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VERSION:2.0
PRODID:icalendar-ruby
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METHOD:PUBLISH
BEGIN:VEVENT
DTSTAMP:20260414T055228Z
UID:https://www.mpsd.mpg.de/events/11637/42303
DTSTART:20171208T103000Z
DTEND:20171208T113000Z
CLASS:PUBLIC
CREATED:20171120T143305Z
DESCRIPTION: Investigation of the ultrafast photoexcited electronic respons
 e in semiconductors has provided invaluable insights into carrier dynamics
 . Germanium and its alloys with Si have promise for creating multi-junctio
 n solar cells with higher efficiency and mid-infrared optoelectronics. How
 ever\, the dynamics are complicated by multiple energetically similar vall
 eys\, rendering an understanding of carrier thermalization and population 
 inversion following photoexcitation difficult. Attosecond transient absorp
 tion spectroscopy (ATAS) has recently been employed to probe ultrafast ele
 ctron and hole dynamics in germanium at the M<sub>4\,5</sub>-edge (~30 eV)
 . In the experiment\, a 5 fs VIS-NIR pump pulse excites carriers across th
 e direct band gap and the dynamics are probed with a time-delayed broadban
 d extreme ultraviolet pulse generated by high harmonic generation in xenon
  spanning ~20-45 eV. The observed transient absorption signal contains the
  energetic distribution of both carriers\, electrons and holes\, due to st
 ate blocking as well as spectroscopic features induced by bandshifts (e.g.
  due to band gap renormalization) and broadening (e.g. due to many body ef
 fects). By iterative procedures the measured signal can be successfully de
 coupled into these contributions resolving the carrier and band dynamics w
 ith excellent time and energy resolution. Hot carrier relaxation on a 100-
 fs time scale and carrier recombination on a 1-ps time scale are observed 
 in nanocrystalline Germanium. Going from bulk semiconductor to two-dimensi
 onal layers\, long-lived core-exciton states are observed at the MoN<sub>2
 \,3</sub> edge between 32 and 35 eV in MoS<sub>2</sub>. Comparing the XUV 
 absorption spectra of bulk and monolayer MoS<sub>2</sub>\, a ~4 eV red-shi
 ft suggests a tightly bound core-exciton. The lifetime of the core-exciton
  states can be directly measured in the time domain. Furthermore\, transie
 nt Stark shifts\, coherences\, and coherent population transfer between di
 fferent core-exciton states are observed.\nVortragende(r): Michael Zürch
LAST-MODIFIED:20171120T151329Z
LOCATION:CFEL (Bldg. 99)\, Raum: Seminar Room IV\, O1.111
ORGANIZER;CN=Andrea Cavalleri:mailto:
SUMMARY:MPSD Seminar: Michael Zürch - Photoexcitation dynamics in semicond
 uctors and two-dimensional semiconductors observed by attosecond core-leve
 l spectroscopy 
URL;VALUE=URI:https://www.mpsd.mpg.de/events/11637/42303
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