Kiran Kumar Manga

High-Yield Synthesis of Few-Layer Graphene Flakes through Electrochemical Expansion of Graphite in Propylene Carbonate Electrolyte

High-yield production of few-layer graphene flakes from graphite is important for the scalable synthesis and industrial application of graphene. However, high-yield exfoliation of graphite to form graphene sheets without using any oxidation process or super-strong acid is challenging. Here we demonstrate a solution route inspired by the lithium rechargeable battery for the high-yield (>70%) exfoliation of graphite into highly conductive few-layer graphene flakes (average thickness <5 layers). A negative graphite electrode can be electrochemically charged and expanded in an electrolyte of Li salts and organic solvents under high current density and exfoliated efficiently into few-layer graphene sheets with the aid of sonication. The dispersible graphene can be ink-brushed to form highly conformal coatings of conductive films (15 ohm/square at a graphene loading of <1 mg/cm(2)) on commercial paper.

Fluorinated graphene for promoting neuro-induction of stem cells.

Surface engineering of substrates offers the possibility of controlling the physiological functions of cells at the molecular level. Fluorinated graphene promotes the differentiation of MSCs towards neuronal lineages. Cell alignment using printed polydimethylsiloxane channel arrays on fluorinated graphene further enhances the neuro-induction of MSCs even in the absence of chemical inducers.

High-gain graphene-titanium oxide photoconductor made from inkjet printable ionic solution.

As an alternative to such layer-by-layer assembled fi lms, which require multiple dipping cycles in different solutions, it is interesting to consider whether an optically transparent and electrically conducting matrix comprising of homogeneously dispersed TiO 2 and graphene can be synthesized. Ideally this composite blend would be derived from a homogenized mixture that acts as a precursor source and that can be spin-coated or inkjet-printed onto any substrate to be thermally sintered into a transparent conductor or light-harvesting photoconductor fi lm. Here, we show that a conventional sol-gel chemistry approach used previously for the formation of graphene-silica composites [ 6 ] is not applicable to GO-TiO 2 systems. Instead, we report a strategy based on blending GO sheets with a titanium hydroxide-based ionic salt to produce a chemically tunable graphene-TiO 2 composite, which can be used as a printable photodetector. The fabricated structure exploits the desirable charge injection and separation properties at dispersed heterojunctions, and thus opens a widely applicable fabrication strategy for graphene-based composites in photoconductors, sensors, and photovoltaics. Looking at their chemical structure, GO sheets are wellsuited to blending with titanium alkoxide precursors in solgel synthesis because of their water solubility and hydrogenbonding ability (Schematic 1 a). GO sheets are composed of planar, graphene-like aromatic domains and the basal planes and edges are decorated by hydroxyl, epoxy, ether, or carboxylic groups. [ 7 ] These hydroxyl functionalities in GO can participate in oxoor hydroxobridges with metal centers. The formation of titanium oxide in sol-gel synthesis involves interconnecting

High‐Performance Broadband Photodetector Using Solution‐Processible PbSe–TiO2–Graphene Hybrids

Highly sensitive, multicomponent broadband photodetector devices are made from PbSe/graphene/TiO(2). TiO(2) and PbSe nanoparticles act as light harvesting photoactive materials from the UV to IR regions of the electromagnetic spectrum, while the graphene acts as a charge collector for both photogenerated holes and electrons under an applied electric field.

Transient photoconductivity and femtosecond nonlinear optical properties of a conjugated polymer-graphene oxide composite.

A water soluble conjugated thiophene polymer, sodium salt of poly[2-(3-thienyl)ethoxy-4-butylsulfonate] (TPP), and graphene oxide (GO) composite film (GO-TPP) device was prepared. Transient photoconductivity measurements were carried out on the GO-TPP composite film using 150 ns laser pulses of 527 nm wavelength. Highly efficient photocurrent generation was observed from the GO-TPP film. The relationships of the film photoconductivity, photocurrent decay time and electron decay times with the incident light intensity were investigated. The photoconductive gain of the film was determined to be greater than 40% and to be independent of the light intensity. Furthermore, the femtosecond nonlinear optical properties of the GO-TPP film were measured using 800 nm femtosecond laser pulses and the composite film exhibited high nonlinear absorption and nonlinear refraction coefficients.

Ionic liquid-functionalized carbon nanoparticles-modified cathode for efficiency enhancement in polymer solar cells

The power conversion efficiency (PCE) of regioregular poly(3-hexylthiophene) (P3HT) and {6,6}-phenyl C61-butyric acid methylester (PCBM)-based polymer solar cells was increased using an ionic liquid-functionalized carbon nanoparticles (ILCNs) thin film-modified cathode. The PCE of P3HT:PCBM based-polymer solar cells with a conventional aluminum (Al)-only cathode was increased by 20%–30% when the identical devices were made with an ILCNs-modified Al cathode, but its PCE was 10% lower than that of devices with LiF/Al cathode, measured under AM1.5G illumination of 100 mW/cm2. The ILCN interlayer approach, however, offers practical advantages to LiF in terms of its solution-processability, which is compatible with low cost, large area, and flexible solar cell fabrication.The power conversion efficiency (PCE) of regioregular poly(3-hexylthiophene) (P3HT) and {6,6}-phenyl C61-butyric acid methylester (PCBM)-based polymer solar cells was increased using an ionic liquid-functionalized carbon nanoparticles (ILCNs) thin film-modified cathode. The PCE of P3HT:PCBM based-polymer solar cells with a conventional aluminum (Al)-only cathode was increased by 20%–30% when the identical devices were made with an ILCNs-modified Al cathode, but its PCE was 10% lower than that of devices with LiF/Al cathode, measured under AM1.5G illumination of 100 mW/cm2. The ILCN interlayer approach, however, offers practical advantages to LiF in terms of its solution-processability, which is compatible with low cost, large area, and flexible solar cell fabrication.

Wrapping Graphene Sheets Around Organic Wires for Making Memory Devices

Hybrids of organic semiconductors and graphene can generate a whole new class of materials with enhanced properties. A simple solution-phase route to synthesize a hybrid material made of organic nanowires and graphene oxide (GO) sheets is demonstrated by sonicating tetracene molecules and GO together in diluted fuming nitric acid. The self-assembled tetracene-derived organic wires become encapsulated by GO sheets during the reaction to produce an interconnected, one-dimensional/two-dimensional lamellar film. Memory devices fabricated using the hybrid film as the sandwiched layer between aluminum electrodes exhibit excellent electrical bistability. The charge retention properties are attributed to charge transfer and a charge-trapping/detrapping mechanism operational at the interfaces and isolated matrices of the GO-tetracene hybrid.