Search

This article is written on behalf of many colleagues, collaborators, and researchers in the field of complex oxides as well as current and former students and postdocs who continue to enable and undertake cutting-edge research in the field of multiferroics, magnetoelectrics, and the pursuit of electric-field control of magnetism. What I present is something that is extremely exciting from both a fundamental science and applications perspective and has the potential to revolutionize our world, particularly from a sustainability perspective. To realize this potential will require numerous new innovations, both in the fundamental science arena as well as translating these scientific discoveries into real applications. Thus, this article will attempt to bridge the gap between fundamental materials physics and the actual manifestations of the physical concepts into real-life applications. I hope this article will help spur more translational research within the broad materials community.

This article is written on behalf of a large number of colleagues, collaborators, and researchers in the field of complex oxides as well as current and former students and postdocs who continue to enable and undertake cutting-edge research in the field of multiferroics, magnetoelectrics, and the pursuit of electric-field control of magnetism. What we present is something that is extremely exciting from both a fundamental science and applications perspective and has the potential to revolutionize our world. Needless to say, to realize this potential will require numerous new innovations, both in the fundamental science arena as well as translating these scientific discoveries into real applications. Thus, this article will attempt to bridge the gap between fundamental condensed-matter physics and the actual manifestations of the physical concepts into real-life applications. We hope this article will help spur more translational research within the broad materials physics community.

The growth and characterization of functional oxide thin films that are ferroelectric, magnetic, or both at the same time are reviewed. The evolution of synthesis techniques and how advances in in situ characterization have enabled significant acceleration in improvements to these materials are described. Methods for enhancing the properties of functional materials or creating entirely new functionality at interfaces are covered, including strain engineering and layering control at the atomic-layer level. Emerging applications of these functional oxides such as achieving electrical control of ferromagnetism and the future of these complex functional oxides is discussed. © 2010 Elsevier B.V. All rights reserved.

The development of next-generation piezoelectric micro-electro-mechanical systems (piezo-MEMS) demands reliable and reproducible processes to fulfil the ever-growing requirements. Research on doped PZT thin films with improved ferroelectric and piezoelectric thin films is on the rise; however, most of them mainly discuss the fabrication process flows and results. This paper attempts to present an overview of some of the key issues and challenges encountered in the device level fabrication of piezo-MEMS acoustic sensors using PZT thin films doped with Strontium and Lanthanum for underwater applications. A recipe on the technical challenges would have saved more time and cost for the researchers as several unsuccessful fabrications and damages were encountered. This paper discusses the issues starting from fabrication of sputtering target to deposition, annealing, patterning and isolation of device layers, electrical contacts, packaging as per the application requirements, etc. in detail. [ABSTRACT FROM AUTHOR]

Fabrication of economically feasible photocathode for hydrogen energy production through solar water splitting is a major research among the scientific community for a decade. P-type compound Cu2ZnSnS4 (CZTS) is very interesting material due to its absorption property, earth-abundant constituents and environmental friendliness that serves as a suitable candidate to act as a photocathode. In the present work, Cu2ZnSnS4 (CZTS) nanoparticles are synthesized by simple one-step chemical method and annealed at 350 °C for three different times (60 min, 90 min, and 120 min). The effect of annealing time on the structural, optical and photoelectrochemical properties are investigated. XRD pattern indicates the formation of tetragonal crystal structure and the crystallinity increases according to the annealing time. 2D nanoplate morphology is obtained for the sample that was annealed for 120 min. From the absorption spectra, it was found that the bandgap decreases with increase of annealing time. Further, the prepared nanoparticle thin films are used as a cathode for photoelectrochemical water splitting application. Among these, the nanoparticles that are annealed for 120 min showed higher photocurrent density when compared to nanoparticles annealed for 60 min and 90 min. [ABSTRACT FROM AUTHOR]

Pure and other concentrations of cobalt (Co2+) ions incorporated into cuprous oxide Cu2−xCoxO (x = 0–14 mM) thin films were successfully deposited in fluorine-doped tin oxide (FTO) glass substrate by employing electro deposition technique. The crystallite size of pure and Co-doped thin films was investigated from 29.03 to 43.38 nm using X-ray diffraction (XRD) patterns. Scanning electron microscope (SEM) images display three-sided pyramid shape morphology of pure Cu2O thin films that get significantly changed, as and when Co concentrations get increased. The optical bandgap value gets continuously increased from 2.128 to 2.297 eV for a 0–14 mM change in Co doping concentration. Vibrating sample magnetometer (VSM) pictures the film that exhibits a better ferromagnetic property with a saturation magnetism of 159.96 E−6 emu for 14 mM Co dopant. X-ray photoelectron spectroscopy (XPS) confirm the presence of cobalt (Co2+) as a dopant in the host Cu2O thin films. The Cu2−86Co14O (x = 14 mM) thin film has a higher specific capacitance of 164.90 F/g with 3.66 Wh/kg energy density at the current density of 2 A/g. It has a good energy and a power density in the higher concentration Co-doped Cu2O thin films applicable for energy storage devices. [ABSTRACT FROM AUTHOR]

Doped lead–zirconate–titanate (PZT) thin films are preferred for the development of micro–electro–mechanical systems (MEMS)-based acoustic sensors because of their inherent higher dielectric and piezoelectric coefficients. Patterning process is used to develop such MEMS devices which is highly complex even for undoped PZT thin films; therefore, the problem is further cumbersome for doped PZT thin films due to the presence of added dopant elements and their associated chemistry. This paper presents patterning of strontium (Sr) and lanthanum (La) co-doped PZT thin film (PSLZT) deposited on platinized silicon substrate using wet and dry etching processes for fabricating a diaphragm structure with thickness of 15–25 μ m and diameter of 1.4–2 mm, suitable for acoustic sensing applications. The effects of various etching conditions have been studied and the results are reported. It is found that the dry etching is the most suited process for realizing the piezoelectric MEMS structure due to its higher etching resolution. An appreciable etching rate of 260–270 nm/min with smooth vertical sidewalls is achieved. The silicon diaphragm with patterned PSLZT thin film is found to retain more than 80% of its dielectric and piezoelectric coefficients and has a resonance of 1.43 MHz. [ABSTRACT FROM AUTHOR]

Ferroelectric domain structures of (001)c, (101)c, and (111)c oriented epitaxial BiFeO3 thin films were studied by using the phase-field approach. Long-range elastic and electrostatic interactions were taken into account. The effects of various types of substrate constraint on the domain morphologies were systematically analyzed. It is demonstrated that domain structures of BiFeO3 thin films could be controlled by selecting proper film orientations and substrate constraint. The dependence of the {110}c-type domain wall orientation on substrate constraint for the (001)c oriented BiFeO3 thin film was also discussed. [ABSTRACT FROM AUTHOR]

The synthesis and fundamental material properties of layered TiAl/Cu/Ta electrodes were investigated to achieve the integration of Cu electrodes with high-dielectric constant (κ) oxide thin films for application to the fabrication of high-frequency devices. The Ta layer is an excellent diffusion barrier to inhibit deleterious Cu diffusion into the Si substrate, while the TiAl layer provides an excellent barrier against oxygen diffusion into the Cu layer to inhibit Cu oxidation during the growth of the high-κ layer in an oxygen atmosphere. Polycrystalline (Ba[sub x]Sr[sub 1-x])TiO[sub 3] (BST) thin films were grown on the Cu-based bottom electrode by rf magnetron sputtering at temperatures in the range 400–600 °C in oxygen, to investigate the performance of BST/Cu-based capacitors. Characterization of the Cu-based layered structure using surface analytical methods showed that two amorphous oxide layers were formed on both sides of the TiAl barrier, such that the oxide layer on the free surface of the TiAl layer correlates with TiAlO[sub x], while the oxide layer at the TiAl/Cu interface is an Al[sub 2]O[sub 3]-rich layer. This double amorphous barrier layer structure effectively prevents oxygen penetration towards the underlying Cu and Ta layers. The TiAlO[sub x] interfacial layer, which has a relatively low dielectric constant compared with BST, reduced the total capacitance of the BST thin film capacitors. In addition, the layered electrode-oxide interface roughening observed during the growth of BST films at high temperature, due to copper grain growth, resulted in large dielectric loss on the fabricated BST capacitors. These problems were solved by growing the BST layer at 450 °C followed by a rapid thermal annealing at 700 °C. This process significantly reduced the thickness of the TiAlO[sub x] layer and interface roughness resulting in BST capacitors exhibiting properties suitable for the fabrication of high-performance high-frequency devices. In summary, relatively high dielectric constant (280), low dielectric loss (0.007), and low leakage current (<2×10[sup -8] A/cm[sup 2] at 100 kV/cm) were achieved for BST thin film capacitors with Cu-based electrodes. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Landau–Devonshire-type phenomenological thermodynamic theory is employed to explain the electric field dependence of piezoelectric properties of tetragonal single domain PbZr[sub x]Ti[sub 1-x]O[sub 3] (PZT). The strong nonlinearity of the converse piezoelectric coefficient under a large external electric field is proved to be intrinsic both in bulk crystal and epitaxial tetragonal PZT thin films. The tunability of piezoelectric responses by an external electric field and its dependence on the film/substrate misfit and elastic compliance of thin films are characterized quantitatively. The theoretical predictions are in good agreement with the experimental results of piezoresponse scanning microscopy. Due to the large tunability of piezoresponse in it, PZT 50/50 (x=0.5) epitaxial film is a promising candidate for use in future tunable devices. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Presents a study concerning the colossal magnetoresistance in La-Ca-Mn-O ferromagnetic thin films. Experimental procedure; Results and discussion.

Investigates the magnetic characterization of epitaxial Y[sub5]Fe[sube]O[sub12]/Bi[sub3]Fe[sub5]O[sub12] and Y[sub5]Fe[sub3]O[sub12]/Eu[sub1]Bi[sub2]Fe[sub5]O[sub12] heterostructures grown by pulsed laser deposition. Methods used to examine the effects of layer thickness ratios on the composition, microstructure and magnetic properties of the films; Examples of material systems that are used for magneto-optical applications; Information on the YIG/BIG series.

Presents a study which determined the Hall effect in coherent epitaxial τ (Mn,Ni)Al thin films on gallium arsenide. Indication of the measurements of the Hall effect; Structure and properties of the films; Possibility of further reductions in coercivity.

Recently, a methodology for fabricating polycrystalline metal-organic framework (MOF) membranes has been introduced - referred to as interfacial microfluidic membrane processing - which allows parallelizable fabrication of MOF membranes inside polymeric hollow fibers of microscopic diameter. Such hollow fiber membranes, when bundled together into modules, are an attractive way to scale molecular sieving membranes. The understanding and engineering of fluidic processing techniques for MOF membrane fabrication are in their infancy. Here, a detailed mechanistic understanding of MOF (ZIF-8) membrane growth under microfluidic conditions in polyamide-imide hollow fibers is reported, without any intermediate steps (such as seeding or surface modification) or post-synthesis treatments. A key finding is that interfacial membrane formation in the hollow fiber occurs via an initial formation of two distinct layers and the subsequent rearrangement into a single layer. This understanding is used to show how nonisothermal processing allows fabrication of thinner (5 μm) ZIF-8 films for higher throughput, and furthermore how engineering the polymeric hollow fiber support microstructure allows control of defects in the ZIF-8 membranes. The performance of these engineered ZIF-8 membranes is then characterized, which have H2/C3H8 and C3H6/C3H8 mixture separation factors as high as 2018 and 65, respectively, and C3H6 permeances as high as 66 GPU. [ABSTRACT FROM AUTHOR]

Multiferroic BiFeO3 (BFO)/La0.7.Sr0.3MnO3 heterostructured thin films were grown by pulsed laser deposition on polished spark plasma sintered LaAlO3 (LAO) polycrystalline substrates. Both polycrystalline LAO substrates and BFO films were locally characterized using electron backscattering diffraction, which confirmed the high-quality local epitaxial growth on each substrate grain. Piezoforce microscopy was used to image and switch the piezo-domains, and the results are consistent with the relative orientation of the ferroelectric variants with the surface normal. This high-throughput synthesis process opens the routes towards wide survey of electronic properties as a function of crystalline orientation in complex oxide thin film synthesis. [ABSTRACT FROM AUTHOR]

We demonstrate that thermal annealing in cation controlled environments is an effective means to obtain atomically flat and chemically single terminated surfaces of a layer structured substrate. The effectiveness of the cation controlled annealing method is proved with SrLaAlO4, which is a representative layer structured substrate of A2BO4 type. Potassium ion scattering, in particular, shows that the method allows not only single termination but also selective termination of either A- or B-site on the substrate. We further demonstrate that the chemical nature of underlying SrLaAlO4 substrates is of critical importance in the growth of SrRuO3 thin films resulting in different morphologies and transport properties. [ABSTRACT FROM AUTHOR]

Abstract: The authors developed a rigorous framework to model nanofiltration (NF) membrane selectivity at high feed water recoveries and verify it experimentally. The phenomenological model and the Donnan steric partitioning pore model (DSPM) were incorporated into a differential element approach for predicting removal of a variety of solutes from single salt solutions and natural water by NF membranes up to 90% feed water recovery in the temperature range 5–41 °C. In this approach, the entire membrane ensemble was divided into numerous sub-elements analogous to real-world full-scale NF installations, where concentrate (or reject) from one element feeds into the next element. Fundamental membrane properties (average pore radius, surface charge density, and ratio of thickness to porosity) and the reflection coefficient and permeability coefficient were first independently obtained for each solute–membrane–temperature combination using separate low recovery experiments with negligible concentration polarization and later used as model inputs to calculate solute removal in a purely predictive fashion for 5–90% recovery. This modeling approach accurately predicted removals from single salt solutions of NaCl and MgSO4 as well as natural organic matter, disinfection by-product precursors, and several ions from pretreated Lake Houston water in a wide range of operating conditions demonstrating its use to simulate NF permeate water quality under real-world conditions of high feed water recovery. [Copyright &y& Elsevier]

We write this article in honor of Professor Vitaly L. Ginzburg, truly the father of the field of ferroelectricity. This article serves as a review of the current state of research pertaining to multiferroic BiFeO3 thin films. In this review we will delve into details of the growth of BiFeO3 thin films and the use of piezoforce microscopy and x-ray reciprocal space mapping to characterize the crystal structure and domain structure of BiFeO3. We will also discuss the use of vicinal and asymmetric substrates to simplify the domain structure in BiFeO3. By simplifying the domain structure we can, in turn, control the ferroelectric switching mechanisms in BiFeO3. Finally we describe the basic ferroelectric properties of BFO films and discuss the critical issues needed to be solved in BiFeO3 films including leakage, complex domain structure, coercivity, and reliability. Such results are promising for continued exploration for detailed multiferroic-coupling studies in the magnetoelectric BiFeO3 system and BiFeO3, in turn, provides a model platform with which to realize the exciting possibility of electrically control magnetism. [ABSTRACT FROM AUTHOR]

A short review of recent progress in the field of multiferroic thin films and heterostructures is given. We focus on the bismuth iron oxide system due to its desirable properties, namely high ferroelectric Curie temperature and antiferromagnetic Neel temperature. Epitaxial growth of this model system in various crystallographic orientations has conclusively demonstrated the large ferroelectric polarization in this system. Piezoforce microscopy reveal a complex domain structure, especially on (100) SrTiO3 substrates. Electrical switching experiments show the co-existence of 71°, 109° and 180° domain switching mechanisms in such films. Preliminary work has shown promise for electrically controllable exchange bias in ferromagnet-multiferroic heterostructures. [ABSTRACT FROM AUTHOR]

Multiferroic materials, which show simultaneous ferroelectric and magnetic ordering, exhibit unusual physical properties — and in turn promise new device applications — as a result of the coupling between their dual order parameters. We review recent progress in the growth, characterization and understanding of thin-film multiferroics. The availability of high-quality thin-film multiferroics makes it easier to tailor their properties through epitaxial strain, atomic-level engineering of chemistry and interfacial coupling, and is a prerequisite for their incorporation into practical devices. We discuss novel device paradigms based on magnetoelectric coupling, and outline the key scientific challenges in the field. [ABSTRACT FROM AUTHOR]

Even though polymeric nanofiltration (NF) and reverse osmosis (RU) membranes often operate on surface waters and surficial groundwaters whose temperature varies over time and with season, very little detailed mechanistic information on temperature effects on membrane selectivity is available to date. Hence, a study was undertaken to investigate the effects of operating temperature (5-41 °C) on the morphology and structure of two commercially available thin film composite NF membranes. Application of hydrodynamic models to experimental rejection of dilute solutions of hydrophilic neutral alcohols, sugars, and poly(ethylene glycol)s revealed changes in both the sieving coefficient and permeability of solutes below the membrane glass transition temperature. The vast majority of pores were smaller than 2 nm for both membranes (network pores) even though evidence for a small fraction of larger aggregate pores (∼30 nm) was also obtained for one membrane. Increasing temperature appears to cause structural changes in network pores by increasing its pore size while simultaneously decreasing pore density. These increases in pore sizes partially explain reported reductions in contaminant (e.g. arsenic, salts, natural organic matter, hardness, etc.) removal by NF and RO membranes with increasing temperature. [ABSTRACT FROM AUTHOR]

Wetting of the pore walls of porous templates is a simple and convenient method to prepare nanotubes. Ferroelectric lead zirconate titanate and barium titanate nanotubes were fabricated by wetting of porous silicon templates of polymeric precursors. The ferro- and piezoelectric properties of an individual ferroelectric either of a PZT or a BaTiO 3 nanotube were electrically characterized by measuring the local piezoelectric hysteresis. A sharp switching at the coercive voltage of about 2 V was shown from the hysterisis loop. The corresponding effective remnant piezoelectric coefficient is about 90 pm/V. We also expect that free-standing ferroelectric nanotubes obtained by partial etching of the silicon template will be used as building blocks of miniaturized devices and can have a significant impact in the field of nano-electromechanical systems. [ABSTRACT FROM AUTHOR]

Using Scanning Nonlinear Dielectric Microscopy (SNDM) which has attained sub-nanometer resolution, we measured the linear dielectric constant of a-domains and c-domains in the (1,0,0) and (0,0,1) oriented PbZr 0.2 Ti 0.8 O 3 thin film and confirmed that the dielectric constant of a-domain is higher than that of c-domain. Next, we observed 90° domain walls (a-c domain walls) and 180° domain walls (c-c domain walls) and we obtained the minimum value of 180° c-c domain wall thickness was 1.87 nm and 90° a-c domain wall was 2.52 nm. [ABSTRACT FROM AUTHOR]

Epitaxial and random-oriented Pb(Zr,Ti)O 3 (PZT) films were fabricated at 450-550°C on SrRuO 3 (SRO)/SrTiO 3 /Si and SRO/amorphous Ti-Al layer-Si substrates, respectively, using a modified sol-gel process. For comparison, polycrystalline PZT films were also prepared on Pt-Si substrates using the same method. Thermogravimetric and differential thermal analysis (TG-DTA) of the modified sol-gel solution indicated that the solution began crystallization below 400°C. Both SRO/epitaxial PZT/SRO and SRO/random-oriented PZT/SRO capacitors processed at the same temperature had similar polarization values, and all the SRO/PZT/SRO capacitors processed at 450-550°C exhibited the favorable electrical characteristics including high polarization, high resistivity, small pulse width dependence, and good fatigue endurance. While the Pt/PZT/Pt capacitors processed at 450°C showed considerably low polarization compared to the SRO/PZT/SRO capacitors processed at the same temperature. High-quality SRO/PZT/SRO capacitors processed at low temperature have a bright prospect of fabrication of potential Si devices integrated PZT capacitors without thermal degradation. [ABSTRACT FROM AUTHOR]

Examines the near-field second harmonic imaging of the c/a/c/a polydomain structure of epitaxial PbZr[sub x]-[sub x]O[sub 3] thin films. Comparison of the near-field optical images, atomic force microscopy and X-ray diffraction; Optical contrast between the local second harmonic generation in c- and a-domains; Sensitivity of the optical second harmonic generation technique.

We report on the performance of a Ku-band gold/Ba0.5Sr0.5TiO3/LaAlO3 (Au/BSTO/LAO) coupled microstip line phase shifter fabricated with a 370 nm thick BSTO film. Two hundred degrees of contiguous relative insertion phase shift (ΔφS21), with insertion losses of 4.6 dB, were measured at room temperature, 14.3 GHz, and maximum dc voltage of 400 V. These results represent significant progress toward viable compact, low-loss, thin-film ferroelectric-based phase shifters at room temperature. ©1999 John Wiley & Sons, Inc. Microwave Opt Technol Lett 20: 53–56, 1999. [ABSTRACT FROM AUTHOR]

In order to investigate band gap tunability in polar oxides, we measured the optical properties of a series of Bi(Fe1-xMnx)O3 thin films. The absorption response of the mixed metal solid solutions is approximately a linear combination of the characteristics of the two end members, a result that demonstrates straightforward band gap tunability in this system. [ABSTRACT FROM AUTHOR]

Optical transmission spectroscopy and spectroscopic ellipsometry were used to extract the optical properties of an epitaxially grown quasi-tetragonal BiFeO3 thin film in the near infrared to near ultraviolet range. The absorption spectrum is overall blue shifted compared with that of rhombohedral BiFeO3, with an absorption onset near 2.25 eV, a direct 3.1 eV band gap, and charge transfer excitations that are ∼0.4 eV higher than those of the rhombohedral counterpart. We interpret these results in terms of structural strain and local symmetry breaking. [ABSTRACT FROM AUTHOR]

The epitaxial (001)-oriented 250 nm BiFeO3/50 nm SrRuO3 films were deposited on DyScO3 and SrTiO3 substrates, respectively. Following the growth, the cooling in lower oxygen pressure results in the creation of oxygen vacancies at the surface of the BiFeO3 film and the epitaxial strain drives these vacancies to diffuse from the film surface to the film interface. The SrTiO3 substrate strongly absorbs oxygen vacancies from the BiFeO3 film while the DyScO3 substrate does not. Therefore, the depth distribution of oxygen vacancies depends on the oxygen pressure during cooling, the epitaxial strain, and the substrate absorbing oxygen vacancies. [ABSTRACT FROM AUTHOR]

The authors report on the depth-resolved cathodoluminescence spectroscopy studies of the surface, bulk, and interface-localized electronic states in the band gap of epitaxial BiFeO3 thin films. The BiFeO3 films show a near band edge emission at 2.7 eV and defect emissions at energies varying from 2.0 to 2.5 eV. The overall results clearly suggest that the electronic structure, especially the defect states and their spatial distributions, of BiFeO3 films are strongly dependent on the growth conditions and method, stoichiometry, and strain, so that understanding and controlling them are crucial to optimize BiFeO3 film properties. [ABSTRACT FROM AUTHOR]

Twin structure engineering in sputtered films close to the Heusler stoichiometry Ni2MnGa (001) is used to demonstrate temperature and magnetic control of the phase transformation behavior. A custom heating apparatus integrated with a commercial microscope allows the observation of the austenite-martensite transition in epitaxially clamped films. Intermartensitic twin boundaries on cantilevers released from the epitaxial strain by focused ion beam etching are shown to move in response to an applied magnetic field with a strength of 0.6 T. We also report the observation of two coexisting twin morphologies. [ABSTRACT FROM AUTHOR]

Lead vanadate (PbVO3) is a multifunctional material which is both polar and magnetic. Its optical properties, important for linear and nonlinear optical spectroscopy of the material, are presented. Using spectroscopic ellipsometry, the refractive index and absorption versus wavelength of lead vanadate thin films at 295 K is reported. Using optical second harmonic generation, the nonlinear optical coefficients were determined to be d15/d31=0.20±0.02, d33/d31=316.0±4.4, and |d33|=10.40±0.35 pm/V at a fundamental wavelength of 800 nm. [ABSTRACT FROM AUTHOR]

We report the observation that thermoelectric thin films of La-doped SrTiO3 grown on SrTiO3 substrates yield anomalously high values of thermopower to give extraordinary values of power factor at 300 K. Thin films of Sr0.98La0.02TiO3, grown via pulsed laser deposition at low temperature and low pressure (450 °C, 10-7 Torr), do not yield similarly high values when grown on other substrates. The thin-film growth induces oxygen reduction in the SrTiO3 crystals, doping the substrate n type. It is found that the backside resistance of the SrTiO3 substrates is as low (∼12Ω/□) as it is on the film side after film growth. [ABSTRACT FROM AUTHOR]

A prominent band centered at ∼1000–1300 cm-1 and associated with resonant enhancement of two-phonon Raman scattering is reported in multiferroic BiFeO3 thin films and single crystals. A strong anomaly in this band occurs at the antiferromagnetic Neel temperature, TN∼375 °C. This band is composed of three peaks, assigned to 2A4, 2E8, and 2E9 Raman modes. While all three peaks were found to be sensitive to the antiferromagnetic phase transition, the 2E8 mode, in particular, nearly disappears at TN on heating, indicating a strong spin-two-phonon coupling in BiFeO3. [ABSTRACT FROM AUTHOR]

BiFeO3 thin films have been deposited on (111) SrTiO3 single crystal substrates by reactive molecular-beam epitaxy in an adsorption-controlled growth regime. This is achieved by supplying a bismuth overpressure and utilizing the differential vapor pressures between bismuth oxides and BiFeO3 to control stoichiometry. Four-circle x-ray diffraction reveals phase-pure, untwinned, epitaxial, (0001)-oriented films with rocking curve full width at half maximum values as narrow as 25 arc sec (0.007°). Second harmonic generation polar plots combined with diffraction establish the crystallographic point group of these untwinned epitaxial films to be 3m at room temperature. [ABSTRACT FROM AUTHOR]

Epitaxial growth of (0001)-oriented BiFeO3 thin films on the (0001) surface of GaN has been realized using intervening epitaxial (111) SrTiO3/(100) TiO2 buffer layers. The epitaxial BiFeO3 thin films have two in-plane orientations: [1120]BiFeO3∥[1120]GaN plus a twin variant related by a 180° in-plane rotation. BiFeO3 shows an out-of-plane remanent polarization of ∼90 μC/cm2, which is comparable to the remanent polarization of BiFeO3 prepared on (111) SrTiO3 single crystal substrates. The orientation of BiFeO3 realized on GaN provides the maximal out-of-plane polarization of BiFeO3, which is equivalent to a surface charge of 5×1014 electrons/cm2. [ABSTRACT FROM AUTHOR]

The authors report results of transport studies on high quality, fully epitaxial BiFeO3 thin films grown via pulsed laser deposition on SrRuO3/DyScO3 (110) substrates. Ferroelectric tests were conducted using symmetric and asymmetric device structures with either SrRuO3 or Pt top electrodes and SrRuO3 bottom electrodes. Comparison between these structures demonstrates the influence of electrode selection on the dominant transport mechanism. Analysis of film electrical response suggests Poole-Frenkel emission as the limiting leakage current mechanism in the symmetric structure. Temperature dependent measurements yield trap ionization energies of ∼0.65–0.8 eV. No clear dominant leakage mechanism was observed for the asymmetric structure. [ABSTRACT FROM AUTHOR]

Multifunctional materials promise to provide the foundation for a new class of devices in which functional properties are coupled to one another. Examples include magnetoelectric materials in which magnetic and ferroelectric properties are coupled. Here the authors report the successful growth of single phase, fully epitaxial thin films of the multifunctional material, PbVO3, using pulsed laser deposition. This growth offers an alternative means for the production of PbVO3 outside of high-temperature and high-pressure techniques through growth of epitaxial thin films on various substrates. The structure of this highly distorted perovskite is examined using x-ray diffraction, Raman spectroscopy, and transmission electron microscopy. [ABSTRACT FROM AUTHOR]

A phase-field model was developed for studying the magnetoelectric coupling effect in epitaxial ferroelectric and magnetic nanocomposite thin films. The model can simultaneously take into account the ferroelectric and magnetic domain structures, the electrostrictive and magnetostrictive effects, substrate constraint, as well as the long-range interactions such as magnetic, electric, and elastic interactions. As an example, the magnetic-field-induced electric polarization in BaTiO3–CoFe2O4 nanocomposite film was analyzed. The effects of the film thickness, morphology of the nanocomposite, and substrate constraint on the degree of magnetoelectric coupling were discussed. [ABSTRACT FROM AUTHOR]

The structure and the interface chemistry of epitaxial BiFeO3–NiFe2O4 nanocomposite thin films on SrTiO3(001) substrates were investigated using the Z-contrast imaging and the electron exit-wave reconstruction methods at the atomic scale. The results show that the NiFe2O4 pillars are nonwetting with respect to the substrate and exhibit {111} facets at the surface. The interface between BiFeO3 and NiFe2O4 lies in the {110} planes and is semicoherent. The atomic configuration of the interface, with the BiFeO layer bonding to the [Ni,Fe]O2 layer, was shown to have the maximized structure continuity and minimized interface charging. [ABSTRACT FROM AUTHOR]