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All carbon-based photodetectors: an eminent integration of graphite quantum dots and two dimensional graphene.

ABSTRACT: Photodetectors with ultrahigh sensitivity based on the composite made with all carbon-based materials consisting of graphite quantum dots (QDs), and two dimensional graphene crystal have been demonstrated. Under light illumination, remarkably, a photocurrent responsivity up to 4 × 10(7) AW(-1) can be obtained. The underlying mechanism is attributed to the spatial separation of photogenerated electrons and holes due to the charge transfer caused by the appropriate band alignment across the interface between graphite QDs and graphene. Besides, the large absorptivity of graphite QDs and the excellent conductivity of the graphene sheet also play significant roles. Our result therefore demonstrates an outstanding illustration for the integration of the distinct properties of nanostructured carbon materials with different dimensionalities to achieve highly efficient devices. Together with the associated mechanism, it paves a valuable step for the further development of all carbon-based, cheap, and non-toxic optoelectronics devices with excellent performance.

SUBMITTER: Cheng SH

PROVIDER: S-EPMC3776196 | biostudies-other | 2013

REPOSITORIES: biostudies-other

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Project description:Graphene has unprecedented physical, chemical, and electronic properties, but need of the hour is to develop low-dimensional nanomaterials, such as graphene quantum dots (GQDs), that could be incorporated into nanoscale devices. This article depicts the production of GQDs from ultrafine, thin (0.8-1 nm), bilayer graphene sheets (GSs) possessing large micron-sized lateral dimension, low defect density (I D/I G: 0.1), and oxidation degree (C/O ratio: 27) of lowest level, in contrast to many other techniques where synthesis of GSs was done using analytical-grade expensive graphite electrodes. This low-cost manufacturing of GSs for industrial-scale applications was achieved by utilizing only 99%-purity graphite electrodes. The variants of such graphite electrodes (graphite rod, film, pencil) are etched in different pH electrolytes (H2SO4, NaCl, NaOH) via prompt electrochemical exfoliation, each giving more than 50% yield. Nowadays, semiconductor quantum dots (QDs) are utilized in smart device production industries, but their toxicity is a major issue of concern. Therefore, the dimension of this two-dimensional (2D) material is reduced to <10 nm to generate GQDs. A facile and highly reproducible approach has been reported for the large-scale generation of GQDs (size ca. 6-10 nm) with minimal surface defects. The protocol followed in this article to synthesize GQDs involves the use of ethylenediamine (en), which passivates the surface and reduces defects, thereby enhancing the optical properties. We demonstrate the correlation of the electrochemical and hydrothermal parameters with the growth mechanism and morphological, structural, chemical, and optical properties of the graphene nanomaterials. Raman spectroscopy and X-ray diffraction (XRD) reveal the structural configurations of GSs and GQDs to investigate the nature of defects. Field emission scanning electron microscopy (FESEM) confirms the morphological characteristics of the as-prepared GSs and GQDs with energy-dispersive X-ray (EDX) analysis determining the C/O ratio. The optical properties like UV-visible absorption and fluorescence assays show the quantum confinement effect phenomenon in GQDs. The obtained GSs and GQDs display enhanced solution stability in DI water and other solvents due to controllable oxidation degree as elucidated through Fourier transform infrared (FTIR) analysis.

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All carbon-based photodetectors: an eminent integration of graphite quantum dots and two dimensional graphene.

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