# Epitaxy enhancement in oxide/tungsten heterostructures by harnessing the interface adhesion

**Authors:** Anna L. Ravensburg, Rimantas Brucas, Denis Music, Lennart Spode, Gunnar K. Pálsson, Peter Svedlindh, Vassilios Kapaklis  
**arXiv:** [2306.12233](https://arxiv.org/abs/2306.12233)  
**Date:** 2023-06-21  
**Summary page:** https://www.summarizepaper.com/en/paper/2306.12233v2/

## Key points

- Single crystalline tungsten (W) thin films grown on Al$_{2}$O$_{3}$ ($11\bar{2}0$) substrates exhibit enhanced crystal quality compared to those grown on MgO ($001$) substrates
- The stronger adhesion and chemical bonding with sapphire contribute to the improved crystal quality of W on Al$_{2}$O$_{3}$
- Restructuring of the W layers near the interface also plays a role in achieving high crystal quality
- Ab initio calculations using density functional theory support the findings
- Magnetic heterostructures consisting of high-quality W layers combined with ferromagnetic CoFe layers are demonstrated, which have potential applications in spintronics
- X-ray scattering techniques, including reflectometry (XRR) and diffraction (XRD), were used to analyze the epitaxial growth of W thin films
- Scanning transmission electron microscopy (STEM) imaging confirmed the epitaxial growth mechanism
- Electrical properties of the W thin films were investigated through Hall coefficient and resistivity measurements
- Understanding how high crystal quality can be achieved despite lattice mismatch between substrate and film is crucial for future spintronic applications involving W-CoFe bilayers
- The research was supported by funding from various sources, including the Swedish Research Council and the Olle Engkvist Foundation

## Summary

This study investigates the growth and interface structure of single crystalline tungsten (W) thin films on two different metal oxide substrates, Al$_{2}$O$_{3}$ ($11\bar{2}0$) and MgO ($001$). Despite a significant lattice mismatch between W and the substrates, enhanced crystal quality is observed for W grown on sapphire substrates. This is attributed to stronger adhesion and chemical bonding with sapphire compared to magnesium oxide, along with restructuring of the W layers near the interface. The findings are supported by ab initio calculations using density functional theory. Additionally, the study demonstrates the growth of magnetic heterostructures consisting of high-quality W layers combined with ferromagnetic CoFe layers, which have potential applications in spintronics. The epitaxial growth of W thin films was analyzed using extensive x-ray scattering techniques, including reflectometry (XRR) and diffraction (XRD). XRR measurements were performed using a Bede D1 diffractometer equipped with a Cu Kα1 x-ray source. The data obtained from XRR analysis allowed for the determination of the scattering length density profile, providing information on layer thickness and roughness. XRD measurements involved coupled 2θ-θ and rocking curve scans to analyze peak positions and texture analysis through rotational ϕ scans at different sample tilts χ. In addition to x-ray scattering analysis, scanning transmission electron microscopy (STEM) imaging was conducted to confirm the epitaxial growth. The high-resolution STEM images provided detailed insights into the growth mechanism of these epitaxial thin films. The study also investigated the electrical properties of the W thin films. Hall coefficient and resistivity measurements were carried out using a 4-point probe setup in a van der Pauw geometry. The results contribute to an understanding of how high crystal quality can be achieved in spite of lattice mismatch between substrate and film. This understanding is crucial for the development of future spintronic applications that may require bilayers of W and CoFe. The research was supported by funding from the Swedish Research Council, the Swedish Energy Agency, and the Olle Engkvist Foundation. The computations were enabled by resources provided by the National Academic Infrastructure for Supercomputing in Sweden (NAISS) at National Supercomputer Centre (NSC). The data supporting the findings of this study are available from the authors upon reasonable request. In summary, this study provides valuable insights into the growth and interface structure of W thin films on metal oxide substrates. It highlights the importance of adhesion, chemical bonding, and restructuring near the interface in achieving high crystal quality. The findings have implications for spintronic applications involving W-CoFe heterostructures.