Hajo Söde - Academia.edu (original) (raw)
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Leibniz Institute for Age Research - Fritz LipmannInstitute
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Papers by Hajo Söde
Physical Review B, 2015
The electronic structure of atomically precise armchair graphene nanoribbons of width N = 7 (7-AG... more The electronic structure of atomically precise armchair graphene nanoribbons of width N = 7 (7-AGNRs) are investigated by scanning tunneling spectroscopy (STS) on Au(111). We record the standing waves in the local density of states of finite ribbons as a function of sample bias and extract the dispersion relation of frontier electronic states by Fourier transformation. The wavevector-dependent contributions from these states agree with density functional theory calculations, thus enabling the unambiguous assignment of the states to the valence band, the conduction band and the next empty band with effective masses of 0.41 ± 0.08 m e , 0.40 ± 0.18 m e and 0.20 ± 0.03 m e , respectively. By comparing the extracted dispersion relation for the conduction band to corresponding height-dependent tunneling spectra, we find that the conduction band edge can be resolved only at small tip-sample separations and has not been observed before. As a result, we report a band gap of 2.37 ± 0.06 eV for 7-AGNRs adsorbed on Au(111).
Nature communications, 2014
Narrow graphene nanoribbons exhibit substantial electronic bandgaps and optical properties fundam... more Narrow graphene nanoribbons exhibit substantial electronic bandgaps and optical properties fundamentally different from those of graphene. Unlike graphene--which shows a wavelength-independent absorbance for visible light--the electronic bandgap, and therefore the optical response, of graphene nanoribbons changes with ribbon width. Here we report on the optical properties of armchair graphene nanoribbons of width N=7 grown on metal surfaces. Reflectance difference spectroscopy in combination with ab initio calculations show that ultranarrow graphene nanoribbons have fully anisotropic optical properties dominated by excitonic effects that sensitively depend on the exact atomic structure. For N=7 armchair graphene nanoribbons, the optical response is dominated by absorption features at 2.1, 2.3 and 4.2 eV, in excellent agreement with ab initio calculations, which also reveal an absorbance of more than twice the one of graphene for linearly polarized light in the visible range of wavel...
Journal of the American Chemical Society, 2013
Atomically precise graphene nanoribbons (GNRs) can be obtained via thermally induced polymerizati... more Atomically precise graphene nanoribbons (GNRs) can be obtained via thermally induced polymerization of suitable precursor molecules on a metal surface. This communication discusses the atomic structure found at the termini of armchair GNRs obtained via this bottom-up approach. The short zigzag edge at the termini of the GNRs under study gives rise to a localized midgap state with a characteristic signature in scanning tunneling microscopy (STM). By combining STM experiments with large-scale density functional theory calculations, we demonstrate that the termini are passivated by hydrogen. Our results suggest that the length of nanoribbons grown by this protocol may be limited by hydrogen passivation during the polymerization step.
Nature Nanotechnology
http://www.nature.com/nnano/journal/vaop/ncurrent/full/nnano.2014.184.html Despite graphene's... more http://www.nature.com/nnano/journal/vaop/ncurrent/full/nnano.2014.184.html Despite graphene's remarkable electronic properties, the lack of an electronic bandgap severely limits its potential for applications in digital electronics. In contrast to extended films, narrow strips of graphene (called graphene nanoribbons) are semiconductors through quantum confinement, with a bandgap that can be tuned as a function of the nanoribbon width and edge structure. Atomically precise graphene nanoribbons can be obtained via a bottom-up approach based on the surface-assisted assembly of molecular precursors. Here we report the fabrication of graphene nanoribbon heterojunctions and heterostructures by combining pristine hydrocarbon precursors with their nitrogen-substituted equivalents. Using scanning probe methods, we show that the resulting heterostructures consist of seamlessly assembled segments of pristine (undoped) graphene nanoribbons (p-GNRs) and deterministically nitrogen-doped grap...
Physical Review B, 2015
The electronic structure of atomically precise armchair graphene nanoribbons of width N = 7 (7-AG... more The electronic structure of atomically precise armchair graphene nanoribbons of width N = 7 (7-AGNRs) are investigated by scanning tunneling spectroscopy (STS) on Au(111). We record the standing waves in the local density of states of finite ribbons as a function of sample bias and extract the dispersion relation of frontier electronic states by Fourier transformation. The wavevector-dependent contributions from these states agree with density functional theory calculations, thus enabling the unambiguous assignment of the states to the valence band, the conduction band and the next empty band with effective masses of 0.41 ± 0.08 m e , 0.40 ± 0.18 m e and 0.20 ± 0.03 m e , respectively. By comparing the extracted dispersion relation for the conduction band to corresponding height-dependent tunneling spectra, we find that the conduction band edge can be resolved only at small tip-sample separations and has not been observed before. As a result, we report a band gap of 2.37 ± 0.06 eV for 7-AGNRs adsorbed on Au(111).
Nature communications, 2014
Narrow graphene nanoribbons exhibit substantial electronic bandgaps and optical properties fundam... more Narrow graphene nanoribbons exhibit substantial electronic bandgaps and optical properties fundamentally different from those of graphene. Unlike graphene--which shows a wavelength-independent absorbance for visible light--the electronic bandgap, and therefore the optical response, of graphene nanoribbons changes with ribbon width. Here we report on the optical properties of armchair graphene nanoribbons of width N=7 grown on metal surfaces. Reflectance difference spectroscopy in combination with ab initio calculations show that ultranarrow graphene nanoribbons have fully anisotropic optical properties dominated by excitonic effects that sensitively depend on the exact atomic structure. For N=7 armchair graphene nanoribbons, the optical response is dominated by absorption features at 2.1, 2.3 and 4.2 eV, in excellent agreement with ab initio calculations, which also reveal an absorbance of more than twice the one of graphene for linearly polarized light in the visible range of wavel...
Journal of the American Chemical Society, 2013
Atomically precise graphene nanoribbons (GNRs) can be obtained via thermally induced polymerizati... more Atomically precise graphene nanoribbons (GNRs) can be obtained via thermally induced polymerization of suitable precursor molecules on a metal surface. This communication discusses the atomic structure found at the termini of armchair GNRs obtained via this bottom-up approach. The short zigzag edge at the termini of the GNRs under study gives rise to a localized midgap state with a characteristic signature in scanning tunneling microscopy (STM). By combining STM experiments with large-scale density functional theory calculations, we demonstrate that the termini are passivated by hydrogen. Our results suggest that the length of nanoribbons grown by this protocol may be limited by hydrogen passivation during the polymerization step.
Nature Nanotechnology
http://www.nature.com/nnano/journal/vaop/ncurrent/full/nnano.2014.184.html Despite graphene's... more http://www.nature.com/nnano/journal/vaop/ncurrent/full/nnano.2014.184.html Despite graphene's remarkable electronic properties, the lack of an electronic bandgap severely limits its potential for applications in digital electronics. In contrast to extended films, narrow strips of graphene (called graphene nanoribbons) are semiconductors through quantum confinement, with a bandgap that can be tuned as a function of the nanoribbon width and edge structure. Atomically precise graphene nanoribbons can be obtained via a bottom-up approach based on the surface-assisted assembly of molecular precursors. Here we report the fabrication of graphene nanoribbon heterojunctions and heterostructures by combining pristine hydrocarbon precursors with their nitrogen-substituted equivalents. Using scanning probe methods, we show that the resulting heterostructures consist of seamlessly assembled segments of pristine (undoped) graphene nanoribbons (p-GNRs) and deterministically nitrogen-doped grap...