Browsing by Author "Satbir Singh"

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High-performance field emission device utilizing vertically aligned carbon nanotubes-based pillar architectures
(American Institute of Physics Inc., 2018) Bipin Kumar Gupta; Garima Kedawat; Amit Kumar Gangwar; Kanika Nagpal; Pradeep Kumar Kashyap; Shubhda Srivastava; Satbir Singh; Pawan Kumar; Sachin R. Suryawanshi; Deok Min Seo; Prashant Tripathi; Mahendra A. More; O.N. Srivastava; Myung Gwan Hahm; Dattatray J. Late
The vertical aligned carbon nanotubes (CNTs)-based pillar architectures were created on laminated silicon oxide/silicon (SiO2/Si) wafer substrate at 775 °C by using water-assisted chemical vapor deposition under low pressure process condition. The lamination was carried out by aluminum (Al, 10.0 nm thickness) as a barrier layer and iron (Fe, 1.5 nm thickness) as a catalyst precursor layer sequentially on a silicon wafer substrate. Scanning electron microscope (SEM) images show that synthesized CNTs are vertically aligned and uniformly distributed with a high density. The CNTs have approximately 2-30 walls with an inner diameter of 3-8 nm. Raman spectrum analysis shows G-band at 1580 cm-1 and D-band at 1340 cm-1. The G-band is higher than D-band, which indicates that CNTs are highly graphitized. The field emission analysis of the CNTs revealed high field emission current density (4mA/cm2 at 1.2V/μm), low turn-on field (0.6 V/μm) and field enhancement factor (6917) with better stability and longer lifetime. Emitter morphology resulting in improved promising field emission performances, which is a crucial factor for the fabrication of pillared shaped vertical aligned CNTs bundles as practical electron sources. © 2018 Author(s).
High-Performance Flexible Supercapacitors obtained via Recycled Jute: Bio-Waste to Energy Storage Approach
(Nature Publishing Group, 2017) Camila Zequine; C.K. Ranaweera; Z. Wang; Petar R. Dvornic; P.K. Kahol; Sweta Singh; Prashant Tripathi; O.N. Srivastava; Satbir Singh; Bipin Kumar Gupta; Gautam Gupta; Ram K. Gupta
In search of affordable, flexible, lightweight, efficient and stable supercapacitors, metal oxides have been shown to provide high charge storage capacity but with poor cyclic stability due to structural damage occurring during the redox process. Here, we develop an efficient flexible supercapacitor obtained by carbonizing abundantly available and recyclable jute. The active material was synthesized from jute by a facile hydrothermal method and its electrochemical performance was further enhanced by chemical activation. Specific capacitance of 408 F/g at 1 mV/s using CV and 185 F/g at 500 mA/g using charge-discharge measurements with excellent flexibility (∼100% retention in charge storage capacity on bending) were observed. The cyclic stability test confirmed no loss in the charge storage capacity of the electrode even after 5,000 charge-discharge measurements. In addition, a supercapacitor device fabricated using this carbonized jute showed promising specific capacitance of about 51 F/g, and improvement of over 60% in the charge storage capacity on increasing temperature from 5 to 75 °C. Based on these results, we propose that recycled jute should be considered for fabrication of high-performance flexible energy storage devices at extremely low cost. © 2017 The Author(s).
Unexplored photoluminescence from bulk and mechanically exfoliated few layers of Bi2Te3
(Nature Publishing Group, 2018) Bipin Kumar Gupta; Rabia Sultana; Satbir Singh; Vijeta Singh; Geet Awana; Anurag Gupta; Bahadur Singh; A.K. Srivastava; O.N. Srivastava; S. Auluck; V.P.S. Awana
We report the exotic photoluminescence (PL) behaviour of 3D topological insulator Bi2Te3 single crystals grown by customized self-flux method and mechanically exfoliated few layers (18 ± 2 nm)/thin flakes obtained by standard scotch tape method from as grown Bi2Te3 crystals. The experimental PL studies on bulk single crystal and mechanically exfoliated few layers of Bi2Te3 evidenced a broad red emission in the visible region from 600-690 nm upon 375 nm excitation wavelength corresponding to optical band gap of 2 eV. These findings are in good agreement with our theoretical results obtained using the ab initio density functional theory framework. Interestingly, the observed optical band gap is several times larger than the known electronic band gap of ∼0.15 eV. The experimentally observed 2 eV optical band gap in the visible region for bulk as well as for mechanically exfoliated few layers Bi2Te3 single crystals clearly rules out the quantum confinement effects in the investigated samples which are well known in the 2D systems like MoS2,WS2, WSe2, and MoSe2 for 1-3 layers. © 2018 The Author(s).