Quantification and Healing of Defects in Atomically Thin Molybdenum Disulfide: Beyond the Controlled Creation of Atomic Defects

Kazunori Fujisawa; Bruno R Carvalho; Tianyi Zhang; Néstor Perea-López; Zhong Lin; Victor Carozo; Sérgio L L M Ramos; Ethan Kahn; Adam Bolotsky; He Liu; Ana Laura Elías; Mauricio Terrones

doi:10.1021/acsnano.0c10897

Quantification and Healing of Defects in Atomically Thin Molybdenum Disulfide: Beyond the Controlled Creation of Atomic Defects

ACS Nano. 2021 Jun 22;15(6):9658-9669. doi: 10.1021/acsnano.0c10897. Epub 2021 Mar 23.

Authors

Kazunori Fujisawa^{1

2

3}, Bruno R Carvalho^{1

2

4}, Tianyi Zhang^{2

5}, Néstor Perea-López^{1

2}, Zhong Lin^{1

2}, Victor Carozo^{1

2

6}, Sérgio L L M Ramos⁷, Ethan Kahn^{2

5}, Adam Bolotsky^{1

2}, He Liu^{2

8}, Ana Laura Elías^{1

2

9}, Mauricio Terrones^{1

2

3

5

8}

Affiliations

¹ Department of Physics, The Pennsylvania State University, University Park, Pennsylvania 16802, United States.
² Center for 2-Dimensional and Layered Materials, The Pennsylvania State University, University Park, Pennsylvania 16802, United States.
³ Research Initiative for Supra Materials, Shinshu University, 4-17-1 Wakasato, Nagano 380-8553, Japan.
⁴ Departamento de Física, Universidade Federal do Rio Grande do Norte, Natal, Rio Grande do Norte 59078-970, Brazil.
⁵ Department of Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802, United States.
⁶ Department of Physics, Pontifical Catholic University of Rio de Janeiro, Rio de Janeiro, Rio de Janeiro 22451900, Brazil.
⁷ Centro de Tecnologia em Nanomateriais (CT Nano), Universidade Federal de Minas Gerais, Belo Horizonte, Minas Gerais 30161-970, Brazil.
⁸ Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802, United States.
⁹ Department of Physics, Binghamton University, Binghamton, New York 13902, United States.

PMID: 33754710
DOI: 10.1021/acsnano.0c10897

Abstract

Atomically thin 2D materials provide an opportunity to investigate the atomic-scale details of defects introduced by particle irradiation. Once the atomic configuration of defects and their spatial distribution are revealed, the details of the mesoscopic phenomena can be unveiled. In this work, we created atomically small defects by controlled irradiation of gallium ions with doses ranging from 4.94 × 10¹² to 4.00 × 10¹⁴ ions/cm² on monolayer molybdenum disulfide (MoS₂) crystals. The optical signatures of defects, such as the evolution of defect-activated LA-bands and a broadening of the first-order (E' and A'₁) modes, can be studied by Raman spectroscopy. High-resolution scanning transmission electron microscopy (HR-STEM) analysis revealed that most defects are vacancies of few-molybdenum atoms with surrounding sulfur atoms (V_xMo+yS) at a low ion dose. When increasing the ion dose, the atomic vacancies merge and form nanometer-sized holes. Utilizing HR-STEM and image analysis, we propose the estimation of the finite crystal length (L_fc) via the careful quantification of 0D defects in 2D systems through the formula L_fc = 4.41/ $\sqrt{η_{ion}}$ , where η_ion corresponds to the ion dose. Combining HR-STEM and Raman spectroscopy, the formula to calculate L_fc from Raman features, I(LA)/I(A'₁) = 5.09/L_fc², is obtained. We have also demonstrated an effective route to healing the ion irradiation-induced atomic vacancies by annealing defective MoS₂ in a hydrogen disulfide (H₂S) atmosphere. The H₂S annealing improved the crystal quality of MoS₂ with L_fc greater than the calculated size of the A exciton wave function, which leads to a partial recovery of the photoluminescence signal after its quenching by ion irradiation.

Keywords: defect healing; defects; electronic properties; molybdenum disulfide; transition metal dichalcogenides; two-dimensional material; vibrational properties.