title: Chemical Stabilization of 1T' Phase Transition Metal Dichalcogenides with Giant Optical Kerr Nonlinearity.
abstract: The 2H-to-1T' phase transition in transition metal dichalcogenides (TMDs) has been exploited to phase-engineer TMDs for applications in which the metallicity of the 1T' phase is beneficial. However, phase-engineered 1T'-TMDs are metastable; thus, stabilization of the 1T' phase remains an important challenge to overcome before its properties can be exploited. Herein, we performed a systematic study of the 2H-to-1T' phase evolution by lithiation in ultrahigh vacuum. We discovered that by hydrogenating the intercalated Li to form lithium hydride (LiH), unprecedented long-term (>3 months) air stability of the 1T' phase can be achieved. Most importantly, this passivation method has wide applicability for other alkali metals and TMDs. Density functional theory calculations reveal that LiH is a good electron donor and stabilizes the 1T' phase against 2H conversion, aided by the formation of a greatly enhanced interlayer dipole-dipole interaction. Nonlinear optical studies reveal that air-stable 1T'-TMDs exhibit much stronger optical Kerr nonlinearity and higher optical transparency than the 2H phase, which is promising for nonlinear photonic applications.
authors.affiliation: Department of Chemistry, National University of Singapore , Singapore 117543, Singapore.|NUS Graduate School for Integrative Sciences and Engineering, Centre for Life Sciences, National University of Singapore , #05-01, 28 Medical Drive, Singapore 117456, Singapore.
authors.forename: Sherman J R
authors.identifier: 0000-0003-1591-3497
authors.initials: SJ
authors.lastname: Tan
authors.affiliation: Department of Chemistry, National University of Singapore , Singapore 117543, Singapore.|NUS Graduate School for Integrative Sciences and Engineering, Centre for Life Sciences, National University of Singapore , #05-01, 28 Medical Drive, Singapore 117456, Singapore.
authors.forename: Ibrahim
authors.initials: I
authors.lastname: Abdelwahab
authors.affiliation: SZU-NUS Collaborative Innovation Center for Optoelectronic Science & Technology, Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province, College of Optoelectronic Engineering, Shenzhen University , Shenzhen 518060, China.|Department of Physics, National University of Singapore , Singapore 117551, Singapore.
authors.forename: Zijing
authors.initials: Z
authors.lastname: Ding
authors.affiliation: Department of Chemistry, National University of Singapore , Singapore 117543, Singapore.|NUS Graduate School for Integrative Sciences and Engineering, Centre for Life Sciences, National University of Singapore , #05-01, 28 Medical Drive, Singapore 117456, Singapore.
authors.forename: Xiaoxu
authors.initials: X
authors.lastname: Zhao
authors.affiliation: Centre for Micro-Photonics, Faculty of Science Engineering and Technology, Swinburne University of Technology , Hawthorn, Victoria 3122, Australia.
authors.forename: Tieshan
authors.initials: T
authors.lastname: Yang
authors.affiliation: Department of Physics, National University of Singapore , Singapore 117551, Singapore.
authors.forename: Gabriel Z J
authors.initials: GZ
authors.lastname: Loke
authors.affiliation: Centre for Micro-Photonics, Faculty of Science Engineering and Technology, Swinburne University of Technology , Hawthorn, Victoria 3122, Australia.
authors.forename: Han
authors.initials: H
authors.lastname: Lin
authors.affiliation: Department of Physics, National University of Singapore , Singapore 117551, Singapore.|Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore , Singapore 117546, Singapore.
authors.forename: Ivan
authors.initials: I
authors.lastname: Verzhbitskiy
authors.affiliation: Department of Chemistry, National University of Singapore , Singapore 117543, Singapore.|NUS Graduate School for Integrative Sciences and Engineering, Centre for Life Sciences, National University of Singapore , #05-01, 28 Medical Drive, Singapore 117456, Singapore.
authors.forename: Sock Mui
authors.initials: SM
authors.lastname: Poh
authors.affiliation: Department of Chemistry, National University of Singapore , Singapore 117543, Singapore.
authors.forename: Hai
authors.initials: H
authors.lastname: Xu
authors.affiliation: Department of Chemistry, National University of Singapore , Singapore 117543, Singapore.
authors.forename: Chang Tai
authors.initials: CT
authors.lastname: Nai
authors.affiliation: Materials Science & Technology Division, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States.
authors.forename: Wu
authors.initials: W
authors.lastname: Zhou
authors.affiliation: Department of Chemistry, National University of Singapore , Singapore 117543, Singapore.|Department of Physics, National University of Singapore , Singapore 117551, Singapore.|Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore , Singapore 117546, Singapore.
authors.forename: Goki
authors.initials: G
authors.lastname: Eda
authors.affiliation: Centre for Micro-Photonics, Faculty of Science Engineering and Technology, Swinburne University of Technology , Hawthorn, Victoria 3122, Australia.
authors.forename: Baohua
authors.initials: B
authors.lastname: Jia
authors.affiliation: Department of Chemistry, National University of Singapore , Singapore 117543, Singapore.|Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore , Singapore 117546, Singapore.
authors.forename: Kian Ping
authors.identifier: 0000-0002-1491-743X
authors.initials: KP
authors.lastname: Loh