Ultrafast XAFS Measurements on Laser Excited Ge Films
- UWASH
Laser-pump/x-ray-probe measurements were made on Ge films with nominal time-delay steps of 18 ps. The response of the Ge lattice to the excitation of a high efficiency 200 fs pulse laser operating at 800 nm wavelength and at the Advanced Photon Source (APS) ring frequency of 272 kHz is probed by x-ray absorption fine structure (XAFS) measurements which determine the time dependences of the local structure. Initially the lattice response is dominated by a large increase of the RMS nearest neighbor bond disorder that decays within a single delay step. The next nearest neighbor RMS disorder shows an increase delayed by {approx} 30 ps, consistent with only optical modes dominating the initial lattice response and other phonons being excited more slowly. The different rate of excitation of optical than the rest of phonons require a different mechanism for exciting the optical phonons. Because the laser excites electrons from binding to anti-binding states, a Franck-Condon like effect is suggested as the cause of this initial response, instead of the standard hot electron-hole coupling to phonons.
- Research Organization:
- Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 1009010
- Resource Relation:
- Conference: 13th International Conference on X-ray Absorption Fine Structure-XAFS13;9-14 July 2006;Stanford, California, USA
- Country of Publication:
- United States
- Language:
- ENGLISH
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