Evolution of structural and magnetic properties of Ar2+ ion irradiated TiO2 thin films annealed under argon atmosphere

B Bharati,Chandana Rath

doi:10.1063/9.0000233

Abstract

In this report, the evolution of structural as well as magnetic state of 900 °C annealed TiO2 films under argon (Ar) environment have been examined before and after irradiating with the Ar2+ ions of energy 500 keV. The pristine film stabilized with Magneli phase (Ti4O7), the film retains its crystallinity but phase get transformed to anatase TiO2, irradiating with the lowest fluence, 1 × 1014 ions/cm2. After rising up to 5 × 1016 ions/cm2 ion fluence, film again stabilize with the Magneli phase (Ti4O7). In the previous report, we have demonstrated an unusual phase change from anatase TiO2 to brookite, where films are annealed in O2 atmosphere. In contrast to that here we have obtained TiO2 from Ti4O7 at lowest fluence but at highest fluence again Ti4O7 is obtained. The energy deposited by the ion beam passed to the lattice and collision cascades are formed which brings atomic displacement in the lattice, results the structural transformation. Surface topography is not affected much after the irradiation as observed from atomic force microscopy (AFM). Interesting, ferromagnetic behavior at room temperature stems in all the films as a consequence of the controlled introduction of anionic defects (oxygen vacancies).

Highlights

TiO2 is an essential and resourceful material with extensive range of applications.1–5 In general TiO2 crystallizes in three different forms i.e. anatase, brookite and rutile with the crystal structure, tetragonal (D149h), orthorhombic (D145h) and tetragonal (D144h), respectively
We have shown irradiation outcome of 500 keV Ar2+ ion in oxygen environment annealed TiO2 thin films
We have carried out irradiation of 100 MeV Ag7+ ions on undoped and Co doped TiO2 thin films which are deposited through pulsed laser deposition (PLD) technique

Summary

Introduction

TiO2 is an essential and resourceful material with extensive range of applications. In general TiO2 crystallizes in three different forms i.e. anatase, brookite and rutile with the crystal structure, tetragonal (D149h), orthorhombic (D145h) and tetragonal (D144h), respectively. The anatase, brookite and rutile phase shows band gap 3.19, 3.11 and 3.03 eV, respectively.. The anatase, brookite and rutile phase shows band gap 3.19, 3.11 and 3.03 eV, respectively.6,7 In addition to these phases of TiO2, titanium sub-oxides (Magneli phase compounds, TinO2n-1, 4≤n≤10) have been explored for its electrochemical applications. Out of all the Magneli phase compounds Ti4O7 is having highest electrical conductivity.. Out of all the Magneli phase compounds Ti4O7 is having highest electrical conductivity.8,9 It is generally derived from the reduction of TiO2.8,9 Ion irradiation has been used as a unique tool in material modification.. While anatase phase to brookite transformation was observed after irradiating 500 keV Ar2+ ions, followed by amorphization, 100 MeV Ag7+ ion beam irradiation makes the films amorphous.

Methods

Results

Conclusion