Optimizing and monitoring the growth conditions of Pt films, often used as bottom electrodes in multiferroic material systems, represents a highly relevant issue that is of importance for controlling the crystalline quality and performance of ferroelectric oxides such as, e.g. LuFeO 3 . We performed a time-resolved monitoring of the growth and morphology of Pt films during pulsed laser deposition (PLD) in dependence on the grown film effective thickness and on the growth temperature Tg using in situ grazing incidence small-angle X-ray scattering (GISAXS). Through real-time analysis and modeling of GISAXS patterns, we could fully characterize the influence of Tg on the morphology and on the growth kinetics of the Pt layers. Consequently, critical and characteristic effective thicknesses for the transitions nucleation phase (I)/coalescence phase (II) and coalescence phase (II)/coarsening phase (III) could be determined. In combination with complementary microscopic imaging and chemical mapping via combined SEM/EDXS, we demonstrate the occurrence of a morphological progression in the Pt PLD-grown Pt films, changing from grains at room temperature to a 3D-island morphology at 300 °C, further to a hole-free structure at 500 °C, and finally to a channel structure for 700 and 900 °C. The film topography, as characterized by atomic force microscopy (AFM), favors the PLD growth of Pt layers at temperatures beyond 700 °C where the film is homogeneous, continuous, and hole-free with a flat and smooth surface. The double dependency of the percolation transition on the film effective thickness and on the growth temperature has been established by measuring the electrical conductivity.
High-quality BaFe12O19 (BaM) films with high uniaxial anisotropy fields of HA = 17.5 and 18.5 kOe were obtained by pulsed laser deposition (PLD) at two fluences of 1.5 and 5.1 J/cm2 on YSZ(111) substrate, using a platinum interlayer for reducing lattice mismatch. We demonstrated that the microstructure, morphology, and stoichiometry of the hexaferrite BaFe12O19 films can be affected by raising the corresponding energy per pulse from 25 to 75 mJ. However, we also concluded that the increase of fluence leads to the formation of a non-stoichiometric BaM film through two nucleation steps and an output growth of small grains in addition to the increase of the defect density. In turn, this has contributed to the enhancement of the coercive field from Hc = 1769 Oe to Hc = 2166 Oe as it is required for the improvement of perpendicular recording resolution. We found that both the lateral coherent block size and misorientation of mosaic blocks are remarkably affected by the growth kinetics, which itself depends on the energy per pulse. For a deep understanding of the effect of laser fluence on the microstructure, chemical composition, and on the magnetic properties of thin BaM films, the results of complementary methods are combined. These methods comprise high-resolution X-ray diffraction, atomic force microscopy, high-resolution transmission electron microscopy (TEM), scanning TEM combined with energy-dispersive X-ray spectroscopy, and vibrating sample magnetometer. Graphical abstract
Atomistic processes during pulsed-laser deposition (PLD) growth influence the physical properties of the resulting films. We investigated the PLD of epitaxial layers of hexagonal LuFeO$$_3$$ 3 by measuring the X-ray diffraction intensity in the quasiforbidden reflection 0003 in situ during deposition. From measured X-ray diffraction intensities we determined coverages of each layer and studied their time evolution which is described by scaling exponent $$\beta$$ β directly connected to the surface roughness. Subsequently we modelled the growth using kinetic Monte Carlo simulations. While the experimentally obtained scaling exponent $$\beta$$ β decreases with the laser frequency, the simulations provided the opposite behaviour. We demonstrate that the increase of the surface temperature caused by impinging ablated particles satisfactorily explains the recorded decrease in the scaling exponent with the laser frequency. This phenomena is often overlooked during the PLD growth.
We investigated the pulsed-laser deposition of epitaxial layers of hexagonal LuFeO3 by measuring the X-ray diffraction intensity in the quasi-forbidden reflection 0003 in situ during deposition. For this purpose, we used a growth chamber attached to the NANO beamline at KARA storage ring of Karlsruhe, Germany.The dependence of the diffracted intensity exhibited characteristic oscillating behaviour, the period of the oscillation is inversely proportional to the growth rate and the decay of the oscillation visibility relates to the growth kinetics, especially to the transition from two-dimensional to three-dimensional growth mode.The experimental data were compared to numerical simulations, for which we developed a novel growth model. The model is based on the solution of equations describing the time evolution of monolayer coverages and numbers of mobile particles at surface terraces. From the model it follows that the widths of the monolayer coverage profiles exhibit a power law dependence on the deposition time and the exponent of this law sensitively depends on the width of the diffuse Ehrlich-Schwoebel barrier, as well as on the effective temperature of two-dimensional gas of mobile molecules on the growing surface.
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