Electronic Self-Passivation of Single Vacancy in Black Phosphorus via Ionization

Hanyan Fang, Aurelio Gallardo, Dikshant Dulal, Zhizhan Qiu, Jie Su, Mykola Telychko, Harshitra Mahalingam, Pin Lyu, Yixuan Han, Yi Zheng, Yongqing Cai, Aleksandr Rodin, Pavel Jelínek, and Jiong Lu

Phys. Rev. Lett. 128, 176801 – Published 26 April 2022

Abstract

We report that monoelemental black phosphorus presents a new electronic self-passivation scheme of single vacancy (SV). By means of low-temperature scanning tunneling microscopy and noncontact atomic force microscopy, we demonstrate that the local reconstruction and ionization of SV into negatively charged ${SV}^{-}$ leads to the passivation of dangling bonds and, thus, the quenching of in-gap states, which can be achieved by mild thermal annealing or STM tip manipulation. SV exhibits a strong and symmetric Friedel oscillation (FO) pattern, while ${SV}^{-}$ shows an asymmetric FO pattern with local perturbation amplitude reduced by one order of magnitude and a faster decay rate. The enhanced passivation by forming ${SV}^{-}$ can be attributed to its weak dipolelike perturbation, consistent with density-functional theory numerical calculations. Therefore, self-passivated ${SV}^{-}$ is electrically benign and acts as a much weaker scattering center, which may hold the key to further enhance the charge mobility of black phosphorus and its analogs.

Received 7 July 2021
Revised 28 February 2022
Accepted 11 March 2022

DOI:https://doi.org/10.1103/PhysRevLett.128.176801

Physics Subject Headings (PhySH)

Point defects Vacancies

Elemental semiconductors Phosphorene

Density functional theory Noncontact atomic force microscopy Scanning tunneling microscopy Scanning tunneling spectroscopy

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Hanyan Fang ^1,†, Aurelio Gallardo ^2,3,†, Dikshant Dulal ⁴, Zhizhan Qiu¹, Jie Su¹, Mykola Telychko¹, Harshitra Mahalingam ⁴, Pin Lyu¹, Yixuan Han¹, Yi Zheng ⁵, Yongqing Cai⁶, Aleksandr Rodin ^4,7,*, Pavel Jelínek ^2,8,*, and Jiong Lu ^1,7,*

¹Department of Chemistry, National University of Singapore, Singapore 117543, Singapore
²Institute of Physics, Academy of Sciences of the Czech Republic, Prague 162 00, Czech Republic
³Department of Condensed Matter Physics, Faculty of Mathematics and Physics, Charles University, V Holešovičkách 2, Prague 180 00, Czech Republic
⁴Yale-NUS College, 16 College Avenue West, Singapore 138527, Singapore
⁵Zhejiang Province Key Laboratory of Quantum Technology and Device, Department of Physics, Zhejiang University, Hangzhou 312007, China
⁶Joint Key Laboratory of Ministry of Education, Institute of Applied Physics and Materials Engineering, University of Macau, Taipa, Macau 999078, China
⁷Centre for Advanced 2D Materials (CA2DM), National University of Singapore, Singapore 117543, Singapore
⁸Regional Centre of Advanced Technologies and Materials, Czech Advanced Technology and Research Institute (CATRIN), Palacký University Olomouc, Olomouc 78371, Czech Republic

^*Corresponding author.
^†These authors contributed equally to this work.

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Issue

Vol. 128, Iss. 17 — 29 April 2022

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Images

Figure 1
Thermally driven self-passivation of SV into ${SV}^{-}$ via local reconstruction and ionization. (a),(b) Schematics highlight unsaturated SV with dangling bonds and self-passivated ( ${SV}^{-}$ ), respectively. (c),(d) STM images of BP surface taken before and after the thermal annealing at 453 K followed by rapid cooling. The crystallographic directions are indicated in (d). STM set points: $V_{S} = - 1.0 V$ and $I = 0.3 nA$ .
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Figure 2
Physical characterizations of ${SV}^{-}$ . (a) High-resolution STM image of ${SV}^{-}$ ( $V_{S} = - 0.6 V$ and $I = 0.3 nA$ ). (b) Atomic structure for ${SV}^{-}$ with labeled crystallographic directions and the corresponding side view (bottom panel). The yellow (violet) atoms indicate the P atoms at the top (bottom) sublayers. (c) Atom-resolved nc-AFM image of ${SV}^{-}$ . (d) Simulated nc-AFM image of ${SV}^{-}$ by the probe particle model. (e) $x − z$ color mapping of spatial-dependent LCPD extracted from KPFM measurements across ${SV}^{-}$ , along the line marked at the bottom of the STM image. (f) Frequency shift ( $d f$ ) measured as a function of the applied sample bias right over and 2.12 nm away from ${SV}^{-}$ at a relative height of $Z = - 40 pm$ with respect to the reference point: $Z = 0 pm$ ( $V_{S} = - 1.0 V$ and $I = 50 pA$ ). Parabolic fits and corresponding parabolic maximum values are indicated in the plot.
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Figure 3
Electronic structure of ${SV}^{-}$ . (a),(b) Color-coded $d I / d V$ spectra taken along armchair direction across SV (a) and ${SV}^{-}$ (b), where the positions taken for the line spectra are marked by white dashed lines in the corresponding STM images (upper panel). Point $d I / d V$ spectra taken above SV ( ${SV}^{-}$ ) are compared with the pristine surface in the right panels. (c),(d) Calculated DOS for SV ( ${SV}^{-}$ ) and pristine BP (indicated by dashed lines). (e),(f) $d I / d V$ maps taken for ${SV}^{-}$ at $V_{S} = 0.4 V$ and $V_{S} = - 0.1 V$ . (g),(h) Simulated $d I / d V$ maps at an energy of 0.47 and $- 0.47 V$ , which are indicated by gray dashed lines in (d).
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Figure 4
Probing Friedel oscillations of SV and ${SV}^{-}$ . (a),(b) Spatial $d I / d V$ spatial maps taken at $V_{S} = - 0.6 V$ for SV and ${SV}^{-}$ , respectively. (c),(d) Cross-section data across the center of SV and ${SV}^{-}$ along the armchair direction. The fitted curves for FO at both sides of defect are presented in red. Note that the discrepancy in the oscillation wavelength close to the defect center between experiment and theory can be attributed to a strong LDOS modulation at the VB edge of SV that may modify the local bulk bands. (e),(f) Simulated spectral function maps at $- 0.6 eV$ for SV and ${SV}^{-}$ , respectively.
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