Imaging Field-Driven Melting of a Molecular Solid at the Atomic Scale

Franklin Liou; Hsin-Zon Tsai; Zachary A H Goodwin; Andrew S Aikawa; Ethan Ha; Michael Hu; Yiming Yang; Kenji Watanabe; Takashi Taniguchi; Alex Zettl; Johannes Lischner; Michael F Crommie

doi:10.1002/adma.202300542

Imaging Field-Driven Melting of a Molecular Solid at the Atomic Scale

Adv Mater. 2023 Sep;35(39):e2300542. doi: 10.1002/adma.202300542. Epub 2023 Jul 13.

Authors

Franklin Liou^{1

2

3}, Hsin-Zon Tsai^{1

2}, Zachary A H Goodwin^{4

5

6}, Andrew S Aikawa^{1

2}, Ethan Ha¹, Michael Hu¹, Yiming Yang¹, Kenji Watanabe⁷, Takashi Taniguchi⁸, Alex Zettl^{1

2

3}, Johannes Lischner⁴, Michael F Crommie^{1

2

3}

Affiliations

¹ Department of Physics, University of California at Berkeley, Berkeley, CA, 94720, USA.
² Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA.
³ Kavli Energy NanoSciences Institute at the University of California at Berkeley, Berkeley, CA, 94720, USA.
⁴ Department of Materials, Imperial College London, Prince Consort Rd, London, SW7 2BB, UK.
⁵ National Graphene Institute, University of Manchester, Booth St. E. Manchester M13 9PL, Manchester, UK.
⁶ School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester, M13 9PL, UK.
⁷ Research Center for Electronic and Optical Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba, 305-0044, Japan.
⁸ Research Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba, 305-0044, Japan.

PMID: 37317869
DOI: 10.1002/adma.202300542

Abstract

Solid-liquid phase transitions are basic physical processes, but atomically resolved microscopy has yet to capture their full dynamics. A new technique is developed for controlling the melting and freezing of self-assembled molecular structures on a graphene field-effect transistor (FET) that allows phase-transition behavior to be imaged using atomically resolved scanning tunneling microscopy. This is achieved by applying electric fields to 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane-decorated FETs to induce reversible transitions between molecular solid and liquid phases at the FET surface. Nonequilibrium melting dynamics are visualized by rapidly heating the graphene substrate with an electrical current and imaging the resulting evolution toward new 2D equilibrium states. An analytical model is developed that explains observed mixed-state phases based on spectroscopic measurement of solid and liquid molecular energy levels. The observed nonequilibrium melting dynamics are consistent with Monte Carlo simulations.

Keywords: field-driven phase transitions; graphene field-effect transistor; molecular solids; nonequilibrium dynamics; solid-liquid phase coexistence.

Abstract

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