Supplemental material for publication: Terahertz transmission
characteristics across the phase transition in VO2 films deposited
on Si, sapphire and SiO2 substrates
Qiwu Shi,1 Wanxia Huang,1,a) Jing Wu,1 Yaxin Zhang,2 Yuanjie Xu,1 Yang Zhang,1
Shen Qiao,2 and Jiazhen Yan1
College of Materials Science and Engineering, Sichuan University, Chengdu, 610064, People’s
1
Republic of China
2
Terahertz Science and Technology Research Center, University of Electronic Science and
Technology of China, Chengdu,610054, People’s Republic of China
a)
Corresponding author: huangwanxiascu@yahoo.com.cn
Interpretation of the XPS characterization
Table S1 Binding energy (BE) and area of the fitted V2p3/2 lines of the VO2 films on Si, sapphire
and SiO2 substrates
V5+ 2p3/2
V4+ 2p3/2
BE/eV
Area
BE/eV
Area
Si
517.2
3022.33
516.1
7234.26
Sapphire
516.9
2279.27
515.7
7378.66
SiO2
517.3
1506.61
516.1
5128.45
In the manuscript, the peak position of V2p3/2 has been fitted using a Shirley
function with the XPS Peak 4.1 software. For all three films, two valence states of
vanadium, +4 valence (with a binding energy of 515.7-516.2 eV) and +5 valence
(with a binding energy of 516.0-517.2 eV) were detected. Both of the binding energy
for the two valence states of vanadium were in agree with the reported researches.1,2
In order to obtain the relative concentrations of atoms in a homogeneous system, one
1
simply divides each atom’s peak intensity by its sensitivity factor and takes the ratio,
giving the general relation:3,4
n A I A SB

nB I B S A
(1)
Where I is the peak intensity of atom, S is the sensitivity factor and n is the atomic
concentration, respectively.
According to it, the concentrations of the vanadium with different valence states
were determined by calculating from the following equations:
n V 4 
I V 4  SV 5 
I V 4  SV 5   I V 5  SV 4 
(2),
n V 5 
I V 5  SV 4 
I V 4  SV 5   I V 5  SV 4 
(3)
Noting that the S values for both of the two valences have been taken as the same as
a standard (S=1). The binding energy (BE) and area of the fitted V2p lines of the films
on Si, sapphire and SiO2 substrates are given in Table S1. Then, the +4 valence in the
VO2 film on the Si, sapphire and SiO2 substrate is calculated as 70.53%, 76.4% and
77.29% respectively.
AFM graphics of the VO2 film on the Si, sapphire and SiO2 substrates
Although the surface parameters of the VO2 films grown on the Si, sapphire and
SiO2 substrates have been investigated by AFM in our manuscript, the scan range was
small with just 1 μm×1 μm. We have made multiple scans on the films with larger
scale to get more average results. The AFM graphics of the films with 2×2 μm scan
rage were shown in Figure S1. Herein, the size distribution of grains and the average
surface roughness (Ra) are still quite different for the three films. Especially, the VO2
film on Si substrate shows the widest variation in size distribution and SiO2 the least,
which is consistent with the results illustrated in Figure 3 in our manuscript.
2
FIG. S1. Left: two-dimensional AFM photographs of the VO2 films on (a) Si, (b) sapphire, and (c)
SiO2 substrates. Right: three-dimensional AFM photographs of the VO2 films on (a) Si, (b)
sapphire, and (c) SiO2 substrates.
A supplement for the terahertz transmission data of the high-purity
Si substrate at 25 °C and 90 °C
3
The high-purity Si is not only one of the most transparent but also the least
dispersive mediums in the terahertz region.5,6 The Si substrate employed in our
presented work is high-purity relatively, with a resistivity about 2000 Ω cm. Figure S2
shows the time-domain transmission signals for the sample at 25 °C and 90 °C. There
was nearly no decrease in the transmission signals for the Si substrate with the
temperature at this range. However, the resistivity of the Si substrate is still finite
compared with the SiO2 and sapphire substrates, so we can’t assert that the Si
substrate does not contribute to the THz transmission of the sample totally. In order to
diminish the effect of substrate, we normalized the transmission signal of VO2 films
by comparing the THz signals transmitted through the VO2 on substrates to that
through the bare substrates, as described in the manuscript. Then we could propose
that the THz transmission signals displayed in Figure 5 reflect the THz transmitted
through the VO2 films mainly. It is worth noting that the common used “normalizing
method” may need further improvement, to realize more precise results.
FIG. S2. Time-domain transmission signals for the bare Si substrate at 25 °C and 90 °C.
4
References
1Z.
T. Zhang, Y. F. Gao, Z. Chen, J. Du, C. X. Cao, L. T. Kang, and H. J. Luo, Langmuir 26, 10738
(2010).
2
N. Alov, D. Kutsko, I. Spirovová, Z. Bastl, Sur. Sci, 600, 1628 (2006).
3
J. E. Bowen Katari, V. L. Colvin, and A. P. Alivisatos, J. Phys. Chem. 98, 4109 (1994).
4A.
Jablonski, Sur. Sci. 630, 1342 (2009).
5
T. I. Jeon, and D. Grischkowsky, Phys. Rev. lett. 78, 1106 (1997).
6J.
M. Dai, J. Q. Zhang, W. L. Zhang, and D. Grischkowsky, J. Opt. Soc. Am. B 21, 1379 (2004).
5