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Search Results: 1 - 10 of 200582 matches for " P. Magudapathy "
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Growth of silver nanoclusters embedded in soda glass matrix
P. Gangopadhyay,P. Magudapathy,R. Kesavamoorthy,B. K. Panigrahi,K. G. M. Nair,P. V. Satyam
Physics , 2004, DOI: 10.1016/j.cplett.2004.03.055
Abstract: Temperature-controlled-growth of silver nanoclusters in soda glass matrix is investigated by low-frequency Raman scattering spectroscopy. Growth of the nanoclusters is ascribed to the diffusion-controlled precipitation of silver atoms due to annealing the silver-exchanged soda glass samples. For the first time, Rutherford backscattering measurements performed in this system to find out activation energy for the diffusion of silver ions in the glass matrix. Activation energy for the diffusion of silver ions in the glass matrix estimated from different experimental results is found to be consistent.
Effects of argon ion irradiation on nucleation and growth of silver nanoparticles in a soda-glass matrix
P. Gangopadhyay,P. Magudapathy,S. K. Srivastava,K. G. M. Nair
AIP Advances , 2011, DOI: 10.1063/1.3623737
Abstract: The present article explores an experimental study for nucleation and non-equilibrium growth of silver nanoparticles in a soda-glass matrix. Ion-irradiation induced recoiling of silver atoms with argon ions (at energy 100 keV) facilitates nucleation as well as growth of the silver nanoparticles in the soda-glass matrix. Small growth of the silver nanoparticles in the soda-glass matrix has been experimentally observed after the irradiation with higher fluences of the argon ions. Role of the argon ions for the evolution of the silver nanoparticles in the soda-glass matrix has been elucidated in the present report. With increase of the argon-ion fluences, while slight athermal growth of the silver nanoparticles has been estimated, drastic increase in the optical responses and Rutherford backscattering (RBS) yields of the silver nanoparticles have been observed in the sample with the maximum fluences. Possible correlations of increase of argon-ion fluences and the observed experimental results (optical and RBS, in particular) have been explained in this article. Although it has been demonstrated using the silver metal film on a soda-glass substrate as a model example, the non-equilibrium approach of nucleation and ion-beam controlled growth of metal nanoparticles in a matrix should be applicable to other immiscible systems as well.
Blueshift of plasmon resonance with decreasing cluster size in Au nanoclusters embedded in silica matrix
S. Dhara,B. Sundaravel,T. R. Ravindran,K. G. M. Nair,B. K. Panigrahi,P. Magudapathy
Physics , 2004,
Abstract: Gold nanoclusters are grown by 1.8 MeV Au++ implantation in silica matrix and subsequent air annealing in the temperature range of 873K-1273K. Post-annealed samples show plasmon resonance in the optical region (~ 2.38-2.51 eV) for average cluster radii ~1.04-1.74 nm. A blueshift of the plasmon peak is observed with decreasing cluster size in the annealed samples. Similar trend of blueshift with decreasing cluster size in case of Au nanoclusters embedded in the porous alumina matrix [B. Palpant, et al., Phys. Rev. B 57, 1963 (1998)] has convinced us to assume a possible role of 'rind' like porosity at the Au nanocluster-matrix interface with available open volume defects in the amorphous silica matrix.
Optical absorption and photoluminescence spectroscopy of the growth of silver nanoparticles
P. Gangopadhyay,R. Kesavamoorthy,Santanu Bera,P. Magudapathy,K. G. M. Nair,B. K. Panigrahi,S. V. Narasimhan
Physics , 2005, DOI: 10.1103/PhysRevLett.94.047403
Abstract: Results obtained from the optical absorption and photoluminescence (PL) spectroscopy experiments have shown the formation of excitons in the silver-exchanged glass samples. These findings are reported here for the first time. Further, we investigate the dramatic changes in the photoemission properties of the silver-exchanged glass samples as a function of postannealing temperature. Observed changes are thought to be due to the structural rearrangements of silver and oxygen bonding during the heat treatments of the glass matrix. In fact, photoelectron spectroscopy does reveal these chemical transformations of silver-exchanged soda glass samples caused by the thermal effects of annealing in a high vacuum atmosphere. An important correlation between temperature-induced changes of the PL intensity and thermal growth of the silver nanoparticles has been established in this Letter through precise spectroscopic studies.
Optical characterization of GaN by N+ implantation into GaAs at elevated temperature
S. Dhara,P. Magudapathy,R. Kesavamoorthy,S. Kalavathi,K. G. M. Nair,G. M. Hsu,L. C. Chen,K. H. Chen,K. Santhakumar,T. Soga
Physics , 2007, DOI: 10.1063/1.2099542
Abstract: Both hexagonal wurtzite and cubic zinc blend GaN phases were synthesized in GaAs by 50 keV N+ implantation at 400 deg C and subsequent annealing at 900 deg C for 15 min in N2 ambient. Crystallographic structural and Raman scattering studies revealed that GaN phases were grown for fluence above 2x1017 cm-2. Temperature-dependent photoluminescence study showed sharp direct band-to-band transition peak ~3.32 eV at temperature <= 200K. The intermediate bandgap value, with respect to ~3.4 eV for hexagonal and ~3.27 eV for cubic phases of GaN is an indicative for the formation of mixed hexagonal and cubic phases.
Nitrogen ion beam synthesis of InN in InP (100) at elevated temperature
S. Dhara,P. Magudapathy,R. Kesavamoorthy,S. Kalavathi,V. S. Sastry,K. G. M. Nair,G. M. Hsu,L. C. Chen,K. H. Chen,K. Santhakumar,T. Soga
Physics , 2007, DOI: 10.1063/1.2186101
Abstract: InN phase is grown in crystalline InP(100) substrates by 50 keV N+ implantation at an elevated temperature of 400 deg C followed by annealing at 525 deg C in N2 ambient. Crystallographic structural and Raman scattering studies are performed for the characterization of grown phases. Temperature- and power-dependent photoluminescence studies show direct band-to-band transition peak ~1.06 eV at temperatures <=150K. Implantations at an elevated temperature with a low ion beam current and subsequent low temperature annealing step are found responsible for the growth of high-quality InN phase.
'Spillout' effect in gold nanoclusters embedded in c-Al2O3(0001) matrix
S. Dhara,B. Sundaravel,T. R. Ravindran,K. G. M. Nair,C. David,B. K. Panigrahi,P. Magudapathy,K. H. Chen
Physics , 2004, DOI: 10.1016/j.cplett.2004.10.011
Abstract: Gold nanoclusters are grown by 1.8 MeV Au^\sup{2+} implantation on c-Al\sub{2}O\sub{3}(0001)substrate and subsequent air annealing at temperatures 1273K. Post-annealed samples show plasmon resonance in the optical (561-579 nm) region for average cluster sizes ~1.72-2.4 nm. A redshift of the plasmon peak with decreasing cluster size in the post-annealed samples is assigned to the 'spillout' effect (reduction of electron density) for clusters with ~157-427 number of Au atoms fully embedded in crystalline dielectric matrix with increased polarizability in the embedded system.
Blue luminescence of Au nanoclusters embedded in silica matrix
S. Dhara,Sharat Chandra,P. Magudapathy,S. Kalavathi,B. K. Panigrahi,K. G. M. Nair,V. S. Sastry,C. W. Hsu,C. T. Wu,K. H. Chen,L. C. Chen
Physics , 2004, DOI: 10.1063/1.1814939
Abstract: Photoluminescence study using the 325 nm He-Cd excitation is reported for the Au nanoclusters embedded in SiO2 matrix. Au clusters are grown by ion beam mixing with 100 KeV Ar+ irradiation on Au [40 nm]/SiO2 at various fluences and subsequent annealing at high temperature. The blue bands above ~3 eV match closely with reported values for colloidal Au nanoclusters and supported Au nanoislands. Radiative recombination of sp electrons above Fermi level to occupied d-band holes are assigned for observed luminescence peaks. Peaks at 3.1 eV and 3.4 eV are correlated to energy gaps at the X- and L-symmetry points, respectively, with possible involvement of relaxation mechanism. The blue shift of peak positions at 3.4 eV with decreasing cluster size is reported to be due to the compressive strain in small clusters. A first principle calculation based on density functional theory using the full potential linear augmented plane wave plus local orbitals (FP-LAPW+LO) formalism with generalized gradient approximation (GGA) for the exchange correlation energy is used to estimate the band gaps at the X- and L-symmetry points by calculating the band structures and joint density of states (JDOS) for different strain values in order to explain the blueshift of ~0.1 eV with decreasing cluster size around L-symmetry point.
Hybrid Fuzzy Controller Based Frequency Regulation in Restructured Power System  [PDF]
P. Anitha, P. Subburaj
Circuits and Systems (CS) , 2016, DOI: 10.4236/cs.2016.76065
Abstract: This paper discusses the implementation of Load Frequency Control (LFC) in restructured power system using Hybrid Fuzzy controller. The formulation of LFC in open energy market is much more challenging; hence it needs an intelligent controller to adapt the changes imposed by the dynamics of restructured bilateral contracts. Fuzzy Logic Control deals well with uncertainty and indistinctness while Particle Swarm Optimization (PSO) is a well-known optimization tool. Abovementioned techniques are combined and called as Hybrid Fuzzy to improve the dynamic performance of the system. Frequency control of restructured system has been achieved by automatic Membership Function (MF) tuned fuzzy logic controller. The parameters defining membership function has been tuned and updated from time to time using Particle Swarm Optimization (PSO). The robustness of the proposed hybrid fuzzy controller has been compared with conventional fuzzy logic controller using performance measures like overshoot and settling time following a step load perturbation. The motivation for using membership function tuning using PSO is to show the behavior of the controller for a wide range of system parameters and load changes. Error based analysis with parametric uncertainties and load changes is tested on a two-area restructured power system.
Integral Performance Criteria Based Analysis of Load Frequency Control in Bilateral Based Market  [PDF]
P. Anitha, P. Subburaj
Circuits and Systems (CS) , 2016, DOI: 10.4236/cs.2016.76086
Abstract: Performance index based analysis is made to examine and highlight the effective application of Particle Swarm Optimization (PSO) to optimize the Proportional Integral gains for Load Frequency Control (LFC) in a restructured power system that operates under Bilateral based policy scheme. Various Integral Performance Criteria measures are taken as fitness function in PSO and are compared using overshoot, settling time and frequency and tie-line power deviation following a step load perturbation (SLP). The motivation for using different fitness technique in PSO is to show the behavior of the controller for a wide range of system parameters and load changes. Error based analysis with parametric uncertainties and load changes are tested on a two-area restructured power system. The results of the proposed PSO based controller show the better performance compared to the classical Ziegler-Nichols (Z-N) tuned PI andFuzzy Rule based PI controller.
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