TY - JOUR
T1 - Improving the Optical Quality of MoSe2and WS2Monolayers with Complete h-BN Encapsulation by High-Temperature Annealing
AU - Hua, Xiang
AU - Axenie, Theodor
AU - Goldaraz, Mateo Navarro
AU - Kang, Kyungnam
AU - Yang, Eui Hyeok
AU - Watanabe, Kenji
AU - Taniguchi, Takashi
AU - Hone, James
AU - Kim, Bumho
AU - Herman, Irving P.
N1 - Publisher Copyright:
© 2021 American Chemical Society.
PY - 2022/1/12
Y1 - 2022/1/12
N2 - We improved the optical quality and stability of an exfoliated monolayer (ML) MoSe2 and chemical vapor deposition (CVD)-grown WS2 MLs by encapsulating and sealing them with both top and bottom few-layer h-BN, as tested by subsequent high-temperature annealing up to 873 K and photoluminescence (PL) measurements. These transition-metal dichalcogenide (TMD) MLs remained stable up to this maximum temperature, as seen visually. After the heating/cooling cycle, the integrated photoluminescence (PL) intensity at 300 K in the MoSe2 ML was ∼4 times larger than that before heating and that from exciton and trion PL in the analogous WS2 ML sample was ∼14 times and ∼2.5 times larger at 77 K and the exciton peak was ∼9.5 times larger at 300 K. This is attributed to the reduction of impurities, the lateral expulsion of contamination leading to clean and atomically flat surfaces, and the sealing provided by the h-BN layers that prevents the diffusion of molecules such as trace O2 and H2O to the TMD ML. Stability and optical performance are much improved compared to that in earlier work using top h-BN only, in which the WS2 ML PL intensity decreased even for an optimal gas environment. This complete encapsulation is particularly promising for CVD-grown TMD MLs because they have relatively more charge and other impurities than do exfoliated MLs. These results open a new route for improving the optical properties of TMD MLs and their performance and applications both at room and higher temperatures.
AB - We improved the optical quality and stability of an exfoliated monolayer (ML) MoSe2 and chemical vapor deposition (CVD)-grown WS2 MLs by encapsulating and sealing them with both top and bottom few-layer h-BN, as tested by subsequent high-temperature annealing up to 873 K and photoluminescence (PL) measurements. These transition-metal dichalcogenide (TMD) MLs remained stable up to this maximum temperature, as seen visually. After the heating/cooling cycle, the integrated photoluminescence (PL) intensity at 300 K in the MoSe2 ML was ∼4 times larger than that before heating and that from exciton and trion PL in the analogous WS2 ML sample was ∼14 times and ∼2.5 times larger at 77 K and the exciton peak was ∼9.5 times larger at 300 K. This is attributed to the reduction of impurities, the lateral expulsion of contamination leading to clean and atomically flat surfaces, and the sealing provided by the h-BN layers that prevents the diffusion of molecules such as trace O2 and H2O to the TMD ML. Stability and optical performance are much improved compared to that in earlier work using top h-BN only, in which the WS2 ML PL intensity decreased even for an optimal gas environment. This complete encapsulation is particularly promising for CVD-grown TMD MLs because they have relatively more charge and other impurities than do exfoliated MLs. These results open a new route for improving the optical properties of TMD MLs and their performance and applications both at room and higher temperatures.
KW - MoSemonolayers
KW - WSmonolayers
KW - exciton
KW - h-BN encapsulation
KW - high temperature processing
KW - photoluminescence
KW - trion
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U2 - 10.1021/acsami.1c18991
DO - 10.1021/acsami.1c18991
M3 - Article
C2 - 34969239
AN - SCOPUS:85122666374
SN - 1944-8244
VL - 14
SP - 2255
EP - 2262
JO - ACS Applied Materials and Interfaces
JF - ACS Applied Materials and Interfaces
IS - 1
ER -