Supporting Information
Nano-patterning of the electron gas at the
LaAlO3/SrTiO3 interface using low-energy ion
beam irradiation
Pier Paolo Aurino,1,* Alexey Kalabukhov,1,3Nikolina Tuzla,2 Eva Olsson,2Tord Claeson,1 and Dag
Winkler1
1
Department of Microtechnology and Nanoscience – MC2, Chalmers University of Technology, SE-
412 96 Gothenburg, Sweden
2
Department of Applied Physics, Chalmers University of Technology, SE-412 96 Gothenburg,
Sweden
3
Skobeltsyn Institute of Nuclear Physics, Department of Physics, Moscow State University, 119899
Moscow, Russia
* Address correspondence to: aurino@chalmers.se
Section 1 - SRIM results
Ion induced damage during Ar+ irradiation in the LAO/STO heterostructure was simulated using
the “Stopping and Range of Ions in Matter” (SRIM) simulation software.1 The results of the
simulations using very similar conditions as in our experiment (Ar+ ions, 30° incident angle,
number of ions corresponding to the dose rates used in the experiment) are shown in Fig.S.1. The
150 eV Ar+ ions are effectively stopped by the 10 uc thick LAO film, see Fig.S.1a, and therefore do
not reach the interface at least in the beginning of the irradiation process. The penetration depth of
ions increases at higher beam voltages (Fig. S.1b and Fig. S.1c) and the beam trajectories start to
reach the STO substrate. This implies that the observed behavior of the electrical resistance in our
experiment can be related to the formation of oxygen vacancies in the STO layer. This is further
supported by the simulations of oxygen vacancies produced by incident ions in the LAO/STO
heterostructure at different beam voltages, see Fig. S.1d-f. At low energies, the effect of the ion
damage on oxygen in the STO substrate is negligible, in agreement with our experimental results.
At higher beam voltages, oxygen vacancies are formed in the beginning of the irradiation process
and this causes a rapid decrease in the electrical resistance of the sample. The simulations do not
take into account the possible physical etching of the LAO layer during the irradiation process. For
the low energy beam, the formation of oxygen vacancies in the STO substrate requires much higher
doses (up to 1018 Ar+cm-2) due to the slow etching and thus provides a suitable time interval for the
patterning of a conducting interface in the LAO/STO.
Figure S.1 The Stopping and Range of Ions in Matter simulations of Ar+ ion induced damage in
a10 unit cell thick LaAlO3/SrTiO3 sample. Incident ion trajectories at 30° incidence with (a) 150,
(b) 250 and (c) 350 V acceleration voltage and corresponding oxygen vacancies produced by
collision events(d-f). The number of ions per unit cell in simulations corresponds to the actual ion
beam dose in the experiment.
Section 2 - Kelvin Probe AFM measurements
Kelvin probe AFM (KPFM) measurements were performed in order to investigate the confinement
of electrical conductivity in the fabricated structures in the LAO/STO interface. We have shown
earlier that Kelvin probe can be used to directly image the contrast between conducting and
insulating areas in the LAO/STO interface.2 AFM topography and Kelvin probe images of 1 µm
wide bridges are shown in Fig.S.2a. The contrast in Kelvin probe images corresponds well to the
geometric size of the bridges. The cross-section profile (Fig. S.2c) also shows the presence of a
double-step structure with the size of the second step about 0.5 μm for all structures. The presence
of the second step may be related to the change of the width of the resist mask during the irradiation
process, the limited resolution of the Kelvin probe AFM, or a combination of both factors.
Figure S.2 a) Kelvin probe AFM image of 1 μm wide bridge. The inset shows corresponding AFM
topography image of the same area. b) Schematic representation of the resist trapezoidal shape at
the beginning of irradiation. c) Section profile of the voltage measured for the bridge with side
areas.
Section 3 – RHEED analysis
We also checked if the interface electrical conductivity can be restored by a post annealing of the
irradiated film. RHEED analysis of the LAO film after ion beam irradiation shows that the surface
is amorphized, see Fig.5b. The crystalline surface of the film was fully recovered after annealing at
600 °C in 500 mbar O2, see Fig. 5c. The RHEED images of annealed film and film before
irradiation (Fig. 5a) show identical surface structure without presence of surface reconstructions.
However, the sample remained insulating after the post annealing.
Figure S.3 Reflection high-energy electron diffraction images of LaAlO3 film: a) after deposition,
b) after Ar+ ion beam irradiation and c) after annealing at 700 °C, 10-4 mbar O2.
REFERENCES
1. Ziegler J.; Biersack J.; Littmark U.; The Stopping of Ions in Matter. 1985, Pergamon, New
York; www.srim.org.
2. Popok, V.; Kalabukhov, A.; Gunnarsson, R.; Lemeshko, S.; Claeson, T.; Winkler, D.;
Kelvin Probe Force Microscopy Study of LaAlO3/SrTiO3 Heterointerfaces. Journal of
Advanced Microscopy Research 2010, 5, 1-5.