Stengl V, Henych J (2013) Strongly luminescent monolayered MoS 2 prepared by effective ultrasound exfoliation. Gan ZX, Liu LZ, Wu HY, Hao YL, Shan Y, Wu XL, Chu PK (2015) Quantum confinement effects across two-dimensional planes in MoS 2 quantum dots. Yong Y, Cheng X, Bao T, Zu M, Yan L, Yin W, Ge C, Wang CD, Gu Z, Zhao Y (2015) Tungsten sulfide quantum dots as multifunctional nanotheranostics for In-vivo dual-modal image-guided photothermal/radiotherapy synergistic therapy. Nano Lett 10:1271–1275īromley RA, Murray RB, Yoffe AD (1972) The band structures of some transition metal dichalcogenides III. Splendiani A, Sun L, Zhang Y, Li T, Kim J, Jonghwan Chim CY, Galli G, Wang F (2010) Emerging photoluminescence in monolayer MoS 2. Mak KF, Lee C, Hone J, Shan J, Heinz TF (2010) Atomically thin MoS 2: a new direct-gap semiconductor. Sci Rep 6:32690ĭankert A, Langouche L, Kamalakar MV, Dash SP (2014) High-performance molybdenum disulfide field-effect transistors with spin tunnel contacts. Pandey K, Yadav P, Singh D, Gupta SK, Sonvane Y, Lukaacevic I, Kim J, Kumar M (2016) First step to investigate nature of electronic states and transport in flower-like MoS 2: combining experimental studies with computational calculations. Kuc A, Zibouche N, Heine T (2011) Influence of quantum confinement on the electronic structure of the transition metal sulphide. Chem Rev 110:132–145Ĭhoi W, Lahiri I, Seelaboyina R, Kang YS (2010) Synthesis of graphene and its applications: a review. Matthew JA, Vincent CT, Richard BK (2010) Honeycomb carbon: a review of graphene. Wang QH, Zadeh K, Kis A, Coleman JN, Strano MS (2012) Electronics and optoelectronics of two-dimensional transition-metal dichalcogenides. Geim AK, Novoselov KS (2007) The rise of graphene. These results suggest that quantum confinement effects together with band gap transformation from indirect to direct, not only shift the band edge in the ultraviolet region but also give rise to enhancement in the photoluminescence emission. Further, the photoluminescence spectra shifts with the excitation wavelength, a signature of size-dependent photoluminescence emission from these nanostructures. The average statistical size distribution of quantum dots was found to be 3–4.5 nm and corresponds to a band gap of 6 and 3.4 eV, respectively, under effective mass approximation. The UV–Vis spectra from these nanostructures display strong excitonic absorptions together with band edge absorption at ≈5.1 eV, sufficiently larger than the indirect band gap (≈1.3 eV) of bulk WS 2. The nanostructures so obtained exhibit strong photoluminescence, which is otherwise difficult to detect (due to low quantum yield) when WS 2 is in bulk form. The X-rays diffraction analysis confirmed the presence of hexagonal as well as tetragonal phase of WS 2 in quantum dots.
Crystalline and hetero-dimensional nanostructures of WS 2 quantum dots and a few layered sheets have been successfully synthesized in a single-step process using liquid exfoliation in deionized water.
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