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Title: Observation of two distinct negative trions in tungsten disulfide monolayers

Abstract

We report on the observation of two distinct photogenerated negative trion states T A and T B in two-dimensional tungsten disulfide (2D-WS 2) monolayers. These trions are postulated to emerge from their parent excitons X A and X B, which originate from spin-orbit-split (SOS) levels in the conduction band (CB) and valence band (VB). Time-resolved spectroscopy measurements suggests that Pauli blocking controls a competition process between T A and T B photoformation, following dissociation of X A and X B through hole trapping at internal or substrate defect sites. While T A arises directly from its parent X A, T B emerges through a different transition accessible only after X B dissociates through a hole trapping channel. This discovery of additional optically-active band-edge transitions in atomically-thin metal dichalcogenides may revolutionize optoelectronic applications and fundamental research opportunities for many-body interaction physics. Ultrafast pump-probe spectroscopy of two-dimensional tungsten disulfide monolayers (2D-WS 2) grown on sapphire substrates revealed two transient absorption spectral peaks that are attributed to distinct negative trions at ~2.02 eV (T 1) and ~1.98 eV (T 2). The dynamics measurements indicate that trion formation by the probe is enabled by photodoped electrons that remain after trapping of holes from excitonsmore » or free electron-hole pairs at defect sites in the crystal or on the substrate. Dynamics of the excitons X A and X B’s characteristic absorption bands, at ~2.03 and ~2.40 eV, respectively, were separately monitored and compared with the photoinduced absorption features. Selective excitation of the lowest exciton level X A using λ pump < 2.4 eV forms only trion T 1, which implies that the electron that remains from the dissociation of exciton X A is involved in the creation of this trion with a binding energy ~ 10 meV with respect to X A. The absorption peak that corresponds to trion T 2 appears when λ pump > 2.4 eV, which is just sufficient to excite exciton X B. The dynamics of trion T 2 formation are found to correlate with the disappearance of the bleach of X B exciton, which indicates the involvement of holes participating in the bleach dynamics of exciton X B. Static electrical-doping photoabsorption measurements confirm the presence of an induced absorption peak similar to that of T 2. Since the proposed trion formation process here involves exciton dissociation through hole-trapping by defects in the 2D crystal or substrate, this discovery highlights the strong role that defects have in defining the optical and electrical properties of 2D metal chalcogenides, which is relevant to a broad spectrum of basic science and technology applications.« less

Authors:
 [1];  [1];  [1];  [1];  [1];  [1];  [1];  [1];  [1];  [1];  [1]
  1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Center for Nanophase Materials Sciences (CNMS)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1222550
Alternate Identifier(s):
OSTI ID: 1224633
Grant/Contract Number:  
AC05-00OR22725; AC02-05CH11231
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Physical Review. B, Condensed Matter and Materials Physics
Additional Journal Information:
Journal Volume: 92; Journal Issue: 11-15; Journal ID: ISSN 1098-0121
Publisher:
American Physical Society (APS)
Country of Publication:
United States
Language:
English
Subject:
77 NANOSCIENCE AND NANOTECHNOLOGY; trions; excitons; ultrafast dynamics

Citation Formats

Boulesbaa, Abdelaziz, Huang, Bing, Wang, Kai, Lin, Ming-Wei, Mahjouri-Samani, Masoud, Rouleau, Christopher M., Xiao, Kai, Yoon, Mina, Sumpter, Bobby G., Puretzky, Alexander A., and Geohegan, David B. Observation of two distinct negative trions in tungsten disulfide monolayers. United States: N. p., 2015. Web. doi:10.1103/PhysRevB.92.115443.
Boulesbaa, Abdelaziz, Huang, Bing, Wang, Kai, Lin, Ming-Wei, Mahjouri-Samani, Masoud, Rouleau, Christopher M., Xiao, Kai, Yoon, Mina, Sumpter, Bobby G., Puretzky, Alexander A., & Geohegan, David B. Observation of two distinct negative trions in tungsten disulfide monolayers. United States. doi:10.1103/PhysRevB.92.115443.
Boulesbaa, Abdelaziz, Huang, Bing, Wang, Kai, Lin, Ming-Wei, Mahjouri-Samani, Masoud, Rouleau, Christopher M., Xiao, Kai, Yoon, Mina, Sumpter, Bobby G., Puretzky, Alexander A., and Geohegan, David B. Fri . "Observation of two distinct negative trions in tungsten disulfide monolayers". United States. doi:10.1103/PhysRevB.92.115443. https://www.osti.gov/servlets/purl/1222550.
@article{osti_1222550,
title = {Observation of two distinct negative trions in tungsten disulfide monolayers},
author = {Boulesbaa, Abdelaziz and Huang, Bing and Wang, Kai and Lin, Ming-Wei and Mahjouri-Samani, Masoud and Rouleau, Christopher M. and Xiao, Kai and Yoon, Mina and Sumpter, Bobby G. and Puretzky, Alexander A. and Geohegan, David B.},
abstractNote = {We report on the observation of two distinct photogenerated negative trion states TA and TB in two-dimensional tungsten disulfide (2D-WS2) monolayers. These trions are postulated to emerge from their parent excitons XA and XB, which originate from spin-orbit-split (SOS) levels in the conduction band (CB) and valence band (VB). Time-resolved spectroscopy measurements suggests that Pauli blocking controls a competition process between TA and TB photoformation, following dissociation of XA and XB through hole trapping at internal or substrate defect sites. While TA arises directly from its parent XA, TB emerges through a different transition accessible only after XB dissociates through a hole trapping channel. This discovery of additional optically-active band-edge transitions in atomically-thin metal dichalcogenides may revolutionize optoelectronic applications and fundamental research opportunities for many-body interaction physics. Ultrafast pump-probe spectroscopy of two-dimensional tungsten disulfide monolayers (2D-WS2) grown on sapphire substrates revealed two transient absorption spectral peaks that are attributed to distinct negative trions at ~2.02 eV (T1) and ~1.98 eV (T2). The dynamics measurements indicate that trion formation by the probe is enabled by photodoped electrons that remain after trapping of holes from excitons or free electron-hole pairs at defect sites in the crystal or on the substrate. Dynamics of the excitons XA and XB’s characteristic absorption bands, at ~2.03 and ~2.40 eV, respectively, were separately monitored and compared with the photoinduced absorption features. Selective excitation of the lowest exciton level XA using λpump < 2.4 eV forms only trion T1, which implies that the electron that remains from the dissociation of exciton XA is involved in the creation of this trion with a binding energy ~ 10 meV with respect to XA. The absorption peak that corresponds to trion T2 appears when λpump > 2.4 eV, which is just sufficient to excite exciton XB. The dynamics of trion T2 formation are found to correlate with the disappearance of the bleach of XB exciton, which indicates the involvement of holes participating in the bleach dynamics of exciton XB. Static electrical-doping photoabsorption measurements confirm the presence of an induced absorption peak similar to that of T2. Since the proposed trion formation process here involves exciton dissociation through hole-trapping by defects in the 2D crystal or substrate, this discovery highlights the strong role that defects have in defining the optical and electrical properties of 2D metal chalcogenides, which is relevant to a broad spectrum of basic science and technology applications.},
doi = {10.1103/PhysRevB.92.115443},
journal = {Physical Review. B, Condensed Matter and Materials Physics},
issn = {1098-0121},
number = 11-15,
volume = 92,
place = {United States},
year = {2015},
month = {9}
}

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