Direct observation of electron dynamics in the attosecond domain

• Published in: Nature Vol. 436; no. 7049; pp. 373 - 376
• Main Authors: Wurth, W, Föhlisch, A, Feulner, P, Hennies, F, Fink, A, Menzel, D, Sanchez-Portal, D, Echenique, P. M
• Format: Journal Article
• Language: English
• Published: London Nature Publishing 21-07-2005; Nature Publishing Group
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Electrochemistry; Electron transfer; Electrons; Exact sciences and technology; Fundamental areas of phenomenology (including applications); Nonlinear optics; Optical properties and condensed-matter spectroscopy and other interactions of matter with particles and radiation; Optics; Physics; Ruthenium; Solar cells; Time & motion studies; Time-resolved optical spectroscopies and other ultrafast optical measurements in condensed matter; Ultrafast processes; optical pulse generation and pulse compression; Autoionization; as range; Ruthenium; X-ray spectroscopy; Coster-Kronig transitions; Ultrafast optics
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/nature03833

Dynamical processes are commonly investigated using laser pump-probe experiments, with a pump pulse exciting the system of interest and a second probe pulse tracking its temporal evolution as a function of the delay between the pulses. Because the time resolution attainable in such experiments depends on the temporal definition of the laser pulses, pulse compression to 200 attoseconds (1 as = 10-18 s) is a promising recent development. These ultrafast pulses have been fully characterized, and used to directly measure light waves and electronic relaxation in free atoms. But attosecond pulses can only be realized in the extreme ultraviolet and X-ray regime; in contrast, the optical laser pulses typically used for experiments on complex systems last several femtoseconds (1 fs = 10-15 s). Here we monitor the dynamics of ultrafast electron transfer-a process important in photo- and electrochemistry and used in solid-state solar cells, molecular electronics and single-electron devices-on attosecond timescales using core-hole spectroscopy. We push the method, which uses the lifetime of a core electron hole as an internal reference clock for following dynamic processes, into the attosecond regime by focusing on short-lived holes with initial and final states in the same electronic shell. This allows us to show that electron transfer from an adsorbed sulphur atom to a ruthenium surface proceeds in about 320 as.