Download Leone Group Poster - cchem.berkeley.edu

Ultrafast Molecular Dynamics
High Harmonic Generation (HHG)
Attosecond transient absorpt
ion spectroscopy around the
bromine M-edge reveals mult
iple dynamics initiated by a st
rong few-cycle (3.5 fs) NIR pul
se in methyl bromide. In the n
eutral, C-Br bond vibration (1
), with a period of 40 fs, is visi
ble. The coupled dynamics (3)
of the signals converging to 5s
a1 (65.2 eV) and Br P3/2 (64.3
eV) is instead signature of a fr
agmentation pathway throug
h multiple conical intersectio
ns. In the ion, a spin-orbit wa
vepacket in the ground state (
2), with a period of 13 fs, is re
solved.
Attosecond Electronic
Dynamics in Molecules
http://www.jaslab.ca/atto2_e.html
(a)pulse
Slow ion
The electric field from a femtosecond NIR laser
tunnel ionizes an electron away from the nucleus of an
atom. Half an optical cycle later when the electric field
of the laser reverses direction, the electron is
accelerated back towards the nucleus, coherently
emitting an XUV photon, with energy that is an oddorder harmonic of the original NIR.
We utilize attosecond pulses in
conjunction with noncollinear
NIR pulses to generate four
wave mixing (FWM) emission
signals. Attosecond FWM allows
for highly selective, backgroundfree measurements of coherent
superpositions of electronic
states. The delay dependent
FWM emission signal generated
in argon reveals NIR-induced
coupling with states within the
bandwidth of the NIR pulses. We
will extend this technique in
order to study dynamic ultrafast
processes such as autoionization,
Auger
decay,
dissociation, and curve
crossings in the time domain.
Kristina, Maurizio, Yuki
Femtosecond X-ray Spectroscopy of Photochemical Reactions
Attosecond spectroscopy
at the carbon K-edge
2A State
(2p/1p*)
Sample interaction
The ultrafast light-activated
ring-opening reaction of 1,3cyclohexadiene is investigated
using femtosecond soft x-ray
spectroscopy near the carbon
k-edge (~284 eV) on a tabletop apparatus.
2A State
(2p/1p*)
Soft x-ray
spectrometer
The evolution of the valence electronic structure during this
ubiquitous reaction is directly revealed and the x-ray spectroscopic
signatures of the elusive intermediate states are characterized.
Ultrafast Solid State Dynamics
Ultrafast Charge Carrier Dynamics by XUV Transient Absorption
The initial excited state of aFe2O3 is given by a ligand-tometal charge transfer.
Relaxation happens through
electron-phonon coupling
leading to polaron formation.
High-harmonic
generation
Recombination with
pump pulse (IR to visible)
A high power attosecond pulse source
is developed in collaboration with
Chang group at University of Central
Florida, which will enable the first
true attosecond-pump attosecondprobe experiments.
Andrew R., Peter
Attosecond Solid State XUV Transient Absorption
Marieke, Chris
Attosecond Transient Reflectivity in XUV
Broadband attosecond
XUV pulses are utilized to
probe electron dynamics
in semiconductors such
as Ge and GaAs.
The valley dependent carrier
relaxation dynamics of Si are
observed. The different
relaxation processes known
to occur in semiconductors
can be followed with
unprecedented detail,
further demonstrating the
promise of transient XUV
absorption.
Transient reflectivity gives experimental access to the complex-valued
index of refraction n or to the dielectric function e = e0 n2 / m02.
Attosecond transient absorption simultaneously tracks
electron and hole dynamics in germanium thin films
Hung-Tzu, Michael
Lucas, Scott, Ilana, Angela
Ultrafast Charge Carrier Dynamics at Semiconductor Interfaces
1.4 fs oscillations during photoexcitation as a consequence of a
laser-induced polarization of the bands.
Broadening of hole feature over 10 fs indicates collective electron
response time.
Peter, Chris, Andrew R., Marieke
Single Molecule Spectroscopy
Fluorescence Spectroscopy of Semiconductor Nanostructures
In this experiment we investigate the ultrafast charge carrier
dynamics at three different interfaces, i.e. semiconductor-gas
phase, semiconductor-metal, and semiconductor-semiconductor,
by monitoring the full suite of steps from charge excitation to
charge separation and subsequent charge recombination. Here is
presented an experiment in which the charge carrier dynamics at
the n-TiO2/p-Si(100) interface is investigated.
E
Atto-Atto Endstation
(collaboration project with UCF)
A new beamline is developed which will enable the first
experiments in the soft x-ray region with attosecond resolution:
This enables access to carbon-containing gases and materials
through element-specific probing of the dynamics at the carbon
K-edge by exciting 1s electrons of carbon into the valence states.
Proposed experiments include electron dynamics in small carbon
containing molecules as well as graphene and silicon carbide.
Andrew, Aditi, Kirsten, Marina, Chris X.
We study the charge carrier dynamics in semiconductor materials after excitation by visible
light. Transient XUV absorption spectroscopy has advantages of element/chemical valence
specificity and low femtosecond temporal resolution, which is suitable to study ultrafast
electron migration processes in semiconductor heterostructures.
Erika, Ashley, Hugo
New Attosecond Projects
1s→2p/1p*
Science (2017)
Attosecond Four-Wave Mixing Spectroscopy
We investigate charge carrier dynamics in semiconductor nanostructures at the single molecule limit. Transfer,
trapping and recombination of charges can be studied in individual molecules using a combination of confocal
fluorescence microscopy and time-correlated single photon counting. These techniques are being used to study
emerging, all-inorganic perovskite materials.
Single CsPbBr3 perovskite nanowires
exhibit low-threshold and wavelengthtunable lasing, which persists over one
billion excitation cycles, even in
ambient atmosphere, demonstrating
unprecedented stability in perovskite
nanowires.
E
2 μm
Charge carrier dynamics at the n-TiO2/p-Si(100) interface
Brett, Bethany
Charge carrier trapping leading to
fluorescence intermittency or blinking
is being studied in CsPbBr3 nanocubes
and nanoplates.
Natalie