Subscriber access provided by READING UNIV
Article
Robust Stacking-Independent Ultrafast Charge Transfer in MoS2/WS2 Bilayers Ziheng Ji, Hao Hong, Jin Zhang, Qi Zhang, Wei Huang, Ting Cao, Ruixi Qiao, Can Liu, Jing Liang, Chuanhong Jin, Liying Jiao, Kebin Shi, Sheng Meng, and Kaihui Liu ACS Nano, Just Accepted Manuscript • DOI: 10.1021/acsnano.7b04541 • Publication Date (Web): 08 Nov 2017 Downloaded from http://pubs.acs.org on November 8, 2017
Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
ACS Nano is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Nano
SUREH SXPS
û5 5
Page 1 of 28
Î N âÙ Œ™
FKDUJH WUDQVIHU
0R6
:6
7LPH GHOD\ IV
72&
ACS Paragon Plus Environment
ACS Nano
a
θ = 0°
b
θ = 60°
c
θ = 38°
10 μm
e
d
Ⅰ
8
Ⅱ
15
θ=60°
10
θ=0° θ=38°
5 0
×0.2
ML MoS2
600 650 700 750 800 Wavelength (nm)
Raman (a.u.)
20 PL (a.u.)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58
Page 2 of 28
C LBM
6 4 2 0
-60 -40 -20 20 40 60 Wavenumber (cm-1)
Figure 1 ACS Paragon Plus Environment
Page 3 of 28
a
Laser
Sample
Time-delay
OPO
PCF
Filter Spec.
Lock-in
PMT
b
c
probe pump
CT
-ΔR/R (%)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58
ACS Nano
MoS2 θ=0° θ=60° θ=38°
0.8
×4
0.4
0.0 -300 MoS2
WS2
0 300 600 900 Time delay (fs)
Figure 2 ACS Paragon Plus Environment
ACS Nano
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58
Page 4 of 28
a
1 nm
b
Interlayer tensile shift
Figure 3 ACS Paragon Plus Environment
Page 5 of 28
a
d 0.4
𝐀𝐁𝟏′
θ=0°
e
t=230 fs
θ=60°
f
t=240 fs
0.4
θ=38°
0.3
0.3
0.3
0.2
0.2
0.2
0.1
0
30
60
90 120
Time (fs)
g
c
b 𝐀𝐀′𝟏
Charge (e)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58
ACS Nano
0
30
60
90 120
0
t=280 fs
30 60 90 120
Time (fs)
Time (fs)
𝐀𝐀 𝟑
𝐀𝐀 𝟏
t=180 fs
𝐀𝐀′𝟏
WS2
t=230 fs
t=1500 fs MoS2
Figure 4 ACS Paragon Plus Environment
ACS Nano
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Robust Stacking-Independent Ultrafast Charge Transfer in MoS2/WS2 Bilayers Ziheng Ji1#, Hao Hong1#, Jin Zhang2#, Qi Zhang3#, Wei Huang4, Ting Cao5, Ruixi Qiao1, Can Liu1, Jing Liang1, Chuanhong Jin4*, Liying Jiao3, Kebin Shi1,6*, Sheng Meng2,6, Kaihui Liu1,6* 1
State Key Laboratory for Mesoscopic Physics, School of Physics, Peking University, Beijing 100871, China
2
Beijing National Laboratory for Condensed Matter Physics, and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
3
Key Laboratory of Organic Optoelectronics and Molecular Engineering of the Ministry of Education, Department of Chemistry, Tsinghua University, Beijing 100084, China
4
State Key Laboratory of Silicon Materials, Key Laboratory of Advanced Materials and Applications for Batteries of Zhejiang Province, School of Materials Science and Engineering, Zhejiang University, Hangzhou, Zhejiang 310027, China.
5
Department of Physics, University of California at Berkeley, Berkeley, California 94720, USA
6
Collaborative Innovation Centre of Quantum Matter, Beijing 100871, China
# These authors contributed equally to this work * Correspondence:
[email protected];
[email protected];
[email protected] / 23Environment ACS Paragon 1Plus
Page 6 of 28
Page 7 of 28
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Nano
Abstract Van der Waals-coupled two-dimensional (2D) heterostructures have attracted great attentions recently due to their high potential in the next-generation photodetectors and solar cells. The understanding of charge-transfer process between adjacent atomic layers is the key to design optimal devices as it directly determines the fundamental response speed and photon-electron conversion efficiency. However, general belief and theoretical studies have shown that the charge transfer behaviour depends sensitively on interlayer configurations, which is difficult to control accurately, bringing great uncertainties in device designing. Here we investigate the ultrafast dynamics of interlayer charge transfer in a prototype heterostructure, the MoS2/WS2 bilayer with various stacking configurations, by optical two-colour ultrafast pump-probe spectroscopy. Surprisingly, we found that the charge transfer is robust against varying interlayer twist angles and interlayer coupling strength, in time scale of ~ 90 fs. Our observation, together with atomic-resolved transmission electron characterization and time-dependent density functional theory simulations, reveal that the robust ultrafast charge transfer is attributed to the heterogeneous interlayer stretching/sliding which provides additional channels for efficient charge transfer previously unknown. Our results elucidate the origin of transfer rate robustness against interlayer stacking configurations in optical devices based on 2D heterostructures, facilitating their applications in ultrafast and high-efficient optoelectronic and photovoltaic devices in the near future.
/ 23Environment ACS Paragon 2Plus
ACS Nano
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Keywords: 2D heterostructures, stacking configuration, van der Waals coupling, robust ultrafast charge transfer, time-dependent density functional theory
/ 23Environment ACS Paragon 3Plus
Page 8 of 28
Page 9 of 28
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Nano
The family of two-dimensional (2D) materials, ranging from semi-metallic graphene and infrared-gapped black phosphorus to semiconducting molybdenum disulfide (MoS2) and insulating hexagonal boron nitride (h-BN), have demonstrated distinct electronic, optical and mechanical properties from conventional bulk materials. Stacking different 2D materials vertically leads to van der Waals heterostructures, which have emerged as a new class of materials and opened up significant opportunities for exploring novel physics and device applications.1-5 Among various van der Waals heterostructure, those formed by two different transition-metal dichalcogenides (MX2) monolayers are especially intriguing because of their giant tunability of bandgap size from infrared to visible range and enhanced light-matter interaction.6,7 Moreover, many MX2 heterostructures form type II band alignment, indicating the photoexcited electrons and holes naturally separate into the two different layers through charge transfer process.8-11 Despite the large interlayer momentum mismatch and the weak interlayer coupling between layers, which usually hinders the charge transfer process, both experiments12-16 and theoretical calculations17-20 elucidate that this process is ultrafast, and happens in a time scale of 100 fs. Several mechanisms for the charge transfer, such as exciton localization,17 interlayer hot excitons formation,14,17 and coherent charge transfer,15,18 have been proposed, while a comprehensive understanding is still lacking so far. Interfacial stacking configuration is demonstrated to be an efficient degree of freedom to engineer the physical properties of Van der Waals-coupled materials, e.g., interfacial states and wavefunction coupling.21,22 Therefore, how the charge-transfer time evolves with the interfacial
/ 23Environment ACS Paragon 4Plus
ACS Nano
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 10 of 28
stacking configuration is both fundamental and important for understanding the interlayer charge transfer and optimizing applications of 2D heterostructures. Several groups have reported the charge transfer time is ultrafast in tens femtosecond time scale regardless of different interlayer twist angle and thus different interlayer momentum mismatch.12,13,16 Their experiments are all based on transferred MX2 heterostructures with random twisted angle (0°
