Dynamic Scaling and Island Growth Kinetics in Pulsed Laser Deposition of SrTiO_{3}

We use real-time diffuse surface x-ray diffraction to probe the evolution of island size distributions and its effects on surface smoothing in pulsed laser deposition (PLD) of SrTiO_{3}. We show that the island size evolution obeys dynamic scaling and two distinct regimes of island growth kinetics. Our data show that PLD film growth can persist without roughening despite thermally driven Ostwald ripening, the main mechanism for surface smoothing, being shut down. The absence of roughening is concomitant with decreasing island density, contradicting the prevailing view that increasing island density is the key to surface smoothing in PLD. We also report a previously unobserved crossover from diffusion-limited to attachment-limited island growth that reveals the influence of nonequilibrium atomic level surface transport processes on the growth modes in PLD. We show by direct measurements that attachment-limited island growth is the dominant process in PLD that creates step flowlike behavior or quasistep flow as PLD "self-organizes" local step flow on a length scale consistent with the substrate temperature and PLD parameters.

Full Electroresistance Modulation in a Mixed-Phase Metallic Alloy

We report a giant, ∼22%, electroresistance modulation for a metallic alloy above room temperature. It is achieved by a small electric field of 2  kV/cm via piezoelectric strain-mediated magnetoelectric coupling and the resulting magnetic phase transition in epitaxial FeRh/BaTiO_{3} heterostructures. This work presents detailed experimental evidence for an isothermal magnetic phase transition driven by tetragonality modulation in FeRh thin films, which is in contrast to the large volume expansion in the conventional temperature-driven magnetic phase transition in FeRh. Moreover, all the experimental results in this work illustrate FeRh as a mixed-phase model system well similar to phase-separated colossal magnetoresistance systems with phase instability therein.

Strain response of magnetic order in perovskite-type oxide films

The role of elastic strain for magnetoelectric materials and devices is twofold. It can induce ferroic orders in thin films of otherwise non-ferroic materials. On the other hand, it provides the most exploited coupling mechanism in two-phase magnetoelectric materials and devices today. Complex oxide films (perovskites, spinels) are promising for both routes. The strain control of magnetic order in complex oxide films is a young research field, and few ab initio simulations are available for magnetic order in dependence on lattice parameters and lattice symmetry. Here, an experimental approach for the evaluation of how elastic strain in thin epitaxial films alters their magnetic order is introduced. The magnetic films are grown epitaxially in strain states controlled by buffer layers onto piezoelectric substrates of 0.72Pb(Mg1/3Nb2/3)O3-0.28PbTiO3(001). As an example, the strain dependence of the ordered magnetic moment of SrRuO3 has been investigated. At a tensile strain level of approximately 1%, SrRuO3 is tetragonal, and biaxial elastic strain induces a pronounced suppression of the ordered magnetic moment. As a second example, a strain-driven transition from a ferromagnetic to a magnetically disordered phase has been observed in epitaxial La0.8Sr0.2CoO3 films.

Phase transitions, phase coexistence, and piezoelectric switching behavior in highly strained BiFeO(3) films

Highly strained BiFeO3 films transition into a true tetragonal state at 430 °C but remain polar to much higher temperatures (∼800 °C). Piezoelectric switching is only possible up to 300 °C, i.e., at temperatures for which strain stabilizes the stripe-like coexistence of multiple polymorphs.

Controlling the magnetic properties of LaMnO3 thin films on SrTiO3(100) by deposition in a O2/Ar gas mixture

The magnetic, structural, and transport properties of pulsed-laser deposited LaMnO(3) thin films are analyzed as a function of the O(2) partial pressure in the growth environment (using an O(2)/Ar gas mixture). Interestingly, the magnetic properties do not change gradually as the O(2) content increases. Instead, ferromagnetism emerges rapidly with the oxygen; a critical amount of Ar is needed to suppress ferromagnetism effectively in LaMnO(3) thin films. The most dramatic suppression of ferromagnetism occurs only in the narrow window below 10% oxygen, where the ferromagnetic moments decrease by a factor of 17. Above a certain oxygen concentration, the ferromagnetic moment no longer increases with oxygen. The sample grown in pure oxygen shows a metal-insulator transition at ∼200 K, but exhibits an insulating behavior again below ∼150 K. This intermediate metallic behavior is significantly suppressed by using the O(2)/Ar gas mixture.

Characterizing the two- and three-dimensional resolution of an improved aberration-corrected STEM

The successful development of third-order aberration correctors in transmission electron microscopy has seen aberration-corrected electron microscopes evolve from specialist projects, custom built at a small number of sites to common instruments in many modern laboratories. Here we describe some initial results illustrating the two- and three-dimensional (3D) performance of an aberration-corrected scanning transmission electron microscope with a prototype improved aberration corrector designed to also minimize fifth-order aberrations and a new, higher brightness gun. We show that atomic columns separated by 0.63 A can be resolved and demonstrate detection of single dopant atoms with 3D sensitivity.

Recent advances in pulsed-laser deposition of complex oxides

Pulsed-laser deposition (PLD) is one of the most promising techniques for the formation of complex-oxide heterostructures, superlattices, and well controlled interfaces. The first part of this paper presents a review of several useful modifications of the process, including methods inspired by combinatorial approaches. We then discuss detailed growth kinetics results, which illustrate that 'true' layer-by-layer (LBL) growth can only be approached, not fully met, even though many characterization techniques reveal interfaces with unexpected sharpness. Time-resolved surface x-ray diffraction measurements show that crystallization and the majority of interlayer mass transport occur on timescales that are comparable to those of the plume/substrate interaction, providing direct experimental evidence that a growth regime exists in which non-thermal processes dominate PLD. This understanding shows how kinetic growth manipulation can bring PLD closer to ideal LBL than any other growth method available today.

Spectroscopic imaging of single atoms within a bulk solid

The ability to localize, identify, and measure the electronic environment of individual atoms will provide fundamental insights into many issues in materials science, physics, and nanotechnology. We demonstrate, using an aberration-corrected scanning transmission electron microscope, the spectroscopic imaging of single La atoms inside CaTiO3. Dynamical simulations confirm that the spectroscopic information is spatially confined around the scattering atom. Furthermore, we show how the depth of the atom within the crystal may be estimated.

Antiferroelectric behavior in symmetric KNbO(3)/KTaO(3) superlattices

Antiferroelectric behavior is observed in artificially layered KTaO (3)/KNbO (3) perovskite superlattices. While KTaO (3) and KNbO (3) are ferroelectric and paraelectric, respectively, the superlattice appears antiferroelectric based on an increase in the dielectric constant with applied dc bias. This dielectric behavior is inconsistent with the nonlinear response for either paraelectric or ferroelectric materials. However, an increase in the dielectric constant with applied electric field is consistent with antiferroelectric behavior. The antiferroelectric ordering appears to be induced by cation modulation imposed by the superlattice.