Owing to its relativistic low-energy charge carriers, the interaction between graphene and variou... more Owing to its relativistic low-energy charge carriers, the interaction between graphene and various impurities leads to a wealth of new physics and degrees of freedom to control electronic devices. In particular, the behavior of graphene's charge carriers in response to potentials from charged Coulomb impurities is predicted to differ significantly from that of most materials. Scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) can provide detailed information on both the spatial and energy dependence of graphene's electronic structure in the presence of a charged impurity. The design of a hybrid impurity-graphene device, fabricated using controlled deposition of impurities onto a back-gated graphene surface, has enabled several novel methods for controllably tuning graphene's electronic properties.(1-8) Electrostatic gating enables control of the charge carrier density in graphene and the ability to reversibly tune the charge(2) and/or molecular(5) states of an impurity. This paper outlines the process of fabricating a gate-tunable graphene device decorated with individual Coulomb impurities for combined STM/STS studies.(2-5) These studies provide valuable insights into the underlying physics, as well as signposts for designing hybrid graphene devices.
Twisted bilayer graphene (tBLG) forms a quasicrystal whose structural and electronic properties d... more Twisted bilayer graphene (tBLG) forms a quasicrystal whose structural and electronic properties depend on the angle of rotation between its layers. Here, we present a scanning tunneling microscopy study of gate-tunable tBLG devices supported by atomically smooth and chemically inert hexagonal boron nitride (BN). The high quality of these tBLG devices allows identification of coexisting moir´e patterns and moir´e super-superlattices produced by graphene-graphene and graphene-BN interlayer interactions. Furthermore, we examine additional tBLG spectroscopic features in the local density of states beyond the first van Hove singularity. Our experimental data are explained by a theory of moir´e bands that incorporates ab initio calculations and confirms the strongly nonperturbative character of tBLG interlayer coupling in the small twist-angle regime.
Gate-controlled tuning of the charge carrier density in graphene devices provides new opportuniti... more Gate-controlled tuning of the charge carrier density in graphene devices provides new opportunities to control the behavior of molecular adsorbates. We have used scanning tunneling microscopy (STM) and spectroscopy (STS) to show how the vibronic electronic levels of 1,3,5-tris(2,2dicyanovinyl)benzene molecules adsorbed onto a graphene/BN/SiO 2 device can be tuned via application of a backgate voltage. The molecules are observed to electronically decouple from the graphene layer, giving rise to well-resolved vibronic states in dI/dV spectroscopy at the single-molecule level. Density functional theory (DFT) and many-body spectral function calculations show that these states arise from molecular orbitals coupled strongly to carbonÀhydrogen rocking modes. Application of a back-gate voltage allows switching between different electronic states of the molecules for fixed sample bias.
Owing to its relativistic low-energy charge carriers, the interaction between graphene and variou... more Owing to its relativistic low-energy charge carriers, the interaction between graphene and various impurities leads to a wealth of new physics and degrees of freedom to control electronic devices. In particular, the behavior of graphene's charge carriers in response to potentials from charged Coulomb impurities is predicted to differ significantly from that of most materials. Scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) can provide detailed information on both the spatial and energy dependence of graphene's electronic structure in the presence of a charged impurity. The design of a hybrid impurity-graphene device, fabricated using controlled deposition of impurities onto a back-gated graphene surface, has enabled several novel methods for controllably tuning graphene's electronic properties.(1-8) Electrostatic gating enables control of the charge carrier density in graphene and the ability to reversibly tune the charge(2) and/or molecular(5) states of an impurity. This paper outlines the process of fabricating a gate-tunable graphene device decorated with individual Coulomb impurities for combined STM/STS studies.(2-5) These studies provide valuable insights into the underlying physics, as well as signposts for designing hybrid graphene devices.
Owing to its relativistic low-energy charge carriers, the interaction between graphene and variou... more Owing to its relativistic low-energy charge carriers, the interaction between graphene and various impurities leads to a wealth of new physics and degrees of freedom to control electronic devices. In particular, the behavior of graphene's charge carriers in response to potentials from charged Coulomb impurities is predicted to differ significantly from that of most materials. Scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) can provide detailed information on both the spatial and energy dependence of graphene's electronic structure in the presence of a charged impurity. The design of a hybrid impurity-graphene device, fabricated using controlled deposition of impurities onto a back-gated graphene surface, has enabled several novel methods for controllably tuning graphene's electronic properties.(1-8) Electrostatic gating enables control of the charge carrier density in graphene and the ability to reversibly tune the charge(2) and/or molecular(5) states of an impurity. This paper outlines the process of fabricating a gate-tunable graphene device decorated with individual Coulomb impurities for combined STM/STS studies.(2-5) These studies provide valuable insights into the underlying physics, as well as signposts for designing hybrid graphene devices.
Twisted bilayer graphene (tBLG) forms a quasicrystal whose structural and electronic properties d... more Twisted bilayer graphene (tBLG) forms a quasicrystal whose structural and electronic properties depend on the angle of rotation between its layers. Here, we present a scanning tunneling microscopy study of gate-tunable tBLG devices supported by atomically smooth and chemically inert hexagonal boron nitride (BN). The high quality of these tBLG devices allows identification of coexisting moir´e patterns and moir´e super-superlattices produced by graphene-graphene and graphene-BN interlayer interactions. Furthermore, we examine additional tBLG spectroscopic features in the local density of states beyond the first van Hove singularity. Our experimental data are explained by a theory of moir´e bands that incorporates ab initio calculations and confirms the strongly nonperturbative character of tBLG interlayer coupling in the small twist-angle regime.
Gate-controlled tuning of the charge carrier density in graphene devices provides new opportuniti... more Gate-controlled tuning of the charge carrier density in graphene devices provides new opportunities to control the behavior of molecular adsorbates. We have used scanning tunneling microscopy (STM) and spectroscopy (STS) to show how the vibronic electronic levels of 1,3,5-tris(2,2dicyanovinyl)benzene molecules adsorbed onto a graphene/BN/SiO 2 device can be tuned via application of a backgate voltage. The molecules are observed to electronically decouple from the graphene layer, giving rise to well-resolved vibronic states in dI/dV spectroscopy at the single-molecule level. Density functional theory (DFT) and many-body spectral function calculations show that these states arise from molecular orbitals coupled strongly to carbonÀhydrogen rocking modes. Application of a back-gate voltage allows switching between different electronic states of the molecules for fixed sample bias.
Owing to its relativistic low-energy charge carriers, the interaction between graphene and variou... more Owing to its relativistic low-energy charge carriers, the interaction between graphene and various impurities leads to a wealth of new physics and degrees of freedom to control electronic devices. In particular, the behavior of graphene's charge carriers in response to potentials from charged Coulomb impurities is predicted to differ significantly from that of most materials. Scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) can provide detailed information on both the spatial and energy dependence of graphene's electronic structure in the presence of a charged impurity. The design of a hybrid impurity-graphene device, fabricated using controlled deposition of impurities onto a back-gated graphene surface, has enabled several novel methods for controllably tuning graphene's electronic properties.(1-8) Electrostatic gating enables control of the charge carrier density in graphene and the ability to reversibly tune the charge(2) and/or molecular(5) states of an impurity. This paper outlines the process of fabricating a gate-tunable graphene device decorated with individual Coulomb impurities for combined STM/STS studies.(2-5) These studies provide valuable insights into the underlying physics, as well as signposts for designing hybrid graphene devices.
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Papers by Youngkyou Kim
the angle of rotation between its layers. Here, we present a scanning tunneling microscopy study of gate-tunable
tBLG devices supported by atomically smooth and chemically inert hexagonal boron nitride (BN). The high
quality of these tBLG devices allows identification of coexisting moir´e patterns and moir´e super-superlattices
produced by graphene-graphene and graphene-BN interlayer interactions. Furthermore, we examine additional
tBLG spectroscopic features in the local density of states beyond the first van Hove singularity. Our experimental
data are explained by a theory of moir´e bands that incorporates ab initio calculations and confirms the strongly
nonperturbative character of tBLG interlayer coupling in the small twist-angle regime.
the angle of rotation between its layers. Here, we present a scanning tunneling microscopy study of gate-tunable
tBLG devices supported by atomically smooth and chemically inert hexagonal boron nitride (BN). The high
quality of these tBLG devices allows identification of coexisting moir´e patterns and moir´e super-superlattices
produced by graphene-graphene and graphene-BN interlayer interactions. Furthermore, we examine additional
tBLG spectroscopic features in the local density of states beyond the first van Hove singularity. Our experimental
data are explained by a theory of moir´e bands that incorporates ab initio calculations and confirms the strongly
nonperturbative character of tBLG interlayer coupling in the small twist-angle regime.