ZnO is a wide used ferroelectric material with a variety of applications. This study investigates ZnO thin films doped by Ti as showing structure change from ZnO wurtzite up to ZnTiO₃ perovskite.

ZnO:Ti thin films were prepared by RF reactive magnetron co-sputtering in Ar/O₂ atmosphere from pure Zinc and Titanium targets (99.99%). Changes of amount of Ti in films were documented by EDS and EELS measurements, structure changes were measured by electron diffraction from thin film cross section (XTEM ED) and two geometries of XRD together with measurement of material optical properties.

Pure ZnO wurtzite structure show with increasing amount of Ti texture change from 8 degrees for 2.4 at % Ti to the 39 degrees for 8.7 at % Ti as it can be seen on electron diffraction patterns on figure 1a together with figure 1b. Structure measured by XRD appear to be more amorphous with Ti increasing as intensity of diffraction lines decreases and interatomic distances change from wurtzite to perovskite ZnTiO₃ structure (fig. 2).

Diffraction measurement is by the Voight function method also capable to measure from single diffraction line size and lattice distortions of the diffracted particles. In our case results for 2.4 at % Ti ZnO line 002 is 52 nm and for 7.8 at % Ti ZnTiO₃ line 104 is 19 nm, both with dualism indicates two regions of low and highly distorted part of particles. This correspond to relaxed core and distorted surface of the grains as it can be seen on figure 1c and d for Ti content 2.4 at % Ti or 8.7 at % Ti respectively.

Electron diffraction pattern from cross section is also capable to show and compare information from XRD measurements in two different geometries; situation is illustrated on figure 3. Circle integration of ED by ProcessDiffraction program [1] is capable to compare JCPDS diffraction database with electron diffraction pattern, however, this procedure do not take into consideration texture of investigated materials. Different geometries of XRD measurement takes in case of textured material different places indicated on XTEM electron diffraction pattern on Fig.3. Comparing of both results have to be carefully considered.

Direct comparation of measured interplanar distances is illustrated in Fig.4.

[1]       J.L. Lábár: Consistent indexing of a (set of) SAED pattern(s) with the Process Diffraction program, Ultramicroscopy, 103 (2005) 237-249.

Figures:

Fig. 1: HR-TEM and electron diffraction from XTEM ZnO:Ti thin films with 2.4 or 8.7 at % Ti respectively.

XRD measurement of ZnO thin films with 0.1 or 4.2 at % Ti respectively.

XRD with two geometries compared with processed electron diffraction pattern from ZnO:Ti thin film with 8.7 at % Ti.

HR-TEM measurement of interplanar distances for ZnO:Ti thin films with 2.4 or 8.7 at % Ti respectively.

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EMC Abstracts - https://emc-proceedings.com/abstract/investigation-of-structural-changes-of-znoti-thin-films-prepared-by-rf-sputtering/