Dynamic layer rearrangement during growth of layered oxide films by molecular beam epitaxy

Abstract

The A(n+1)B(n)O(3n+1) Ruddlesden-Popper homologous series offers a wide variety of functionalities including dielectric, ferroelectric, magnetic and catalytic properties. Unfortunately, the synthesis of such layered oxides has been a major challenge owing to the occurrence of growth defects that result in poor materials behaviour in the higher-order members. To understand the fundamental physics of layered oxide growth, we have developed an oxide molecular beam epitaxy system with in situ synchrotron X-ray scattering capability. We present results demonstrating that layered oxide films can dynamically rearrange during growth, leading to structures that are highly unexpected on the basis of the intended layer sequencing. Theoretical calculations indicate that rearrangement can occur in many layered oxide systems and suggest a general approach that may be essential for the construction of metastable Ruddlesden-Popper phases. We demonstrate the utility of the new-found growth strategy by performing the first atomically controlled synthesis of single-crystalline La3Ni2O7.

Massive band gap variation in layered oxides through cation ordering

“…To realize our theoretical predictions, we suggest thin film growth methods like oxide molecular beam epitaxy (MBE) to be well-suited for experimentally achieving the proposed cation ordering variants [37][38][39] . Recently, A-site cation ordered LaSrNiO 4 and LaSrMnO 4 RP oxides were experimentally grown with precise atomic control using oxide-MBE techniques 40,41 .…”

Epitaxial-strain-induced polar-to-nonpolar transitions in layered oxides

“…The P-NP phase transition seems to be a general feature in epitaxially strained (001) RP thin films exhibiting HIF in bulk; the nonpolar phase should be considered as a competing state when studying the phase diagram, dielectric properties, and P switching paths of such thin films. Owing to the appearance of the P-NP transition in (001) films of Ca 3 Mn 2 O 7 and Sr 3 Zr 2 O 7 and the advances in epitaxial growth of highquality layered-perovskite oxides 29 , we anticipate that compounds exhibiting multimode anharmonic interactions will serve as a platform to uncover additional hidden functionalities through an improved understanding of strain-induced phenomena.…”

Quick X-ray reflectivity using monochromatic synchrotron radiation for time-resolved applications

“…Excluding applications of qXRR, there are two ways in the literature that timeresolved XRR measurements are typically performed: either by performing Parratt reflectivity scans with low time resolution on processes that are sufficiently slow or that can be halted (Sinsheimer et al, 2013;Lee et al, 2014;Devloo-Casier et al, 2014) or by recording the intensity at one q z -point as a function of time, typically near the anti-Bragg (Nahm & Engstrom, 2016;Golks et al, 2012;Fleet et al, 2005). We show two sets of qXRR data that are analogous to each of these methods.…”