Field Emission with Ultra low Turn On Voltage from Metal Decorated Carbon Nanotubes

A simple and scalable method of decorating 3D-carbon nanotube (CNT) forest with metal particles has been developed. The results observed in aluminum (AI) decorated CNTs and copper (Cu) decorated CNTs on silicon (Si) and Inconel are compared with undecorated samples. A significant improvement in the field emission characteristics of the cold cathode was observed with ultralow turn on voltage (E-to similar to 0.1 V/mu m) due to decoration of CNTs with metal nanoparticles. Contact resistance between the CNTs and the substrate has also been reduced to a large extent, allowing us to get stable emission for longer duration without any current degradation, thereby providing a possibility of their use in vacuum microelectronic devices.

Application of lateral photovoltage towards contactless light beam induced current measurements and its dependence on the finite beam size

The nature of the signal due to light beam induced current (LBIC) at the remote contacts is verified as a lateral photovoltage for non-uniformly illuminated planar p-n junction devices; simulation and experimental results are presented. The limitations imposed by the ohmic contacts are successfully overcome by the introduction of capacitively coupled remote contacts, which yield similar results without any significant loss in the estimated material and device parameters. It is observed that the LBIC measurements introduce artefacts such as shift in peak position with increasing laser power. Simulation of LBIC signal as a function of characteristic length L-c of photo-generated carriers and for different beam diameters has resulted in the observed peak shifts, thus attributed to the finite size of the beam. Further, the idea of capacitively coupled contacts has been extended to contactless measurements using pressure contacts with an oxidized aluminium electrodes. This technique avoids the contagious sample processing steps, which may introduce unintentional defects and contaminants into the material and devices under observation. Thus, we present here, the remote contact LBIC as a practically non-destructive tool in the evaluation of device parameters and welcome its use during fabrication steps. (C) 2014 AIP Publishing LLC.

Digestive ripening and green synthesis of ultra-small (r < 2 nm) stable ZnO quantum dots

Given the recent reports pertaining to novel optical properties of ultra-small quantum dots (QDs) (r <2 nm), this nanomaterial is of relevance to both technology and science. However it is well known that in these size regimes most chalocogenide QD dispersions are unstable. Since applications often require use of QD dispersions (e.g. for deployment on a substrate), stabilizing these ultra-small particles is of practical relevance. In this work we demonstrate a facile, green, solution approach for synthesis of stable, ultra-small ZnO QDs having radius less than 2 nm. The particle size is calculated using Brits' equation and confirmed by transmission electron micrographs. ZnO QDs reported remain stable for > 120 days in ethanol (at similar to 298-303 K). We report digestive ripening (DR) in TEA capped ZnO QDs; this occurs rapidly over a short duration of 5 min. To explain this observation we propose a suitable mechanism based on the Lee's theory, which correlates the tendency of DR with the observed zeta potentials of the dispersed medium. To the best of our knowledge this is the (i) first report on DR in oxide QDs, as well as the first direct experimental verification of Lee's theory, and (ii) most rapid DR reported so far. The facile nature of the method presented here makes ultra-small ZnO readily accessible for fundamental exploration and technologically relevant applications. (C) 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Oxovanadium(IV) catecholates of terpyridine bases for cellular imaging and photocytotoxicity in red light

Oxovanadium(IV) catecholates of terpyridyl bases, viz. VO(cat)(L)] (L - phtpy, 1; stpy, 2) and VO(dopa-NBD)(L)] (L = phtpy, 3; stpy, 4), where cat is benzene-1,2-diolate, dopa-NBD is 4-(2-(4-nitrobenzoc]1,2,5]oxadiazol-7-ylamino)ethyl)benzene-1,2-di olate, phtpy is (4'-phenyl)-2,2':6',2 `'-terpyridine and stpy is (2,2':6',2 `'-terpyridin-4'-oxy)ethyl-beta-D-glucopyranoside, were prepared and characterized, and their DNA binding, DNA photo-cleavage activity, photocytotoxicity in red light (600-720 nm), cellular uptake and intracellular localization behaviour were studied. The complexes showed an intense ligand-to-metal charge transfer (LMCT) band at similar to 500 nm. The sugar appended complexes 2 and 4 showed significant uptake into the cancer cells. The dopa-NBD complexes 3 and 4 showing green emission were used for cellular imaging. The complexes showed diffused cellular localization mainly in the cytosol and to a lesser extent into the nucleus as evidenced from the confocal microscopy study. Complexes 1-4 showed significant photocytotoxicity in the PDT spectral window giving low IC50 values, while remaining relatively non-toxic in dark.

Iron(III) Catecholates for Cellular Imaging and Photocytotoxicity in Red Light

Iron(III) complexes Fe(L)(L') (NO3)]-in which L is phenyl-N, N-bis(pyridin-2-yl) methyl]methanamine (1), (anthracen-9-yl)N, N-bis(pyridin-2-yl) methyl] methanamine (2), (pyreny-1-yl)-N, N-bis(pyridin- 2-yl) methyl] methanamine (3-5), and L' is catecholate (1-3), 4-tert-butyl catecholate (4), and 4-(2-aminoethyl)benzene- 1,2-diolate (5)-were synthesized and their photocytotoxic proper-ties examined. The five electron-paramagnetic complexes displayed a FeIII/ Fe-II redox couple near similar to 0.4 V versus a saturated calomel electrode (SCE) in DMF/0.1m tetrabutylammonium perchlorate (TBAP). They showed unpre-cedented photocytotoxicity in red light (600-720 nm) to give IC50-15 mm in various cell lines by means of apoptosis to generate reactive oxygen species. They were ingested in the nucleus of HeLa and HaCaT cells in 4 h, thereby interacting favorably with calf thymus (ct)-DNA and photocleaving pUC19 DNA in red light of 785 nm to form hydroxyl radicals.

High resolution light-sheet based high-throughput imaging cytometry system enables visualization of intra-cellular organelles

Visualization of intracellular organelles is achieved using a newly developed high throughput imaging cytometry system. This system interrogates the microfluidic channel using a sheet of light rather than the existing point-based scanning techniques. The advantages of the developed system are many, including, single-shot scanning of specimens flowing through the microfluidic channel at flow rate ranging from micro-to nano- lit./min. Moreover, this opens-up in-vivo imaging of sub-cellular structures and simultaneous cell counting in an imaging cytometry system. We recorded a maximum count of 2400 cells/min at a flow-rate of 700 nl/min, and simultaneous visualization of fluorescently-labeled mitochondrial network in HeLa cells during flow. The developed imaging cytometry system may find immediate application in biotechnology, fluorescence microscopy and nano-medicine. (C) 2014 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.

Combinatorial effect of rolling and carbonaceous nanoparticles on the evolution of crystallographic texture and structural properties of ultra high molecular weight polyethylene

Ultra high molecular weight polyethylene (PE) is a structural polymer widely used in biomedical implants. The mechanical properties of PE can be improved either by controlled crystalline orientation (texture) or by the addition of reinforcing agents. However, the combinatorial effect has not received much attention. The objective of this study was to characterize the structure and mechanical properties of PE composites incorporating multiwall carbon nanotubes (MWCNT) and reduced graphene oxide (RGO) subjected to hot rolling. The wide angle X-ray diffraction studies revealed that mechanical deformation resulted in a mixture of orthorhombic and monoclinic crystals. Furthermore, the presence of nanoparticles resulted in lower crystallinity in PE with smaller crystallite size, more so in RGO than in MWCNT composites. Rolling strengthened the texture of both orthorhombic and the monoclinic phases in PE. Presence of RGO weakened the texture of both phases of PE after rolling whereas MWCNT only mildly weakened the texture. This resulted in a reduction in the elastic modulus of RGO composites whereas moduli of neat polymer and the MWCNT composite increased after rolling. This study provides new insight into the role of nanoparticles in texture evolution during polymer processing with implications for processing of structural polymer composites.

Structural and magnetic properties of ultra-small scale eutectic CoFeZr alloys

Aiming to develop high mechanical strength and toughness by tuning ultrafine lamellar spacing of magnetic eutectic alloys, we report the mechanical and magnetic properties of the binary eutectic alloys Co90.5Zr9.5 and Fe90.2Zr9.8, as well as the pseudo-binary eutectic alloys Co82.4Fe8Zr9.6, Co78Fe12.4Zr9.6 and Co49.2Fe49.2Zr9.6 developed by suction-casting. The lower lamellar spacing around 100 nm of the eutectics Co49.2Fe49.2Zr9.6 yields a high hardness of 713(+/- 20) VHN. Magnetic measurements reveal high magnetic moment of 1.92 mu B (at 5 K) and 1.82 mu B (at 300 K) per formula unit for this composition. The magnetization vs. applied field data at 5 K show a directional preference to some extent and therefore smaller non-collinear magnetization behavior compared to Co11Zr2 reported in the literature due to exchange frustration and transverse spin freezing owing to the presence of smaller Zr content. The decay of magnetization as a function of temperature along the easy axis of magnetization of all the eutectic compositions can be described fairly well by the spin wave excitation equation Delta M/M(0) = BT3/2 + CT5/2. (C) 2014 Elsevier B.V. All rights reserved.

Throwing light on platinized carbon nanostructured composites for hydrogen generation

In the present study, we have synthesised carbon nanoparticles (CNPs) through a relatively simple process using a hydrocarbon precursor. These synthesised CNPs in the form of elongated spherules and/or agglomerates of 30-55 nm were further used as a support to anchor platinum nanoparticles. The broad light absorption (300-700 nm) and a facile charge transfer property of CNPs in addition to the plasmonic property of Pt make these platinized carbon nanostructures (CNPs/Pt) a promising candidate in photocatalytic water splitting. The photocatalytic activity was evaluated using ethanol as the sacrificial donor. The photocatalyst has shown remarkable activity for hydrogen production under UV-visible light while retaining its stability for nearly 70 h. The broadband absorption of CNPs, along with the Surface Plasmon Resonance (SPR) effect of PtNPs singly and in composites has pronounced influence on the photocatalytic activity, which has not been explored earlier. The steady rate of hydrogen was observed to be 20 mu mol h(-1) with an exceptional cumulative hydrogen yield of 32.16 mmol h(-1) g(-1) observed for CNPs/Pt, which is significantly higher than that reported for carbon-based systems.

TiO2/ZnO core/shell nano-heterostructure arrays as photo-electrodes with enhanced visible light photoelectrochemical performance

The present article reports a facile method for preparing the vertically-aligned 1D arrays of a new type of type II n-n TiO2/ZnO core/shell nano-heterostructures by growing the nano-shell of ZnO on the electrochemically fabricated TiO2 nanotubes core for visible light driven photoelectrochemical applications. The strong interfacial interaction at the type II heterojunction leads to an effective interfacial charge separation and charge transport. The presence of various defects such as surface states, interface states and other defects in the nano-heterostructure enable it for improved visible light photoelectrochemical performance. The presence of such defects has also been confirmed by the UV-vis absorption, cathodoluminescence, and crystallographic studies. The TiO2/ZnO core/shell nano-heterostructures exhibit strong green luminescence due to the defect transitions. The TiO2/ZnO core/shell nano-heterostructures photo-electrode show significant enhancement of visible light absorption and it provides a photocurrent density of 0.7 mA cm(-2) at 1 V vs. Ag/AgCl, which is almost 2.7 times that of the TiO2/ZnO core/shell nano-heterostructures under dark conditions. The electrochemical impedance spectroscopy results demonstrate that the substantially improved photoelectrochemical and photo-switching performance of the nano-heterostructures photo-anode is because of the enhancement of interfacial charge transfer and the increase in the charge carrier density caused by the incorporation of the ZnO nano-shell on TiO2 nanotube core.

MRT Letter: Two-Photon Excitation-Based 2pi Light-Sheet System for Nano-Lithography

We propose two-photon excitation-based light-sheet technique for nano-lithography. The system consists of 2 -configured cylindrical lens system with a common geometrical focus. Upon superposition, the phase-matched counter-propagating light-sheets result in the generation of identical and equi spaced nano-bump pattern. Study shows a feature size of as small as few tens of nanometers with a inter-bump distance of few hundred nanometers. This technique overcomes some of the limitations of existing nano-lithography techniques, thereby, may pave the way for mass-production of nano-structures. Potential applications can also be found in optical microscopy, plasmonics, and nano-electronics. Microsc. Res. Tech. 78:1-7, 2015. (c) 2014 Wiley Periodicals, Inc.

Amorphous W-S-N thin films: The atomic structure behind ultra-low friction

Amorphous W-S-N in the form of thin films has been identified experimentally as an ultra-low friction material, enabling easy sliding by the formation of a WS2 tribofilm. However, the atomic-level structure and bonding arrangements in amorphous W-S-N, which give such optimum conditions for WS2 formation and ultra-low friction, are not known. In this study, amorphous thin films with up to 37 at.% N are deposited, and experimental as well as state-of-the-art ab initio techniques are employed to reveal the complex structure of W-S-N at the atomic level. Excellent agreement between experimental and calculated coordination numbers and bond distances is demonstrated. Furthermore, the simulated structures are found to contain N bonded in molecular form, i.e. N-2, which is experimentally confirmed by near edge X-ray absorption fine structure and X-ray photoelectron spectroscopy analysis. Such N-2 units are located in cages in the material, where they are coordinated mainly by S atoms. Thus this ultra-low friction material is shown to be a complex amorphous network of W, S and N atoms, with easy access to W and S for continuous formation of WS2 in the contact region, and with the possibility of swift removal of excess nitrogen present as N-2 molecules. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Facile synthesis of PbWO4: Applications in photoluminescence and photocatalytic degradation of organic dyes under visible light

Stolzite polymorph of PbWO4 catalyst was prepared by the facile room temperature precipitation method. Structural parameters were refined by the Rietveld analysis using powder X-ray data. PbWO4 was crystallized in the scheelite-type tetragonal structure with space group I4(1)/a (No. 88). Field emission scanning electron microscopy revealed leaf like morphology. Photoluminescence spectra exhibit broad blue emission (425 nm) under the excitation of 356 nm. The photocatalytic degradation of Methylene blue, Rhodamine B and Methyl orange dyes were measured under visible illumination. The 100% dye degradation was observed for MB and RhB dyes within 60 and 105 min. The rate constant was found to be in the decreasing order of MB > RhB > MO which followed the 1st order kinetic mechanism. Therefore, PbWO4 can be a potential candidate for blue component in white LEDs and also acts as a catalyst for the treatment of toxic and non-biodegradable organic pollutants in water. (C) 2014 Elsevier B.V. All rights reserved.

Visible light assisted photocatalytic degradation of organic dyes on TiO2-CNT nanocomposites

Carbon nanotubes (CNTs) uniformly decorated with nano-anatase TiO2 particles corresponding to different TiO2-CNT weight ratios (up to 90 % TiO2:10 % CNT) were prepared by employing sol-gel process. The nanocomposites were characterized by X-ray diffraction, IR, Raman, Scanning electron microscopy, Transmission electron microscopy, Photoluminescence, BET surface area and diffuse reflectance measurements. The composites show visible light assisted photocatalytic property, for example, the 90 % TiO2-10 % CNT composite completely degrades Indigo Carmine dye within 1 h of exposure to visible light. Similarly, Orange G and Congo Red dyes were decomposed within 2 h under visible light irradiation. The excellent visible light photocatalytic property of the composite is attributed to the synergetic effect of photoexcitation and photosensitization. This is due to the special nanoarchitecture wherein TiO2 nanoparticles are anchored to CNT surface that provides high specific interfacial area for photon absorption and electron trapping. Visible light assisted degradation profile of Indigo Carmine in the presence of TiO2-CNT nanocomposite and TEM image of the TiO2-CNT nanocomposite.

Remarkable Selectivity and Photo-Cytotoxicity of an Oxidovanadium(IV) Complex of Curcumin in Visible Light

Oxidovanadium(IV) complexes of 2-(2'-pyridyl)-1,10-phenanthroline (pyphen), viz. VO(pyphen)(acac)](ClO4) (1), VO(pyphen)(anacac)](ClO4) (2) and VO(pyphen)(cur)](ClO4) (3), where acac is acetylacetonate (in 1), anacac is anthracenylacetylacetonate (in 2) and cur is curcumin monoanion (in 3) were synthesized, characterized and their photo-induced DNA cleavage activities and photo-cytotoxicities studied. The complexes are 1: 1 electrolytes in DMF. The one-electron paramagnetic complexes show a d-d band near 760 nm in DMF. Complexes 2 and 3 are blue and green emissive, respectively, in DMSO. The complexes exhibit irreversible V-IV/V-III reductive responses near -1.1 V and V-V/V-IV oxidative responses near 0.85 V vs. SCE in DMF-0.1 M TBAP. Complexes 2 and 3 display significant and selective photo-cytotoxicity upon irradiation with visible light giving an IC50 value of about 5 mu M against HeLa and MCF-7 cancer cells; they are significantly less-toxic against normal 3T3 control cells and in the absence of light. Complex 1 was used as a control. Both cytosolic and nuclear localization of the complexes were observed on the basis of fluorescence imaging. The complexes, avid binders to calf thymus (ct) DNA, were found to photocleave supercoiled pUC19 DNA upon irradiation with near-IR light (785 nm) by generating hydroxyl radical (OH) as the reactive oxygen species (ROS). Cell death events noted with HeLa and MCF-7 cell lines likely are attributable to apoptotic pathways involving light-assisted generation of intracellular ROS.