Irreversible material dynamics studied with time-resolved X-ray
scattering
T. J. Albert, and K. Sokolowski-Tinten
1Faculty of Physics and Center for Nanointegration Duisburg-Essen, University of Duisburg-Essen, Lotharstrasse 1, 47057 Duisburg, Germany.
Introduction
Sample scheme to study irreversible dynamics
Irradiation of a solid with an ultrashort laser pulse leads to states of strong
23 mm
Sample film
electronic excitation, high temperatures, and high pressure. The complex
1000
580 µm
300 µm
50 mm
structural changes and phase transitions, often along unusual paths and
Temperature [K]
relaxation processes that occur after energy deposition can lead to ultrafast
under strong non-equilibrium conditions. Understanding these processes
does not only address fundamentally important questions but is also highly
relevant for many applications of short-pulse lasers. This ranges from
materials processing and synthesis to data storage in phase change
Si3N4 (50 nm)
30 nm Sb
7 nm Sb
500
50 nm Si N
3
2.001 windows
300 x 300 µm2
pitch 680 µm
materials.
Time-resolved diffraction experiments at X-ray free-electron lasers (XFELs)
allow to investigate the transient and irreversible dynamics of laser-excited
laser heating
1014 -1015 K/s
materials on the relevant time (fs to µs) and length (Å to nm) scales.
Here, we discuss some examples of our recent work at XFELs. By applying
0 0.005
with a unique thin-film sample design we have investigated the non-
4
0.1
1
10
Time [ns]
cooling
≈ -1012 K/s
≈ ns
time-resolved wide-angle and small-angle X-ray scattering in combination
temperature
plateau
lat. cooling
to frame
≲ ms
Thin films, deposited on
free standing Si3N4-membranes
Rapid quenching & isothermal conditions
equilibrium structural dynamics of various materials after short pulse laser
excitation.
Rapidly quenched Sb: t.r. WAXS XPP @ LCLS
Strong laser-excitation of solids
Al
7 nm Sb on
50 nm Si3N4
static synchrotron data (APS)
transient cooling rate:
𝛾! "# =
30 nm Sb on
50 nm Si3N4
−0.096 Å$%/𝑛𝑠
9.206×10$& Å$%/𝐾
= −𝟏. 𝟎𝟒×𝟏𝟎𝟏𝟐 𝑲/𝒔
𝛾)* "# =
−0.015 Å$%/𝑛𝑠
9.206×10$& Å$%/𝐾
= −𝟏. 𝟔𝟑×𝟏𝟎𝟏𝟏 𝑲/𝒔
• strong electronic excitation (fs)
Laser-induced phase transitions in thin Fe-films: FXE @ EuXFEL
Ø changes of interatomic forces
non-thermal processes
-5 ps
• rapid heating (≈ ps)
Ø states at high (T, P)
Ø overheating & melting
Ø solid-plasma transition
• material expansion & cooling (10 ps - µs)
Diffraction siganl [norm.]
1.4 ×Fm@30 ps
1
a (110)
𝟎. 𝟗×𝑭𝒎
g-Fe (111)
0.5
𝟏. 𝟒×𝑭𝒎
0
2.6
2.8
3
3.2
3.4
liq.-Fe
-1
Ø ablation
a-Fe
q [Å ]
30ps
Diffraction siganl [norm.]
Ø rapid solidification
Time-resolved X-ray scattering
scattering pattern
1
𝟐. 𝟒×𝑭𝒎
30 ps
hypothesis: a → g transition
0.5
𝟒. 𝟎×𝑭𝒎
𝝉𝒎 ≈ 𝟕𝟎𝟎𝒇𝒔
𝐹# =
< 𝑇, = 20℃ → 𝑇# = 1538℃
0
2.6
2.8
3
3.2
3.4
-1
q [Å ]
1.4 × Fm
𝐹-. ≈ 0.6×𝐹#
⇒ 𝑇-. ≈ 𝑇, + 0.6× 𝑇# − 𝑇, = 930℃
Acknowledgements
Collaborators
opt. laser
XPP @ LCLS: L. Kremeyer, P. Zalden, R. Sobierajski, J. Antonowicz, S. Wei, P. Sun, J. Hastings, M. Z. Mo, M. Zajac, A. Gleason,
T. Sato, D. Zhu
FXE @ EuXFEL: A. Olczak, W. Gawełda, K. Georgarakis, P. Sun, P. Zalden, R. Sobierajski, J. Antonowicz
Δt
fs FEL X-ray pulse
thin film sample
on Si3N4-membrane
Optical pump – X-ray probe experiment
Use of the Linac Coherent Light Source (LCLS), SLAC National Accelerator Laboratory, is supported by the U.S. Department of
Energy, Office of Science, Office of Basic Energy Sciences under Contract No. DE-AC02-76SF00515.
We acknowledge European XFEL in Schenefeld, Germany, for provision of X-ray free-electron laser beamtime at
FXE and would like to thank the staff for their assistance.
Funding
Deutsche Forschungsgemeinschaft DFG in the frame of the Collaborative Research Center SFB1242 ‘Non-Equilibrium Dynamics
of Condensed Matter in the Time Domain’
irreversible dynamics
Contact
bright sources
X-ray free-electron lasers
thies.albert@uni-due.de