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