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Abstract Although metal–organic (MO) precursors are widely used in technologically relevant deposition techniques, reports on their temperature-dependent evaporation and decomposition behaviors are scarce. Here, MO precursors of the metals Ti, V, Al, Hf, Zr, Ge, Ta, and Pt were subjected to thermogravimetric analysis to experimentally determine their vapor pressure curves and to gain insight into their temperature-dependent decomposition kinetics. Benzoic acid was used as a calibration standard and vapor pressure curves were extracted from thermogravimetric measurements using the Langmuir equation. The obtained data is used to discuss the suitability of these MO precursors in chemical vapor deposition-based thin film growth approaches in general, and hybrid molecular beam epitaxy in particular. All MOs, except for Ta- and one Ti-based MOs, were deemed suitable for gas inlet systems. The Ta-based MO demonstrated suitability for an effusion cell, while all MOs showed compatibility with cracker usage. Graphical Abstract 

Abstract BaTiO₃is a technologically relevant material in the perovskite oxide class with above‐room‐temperature ferroelectricity and a very large electro‐optical coefficient, making it highly suitable for emerging electronic and photonic devices. An easy, robust, straightforward, and scalable growth method is required to synthesize epitaxial BaTiO₃thin films with sufficient control over the film's stoichiometry to achieve reproducible thin film properties. Here the growth of BaTiO₃thin films by hybrid molecular beam epitaxy is reported. A self‐regulated growth window is identified using complementary information obtained from reflection high energy electron diffraction, the intrinsic film lattice parameter, film surface morphology, and scanning transmission electron microscopy. Subsequent optical characterization of the BaTiO₃films by spectroscopic ellipsometry revealed refractive index and extinction coefficient values closely resembling those of stoichiometric bulk BaTiO₃crystals for films grown inside the growth window. Even in the absence of a lattice parameter change of BaTiO₃thin films, degradation of optical properties is observed, accompanied by the appearance of a wide optical absorption peak in the IR spectrum, attributed to optical transitions involving defect states present. Therefore, the optical properties of BaTiO₃can be utilized as a much finer and more straightforward probe to determine the stoichiometry level present in BaTiO₃films. 

Among ABO3 perovskites, SrMoO3 possesses the lowest electrical resistivity in addition to having high optical transparency in the visible spectrum. This unusual combination of material properties allows it to be a potential replacement for indium tin oxide as a transparent electrode. Thus far, its thin film synthesis has been challenging and limited primarily to pulsed laser deposition and sputtering. Here, we report the growth of SrMoO3 thin films by suboxide molecular beam epitaxy. We demonstrate that optically transparent and conductive SrMoO3 films can be grown by supplying elemental strontium via a conventional effusion cell and thermally evaporating MoO3 pellets as a molybdenum source. The direct supply of a molecular oxygen flux to the MoO3 charge was utilized to prevent reduction to lower oxidation states of the charge to ensure congruent evaporation and, thus, a stable MoO3 molecular flux. The optimal growth conditions were found by varying the Sr to MoO3 flux ratio determined from quartz crystal microbalance measurements and monitoring the growth by reflection high-energy electron diffraction. SrMoO3 thin films with 21 nm thickness were confirmed to be optically transparent with transmission between 75 and 91% throughout the visible spectral range and electrically conducting with a room temperature resistivity of 5.0 × 10−5 Ω cm. This realization of this thin film growth method can be further expanded to the growth of other transition metal perovskites in which cations have extremely low vapor pressure and cannot be evaporated in elemental forms. 

We report the synthesis and electronic properties of the correlated metal CaVO3, grown by hybrid molecular beam epitaxy. Films were grown on (100) LaAlO3 substrates at a temperature of 900 °C by supplying a flux of elemental Ca through a thermal effusion cell and metalorganic precursor, vanadium oxitriisopropoxide, as a source of vanadium. The presence of a self-regulated growth regime was revealed by the appearance of a specific surface reconstruction detected by reflection high-energy electron diffraction. Films grown within the growth window were characterized by atomically flat surfaces. X-ray reciprocal space maps revealed that the films were coherently strained to the substrate and inherited its twinned microstructure. Despite the presence of twin walls, CaVO3 thin films, grown within the stoichiometric growth window, revealed very low electrical resistivities at low temperatures, with residual resistivity ratios exceeding 90, while films grown at either Ca- or V-excess show deteriorated transport properties, attributed to the presence of extrinsic defects arising from the non-stoichiometry present in these films. 

Exotic material properties and topological nontrivial surface states have been theoretically predicted to emerge in [111]-oriented perovskite layers. The realization of such [111]-oriented perovskite superlattices has been found challenging, and even the growth of perovskite oxide films along this crystallographic direction has been proven as a formidable task, attributed to the highly polar character of the perovskite (111) surface. Successful epitaxial growth along this direction has so far been limited to thin film deposition techniques involving a relatively high kinetic energy, specifically pulsed laser deposition and sputtering. Here, we report on the self-regulated growth of [111]-oriented high-quality SrVO3 by hybrid molecular beam epitaxy. The favorable growth kinetics available for the growth of perovskite oxides by hybrid molecular beam epitaxy on non-polar surfaces was also present for the growth of [111]-oriented films, resulting in high-quality SrVO3(111) thin films with residual resistivity ratios exceeding 20. The ability to grow high-quality perovskite oxides along energetically unfavorable crystallographic directions using hybrid molecular beam epitaxy opens up opportunities to study the transport properties of topological nontrivial and correlated electron systems.