LaCrO3 heteroepitaxy on SrTiO3(001) by molecular beam epitaxy

Abstract

Stoichiometric, epitaxial LaCrO 3 films have been grown on TiO 2 -terminated SrTiO 3 (001) substrates by molecular beam epitaxy using O 2 as the oxidant. Film growth occurred in a layer-by-layer fashion, giving rise to structurally excellent films and surfaces which preserve the step-terrace structure of the substrate. The critical thickness is in excess of 500 Å. Near-surface Cr(III) is highly susceptible to further oxidation to Cr(V), leading to the formation of a disordered phase upon exposure to atomic oxygen. Recovery of the original epitaxial LaCrO 3 phase is readily achieved by vacuum annealing. 2Complex oxides exhibit a range of physical properties unparalleled by any other class of materials. Their electronic, magnetic, and optical characteristics span the field of possibilities, and a wealth of applications awaits our ability to understand and control these properties. Materials synthesis is key to realizing the full potential of complex oxides, particularly in thin-film form. In the bulk, this perovskite exhibits an orthorhombic structure (space group Pbnm) with lattice parameters a = 5.513 Å, b = 5.476 Å, c = 7.759 Å. 4 However, isolation of a pseudocubic cell within the orthorhombic structure yields a = b = c = 3.885 Å (see structural models in Fig. 1). Thus, LCO is a candidate for heteroepitaxy on SrTiO 3 (001), for which a = b = c = 3.905 Å.In this Letter, we describe the epitaxial growth of LCO on SrTiO 3 (001) by MBE. 5 Atomically flat, TiO 2 -terminated SrTiO 3 (STO) substrates were prepared as described previously. 6 La and Cr were evaporated from an effusion cell and an electron beam evaporator, respectively, and the O 2 partial pressure was kept constant at ~6 × 10 -8 Torr.The La flux was measured before and after deposition by a quartz crystal oscillator (QCO), and the Cr flux was monitored and controlled during deposition by atomic with an AFM image and a line profile. The surface periodicity evolves from (1×1) for the substrate to (2×2) for the film surface. Moreover, the film surface exhibits a well-defined terrace-step structure with typical step heights of ~ 4 Å, the c value for pseudocubic LCO.This result confirms the layer-by-layer growth mode revealed by RHEED oscillations and the presence of a single surface termination, which we expect is CrO 2 , based on the fact that all growths were terminated after an integral number of oscillations were recorded.We show in Fig. 2

Effect of cation arrangement on the electronic structures of the perovskite solid solutions <span class="aps-inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mrow><mo>(</mo><mi>SrTiO</mi></mrow><mn>3</mn></msub><mo>)</mo><msub><mrow></mrow><mrow><mn>1</mn><mo>−</mo><mi>x</mi></mrow></msub><msub><mrow><mo>(</mo

“…An alternating layer of a LCO-LaFeO 3 superlattice with [100] stacking direction that is very similar to our proposed structure has been synthesized using a multitarget pulsed laser deposition technique [43]. Such thin film can be grown on a substrate with a step-terrace structure so that the side of the thin film will be largely exposed for charge transfer out of the material [44]. Apart from epitaxial thin-film growth techniques, low-temperature soft chemistry routes are also capable of preparing nonthermodynamically stable (metastable) phases that are not accessible by conventional solid state reactions.…”

Band Alignment, Built-In Potential, and the Absence of Conductivity at theLaCrO3/SrTiO3(001)Heterojunction

“…LCO films with La:Cr atom ratios within a few percent of 1.00 were grown by MBE [12]. Band alignment and potential gradients were determined by means of in situ high-energy-resolution XPS using a Gamma Data/Scienta SES 200 analyzer with monochromatic AlK x rays.…”

Visible light carrier generation in co-doped epitaxial titanate films

“…of STO to prevent overoxidation of Cr during the cooling process. 17 STO control films were grown using an electron cyclotron resonance microwave oxygen plasma source to ensure full oxidation, though this is not absolutely necessary for the growth conditions. 18 An additional 20 nm thick 10% SLTCO film was fabricated for photoelectrochemical (PEC) experiments with a 5 nm thick 3% La-doped STO bottom electrode and a 5 nm thick STO capping layer.…”