Commensurate-incommensurate transition and strain relief patterns in monolayer ${\mathrm{C}}_{60}$ on Cd(0001)

Commensurate-incommensurate transition and strain relief patterns in monolayer $C_{60}$ on Cd(0001)

Zilong Wang, Kai Sun, Minlong Tao, Daxiao Yang, Mingxia Shi, Zuo Li, and Junzhong Wang

Phys. Rev. B 103, 245430 – Published 23 June 2021

Abstract

We have studied the commensurate-incommensurate phase transition, rotation epitaxy, and strain relief patterns in $C_{60}$ overlayers grown on Cd(0001) with a low-temperature scanning tunneling microscopy. When deposited at low temperature (∼200 K), $C_{60}$ molecules form the 10×10 high-order commensurate (HOC) phase with two different half-unit cells, resembling the $Si (111) − 7 \times 7$ surface. Postannealing at room temperature (RT) results in the transition from HOC phase to incommensurate phase, in which strain relaxation takes place in the form of periodic vacancies and $C_{60}$ heptamer arrays. In the case of RT deposition, parallel stripe domain walls appeared in the commensurate $2 \sqrt{3} \times 2 \sqrt{3}$ R30° phase. These results provide essential information for understanding the strain relaxation mechanism, and the role of substrate temperatures in the process of $C_{60}$ thin films growth.

Received 13 April 2021
Revised 30 May 2021
Accepted 15 June 2021

DOI:https://doi.org/10.1103/PhysRevB.103.245430

Physics Subject Headings (PhySH)

Epitaxial strain Surface & interfacial phenomena

2-dimensional systems Graphene Monolayer films

Epitaxy Scanning tunneling microscopy

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Zilong Wang , Kai Sun^*, Minlong Tao, Daxiao Yang , Mingxia Shi, Zuo Li , and Junzhong Wang^*

School of Physical Science and Technology, Southwest University, Chongqing 400715, China

^*Corresponding authors: skqtt@swu.edu.cn; jzwangcn@swu.edu.cn

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Comment on “Commensurate-incommensurate transition and strain relief patterns in monolayer $C_{60}$ on Cd(0001)”

Roman Forker and Torsten Fritz

Phys. Rev. B 106, 047401 (2022)

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Vol. 103, Iss. 24 — 15 June 2021

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Figure 1
The 10×10 high-order commensurate (HOC) phase and incommensurate phase of $C_{60}$ monolayer on Cd(0001). (a) Filled-state STM image of the HOC phase obtained by low-temperature deposition (200 K), −0.4 V. (b) Empty-state STM image of the HOC phase showing the distinct contrasts between the two half-unit cells (HUCs), 0.2 V. (c) Close-up view of the HOC phase, 0.2 V. (d) Schematic structural model of the 10×10 HOC phase. (e) Periodic vacancies and $C_{60}$ heptamer arrays appeared in the incommensurate phase of R2° domain after annealing to RT, 1.5 V. (f) Line scan corresponding to the red line in (e). The images sizes are 20 nm×19.5 nm for (a) and (b), 10 nm×10 nm for (c), 14.6 nm×13.9 nm for (e).
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Figure 2
Optimized configurations of a $C_{60}$ molecule adsorbed on Cd(0001) surface. Top views of the structural models (a)–(e) and simulated empty-state STM images (a′)–(e′) of five kinds of high-symmetry orientations corresponding to the $C_{60}$ with a 6:6 bond (a), (a′), hexagon (b), (b′), carbon atom (c), (c′), pentagon (d), (d′), and 5:6 bond (e), (e′) facing up, respectively.
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Figure 3
Stripe domain walls in the commensurate 2√3×2√3 R30° phase obtained by RT deposition. (a) The $C_{60}$ molecules inside the two neighboring domains show the opposite orientations. The antiphase domain boundaries constitute stripe domain walls, 20 nm×20 nm, 1.8 V (b) Close-up view of the 2√3×2√3 R30° phase, 10 nm×10 nm, 1.8 V. The $C_{60}$ molecules exhibit a bright round protrusion with a small off-center hole. (c) Differential conductance $d I / d V$ spectrum acquired in the commensurate 2√3×2√3 R30° domain with a set point of $U = 1.0 V, I = 70 pA$ . The LUMO level splits into two discrete peaks at 0.34 and 0.68 eV, respectively, and the HOMO-LUMO gap is 2.5 eV.
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Figure 4
Second $C_{60}$ layer obtained by RT deposition. (a) Kagome structure showing √13×√13 superstructure in a R17° domain, 15 nm×15 nm, −0.5 V. (b) Zoom-in image of the kagome structure, 6 nm×6 nm, −0.5 V. The central $C_{60}$ molecule is surrounded by six molecules at the inner small hexagon and 12 molecules at outer large hexagon. (c) Schematic model of the kagome structure. The six small triangles made of three molecules are located at the asymmetric positions with respect to the large hexagon, constituting the anticlockwise pinwheel pattern.
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Figure 5
(a) A $C_{60}$ monolayer island showing triangular domains formed at 330 K, 60 nm×60 nm, 0.4 V. (b) Close-up view of the triangular domain, 25 nm×25 nm, 0.4 V.
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Physical Review B

covering condensed matter and materials physics

Commensurate-incommensurate transition and strain relief patterns in monolayer $C_{60}$ on Cd(0001)

Zilong Wang, Kai Sun, Minlong Tao, Daxiao Yang, Mingxia Shi, Zuo Li, and Junzhong Wang

Phys. Rev. B 103, 245430 – Published 23 June 2021

Abstract

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Comment on “Commensurate-incommensurate transition and strain relief patterns in monolayer $C_{60}$ on Cd(0001)”

Roman Forker and Torsten Fritz

Phys. Rev. B 106, 047401 (2022)

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Physical Review B

covering condensed matter and materials physics

Commensurate-incommensurate transition and strain relief patterns in monolayer C60 on Cd(0001)

Zilong Wang, Kai Sun, Minlong Tao, Daxiao Yang, Mingxia Shi, Zuo Li, and Junzhong Wang

Phys. Rev. B 103, 245430 – Published 23 June 2021

Abstract

Physics Subject Headings (PhySH)

Authors & Affiliations

Comments & Replies

Comment on “Commensurate-incommensurate transition and strain relief patterns in monolayer C60 on Cd(0001)”

Roman Forker and Torsten Fritz

Phys. Rev. B 106, 047401 (2022)

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Commensurate-incommensurate transition and strain relief patterns in monolayer $C_{60}$ on Cd(0001)

Comment on “Commensurate-incommensurate transition and strain relief patterns in monolayer $C_{60}$ on Cd(0001)”