Supporting Information to the manuscript:
Structures and physical properties of transparent conducting, amorphous Zndoped SnO2 films
Q. Zhu,‡ Q. Ma,§, ‡ D. B. Buchholz, ‡ R. P. H. Chang, ‡ M. J. Bedzyk, ‡ T. O. Mason‡
‡
§
Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208, USA
DND-CAT, Northwestern Synchrotron Research Center at Advanced Photon Source, Argonne, Illinois 60439, USA
1. Local structure change with annealing
Fig. S1 shows the Zn K-edge EXAFS spectra and their Fourier transforms (FTs) of the asdeposited and post-annealed a-ZTO90 film films. Higher magnitudes of second shell peaks were
observed after one hour annealing at 450°C, when crystallization has occurred as evidenced by
GIXRD (see Fig. 1 in the main text). The change of the local structure around Zn could be
evidenced by the first (Table 1) and second shell fitting results (Table S1).
Figure S1. The Zn K-edge k3-weighted EXAFS spectra (left) and their Fourier transforms (right)
measured on ZTO90 films deposited at 10 mTorr (a) and air-annealed at 300°C (b), 400°C (c), 450°C (d),
respectively. The smaller coordination numbers of Zn-O for the 450°C-annealed sample compared to the
as-prepared sample (see Table 1) is also reflected in the decrease in the magnitude of the respective FTs.
Table S1. EXAFS determined structural parameters for the second coordination shells.
Samples
R (Å)
N
σ2(Å2)
Sn-Sn
Zn-Sn
Sn-Sn
Zn-Sn
Sn-Sn
Zn-Sn
a-SnO2
3.22
-
1.9
-
0.0093
-
a-ZTO90
3.26
3.08
1.9
1.5
0.0085
0.017
(300°C)
3.26
3.07
1.9
1.5
0.0085
0.016
(400°C)
3.25z
3.08
2.0
1.1
0.0093
0.018
(450°C)
3.18
3.12
2.1
2.6
0.0093
0.017
Figure S2. Fourier transforms of k3-weighted EXAFS (solid lines) and the best fits including the second
shells (dashed lines) of Sn and Zn K-edges for the as deposited a-ZTO90 film (10 mTorr).
2. Double-shell modeling of the first coordination shell around Sn
Fig. S3 presents the 𝑆02 values as function of the the data range used for fitting of Sn K-edge.
Strong dependence on the EXAFS data range was observed in the cases of 300°C- and 400°Cannealed ZTO90 films as well as the a-SnO2 film, where N around Sn decreased monotonically
up to 5% from increasing the EXAFS data range from 9.5 to 12.4 Å-1. Meanwhile, the figure of
merit for the fittings deteriorates by nearly 4-fold. In contrast, such a relation is much weaker, if
any, for the as-prepared a-ZTO90 film. This correlation with kmax can be removed with a doubleshell model. In the double-shell model, two Sn-O bond distances with a small separation were
assumed, and the total coordination number N is fixed at 6 (=N1 + N2). When considering a small
structural change (1-2%), fitting may not produce fully reliable results due to the difficulties in
the fitting algorithm, precision of calculated phases (k) and amplitudes f(k), and strong
correlation between the parameters, such as that between N and σ2. However, with the
observation of a beating characteristic around 9 Å-1 as shown in Fig. 7, this suggests the
development of two Sn-O bond distances in the first shell around Sn. Therefore, the double-shell
model is believed to better approximate the true structure. See the reference 31 for more details.
Figure S3. kmax-dependence of 𝑆02 for Sn K-edges of a-SnO2 and a-ZTO films. The fitting results were
obtained by assuming a single Sn-O distance and N = 6. Line of a-SnO2 is for eye guidance only. 𝑆02 of cSnO2, which is 1.02, is determined using the data up to 14.7 Å-1 where the first shell EXAFS oscillations
are included in complete.
3. Data processing of the X-ray scattering measurements
Figure S4. The incident x-ray intensity normalized, raw scattered intensity and Zn K fluorescence data
of a-ZTO90 along with background data with no sample.
Figure S5. Raw data from Fig. S4 after background corrections and compared to a calculated XRD pattern
from polycrystalline rutile c-SnO2.
Figure S6. The scattered intensity data from Fig. S5 after normalization to the calculated elastic and
inelastic scattering background using the high-angle method. q = 4πsin(2Theta/2)/λ.
Figure S7. Structure factor of a-ZTO from data shown in Fig. S6.
Figure S8. Pair distribution functions (PDF) obtained by Fourier transforms of Fig. S7 data over q-ranges
with different qmax cut-offs as labeled. The upper most curve is the data shown in Fig. 2 in the main text.