Fingerprints of single nuclear spin energy levels using STM - ENDOR

TL;DR

This paper demonstrates STM-ENDOR as a powerful technique for detecting and analyzing single nuclear spin energy levels with high precision, surpassing traditional ESR-STM limitations, enabling detailed chemical and nuclear structure analysis at the nanoscale.

Contribution

The study introduces STM-ENDOR for single nuclear spin detection, providing enhanced resolution and capability to distinguish isotopes and quadrupole spectra, advancing nanoscale chemical analysis.

Findings

Accurate determination of hyperfine values including remote nuclei

Ability to measure single nuclear Zeeman frequencies

Detection of quadrupole spectra at the nanoscale

Abstract

We performed STM-ENDOR experiments where the intensity of one of the hyperfine components detected in ESR-STM is recorded while an rf power is irradiated into the tunneling junction and its frequency is swept. When the latter frequency is near a nuclear transition a dip in ESR-STM signal is observed. This experiment was performed in three different systems: near surface SiC vacancies where the electron spin is coupled to a next nearest neighbor 29Si nucleus; Cu deposited on Si(111)7x7 surface, where the unpaired electron of the Cu atom is coupled to the Cu nucleus (63Cu, 65Cu) and on Tempo molecules adsorbed on Au(111), where the unpaired electron is coupled to Nitrogen nucleus (14N). While some of the hyperfine values are unresolved in the ESR-STM data due to linewidth we find that they are accurately determined in the STM-ENDOR data including those from remote nuclei, which are not detected in the ESR-STM spectrum. Furthermore, STM-ENDOR can measure single nuclear Zeeman frequencies, distinguish between isotopes through their different nuclear magnetic moments and detect quadrupole spectra. We also develop and solve a Bloch type equation for the coupled electron-nuclear system that facilitates interpretation of the data. The improved spectral resolution of STM - ENDOR opens many possibilities for nanometric scale chemical analysis.