Controlled Layer-by-Layer Etching of MoS₂

Abstract

Two-dimensional (2-D) metal dichalcogenides like molybdenum disulfide (MoS 2 ) may provide a pathway to high-mobility channel materials that are needed for beyondcomplementary metal-oxide-semiconductor (CMOS) devices. Controlling the thickness of these materials at the atomic level will be a key factor in the future development of MoS 2 devices. In this study, we propose a layer-by-layer removal of MoS 2 using the atomic layer etching (ALET) that is composed of the cyclic processing of chlorine (Cl)-radical adsorption and argon (Ar) + ion-beam desorption. MoS 2 etching was not observed with only the Clradical adsorption or low-energy (< 20 eV) Ar + ion-beam desorption steps; however, the use of sequential etching that is composed of the Cl-radical adsorption step and a subsequent Ar + ion-beam desorption step resulted in the complete etching of one monolayer MoS 2 . Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM) indicated the removal of one monolayer MoS 2 with each ALET cycle; therefore, the number of MoS 2 layers could be precisely controlled by using this cyclical etch method. In addition, no noticeable damage or etch residue was observed on the exposed MoS 2 .

Topography preserved microwave plasma etching for top-down layer engineering in MoS2and other van der Waals materials

“…Though various etching schemes have been explored, [19][20][21][22][23][24][25][26][27][28][29] a scalable and controllable thickness reduction down to the mono-or few-layer regimes starting from arbitrary thickness and area has not been demonstrated. Methods utilizing material chemistry exploit either harsh chemicals 19 or reactive plasma environment, are material specific.…”

“…Methods utilizing material chemistry exploit either harsh chemicals 19 or reactive plasma environment, are material specific. [21][22][23]28 Physical etching involves high temperature annealing, 25,27 laser assisted thermal ablation 20 or plasma environments, 24,26,29 results in degraded electrical properties. Postetch electrical characterization has not been performed in most cases, except for a few.…”

Etching Techniques in 2D Materials

“…MoS 2 has a stable structure and does not react with common acids (hydrochloric acid, nitric acid, sulfuric acid) and common alkali (KOH, NaOH) at room temperature. The interaction between Cl plasma as an adsorbent and low‐energy Ar ions as a desorption adsorbent enables controlled layer‐by‐layer etching of MoS 2 . Figure c shows that each cycle etched one layer and the layer number of MoS 2 reduced in argon plasma while MoS 2 kept undamaged in chlorine plasma.…”

“…c) The change of the gap distance between E 1 2g and A 1 g peaks of the MoS 2 Raman spectra during each step of the three ALET cycles. Reproduced with permission . Copyright 2015, American Chemical Society.…”

Applications of Pyrolytic Polyaniline for Renewable Energy Storage

“…This anode exhibited terrific long-term cycling performance with a large capacity of 1203 mAh g À 1 under high current density (2 A g À 1 ) after 2000 cycles. Lin et al [22] endowed negatively charged Si surface with positive charge by in situ polymerization of polyaniline to form S@PANISi@PANI. Then Si@PANI composites were self-assembled with negatively charged graphene oxide (GO) through electrostatic interaction, followed by pyrolysis of Si@PANI/GO to get Si@C/RGO.…”