Supporting Information
Heterointerface design and strain tuning in epitaxial
BiFeO3:CoFe2O4 nanocomposite films
Wenrui Zhang,1 Meng Fan,2 Leigang Li,1 Aiping Chen,3 Qing Su,1 Quanxi Jia, 3 Judith L.
MacManus-Driscoll, 4 Haiyan Wang 1,2,a)
1
Department of Materials Science and Engineering, Texas A&M University, College Station, TX 77843, USA
2
Department of Electrical and Computer Engineering, Texas A&M University, College Station, TX 77843, USA
3
Center for Integrated Nanotechnologies (CINT), Los Alamos National Laboratory, Los Alamos, NM 87545, USA
4
Department of Materials Science and Metallurgy, University of Cambridge, Pembroke Street, Cambridge CB2 3QZ, UK
The supporting information includes:
Reciprocal space map of Film 1 near the (002) STO peak.
Statistical distribution histograms of CFO pillar size obtained from (a)-(d) SEM and (e)(h) AFM images.
Cross-sectional TEM images of (a) Film 3 and (d) Film 4. High resolution TEM images of
the BFO-CFO interface of (b) Film 3 and (c) Film 4 showing different interface couplings.
(c) and (f) Corresponding Fast Fourier transform (FFT) images of the marked area in (b)
and (e), respectively.
An electron diffraction pattern of Film 1 showing the high crystalline quality of both BFO
and CFO phases.
High-resolution TEM image and corresponding FFT images of the interface of (a,b) Film
1, (c,d) Film 4, (e,f) Film 2, (g,h) Film 3. The dislocation line density is calculated by the
number of identified dislocations along the interface.
Out-of-plane magnetic hysteresis loops of two BFO:CFO films deposited with the same
deposition parameters with (a) Film 2 and (b) Film 3 confirming the repeatability of the
results. Out-of-plane magnetic hysteresis loops of pure CFO films deposited by (a) 10 Hz
and (b) 1 Hz.
PFM Phase and amplitude switching behavior as a function of tip bias of (a) Film 1and (b)
Film 4.
1
Fig. S1. Reciprocal space map of Film 1 near the (002) STO peak.
2
Fig. S2. Statistical distribution histograms of CFO pillar size obtained from (a)-(d) SEM
and (e)-(h) AFM images. The minimum, maximum and average sizes are listed in
corresponding figures.
Fig. S2 is the statistical distribution histogram of CFO pillar size obtained from SEM and
AFM images. The minimum (Min), maximum (Max) and average (Avg) column sizes have
been obtained, which show a good agreement between the SEM and AFM results. In the
manuscript, we used the AFM results to estimate the average CFO pillar sizes, as AFM is
more sensitive to surface topography.
3
Fig. S3. Cross-sectional TEM images of (a) Film 3 and (d) Film 4. High resolution TEM
images of the BFO-CFO interface of (b) Film 3 and (c) Film 4 showing different interface
couplings. (c) and (f) Corresponding Fast Fourier transform (FFT) images of the marked
area in (b) and (e), respectively.
Fig. S3 uses Film 3 and Film 4 as two representative examples to demonstrate two different
interface structures of films deposited by multiple and single frequency. In Film 3, the
periodic lattice distortion of BFO is formed at the vertical interface, which is seen from the
formation of Moiré patterns (Fig. S3b) and double diffraction characteristics in its FFT
image (Fig. S3c). On the other hand, the vertical interface of Film 4 shows a much cleaner
lattice match between BFO and CFO (Fig. S3e), which is also evidenced by the clear
diffraction dots in the FFT image (Fig. S3f).
4
Fig. S4. Electron diffraction pattern of Film 1 showing the high crystalline quality of both
BFO and CFO phases.
5
Fig. S5. High-resolution TEM image and corresponding FFT images of the interface of
(a,b) Film 1, (c,d) Film 2, (e,f) Film 3, (g,h) Film 4. The dislocation line density is
calculated by the number of identified dislocations along the interface. Paired (unpaired)
dislocations are in light (dark) red color.
Fig. S5 shows their HRTEM images and corresponding Fast Fourier Transform (FFT)
images for a quantitative estimation. The VAN films deposited by multiple frequencies
have a larger dislocation line density (2.07-2.30108 m-1) than those by a single frequency
(1.48-1.69108 m-1). It should be noted that the presence of lattice distortion makes it
challenging to quantitatively estimate how dislocations relax the lattice strain only based
on the TEM observation. Based on the XRD results, a larger residual strain is maintained
in CFO even with a higher dislocation density. The strain in BFO is more complex since
the lattice distortion can be an additional source for strain relaxation. For example, in the
presence of significant lattice distortion in Film 2 (the large spread of Moiré patterns in Fig.
2(e)), the strain in BFO is largely relaxed to 0.44%, compared to 1.01% in Film 3.
6
Fig. S6. Out-of-plane magnetic hysteresis loops of two BFO:CFO films deposited with the
same deposition parameters with (a) Film 2 and (b) Film 3 confirming the repeatability of
the results.
7
Fig. S7. Out-of-plane magnetic hysteresis loops of pure CFO films deposited by (a) 10 Hz
and (b) 1 Hz.
8
Fig. S8. PFM Phase and amplitude switching behavior as a function of tip bias of (a) Film
1 and (b) Film 4.
9