This shows the three-dimensional AFM images (1×1 μm² ) of ITO film grown on PMMA substrate at different Ar partial pressure of 0.8Pa (a), 1.1Pa (b), and 1.4Pa (c), respectively. The surface roughness decreased from 0.923nm to 0.813nm with the increasing Ar partial pressure from 0.8Pa to 1.1Pa. On the other hand, the surface of the film grown on PMMA substrate at Ar partial pressure 1.4Pa exhibited a great deal of roughness of 1.252nm. Three-dimensional grains 80-100 nm in diameter were observed, as shown in Figure 1 (a), which indicated typical columnar growth. The grain diameter became smaller, which was reduced to 50-60 nm as shown in Figure 1 (c), and it decreased further to 10-20nm at Ar partial pressure 1.1Pa as shown in Figure 1 (b). The kinetic energy of the deposited atoms during film growth should decrease with increasing Ar partial pressure, which suppressed atomic migration and reduces the growth rate of ITO. Therefore, Ar gas partial pressure during film growth is a key factor in controlling the film growth rate, leading to the improvement of surface smoothness observed in Figure 1 (b).

Fig. 1. The three-dimensional AFM images of ITO film grown on PMMA substrate at different Ar partial pressure. (a) Ar partial pressure 0.8Pa, surface roughness 0.923nm, (b) Ar partial pressure 1.1Pa, surface roughness 0.813nm, (c) Ar partial pressure 1.4Pa, surface roughness 1.252nm [1].

Reference:

[1] Tang, W. , Chao, Y. , Weng, X. , Deng, L. , & Xu, K. . Optical property and the relationship between resistivity and surface roughness of indium tin oxide thin films. 18TH INTERNATIONAL VACUUM CONGRESS (IVC-18).

The compositional information of ITO can be obtained from XRD spectra, in which the peak position implies different diffraction plane, and the peak intensity ratio gives out the elemental relative content ratio. In ITO, certain positions are substituted by and SnO₂ crystal forms in original crystal. Their crystal structures are different and thus their peak positions are different. The more amount of certain components, the stronger the peaks. So, the atomic ratio of Indium (In), Tin (Sn), Oxygen (O), and Carbon (C) can be calculated based on the intensity of peaks.

Fig. 1. XRD spectrum of ITO with different wt% of Sn.[1]

The Sn substitution causes the change in crystal structure and forms the second phase of SnO₂ in the original. The amount of Sn and In can be calculated based on the intensity of peaks. The precision of the result is dependent on the process of peak-splitting and peak area integration. As shown in figure 1, the existence of Sn can be detected when wt% of Sn exceeds 10 wt%. This value is lower than the doping ratio in industrial manufacturing ^[2], so XRD is accurate enough for characterization. In conclusion, XRD can give quantitative information about the composition of ITO material.

Reference:

[1] Kőrösi, L., etc. (2011). Preparation of transparent conductive indium tin oxide thin films from nanocrystalline indium tin hydroxide by dip-coating method. Thin Solid Films, 519(10), 3113-3118.

[2] Bhuvaneswari, S., etc. (2021). Fabrication and characterization of p-Si/n-In2O3 and p-Si/n-ITO junction diodes for optoelectronic device applications. Surfaces And Interfaces, 23, 100992.