Growth control of oxygen stoichiometry in homoepitaxial SrTiO3 films by pulsed laser epitaxy in high vacuum.

Ho Nyung Lee,Woo Seok Choi,Christopher M Rouleau,Sung S Ambrose Seo

doi:10.1038/srep19941

Ho Nyung Lee, Woo Seok Choi + Show 2 more

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https://doi.org/10.1038/srep19941

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Abstract

In many transition metal oxides, oxygen stoichiometry is one of the most critical parameters that plays a key role in determining the structural, physical, optical, and electrochemical properties of the material. However, controlling the growth to obtain high quality single crystal films having the right oxygen stoichiometry, especially in a high vacuum environment, has been viewed as a challenge. In this work, we show that, through proper control of the plume kinetic energy, stoichiometric crystalline films can be synthesized without generating oxygen defects even in high vacuum. We use a model homoepitaxial system of SrTiO3 (STO) thin films on single crystal STO substrates. Physical property measurements indicate that oxygen vacancy generation in high vacuum is strongly influenced by the energetics of the laser plume, and it can be controlled by proper laser beam delivery. Therefore, our finding not only provides essential insight into oxygen stoichiometry control in high vacuum for understanding the fundamental properties of STO-based thin films and heterostructures, but expands the utility of pulsed laser epitaxy of other materials as well.

Highlights

In many transition metal oxides, oxygen stoichiometry is one of the most critical parameters that plays a key role in determining the structural, physical, optical, and electrochemical properties of the material
When layer-by-layer growth is critical for sample quality and digital synthesis of artificial materials, e.g. epitaxial heterostructures and superlattices, the use of high oxygen partial pressure limits the choice of materials, and hinders obtaining atomically abrupt interfaces because high pressure synthesis tends to yield three-dimensional or island growth[28]
The inability to grow in low oxygen partial pressure whilst maintaining stoichiometry and sharp interfaces represents a serious obstacle in advancing our understanding on the physics of oxide thin films and interfaces

Summary

Introduction

In many transition metal oxides, oxygen stoichiometry is one of the most critical parameters that plays a key role in determining the structural, physical, optical, and electrochemical properties of the material. Our finding provides essential insight into oxygen stoichiometry control in high vacuum for understanding the fundamental properties of STO-based thin films and heterostructures, but expands the utility of pulsed laser epitaxy of other materials as well. We report a new approach that pushes the boundary of PLE optimal growth toward conditions that were once believed impossible – i.e., the growth of highly insulating, stoichiometric STO films in high vacuum. This was achieved by controlling the kinetic energy of the plume and prolonging the nucleus ripening time to better incorporate atomic oxygen provided by the target

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