title: Atomic Layer Etching Mechanism of MoS2for Nanodevices.
abstract: Among the layered transition metal dichalcogenides (TMDs) that can form stable two-dimensional crystal structures, molybdenum disulfide (MoS2) has been intensively investigated because of its unique properties in various electronic and optoelectronic applications with different band gap energies from 1.29 to 1.9 eV as the number of layers decreases. To control the MoS2layers, atomic layer etching (ALE) (which is a cyclic etching consisting of a radical-adsorption step such as Cl adsorption and a reacted-compound-desorption step via a low-energy Ar+-ion exposure) can be a highly effective technique to avoid inducing damage and contamination that occur during the reactive steps. Whereas graphene is composed of one-atom-thick layers, MoS2is composed of three-atom-thick S(top)-Mo(mid)-S(bottom)layers; therefore, the ALE mechanisms of the two structures are significantly different. In this study, for MoS2ALE, the Cl radical is used as the adsorption species and a low-energy Ar+ion is used as the desorption species. A MoS2ALE mechanism (by which the S(top), Mo(mid), and S(bottom)atoms are sequentially removed from the MoS2crystal structure due to the trapped Cl atoms between the S(top)layer and the Mo(mid)layer) is reported according to the results of an experiment and a simulation. In addition, the ALE technique shows that a monolayer MoS2field effect transistor (FET) fabricated after one cycle of ALE is undamaged and exhibits electrical characteristics similar to those of a pristine monolayer MoS2FET. This technique is also applicable to all layered TMD materials, such as tungsten disulfide (WS2), molybdenum diselenide (MoSe2), and tungsten diselenide (WSe2).
authors.forename: Ki Seok
authors.initials: KS
authors.lastname: Kim
authors.forename: Ki Hyun
authors.initials: KH
authors.lastname: Kim
authors.forename: Yeonsig
authors.initials: Y
authors.lastname: Nam
authors.forename: Jaeho
authors.initials: J
authors.lastname: Jeon
authors.affiliation: School of Materials Science and Engineering, Korea Advanced Institute of Science and Technology (KAIST) , 291 Daehak-ro, Yuseong-gu, Daejeon 305-701, Republic of Korea.
authors.forename: Soonmin
authors.initials: S
authors.lastname: Yim
authors.affiliation: Department of Computer Science, Stanford University , Stanford, California 94305, United States.
authors.forename: Eric
authors.initials: E
authors.lastname: Singh
authors.forename: Jin Yong
authors.identifier: http://orcid.org/0000-0003-0360-5059
authors.initials: JY
authors.lastname: Lee
authors.forename: Sung Joo
authors.identifier: http://orcid.org/0000-0003-1284-3593
authors.initials: SJ
authors.lastname: Lee
authors.affiliation: School of Materials Science and Engineering, Korea Advanced Institute of Science and Technology (KAIST) , 291 Daehak-ro, Yuseong-gu, Daejeon 305-701, Republic of Korea.
authors.forename: Yeon Sik
authors.identifier: http://orcid.org/0000-0002-7709-8347
authors.initials: YS
authors.lastname: Jung
authors.forename: Geun Young
authors.identifier: http://orcid.org/0000-0001-7516-8404
authors.initials: GY
authors.lastname: Yeom
authors.forename: Dong Woo
authors.initials: DW
authors.lastname: Kim
keywords: atomic layer etching (ALE); field effect transistors (FETs); low-energy Ar+-ion; molybdenum disulfide (MoS2); transition metal dichalcogenides (TMDs)