TY - JOUR
T1 - Stabilization of Chemical-Vapor-Deposition-Grown WS2Monolayers at Elevated Temperature with Hexagonal Boron Nitride Encapsulation
AU - Hua, Xiang
AU - Zhang, Datong
AU - Kim, Bumho
AU - Seo, Dongjea
AU - Kang, Kyungnam
AU - Yang, Eui Hyeok
AU - Hu, Jiayang
AU - Chen, Xianda
AU - Liang, Haoran
AU - Watanabe, Kenji
AU - Taniguchi, Takashi
AU - Hone, James
AU - Kim, Young Duck
AU - Herman, Irving P.
N1 - Publisher Copyright:
©
PY - 2021/7/7
Y1 - 2021/7/7
N2 - Chemical vapor deposition (CVD)-grown flakes of high-quality monolayers of WS2 can be stabilized at elevated temperatures by encapsulation with several layer hexagonal boron nitride (h-BN), but to different degrees in the presence of ambient air, flowing N2, and flowing forming gas (95% N2, 5% H2). The best passivation of WS2 at elevated temperature occurs for h-BN-covered samples with flowing N2 (after heating to 873 K), as judged by optical microscopy and photoluminescence (PL) intensity after a heating/cooling cycle. Stability is worse for uncovered samples, but best with flowing forming gas. PL from trions, in addition to that from excitons, is seen for covered WS2 only for forming gas, during cooling below ?323 K; the trion has an estimated binding energy of ?28 meV. It might occur because of doping level changes caused by charge defect generation by H2 molecules diffusing between the h-BN and the SiO2/Si substrate. The decomposition of uncovered WS2 flakes in air suggests a dissociation and chemisorption energy barrier of O2 on the WS2 surface of ?1.6 eV. Fitting the high-temperature PL intensities in air gives a binding energy of a free exciton of ?229 meV.
AB - Chemical vapor deposition (CVD)-grown flakes of high-quality monolayers of WS2 can be stabilized at elevated temperatures by encapsulation with several layer hexagonal boron nitride (h-BN), but to different degrees in the presence of ambient air, flowing N2, and flowing forming gas (95% N2, 5% H2). The best passivation of WS2 at elevated temperature occurs for h-BN-covered samples with flowing N2 (after heating to 873 K), as judged by optical microscopy and photoluminescence (PL) intensity after a heating/cooling cycle. Stability is worse for uncovered samples, but best with flowing forming gas. PL from trions, in addition to that from excitons, is seen for covered WS2 only for forming gas, during cooling below ?323 K; the trion has an estimated binding energy of ?28 meV. It might occur because of doping level changes caused by charge defect generation by H2 molecules diffusing between the h-BN and the SiO2/Si substrate. The decomposition of uncovered WS2 flakes in air suggests a dissociation and chemisorption energy barrier of O2 on the WS2 surface of ?1.6 eV. Fitting the high-temperature PL intensities in air gives a binding energy of a free exciton of ?229 meV.
KW - WS
KW - elevated temperature
KW - excitons
KW - h-BN encapsulation
KW - monolayer
KW - photoluminescence
KW - transition-metal dichalcogenide (TMD) monolayers
KW - trions
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U2 - 10.1021/acsami.1c06348
DO - 10.1021/acsami.1c06348
M3 - Article
C2 - 34170658
AN - SCOPUS:85110325343
SN - 1944-8244
VL - 13
SP - 31271
EP - 31278
JO - ACS Applied Materials and Interfaces
JF - ACS Applied Materials and Interfaces
IS - 26
ER -