Critical thickness and strain relaxation in molecular beam epitaxy-grown SrTiO3 films

Abstract

We report on the study of the critical thickness and the strain relaxation in epitaxial SrTiO3 film grown on (La0.3Sr0.7)(Al0.65Ta0.35)O3 (001) (LSAT) substrate using the hybrid molecular beam epitaxy approach. No change in the film's lattice parameter (both the in-plane and the out-of-plane) was observed up to a film thickness of 180 nm, which is in sharp contrast to the theoretical critical thickness of ∼12 nm calculated using the equilibrium theory of strain relaxation. For film thicknesses greater than 180 nm, the out-of-plane lattice parameter was found to decrease hyperbolically in an excellent agreement with the relaxation via forming misfit dislocations. Possible mechanisms are discussed by which the elastic strain energy can be accommodated prior to forming misfit dislocations leading to such anomalously large critical thickness.

In Situ Impedance Analysis of Oxygen Exchange on Growing La0.6Sr0.4CoO3−δ Thin Films

“…However, SrTiO 3 films, another perovskite-type oxide, deposited by molecular beam epitaxy on La 0.7 Sr 0.3 Al 0.65 Ta 0.35 O 3 or DyScO 3 lead to slightly larger strain values (−0.95% and 1.09%) and studies suggest a critical thickness of 30–180 nm. 56,57 For larger strains, for example, LaAlO 3 deposited on SrTiO 3 (3.17%) by PLD, strain relaxation occurs earlier (20–50 nm). 58 In our study, neither the surface exchange resistance (Figure 9a), saturating to a constant level, nor the electrode capacitance (Figure 9b), increasing linearly with increasing film thickness, give any evidence of thickness dependent strain relaxation.…”

Chemistry, growth kinetics, and epitaxial stabilization of Sn2+ in Sn-doped SrTiO3 using (CH3)6Sn2 tin precursor

“…Figure 1(b) shows high-resolution 2θ − ω scans of these films indicating an expansion of the film's lattice parameter accompanied by the increased separation between substrate and film (002) peaks. The film with a smaller Ti BEP (1.12 × 10 6 Torr) was grown slightly outside the "MBE growth window" 23,24 and developed an additional low-intensity peak consisent with the Sr 3 Ti 2 O 7 phase, indicating Ti-deficient conditions. However, films with Ti BEP > 1.12 × 10 6 Torr were phase-pure and within the "MBE growth window" for stoichiometric composition.…”

“…Details of our hybrid MBE approach for a stoichiometric SrTiO 3 film are discussed elsewhere; 23,24 hexamethylditin (HMDT) 25 and titanium tetraisopropoxide (TTIP) were used as the metal-organic chemical precursors for Sn and Ti, respectively. Sr was evaporated using effusion cells, and oxygen was supplied using an RF plasma source.…”

Stoichiometry-driven metal-to-insulator transition in NdTiO3/SrTiO3 heterostructures

“…Growth conditions for cation stoichiometric NdTiO 3 were identified at the substrate temperature of 900 C (thermocouple) by varying the TTIP/Nd flux ratio, where the TTIP flux was kept constant and the Nd flux was varied by changing effusion cell temperature between 960 C and 1015 C. To grow NdTiO 3 /SrTiO 3 heterostructures, a $ 3 nm thick coherently strained, stoichiometric SrTiO 3 buffer layer was grown prior to NdTiO 3 thin films, using the same approach as described elsewhere. 22 The growth mode, film thickness, and surface morphology were obtained using in-situ Reflection High-Energy Electron Diffraction (RHEED) (Staib Instruments) technique. Further structural characterizations were performed using ex-situ techniques including high-resolution x-ray diffraction using a Philips Panalytical X'Pert thin-film diffractometer with Cu K a radiation, x-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and scanning transmission electron microscopy (STEM).…”