arXiv subjects

Hiroshi Imada

Publications and source records attributed to Hiroshi Imada.

3 recordsLinked to original sources

arXiv2025

Single-molecule phosphorescence and intersystem crossing in a coupled exciton-plasmon system

Scanning the sharp metal tip of a scanning tunneling microscope (STM) over a molecule allows tuning the coupling between the tip plasmon and a molecular fluorescence emitter. This allows access to local variations of fluorescence field enhancement and wavelength shifts, which are central parameters for characterizing the plasmon-exciton coupling. Performing the same for phosphorescence with molecular scale resolution remains a significant challenge. In this study, we present the investigation of phosphorescence from isolated Pt-Phthalocyanine molecules by analyzing tip-enhanced emission spectra in both current-induced and laser-induced phosphorescence. The latter directly monitors singlet-to-triplet state intersystem crossing of a molecule below the tip. The study contributes to a detailed understanding of triplet excitation pathways and their potential control at sub-molecular length scales. Additionally, the coupling of organic phosphors to plasmonic structures is a promising route for improving light-emitting diodes.

cond-mat.mes-hall↗

arXiv2016

Orbital-selective single molecule excitation and spectroscopy based on plasmon-exciton coupling

The electronic excitation of molecules triggers diverse phenomena such as luminescence and photovoltaic effects, which are the bases of various energy-converting devices. Understanding and control of the excitations at the single-molecule level are long standing targets, however, they have been hampered by the limited spatial resolution in optical probing techniques. Here we investigate the electronic excitation of a single molecule with sub-molecular precision using a localised plasmon at the tip apex of a scanning tunnelling microscope (STM) as an excitation probe. Coherent energy transfer between the plasmon and molecular excitons is discovered when the plasmon is located in the proximity of isolated molecules, which is corroborated by a theoretical analysis. The polarised plasmonic field enables selective excitation of an electronic transition between anisotropic frontier molecular orbitals. Our findings have established the foundation of a novel single-molecule spectroscopy with STM, providing an integrated platform for real-space investigation of localised excited states.

physics.chem-ph↗

arXiv2014

Energy dissipation of electrons at a p-type GaAs(110) surface

Electron injection from the tip of a scanning tunneling microscope into a p-type GaAs(110) surface have been used to induce luminescence in the bulk. Atomically-resolved photon maps revealed significant reduction of luminescence intensity at surface states localized near Ga atoms. Quantitative analysis based on the first principles calculation and a rate equation approach was performed to describe overall energy dissipation processes of the incident tunneling electrons. Our study shows that the recombination processes in the bulk electronic states are suppressed by the fast electron scattering at the surface, and the electrons dominantly undergo non-radiative recombination through the surface states.

cond-mat.mes-hall↗