TY  - JOUR
A1  - Sorgenfrei, Nomi
A1  - Giangrisostomi, Erika
A1  - Jay, Raphael Martin
A1  - Kühn, Danilo
A1  - Neppl, Stefan
A1  - Ovsyannikov, Ruslan
A1  - Sezen, Hikmet
A1  - Svensson, Svante
A1  - Föhlisch, Alexander
T1  - Photodriven transient picosecond top-layer semiconductor to metal phase-transition in p-doped molybdenum disulfide
JF  - Advanced materials
N2  - Visible light is shown to create a transient metallic S-Mo-S surface layer on bulk semiconducting p-doped indirect-bandgap 2H-MoS2. Optically created electron-hole pairs separate in the surface band bending region of the p-doped semiconducting crystal causing a transient accumulation of electrons in the surface region. This triggers a reversible 2H-semiconductor to 1T-metal phase-transition of the surface layer. Electron-phonon coupling of the indirect-bandgap p-doped 2H-MoS2 enables this efficient pathway even at a low density of excited electrons with a distinct optical excitation threshold and saturation behavior. This mechanism needs to be taken into consideration when describing the surface properties of illuminated p-doped 2H-MoS2. In particular, light-induced increased charge mobility and surface activation can cause and enhance the photocatalytic and photoassisted electrochemical hydrogen evolution reaction of water on 2H-MoS2. Generally, it opens up for a way to control not only the surface of p-doped 2H-MoS2 but also related dichalcogenides and layered systems. The findings are based on the sensitivity of time-resolved electron spectroscopy for chemical analysis with photon-energy-tuneable synchrotron radiation.
KW  - catalysis
KW  - dichalcogenides
KW  - hydrogen evolution reaction
KW  - phase transitions
KW  - photoelectron spectroscopy
Y1  - 2021
U6  - https://doi.org/10.1002/adma.202006957
SN  - 0935-9648
SN  - 1521-4095
VL  - 33
IS  - 14
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Sorgenfrei, Nomi
A1  - Giangrisostomi, Erika
A1  - Kühn, Danilo
A1  - Ovsyannikov, Ruslan
A1  - Föhlisch, Alexander
T1  - Time and angle-resolved time-of-flight electron spectroscopy for functional materials science
JF  - Molecules : a journal of synthetic chemistry and natural product chemistry
N2  - Electron spectroscopy with the unprecedented transmission of angle-resolved time-of-flight detection, in combination with pulsed X-ray sources, brings new impetus to functional materials science. 
We showcase recent developments towards chemical sensitivity from electron spectroscopy for chemical analysis and structural information from photoelectron diffraction using the phase transition properties of 1T-TaS2. 
Our development platform is the SurfaceDynamics instrument located at the Femtoslicing facility at BESSY II, where femtosecond and picosecond X-ray pulses can be generated and extracted. 
The scientific potential is put into perspective to the current rapidly developing pulsed X-ray source capabilities from Lasers and Free-Electron Lasers.
KW  - photoelectron spectroscopy
KW  - surface science
KW  - time-resolved
KW  - ultrafast
KW  - instrumentation
KW  - dichalcogenides
KW  - phase transition
Y1  - 2022
U6  - https://doi.org/10.3390/molecules27248833
SN  - 1420-3049
VL  - 27
IS  - 24
PB  - MDPI
CY  - Basel
ER  -