Substrate Doping Effect and Unusually Large Angle van Hove Singularity Evolution in Twisted Bi‐ and Multilayer Graphene

Abstract

Graphene is a 2D honeycomb carbon crystal that exhibits unusual electronic structures and physical properties [1][2][3][4] that make it attractive for high-performance devices, such as transistors, [5][6][7][8] optical modulators, [9,10] and photodetectors. [9,11] Compared to single layer graphene, when two or more layers of graphene are stacked together with a twist angle, their electronic structure can be further enriched, giving rise to the van Hove singularity (vHS) with greatly enhanced carrier density of states, thus leading to enhanced optical absorption for selective photon energies. [12][13][14][15][16][17][18] With large tuning range of the twist angle and vHS binding energy, twisted bi-and multilayer graphene provide a promising material base for fabricating broad band wavelength-selective ultrafast photodetectors from the infrared to the ultraviolet regime.Graphene has demonstrated great potential in new-generation electronic applications due to its unique electronic properties such as large carrier Fermi velocity, ultrahigh carrier mobility, and high material stability. Interestingly, the electronic structures can be further engineered in multilayer graphene by the introduction of a twist angle between different layers to create van Hove singularities (vHSs) at adjustable binding energy. In this work, using angleresolved photoemission spectroscopy with sub-micrometer spatial resolution, the band structures and their evolution are systematically studied with twist angle in bilayer and trilayer graphene sheets. A doping effect is directly observed in graphene multilayer system as well as vHSs in bilayer graphene over a wide range of twist angles (from 5° to 31°) with wide tunable energy range over 2 eV. In addition, the formation of multiple vHSs (at different binding energies) is also observed in trilayer graphene. The large tuning range of vHS binding energy in twisted multilayer graphene provides a promising material base for optoelectrical applications with broadband wavelength selectivity from the infrared to the ultraviolet regime, as demonstrated by an example application of wavelength selective photodetector.

Observation of Electrically Tunable van Hove Singularities in Twisted Bilayer Graphene from NanoARPES

“…[23][24][25] By electrostatically gating twBLG it is possible to alter these optical properties altogether as the electronic dispersion and correlation effects are modified, [26] which will profoundly affect the carrier dynamics and time-dependent response of the electronic structure to an optical excitation compared to standard Bernal-stacked bilayer graphene. [27] The energy-and momentum-dependent evolution of the interlayer hybridization between the Dirac cones of twisted graphene layers has been observed in angle-resolved photoemission spectroscopy (ARPES) experiments for large twists [28,29] and near the magic angle, [30,31] but the effect of gating in a functional device has not been previously explored. We achieve this…”

A Perspective on the Application of Spatially Resolved ARPES for 2D Materials

“…In this review the preparation methods employed to produce 2D material are discussed briefly, and include Chemical Vapor Deposition (CVD) [ 7 ], Physical Vapor Deposition (PVD) [ 8 ], and mechanical exfoliation. The latter is the easiest way to prepare high-quality 2D materials in a laboratory; it can be applied to the most innovative materials because it is possible as soon as small bulk pieces of a material are produced.…”

“…This paper features some of the most interesting results obtained to date on graphene, transition metal dichalcogenides (TMDCs), and 2D heterostructures along with discussions about future instrument upgrades for spatially-, spin-, and time-resolved acquisitions. Graphene was a starting point for the investigation by spatially localized ARPES of 2D materials, an example of advanced spatially localized investigations on polycrystalline few layer graphene has been reported [ 7 ]. TMDCs have intriguing electronic, spintronic, and photonic properties, and the study of their band structure is of fundamental importance.…”

Van der Waals interlayer potential of graphitic structures: From Lennard–Jones to Kolmogorov–Crespy and Lebedeva models

“…It is known that there are three types of stacking, an AA one, which is simple hexagonal (it is not found in natural graphite and exists only in intercalated compounds such as C 6 Li and C 8 K, an AB stacking, hexagonal, known also as Bernal, and a rhombohedral ABC stacking. Additionally, a random stacking of these three types is called a turbostratic TS structure and often is obtained in laboratories.…”

“…Recently, in bilayer graphene twisted at 1.1 degree superconductivity was found with critical temperature of 1.7K [5]. By manipulating doping levels these singularities are observed at angles up to 31 degrees [6]. It was shown that free-standing vdW heterostructure of graphene on hexagonal boron nitride (hBN), where a small lattice mismatch exists shows a buckled atomic structure formed as Moiré pattern [7].…”