Fluorographene is one of the most interesting 2D materials owing to its span of electronic properties, from a conductor to wide-gap insulator, controlled by the compositional carbon to fluorine ratio. Unlike the chemically inert graphene, fluorographene is recognized for its rich chemistry, particularly at ambient, allowing tailoring its physical properties. Here, we report on single step, catalyst free, wafer-scale synthesis of fluorographene oxide (FGO) ultra-thin films (∼4 nm thickness) by physical vapour deposition. The FGO, possessing 7% fluorine content, comprises few-nanometer domains of sp2-sp3 carbon with high thermal stability, as confirmed by several analytical methods. We show that FGO can be utilized as an active hetero-layer on a few-layer MoS2 field effect transistor (FET), significantly improving the performance of MoS2 optoelectronic devices with an extended spectral response towards the near infrared and responsivity of up to 6 A/W. The FGO-MoS2 band alignment, as derived from the measured work function of FGO (4.69 eV), indicates a plausible photoconductive gain mechanism with a fast transit time of holes mediated by FGO quasi-continuous defect states.
|Number of pages||9|
|Journal||Applied Materials Today|
|State||Published - Dec 2018|
Bibliographical noteFunding Information:
Further investigation of the show dark and bright field (respectively) STEM images of the FGO transferred onto the TEM Cu grid (see the experimental section and supporting information for details). Insets show the lattice pattern of the single FGO flake, corresponding to the hexagonal lattice of sp 2 -sp 3 carbon domains and their grain sizes in the as-grown FGO was performed by high angle annular dark field scanning transmission electron microscopy (HAADF-STEM). Fig. 2 (a-b) sp 2 carbon in the labelled domains. The variation in the HAADF intensity within flakes is attributed to the thickness uniformity of FGO films and its resulting electron scattering. Fig. 2 (c) depicts a high-resolution HAADF-STEM image of a single flake with the sp 2 (graphene like) and sp 3 (diamond like) carbon domains labelled, and the corresponding bright field STEM image is shown Fig. 2 (d). The hexagonal lattice diffraction pattern of sp 2 carbon is clearly observed in the FFT of the rectangular marked portion in Fig. 2 (d) (left inset in Fig. 2 (c)), while other marked portions correspond to sp 3 carbon sites within a single FGO flake. HAADF-STEM imaging confirms the number of atomic layers in FGO films to be 6–7 layers (see supporting information, Fig. S3). This thickness estimate is also supported by the XPS results below.
TNN, RS, and KRS acknowledge the funding support from Tata Institute of Fundamental Research (TIFR), India. TNN also acknowledges DST-SERB, India for the funding support in the form of extramural research grant for working on van der Waals solids based structures (EMR/2017/000513). OS is grateful for the help of Ms. Michal Wasserman with the electrical measurements and microscopy of some of the samples. DN thanks the Israel Science Foundation for grant No. 1055/15. RKB acknowledges Marie-Sklodowska-Curie individual fellowship under EU H2020 programme (H2020_IF_2017; Grant Number: 750929) and postdoctoral fellowship from SERB-NPDF (PDF/2016/002642), India. Authors also thank Dr. Balakrishna Ananthoju and Prof. Robert Dryfe, The University of Manchester for the Raman streamline mapping measurements of FG samples. Authors also thank Dr. Kanchan Garai and his students at TIFR-H for helping us in conducting AFM measurements. TNN dedicates this article to his beloved teacher (Late) Prof. V.C. Kuriakose, CUSAT, India.
© 2018 Elsevier Ltd
- Electronic transport
- Field effect transistor
- Fluorographene oxide
- Physical vapour deposition
- Wafer scale synthesis