Department of Physics

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In organic memory devices, we introduce non-interacting "write" and "read" processes so that the state of a device is not perturbed during the "read" process. We have used heterojunction devices based on suitable materials in such a way that they can generate photovoltage and photocurrent upon illumination. Both open-circuit voltage or short-circuit current of the device have responded to conductance switching. We have showed that the device can be switched to a high-conducting state by applying a suitable voltage pulse and its state can be probed or "read" by measuring open-circuit voltage or short-circuit current. The results show newer parameters to probe organic memory devices. © 2008 Elsevier B.V. All rights reserved.

World University root node

Organic Electronics

Non-interacting write and read processes in organic memory devices

We study the geometric phase of an open two-level quantum system under the influence of a squeezed, thermal environment for both non-dissipative as well as dissipative system-environment interactions. In the non-dissipative case, squeezing is found to have a similar influence as temperature, of suppressing geometric phase, while in the dissipative case, squeezing tends to counteract the suppressive influence of temperature in certain regimes. Thus, an interesting feature that emerges from our work is the contrast in the interplay between squeezing and thermal effects in non-dissipative and dissipative interactions. This can be useful for the practical implementation of geometric quantum information processing. By interpreting the open quantum effects as noisy channels, we make the connection between geometric phase and quantum noise processes familiar from quantum information theory. © 2007 EDP Sciences/Società Italiana di Fisica/Springer-Verlag.

Fulltext

European Physical Journal D

Geometric phase of a qubit interacting with a squeezed-thermal bath

We report the structural and optical properties of x SnO2 -y Fe2 O3 nanocrystalline composite thin films. SnO2 and Fe2 O3 exhibit strong phase separation instability and their particle size and crystallinity are tunable by changing their composition and annealing temperature. The bandgap for these composites continuously increases from 2.3 to 3.89 eV. We discuss the increasing bandgap values in terms of the quantum confinement effect manifested by the decreasing size of Fe2 O3 crystallites. The method provides a generic approach for the tuning of the bandgap in nanocomposite systems. © 2008 American Institute of Physics.

Applied Physics Letters

Bandgap engineering by tuning particle size and crystallinity of SnO 2 - Fe2O3 nanocrystalline composite thin films

CdS/PbS core-shell nanoparticles are grown via ion-exchange reaction route. Devices based on such nanoparticles exhibit electrical bistability and memory phenomena. We show that the bistability is due to charge confinement in the nanoparticles. Here, although the low-bandgap material allows facile carrier injection from the electrodes, the high-bandgap one traps and confines charges to yield high-conducting state. The results show that the degree of electrical bistability or On/Off ratio in some of the CdS/PbS core-shell nanoparticles is several orders higher in magnitude than that in the individual components. We show how the shell/core ratio controls charge confinement and hence electrical bistability. Core-shell nanoparticles hence provide a newer route to optimize electrical bistability and memory phenomena. © 2008 American Chemical Society.

Journal of Physical Chemistry C

Core-shell nanoparticles: An approach to enhance electrical bistability

We have investigated the properties of sputter deposited InN thin films prepared from an In-metal (InN-MT) and an In2O3 target (InN-OT). The excess oxygen present in the InN-OT films alters the microstructure by introducing additional disorder. Depth dependent x-ray photoelectron spectroscopy measurements indicate the presence of higher concentrations of oxygen in InN-OT. Raman spectra show evidence for the presence of an In2O3 secondary phase in both samples. Although the InN-OT film has a higher oxygen concentration, both films show similar electrical and optical properties. © 2008 American Institute of Physics.

Phase separation and optical properties in oxygen-rich InN films

We have grown core-shell nanotubes with CNTs in the core and CdS as the shell. The thickness of the shell has been varied by controlling the reaction parameters. In devices based on such core-shell nanotubes, the nanotubes act as carrier-transporting channels to augment charge confinement in the shell. Increasing the density of confined carriers results in enhanced electrical bistability and memory phenomena in CdS. With widely separated low- and high-conducting states, we were able to scale the high-state, so that different high-conducting states could be achieved for multi-level memory applications. © 2008 The Royal Society of Chemistry.

Journal of Materials Chemistry

Core-shell nanotubes to enhance electrical bistability for 2-bit memory

We present multifunctionality in heterostructure devices based on poly(3-hexylthiophene) and copper phthalocyanine layers. Under solar light illumination, the devices yield photovoltage in an open-circuit condition. They, in addition, emit light in the forward bias and can also detect a trace of light in the reverse-bias direction. Highest occupied molecular orbitais and lowest unoccupied molecular orbitais of the two materials, along with the metal work functions, are suitable for the three functionalities at different bias modes. While the electroluminescence spectrum of the device has been compared with the photoluminescence spectra of the components, the spectral response of the photocurrent matched well with the electronic absorption spectrum of the poly(3-hexylthiophene)/copper phthalocyanine heterojunction. © 2008 American Chemical Society.

Multifunctionality of organic devices: Light emission, photovoltage generation, and photodetection

Creep damage behaviour of water quenched 5Cr-0.5Mo steel has been studied using magnetic Barkhausen emissions (MBE) technique. The results were compared with the materials having same composition but used in service for 15 years to demonstrate the potentiality of the magnetic technique for in-situ evaluation of extent of creep damage of components. The rms voltage of magnetic Barkhausen signal for the virgin sample decreased at the initial stage of the expended creep life where new carbides are formed. As soon as the growth of the carbides took place at the expense of the smaller ones, MBE voltage started increasing due to the decrease of pinning density. However, in case of 15 years of service exposed sample, growth of carbides already took place and hence MBE voltage increased even during the initial stage of laboratory creep testing. As soon as the void started forming in the samples (both for virgin and service exposed one), the rate of increase of MBE voltage started decreasing. The formations of such cavities were observed through SEM micrograph analysis. © 2008 Elsevier B.V. All rights reserved.

Journal of Magnetism and Magnetic Materials

Creep behaviour study of virgin and service exposed 5Cr-0.5Mo steel using magnetic Barkhausen emissions technique

We study the constraints on possible new physics contributions to the forward-backward asymmetry of muons, AFB(q2), in B→Kμ+μ-. New physics in the form of vector/axial-vector operators does not contribute to AFB(q2), whereas new physics in the form of scalar/pseudoscalar operators can enhance AFB(q2) only by a few percent. However, new physics in the form of tensor operators can take the peak value of AFB(q2) to as high as 40% near the high-q2 end point. In addition, if both scalar/pseudoscalar and tensor operators are present, then AFB(q2) can be more than 15% for the entire high-q2 region q2>15GeV2. The observation of significant AFB would imply the presence of new physics tensor operators, whereas its q2 dependence could further indicate the presence of new scalar/pseudoscalar physics. © 2008 The American Physical Society.

Physical Review D - Particles, Fields, Gravitation and Cosmology

Large forward-backward asymmetry in B→Kμ+μ- from new physics tensor operators

We study the constraints on the contribution of new physics in the form of scalar/pseudoscalar operators to the average forward-backward asymmetry AFB of muons in B→Kμ+μ- and the longitudinal polarization asymmetry ALP of muons in Bs→μ+μ-. We find that the maximum possible value of AFB allowed by the present upper bound on B(Bs→μ+μ-) is about 1% at 95% C.L. and hence will be very difficult to measure. On the other hand, the present bound on B(Bs→μ+μ-) fails to put any constraints on ALP, which can be as high as 100% even if B(Bs→μ+μ-) is close to its standard model prediction. The measurement of ALP will be a direct evidence for an extended Higgs sector, and combined with the branching ratio B(Bs→μ+μ-) it can even separate the new physics scalar and pseudoscalar contributions. © 2008 The American Physical Society.