Growing a LaAlO3/SrTiO3 heterostructure on Ca2Nb3O10 nanosheets

Alexander J H Van Der Torren,Guus J H M Rijnders,Jan Aarts,Mark Huijben,Johan E Ten Elshof,Huiyu Yuan,Gertjan Koster,Sense Van Der Molen,Zhaoliang Liao,Marcel B S Hesselberth,Johannes Jobst

doi:10.1038/s41598-019-53438-1

Alexander J H Van Der Torren, Guus J H M Rijnders + Show 9 more

Open Access

https://doi.org/10.1038/s41598-019-53438-1

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Abstract

The two-dimensional electron liquid which forms between the band insulators LaAlO3 (LAO) and SrTiO3 (STO) is a promising component for oxide electronics, but the requirement of using single crystal SrTiO3 substrates for the growth limits its applications in terms of device fabrication. It is therefore important to find ways to deposit these materials on other substrates, preferably Si, or Si-based, in order to facilitate integration with existing technology. Interesting candidates are micron-sized nanosheets of Ca2Nb3O10 which can be used as seed layers for perovskite materials on any substrate. We have used low-energy electron microscopy (LEEM) with in-situ pulsed laser deposition to study the subsequent growth of STO and LAO on such flakes which were deposited on Si. We can follow the morphology and crystallinity of the layers during growth, as well as fingerprint their electronic properties with angle resolved reflected electron spectroscopy. We find that STO layers, deposited on the nanosheets, can be made crystalline and flat; that LAO can be grown in a layer-by-layer fashion; and that the full heterostructure shows the signature of the formation of a conducting interface.

Highlights

We have used a Low Energy Electron Microscope with built-in pulsed-laser-deposition capability to study the feasibility of growing an SrTiO3/LaAlO3 bilayer with a two-dimensional electron system (2DES) at its interface on lattice-matching nanosheets of Ca2Nb3O10, which in turn were deposited on the native oxide on top of a Si substrate
Apart from electron diffraction as a characterization tool, we show how to use the intensity-versus-energy characteristics to obtain more information on the electronic structure of the layers we deposit, and we use Angle-resolved reflected-electron spectroscopy (ARRES) to study the electronic structure of the completed sample
We find conditions leading to a TiO2-terminated STO surface, we demonstrate that we can use intensity oscillations during growth in order to count the number of LAO unit cels, and we infer from ARRES maps that the surface of the sample shows an electronic structure similar to what was found for samples with a conducting interface

Summary

Methods

Ca2Nb3O10 nanosheets were synthesized and deposited by Langmuir-Blodgett (LB) deposition on Si (001) substrates cut from single crystal wafers with native oxide layers as described elsewhere[8]. The samples were transferred into the ESCHER LEEM system[23,24,25,26] with in-situ pulsed laser deposition as described in ref. PLD was performed with a laser fluence of 1.4 J/cm[2] and a 1 Hz repetition rate in 5 × 10−5 mbar oxygen[16]. This may result in slightly off-stoichiometric growth of STO18, but in our microscope it is not possible to increase the pressure and further optimize the growth conditions. Three samples were made with a specific number of laser pulses, namely 360 (sample A), 600 (sample B) and 580

Results

Discussion

Conclusion