ELECTRON-SPIN RESONANCE-SCANNING TUNNELING MICROSCOPY EXPERIMENTS ON THERMALLY OXIDIZED SI(111)

In this paper several electron spin resonance-scanning tunneling micro scopy (ESR-STM) experiments are described. In this technique, the tip of a STM scans a surface that contains isolated paramagnetic spin cent ers. The individual spin centers apply a time-dependent perturbation o n the tunneling electrons, giving rise to a time-dependent component o f the tunneling current-at the Larmor frequency V(omega(L))]. This occ urs only when the tunneling region is close to the spin center. Theref ore, J(omega(L)) is spatially localized. Reproducibility of the spatia l localization together with a reproducible tip-dependent frequency sh ift were observed. In higher magnetic fields the average linewidths, t ogether with the fluctuations in the frequency of the signal (probably due to the electric fields near the spin center), are larger. The pro posed mechanism is that electric-dipole-moment oscillations, which are modulated by the Larmor frequency (the Zeeman effect), will give a si gnificant J(omega(L)) component close to the tunneling region by modul ating both the barrier height and width.