Novel Feature of Molecules

Induced by the Interaction with Substrate

Maki Kawai

Institute for Molecular Science, National Institute of Natural Sciences, Okazaki 444-8585, Japan

Molecules adsorbed at metal surfaces exhibit interesting feature such as catalysis. Projected density of states of molecules appearing near the Fermi level enables excitation of molecular states at moderate condition. Chemical reaction, double layer formation at solid liquid interface and spin state of molecules at the interface are some of the examples of the interesting features.

Spectroscopy using scanning tunneling microscope (STM/ STS) utilizing the ultimate spatial resolution of STM is a useful tool to unveil the site specific character of molecules at surfaces. STS including inelastic electron tunneling spectroscopy (IETS) is not only applied to the static spectroscopy but also reflects dynamical phenomena as motion or reaction of molecules induced by the excitation of molecular states, and is utilized to identify the quantum states of the materials. Dynamical information includes as how molecular vibrations can couple with the relevant dynamical processes et al [1-3]. At the conference I will present some typical examples of how the fundamental excitation of vibration modes are coupled to chemical reactions at surfaces. Inelastic electron tunneling spectroscopy (IETS) is widely used to identify the electronic states and is especially useful when the molecule is in contact with solid surfaces. Utilizing the tunneling feature of electron as Multiple Andreev reflection caused between superconductor electrodes, we have recently succeeded to unveil the electron transfer channels though a molecule sandwiched within superconducting metals [4]. Spin state of the molecule is one of the examples, where it depends on the strength of the coupling between the molecule and substrate. With strong coupling with Cu(110) the spin of FePc is completely killed whereas if decoupled as on Cu(110) 2x1-O, spin survives with change in the direction of easy axis [5]. On Au, weak coupling leads to appearance of Kondo state, where a competition between the RKKY interaction affects the spin state [6]. Kondo state of FePc on Au depends on the adsorption site, where the difference was originating from the coupling with the substrate electrons [7]. When FePc on Au is connected to metal tip of STM the Knodo feature changes to normal spin state where the competition between the Kondo resonance and Spin-orbit coupling appear.[8]

References:

[1]Y. Kim, et al., Progress in Surface Science, 90 (2015) 85-143., and the references within.

[2] Kenta Motobayashi, et al.,Surf. Sci.634 (2016) 18-22.

[3] Oh, Phys. Rev. Lett.116 (2016) 056101.

[4] R. Hiraoka, et al., Phys. Rev. B90 (2014) 241405(R).

[5] N. Tsukahara, et al., Phys. Rev. Lett.102 (2009) 167203.

[6] N. Tsukahara, et al., Phys. Rev. Lett.106 (2011) 187201.

[7] E. Minamitani, et al., Phys. Rev. Lett.109 (2012) 086602.

[8] R. Hiraoka et al., Nature Commun. (2017)in press.