Anomalous charge transport in reduced graphene oxide films on a uniaxially strained elastic substrate.

We investigate temperature-dependent charge transport in reduced graphene oxide (rGO) films coated on flexible polydimethylsiloxane (PDMS) substrates which are subject to uniaxial strain. Variable strain, up to 10%, results in an anisotropic morphology comprising of quasi-periodic linear array of deformations which are oriented perpendicular to the direction of strain. The anisotropy is reflected in the charge transport measurements, when conduction in the direction parallel and perpendicular to the applied strain are compared. Temperature dependence of resistance is measured for different values of strain in the temperature interval 80-300 K. While the resistance increases significantly upon application of strain, the temperature-dependent response shows anomalous decrease in resistance ratio R 80 K/R 300 K upon application of strain. This observation of favorable conduction processes under strain is further corroborated by reduced activation energy analysis of the temperature-dependent transport data. These anomalous transport features can be reconciled based on mutually competing effects of two processes: (i) thinning of graphene at the sites of periodic deformations, which tends to enhance the overall resistance by a purely geometrical effect, and (ii) locally enhanced inter-flake coupling in these same regions which contributes to improved temperature-dependent conduction.

Reduced graphene oxide-ZnO self-assembled films: tailoring the visible light photoconductivity by the intrinsic defect states in ZnO.

ZnO is a wide direct bandgap semiconductor; its absorption can be tuned to the visible spectral region by controlling the intrinsic defect levels. Combining graphene with ZnO can improve its performance by photo-induced charge separation by ZnO and electronic transport through graphene. When reduced graphene oxide-ZnO is prepared by a hydrothermal method, the photophysical studies indicate that oxygen vacancy defect states are healed out by diffusion of oxygen from GO to ZnO during its reduction. Because of the passivation of oxygen vacancies, the visible light photoconductivity of the hybrid is depleted, compared to pure ZnO. In order to overcome this reduction in photocurrent, a photoelectrode is fabricated by layer-by-layer (LBL) self-assembly of ZnO and reduced graphene oxide. The multilayer films are fabricated by the electrostatic LBL self-assembly technique using negatively charged poly(sodium 4-styrene sulfonate)-reduced graphene oxide (PSS-rGO) and positively charged polyacrylamide-ZnO (PAM-ZnO) as building blocks. The multilayer films fabricated by this technique will be highly interpenetrating; it will enhance the interaction between the ZnO and rGO perpendicular to the electrode surface. Upon illumination under bias voltage defect assisted excitation occurs in ZnO and the photogenerated charge carriers can transfer to graphene. The electron transferred to graphene sheets can recombine in two ways; either it can recombine with the holes in the valence band of ZnO in its bilayer or the ZnO in the next bilayer. This type of tunnelling of electrons from graphene to the successive bilayers will result in efficient charge transfer. This transfer and propagation of electron will enhance as the number of bilayers increases, which in turn improve the photocurrent of the multilayer films. Therefore this self-assembly technique is an effective approach to fabricate semiconductor-graphene films with excellent conductivity.

Defect engineering in ZnO nanocones for visible photoconductivity and nonlinear absorption.

Nanostructured ZnO is a promising material for optoelectronic and nonlinear optical applications because of the flexibility of band gap engineering by means of various defect states present in it. Employing the time-correlated single photon counting photoluminescence technique, the correlation between defect levels and optoelectronic and nonlinear optical properties of ZnO is explored in this work. By a facile solution method, ZnO nanocones with a dominating preferential orientation along energetically less favorable, oxygen terminated (10̄11) facets were synthesized using a passivating capping agent. Photoluminescence spectra demonstrate that the as-grown samples have both oxygen and zinc vacancies, and after calcination in air oxygen vacancies vanish, but zinc vacancies are enhanced. Photoconductivity of the samples reduces significantly upon calcination, confirming the reduction in oxygen vacancies. However, the samples exhibit a significant enhancement in the nonlinear optical absorption coefficient upon calcination, indicating that the effective two-photon absorption causing the nonlinear optical behaviour originates from zinc vacancies. These results illustrate the vast possibilities of band gap engineering in intrinsic ZnO for future optoelectronic applications.

Multifunctional carbon nanospheres with magnetic and luminescent probes: probable brain theranostic agents.

Multi-functional carbon nanospheres with magnetic Prussian blue nanoparticles and luminescent lanthanide ions have been prepared. The negatively charged surface of the glucose derived carbon sphere facilitates the nucleation of Prussian blue nanoparticles on its surface. The luminescent lanthanide probes were attached to the surface of the carbon sphere through a benzene tricarboxylic acid linker. These multifunctional hybrid organic-inorganic composites are superparamagnetic and show enhanced luminescent properties. Their ability to cross the blood-brain barrier (enter the brain cell nucleus with no animal toxicity) in a mouse model indicate that these nanocomposites are promising theranostic agents for the treatment of brain diseases.

'O' set connector system in CAPD.

51 CAPD patients (age 55.5 +/- 14.5 yrs, 35 male, 16 female) on CAPD using 'O' set were studied retrospectively during the period January 1993 to April 1995. Etiology of ESRD was Diabetic nephropathy-25(49%) and the other causes-26(51%). The total duration of observation on 'O' set was 553 patient months, the mean duration was 10.8 +/- 6.1 months. 24 patients (47%) developed total of 30 episodes of peritonitis. The incidence of peritonitis was 18.4 patient months per episode of peritonitis. The organisms responsible for peritonitis were Gram positive-6(20%), Gram negative-3(10%), Fungal-1(3.3%), Mycobacterial-1(3.3%), Eosinophilic-1(3.3%), Sterile-12(40%) and unknown-6(20%) 2 patients of bacterial peritonitis and a patient with tuberculous peritonitis died while rest of the patients responded favourably to antibiotics. 13(52%) diabetic patients and 11(42%) non-diabetic patients had peritonitis (p-NS) and the peritonitis rates in diabetics and non diabetics were 18.3 and 18.6 patient months per episode respectively (p-NS). Exit site infection was seen in 5 patients (10%) (Staph aureus-4, Enterococci-1) and all responded to antibiotic therapy. 7 patients had total of 10 episodes of symptomatic accidental intraperitoneal sodium hypochlorite instillation, none had any long term adverse effects. The 'O' set procedure was done by self in 10(20%) and by others in 41(80%) cases. The peritonitis rates when performed by self and others were 18.5 and 18.4 patient months per episode respectively (p-NS). The cost of being on CAPD using 'O' set, Y-bag and twin bag were Rs. 1,50,000, 2,10,000 and 3,72,000 per annum respectively and cost of maintenance haemodialysis was 1,36,800 per annum. The cost of CAPD using 'O' set was comparable to that of maintenance haemodialysis. The 'O' set connector system in CAPD is found to be safe, cost effective and efficient.