Layer specific optical band gap measurement at nanoscale in MoS{sub 2} and ReS{sub 2} van der Waals compounds by high resolution electron energy loss spectroscopy
- New Chemistry Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore 560064 (India)
Layer specific direct measurement of optical band gaps of two important van der Waals compounds, MoS{sub 2} and ReS{sub 2}, is performed at nanoscale by high resolution electron energy loss spectroscopy. For monolayer MoS{sub 2}, the twin excitons (1.8 and 1.95 eV) originating at the K point of the Brillouin zone are observed. An indirect band gap of 1.27 eV is obtained from the multilayer regions. Indirect to direct band gap crossover is observed which is consistent with the previously reported strong photoluminescence from the monolayer MoS{sub 2}. For ReS{sub 2}, the band gap is direct, and a value of 1.52 and 1.42 eV is obtained for the monolayer and multilayer, respectively. The energy loss function is dominated by features due to high density of states at both the valence and conduction band edges, and the difference in analyzing band gap with respect to ZnO is highlighted. Crystalline 1T ReS{sub 2} forms two dimensional chains like superstructure due to the clustering between four Re atoms. The results demonstrate the power of HREELS technique as a nanoscale optical absorption spectroscopy tool.
- OSTI ID:
- 22596910
- Journal Information:
- Journal of Applied Physics, Vol. 119, Issue 11; Other Information: (c) 2016 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA); ISSN 0021-8979
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
GENERAL PHYSICS
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ABSORPTION SPECTROSCOPY
BRILLOUIN ZONES
DENSITY OF STATES
ELECTRONS
ENERGY LOSSES
ENERGY-LOSS SPECTROSCOPY
LAYERS
MOLYBDENUM SULFIDES
NANOSTRUCTURES
PHOTOLUMINESCENCE
RESOLUTION
RHENIUM SULFIDES
SILICON OXIDES
TWO-DIMENSIONAL CALCULATIONS
VAN DER WAALS FORCES
ZINC OXIDES