Position-controlled functional oxide lateral heterostructures consisting of artificially aligned (Fe,Zn)₃O₄nanodots and BiFeO₃matrix

Abstract

We demonstrate an advanced fabrication method for perfectly position-controlled ferromagnetic semiconductor (Fe,Zn)(3)O(4) nanodot arrays down to several hundred nanometers in size surrounded by a ferroelectric BiFeO(3) matrix. By performing position-selective crystal growth of perovskite BiFeO(3) on the position-controlled epitaxial spinel (Fe,Zn)(3)O(4) nanodot-seeding template, which is prepared using a hollow molybdenum mask lift-off nanoimprint lithography process on a perovskite La-doped SrTiO(3)(001) substrate, we produce functional oxide three-dimensional lateral heterojunctions. The position-selectivity can be explained based on standard surface diffusion theory with a critical nucleation point. Establishing this fabrication process could lead to innovative nanointegration techniques for spintronic oxide materials.

Compositionally Modulated Magnetic Epitaxial Spinel/Perovskite Nanocomposite Thin Films

“…Though the pillars protrude 12–15 nm above the BFO matrix, the tops of the pillars were not buried until the BFO blocking thickness reached 25 nm; the BFO initially covered the edge of the pillars as shown in the inset of Figure b and then finally covered the whole area as in the inset of Figure a. Sakamoto et al reported BFO growth on spinel (Fe,Zn) 3 O 4 (FZO) particles at 650 °C and showed that the FZO was surrounded by BFO when the FZO particles were below 500 nm diameter . Because the width of the pillars (20–50 nm) in our system is much smaller than the critical terrace width for nucleation, BFO did not nucleate on top of the pillars and instead had to cover them by growth from the sides.…”

Microstructural effects of chemical island templating in patterned matrix-pillar oxide nanocomposites

“…An initial BFO layer calibrated to be 1 nm thick was grown to wet the surface of the substrate and prevent nucleation of CFO pillars away from the template sites. The lattice and crystal symmetry mismatch between the perovskite BFO and spinel CFO leads to preferential diffusion of BFO flux off of the CFO island sites, 27 leaving them exposed for subsequent growth. The second electron gun was then activated and a composite film was grown by co-depositing from the CFO and BFO targets, with the total BFO matrix thickness calibrated to be approximately 25 nm.…”

Self‐Organized Epitaxial Vertically Aligned Nanocomposites with Long‐Range Ordering Enabled by Substrate Nanotemplating

“…However most of the as‐grown VAN films demonstrated till date present very limited short‐range ordering and no long‐range ordering . Since such in‐plane ordering of the pillars could dramatically enrich the practical applications for the VAN films, several lithography and seeding techniques have been explored in achieving directed ordered growth, while with limited success . Most of the demonstrations are on a specific system, i.e., CoFe 2 O 4 (CFO)/BiFeO 3 (BFO).…”

“…Etch pits fabricated by focused ion beam (FIB) and etched with mask of triblock terpolymer film were used to seed the CFO growth recently, benefited from the difference in surface energy between CFO and the substrates. Similar seeding method has also been utilized in controlled growth of Fe/LaSrFeO 4 and (Fe, Zn) 3 O 4 /BiFeO 3 nanodots arrays with nanoimprint lithography (NIL) . Although these approaches achieved well‐ordered structures, they all involve sophisticated seeding procedure employing EBL, FIB, NIL, or complex etching/lift‐off process, the ordered areas are limited in size and the scale‐up could be challenging.…”