12:00 〜 12:15
▼ [15a-2E-10] Terahertz spectroscopy of single Ce@C82 molecules using sub-nm scale gap electrodes
キーワード：Terahertz spectroscopy,Single molecule
Terahertz (THz) spectroscopy is a powerful tool for clarifying electronic structures and vibrational dynamics of various kinds of molecules. However, it is a great challenge to greatly exceed the diffraction limit [1] and perform single molecule spectroscopy, because there is a huge size difference (a factor of ~105) between the THz wavelength (~100 mm) and the size of single molecules (~1 nm).
In this work, we propose a novel method for performing THz spectroscopy on single molecules. THz vibrational spectra of a single Ce@C82 molecule have been measured by using a single molecule transistor (SMT) geometry, which consists of a single molecule and metal nanogap electrodes, as a THz detector. The inset of Fig. 1(b) shows an SEM image of a fabricated Ce@C82 SMT structure. We created a sub-nm gap in a metal nanojunction by using electromigration. By using the nanogap electrode as a THz antenna, this sample structure allows us to overcome the diffraction limit and focus THz radiation onto a single molecule. Figure 1(a) shows the Coulomb stability diagram of a Ce@C82 SMT. The crossing pattern indicates that we capture a single molecule in the nanogap. THz signal of a single Ce@C82 molecule was obtained by measuring the THz-induced photocurrent in the SMT sample. Figure 1(b) shows the obtained THz spectra of a single Ce@C82 molecule. Broad photocurrent peaks appear around 50 cm-1 and 110 cm-1. Although the origin of these peaks is not clear at present, we think it is related with dynamical motion of the encapsulated Ce atom in the C82 cage [2]. This is the first successful measurement of THz spectra of a single molecule.
Reference: [1] Y. Zhang et al, Nano Lett. 15, 1166 (2015). [2] W. Andreoni and A. Curioni, Phys. Rev. Lett., 77, 834 (1996).
In this work, we propose a novel method for performing THz spectroscopy on single molecules. THz vibrational spectra of a single Ce@C82 molecule have been measured by using a single molecule transistor (SMT) geometry, which consists of a single molecule and metal nanogap electrodes, as a THz detector. The inset of Fig. 1(b) shows an SEM image of a fabricated Ce@C82 SMT structure. We created a sub-nm gap in a metal nanojunction by using electromigration. By using the nanogap electrode as a THz antenna, this sample structure allows us to overcome the diffraction limit and focus THz radiation onto a single molecule. Figure 1(a) shows the Coulomb stability diagram of a Ce@C82 SMT. The crossing pattern indicates that we capture a single molecule in the nanogap. THz signal of a single Ce@C82 molecule was obtained by measuring the THz-induced photocurrent in the SMT sample. Figure 1(b) shows the obtained THz spectra of a single Ce@C82 molecule. Broad photocurrent peaks appear around 50 cm-1 and 110 cm-1. Although the origin of these peaks is not clear at present, we think it is related with dynamical motion of the encapsulated Ce atom in the C82 cage [2]. This is the first successful measurement of THz spectra of a single molecule.
Reference: [1] Y. Zhang et al, Nano Lett. 15, 1166 (2015). [2] W. Andreoni and A. Curioni, Phys. Rev. Lett., 77, 834 (1996).