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VERSION:2.0
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BEGIN:VEVENT
DTSTAMP:20240329T082851Z
UID:https://www.mpsd.mpg.de/events/11637/2724
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 M4\,5-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 MoN2
\,3 edge between 32 and 35 eV in MoS2. Comparing the XUV
absorption spectra of bulk and monolayer MoS2\, 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:Andrea Cavalleri
SUMMARY:MPSD Seminar: Michael Zürch - Photoexcitation dynamics in semicond
uctors and two-dimensional semiconductors observed by attosecond core-leve
l spectroscopy
URL:https://www.mpsd.mpg.de/events/11637/2724
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