Di-erbium and di-erbium-carbide endohedral metallofullerenes with a C(82) cage such as Er(2)@C(82... more Di-erbium and di-erbium-carbide endohedral metallofullerenes with a C(82) cage such as Er(2)@C(82) (isomers I, II, and III) and (Er(2)C(2))@C(82) (isomers I, II, and III) have been synthesized and chromatographically isolated (99%). The structures of Er(2)@C(82) (I, II, III) and (Er(2)C(2))@C(82) (I, II, III) metallofullerenes are characterized by comparison with the UV-vis-NIR absorption spectra of (Y(2)C(2))@C(82) (I, II, III), where molecular symmetries of the structures are determined to be C(s), C(2v) and C(3v), respectively. Furthermore, enhanced near-infrared photoluminescence (PL) at 1520 nm from Er(3+) ions in Er(2)@C(82) (I, III) and (Er(2)C(2))@C(82) (I, III) have been observed at room temperature. The PL intensities have been shown to depend on the symmetry of the C(82) cage. In particular, the PL intensity of (Er(2)C(2))@C(82) (III) has been the strongest among the isomers of Er(2)@C(82) and (Er(2)C(2))@C(82). Optical measurements indicate that the PL properties of Er(2)@C(82) (I, II, III) and (Er(2)C(2))@C(82) (I, II, III) correlate strongly with the absorbance at 1520 nm and the HOMO-LUMO energy gap of the C(82) cage.
We have investigated the energetics and electronic structure of monolayer MoS2 with periodic stru... more We have investigated the energetics and electronic structure of monolayer MoS2 with periodic structural corrugations by density functional theory. The total energy of corrugated MoS2 slightly increases with increasing corrugation height, which indicates that the MoS2 sheet intrinsically and extrinsically possesses nanometer scale structural corrugation. The corrugation causes an upward shift of the valence band edge and a downward shift of the conduction band edge owing to the local strain at the wrinkle peak. Accordingly, by injecting holes using the external electric field, the corrugation leads to a one-dimensional conducting channel in the MoS2 sheet. This indicates that corrugation is a plausible procedure to control the dimensionality of the electrons and holes in two-dimensional materials without implementing one-dimensional boundary conditions.
The synthesis of graphene and hexagonal boron nitride (hBN) hybrid sheets has been achieved using... more The synthesis of graphene and hexagonal boron nitride (hBN) hybrid sheets has been achieved using a two-step chemical vapor deposition (CVD) process. Individual grains of single-layer graphene are grown from methane, and hBN is, then, synthesized from ammonia borane on the same copper (Cu) foil. Optical absorption and Raman measurements reveal that the hBN is formed on the bare surface of Cu foil and the graphene grains play a crucial role as an inactive protective layer of Cu foil for the ammonia borane CVD. Furthermore, the hBN growth is found to be initiated preferentially by the edge of graphene grains.
In this study, we develop a new approach for stabilization of metallic phases of monolayer MoS2 t... more In this study, we develop a new approach for stabilization of metallic phases of monolayer MoS2 through the formation of lateral heterostructures composed of semiconducting/metallic MoS2. The structure of metallic (a mixture of T and T′) and semiconducting (2H) phases was unambiguously characterized by Raman spectroscopy, x-ray photoelectron spectroscopy, photoluminescence imaging, and transmission electron microscope observations. The amount of NaCl, reaction temperature, reaction time, and locations of substrates are essential for controlling the percentage of metallic/semiconducting phases in lateral heterostructures; loading a large amount of NaCl at low temperatures with short reaction times prefers metallic phases. The existence of the semiconducting phase in MoS2 lateral heterostructures significantly enhances the stability of the metallic phases through passivation of reactive edges. The same approach can be applied to other transition metal dichalcogenides (TMDs), such as W...
Di-erbium and di-erbium-carbide endohedral metallofullerenes with a C(82) cage such as Er(2)@C(82... more Di-erbium and di-erbium-carbide endohedral metallofullerenes with a C(82) cage such as Er(2)@C(82) (isomers I, II, and III) and (Er(2)C(2))@C(82) (isomers I, II, and III) have been synthesized and chromatographically isolated (99%). The structures of Er(2)@C(82) (I, II, III) and (Er(2)C(2))@C(82) (I, II, III) metallofullerenes are characterized by comparison with the UV-vis-NIR absorption spectra of (Y(2)C(2))@C(82) (I, II, III), where molecular symmetries of the structures are determined to be C(s), C(2v) and C(3v), respectively. Furthermore, enhanced near-infrared photoluminescence (PL) at 1520 nm from Er(3+) ions in Er(2)@C(82) (I, III) and (Er(2)C(2))@C(82) (I, III) have been observed at room temperature. The PL intensities have been shown to depend on the symmetry of the C(82) cage. In particular, the PL intensity of (Er(2)C(2))@C(82) (III) has been the strongest among the isomers of Er(2)@C(82) and (Er(2)C(2))@C(82). Optical measurements indicate that the PL properties of Er(2)@C(82) (I, II, III) and (Er(2)C(2))@C(82) (I, II, III) correlate strongly with the absorbance at 1520 nm and the HOMO-LUMO energy gap of the C(82) cage.
We have investigated the energetics and electronic structure of monolayer MoS2 with periodic stru... more We have investigated the energetics and electronic structure of monolayer MoS2 with periodic structural corrugations by density functional theory. The total energy of corrugated MoS2 slightly increases with increasing corrugation height, which indicates that the MoS2 sheet intrinsically and extrinsically possesses nanometer scale structural corrugation. The corrugation causes an upward shift of the valence band edge and a downward shift of the conduction band edge owing to the local strain at the wrinkle peak. Accordingly, by injecting holes using the external electric field, the corrugation leads to a one-dimensional conducting channel in the MoS2 sheet. This indicates that corrugation is a plausible procedure to control the dimensionality of the electrons and holes in two-dimensional materials without implementing one-dimensional boundary conditions.
The synthesis of graphene and hexagonal boron nitride (hBN) hybrid sheets has been achieved using... more The synthesis of graphene and hexagonal boron nitride (hBN) hybrid sheets has been achieved using a two-step chemical vapor deposition (CVD) process. Individual grains of single-layer graphene are grown from methane, and hBN is, then, synthesized from ammonia borane on the same copper (Cu) foil. Optical absorption and Raman measurements reveal that the hBN is formed on the bare surface of Cu foil and the graphene grains play a crucial role as an inactive protective layer of Cu foil for the ammonia borane CVD. Furthermore, the hBN growth is found to be initiated preferentially by the edge of graphene grains.
In this study, we develop a new approach for stabilization of metallic phases of monolayer MoS2 t... more In this study, we develop a new approach for stabilization of metallic phases of monolayer MoS2 through the formation of lateral heterostructures composed of semiconducting/metallic MoS2. The structure of metallic (a mixture of T and T′) and semiconducting (2H) phases was unambiguously characterized by Raman spectroscopy, x-ray photoelectron spectroscopy, photoluminescence imaging, and transmission electron microscope observations. The amount of NaCl, reaction temperature, reaction time, and locations of substrates are essential for controlling the percentage of metallic/semiconducting phases in lateral heterostructures; loading a large amount of NaCl at low temperatures with short reaction times prefers metallic phases. The existence of the semiconducting phase in MoS2 lateral heterostructures significantly enhances the stability of the metallic phases through passivation of reactive edges. The same approach can be applied to other transition metal dichalcogenides (TMDs), such as W...
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Papers by Ryo Kitaura