2023 User Research Highlights
Confined Monolayer Ag As a Large Gap 2D Semiconductor and Its Momentum Resolved Excited States

Project Summary: 2D materials have intriguing quantum phenomena that are distinctively different from their bulk counterparts. Recently, epitaxially synthesized wafer-scale 2D metals, composed of elemental atoms, are attracting attention not only for their potential applications but also for exotic quantum effects such as superconductivity. By mapping momentum-resolved electronic states using time-resolved and angle-resolved photoemission spectroscopy (ARPES), we reveal that monolayer Ag confined between bilayer graphene and SiC is a large gap (>1 eV) 2D semiconductor, consistent with ab initio GW calculations. The measured valence band dispersion matches the GW quasiparticle band structure. However, the conduction band dispersion shows an anomalously large effective mass of 2.4 m0. Possible mechanisms for this large enhancement in the “apparent mass” are discussed.

The detailed findings are published in Nano Lett. 2022, 22, 19, 7841–7847

2DCC Role:  2DCC provided epitaxial graphene to the Penn State Center for Nanoscale Science, who formed the 2D silver for study at the University of Texas at Austin. 2DCC also supported the theoretical understanding of the 2D-Ag via DFT-GW calculations.


What Has Been Achieved: This work reveals that thinning silver down to a monolayer leads to the metal transforming to a semiconductor.

Importance of the Achievement: This work demonstrates that new semiconductors can be formed from transition 2D metals, with the potential for next generation devices for beyond silicon CMOS.

Unique Feature(s) of the MIP that Enabled this Achievement:  The combined capacity of epitaxial graphene growth and advanced characterization, along with Theory at 2DCC-MIP enables this achievement.

Publication: Confined Monolayer Ag As a Large Gap 2D Semiconductor and Its Momentum Resolved Excited States; Woojoo Lee, Yuanxi Wang, Wei Qin, Hyunsue Kim, Mengke Liu, T. Nathan Nunley, Bin Fang, Rinu Maniyara, Chengye Dong, Joshua A. Robinson, Vincent H. Crespi, Xiaoqin Li, Allan H. MacDonald, and Chih-Kang Shih; Nano Lett. 2022, 22, 19, 7841–7847

Acknowledgements: This work was primarily supported by the National Science Foundation through the Center for Dynamics and Control of Materials: an NSF MRSEC under Cooperative Agreement No. DMR-1720595. Other support includes NSF Grant Nos. DMR-1808751 and the Welch Foundation F-1672. Support for synthesis comes from The Penn State Center for Nanoscale Science (NSF Grant DMR-2011839) and the Penn State 2DCC-MIP (NSF DMR-1539916).