Low Temperature Epitaxial Oxide Ultrathin Films and Nanostructures by Atomic Layer Deposition

Abstract

Highly epitaxial and pure (001) CeO2 ultrathin films have been prepared by atomic layer deposition (ALD) at 275 °C on Y-stabilized ZrO2 cubic fluorite single crystal substrate using cerium β-diketonate (Ce(thd)4) and ozone (O3) as precursors. Substrate temperature and precursor pulses have been optimized to set the ALD window obtaining a growth per cycle of ≈0.2 Å/cycle. This extremely low growth rate has been identified as a key parameter to ensure epitaxial growth at these low temperatures. Post-thermal treatments at 900 °C in oxygen further improve ALD-CeO2 film texture while maintaining film stoichiometry and ultrasmooth surface, rms < 0.4 nm. ALD-CeO2 thin film growth has also been tested on perovskite single crystal substrates, SrTiO3 and LaAlO3, exhibiting CeO2 epitaxial growth and thus validating ALD as an outstanding method for low temperature epitaxial growth. Furthermore, we demonstrate that by combining e-beam lithography and ALD it is feasible to obtain size-controlled CeO2 nanostructures.

Nanocrystalline Ferroelectric BiFeO3 Thin Films by Low-Temperature Atomic Layer Deposition

“…[30][31][32] Most as-deposited ALD films are amorphous or polycrystalline, although epitaxial oxides can also be obtained in the as-deposited stage (< 300ºC) using structurally compatible buffer layers and single crystal substrates. [33][34][35][36] Among the ferroelectric perovskites, BiFeO 3 (BFO) is a stable, lead-free material that simultaneously presents ferroelectric and magnetic order at room temperature. 9,[37][38][39] In the literature, resistive-switching and photovoltaic responses have also been reported.…”

Integration of atomic layer deposition CeO2 thin films with functional complex oxides and 3D patterns

“…1(c), a high resolution Z-contrast image, shows a coherent and sharp interface between LSMO and STO and a sharp interface between the LSMO layer and the ceria. Poor epitaxy is observed above a couple of atomic layers, which might be attributed to a high interfacial energy between defective perovskite and fluorite structures [11,46] rather than a difference in the lattice misfit (ε = +1.21%), as epitaxial ALD-CeO 2 has been achieved on fluorite YSZ single crystal substrates with a much higher lattice misfit (ε = −4.8%) [17]. Based on our early work, it is expected that the epitaxial quality of ALD-CeO 2 on CSD-LSMO could be further improved by optimizing the ALD process for this particular substrate and also by performing high temperature post annealing treatments, at least similarly to those where high quality epitaxial CSD-CeO 2 nanostructures are achieved on perovskite substrates [11].…”

“…The as-deposited films are usually amorphous or barely crystalline and, in many cases, it would be beneficial to obtain them epitaxial directly in the as-deposited state. In fact, it has recently reported the possibility to obtain epitaxial oxide ALD thin films at 275°C [17]. Also, other authors have shown that ultrathin homoepitaxial layers with modified nanostructure can generate enhanced functionalities [18].…”

“…Controlling such interaction provides an opportunity to nanoengineer the surface properties and to control the thin film growth in designated areas and in 3D nanostructures to give rise to interesting and unexpected functionalities [19,20]. Area selective ALD-based methods have been pursued to overcome these issues [17,[21][22][23][24]. Among them, the use of self-assembled monolayers and polymethyl methacrylate (PMMA) resist layer [25,26] is a particularly attractive route to inhibit or activate selected areas of the substrate [23,[27][28][29][30][31] but the robustness of these organic films against certain ALD conditions is rather poor, being an ineffective selective barrier layer for many ALD processes.…”

Tunability and Electrical Properties of Yttria-doped-ceria Films Fabricated via Atomic Layer Deposition

“…5 It is possible to achieve precise film compositions and thickness control using ALD. 6 ALD functions by exposing a substrate to repeated pulses of a precursor gas containing a rare earth metal (RE) followed by a separate pulse of an oxidizing gas. Both gases undergo self-limiting reactions with the OH tails on the substrate surface.…”