Bound Hole States Associated to Individual Vanadium Atoms Incorporated into Monolayer ${\mathrm{WSe}}_{2}$

Bound Hole States Associated to Individual Vanadium Atoms Incorporated into Monolayer ${WSe}_{2}$

Pierre Mallet, Florian Chiapello, Hanako Okuno, Hervé Boukari, Matthieu Jamet, and Jean-Yves Veuillen

Phys. Rev. Lett. 125, 036802 – Published 13 July 2020

Abstract

Doping a two-dimensional semiconductor with magnetic atoms is a possible route to induce magnetism in the material. We report on the atomic structure and electronic properties of monolayer ${WSe}_{2}$ intentionally doped with vanadium atoms by means of scanning transmission electron microscopy and scanning tunneling microscopy and spectroscopy. Most of the V atoms incorporate at W sites. These $V_{W}$ dopants are negatively charged, which induces a localized bound state located 140 meV above the valence band maximum. The overlap of the electronic potential of two charged $V_{W}$ dopants generates additional in-gap states. Eventually, the negative charge may suppress the magnetic moment on the $V_{W}$ dopants.

Received 19 December 2019
Accepted 9 June 2020

DOI:https://doi.org/10.1103/PhysRevLett.125.036802

Physics Subject Headings (PhySH)

Dopants Local density of states

Transition metal dichalcogenides

Scanning tunneling spectroscopy

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Pierre Mallet^1,2,*, Florian Chiapello ^1,2, Hanako Okuno³, Hervé Boukari ^1,2, Matthieu Jamet⁴, and Jean-Yves Veuillen^1,2

¹Université Grenoble Alpes, Institut Neel, F-38042 Grenoble, France
²CNRS, Institut Neel, F-38042 Grenoble, France
³Université Grenoble Alpes, CEA, IRIG-MEM, 38000 Grenoble, France
⁴Université Grenoble Alpes, CEA, CNRS, Grenoble INP, IRIG-SPINTEC, 38000 Grenoble, France

^*pierre.mallet@neel.cnrs.fr

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Vol. 125, Iss. 3 — 17 July 2020

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Figure 1
STM and ADF-STEM images of individual substitutional $V_{W}$ dopants incorporated in monolayer ${WSe}_{2}$ . (a),(b) STM images of a single $V_{W}$ dopant, at sample bias $V_{S} = - 1.5 V$ (a) and $V_{S} = + 1.2 V$ (b). Image sizes: $4 \times 4 {nm}^{2}$ . (c) Apparent height of the individual dopant, measured along the dashed lines drawn on (a) and (b) (red and blue curves, respectively). (d) ADF-STEM image of a V-doped ${WSe}_{2}$ monolayer, centered on a substitutional $V_{W}$ dopant. (e) Intensity profile along the vertical arrow in (d).
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Figure 2
STS performed at 8.5 K on two neighboring $V_{W}$ dopants on 1L ${WSe}_{2}$ on single-layer graphene (SLG). (a) Local $d I / d V (V)$ spectra of the two dopants labeled $B$ and $C$ (respectively, purple and red curves). The black curve corresponds to a spectrum performed on a nearby defect-free ${WSe}_{2}$ area, the letter $Γ$ indicating the $Γ$ peak, corresponding to the energy position of the valence band maximum at $Γ$ point. The inset shows a constant current STM image of the two dopants. (b) Same as (a) with a magnified vertical scale. The white box corresponds to the TMD band gap. VBM: valence band maximum, CBM: conductance band minimum. Spectra measured above the two $V_{W}$ dopants are almost identical, both show a bound state (labeled $*$ ) located $\sim 0.14 eV$ above the VBM of the TMD. The red and purple curves are shifted vertically for clarity.
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Figure 3
STS results on a single $V_{W}$ dopant on 1L ${WSe}_{2}$ on bilayer graphene. (a) $d I / d V (x, V)$ map taken along the 10-nm-long line crossing the dopant. The energy positions of the VBM, CBM, and $Γ$ peak are indicated on the map. The bound state is indicated by the white arrow. The inset shows an STM map of the area, the white line indicating the path of the tip for the map shown on (a). (b) Two $d I / d V (V)$ spectra performed at two different $x$ positions measured from the defect center, as indicated in the inset of (a). The red curve is shifted by $δ = + 30 mV$ with respect to the green curve (see text). (c) Plot of the shift $δ$ as a function of $x$ , evidencing a band bending by 50 meV over 2 nm.
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Figure 4
STS data taken on a pair of $V_{W}$ dopants separated by 1.3 nm. (a) Constant current STM image of the region. The 1L- ${WSe}_{2}$ flake lies on SLG. Image size: $20.0 \times 9.5 {nm}^{2}$ , $V_{S} = - 1.5 V$ . (b) $d I / d V (x, V)$ map, plotted in logarithmic color scale, taken along the 7.0-nm-long line indicated by the green arrow on (a). Three conductance peaks are highlighted, labeled 1, 2, and 3. (c) Individual spectra measured on the two lobes of the dimer indicated by the vertical arrows on (b).
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Physical Review Letters

Bound Hole States Associated to Individual Vanadium Atoms Incorporated into Monolayer WSe2

Pierre Mallet, Florian Chiapello, Hanako Okuno, Hervé Boukari, Matthieu Jamet, and Jean-Yves Veuillen

Phys. Rev. Lett. 125, 036802 – Published 13 July 2020

Abstract

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Bound Hole States Associated to Individual Vanadium Atoms Incorporated into Monolayer ${WSe}_{2}$