Aldin Radetinac

Effect of composition and strain on the electrical properties of LaNiO3 thin films

The Ni content of LaNi1−xO3 epitaxial thin films grown by pulsed laser deposition has been varied by ablation from targets with different composition. While tensile strain and Ni substoichiometry reduce the conductivity, nearly stoichiometric and unstrained films show reproducibly resistivities below 100 μΩ × cm. Since the thermodynamic instability of the Ni 3+ state drives defect formation, Ni defect engineering is the key to obtain highly conducting LaNiO3 thin films.

Single-Crystalline CaMoO3 and SrMoO3 Films Grown by Pulsed Laser Deposition in a Reductive Atmosphere

Single-crystalline thin films of CaMoO3 and SrMoO3 with a Mo4+ state perovskite structure have been epitaxially grown by pulsed-laser deposition from Mo6+ state ceramic targets. Phase-pure films were obtained on nearly lattice-matched perovskite substrates using argon gas flow during the deposition. Transport properties of the films are consistent with those of paramagnetic and metallic phases, whereas the residual resistivities are far lower than those reported previously for films and bulk polycrystals. These results indicate that this growth method can be useful for exploring the interfaces and junction properties of 4d and 5d transition metal oxides that are unstable in a conventional oxidative atmosphere.

Nano- and microstructured silver films synthesised by halide-assisted electroless plating

Electroless silver plating baths were modified with different amounts of chloride and bromide, and the effect on the deposition kinetics and the morphology of the resulting silver films was evaluated. The baths were based on silver nitrate and tartrate as the metal source and the reducing agent. Ethylenediamine was used as the complexing agent to suppress silver halide precipitation. With increasing halide concentration, a reduction in the deposition rate and a decreased tendency towards three-dimensional nucleation was found. Bromide affected the plating reaction more strongly than chloride. The deposit morphologies range from coarse-grained, compact particle aggregates over bimodal structures composed of island-like microparticles and smaller particles of varying geometry to shape-controlled films dominated by plates with a triangular or hexagonal shape. The fabrication of silver films of adjustable micro- and nanostructure is relevant for various applications such as heterogeneous catalysis, sensing and plasmonics. As an example for structural tailoring enabled by the outlined reaction system, we created a biomimetic, self-cleaning coating possessing a static contact angle of 165 ± 3° and a tilt angle of <3°. To this end, a hydrophobic metal surface was designed which exhibits a superimposed roughness on the micrometre and submicron scale. The former was defined by the silver deposition, the latter by consecutive galvanic replacement. To achieve superhydrophobic properties, the metal surface was coated with an alkanethiol self-assembled monolayer.

The role of cationic and anionic point defects in pulsed laser deposition of perovskites

Pulsed laser-deposited thin films often show properties that are less optimized compared to single crystalline materials, or thin films grown by molecular beam epitaxy. The main reasons include the high particle energies and the dynamics of the laser plasma. Furthermore, point defect engineering is difficult to achieve experimentally since the adjustable parameters show a complex interplay. Using the examples of the simple perovskite SrMoO3 and the double perovskite Sr2CrWO6 we discuss the role of cationic and anionic point defects, and how far they can be engineered during pulsed laser deposition.

Joint effect of composition and strain on the anomalous transport properties of LaNiO3 films

In the present work, epitaxial LaNi1−xO3 films were grown on SrTiO3, (LaAlO3)0.3(Sr2AlTaO6)0.7, and LaAlO3 substrates by pulsed laser deposition from targets with different Ni stoichiometry. Effect of Ni content on the transport properties of LaNiO3 films was investigated under different strain states. It is found that under tensile strain the carriers in the LaNi0.98O3 films behave according to the Fermi-liquid theory, while under compressive strain an anomalous T1.5 dependence of the resistivity which does not agree with the Fermi-liquid theory is observed in the films. On the other hand, only T1.5 dependence is observed in the LaNi1.20O3 films irrespective of strain states. The results show that strain has a profound influence on the transport properties of LNO films with Ni deficiency and the effect of strain is eliminated in the LNO films with excess Ni. Combined with the XRD results, it is proposed that the change in transport behavior is closely related to the stoichiometry of the LNO films. The mechanism behind is investigated based on the intrinsic and extrinsic factors of the films under different strains.

Highly conducting SrMoO3 thin films for microwave applications

We have measured the microwave resistance of highly conducting perovskite oxide SrMoO3 thin film coplanar waveguides. The epitaxial SrMoO3 thin films were grown by pulsed laser deposition and showed low mosaicity and smooth surfaces with a root mean square roughness below 0.3 nm. Layer-by-layer growth could be achieved for film thicknesses up to 400 nm as monitored by reflection high-energy electron diffraction and confirmed by X-ray diffraction. We obtained a constant microwave resistivity of 29 μΩ·cm between 0.1 and 20 GHz by refining the frequency dependence of the transmission coefficients. Our result shows that SrMoO3 is a viable candidate as a highly conducting electrode material for all-oxide microwave electronic devices.

Origin of superstructures in (double) perovskite thin films

We have investigated the origin of superstructure peaks as observed by X-ray diffraction of multiferroic Bi(Fe0.5Cr0.5)O3 thin films grown by pulsed laser deposition on single crystal SrTiO3 substrates. The photon energy dependence of the contrast between the atomic scattering factors of Fe and Cr is used to rule out a chemically ordered double perovskite Bi2FeCrO6 (BFCO). Structural calculations suggest that the experimentally observed superstructure occurs due to unequal cation displacements along the pseudo-cubic [111] direction that mimic the unit cell of the chemically ordered compound. This result helps to clarify discrepancies in the correlations of structural and magnetic order reported for Bi2FeCrO6. The observation of a superstructure in itself is not a sufficient proof of chemical order in double perovskites.

Strain engineering in epitaxial La1−xSr1+xMnO4 thin films

We have synthesized epitaxial thin films of La1−xSr1+xMnO4 with x = 0.0 and x = 0.5 by pulsed laser deposition on NdGaO3 and LaSrAlO4 substrates with different lattice mismatch. X-ray analysis shows that these layered doped manganites can be grown fully strained allowing to tune the lattice degrees of freedom which otherwise are a function of chemical composition x. Since the crystal structure is strongly coupled to the magnetic, orbital, and charge degrees of freedom in the doped manganites, the demonstrated strain engineering is the base for an extrinsic control of, e.g., charge-orbital order.

Optical properties of single crystalline SrMoO3 thin films

The optical properties of pulsed laser deposited highly crystalline SrMoO3 thin films were investigated. Due to their low resistivity below 30 μΩ cm, thin films of SrMoO3 are candidates for transparent conductor applications. The transparency of SrMoO3 extends into the ultraviolet range to about 300 nm. In this range, SrMoO3 has a higher transparency at similar sheet resistance as compared to alternative oxide or metallic materials. Density functional theory shows that electron-electron correlation effects are small in SrMoO3 as compared to other low-resistivity transition metal oxides and predicts the optical properties in good agreement with experiment.