Experimental evidence for oxygen sublattice control in polar infinite layer SrCuO2

Supplemental material

Experimental evidence for oxygen sublattice control in polar infinite-layer SrCuO2

D. Samal1, Tan Haiyan2, H. Molegraaf1, B. Kuiper1, W. Siemons4, Sara Bals2, Jo Verbeeck2, Gustaaf Van Tendeloo2_{, Y. Takamura}3_{, Elke Arenholz}5_{, Catherine A. Jenkins}5_{, G. Rijnders}1_,

and Gertjan Koster1*

1_{MESA+ Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500AE,}

Enschede, The Netherlands

2_{EMAT, University of Antwerp, Groenenborgerlaan 171, B-2020 ANTWERP, Belgium} 3_{Department of Chemical Engineering and Materials Science, University of California—}

Davis, Davis, California 95616, United States

4_{Materials Science and Technology Division, Oak Ridge National Laboratory, United States} 5_{Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California,}

United States

Methods; thin film growth.

All the SLs were grown by pulsed laser deposition, using a TSST system and a 248-nm-wavelength KrF excimer laser (LPX 200 from Coherent, Inc.). The most homogeneous part of the laser beam was selected using a 4 by 15 mm rectangular mask and an image of the mask was created on the stoichiometric targets (SrTiO3 and SrCuO2) with a lens, resulting in a spot

size of 1.8 mm2. Before deposition the target was pre-ablated for 2 minutes at a pulse rate of 5 Hz and laser fluence 2 J/cm2 to remove any possible surface contamination. The substrate temperature during the growth was held at 6500_{C and the oxygen partial pressure was}

maintained 0.3 mBar. The deposition was carried out at a pulse rate of 1 Hz and a laser fluence of 2 J/cm2_{. After the deposition, the samples were cooled to room temperature at a}

controlled cooling rate of 100C/minute. These deposition conditions have been optimized to result in the growth of the tetragonal phase of SrCuO2 (See Figure S1).

X-ray scattering

In Figure S1, we show the typical

θ

−2

θ

X-ray diffraction pattern for a (001)-oriented infinite layer SCO tetragonal film (~80 nm) grown on a (001)-oriented STO substrate. The diffraction pattern matches well with the reported data[1] for the tetragonal phase of SCO film with c = 3.432 Å; grown on STO.

Figure S1. θ-2θ XRD spectrum of a tetragonal SCO film. The arrow-marked intense peaks

belong to the STO substrate; the non-arrow-marked ones belong to SCO.

Reflection high-energy electron diffraction and surface morphology by AFM:

In Figure S2 (a) and (b), we show typical streaky RHEED pattern after the growth for m=3 and m=8 SLs respectively, signifying 2D growth. However, an indication for increased overall surface roughness is observed with increase in SCO thickness in the SLs. This is also

20

30

40

50

60

(002)

(STO

)

(001)

(STO)

(001)

(002)

Counts(arb. units)

2

Θ(

degree)

evident if we analyze the RHEED pattern in Figure S2 [(c) and (d)] that compares the successive growth of STO and SCO layers in one of the representative ((SCO)m/(STO)2) SL

with m=3. In particular, (c) represents the RHEED pattern after 10th repetition of

(SCO3/STO2) block i.e. with STO top and (d) represents the RHEED pattern after the growth

of only SCO constituent in the 11th _block.

Figure S2. (a) A streaky 2D like RHEED pattern observed at the end of the growth for (a)

((SCO)3/(STO)2)20 and (b) ((SCO)8/(STO)2)20.(c) and (d) represents the evolution of RHEED

pattern after the successive growth of STO and SCO layers respectively in one of the representative ((SCO)m/(STO)2) SL with m=3.

In Fig. S3 (a) and (b), we show representative AFM images for m=3 and m=8 SLs with rms values of ~0.2 and 0.4 nm, respectively.

(a)

(b)

Figure S3. Ex-situ AFM image of (a) ((SCO)3/(STO)2)20 and (b) ((SCO)8/(STO)2)20 SLs.

REFERENCES:

[1] Y. Terashima et al., Jpn. J. Appl. Phys. 32, L48 (1993).

(b)

(a)