Query: Ultrafast charge transfer in atomically thin MoS2/WS2 heterostructures

Candidate papers:

abstract: Van der Waals heterostructures have recently emerged as a new class of materials, where quantum coupling between stacked atomically thin two dimensional layers, including graphene, hexagonal boron nitride and transition metal dichalcogenides (MX2) give rise to fascinating new phenomena. MX2 heterostructures are particularly exciting for novel optoelectronic and photovoltaic applications, because two dimensional MX2 monolayers can have an optical bandgap in the near infrared to visible spectral range and exhibit extremely strong light matter interactions. Theory predicts that many stacked MX2 heterostructures form type II semiconductor heterojunctions that facilitate efficient electron hole separation for light detection and harvesting. Here, we report the first experimental observation of ultrafast charge transfer in photoexcited MoS2/WS2 heterostructures using both photoluminescence mapping and femtosecond pump probe spectroscopy. We show that hole transfer from the MoS2 layer to the WS2 layer takes place within 50 fs after optical excitation, a remarkable rate for van der Waals coupled two dimensional layers. Such ultrafast charge transfer in van der Waals heterostructures can enable novel two dimensional devices for optoelectronics and light harvesting.
author_names: Xiaoping Hong

Jonghwan Kim

Su-Fei Shi

Yang Zhang

Chenhao Jin

Yinghui Sun

Sefaattin Tongay

Junqiao Wu

Yanfeng Zhang

Feng Wang
title: Ultrafast charge transfer in atomically thin MoS2/WS2 heterostructures.
venue: Nature nanotechnology
year: 2014

abstract: Hybridization of two dimensional (2D) magnetic semiconductors with transition metal dichalcogenides (TMDC) monolayers can significantly engineer the light matter interactions and provide a promising platform for enhanced excitonic systems with artificially tailored band alignments. Here, we report the fabrication of heterostructures with monolayer WS2 on 2D Cr2Ge2Te6 (CGT) which displayed giant photoluminescence enhancement at specific CGT layer numbers. The highly enhanced quantum yield obtained can be explained by novel photoexcited carrier dynamics, facilitated by alternate relaxation channels, resulting in resonance charge transfer at the heterointerface. 2D CGT revealed a strongly layer dependent work function (up to ~750 meV) which greatly modulates the band positioning in the heterostructure. These heterostructures conceived both type I and type II band alignments, which are verified by Kelvin probe force microscopy and PL measurements. In addition to layer modulation, we uncover temperature and power dependence of the resonance charge transfer in the multilayer heterostructure. Our findings provide further insights into the ultrafast charge dynamics occurring at the atomic interfaces. The results may pave the way for novel optoelectronics based on van der Waals heterostructures.
author_names: Sharidya Rahman

Boqing Liu

Bowen Wang

Yilin Tang

Yuerui Lu
title: Giant Photoluminescence Enhancement and Resonant Charge Transfer in Atomically Thin Two Dimensional Cr2Ge2Te6/WS2 Heterostructures.
venue: ACS applied materials interfaces
year: 2021

abstract: Demonstration of van der Waals (vdW) semiconductor/metal heterostructures (SMHs) based on transition metal dichalcogenides has been a central approach in high speed electronics by introducing ultrafast carrier dynamics. In this regard, a Weyl semimetal WTe2 is of great interest due to its vdW layered nature, low work function, and superior electrical properties. However, little is still known about its heterostructures and a few picosecond photocarrier lifetimes hinder its applications in high speed electronics. Here, we propose a SMH; Semimetallic Td phase WTe2 with its sister compound of semiconducting 2H phase MoTe2. Time resolved terahertz spectroscopy demonstrated that WTe2 exhibited the significantly shorter carrier lifetimes of sub ps when forming a junction with MoTe2. We provided explicit characteristic signatures revealing charge transfer across the interface and the subsequent interlayer exciton decay. This work not only offers the extension of the THz detection scope of ultrafast phenomena from atomically thin materials but also provides a building block of vertical SMHs for high speed electronic devices with sub ps photocarrier lifetimes.
author_names: Kyusup Lee

Jianan Li

Liang Cheng

Junyong Wang

Dushyant Kumar

Qisheng Wang

Mengji Chen

Yang Wu

Goki Eda

Elbert E M Chia

Haixin Chang

Hyunsoo Yang
title: Sub Picosecond Carrier Dynamics Induced by Efficient Charge Transfer in MoTe2/WTe2 van der Waals Heterostructures.
venue: ACS nano
year: 2019

abstract: Interlayer coupling in van der Waals heterostructures exhibits unique physical properties and presents a new pathway for diverse applications in materials science and photonics. Interestingly, photo responsivity of graphene with semiconducting transition metal dichalcogenide (TMD) can be enhanced in the UV visible range by interlayer charge/energy transfer. However, such an effect has been studied only for semiconducting materials. In this work, we will discuss ultrafast hot electron transfer in atomically thin metallic layer VSe2/graphene heterostructures investigated by time resolved pump probe spectroscopy. Our experimental finding extends the concepts of conventional two dimensional heterostructures to metallic layer and can provide a new degree of freedom for designing novel functionalized materials and devices.
author_names: Tae Gwan Park

B K Choi

Junho Park

Jungdae Kim

Young Jun Chang

Fabian Rotermund
title: Ultrafast hot electron transfer in metallic VSe2/graphene van der Waals heterostructures (Conference Presentation)
year: 2020

abstract: Van der Waals heterostructures composed of two dimensional transition metal dichalcogenides layers have recently emerged as a new family of materials, with great potential for atomically thin opto electronic and photovoltaic applications. It is puzzling, however, that the photocurrent is yielded so efficiently in these structures, despite the apparent momentum mismatch between the intralayer/interlayer excitons during the charge transfer, as well as the tightly bound nature of the excitons in 2D geometry. Using the energy state resolved ultrafast visible/infrared microspectroscopy, we herein obtain unambiguous experimental evidence of the charge transfer intermediate state with excess energy, during the transition from an intralayer exciton to an interlayer exciton at the interface of a WS2/MoS2 heterostructure, and free carriers moving across the interface much faster than recombining into the intralayer excitons. The observations therefore explain how the remarkable charge transfer rate and photocurrent generation are achieved even with the aforementioned momentum mismatch and excitonic localization in 2D heterostructures and devices.
author_names: Hailong Chen

Xiewen Wen

Jing J Zhang

Tianmin Wu

Yongji Gong

Xiang Zhang

Jiangtan Yuan

Chongyue Yi

Jun Lou

Pulickel M Ajayan

Wei Zhuang

Guangyu Zhang

Junrong Zheng
title: Ultrafast formation of interlayer hot excitons in atomically thin MoS2/WS2 heterostructures
venue: Nature communications
year: 2016

abstract: Atomically thin transition metal dichalcogenides (TMDs) exhibit strong light matter interaction and pronounced excitonic behavior. Understanding the nonequilibrium dynamical processes of photoexcited carriers in such materials is a key step in view of their technological applications. Here, we review the ultrafast photophysics of 2D TMDs and related heterostructures (HSs) measured by femtosecond optical spectroscopy. First, we provide a general introduction on the physics of the materials and a brief explanation of the ultrafast optical techniques. Then we discuss the physical processes governing their nonequilibrium optical response, with a particular emphasis on the intervalley scattering dynamics, and the charge transfer processes in 2D HSs. We conclude by discussing open issues and perspectives for future experiments.
author_names: Stefano Dal Conte

Chiara Trovatello

Christoph Gadermaier

Giulio Cerullo
title: Ultrafast Photophysics of 2D Semiconductors and Related Heterostructures
year: 2020

abstract: Atomically thin and sharp van der Waals heterojunction can be created by vertically stacking p type monolayer tungsten diselenide (WSe2) onto n type molybdenum disulfide (MoS2) Theory predicts that stacked MoS2 and WSe2 monolayer forms type II p n junction, creating a built in electric field across the interface which facilitates electron hole separation and transfer. Gaining insights into the dynamics of charge transfer across van der Waals heterostructure is central to understanding light photocurrent conversion at these ultrathin interfaces. Herein, we investigate the exciton dissociation and charge transfer in a MoS2/WSe2 van der Waals hetero structure. Our results show that ultrafast electron transfer from WSe2 to MoS2 take place within 470 fs upon optical excitation with 99% charge transfer efficiency, leading to drastic photoluminescence quenching and decreased lifetime. Our findings suggest that van der Waals heterostructure may be useful as active components in ultrafast optoelectronic devices.
author_names: Bo Peng

Guannan Yu

Xinfeng Liu

Bo Liu

Xiao Liang

Lei Bi

Longjiang Deng

Tze Chien Sum

Kian Ping Loh
title: Ultrafast charge transfer in MoS 2 /WSe 2 p n Heterojunction
year: 2016

abstract: Van der Waals heterostructures are synthetic quantum materials composed of stacks of atomically thin two dimensional (2D) layers. Because the electrons in the atomically thin 2D layers are exposed to layer to layer coupling, the properties of van der Waals heterostructures are defined not only by the constituent monolayers, but also by the interactions between the layers. Many fascinating electrical, optical and magnetic properties have recently been reported in different types of van der Waals heterostructures. In this Review, we focus on unique excited state dynamics in transition metal dichalcogenide (TMDC) heterostructures. TMDC monolayers are the most widely studied 2D semiconductors, featuring prominent exciton states and accessibility to the valley degree of freedom. Many TMDC heterostructures are characterized by a staggered band alignment. This band alignment has profound effects on the evolution of the excited states in heterostructures, including ultrafast charge transfer between the layers, the formation of interlayer excitons, and the existence of long lived spin and valley polarization in resident carriers. Here we review recent experimental and theoretical efforts to elucidate electron dynamics in TMDC heterostructures, extending from timescales of femtoseconds to microseconds, and comment on the relevance of these effects for potential applications in optoelectronic, valleytronic and spintronic devices.This Review discusses recent experimental and theoretical efforts in electron dynamics in TMDC heterostructures and the relevance of these effects for potential applications in optoelectronic and valleytronic/spintronic devices.
author_names: Chenhao Jin

Eric Yue Ma

Ouri Karni

Emma C Regan

Feng Wang

Tony F Heinz
title: Ultrafast dynamics in van der Waals heterostructures
venue: Nature Nanotechnology
year: 2018

abstract: The performance of a photovoltaic device is strongly dependent on the light harvesting properties of the absorber layer as well as the charge separation at the donor/acceptor interfaces. Atomically thin two dimensional transition metal dichalcogenides (2 D TMDCs) exhibit strong light matter interaction, large optical conductivity, and high electron mobility; thus they can be highly promising materials for next generation ultrathin solar cells and optoelectronics. However, the short optical absorption path inherent in such atomically thin layers limits practical applications. A heterostructure geometry comprising 2 D TMDCs (e.g. MoS2) and a strongly absorbing material with long electron hole diffusion lengths such as methylammonium lead halide perovskites (CH3NH3PbI3) may overcome this constraint to some extent, provided the charge transfer at the heterostructure interface is not hampered by their band offsets. Herein, we demonstrate that the intrinsic band offset at the CH3NH3PbI3/MoS2 interface can be overcome by creating sulfur vacancies in MoS2 using a mild plasma treatment; ultrafast hole transfer from CH3NH3PbI3 to MoS2 occurs within 320 fs with 83% efficiency following photoexcitation. Importantly, our work highlights the feasibility of applying defect engineered 2 D TMDCs as charge extraction layers in perovskite based optoelectronic devices.
author_names: Bo Peng

Guannan Yu

Yawen Zhao

Qiang Xu

Guichuan Xing

Xinfeng Liu

Deyi Fu

Bo Liu

Jun Rong Sherman Tan

Wei Tang

Haipeng Lu

Jianliang Xie

Longjiang Deng

Tze Chien Sum

Kian Ping Loh
title: Achieving Ultrafast Hole Transfer at the Monolayer MoS2 and CH3NH3PbI3 Perovskite Interface by Defect Engineering.
venue: ACS nano
year: 2016

abstract: As an emerging ultrathin semiconductor material, Bi2O2Se exhibits prominent performances in electronics, optoelectronics, ultrafast optics, etc. However, until now, the in plane growth of Bi2O2Se thin films is mostly fulfilled on atomically flat mica substrates with interfacial electrostatic forces setting obstacles for Bi2O2Se transfer to fabricate functional van der Waals heterostructures. In this work, controlled growth of inclined Bi2O2Se ultrathin films is realized with apparently reduced interfacial contact areas upon mica flakes. Consequently, the transfer of Bi2O2Se could be facile by overcoming weaker electrostatic interactions. From cross sectional characterizations at the Bi2O2Se/mica interfaces, it is found that there are no oxide buffer layers in existence for both in plane and inclined growths, while the un neutralized charge density is apparently decreased for inclined films. By mechanical pressing, inclined Bi2O2Se could be transferred onto SiO2/Si substrates, and back gated Bi2O2Se field effect transistors are fabricated, outperforming previously reported in plane Bi2O2Se devices transferred with the assistance of corrosive acids and adhesive polymers. Furthermore, Bi2O2Se/graphene heterostructures are fulfilled by a probe tip to fabricate hybrid phototransistors with pristine interfaces, exhibiting highly efficient photoresponses. The results in this work demonstrate the potential of inclined Bi2O2Se to act as a building block for prospective van der Waals heterostructures.
author_names: Chengyun Hong

Ye Tao

Anmin Nie

Minhao Zhang

Nan Wang

Rui-ping Li

Junquan Huang

Yongqing Huang

Xiaomin Ren

Yingchun Cheng

Xiaolong Liu
title: Inclined Ultrathin Bi2O2Se Films: A Building Block for Functional van der Waals Heterostructures.
venue: ACS nano
year: 2020