Using this innovative setup, we directly
measured the energy band alignment
of the Pt/BTO interface as a function
of the ferroelectric polarization. In the P+
state (FE polarization towards Pt),
the structure can be modeled as back-
to-back diodes showing Schottky-limited
conduction. The experimental conduction-
band offset is 0.40 eV at the Pt/BTO
interface and 0.45 eV at the BTO/NSTO
interface. In the P- state (FE polarization
towards NSTO), the top interface band
alignment remains Schottky-like (+0.90
eV) while at the bottom interface (BTO/
NSTO) the conduction band offset reduces
to zero leading to ohmic conduction,
consistent with the current – voltage
characteristic of the whole structure.
The observed barrier heights depend
on both the interface chemistry and
the FE polarization [3].
Using the time-resolved detection
system available at TEMPO beamline, the
photoemission response of the capacitor
to polarization switching induced by
square voltage pulses has been measured.
An equivalent circuit mo del has been
developed which compares well with the
photoemission response of the system
(Figure
➋
). This shows the potential of
time-resolved photoemission spectroscopy
to follow the chemical/electronic changes
in working model microelectronic devices,
here a ferroelectric capacitor [4].
Electronic pump with synchrotron
based XPS probe is the ideal tool and
appears well-suited to the time-resolved
capabilities of TEMPO. The next step is
in-operando
pump-probe measurements
of the electron dynamics of the switch,
focusing on the response of the
ferroelectric near the electrode interface.
Electronic response to polarization switching
at Pt/BaTiO3 interface
TEMPO beamline
ASSOCIATED PUBLICATION
Interface electronic structure in a metal/
ferroelectric heterostructure under applied bias
J.E. Rault*, G. Agnus, T. Maroutian, V. Pillard,
P. Lecoeur, G. Niu, B. Vilquin, M.G. Silly,
A. Bendounan, F. Sirotti, and N. Barrett
Physical Review B 87(15) (2013), 155146
*Synchrotron SOLEIL, l’Orme des Merisiers,
Saint-Aubin, 91192 Gif-sur-Yvette Cedex,
France
CORRESPONDING AUTHOR
➋
(a)
Time-dependent evolution
of the binding energy (BE) shifts
for the Pd 3d
5/2
(blue circles),
Pt 4f
7/2
(green squares)
and results of the electrical
simulations (solid lines) for the
two core-levels. The blue dotted
curve shows the pulse train
applied on the top electrode;
(b)
Equivalent circuit model
used to fit the experimental
data to theoretical simulations.
27
SOLEIL
HIGHLIGHTS
2013
