[Paper Review] Synthesis of Perovskite SrIrO3 Thin Films by Sputtering Technique

Z.Z. Li, Olivier Schneegans+1 more|arXiv (Cornell University)|Oct 12, 2016

Advanced Condensed Matter Physics3 citations

TL;DR

This study demonstrates the first successful synthesis of high-quality, single-phase, epitaxial SrIrO3 thin films using radiofrequency magnetron sputtering on SrTiO3 (001) substrates. The films exhibit (110) out-of-plane orientation with (001) and (1-10) in-plane, are atomically flat, and show excellent lattice coherence with the substrate, confirming the technique's viability for scalable, reproducible oxide film growth.

ABSTRACT

We report on the synthesis of perovskite SrIrO3 thin films using sputtering technique. Single phase (110) oriented SrIrO$_3$ thin films were epitaxially grown on SrTiO3 (001) substrate. Using off-axis XRD $θ-2θ$ scans, we demonstrate that these films exhibit (110) out-of-plane orientation with (001) and (1-10) lying in-plane. The sputtering grown thin films have a smooth, homogeneous surface, and excellent coherent interface with the substrate.

Motivation & Objective

• To develop a scalable, reproducible method for growing high-quality SrIrO3 thin films using physical vapor deposition.
• To overcome the challenge of SrIrO3 film instability and non-stoichiometry during deposition by using a non-stoichiometric Sr4IrO6 target.
• To achieve epitaxial growth of SrIrO3 on SrTiO3 (001) substrates with controlled orientation and structural coherence.
• To validate the crystallographic orientation and epitaxial quality of sputtered SrIrO3 films using advanced XRD techniques.
• To establish sputtering as a viable alternative to molecular beam epitaxy or pulsed laser deposition for complex oxide films.

Proposed method

• RF magnetron sputtering was employed using a Sr4IrO6 target to compensate for Sr loss during deposition.
• Substrates were heated to 610 °C and cleaned via ultrasonication and plasma treatment prior to deposition.
• Sputtering was performed in an Ar/O2 (1:2) gas mixture at 210 mTorr total pressure with a 40 mm target-to-substrate distance.
• Off-axis θ-2θ XRD scans at 45° sample tilt were used to determine in-plane and out-of-plane crystallographic orientation.
• Reciprocal space mapping (RSM) was used to confirm coherent epitaxial strain and lattice matching between film and substrate.
• X-ray reflectivity and Kiessig fringe analysis were used to determine film thickness with high precision.

Experimental results

Research questions

• RQ1 Can high-quality, single-phase SrIrO3 thin films be synthesized via RF sputtering, a scalable technique not previously reported for this perovskite?
• RQ2 What is the crystallographic orientation of sputtered SrIrO3 films grown on SrTiO3 (001) substrates, and how does it compare to other deposition methods?
• RQ3 To what extent do the films exhibit epitaxial coherence and lattice matching with the SrTiO3 substrate?
• RQ4 How does the use of a Sr4IrO6 target influence stoichiometry and phase purity in sputtered SrIrO3 films?
• RQ5 Can sputtered SrIrO3 films maintain structural stability and high quality at thicknesses up to 100 nm without phase segregation?

Key findings

• Single-phase, epitaxial SrIrO3 thin films were successfully grown on SrTiO3 (001) substrates using RF sputtering with a Sr4IrO6 target.
• The films exhibit (110) out-of-plane orientation, with (001) and (1-10) directions lying in the substrate plane, confirmed by off-axis XRD.
• The out-of-plane lattice spacing of 4.038 Å for the 100 nm film is consistent with bulk SrIrO3 and matches values from PLD-grown films.
• Rocking curve FWHM values of 0.035° for the (220) reflection in the 100 nm film indicate excellent out-of-plane crystalline alignment.
• Reciprocal space mapping confirmed full in-plane lattice coherence between the SrIrO3 film and SrTiO3 substrate, with identical Qx values.
• The films remained phase-pure and stable in ambient air, even at thicknesses as low as a few nanometers, unlike PLD-grown films requiring encapsulation.