title: Effect of electric field gradient on sub-nanometer spatial resolution of tip-enhanced Raman spectroscopy.
abstract: Tip-enhanced Raman spectroscopy (TERS) with sub-nanometer spatial resolution has been recently demonstrated experimentally. However, the physical mechanism underlying is still under discussion. Here we theoretically investigate the electric field gradient of a coupled tip-substrate system. Our calculations suggest that the ultra-high spatial resolution of TERS can be partially attributed to the electric field gradient effect owning to its tighter spatial confinement and sensitivity to the infrared (IR)-active of molecules. Particularly, in the case of TERS of flat-lying H₂TBPP molecules,we find the electric field gradient enhancement is the dominating factor for the high spatial resolution, which qualitatively coincides with previous experimental report. Our theoretical study offers a new paradigm for understanding the mechanisms of the ultra-high spatial resolution demonstrated in tip-enhanced spectroscopy which is of importance but neglected.
authors.affiliation: 1] Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing. 100190, China [2] Department of Physics, Xiamen University, Xiamen. 361005, China.
authors.forename: Lingyan
authors.initials: L
authors.lastname: Meng
authors.affiliation: Department of Physics, Xiamen University, Xiamen. 361005, China.
authors.forename: Zhilin
authors.initials: Z
authors.lastname: Yang
authors.affiliation: 1] Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing. 100190, China [2] Collaborative Innovation Center of Quantum Matter, Beijing 100871, China.
authors.forename: Jianing
authors.initials: J
authors.lastname: Chen
authors.affiliation: Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing. 100190, China.
authors.forename: Mengtao
authors.initials: M
authors.lastname: Sun