ubject Number :S-17-JI-0008

Support Type : Collaborative research,
Proposal Title (English) : Investigating the local chemical constitutions of the transparent conductors by using Transmission Electron Microscope
Username (English) :Emila Panda

Affiliation (English) :Indian Institute of Technology Gandhinagar, Palaj – 382355, Gujarat, India

1. Summary

In this work, zinc segregation after every step of spin coating was observed for both the Al-doped ZnO films, which was associated to its relatively lower surface energy. Additionally, the Al-doped ZnO film, annealed in low vacuum was found to have very less oxygen (i.e., almost metallic), whereas, the film annealed under both the lower and higher vacuum was found to have near stoichiometric composition.

2. Experimental

At JAIST, cross-sectional TEM lamella of two Al-doped ZnO films by means of focused ion beam (FIB) was prepared. These samples were fabricated at IIT Gandhinagar by using a sol-gel followed by spin coating process and then were annealed under different atmospheric conditions (i.e., lower vacuum, lower vacuum followed by the higher vacuum). The high resolution transmission electron microscopy (HR-TEM) and scanning transmission electron microscopy (STEM) were conducted on these samples to understand the nature of the film growth along with the elemental distribution of various elements in these films.

3. Results and Discussion

The HR-TEM of both these samples clearly showed the number of coatings conducted by sol-gel followed by the spin coating process. This is because of the relatively higher temperature drying of these spin-coated samples after each coating (i.e., at 375 K). Further, both these samples showed the surface segregation of zinc (see Fig. 1 (a-c) and (a’-c’)). This is because of the relatively
lower surface energy of zinc (i.e., 753 mJ/m2) as
compared to aluminum (i.e., 840 mJ/m2). Additionally, we found a relatively higher concentration of aluminum and zinc along with a relatively lower concentration of oxygen in the Al-doped ZnO sample subjected only a lower vacuum annealing (see Fig. 1). The analysis and the possible reason are underway.