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ABSTRACT: Despite the attractiveness of low temperature hydrothermal processes, the synthesis of vertical ZnO
nanostructures has mostly been limited to rigid substrates. Moreover, patterned growth of
nanostructures is also commonly carried out on rigid substrates, since conventional optical lithography
is not easily applied to polymeric substrates, as focusing and reaction of the substrate with the organic
solvent used in the lithography process prove to be a challenge. Here, we demonstrate the limited work
on laser writing lithography patterned growth instead of the commonly used soft lithography patterned
growth of nanorods on the transparent flexible substrate polyethylene terephthalate (PET) with
a practical device demonstration. The visibly-transparent nanorods on the PET platform constitute
a superior structural integrity with ohmic electro-conductivity even in a highly bent state. Accordingly,
this can pave the way towards integration of vertically-aligned 1D nanostructures on a flexible platform
for a transparent, conformable, shock-proof and lightweight product.
Journal of Materials Chemistry 01/2012; 22:8518. · 5.97 Impact Factor
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ABSTRACT: A lot of research on nanomaterials has been carried out in recent years. However, there is still a lack of nanostructures that have a combination of superior properties; both efficient electron transport and high surface area. Here, the authors have tried to develop hybrid α-Fe(2)O(3) flower-like morphology which exhibits both superior electron transport and high surface area. Intrigued by the unique properties of Fe(2)O(3) at the nanoscale and its abundance in nature, we have demonstrated a facile template-free solution based synthesis of hybrid α-Fe(2)O(3) comprising nanopetals nucleating radially from a 3D core. Due to its simplicity, the synthesis process can be easily reproduced and scaled up. We carried out in-depth studies on gas sensing and dye-sensitized solar cell (DSSC) device characterization so as to gain an understanding of how surface area and transport properties are affected by variation in morphology. The hybrid α-Fe(2)O(3) nanostructures are studied as potential candidates for gas sensors and for the first time as a working electrode for DSSC.
Nanoscale 11/2011; 4(1):194-205. · 5.91 Impact Factor
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ABSTRACT: In this work, enhancement of ionic conductivity and long-term stability through the addition of diphenylamine (DPA) in poly(ethylene oxide) (PEO) is demonstrated. Potassium iodide (KI) is adopted as the crystal growth inhibitor, and DPA is used as a charge transport enhancer in the electrolyte. The modified electrolyte is used with titanium dioxide (TiO2) nanoparticles, which is systematically tuned to obtain high surface area. The dye-sensitized solar cell (DSSC) showed a photocurrent of 14 mAcm2 with a total conversion efficiency of 5.8% under one sun irradiation. DPA enhances the interaction of the TiO2 nanoparticle film and the I-/I3- electrolyte leading to high ionic conductivity (3.5 × 10-3 Scm-1), without compromising on the electrochemical and mechanical stability. Electrochemical impedance spectroscopy (EIS) studies show that electron transport and electron lifetime are enhanced in the DPA added electrolyte due to reduced sublimation of iodine. The most promising feature of the electrolyte is increased device stability with 89% of the overall efficiency preserved even after 40 days.
ACS Applied Materials & Interfaces 06/2011; 3(7):2383-91. · 4.53 Impact Factor
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ABSTRACT: A facile large-scale synthesis approach for producing intrinsically p-type nanowires with uniform coverage of nanocrystals to form a highly interconnected porous nanowire network is of great demand for p-type sensing. Here, we have demonstrated synthesis of a very high aspect ratio (10(2)-10(5)) open network of interconnected hybrid nanocrystals-nanowire copper and copper oxide nanomaterials. The copper nanowire scaffold is employed to realize a porous and highly interconnected network of hybrid metal-metal oxide nanocrystal-nanowire structures. The structural and composition tunability of the hybrid nanomaterials is demonstrated. The hybrid copper-copper oxide nanowires exhibit enhanced gas/light sensing properties without any operating temperature. This may be attributed to enhanced medium diffusion due to the porous network of highly interconnected nanocrystal-nanowire structures.
Nanotechnology 06/2011; 22(23):235701. · 3.98 Impact Factor
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Progress in Photovoltaics Research and Applications 02/2011; 19(4):464 - 472. · 5.79 Impact Factor
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International conference on materials for advanced technologies (ICMAT), Singapore; 01/2011
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Materials Research Society (MRS) Spring Meeting, San Fransico, USA; 01/2011
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Materials Research Society (MRS) Spring Meeting, San Fransico, USA; 01/2011
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ABSTRACT: A maskless method of employing polymer growth inhibitor layers is used to modulate the conflicting parameters of density and alignment of multi-junction nanowires via large-scale low temperature chemical route. This low temperature chemical route is shown to synthesize multi-junction nanostructures without compromising the crystal quality at the interfaces. The final morphology of an optimized multi-junctions nanowire arrays can be demonstrated on various substrates due to substrate independence and low temperature processing. Here, we also follow-up on device demonstrations whereby p-n junction are created by exposure of secondary nanowires to ammonia plasma, converting them to p-type characteristics and also the density modulated multi-junction nanowires were tuned to infiltrate nanoparticles to create a hybrid hierarchically-structured nanowire/nanoparticles solar cell. The fabrication of hierarchically-structured nanowire/nanoparticles composites presents an advantageous structure, one that allow nanoparticles to provide large surface areas for the dye adsorption, whilst the nanowires can enhance the light harvesting, electron transport rate, and also the mechanical properties of the films. This work can be of great scientific and commercial interest since the technique employed is of low temperature (< 90 °C) and economical for large-scale solution processing, much valued in today’s flexible display and photovoltaic industries. In addition, ZnO nanostructures for gas sensing will be presented.
MRS Proceedings. 12/2010; 1350.
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ABSTRACT: A maskless method of employing polymer growth inhibitor layers is used to modulate the conflicting parameters of density and alignment of multi-junction nanowires via large-scale low temperature chemical route. This low temperature chemical route is shown to synthesize multi-junction nanostructures without compromising the crystal quality at the interfaces. The final morphology of optimized multi-junctions nanowire arrays can be demonstrated on various substrates due to substrate independence and low temperature processing. Here, we also fabricated devices based on density modulated multi-junction nanowires tuned to infiltrate nanoparticles. The fabrication of hierarchically structured nanowire/nanoparticles composites presents an advantageous structure, one that allows nanoparticles to provide large surface areas for dye adsorption, whilst the nanowires can enhance the light harvesting, electron transport rate, and also the mechanical properties of the films. This work can be of great scientific and commercial interest since the technique employed is of low temperature (<90 degrees C) and economical for large-scale solution processing, much valued in today's flexible display and photovoltaic industries.
Nanotechnology 08/2010; 21(31):315602. · 3.98 Impact Factor
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ABSTRACT: Mesophase ordering and structuring are carried out to attain optimized pore morphology, high crystallinity, stable porous framework, and crack-free mesoporous titanium dioxide (TiO(2)) films. The pore structure (quasi-hexagonal and lamellar) can be controlled via the concentration of copolymer, resulting in two different types of micellar packing. The calcination temperature is also controlled to ensure a well-crystalline and stable porous framework. Finally, the synthesized mesoporous TiO(2) film is modified by adding P25 nanoparticles, which act as scattering centers and function as active binders to prevent formation of microcracks. Adding P25 nanoparticles into mesoporous structure helps to provide strong light-harvesting capability and large surface area for high -efficiency dye-sensitized solar cells (DSSC). The short-circuit photocurrent density (J(sc)) of the cell made from mixture of mesoporous TiO(2) and P25 nanoparticles displays a higher efficiency of approximately 6.5% compared to the other homogeneous films. A combination of factors such as increased surface area, introduction of light-scattering particles, and high crystallinity of the mesoporous films leads to enhanced cell performance.
ACS Applied Materials & Interfaces 07/2010; 2(7):1844-50. · 4.53 Impact Factor
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ABSTRACT: Several important synthetic parameters such as precursor concentration, rate of evaporation and reaction time are found to determine the growth of ZnO nanostructures. These reaction parameters can be tailored and tuned to produce a variety of nanostructures ranging from nanoparticles, nanorods and nanospheres. The nanorods are structurally uniform made up of crystallographically oriented attached nanoparticles while the nanospheres are made up of several closely packed and randomly aligned nanocrystallites. XRD spectra of both the nanoparticles and nanorods exhibit typical diffraction peaks of a well-crystalline wurtzite ZnO structure. Finally, solar cells made up of ZnO nanoparticles and nanorods electrodes with absorbed ruthenium dye (N3) were measured to have a power conversion efficiency of 0.87% and 1.32%, respectively.
Nanotechnology 02/2009; 20(4):045604. · 3.98 Impact Factor
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International conference on materials for advanced technologies (ICMAT), Singapore; 01/2009
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01/2009; , ISBN: 9789814267731
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ABSTRACT: Synthesis of well-organized and highly crystalline mesoporous titania (TiO2) film is demonstrated using triblock copolymer (Pluronic P123) as a structure directing template, through the evaporation induced selfassembly (EISA) process. The issue of thermal and structural stability of a mesoporous TiO2 film was addressed via optimization of annealing temperature and time. An anatase phase, high crystallinity TiO2 film with ordered pores was obtained at 430 °C after annealing for 15 min. The synthesized film was crack free with TiO2 nanoparticle size of 10–15 nm, quasi-hexagonal pore diameter in the range of 8–10 nm and film thickness of ~150 nm.
Materials Letters 01/2009; 63:1624. · 2.31 Impact Factor
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ABSTRACT: Tin dioxide (SnO2) nanospheres with various degrees porosity have been successfully synthesized via a facile, easily scalable, and tunable hydrothermal process. The employed method requires no physical templates or environmentally unfriendly additives. Elimination of additives was favorably found to increase the specific surface area and reduce the organic contamination issue in the end product. Investigation of the controllable synthesis and growth mechanism provides valuable insights into studies of the fundamental properties of mesoporous tin oxides nanospheres. The as-synthesized mesoporous SnO2 nanospheres are composed of numerous small nanocrystallites 5−10 nm and possess good size uniformity and large specific surface areas, making them excellent candidates for use in industrial applications such as gas sensors, catalysts, and biomedical drug therapy.
12/2008;
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ABSTRACT: A high-yield synthesis of SnO(2) nanoparticles via a facile, economical and easily scalable solid-state molten salt synthesis method has been demonstrated. The inorganic additive, molar ratios of chemicals and annealing temperature were found to control the size and porosity of the SnO(2) nanoparticles. The synthesized SnO(2) nanostructures were uniform, well dispersed and exhibited high crystallinity. Hydrogen sensors made from the SnO(2) nanoparticles were found to possess high sensitivity and stability. Other than tailoring the material's structure in terms of size and porosity, another potential method of enhancing the gas sensitivity is functionalization with noble Pd metal.
Nanotechnology 06/2008; 19(25):255706. · 3.98 Impact Factor
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ABSTRACT: Bundles of high-aspect-ratio single-crystalline ZnO nanowires were fabricated by a single-step mild hydrothermal condition
without the use of a seeding layer, thus eliminating an annealing step. The growth yields nanowires of high aspect ratio (>200).
No significant lateral growth takes place with prolonged reaction time. The morphology and aspect ratio of the final products
depend on the concentration of the precursors; a highly water-soluble tetradentate cyclic tertiary amine and zinc nitrate
system. The nanowires grow along the [0001] direction and have an average width of <10nm and a narrow distribution of ±5nm.
Photoluminescence measurements of the ultra-thin nanowires exhibit a strong band-edge emission at room temperature. The highly
crystalline sub tens of nanometer scale diameter nanowires can, in combination, be a good one-dimensional candidate to study
optical and electronic properties.
Applied Physics A 01/2007; 86(4):457-462. · 1.63 Impact Factor
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ABSTRACT: We present experimental evidence of nanojunction structures explicitly observed after application of high electric fields on multiwall carbon nanotube arrays. The electric field as well as thermal effects result in carbon–carbon bond breaking and redeposition leading to nanojunction formation. The growth mechanism of the nanojunction is believed to be open-ended topological defect growth in which carbon atoms at two adjacent nanotube tips chemically react and fuse forming an array of nanojunctions. © 2001 American Institute of Physics.
Applied Physics Letters 07/2001; 79(2):260-262. · 3.84 Impact Factor
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ABSTRACT: Vibrio anguillarum and Vibrio damselae are Gram-negative bacteria that cause systemic infections called vibriosis in fish. They can enter fish cells and survive as intracellular parasites. The host-pathogen interactions between these Vibrio species and the fish epithelial cell lines epithelioma papillosum of carp (EPC) and grunt-fin tissue (GF) cells, were examined using phase-contrast, scanning electron and confocal microscopy. In addition, potential signal transduction pathways that precede bacterial internalization were studied by using signal transduction inhibitors. Some Vibrio species induced morphological changes in fish cells and this allowed classification into a cytopathic group and a noncytopathic group. The cytopathic group could be subdivided into two invasive groups (I and II) and a cytotoxic group. Of the invasive strains V. anguillarum 811218-5W (group I) and G/Virus/5(3) (group II), genistein, a tyrosine kinase inhibitor, only inhibited internalization of V. anguillarum G/Virus/5(3) into EPC cells, whereas staurosporine, a protein kinase C inhibitor, accelerated internalization of both strains. Cytochalasin D, an inhibitor of microfilament polymerization, prevented internalization of both strains, whilst vincristin, a microtubule inhibitor, only inhibited internalization of V. anguillarum G/Virus/5(3). For the cytotoxic strain V. damselae ATCC 33539, extracellular products (ECP) alone caused morphological changes in EPC and GF. Bacterial internalization may not be important in the pathogenesis of this group. The non-cytopathic strain V. anguillarum S2/5/93(2) did not enter cells or induce any changes in EPC and GF monolayers. This study has identified some major differences between Vibrio species in their interactions with fish cells in vitro and will thus facilitate future studies of the molecular basis of pathogenesis of vibriosis.
Microbiology 12/1998; 144 ( Pt 11):2987-3002. · 3.06 Impact Factor
