Department of Physics

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Rapidly quenched bilayer magnetostrictive ribbons have been prepared and characterized to investigate phase transformations, interfacial activity and their potentiality as bend sensors. The bilayer ribbons were processed in a way to make the positively magnetostrictive layer Fe77.5Si7.5B15 as the free surface while negatively magnetostrictive Co72.5Si12.5B15 layer as the one in contact with the quenching copper wheel. Elemental concentration profiles obtained through electron probe microanalysis (EPMA) revealed synergistic variation in Fe and Co content at the interface. Devitrification process was also observed from atomic migrations and combinations influencing the interface width. Configuration of the bent layers showed interesting bending parameter output which could be further enhanced through stress relaxation. A detrimental effect of devitrification on bend sensitivity of rapidly quenched bilayers was also displayed. © 2014 Elsevier B.V.

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Journal of Magnetism and Magnetic Materials

Influence of phase transformation on interfacial activity and bend sensitivity of rapidly quenched Fe77.5Si7.5B15/Co72.5Si12.5B15 bilayered magnetostrictive ribbons

2-Dimensional structures with swift optical response have several technological advantages, for example they could be used as components of ultrafast light modulators, photo-detectors, and optical switches. Here we report on the fast photo switching behavior of thin films of liquid phase exfoliated MoS 2, when excited with a continuous laser of λ=658nm (E=1.88eV), over a broad range of laser power. Transient photo-conductivity measurements, using an optical pump and THz probe (OPTP), reveal that photo carrier decay follows a bi-exponential time dependence, with decay times of the order of picoseconds, indicating that the photo carrier recombination occurs via trap states. The nature of variation of photocurrent with temperature confirms that the trap states are continuously distributed within the mobility gap in these thin film of MoS2, and play a vital role in influencing the overall photo response. Our findings provide a fundamental understanding of the photo-physics associated with optically active 2D materials and are crucial for developing advanced optoelectronic devices.

Fulltext

Scientific Reports

Ultrafast intrinsic photoresponse and direct evidence of sub-gap states in liquid phase exfoliated MoS2 thin films

Solution-processed organo-lead halide perovskites are produced with sharp, color-pure electroluminescence that can be tuned from blue to green region of visible spectrum (425-570 nm). This was accomplished by controlling the halide composition of CH3NH3Pb(BrxCl1-x)3 [0 ≥ x ≥ 1] perovskites. The bandgap and lattice parameters change monotonically with composition. The films possess remarkably sharp band edges and a clean bandgap, with a single optically active phase. These chloride-bromide perovskites can potentially be used in optoelectronic devices like solar cells and light emitting diodes (LEDs). Here we demonstrate high color-purity, tunable LEDs with narrow emission full width at half maxima (FWHM) and low turn on voltages using thin-films of these perovskite materials, including a blue CH3NH3PbCl3 perovskite LED with a narrow emission FWHM of 5 nm. © 2015 American Chemical Society.

Nano Letters

Blue-Green Color Tunable Solution Processable Organolead Chloride-Bromide Mixed Halide Perovskites for Optoelectronic Applications

Sources for cosmic neutrino events detected by the IceCube Neutrino Observatory with energy above 30 TeV are hard to find due to their poor angular resolutions. Ultrahigh-energy cosmic rays (UHECRs) are detected with better angular resolutions above 100 EeV energies and can be used to check if the same astrophysical sources are responsible for producing both neutrinos and UHECRs. We test the correlation of UHECR data of the Pierre Auger Observatory, Telescope Array and past cosmic-ray experiments with IceCube neutrino events using statistical methods which emphasize invariant quantities. We find that the arrival directions of the 3yr IceCube detected cosmic neutrinos are correlated with > 100 EeV UHECR arrival directions at confidence level 90% . In our recent approach we have tried to find a correlation of the 4 yr IceCube detected High-Energy Starting Events (HESE) neutrino events with UHECRs from PAO and TA. We found more than 3s correlation for PAO only and TA+PAO UHECRs events > 100 EeV.

Proceedings of Science

A study of correlation between IceCube neutrino events and Ultra high energy cosmic rays

GRB 130427A, is the spectacular gamma ray explosion ever detected. It is believed to be originated from the core collapse of a massive star. It also achieved the record of being one of the most fluent and the longest duration GRB in GeV gamma rays lasting for about 20hrs. The redshift of this GRB has been detected as z=0.34. The Fermi-LAT Gamma-ray Space Telescope has detected a 95-GeV energy photon from GRB 130427A. The after glow radiation of this GRB was recorded by Swift XRT, BAT and UVOT. The Spectral Energy Distribution (SED) and Light curves of the prompt emission and afterglow help us to study the GRBs in detail. We have explained the afterglow SEDs and Light curve detected by LAT, XRT-BAT and UVOT/optical observations for GRB 130427A, by fitting it with the synchrotron emission model from the accelerated electrons for the adiabatic blastwave in both the interstellar medium (ISM) and wind environments. We see a better explanation of the observed data with synchrotron model in wind environment compared to ISM for this GRB.

The spectacular stellar explosion - GRB 130427A: Synchrotron modeling in the wind and the ISM

Detection of 35 very high-energy (VHE) neutrinos by the IceCube Neutrino Observatory has opened a new chapter in multi-messenger astronomy. Due to large errors in measuring the directions of the neutrino shower-type events, which dominate the current event list, it is difficult to identify their astrophysical sources. We perform cross-correlation study of IceCube neutrino events with extragalactic candidate sources using X-ray and gamma-ray selected source catalogues such as Swift-BAT, 3LAC and TeV-Cat. We apply different cuts on the X-ray and gammaray fluxes of the sources in these catalogues, and use different source classes in order to study correlation. We use invariant statistic and Monte Carlo simulations to evaluate statistical significance of any correlation.

Search for extragalactic astrophysical counterparts of IceCube neutrino events

Gamma-Ray Bursts (GRBs), the most powerful sources of gamma rays in the universe, have been detected at energies up to 95 GeV. This energy is at the verge of what is known as the Very High Energy (VHE, above 100 GeV) emission regime. VHE sources are targets for currently running and upcoming ground-based Cherenkov telescopes. It is therefore very important to understand the VHE emission mechanism(s) of GRBs. Synchrotron radiation by electrons accelerated in the external shocks of a GRB blast wave, widely accepted as the mechanism for X-ray to radio afterglow emission, has difficulty to explain and 10 GeV emission hours after the GRB trigger. We model VHE emission from interactions of cosmic-rays which are shock-accelerated in the GRB blast wave. We also compute VHE emission from electron-positron pair cascade formed in the intergalactic space by absorption of and 1 PeV gamma rays from the prompt phase of the GRB. VHE emissions from the GRBS modeled here can be tested by the ground-based air and water Cherenkov telescopes.

Very high energy emission from gamma-ray bursts

It is shown that a realistic controlled bidirectional remote state preparation is possible using a large class of entangled quantum states having a particular structure. Existing protocols of probabilistic, deterministic and joint remote state preparation are generalized to obtain the corresponding protocols of controlled bidirectional remote state preparation (CBRSP). A general way of incorporating the effects of two well-known noise processes, the amplitude-damping and phase-damping noise, on the probabilistic CBRSP process is studied in detail by considering that noise only affects the travel qubits of the quantum channel used for the probabilistic CBRSP process. Also indicated is how to account for the effect of these noise channels on deterministic and joint remote state CBRSP protocols. © 2015, Springer Science+Business Media New York.

Quantum Information Processing

Controlled bidirectional remote state preparation in noisy environment: a generalized view

In this paper, a high current linear aperture radial multichannel Pseudospark switch (LARM-PSS) is reported which has been analyzed for its high current characteristics. In order to enhance hold-off voltage and support hollow cathode effect for the ignition of the discharge in this configuration, the field penetration analysis through circular and linear apertures of the electrodes has been carried out. The linear apertures in the electrodes increase the current handling capacity than that of circular aperture electrodes without significant compromise of the hold-off capacity. The developed LARM-PSS switch is capable to hold voltage up to 25 kV at gas pressure between 10 and 50 Pa for hydrogen. The switch has been operated using a 800 nF capacitor bank and conducted an effective charge up to 1.5 C with peak switch current ∼20 kA at applied voltage 19 kV. © 2015 AIP Publishing LLC.

Review of Scientific Instruments

Investigations of a high current linear aperture radial multichannel pseudospark switch

Irradiation of solids with energetic particles, such as electrons or ions, normally gives rise to the formation of atomic defects in the target and changes the material's properties. However, inspite of the damage, irradiation may overall have a beneficial effect on the target. In the present study, Mn-doped ZnS nanocrystals have been synthesized using an aqueous solution method and irradiated by a C6+ (80MeV) ion beam at fluence (1 × 1013ions/cm2). A photoluminescence study has been carried on in a ZnS:Mn system, which results in emission peaks corresponding to surface states and Mn2+ emission, confirming that optical luminescence in semiconductor nanocrystals can be tuned using impurity concentration as well as swift heavy ion irradiation between nanocrystals band gap and the bulk band gap values. © 2015 © 2015 Taylor & Francis.