arXiv subjects

Akitoshi Shiotari

Publications and source records attributed to Akitoshi Shiotari.

3 recordsLinked to original sources

arXiv2024

Picocavity-Enhanced Raman Spectroscopy of Physisorbed H$_2$ and D$_2$ Molecules

We report on tip-enhanced Raman spectroscopy of H2 and D2 molecules physisorbed within a plasmonic picocavity at 10 K. The intense Raman peaks resulting from the rotational and vibrational transitions are observed at subnanometer gap distances of the junction formed by an Ag tip and an Ag(111) surface, where a picocavity-enhanced field plays a crucial role. A significant redshift of the H-H stretch frequency is observed as the gap distance decreases, while the D-D stretch frequency is unaffected. Density functional theory, path-integral molecular dynamics, and quantum anharmonic vibrational energy calculations suggest that this unexpected isotope effect is explained by a different molecular density between H2 and D2 on the surface.

physics.optics↗

arXiv2024

Scattering near-field optical microscopy at 1-nm resolution using ultralow tip oscillation amplitudes

Scattering-type scanning near-field optical microscopy (s-SNOM) allows for the observation of the optical response of material surfaces with a resolution far below the diffraction limit. Based on amplitude-modulation atomic force microscopy (AFM) with typical tapping amplitudes of tens of nanometers, a spatial resolution of 10-100 nm is routinely achieved in s-SNOM. However, optical imaging and spectroscopy of atomic-scale structures remain a substantial challenge. Here, we developed ultralow tip oscillation amplitude s-SNOM (ULA-SNOM), where the ultra-confined field localized at a 1-nm-scale gap between a plasmonic tip and sample is combined with frequency-modulation (non-contact) AFM in a stable cryogenic ultrahigh vacuum environment. Using a silver tip under visible laser illumination with a constant 1-nm amplitude oscillation, we obtain a material-contrast image of silicon islands on a silver surface with 1-nm lateral resolution, which surpasses the conventional limits of s-SNOM. ULA-SNOM paves the way for the acquisition of optical information from atomic-scale structures, such as single photo-active defects and molecules.

physics.optics↗

arXiv2019

Small bandgap features achieved in atomically precise 17-atom-wide armchair-edged graphene nanoribbons

Graphene nanoribbons (GNRs) synthesized using a bottom-up technique potentially enable future electronic devices owing to the tunable electronic structures depending on the well-defined width and edge geometry. For instance, armchair-edged GNRs (AGNRs) exhibit width-dependent bandgaps. However, the bandgaps of AGNRs synthesized experimentally thus far are relatively large, well above 1 eV. Such a large bandgap may deteriorate device performances due to large Schottky barriers and carrier effective masses. We describe the bottom-up synthesis of AGNRs with a smaller bandgap using dibromobenzene-based precursors. Two types of AGNRs with different widths of 17 and 13 carbon atoms were synthesized on Au(111), and their atomic and electronic structures were investigated by scanning probe microscopy and spectroscopy. We reveal that the 17-AGNRs has the smallest bandgap as well as the smallest electron/hole effective mass among bottom-up AGNRs reported thus far. The successful synthesis of 17-AGNRs is a significant step toward the development of GNR-based electronic devices.

cond-mat.mes-hall↗