TY - JOUR
T1 - Layer Rotation-Angle-Dependent Excitonic Absorption in van der Waals Heterostructures Revealed by Electron Energy Loss Spectroscopy
AU - Gogoi, Pranjal Kumar
AU - Lin, Yung Chang
AU - Senga, Ryosuke
AU - Komsa, Hannu Pekka
AU - Wong, Swee Liang
AU - Chi, Dongzhi
AU - Krasheninnikov, Arkady V.
AU - Li, Lain Jong
AU - Breese, Mark B.H.
AU - Pennycook, Stephen J.
AU - Wee, Andrew T.S.
AU - Suenaga, Kazu
PY - 2019/8/27
Y1 - 2019/8/27
N2 - Heterostructures comprising van der Waals (vdW) stacked transition metal dichalcogenide (TMDC) monolayers are a fascinating class of two-dimensional (2D) materials. The presence of interlayer excitons, where the electron and the hole remain spatially separated in the two layers due to ultrafast charge transfer, is an intriguing feature of these heterostructures. The optoelectronic functionality of 2D heterostructure devices is critically dependent on the relative rotation angle of the layers. However, the role of the relative rotation angle of the constituent layers on intralayer absorption is not clear yet. Here, we investigate MoS2/WSe2 vdW heterostructures using monochromated low-loss electron energy loss (EEL) spectroscopy combined with aberration-corrected scanning transmission electron microscopy and report that momentum conservation is a critical factor in the intralayer absorption of TMDC vdW heterostructures. The evolution of the intralayer excitonic low-loss EEL spectroscopy peak broadenings as a function of the rotation angle reveals that the interlayer charge transfer rate can be about an order of magnitude faster in the aligned (or anti-aligned) case than in the misaligned cases. These results provide a deeper insight into the role of momentum conservation, one of the fundamental principles governing charge transfer dynamics in 2D vdW heterostructures.
AB - Heterostructures comprising van der Waals (vdW) stacked transition metal dichalcogenide (TMDC) monolayers are a fascinating class of two-dimensional (2D) materials. The presence of interlayer excitons, where the electron and the hole remain spatially separated in the two layers due to ultrafast charge transfer, is an intriguing feature of these heterostructures. The optoelectronic functionality of 2D heterostructure devices is critically dependent on the relative rotation angle of the layers. However, the role of the relative rotation angle of the constituent layers on intralayer absorption is not clear yet. Here, we investigate MoS2/WSe2 vdW heterostructures using monochromated low-loss electron energy loss (EEL) spectroscopy combined with aberration-corrected scanning transmission electron microscopy and report that momentum conservation is a critical factor in the intralayer absorption of TMDC vdW heterostructures. The evolution of the intralayer excitonic low-loss EEL spectroscopy peak broadenings as a function of the rotation angle reveals that the interlayer charge transfer rate can be about an order of magnitude faster in the aligned (or anti-aligned) case than in the misaligned cases. These results provide a deeper insight into the role of momentum conservation, one of the fundamental principles governing charge transfer dynamics in 2D vdW heterostructures.
KW - electron energy loss spectroscopy
KW - interlayer excitons
KW - scanning transmission electron microscopy
KW - ultrafast charge transfer
KW - van der Waals heterostructure
UR - http://www.scopus.com/inward/record.url?scp=85070652231&partnerID=8YFLogxK
U2 - 10.1021/acsnano.9b04530
DO - 10.1021/acsnano.9b04530
M3 - Article
C2 - 31345026
AN - SCOPUS:85070652231
SN - 1936-0851
VL - 13
SP - 9541
EP - 9550
JO - ACS Nano
JF - ACS Nano
IS - 8
ER -