Single crystal surfaces probed by polarized nuclei

Nuclear magnetic resonance has developed into a very powerful technique to study the structure and dynamics of atomic and molecular systems, both in liquid and solid phase. However the investigation of single crystal surfaces with “conventional” NMR methods is essentially impossible due to the small sample size of less than 10¹⁵ sites on a cm². To overcome this for the important class of alkali adsorbates on metals and semiconductors, two methods are presented. Common to both is the preparation of a highly nuclear spin polarized atomic beam of ⁶Li in the one case and ⁸Li in the other. The latter isotope is radioactive and undergoes a \beta‐decay with a halflife of 0.84 s. Li adsorbed on the close packed Ru(001) surface is investigated. The T{in1} relaxation rate is the main observable and is used to deduce the local electronic density of states (LDOS(E_F,r=0)) and the Li diffusion barriers at low and high adsorbate coverage. The second experiment uses ⁶Li as an adsorbate, also studied on Ru(001). The nuclear polarization is measured by beam foil spectroscopy. A novel particle detected (photon counting) Fourier‐Transform NMR technique is demonstrated, by observing the time dependent flux of circularly polarized light emitted behind the foil after a 90^\circ‐pulse has been employed at the surface. Development and prospects of the latter technique are presented. This revised version was published online in August 2006 with corrections to the Cover Date.