growth-electrostaticchemical-properties-metallaalo3srtio3

Growth and Electrostatic/chemical Properties of Metal/LaAlO<sub>3</sub>/SrTiO<sub>3</sub> Heterostructures

The quasi 2D electron system (q2DES) that forms at the interface between LaAlO3 (LAO) and SrTiO3 (STO) has attracted much attention from the oxide ...

Université Paris-Saclay

Tohoku University

The quasi 2D electron system (q2DES) that forms at the interface between LaAlO3 and SrTiO3 has attracted much attention from the oxide electronics community. One of its hallmark features is the existence of a critical LaAlO3 thickness of 4 unit-cells (uc) for interfacial conductivity to emerge. In this paper, the chemical, electronic, and transport properties of LaAlO3 /SrTiO3 samples capped with different metals grown in a system combining pulsed laser deposition, sputtering, and in situ X-ray photoemission spectroscopy are investigated. The results show that for metals with low work function a q2DES forms at 1-2 uc of LaAlO3 and is accompanied by a partial oxidation of the metal, a phenomenon that affects the q2DES properties and triggers the formation of defects. In contrast, for noble metals, the critical thickness is increased above 4 uc. The results are discussed in terms of a hybrid mechanism that incorporates electrostatic and chemical effects.

Tuning Up or Down the Critical Thickness in LaAlO3 /SrTiO3 through In Situ Deposition of Metal Overlayers.

The 10 at.% Co-substituted BiFeO₃ films (of thickness 50 nm) were successfully prepared by radio frequency (r.f.) magnetron sputtering on SrTiO₃ (100) substrates with epitaxial relationships of [001](001)Co-BiFeO₃//[001](001)SrTiO₃. In this study, a single phase Co-substituted BiFeO₃ epitaxial film was fabricated by r.f. magnetron sputtering. Sputtering conditions such as Ar, O₂ gas pressure, annealing temperature, annealing atmosphere, and sputtering power were systematically changed. It was observed that a low Ar gas pressure and low sputtering power is necessary to suppress the formation of the secondary phases of BiOx. The Co-substituted BiFeO₃ films were crystalized with post-annealing at 600 °C in air. The process window for single phase films is narrower than that for pure BiFeO₃ epitaxial films. By substituting Fe with Co in BiFeO₃, the magnetization at room temperature increased to 20 emu/cm³. This result suggests that Co-substituted BiFeO₃ films can be used in spin-filter devices.

Fabrication of Multiferroic Co-Substituted BiFeO₃ Epitaxial Films on SrTiO₃ (100) Substrates by Radio Frequency Magnetron Sputtering.

Comprehensive crystal structural study is performed for BiFeO3 (BFO) film grown on KTaO3 (KTO) substrate using transmission electron microscopy (TEM) and x-ray diffraction (XRD). Nano-beam electron diffraction (NBED) combined with structure factor calculation and high resolution TEM images clearly reveal that the crystal structure within BFO thin film is rhombohedral BFO, i.e., bulk BFO phase. Epitaxial relationship found by NBED indicates the BFO film grows in a manner that minimizes lattice mismatch with KTO. It further suggests BFO film is under slight biaxial tensile stress (~0.35%) along in-plane direction. XRD reveals BFO lattice is under compressive stress (~1.6%), along out-of-plane direction as a result of the biaxial tensile strain applied along in-plane direction. This leads to Poisson's ratio of ~0.68. In addition, we demonstrate (1) why hexagonal notation rather than pseudocubic one is required for accurate BFO phase evaluation and (2) a new XRD method that shows how rhombohedral BFO can readily be identified among other phases by measuring a rhombohedral specific Bragg's reflection.

Article	Year
Tuning Up or Down the Critical Thickness in LaAlO3 /SrTiO3 through In Situ Deposition of Metal Overlayers. Advanced materials (Deerfield Beach, Fla.)\| PubMed ID: 28505388	2017
Fabrication of Multiferroic Co-Substituted BiFeO₃ Epitaxial Films on SrTiO₃ (100) Substrates by Radio Frequency Magnetron Sputtering. Materials (Basel, Switzerland)\| PubMed ID: 28879967	2011
Tensile stress effect on epitaxial BiFeO3 thin film grown on KTaO3. Scientific reports\| PubMed ID: 29343784	2018

Hiroshi Naganuma

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