Browsing by Author "Nikam, Revannath Dnyandeo"

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Epitaxial growth of vertically stacked p-MoS2/n-MoS2 heterostructures by chemical vapor deposition for light emitting devices
(2017-02-01)
Nikam, Revannath Dnyandeo
;
Sonawane, Poonam Ashok
;
Sankar, Raman
;
Chen, Yit-Tsong
;
應用化學系
Despite the dramatic advances of two-dimensional vertical heterostructure, the controlled growth and potential applications in light emitting devices of these heterostructures have not yet been well established. Here, we report, for the first time, the epitaxial growth of two-dimensional p-MoS2/n-MoS2 vertical heterostructures by a chemical vapor deposition (CVD) method, where the n-MoS2 was synthesized first, followed by an epitaxial growth of p-MoS2 on top of the n-MoS2 via a control of the growth temperature. Atomic-resolution scanning transmission electron microscopy (STEM) imaging reveals that the vertically stacked bilayer of the hexagramshaped p-MoS2/n-MoS2 preferred the 2H stacking phase during the growth. The structural and optical features of the as-grown p-MoS2/n-MoS2 heterostructure were examined by Raman and photoluminescence (PL) spectroscopy. This novel hybrid heterostructure was demonstrated to be an excellent building block for a highly efficient white light emitting diode (WLED). In addition, we transferred the p-MoS2/n-MoS2 on top of a p-GaN bilayer to fabricate a tetra-layered (4-L) n-MoS2/p-MoS2/p-GaN heterostructure, which could emit electroluminescence (EL) in forward bias. The EL spectra comprise three emission peaks centered at 481 nm (from pGaN), 525 nm (from p-MoS2), and 642 nm (from n-MoS2), with a dominant emission peak located at 642 nm. The WLED device composed of the n-MoS2/p-MoS2/p-GaN heterostructure showed a luminance of 30,548 cd/m(2), luminescence efficiency of 29% and the luminous efficacy of 294 lm/W at a bias voltage of 4 V. This work demonstrates that white light emission can be generated from vertically stacked few-layered 2D materials-based heterostructures, which also hold great potential for constructing color-tunable light emitters for low-cost display, lighting, and optical communication.
Three-Dimensional Heterostructures of MoS2 Nanosheets on Conducting MoO2 as an Efficient Electrocatalyst To Enhance Hydrogen Evolution Reaction
(2015-10-21)
Nikam, Revannath Dnyandeo
;
Lu, Ang-Yu
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Sonawane, Poonarn Ashok
;
Kumar, U. Rajesh
;
Yadav, Kanchan
Molybdenum disulfide (MoS2) is a promising catalyst for hydrogen evolution reaction (HER) because of its unique nature to supply active sites in the reaction. However, the low density of active sites and their poor electrical conductivity have limited the performance of MoS2 in HER. In this work, we synthesized MoS2 nanosheets on three-dimensional (3D) conductive MoO2 via a two-step chemical vapor deposition (CVD) reaction. The 3D MoO2 structure can create structural disorders in MoS2 nanosheets (referred to as 3D MoS2/MoO2), which are responsible for providing the superior HER activity by exposing tremendous active sites of terminal disulfur of S-2(-2) (in MoS2) as well as the backbone conductive oxide layer (of MoO2) to facilitate an interfacial charge transport for the proton reduction. In addition, the MoS2 nanosheets could protect the inner MoO2 core from the acidic electrolyte in the HER. The high activity of the as-synthesized 3D MoS2/MoO2 hybrid material in HER is attributed to the small onset overpotential of 142 mV, a largest cathodic current density of 85 mA cm(-2), a low Tafel slope of 35.6 mV dec(-1), and robust electrochemical durability.