探針増強非線形分光に関する研究成果がThe Journal of Chemical PhysicsのFeatured Articleに選出

2026-03-18 分子科学研究所

分子科学研究所と東北大学の研究チームは、ナノスケールで表面分子の構造や配向を高精度に解析する「探針増強和周波発生分光法」を高度化した。従来は金属基板由来の強いバックグラウンド信号により、微弱な分子振動の検出が困難だったが、時間的に非対称なレーザーパルスとパルス間遅延制御を導入することで信号を効果的に分離・抽出することに成功。その結果、従来比で約1000万倍の信号増強を達成し、分子の絶対配向もナノスケールで決定可能となった。本技術は触媒反応機構の解明や分子デバイス設計に貢献し、将来的には超高速分子ダイナミクス観測への応用も期待される。

＜関連情報＞

時間的に非対称なパルスを用いた先端増強型和周波発生分光法による微弱な振動信号の検出
Tip-enhanced sum frequency generation spectroscopy using temporally asymmetric pulse for detecting weak vibrational signals

Atsunori Sakurai;Shota Takahashi;Tatsuto Mochizuki;Tomonori Hirano;Akihiro Morita;Toshiki Sugimoto
The Journal of Chemical Physics Published:February 19 2026
DOI:https://doi.org/10.1063/5.0310824

Vibrational sum frequency generation (SFG) spectroscopy is a powerful technique for investigating molecular structures, orientations, and dynamics at surfaces. However, its spatial resolution is fundamentally restricted to the micrometer scale by the optical diffraction limit. Tip-enhanced SFG (TE-SFG) using a scanning tunneling microscope has been developed to overcome this limitation. The acquired spectra exhibit characteristic dips originating from vibrational responses located within the strong broadband non-resonant background (NRB), which distorts and obscures the molecular signals. By making the second pulse temporally asymmetric and introducing a controlled delay between the first and second laser pulses, the NRB was effectively suppressed, which led to an optimized ratio between the resonant and non-resonant signals, thereby maximizing the contrast of an interferometric signal and improving the detectability of weak vibrational signals. This interference also made it possible to determine absolute molecular orientations. Furthermore, forward- and backward-scattered signals were simultaneously detected, conclusively confirming that the observed signals originated from tip enhancement rather than far-field contributions. Finally, the signal enhancement factor in TE-SFG was estimated to be 6.3 × 10⁶ − 1.3 × 10⁷, based on the experimental data. This TE-SFG technique overcomes the optical diffraction limit and enables the investigation of molecular vibrations at surfaces with unprecedented detail.