Monolayer charge-neutral graphene on platinum with extremely weak electron-phonon coupling

Wei Yao, Eryin Wang, Ke Deng, Shuzhen Yang, Wenyun Wu, Alexei V. Fedorov, Sung-Kwan Mo, Eike F. Schwier, Mingtian Zheng, Yohei Kojima, Hideaki Iwasawa, Kenya Shimada, Kaili Jiang, Pu Yu, Jia Li, and Shuyun Zhou

Phys. Rev. B 92, 115421 – Published 11 September 2015

Abstract

Epitaxial growth of graphene on transition metal substrates is an important route for obtaining large scale graphene. However, the interaction between graphene and the substrate often leads to multiple orientations, distorted graphene band structure, large doping, and strong electron-phonon coupling. Here we report the growth of monolayer graphene with high crystalline quality on Pt(111) substrate by using a very low concentration of an internal carbon source with high annealing temperature. The controlled growth leads to electronically decoupled graphene: it is nearly charge neutral and has extremely weak electron-phonon coupling (coupling strength $λ \approx 0.056$ ) as revealed by angle-resolved photoemission spectroscopic measurements. The thermodynamics and kinetics of the carbon diffusion process are investigated by density functional theory calculations. Such graphene with negligible graphene-substrate interaction provides an important platform for fundamental research as well as device applications when combined with a nondestructive sample transfer technique.

Received 14 April 2015

DOI:https://doi.org/10.1103/PhysRevB.92.115421

Authors & Affiliations

Wei Yao¹, Eryin Wang¹, Ke Deng¹, Shuzhen Yang¹, Wenyun Wu¹, Alexei V. Fedorov², Sung-Kwan Mo², Eike F. Schwier³, Mingtian Zheng³, Yohei Kojima³, Hideaki Iwasawa³, Kenya Shimada³, Kaili Jiang^1,4, Pu Yu^1,4, Jia Li⁵, and Shuyun Zhou^1,4,*

¹State Key Laboratory of Low Dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing 100084, P.R. China
²Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
³Hiroshima Synchrotron Radiation Center, Hiroshima University, Higashi-Hiroshima 739-0046, Japan
⁴Collaborative Innovation Center of Quantum Matter, Beijing 100084, P.R. China
⁵Key Laboratory of Thermal Management Engineering and Materials, Graduate School at Shenzhen, Tsinghua University, Shenzhen 518055, P.R. China

^*Corresponding author: syzhou@mail.tsinghua.edu.cn

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Vol. 92, Iss. 11 — 15 September 2015

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Images

Figure 1
(a) and (b) LEED patterns after annealing Pt(111) crystal to (a) $850^{\circ} C$ and (b) $1600^{\circ} C$ with electron energy of 140 eV. The red arrow points to the Pt diffraction spot, and the blue arrow points to the graphene diffraction arc or spot. (c) Schematic drawing of the crystal structure with a superlattice of $2 \times 2$ /graphene on $\sqrt{3} \times \sqrt{3} R 30$ °/Pt(111). Blue balls are platinum atoms and orange balls are carbon atoms. The red and green arrows are the unit vectors of the primary cell for graphene and the superlattice. The purple arrows are the unit vectors for the substrate. (d) XPS spectrum of the as-grown graphene measured at a photon energy of 360 eV. (e) Raman spectrum of the as-grown graphene. (f) AFM morphology of the as-grown graphene. The scale bar is 500 nm. (g) Zoom-in 3D view of the AFM image. The step height is about 2.4 Å and the width of the terrace is approximately 300 nm.
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Figure 2
(a) Schematic drawings of the three possible sites for the carbon atom located within the interlayer space of Pt(111)—octahedral site (O) and two tetrahedral sites (UT and DT). The blue ball is the platinum atom and the orange, gray, and green balls are carbon atoms. (b) Possible diffusion paths for carbon atoms escaping from the ${UT}_{34}$ site to the surface. (c) Formation energy of carbon atoms and energy barriers between carbon sites for intralayer and interlayer diffusion.
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Figure 3
(a) Band structure of the graphene on Pt(111) along the $Γ − K$ direction. The clear $π$ bands and $σ$ bands are indicated by the arrows. The other $π$ band at high binding energy comes from the R0° domain along its $Γ − M$ direction. (b) Measured pointlike Fermi surface map of the graphene. The dashed line indicates the Brillouin zone boundary of the R30° domain. (c) Conical dispersion at the $K$ point. (d)–(h) ARPES data measured along the $Γ − K$ direction at photon energies of 50, 54, 58, 62, and 65 eV, respectively. The corresponding reduced $k_{z}$ values are $0.9 c^{*}, 0.05 c^{*}, 0.20 c^{*}, 0.34 c^{*}$ , and $0.44 c^{*}$ ( $c^{*} = 2 π / 6.708$ Å = 0.937 Å $^{- 1}$ ). (i) Extracted dispersions from data shown in (d)–(h).
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Figure 4
(a) ARPES data along the $Γ − K$ direction. (b) MDCs (black) and the fitting curves (red) for (a). The green markers show the peak positions. (c) Extracted dispersion from (b). The upper inset shows the cut direction of (a) and (d). The lower inset shows the MDC peak width of (b). (d) Linear dispersion near $K$ point (vertical to $Γ − K$ direction). (e) MDCs (black) and the fitting curves (red) for (d). (f) Extracted dispersion from (e). The Dirac point locates at 60( $\pm 5$ ) meV above Fermi level.
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