Microscopy of hydrogen and hydrogen-vacancy defect structures on graphene devices

Dillon Wong, Yang Wang, Wuwei Jin, Hsin-Zon Tsai, Aaron Bostwick, Eli Rotenberg, Roland K. Kawakami, Alex Zettl, Arash A. Mostofi, Johannes Lischner, and Michael F. Crommie

Phys. Rev. B 98, 155436 – Published 24 October 2018

Abstract

We have used scanning tunneling microscopy (STM) to investigate two types of hydrogen defect structures on monolayer graphene supported by hexagonal boron nitride $(h − BN)$ in a gated field-effect transistor configuration. The first H-defect type is created by bombarding graphene with 1-keV ionized hydrogen and is identified as two hydrogen atoms bonded to a graphene vacancy via comparison of experimental data to first-principles calculations. The second type of H defect is identified as dimerized hydrogen and is created by depositing atomic hydrogen having only thermal energy onto a graphene surface. Scanning tunneling spectroscopy (STS) measurements reveal that hydrogen dimers formed in this way open a new elastic channel in the tunneling conductance between an STM tip and graphene.

Received 31 July 2018

DOI:https://doi.org/10.1103/PhysRevB.98.155436

Physics Subject Headings (PhySH)

Defects

Graphene

Density functional theory Scanning tunneling microscopy

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Dillon Wong^1,2, Yang Wang^1,2, Wuwei Jin³, Hsin-Zon Tsai^1,2, Aaron Bostwick⁴, Eli Rotenberg⁴, Roland K. Kawakami^5,6, Alex Zettl^1,2,7, Arash A. Mostofi³, Johannes Lischner³, and Michael F. Crommie^1,2,7,*

¹Department of Physics, University of California at Berkeley, Berkeley, California 94720, USA
²Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
³Departments of Materials and Physics, and The Thomas Young Centre for Theory and Simulation of Materials, Imperial College London, London SW7 2AZ, United Kingdom
⁴Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
⁵Department of Physics and Astronomy, University of California, Riverside, California 92521, USA
⁶Department of Physics, The Ohio State University, Columbus, Ohio 43210, USA
⁷Kavli Energy NanoSciences Institute at the University of California, Berkeley and the Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA

^*Author to whom correspondence should be addressed: crommie@berkeley.edu

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Issue

Vol. 98, Iss. 15 — 15 October 2018

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Images

Figure 1
(a) STM topographic image of graphene/ $h − BN$ after bombarding the surface with 1-keV hydrogen ions (hydrogen dose procedure #1). Triangular defects with lima-bean-shaped (LB) centers are seen. (b) Zoomed-in topographic image of one triangular defect. (c) STM topographic image of a triangular defect before rotation of the LB center. (d) Same triangular defect as in (c) after rotating the LB center by 120° due to STM tip raster scan. Tunneling parameters: (a) $V_{s} = 500 mV, I = 2 pA$ ; (b) $V_{s} = 200 mV, I = 500 pA$ ; (c),(d) $V_{s} = 250 mV, I = 50 pA$ .
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Figure 2
(a) Ball-and-stick model adjacent to simulated STM image of a monohydrogen monovacancy $(V_{s} = - 1.36 V)$ . (b) Same as (a) for a dihydrogen monovacancy.
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Figure 3
(a) STM topographic image of graphene/ $h − BN$ surface after deposition of atomic hydrogen at room temperature (hydrogen dose procedure #2). Rounded rectangular protrusions can be observed on the surface in three different rotational configurations indicated by blue dashed lines. (b) Atomically resolved honeycomb lattice of graphene substrate in (a) and its Fourier transform (inset). (c) Zoomed-in topographic image of one rectangular protrusion with the color scale adjusted to reveal four “legs” positioned at the corners. The inset shows a line profile of the protrusion along the dashed blue line. Tunneling parameters: (a) $V_{s} = 500 mV, I = 60 pA$ ; (b) $V_{s} = - 1 V, I = 2 nA$ ; (c) $V_{s} = 500 mV, I = 60 pA$ .
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Figure 4
(a) dI/dV spectrum of $n$ -doped graphene substrate (black curve) and rounded rectangular protrusion (red curve). (b) Same as (a) for neutral graphene. (c) Same as (a) for $p$ -doped graphene. Initial tunneling parameters: $V_{s} = 500 mV, I = 60 pA$ , 6 mV ac modulation; (a) $V_{g} = - 20 V$ ; (b) $V_{g} = - 30 V$ ; (c) $V_{g} = - 40 V$ .
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Figure 5
(a) Sketch of graphene reciprocal space. The blue dashed arrows are primitive reciprocal lattice vectors and the orange hexagon is the graphene Brillouin zone. (b) Real-space representation of graphene. The black circles represent carbon atoms, the black lines are carbon-carbon bonds, and the green arrows are primitive lattice vectors. A pair of H atoms sitting on nearest-neighbor carbon atoms is called an ortho dimer, while a pair of H atoms sitting on opposite sides of a graphene hexagon is called a para dimer. The blue dashed lines connecting the H atoms in a pair are parallel to the reciprocal lattice vectors in (a). (c) Ball-and-stick model and simulated STM image of an ortho dimer (for $V_{s} = - 1.36 V$ on the left and $V_{s} = + 1.36 V$ on the right). (d) Same as (c) for a para dimer.
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