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In this paper, the growth of orthorhombic and monoclinic (Al x Ga1 − x )2O3 thin films on (00.1) Al2O3 by tin-assisted pulsed laser deposition is investigated as a function of oxygen pressure p(O2) and substrate temperature T g . For certain growth conditions, defined by T g ≥ 580°C and p(O2) ≤ 0.016 mbar, the orthorhombic κ-polymorph is stabilized. For T g = 540°C and p(O2) ≤ 0.016 mbar, the κ-, and the β-, as well as the spinel γ-polymorph coexist, as illustrated by XRD 2θ-ω-scans. Further employed growth parameters result in thin films with a monoclinic β-gallia structure. For all polymorphs, p(O2) and T g affect the formation and desorption of volatile suboxides, and thereby the growth rate and the cation composition. For example, low oxygen pressures lead to low growth rates and enhanced Al incorporation. This facilitates the structural engineering of polymorphic, ternary (Al,Ga)2O3 via selection of the relevant process parameters. Transmission electron microscopy (TEM) studies of a κ - (Al0.13Ga0.87)2O3 thin film reveal a more complex picture compared to that derived from x-ray diffraction measurements. Furthermore, this study presents the possibility of controlling the phase formation, as well as the Al-content, of thin films based on the choice of their growth conditions.

High-quality epitaxial LaMnO3/LaAlO3 superlattices (SLs) with (0 0 1), (0 1 1), and (1 1 1) out-of-plane orientation were grown by pulsed laser deposition. This SL material was predicted theoretically as a Chern insulator for realizing the quantum anomalous Hall effect. In our investigations, a paramagnetic-ferromagnetic phase transition is found with decreasing temperature around 100 K, indicating a controllable ferroic order at low temperatures. Electrical transport measurements reveal a thermally activated single-gap behavior with a fitted band gap of 436 meV for the (1 1 1)-oriented SL. With that, the results prove the predictions of a ferromagnetic background in the SLs, and of a gapped band structure.

ZnCoO : Al, ZnCoO : (Al,Cu), and reference samples without Co have been grown by pulsed laser deposition to investigate the influence of Co-dopants and Cu-codopants on the magneto transport properties of ZnO. Positive magnetoresistance and anomalous Hall effect have been observed for ZnCoO : (Al,Cu). Versatile theoretical approaches for modelling positive magnetoresistance in ZnO-based diluted magnetic semiconductors are still to be developed. Negative magnetoresistance due to the scattering of spin-polarized charge carriers at isolated magnetic impurities has been observed in ZnO : (Al,Cu) without Co-dopants and successfully modelled. Cu-codopants enhance the positive and negative magnetoresistance in ZnCoO : Al and ZnO : Al, respectively, by one order of magnitude.

BiFeO3 and BaTiO3 were used to grow homogeneous composite thin films and multilayer heterostructures with 15 double layers by pulsed laser deposition. The perpendicular strain of the films was tuned by employing different substrate materials, i.e. SrTiO3 (0 0 1), MgO(0 0 1) and MgAl2O4 (0 0 1). Multiferroic properties have been measured in a temperature range from room temperature down to 2 K. The composite films show a high ferroelectric saturation polarization of more than 70 C cm-2. The multilayers show the highest magnetization of 2.3 emu cm-3, due to interface magnetic moments and exchange coupling of the included weak ferromagnetic phases. The magnetoelectric coupling of the BaTiO3-BiFeO3 films was investigated by two methods. While the ferroelectric hysteresis loops in magnetic fields up to 8 T show only minor changes, a direct longitudinal AC method yields a magnetoelectric coefficient ME = ∂E/∂H of 20.75 V cm-1 Oe-1 with a low μ0HDC of 0.25 T for the 67% BaTiO3-33% BiFeO3 composite film at 300 K. This value is close to the highest reported in the literature. © 2014 IOP Publishing Ltd. ispartof: Journal of Physics D, Applied Physics vol:47 issue:13 status: published

Fresnoite Ba2TiSi2O8 (BTS) thin films were grown and crystallized in situ using pulsed laser deposition (PLD) with CO2 laser direct heating of the a-plane sapphire (1 1 0) substrates up to 1250 ◦ C. Starting with 775 ◦ C growth temperature, (0 0 1)- and (1 1 0)-textured BTS and BaTiO3 phases, respectively, could be assigned in the films, and the typical fern-like BTS crystallization patterns appear. For higher process temperatures of 1100 to 1250 ◦ C, atomically smooth, terraced surface of the films was found, accompanied by crystalline high-temperature phases of Ba–Ti–Si oxides. HAADF micrographs taken in both scanning transmission electron microscopy and energy-dispersive x-ray spectrometry mode show details of morphology and elemental distribution inside the films and at the interface. To balance the inherent Si deficiency of the BTS films, growth from glassy BTS × 2 SiO2 and BTS × 2.5 SiO2 targets was considered as well. The latter targets are ideal for PLD since the employed glasses possess 100% of the theoretical density and are homogeneous at the atomic scale.

It is our pleasure to introduce this special issue appearing on the occasion of the 25th anniversary of pulsed laser deposition (PLD), which is today one of the most versatile growth techniques for oxide thin films and nanostructures. Ever since its invention, PLD has revolutionized the research on advanced functional oxides due to its ability to yield high-quality thin films, multilayers and heterostructures of a variety of multi-element material systems with rather simple technical means. We appreciate that the use of lasers to deposit films via ablation (now termed PLD) has been known since the 1960s after the invention of the first ruby laser. However, in the first two decades, PLD was something of a 'sleeping beauty' with only a few publications per year, as shown below. This state of hibernation ended abruptly with the advent of high T c superconductor research when scientists needed to grow high-quality thin films of multi-component high T c oxide systems. When most of the conventional growth techniques failed, the invention of PLD by T (Venky) Venkatesan clearly demonstrated that the newly discovered high-T c superconductor, YBa2Cu3O7−δ , could be stoichiometrically deposited as a high-quality nm-thin film with PLD [1]. As a remarkable highlight of this special issue, Venkatesan gives us his very personal reminiscence on these particularly innovative years of PLD beginning in 1986 [2]. After Venky's first paper [1], the importance of this invention was realized worldwide and the number of publications on PLD increased exponentially, as shown in figure 1. Figure 1. Published items per year with title or topic PLD. Data from Thomson Reuters Web of Knowledge in September 2013. After publication of Venky's famous paper in 1987 [1], the story of PLD's success began with a sudden jump in the number of publications, about 25 years ago. A first PLD textbook covering its basic understanding was soon published, in 1994, by Chrisey and Hubler [3]. Within a decade, large-area PLD grown YBa2Cu3O7−δ thin films became a reality for applications in microwave filters for satellite and mobile communication. The material systems that could be covered under the PLD gamut extended to almost all oxides, nitrides and even organics. A second textbook exclusively dedicated to PLD was edited by Rob Eason in 2007 [4], reviewing many possible modifications and extensions of the method. To celebrate 25 years of pulsed laser deposition, Venkatesan organized a symposium on 'Recent Advances in the Pulsed Laser Deposition of Thin Films and Nanostructures' in 2013 [5]. Besides dielectric, ferroelectric and magnetic oxides, the wide-bandgap group II–VI semiconductor ZnO is among the most intensively researched compounds during the last decade. Therefore, this material has become the subject of two introductory reviews in this issue by Opel et al and Tsukazaki et al , to show the state-of-the-art work carried out on ZnO thin films to 2013. The detailed insights into growth parameter control and their impact on the ZnO film performance make both reviews highly instructional not only for specialists, but also for beginners in PLD. The perspective of PLD towards industrial applications largely depends, first, on the ability of the excimer laser suppliers to further increase the laser power and, second, on the deposition schemes to distribute the ablated material homogeneously on technologically relevant substrate areas (8-inch diameter). These developments are explained here by the leading companies dealing with high-power excimer lasers and large-area PLD equipment, such as Coherent Laser Systems GmbH, PVD Products, Inc., and SolMateS B.V. It is also important to note the efforts made by Blank and Rijnders for atomic layer control of PLD by in situ high-pressure reflection high-energy electron diffraction (RHEED), which is now adopted by many groups worldwide. The potential of multi-beam PLD for advanced optical waveguides and of advanced design-of-experiment schemes to shorten the optimization effort for new materials is presented at the end of this methodical section. Further, the issue contains original papers on other prominent PLD activities, such as dielectric SrTiO3 films, magnetic and spintronic La1−x Srx MnO3, and multiferroic BiFeO3. The role of cationic and anionic point defects and their control during PLD is discussed based on the examples of the simple perovskite SrMoO3 and the double perovskite Sr2CrWO6. The final paper in this thin-film-related section provides a good account of in situ high-temperature surface smoothing of Ba2TiSi2O8 fresnoite films and growth from glassy fresnoite targets with 100% theoretical density. The flexibility of the PLD technique has resulted in several schemes to grow nanostructures, which is unique in the nature of PLD. Okada's group succeeded in controlling the growth density of ZnO nanowires by varying the thickness of the ZnO buffer layer, and nanowalls could be patterned by interference phenomenon using laser irradiation. PLD-based methods are further used to grow metal nanoparticle plasmonic films with packing densities up to 1011 particles cm−2, and ZnO nanowires from screw dislocation driven two-dimensional hexagonal stacking on diamond substrates. Overall, this special issue provides an up-to-date overview on the current status, potential and the extraordinary success and development of PLD from a simple laboratory growth method to a viable industrial technique for fabrication of advanced oxide thin films. We thank all the authors and reviewers for their contributions to this special issue. We would like to place on record our gratitude for the timely help extended by the editorial team, Dr Olivia Roche, Dean Williams and Colin Adcock. References [1] Dijkkamp D, Venkatesan T, Wu X D, Shaheen S A, Jisrawi N, Min-Lee Y-H, McLean W L and Croft M 1987 Preparation of YBaCu oxide superconductor thin films using pulsed laser evaporation from high T c bulk material Appl. Phys. Lett. 51 619 [2] Venkatesan T 2014 Pulsed laser deposition—invention or discovery? J. Phys. D: Appl. Phys. 46 034001 [3] D B Chrisey, G H Hubler, 1994 Pulsed Laser Deposition of Thin Films (New York: Wiley) [4] R Eason, 2007 Pulsed Laser Deposition of Thin Films—Applications-Led Growth of Functional Materials (Hoboken, NJ: Wiley-Interscience) [5] MRS Singapore ICMAT Symposia Proceedings, Procedia Engineering (2013) Symposium IRecent Advances in the Pulsed Laser Deposition of Thin Films and Nanostructures at press

Ferromagnetic ordering is found for both undoped and Mn-doped zirconia (ZrO2 : Mn) thin films with 0 at% ≤ Mn ≤ 50 at% grown homoepitaxially on ZrO2 : Y2O3(0 0 1) substrates. Highly crystalline films show ferromagnetic saturation magnetization and coercive field at room temperature up to 1 emu cm−3 and 50 mT, respectively. The Curie temperature is in all ferromagnetic samples above 300 K. Comparing optimum films with different Mn content, cubic ZrO2 : Mn films with about 25 at% Mn show reproducibly the highest magnetization, in relation to monoclinic and tetragonal films. In contrast, less crystalline films grown heteroepitaxially on LaAlO3(0 0 1) or under non-ideal conditions show negligible magnetic effects.The fraction of paramagnetically active Mn atoms in a ZrO2 film with 27% Mn at 5 K is only about 1/5 of the incorporated Mn atoms, corresponding well to the share of 20% Mn4+ in XPS. Magnetic trace impurities in the 100 ppm range cannot account for the observed effects. Our results indicate that the observed defect-induced magnetic ordering in nominally non-magnetic zirconia thin films requires a certain balance of overall crystallinity, dislocation density and film mosaicity.

Scandium is a donor in ZnO, in contradiction to all heavier 3d-elements. Although the Sc3+ ion fits exactly the size of Zn2+, the conductivity of epitaxial Sc-doped ZnO thin films is dominated by a degenerated interface layer with pronounced Sc accumulation in the concentration depth profile. Electron paramagnetic resonance clearly excludes the isovalent oxidation state Sc2+ in ZnO, in agreement with the low resistivity of homoepitaxial ZnO?:?Sc of 1.3???10?2???cm and high Hall mobility of 139?cm2?V?1?s?1 at 300?K. Employing the two-layer Hall model of Look and Molnar, a maximum Hall mobility of the volume part of the ZnO?:?Sc layer of 650?cm2?V?1?s?1 at 95?K was extracted. Thermal activation energies of the donors are 28 and 43?meV for a homoepitaxial ZnO?:?0.1% Sc film. Homoepitaxial ZnO films with 0.1 and 1?at% Sc on c-plane ZnO are almost phase pure and in-plane lattice matched with perpendicular compressive strain up to 1%. Heteroepitaxial ZnO?:?Sc on a-plane sapphire shows secondary XRD peaks, pointing to a limited solubility of Sc in ZnO.

Nd and Mn were codoped into ZnO films which have been grown on a-plane sapphire substrates by pulsed laser deposition with the thickness ranging between 46 and 971 nm. The room temperature resistivity of the codoped films is independent of film thickness. Large positive magnetoresistance and clear anomalous Hall effect were observed at 5 K. Ferromagnetism with clear hysteresis up to 290 K was observed. Codoping is suggested to be an efficient method to introduce energy levels in the ZnO band gap to mediate the electron spins of the magnetic doping ions.