RQC Seminar

66th RQC Seminar

• Speaker

  Dr. Hirofumi Yanagisawa
  ( Shizuoka university )

• Date

  16:00-17:00, July 27, 2023 (Thursday)

• Venue

  Hybrid(ZOOM・ Wako Main Research 3F 345-347 Seminar Room C01）

• Title

  Molecular-orbital switch

• Inquiries

  rqc_info[at]ml.riken.jp

Abstract
In this presentation, we will provide an overview of our work on integrating ultrafast switches based on light-induced electron emission from a metallic needle, with a particular emphasis on recent developments related to single-molecule switches [1,2].
By irradiating a sharp metallic needle with light pulses, we can concentrate optical fields at the apex of the needle [3]. These optical fields then generate electron emissions from the apex, as shown in Figure 1(a). These electron emissions can serve as ultrafast switches that are three to six orders of magnitude faster than current switching devices in modern computers. Moreover, concurrent plasmonic effects allow for spatial control of electron emission at its source on a scale of ten nanometers [4]. By leveraging this phenomenon, one can choose emission sites A or B, as shown in Figure 1(b). This configuration is akin to having two integrated transistor switches, as shown in the accompanying diagram, where each gate can be independently controlled by light. However, further miniaturization of such a spatially controllable electron source through plasmonics is fundamentally challenging, necessitating a paradigm shift. In this context, we realized that paradigm shift by employing a recently identified single-molecule electron source [1]. In this setup, fullerene molecules are positioned on a metallic substrate. Electrons are emitted from the single molecules, with their origin in the substrate and passage through specific molecular orbitals (MOs) in the single molecules, as depicted in Figure 1(c). Depending on the molecular orbitals involved, the electron emission sites differ. In our study, we have optically selected the specific MO through which electrons pass, enabling us to create an electron source with emission site-selectivity on a sub-0.5nm scale [2]. This breakthrough will pave the way for multiple ultrafast switches integrated into a single molecule.

Fig. 1: Conceptual diagrams illustrating the ultrafast emission of electrons from a nano-object upon irradiation with a light pulse (a) and the optical control of emission sites (b).
(c) Conceptual diagram showcasing the spatial modulation of an electron source through resonant electron emissions using a molecule.

[1] H. Yanagisawa, et al., Sci. Rep. 12, 2174 (2022).
[2] H. Yanagisawa, et al., Phys. Rev. Lett. 130, 106204 (2023).
[3] P. Hommelhoff, et al., Phys. Rev. Lett. 96, 077401 (2006).
[4] H. Yanagisawa, et al., Phys. Rev. Lett. 103, 257603 (2009).