery transients in the near vicinity of the cavity is not affected for the reduction in the length of the diffuser plates up to its 10% of the initial size, indicating the design in the first configuration that was tested experimentally has a large factor of margin. The flow stability in the laser cavity is found to be unaffected since a strong and stable shock is located at the leading edge of the diffuser plates while the downstream shock and flow patterns are changed, as one would expect. Results of the study for the different lengths of diffusers in the range of 10% to its full length are presented, keeping the experimentally tested configuration used in the earlier study [1] as the reference length. The conclusions drawn from the analysis is found to be of significance since it provides new design considerations based on the understanding of the intricacies of the flow, allowing for a hardware optimization that can lead to substantial size reduction of the device with no loss of performance.

Computational Analysis of Flow through a Multiple Nozzle Driven Laser Cavity and Diffuser

Computations have been carried out for simulating supersonic flow through a set of converging-diverging nozzles with their expanding jets forming a laser cavity and flow patterns through diffusers, past the cavity. A thorough numerical investigation with 3-D RANS code is carried out to capture the flow distribution which comprises of shock patterns and multiple supersonic jet interactions. The analysis of pressure recovery characteristics during the flow through the diffusers is an important parameter of the simulation and is critical for the performance of the laser device. The results of the computation have shown a close agreement with the experimentally measured parameters as well as other established results indicating that the flow analysis done is found to be satisfactory.