Experimentally informed structure optimization of amorphous TiO₂ films grown by atomic layer deposition

Area of Science:

• Materials Science
• Nanotechnology
• Solid State Physics

Background:

• Amorphous titanium dioxide (a-TiO2) is vital for semiconductor coatings in photoelectrochemical applications.
• Film thickness and structural heterogeneity significantly impact a-TiO2 stability and longevity.
• Understanding a-TiO2 structure-property relationships is key to enhancing performance.

Purpose of the Study:

• To characterize the structural and electronic properties of amorphous titanium dioxide thin films.
• To establish a realistic atomic model for a-TiO2 guided by experimental data and simulations.
• To investigate the impact of medium-range ordering on a-TiO2 properties.

Main Methods:

• Atomic layer deposition (ALD) for growing ~17 nm a-TiO2 thin films on Si.
• 4-dimensional scanning transmission electron microscopy (4D-STEM) to determine fluctuation spectra and angular correlation functions.
• StructOpt code with a genetic algorithm for structure optimization, minimizing energy and matching experimental ordering.

Main Results:

• Distinct medium-range ordering was revealed in the a-TiO2 film using 4D-STEM.
• A StructOpt-optimized a-TiO2 model showed improved agreement with experimental medium-range ordering compared to traditional models.
• Ab initio calculations provided insights into the electronic structure of the optimized a-TiO2 model.

Conclusions:

• This study uncovered crucial medium-range ordering in amorphous titanium dioxide thin films.
• A realistic a-TiO2 structure model was developed for further structure-property relationship investigations.
• The StructOpt package offers an improved approach for complex material structure determination.