The lateral resolution of a surface sensitive low-energy electron microscope (LEEM) has been improved below 4 nm for the first time. This breakthrough has only been possible by simultaneously correcting the unavoidable spherical and chromatic aberrations of the lens system. We present an experimental criterion to quantify the aberration correction and to optimize the electron optical system. The obtained lateral resolution of 2.6 nm in LEEM enables the first surface sensitive, electron microscopic observation of the herringbone reconstruction on the Au(111) surface.

High-resolution x-ray absorption and emission spectra of liquid water exhibit a strong isotope effect. Further, the emission spectra show a splitting of the 1b1 emission line, a weak temperature effect, and a pronounced excitation-energy dependence. They can be described as a superposition of two independent contributions. By comparing with gas phase, ice, and NaOH/NaOD, we propose that the two components are governed by the initial state hydrogen bonding configuration and ultrafast dissociation on the time scale of the O 1s core hole decay.

A Reply to the Comment by L. G. M. Pettersson et al.Received 14 May 2008DOI:https://doi.org/10.1103/PhysRevLett.100.249802©2008 American Physical Society

The isotope effect and excitation-energy dependence have been measured in the oxygen K-edge x-ray emission spectrum (XES). The use of XES to monitor core decay processes provides information about molecular dynamics (MD) on an ultrafast time scale through the O1s lifetime of a few femtoseconds. Different nuclear masses give rise to differences in the dynamics and the observed isotope effect in XES is direct evidence of the importance of such processes. MD simulations show that even the excitation-energy dependence in the XES is mainly related to differences in core-excited-state dynamics.