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Ghosh M.,DST Unit for Nanoscience | Raychaudhuri A.K.,DST Unit for Nanoscience
Applied Physics Letters | Year: 2011

Reversible control of the photoluminescence of ZnO occurring in the visible range, has been achieved by application of a few volts (<5 V) to a device consisting of nanostructured ZnO film sandwiched between indium tin oxide electrode and polyethylene oxide-lithium perchlorate, a solid polymer electrolyte. The photoluminescence intensity shows nearly 100% modulation with a response time less than 30 s, when the bias is applied at the electrolyte electrode. A model is proposed for the observed effect that is based on defect states of ZnO and the band bending at the ZnO-electrolyte interface that can be changed by the applied bias. © 2011 American Institute of Physics.

Das S.,Indian Institute of Technology Kharagpur | Das K.,DST Unit for Nanoscience | Singha R.K.,Indian Institute of Technology Kharagpur | Manna S.,Indian Institute of Technology Kharagpur | And 3 more authors.
Nanoscale Research Letters | Year: 2011

The formation of circularly ordered Ge-islands on Si(001) has been achieved because of nonuniform strain field around the periphery of the holes patterned by focused ion beam in combination with a self-assembled growth using molecular beam epitaxy. The photoluminescence (PL) spectra obtained from patterned areas (i.e., ordered islands) show a significant signal enhancement, which sustained till 200 K, without any vertical stacking of islands. The origin of two activation energies in temperature-dependent PL spectra of the ordered islands has been explained in detail. © 2011 Das et al.

Chakravorty M.,DST Unit for Nanoscience | Das K.,DST Unit for Nanoscience | Raychaudhuri A.K.,DST Unit for Nanoscience | Naik J.P.,University of Birmingham | Prewett P.D.,University of Birmingham
Microelectronic Engineering | Year: 2011

Experimental studies of the temperature dependent resistivity of platinum nanowires grown on an oxidised silicon wafer by using focused ion beam (FIB) have been made. A series of 4-terminal resistivity measurements were carried out in the temperature range 50-300 K on single nanowires of width and thickness ∼100 nm grown by decomposition of an organometallic precursor using Ga + ions of different accelerating voltages from 10 keV to 30 keV. Energy dispersive X-ray spectroscopy showed the nanowires to be composed of more than 60% by volume of carbon, the remainder being principally platinum and gallium. The exact composition depends on the accelerating voltage of the ions used. There is clear evidence from cross-sectional microscopy that the material is a composite consisting of a metallic phase present in the form of nanoscale clusters, randomly distributed in a matrix of carbon. Electrical measurements are consistent with this, showing a critical volume concentration for conduction, which is typical of electron transport in composites with percolating metal phase. Results show an unexpectedly high sensitivity of the temperature dependence of resistivity near the critical volume concentration, which has been explained to arise from thermal strain effects. The anomalous temperature/strain effects observed in this investigation might be exploited in temperature measurement and strain sensor applications. © 2011 Elsevier B.V. All rights reserved.

Das K.,DST Unit for Nanoscience | Das S.,Indian Institute of Technology Kharagpur | R.K.Singha,Indian Institute of Technology Kharagpur | Ray S.K.,Indian Institute of Technology Kharagpur | Raychaudhuri A.K.,DST Unit for Nanoscience
Journal of Nanoparticle Research | Year: 2012

We report the growth of Ge islands on Si (001) substrates with lithographically defined twodimensionally periodic pits using focused ion-beam patterning and molecular beam epitaxy. The formation of circularly ordered Ge islands has been achieved by means of nonuniform strain field around the periphery of the holes due to ion bombardment. Lateral ordering of the Ge islands have been controlled by both the pit size and pit separation. Preferential growth at the pit sites has also been achieved by using appropriate pattern shape and size. © Springer Science+Business Media B.V. 2012.

Chaudhuri S.K.,UGC-DAE Consortium for Scientific Research | Ghosh M.,DST Unit for Nanoscience | Das D.,UGC-DAE Consortium for Scientific Research | Raychaudhuri A.K.,DST Unit for Nanoscience
Journal of Applied Physics | Year: 2010

The present article describes the size induced changes in the structural arrangement of intrinsic defects present in chemically synthesized ZnO nanoparticles of various sizes. Routine x-ray diffraction and transmission electron microscopy have been performed to determine the shapes and sizes of the nanocrystalline ZnO samples. Detailed studies using positron annihilation spectroscopy reveals the presence of zinc vacancy. Whereas analysis of photoluminescence results predict the signature of charged oxygen vacancies. The size induced changes in positron parameters as well as the photoluminescence properties, has shown contrasting or nonmonotonous trends as size varies from 4 to 85 nm. Small spherical particles below a critical size (∼23 nm) receive more positive surface charge due to the higher occupancy of the doubly charge oxygen vacancy as compared to the bigger nanostructures where singly charged oxygen vacancy predominates. This electronic alteration has been seen to trigger yet another interesting phenomenon, described as positron confinement inside nanoparticles. Finally, based on all the results, a model of the structural arrangement of the intrinsic defects in the present samples has been reconciled. © 2010 American Institute of Physics.

Mandal P.,DST Unit for Nanoscience | Das B.,DST Unit for Nanoscience | Das B.,National Changhua University of Education | Raychaudhuri A.K.,DST Unit for Nanoscience
Journal of Applied Physics | Year: 2016

We report an investigation on the stability of single W nanowire (NW) under direct current stressing. The NW of width ≈ 80 nm and thickness ≈ 100 nm was deposited on a SiO2/Si substrate by Focused Ion Beam (FIB) of Ga ions using W(CO)6 as a precursor. Such nanowires, used as interconnects in nanoelectronics, contain C and Ga in addition to W. The stability studies, done for the first time in such FIB deposited NWs, show that under current stressing these NWs behave very differently from that observed in conventional metal NWs or interconnects. The failure of such FIB deposited NW occurs at a relatively low current density (∼1011A/m2) which is an order or more less than that seen in conventional metal NWs. The failure accompanies with formation of voids and hillocks, suggesting ionic migration as the cause of failure. However, the polarities of void and hillock formations are opposite to those observed in conventional metal interconnects. This observation along with preferential agglomeration of Ga ions in hillocks suggests that the ionic migration in such NWs is dominated by direct force as opposed to the migration driven by electron wind force in conventional metal interconnects. © 2016 AIP Publishing LLC.

PubMed | DST Unit for Nanoscience
Type: Journal Article | Journal: Nanotechnology | Year: 2011

We report that ZnO nanostructures synthesized by a chemical route undergo a shape transition at 20nm from spherical to hexagonal morphology thereby changing the spectral components of the blue-green emission. Spherically shaped nanocrystals (size range 11-18nm) show emission in the range of 555-564nm and the emission shifts to the longer wavelength as the size increases. On the other hand, rods and hexagonal platelets (size range 20-85nm), which are the equilibrium morphology after the shape transition, show an emission near 465-500nm which shifts to shorter wavelength as the size increases. The shape transition also leads to relaxation of microstrain in the system. Our analysis shows that the visible emission originates from a defect layer on the nanostructure surface which is affected by the shape transition. The change in the spectral component of the blue-green emission on change of shape has been explained as arising from band bending due to a depletion layer in smaller spherical particles which is absent in the larger particles with flat faces.

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