| المؤلفون: |
Schuler B; Molecular Foundry , Lawrence Berkeley National Laboratory , Berkeley , California 94720 , United States., Lee JH; Molecular Foundry , Lawrence Berkeley National Laboratory , Berkeley , California 94720 , United States.; Department of Physics , University of California at Berkeley , Berkeley , California 94720 , United States., Kastl C; Molecular Foundry , Lawrence Berkeley National Laboratory , Berkeley , California 94720 , United States.; Walter-Schottky-Institut and Physik-Department , Technical University of Munich , Garching 85748 , Germany., Cochrane KA; Molecular Foundry , Lawrence Berkeley National Laboratory , Berkeley , California 94720 , United States., Chen CT; Molecular Foundry , Lawrence Berkeley National Laboratory , Berkeley , California 94720 , United States., Refaely-Abramson S; Molecular Foundry , Lawrence Berkeley National Laboratory , Berkeley , California 94720 , United States.; Department of Materials and Interfaces , Weizmann Institute of Science , Rehovot 7610001 , Israel., Yuan S; Key Laboratory of Artificial Micro- and Nano-structures of Ministry of Education and School of Physics and Technology , Wuhan University , Wuhan 430072 , China., van Veen E; Radboud University of Nijmegen , Institute for Molecules and Materials , Heijendaalseweg 135 , 6525 AJ , Nijmegen , The Netherlands., Roldán R; Instituto de Ciencia de Materiales de Madrid , ICMM-CSIC, Cantoblanco, E-28049 , Madrid , Spain., Borys NJ; Department of Physics , Montana State University , Bozeman , Montana 59717 , United States., Koch RJ; Advanced Light Source , Lawrence Berkeley National Laboratory , Berkeley , California 94720 , United States., Aloni S; Molecular Foundry , Lawrence Berkeley National Laboratory , Berkeley , California 94720 , United States., Schwartzberg AM; Molecular Foundry , Lawrence Berkeley National Laboratory , Berkeley , California 94720 , United States., Ogletree DF; Molecular Foundry , Lawrence Berkeley National Laboratory , Berkeley , California 94720 , United States., Neaton JB; Molecular Foundry , Lawrence Berkeley National Laboratory , Berkeley , California 94720 , United States.; Department of Physics , University of California at Berkeley , Berkeley , California 94720 , United States.; Kavli Energy Nanosciences Institute at Berkeley , Berkeley , California 94720 , United States., Weber-Bargioni A; Molecular Foundry , Lawrence Berkeley National Laboratory , Berkeley , California 94720 , United States. |
| مستخلص: |
Control of impurity concentrations in semiconducting materials is essential to device technology. Because of their intrinsic confinement, the properties of two-dimensional semiconductors such as transition metal dichalcogenides (TMDs) are more sensitive to defects than traditional bulk materials. The technological adoption of TMDs is dependent on the mitigation of deleterious defects and guided incorporation of functional foreign atoms. The first step toward impurity control is the identification of defects and assessment of their electronic properties. Here, we present a comprehensive study of point defects in monolayer tungsten disulfide (WS 2 ) grown by chemical vapor deposition using scanning tunneling microscopy/spectroscopy, CO-tip noncontact atomic force microscopy, Kelvin probe force spectroscopy, density functional theory, and tight-binding calculations. We observe four different substitutional defects: chromium (Cr W ) and molybdenum (Mo W ) at a tungsten site, oxygen at sulfur sites in both top and bottom layers (O S top/bottom), and two negatively charged defects (CD type I and CD type II). Their electronic fingerprints unambiguously corroborate the defect assignment and reveal the presence or absence of in-gap defect states. Cr W forms three deep unoccupied defect states, two of which arise from spin-orbit splitting. The formation of such localized trap states for Cr W differs from the Mo W case and can be explained by their different d shell energetics and local strain, which we directly measured. Utilizing a tight-binding model the electronic spectra of the isolectronic substitutions O S and Cr W are mimicked in the limit of a zero hopping term and infinite on-site energy at a S and W site, respectively. The abundant CDs are negatively charged, which leads to a significant band bending around the defect and a local increase of the contact potential difference. In addition, CD-rich domains larger than 100 nm are observed, causing a work function increase of 1.1 V. While most defects are electronically isolated, we also observed hybrid states formed between Cr W dimers. The important role of charge localization, spin-orbit coupling, and strain for the formation of deep defect states observed at substitutional defects in WS 2 as reported here will guide future efforts of targeted defect engineering and doping of TMDs. |
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