Oxide Electronics

Using density functional theory and phenomenological Landau-Khalatnikov theory, we investigate the effect of spontaneous polarization switching in BaTiO 3 on the oxygen vacancy-induced electron gas at the adjacent SrTiO 3 /EuO interface in epitaxial BaTiO 3 /SrTiO 3 /EuO heterostructures. The ferroelectric field effect, induced by BaTiO 3 (BTO) in oxygen-deficient SrTiO 3 (STO) in the presence of a ferromagnetic semiconductor EuO, results in a spin-polarized carrier gas at the interface due to the magnetoelectric proximity effect.

We investigate the ferroelectric domain architecture and its operando response to an external electric field in BaTiO 3 -based electro-optic heterostructures integrated on silicon. By non-invasive optical second harmonic generation we identify the preexistence of in-plane-(a-) domains dispersed within a predominantly out-of-plane-(c-) oriented matrix. Monitoring the poling behavior of the respective domain populations, we show that the spontaneous polarization of these a-domains lack a predominant orientation in the pristine state, yet can be selectively aligned with an in-plane electric-field, leaving the c-domain population intact. Hence, domain reorientation of a ferroelastic c-to-a-type was directly excluded. Such independent electrical control of ferroelectric a-domains in a c-oriented BaTiO 3 film on silicon is a valuable platform for engineering multidirectional electrooptic functionality in integrated photonic devices.

The electronic and optical properties of transparent conducting oxides (TCOs) are closely linked to their crystallographic structure on a macroscopic (grain sizes) and microscopic (bond structure) level. With the increasing drive towards using reduced film thicknesses in devices and growing interest in amorphous TCOs such as n-type InGaZnO 4 (IGZO), ZnSnO 3 (ZTO), p-type Cu x CrO 2 , or ZnRh 2 O 4 , the task of gaining in-depth knowledge on their crystal structure by conventional X-ray diffraction-based measurements are becoming increasingly difficult. We demonstrate the use of a focal shift based background subtraction technique for Raman spectroscopy specifically developed for the case of transparent thin films on amorphous substrates. Using this technique we demonstrate, for a variety of TCOs CuO, a-ZTO, ZnO:Al), how changes in local vibrational modes reflect changes in the composition of the TCO and consequently their electronic properties.

The electronic and optical properties of transparent conducting oxides (TCOs) are closely linked to their crystallographic structure on a macroscopic (grain sizes) and microscopic (bond structure) level. With the increasing drive towards using reduced film thicknesses in devices and growing interest in amorphous TCOs such as n-type InGaZnO 4 (IGZO), ZnSnO 3 (ZTO), p-type Cu x CrO 2 , or ZnRh 2 O 4 , the task of gaining in-depth knowledge on their crystal structure by conventional X-ray diffraction-based measurements are becoming increasingly difficult. We demonstrate the use of a focal shift based background subtraction technique for Raman spectroscopy specifically developed for the case of transparent thin films on amorphous substrates. Using this technique we demonstrate, for a variety of TCOs CuO, a-ZTO, ZnO:Al), how changes in local vibrational modes reflect changes in the composition of the TCO and consequently their electronic properties.

The electronic and optical properties of transparent conducting oxides (TCOs) are closely linked to their crystallographic structure on a macroscopic (grain sizes) and microscopic (bond structure) level. With the increasing drive towards using reduced film thicknesses in devices and growing interest in amorphous TCOs such as n-type InGaZnO 4 (IGZO), ZnSnO 3 (ZTO), p-type Cu x CrO 2 , or ZnRh 2 O 4 , the task of gaining in-depth knowledge on their crystal structure by conventional X-ray diffraction-based measurements are becoming increasingly difficult. We demonstrate the use of a focal shift based background subtraction technique for Raman spectroscopy specifically developed for the case of transparent thin films on amorphous substrates. Using this technique we demonstrate, for a variety of TCOs CuO, a-ZTO, ZnO:Al), how changes in local vibrational modes reflect changes in the composition of the TCO and consequently their electronic properties.

The observation of a high-mobility two-dimensional electron gas between two insulating complex oxides, especially LaAlO 3 /SrTiO 3 , has enhanced the potential of oxides for electronics. The occurrence of this conductivity is believed to be driven by polarization discontinuity, leading to an electronic reconstruction. In this scenario, the crystal orientation has an important role and no conductivity would be expected, for example, for the interface between LaAlO 3 and (110)-oriented SrTiO 3 , which should not have a polarization discontinuity. Here we report the observation of unexpected conductivity at the LaAlO 3 / SrTiO 3 interface prepared on (110)-oriented SrTiO 3 , with a LaAlO 3 -layer thickness-dependent metal-insulator transition. Density functional theory calculation reveals that electronic reconstruction, and thus conductivity, is still possible at this (110) interface by considering the energetically favourable (110) interface structure, that is, buckled TiO 2 /LaO, in which the polarization discontinuity is still present. The conductivity was further found to be strongly anisotropic along the different crystallographic directions with potential for anisotropic superconductivity and magnetism, leading to possible new physics and applications.

The observation of a high-mobility two-dimensional electron gas between two insulating complex oxides, especially LaAlO 3 /SrTiO 3 , has enhanced the potential of oxides for electronics. The occurrence of this conductivity is believed to be driven by polarization discontinuity, leading to an electronic reconstruction. In this scenario, the crystal orientation has an important role and no conductivity would be expected, for example, for the interface between LaAlO 3 and (110)-oriented SrTiO 3 , which should not have a polarization discontinuity. Here we report the observation of unexpected conductivity at the LaAlO 3 / SrTiO 3 interface prepared on (110)-oriented SrTiO 3 , with a LaAlO 3 -layer thickness-dependent metal-insulator transition. Density functional theory calculation reveals that electronic reconstruction, and thus conductivity, is still possible at this (110) interface by considering the energetically favourable (110) interface structure, that is, buckled TiO 2 /LaO, in which the polarization discontinuity is still present. The conductivity was further found to be strongly anisotropic along the different crystallographic directions with potential for anisotropic superconductivity and magnetism, leading to possible new physics and applications.

The observation of a high-mobility two-dimensional electron gas between two insulating complex oxides, especially LaAlO 3 /SrTiO 3 , has enhanced the potential of oxides for electronics. The occurrence of this conductivity is believed to be driven by polarization discontinuity, leading to an electronic reconstruction. In this scenario, the crystal orientation has an important role and no conductivity would be expected, for example, for the interface between LaAlO 3 and (110)-oriented SrTiO 3 , which should not have a polarization discontinuity. Here we report the observation of unexpected conductivity at the LaAlO 3 / SrTiO 3 interface prepared on (110)-oriented SrTiO 3 , with a LaAlO 3 -layer thickness-dependent metal-insulator transition. Density functional theory calculation reveals that electronic reconstruction, and thus conductivity, is still possible at this (110) interface by considering the energetically favourable (110) interface structure, that is, buckled TiO 2 /LaO, in which the polarization discontinuity is still present. The conductivity was further found to be strongly anisotropic along the different crystallographic directions with potential for anisotropic superconductivity and magnetism, leading to possible new physics and applications.

Ferroelectric materials are characterized by the spontaneous polarization switchable by the applied fields, which can act as a "gate" to control various properties of ferroelectric/insulator interfaces. Here we review the recent studies on the modulation of oxide hetero-/homo-interfaces by ferroelectric polarization. We discuss the potential applications of recently developed four-dimensional scanning transmission electron microscopy and how it can provide insights into the fundamental understanding of ferroelectric polarization-induced phenomena and stimulate future computational studies. Finally, we give the outlook for the potentials, the challenges, and the opportunities for the contribution of materials computation to future progress in the area.

Oxide electronic materials provide a plethora of possible applications and offer ample opportunity for scientists to probe into some of the exciting and intriguing phenomena exhibited by oxide systems and oxide interfaces. In addition to the already diverse spectrum of properties, the nanoscale form of oxides provides a new dimension of hitherto unknown phenomena due to the increased surface-to-volume ratio. Oxide electronic materials are becoming increasingly important in a wide range of applications including transparent electronics, optoelectronics, magnetoelectronics, photonics, spintronics, thermoelectrics, piezoelectrics, power harvesting, hydrogen storage and environmental waste management. Synthesis and fabrication of these materials, as well as processing into particular device structures to suit a specific application is still a challenge. Further, characterization of these materials to understand the tunability of their properties and the novel properties that evolve due to their nanostructured nature is another facet of the challenge. The research related to the oxide electronic field is at an impressionable stage, and this has motivated us to contribute with a roadmap on 'oxide electronic materials and oxide interfaces'. This roadmap envisages the potential applications of oxide materials in cutting edge technologies and focuses on the necessary advances required to implement these materials, including both conventional and novel techniques for the synthesis, characterization, processing and fabrication of nanostructured oxides and oxide-based devices. The contents of this roadmap will highlight the functional and correlated properties of oxides in bulk, nano, thin film, multilayer and heterostructure forms, as well as the theoretical considerations behind both present and future applications in many technologically important areas as pointed out by Venkatesan. The contributions in this roadmap span several thematic groups which are represented by the following authors: novel field effect transistors and bipolar devices by Fortunato, Grundmann, Boschker, Rao, and Rogers; energy conversion and saving by Zaban, Weidenkaff, and Murakami; new opportunities of photonics by Fompeyrine, and Zuniga-Perez; multiferroic materials including novel phenomena by Ramesh, Spaldin, Mertig, Lorenz, Srinivasan, and Prellier; and concepts for topological oxide electronics by Kawasaki, Pentcheva, and Gegenwart. Finally, Miletto Granozio presents the European action 'towards oxide-based electronics' which develops an oxide electronics roadmap with emphasis on future nonvolatile memories and the required technologies. In summary, we do hope that this oxide roadmap appears as an interesting up-to-date snapshot on one of the most exciting and active areas of solid state physics, materials science, and chemistry, which even after many years of very successful development shows in short intervals novel insights and achievements.

Oxide electronic materials provide a plethora of possible applications and offer ample opportunity for scientists to probe into some of the exciting and intriguing phenomena exhibited by oxide systems and oxide interfaces. In addition to the already diverse spectrum of properties, the nanoscale form of oxides provides a new dimension of hitherto unknown phenomena due to the increased surface-to-volume ratio. Oxide electronic materials are becoming increasingly important in a wide range of applications including transparent electronics, optoelectronics, magnetoelectronics, photonics, spintronics, thermoelectrics, piezoelectrics, power harvesting, hydrogen storage and environmental waste management. Synthesis and fabrication of these materials, as well as processing into particular device structures to suit a specific application is still a challenge. Further, characterization of these materials to understand the tunability of their properties and the novel properties that evolve due to their nanostructured nature is another facet of the challenge. The research related to the oxide electronic field is at an impressionable stage, and this has motivated us to contribute with a roadmap on 'oxide electronic materials and oxide interfaces'. This roadmap envisages the potential applications of oxide materials in cutting edge technologies and focuses on the necessary advances required to implement these materials, including both conventional and novel techniques for the synthesis, characterization, processing and fabrication of nanostructured oxides and oxide-based devices. The contents of this roadmap will highlight the functional and correlated properties of oxides in bulk, nano, thin film, multilayer and heterostructure forms, as well as the theoretical considerations behind both present and future applications in many technologically important areas as pointed out by Venkatesan. The contributions in this roadmap span several thematic groups which are represented by the following authors: novel field effect transistors and bipolar devices by Fortunato, Grundmann, Boschker, Rao, and Rogers; energy conversion and saving by Zaban, Weidenkaff, and Murakami; new opportunities of photonics by Fompeyrine, and Zuniga-Perez; multiferroic materials including novel phenomena by Ramesh, Spaldin, Mertig, Lorenz, Srinivasan, and Prellier; and concepts for topological oxide electronics by Kawasaki, Pentcheva, and Gegenwart. Finally, Miletto Granozio presents the European action 'towards oxide-based electronics' which develops an oxide electronics roadmap with emphasis on future nonvolatile memories and the required technologies. In summary, we do hope that this oxide roadmap appears as an interesting up-to-date snapshot on one of the most exciting and active areas of solid state physics, materials science, and chemistry, which even after many years of very successful development shows in short intervals novel insights and achievements.

The ferroelectric and electro-optical properties of LiNbO 3 make it an important material for current and future applications. It has also been suggested as a possible lead-free replacement for present PZTdevices. The atomic layer deposition (ALD) technique offers controlled deposition of films at an industrial scale and thus becomes an interesting tool for growth of LiNbO 3. We here report on ALD deposition of LiNbO 3 using lithium silylamide and niobium ethoxide as precursors, thereby providing good control of cation stoichiometry and films with low impurity levels of silicon. The deposited films are shown to be ferroelectric and their crystalline orientations can be guided by the choice of substrate. The films are polycrystalline on Si (100) as well as epitaxially oriented on substrates of Al 2 O 3 (012), Al 2 O 3 (001), and LaAlO 3 (012). The coercive field of samples deposited on Si (100) was found to be $220 kV cm À1 , with a remanent polarization of $0.4 mC cm À2. Deposition of lithium containing materials is traditionally challenging by ALD, and critical issues with such deposition are discussed.

Electrostatic modulation of interface conduction between semiconductors and insulating oxides is the foundation of semiconductor technology. This field effect concept can be applied on complex oxides, such as high temperature superconductors and colossal magnetoresistive manganites, in order to create new electronic and magnetic phases. Competition and coexistence of multiple nanoscale phases make them exciting to study around phase transitions. This study on hole doped La1-xSrxMnO3 systems has a twofold purpose. One is the demonstration of the field effect on La1-xSrxMnO3 (x = 0.125, 0.2, 0.3, 0.5) thin films. It is an important step towards electrostatic control of material properties; however, a challenging task because of their charge carrier densities of 0.01-1 hole/unit cell, a few orders of magnitude larger than in doped semiconductors. Control by linear dielectrics needs huge, constantly applied bias. Energy efficient tuning with low voltages requires highly polar ferroelectric. Pb(Zr0.2Ti0.8)O3 was chosen, whose remanence provides 0.5 charge carrier/unit cell on the manganite/ferroelectric interface. La1-xSrxMnO3/Pb(Zr0.2Ti0.8)O3 heterostructures were synthesized by pulsed laser epitaxy and remarkable conduction modifications were observed in the La1-xSrxMnO3. This can be a strong foundation of a new tool to research electronic oxides. dissertation research, will always have an impact on my scientific growth. As "civilians" they were always supportive friends outside the lab. People from other groups in the same Laboratory need to be thanked for scientific discussions and sometimes more than that: Dr. Brian C. Sales, Dr. Rongying Jin, Dr.Shiliang Li and Dr. Thomas Zacharia Ward. I got to taste the world of oxide growth by molecular beam epitaxy, which definitely broadened my knowledge and experience, even if that work is not included. For this reason I would like to mention here Dr. Rodney A. McKee as well as Frederick J. Walker. The two years I spent in their lab will always be remembered. Now that I am getting more and more emotional while thinking of my support network, let me dedicate a paragraph to those people who used to shape me as a young student and will always be a huge part of what I will become in Life: my Hungarian

Oxide electronic materials provide a plethora of possible applications and offer ample opportunity for scientists to probe into some of the exciting and intriguing phenomena exhibited by oxide systems and oxide interfaces. In addition to the already diverse spectrum of properties, the nanoscale form of oxides provides a new dimension of hitherto unknown phenomena due to the increased surface-to-volume ratio. Oxide electronic materials are becoming increasingly important in a wide range of applications including transparent electronics, optoelectronics, magnetoelectronics, photonics, spintronics, thermoelectrics, piezoelectrics, power harvesting, hydrogen storage and environmental waste management. Synthesis and fabrication of these materials, as well as processing into particular device structures to suit a specific application is still a challenge. Further, characterization of these materials to understand the tunability of their properties and the novel properties that evolve due to their nanostructured nature is another facet of the challenge. The research related to the oxide electronic field is at an impressionable stage, and this has motivated us to contribute with a roadmap on 'oxide electronic materials and oxide interfaces'. This roadmap envisages the potential applications of oxide materials in cutting edge technologies and focuses on the necessary advances required to implement these materials, including both conventional and novel techniques for the synthesis, characterization, processing and fabrication of nanostructured oxides and oxide-based devices. The contents of this roadmap will highlight the functional and correlated properties of oxides in bulk, nano, thin film, multilayer and heterostructure forms, as well as the theoretical considerations behind both present and future applications in many technologically important areas as pointed out by Venkatesan. The contributions in this roadmap span several thematic groups which are represented by the following authors: novel field effect transistors and bipolar devices by Fortunato, Grundmann, Boschker, Rao, and Rogers; energy conversion and saving by Zaban, Weidenkaff, and Murakami; new opportunities of photonics by Fompeyrine, and Zuniga-Perez; multiferroic materials including novel phenomena by Ramesh, Spaldin, Mertig, Lorenz, Srinivasan, and Prellier; and concepts for topological oxide electronics by Kawasaki, Pentcheva, and Gegenwart. Finally, Miletto Granozio presents the European action 'towards oxide-based electronics' which develops an oxide electronics roadmap with emphasis on future nonvolatile memories and the required technologies. In summary, we do hope that this oxide roadmap appears as an interesting up-to-date snapshot on one of the most exciting and active areas of solid state physics, materials science, and chemistry, which even after many years of very successful development shows in short intervals novel insights and achievements.

Transition metal oxides show remarkably diverse quantum functional properties such as high temperature superconductivity, colossal magnetoresistance, multiferroicity, two-dimensional electron gas, topological insulators, and etc. This diversity manifests as a result of many energy scales of similar magnitude competing rather than any particular one dominating in the system. In this regard, growth of atomically controlled epitaxial thin films and heterostructures would allow to control relevant energy scales by imposing various stimuli, such as reduction of dimensionality, introduction of interfaces, modification of the interfacial octahedral tilts, and symmetry breaking; in turn, modified functional properties or completely new phenomena may emerge in epitaxial films and heterostructures. Also of exceeding importance is the fact that atomically controlled epitaxial thin films/heterostructures of the multifunctional oxides offer promising potentials for next generation oxide electronics. In this short review, we collect representative examples of quantum correlated phenomena arising in epitaxial films and heterostructures of transition metal oxides and highlight some of the progresses achieved in thin film research of various functional oxides in the last couple of decades.

The interaction of oxygen vacancies and ferroelectric domain walls is of great scientific interest because it leads to different domain-structure behaviors. Here, we use high-resolution scanning transmission electron microscopy to study the ferroelectric domain structure and oxygen-vacancy ordering in a compressively strained Bi 0.9 Ca 0.1 FeO 3−δ thin film. It was found that atomic plates, in which agglomerated oxygen vacancies are ordered, appear without any periodicity between the plates in out-of-plane and in-plane orientation. The oxygen non-stoichiometry with δ ≈ 1 in FeO 2−δ planes is identical in both orientations and shows no preference. Within the plates, the oxygen vacancies form 1D channels in a pseudocubic [010] direction with a high number of vacancies that alternate with oxygen columns with few vacancies. These plates of oxygen vacancies always coincide with charged domain walls in a tail-to-tail configuration. Defects such as ordered oxygen vacancies are thereby known to lead to a pinning effect of the ferroelectric domain walls (causing application-critical aspects, such as fatigue mechanisms and countering of retention failure) and to have a critical influence on the domain-wall conductivity. Thus, intentional oxygen vacancy defect engineering could be useful for the design of multiferroic devices with advanced functionality.

Perovskite metal oxide (LiNbO 3) nanomaterial is explored as a magneto-optic sensor. The electromagnetic interaction is described by magneto-optic modulation associated with vacancy-induced room temperature ferromagnetism. The guiding and propagation through single mode fiber (SMF) is via the excitation of core modes through the material-mediated cavity and further modulated by external magnetic field. The sensitivity and resolution of the sensor are found to be 186 pm/mT and 0.51 Oe, respectively. The structure with material integrated optical design resulting in a Fabry-Perrot interferometer (FPI), is implemented as an extrinsic sensor, and sensing mechanism is elaborated.

Oxide electronic materials provide a plethora of possible applications and offer ample opportunity for scientists to probe into some of the exciting and intriguing phenomena exhibited by oxide systems and oxide interfaces. In addition to the already diverse spectrum of properties, the nanoscale form of oxides provides a new dimension of hitherto unknown phenomena due to the increased surface-to-volume ratio. Oxide electronic materials are becoming increasingly important in a wide range of applications including transparent electronics, optoelectronics, magnetoelectronics, photonics, spintronics, thermoelectrics, piezoelectrics, power harvesting, hydrogen storage and environmental waste management. Synthesis and fabrication of these materials, as well as processing into particular device structures to suit a specific application is still a challenge. Further, characterization of these materials to understand the tunability of their properties and the novel properties that evolve due to their nanostructured nature is another facet of the challenge. The research related to the oxide electronic field is at an impressionable stage, and this has motivated us to contribute with a roadmap on 'oxide electronic materials and oxide interfaces'. This roadmap envisages the potential applications of oxide materials in cutting edge technologies and focuses on the necessary advances required to implement these materials, including both conventional and novel techniques for the synthesis, characterization, processing and fabrication of nanostructured oxides and oxide-based devices. The contents of this roadmap will highlight the functional and correlated properties of oxides in bulk, nano, thin film, multilayer and heterostructure forms, as well as the theoretical considerations behind both present and future applications in many technologically important areas as pointed out by Venkatesan. The contributions in this roadmap span several thematic groups which are represented by the following authors: novel field effect transistors and bipolar devices by Fortunato, Grundmann, Boschker, Rao, and Rogers; energy conversion and saving by Zaban, Weidenkaff, and Murakami; new opportunities of photonics by Fompeyrine, and Zuniga-Perez; multiferroic materials including novel phenomena by Ramesh, Spaldin, Mertig, Lorenz, Srinivasan, and Prellier; and concepts for topological oxide electronics by Kawasaki, Pentcheva, and Gegenwart. Finally, Miletto Granozio presents the European action 'towards oxide-based electronics' which develops an oxide electronics roadmap with emphasis on future nonvolatile memories and the required technologies. In summary, we do hope that this oxide roadmap appears as an interesting up-to-date snapshot on one of the most exciting and active areas of solid state physics, materials science, and chemistry, which even after many years of very successful development shows in short intervals novel insights and achievements.

High-k dielectric oxides are supposedly ideal gate-materials for ultra-high doping in graphene and other 2D-crystals. Here, we report a temperature-dependent electronic transport study on chemical vapor deposited-graphene gated with SrTiO 3 (STO) thin film substrate. At carrier densities away from charge neutrality point the temperature-dependent resistivity of our graphene samples on both STO and SiO 2 /Si substrates show metallic behavior with contributions from Coulomb scattering and flexural phonons attributable to the presence of characteristic quasi-periodic nano-ripple arrays. Significantly, for graphene samples on STO substrates we observe an anomalous 'slope-break' in the temperature-dependent resistivity for T 5 50 to 100 K accompanied by a decrease in mobility above 30 K. Furthermore, we observe an unusual decrease in the gate-induced doping-rate at low temperatures, despite an increase in dielectric constant of the substrate. We believe that a complex mechanism is at play as a consequence of the structural phase transition of the underlying substrate showing an anomalous transport behavior in graphene on STO. The anomalies are discussed in the context of Coulomb as well as phonon scattering. G raphene 1 , a 2-dimensional (2D) sheet of carbon atoms in a honeycomb lattice, is poised to transform the electronic industry thus promising a unique platform for many novel device applications, such as, nanoelectronics, optoelectronics, and flexible transparent devices 2-4. As a single-atom-thick layer, the transport property of graphene is highly influenced by the supporting substrate 1,5,6. SiO 2 /Si, a conventional substrate that provides an excellent optical contrast, has been extensively used to understand the charge transport phenomena in graphene in terms of momentum relaxation from charge impurities and interfacial phonons. Wafer-scale growth of graphene by chemical vapor deposition (CVD) methods 7 has made it increasingly feasible to explore a variety of novel functional substrates for engineering specific applications by means of tuning substrate-induced screening and by inducing strain 5,8-11. Replacement of SiO 2 /Si substrate by hexagonal boron nitride improves the carrier mobility by several orders of magnitude while limiting the maximum carrier density (,3 3 10 12 cm 22). Interestingly, at ultra-high doping the possibility of superconductivity in graphene has been theoretically predicted 12,13 while experimentally the optimal doping has still not been achieved to explore such phenomena. In the process, introduction of substrates with high dielectric constant 6,8,9,14 or gating with polymer electrolyte 15 has increased the carrier density by one-to-two orders in magnitude with fascinating electronic transport that can be attributed to screening as well as many-body interactions. The inability to reach expected high carrier densities for graphene gated with high-k dielectrics remains a puzzle-6,8,9,16,17 and points to the need to understand substrate-graphene interaction in detail beyond the expected crucial role of the electron-phonon scattering at the interface 17. Non-linear temperature-dependence of resistance particularly at higher temperatures have been variously attributed to scattering from adatoms or defects, charge impurities, surface optical (SO) phonons of the underlying SiO 2 /Si substrate and to the out-of

The observation of a high-mobility two-dimensional electron gas between two insulating complex oxides, especially LaAlO 3 /SrTiO 3 , has enhanced the potential of oxides for electronics. The occurrence of this conductivity is believed to be driven by polarization discontinuity, leading to an electronic reconstruction. In this scenario, the crystal orientation has an important role and no conductivity would be expected, for example, for the interface between LaAlO 3 and (110)-oriented SrTiO 3 , which should not have a polarization discontinuity. Here we report the observation of unexpected conductivity at the LaAlO 3 / SrTiO 3 interface prepared on (110)-oriented SrTiO 3 , with a LaAlO 3-layer thickness-dependent metal-insulator transition. Density functional theory calculation reveals that electronic reconstruction, and thus conductivity, is still possible at this (110) interface by considering the energetically favourable (110) interface structure, that is, buckled TiO 2 /LaO, in which the polarization discontinuity is still present. The conductivity was further found to be strongly anisotropic along the different crystallographic directions with potential for anisotropic superconductivity and magnetism, leading to possible new physics and applications.

We demonstrate that electronic and magnetic properties of graphene can be tuned via proximity of multiferroic substrate. Our first-principles calculations performed both with and without spin-orbit coupling clearly show that by contacting graphene with bismuth ferrite BiFeO 3 (BFO) film, the spin-dependent electronic structure of graphene is strongly impacted both by the magnetic order and by electric polarization in the underlying BFO. Based on extracted Hamiltonian parameters obtained from the graphene band structure, we propose a concept of six-resistance device based on exploring multiferroic proximity effect giving rise to significant proximity electro-(PER), magneto-(PMR), and multiferroic (PMER) resistance effects. This finding paves a way towards multiferroic control of magnetic properties in two dimensional materials.

Mott insulators have recently been identified as potential solar energy conversion material due to their favorable parameters. In this paper, we have investigated the cell performance by exploring the photovoltaic properties of Mott Insulator LaVO 3 (LVO). The LVO thin films were grown by the sol-gel technique followed by a sintering pathway under various processing conditions. We investigated the influence of processing parameters on the structural, optical and electrical properties of the films through different characterization techniques. A correlation between the material parameters with the device performance has been established to ensure LVO perovskite for photovoltaic applications. This analysis will aid researchers to realize Mott insulators as light absorber material.

High-k dielectric oxides are supposedly ideal gate-materials for ultra-high doping in graphene and other 2D-crystals. Here, we report a temperature-dependent electronic transport study on chemical vapor deposited-graphene gated with SrTiO 3 (STO) thin film substrate. At carrier densities away from charge neutrality point the temperature-dependent resistivity of our graphene samples on both STO and SiO 2 /Si substrates show metallic behavior with contributions from Coulomb scattering and flexural phonons attributable to the presence of characteristic quasi-periodic nano-ripple arrays. Significantly, for graphene samples on STO substrates we observe an anomalous 'slope-break' in the temperature-dependent resistivity for T 5 50 to 100 K accompanied by a decrease in mobility above 30 K. Furthermore, we observe an unusual decrease in the gate-induced doping-rate at low temperatures, despite an increase in dielectric constant of the substrate. We believe that a complex mechanism is at play as a consequence of the structural phase transition of the underlying substrate showing an anomalous transport behavior in graphene on STO. The anomalies are discussed in the context of Coulomb as well as phonon scattering. G raphene 1 , a 2-dimensional (2D) sheet of carbon atoms in a honeycomb lattice, is poised to transform the electronic industry thus promising a unique platform for many novel device applications, such as, nanoelectronics, optoelectronics, and flexible transparent devices 2-4. As a single-atom-thick layer, the transport property of graphene is highly influenced by the supporting substrate 1,5,6. SiO 2 /Si, a conventional substrate that provides an excellent optical contrast, has been extensively used to understand the charge transport phenomena in graphene in terms of momentum relaxation from charge impurities and interfacial phonons. Wafer-scale growth of graphene by chemical vapor deposition (CVD) methods 7 has made it increasingly feasible to explore a variety of novel functional substrates for engineering specific applications by means of tuning substrate-induced screening and by inducing strain 5,8-11. Replacement of SiO 2 /Si substrate by hexagonal boron nitride improves the carrier mobility by several orders of magnitude while limiting the maximum carrier density (,3 3 10 12 cm 22). Interestingly, at ultra-high doping the possibility of superconductivity in graphene has been theoretically predicted 12,13 while experimentally the optimal doping has still not been achieved to explore such phenomena. In the process, introduction of substrates with high dielectric constant 6,8,9,14 or gating with polymer electrolyte 15 has increased the carrier density by one-to-two orders in magnitude with fascinating electronic transport that can be attributed to screening as well as many-body interactions. The inability to reach expected high carrier densities for graphene gated with high-k dielectrics remains a puzzle-6,8,9,16,17 and points to the need to understand substrate-graphene interaction in detail beyond the expected crucial role of the electron-phonon scattering at the interface 17. Non-linear temperature-dependence of resistance particularly at higher temperatures have been variously attributed to scattering from adatoms or defects, charge impurities, surface optical (SO) phonons of the underlying SiO 2 /Si substrate and to the out-of

The observation of a high-mobility two-dimensional electron gas between two insulating complex oxides, especially LaAlO 3 /SrTiO 3 , has enhanced the potential of oxides for electronics. The occurrence of this conductivity is believed to be driven by polarization discontinuity, leading to an electronic reconstruction. In this scenario, the crystal orientation has an important role and no conductivity would be expected, for example, for the interface between LaAlO 3 and (110)-oriented SrTiO 3 , which should not have a polarization discontinuity. Here we report the observation of unexpected conductivity at the LaAlO 3 / SrTiO 3 interface prepared on (110)-oriented SrTiO 3 , with a LaAlO 3-layer thickness-dependent metal-insulator transition. Density functional theory calculation reveals that electronic reconstruction, and thus conductivity, is still possible at this (110) interface by considering the energetically favourable (110) interface structure, that is, buckled TiO 2 /LaO, in which the polarization discontinuity is still present. The conductivity was further found to be strongly anisotropic along the different crystallographic directions with potential for anisotropic superconductivity and magnetism, leading to possible new physics and applications.

We present a method to predict the crystal structure of any given composition using machine learning methods. Then, using the example of bismuth ferrite, we illustrate how crystal structure, decomposed into distortion modes, can be implemented as a feature to explore the energy surface leading to the identification of metastable polymorphs. Crystal structure plays a crucial role in determining the electronic structure and property of any composition. Therefore, it has always been of great interest to predict the crystal structure of any composition without requiring synthesis and characterization. To achieve this goal, we combine machine learning and density functional theory (DFT) calculations. Initially, a classification model predicts the point groups of the given stoichiometries. Based on the predicted point group, a series of high-throughput DFT calculations determine the ground state of non-centrosymmetric crystal structures. In addition to the ground state structure, identifying metastable polymorphs that might get stabilized by controlling the synthetic conditions is of great importance as they can exhibit different functionalities. Therefore, we studied BiFeO3 as a multifunctional compound with a rich low-energy phase space. A training set is constructed by mapping the phase space based on possible distortion modes starting from the cubic perovskite structure. A machine learning model is built using the generated training set predicting the energy surface of BiFeO3 to explore new metastable phases.

Silicon photonics is expected to allow the implementation of a wide range of applications including sensing, datacom and security with the potential to leverage the already existing CMOS fabrication facilities for cost-effective and large production. Among the building blocks to develop, optical modulator is considered as a key device for integrated circuits. The main physical effect to perform optical modulation in silicon is based on plasma dispersion effect. However the maximum modulation speed achievable with this approach is limited by the mobility and recombination time of the carriers. Furthermore, these types of modulators face some limitations in terms of power consumption, chirp and loss that may compromise their future integration in integrated circuits. The purpose of this work is to explore an alternative approach, based on the use of the Pockels effect. Such an effect, commonly used in Lithium-Niobate, allows high speed and low power consumption optical modulation. Unf...

We demonstrate that electronic and magnetic properties of graphene can be tuned via proximity of multiferroic substrate. Our first-principles calculations performed both with and without spin-orbit coupling clearly show that by contacting graphene with bismuth ferrite BiFeO 3 (BFO) film, the spin-dependent electronic structure of graphene is strongly impacted both by the magnetic order and by electric polarization in the underlying BFO. Based on extracted Hamiltonian parameters obtained from the graphene band structure, we propose a concept of six-resistance device based on exploring multiferroic proximity effect giving rise to significant proximity electro-(PER), magneto-(PMR), and multiferroic (PMER) resistance effects. This finding paves a way towards multiferroic control of magnetic properties in two dimensional materials.

The demonstration of a quasi-two-dimensional electron gas (2DEG) and superconducting properties in LaAlO3/SrTiO3 heterostructures has stimulated intense research activity in recent ten years. The 2DEG has unique properties that are promising for applications in all-oxide electronic devices. The superconductivity in such heterostructures has been observed below 300 mK. For superconductivity applications it is desirable to have more wide temperature of the existence range and the ability to control superconductivity properties by external stimulus. Based on first-principles calculations and theoretical consideration we show that all-oxide heterostructures incorporating ferroelectric constituent, such as BaTiO3/La2CuO4, allow creating 2DEG. We predict a possibility of a high temperature guasi-two-dimensional superconductivity state. This state could be switchable between superconducting and conducting states by ferroelectric polarization reversal. We also discuss that such structures must be more simple for preparation. The proposed concept of ferroelectrically controlled interface superconductivity offers the possibility to design novel electronic devices.

Highly mobile 2-dimensional electron gases (2DEGs) at the (001), (011) and (111)-oriented LaAlO3/SrTiO3 (LAO/STO) interfaces are obtained using spin coating chemical method, which is a gentle technique without plasma bombardment of the pulsed laser deposition. As revealed by x-ray diffraction spectrum and x-ray reflectivity analysis, the LAO over layer is epitaxially grown, and has a uniform thickness of ~15 nm, ~29 nm and ~26 nm for (001), (011) and (111) orientations, respectively. The interfaces are well metallic down to 2 K. The carrier mobilities are ~28 000 cm2/Vs, ~22 000 cm2/Vs and ~8300 cm2/Vs at 2 K for the (001), (011) and (111) LAO/STO interfaces, respectively, and ~8 cm2/Vs, ~4 cm2/Vs and ~4 cm2/Vs at room temperature. These results are comparable to or even better than, for the (011) and (111) 2DEGs, the best ones ever reported. The present work shows that the spin coating chemical method is a feasible approach to get high quality 2DEG at both the polar/non-polar and p...

A number of recent studies indicate that the charge conduction of the LaAlO3/SrTiO3 interface at low temperature is confined to filaments which are linked to structural domain walls in the SrTiO3 with drastic consequences for example for the temperature dependence of local transport properties. We demonstrate that as a consequences of this current carrying filaments on the nano-scale the magnetotransport properties of the interface are highly anisotropic. Our magnetoresistance measurements reveal that the magnetoresistance in different nanostructures (< 500nm) is random in magnitude and sign, respectively. Warming up nanostructures above the structural phase transition temperature (105K) results in the significant change in MR. Even a sign change of the magnetoresistance is possible. The results suggest that domain walls that are differently oriented with respect to the surface exhibit different respective magnetoresistance and the total magnetoresistance is a result of a random ...

BaTiO 3 (BTO) is an emergent material in the field of silicon-integrated photonics, as its thin films have been demonstrated to have a very large electro-optic (Pockels) coefficient that can be used for optical modulators. However, BTO grown directly on SrTiO 3 (STO)-buffered Si (STO is required for epitaxial growth) initially grows with a polarization direction not suitable for the geometries currently used in photonic devices. Here, we grow BTO on a BaSnO 3-buffered STO substrate to form orthorhombic mm2 BTO, which has in-plane polarization orientation needed for photonic devices. Extensive crystalline characterization is done to confirm the high quality of the films, along with electro-optic measurements. Theoretical simulations coupled with the experimental results provide a foundational understanding of the properties of strain-stabilized orthorhombic BTO. Large electro-optic coefficients of 121 pm/V are observed in films as thin as 40 nm.

We demonstrate that electronic and magnetic properties of graphene can be tuned via proximity of multiferroic substrate. Our first-principles calculations performed both with and without spin-orbit coupling clearly show that by contacting graphene with bismuth ferrite BiFeO 3 (BFO) film, the spin-dependent electronic structure of graphene is strongly impacted both by the magnetic order and by electric polarization in the underlying BFO. Based on extracted Hamiltonian parameters obtained from the graphene band structure, we propose a concept of six-resistance device based on exploring multiferroic proximity effect giving rise to significant proximity electro-(PER), magneto-(PMR), and multiferroic (PMER) resistance effects. This finding paves a way towards multiferroic control of magnetic properties in two dimensional materials.

The relative importance of atomic defects and electron transfer in explaining conductivity at the crystalline LaAlO3/SrTiO3 interface has been a topic of debate. Metallic interfaces with similar electronic properties produced by amorphous oxide overlayers on SrTiO3 [Y.

Domain switching in polycrystalline BaTiO3 is exploited to realize self-holding phase actuators in Si-photonics. A non-volatile change of the BaTiO3 refractive-index is achieved and poly-BaTiO3-coated silicon photonic circuits are demonstrated.

The development of novel devices for neuromorphic computing and non-traditional logic operations largely relies on the fabrication of well controlled memristive systems with functionalities beyond standard bipolar behavior and digital ON-OFF states. In the present work we demonstrate for Ta2O5-based devices that it is possible to selectively activate/deactivate two series memristive interfaces in order to obtain clockwise or counter-clockwise multilevel squared remanent resistance loops, just by controlling both the electroforming process and the (a)symmetry of the applied stimuli, and independently of the nature of the used metallic electrodes. Based on our thorough characterization, analysis and modeling, we show that the physical origin of this electrical behavior relies on controlled oxygen vacancies electromigration between three different nanoscopic zones of the active Ta2O5-x layer: a central one and two quasi-symmetric interfaces with reduced TaO2-h(y) layers. Our devices fa...

Electrostatic modulation of interface conduction between semiconductors and insulating oxides is the foundation of semiconductor technology. This field effect concept can be applied on complex oxides, such as high temperature superconductors and colossal magnetoresistive manganites, in order to create new electronic and magnetic phases. Competition and coexistence of multiple nanoscale phases make them exciting to study around phase transitions. This study on hole doped La1-xSrxMnO3 systems has a twofold purpose. One is the demonstration of the field effect on La1-xSrxMnO3 (x = 0.125, 0.2, 0.3, 0.5) thin films. It is an important step towards electrostatic control of material properties; however, a challenging task because of their charge carrier densities of 0.01-1 hole/unit cell, a few orders of magnitude larger than in doped semiconductors. Control by linear dielectrics needs huge, constantly applied bias. Energy efficient tuning with low voltages requires highly polar ferroelectric. Pb(Zr0.2Ti0.8)O3 was chosen, whose remanence provides 0.5 charge carrier/unit cell on the manganite/ferroelectric interface. La1-xSrxMnO3/Pb(Zr0.2Ti0.8)O3 heterostructures were synthesized by pulsed laser epitaxy and remarkable conduction modifications were observed in the La1-xSrxMnO3. This can be a strong foundation of a new tool to research electronic oxides. dissertation research, will always have an impact on my scientific growth. As "civilians" they were always supportive friends outside the lab. People from other groups in the same Laboratory need to be thanked for scientific discussions and sometimes more than that: Dr. Brian C. Sales, Dr. Rongying Jin, Dr.Shiliang Li and Dr. Thomas Zacharia Ward. I got to taste the world of oxide growth by molecular beam epitaxy, which definitely broadened my knowledge and experience, even if that work is not included. For this reason I would like to mention here Dr. Rodney A. McKee as well as Frederick J. Walker. The two years I spent in their lab will always be remembered. Now that I am getting more and more emotional while thinking of my support network, let me dedicate a paragraph to those people who used to shape me as a young student and will always be a huge part of what I will become in Life: my Hungarian

The observation of two dimensional electron gas (2DEG), superconductivity and magnetism at the interfaces of LaAlO 3 /SrTiO 3 has further amplified the potential of complex oxides for novel electronics. These multifunctional properties are strongly believed to originate from the polarization discontinuity at the interface between the two oxides along (001) direction. In this scenario, the crystal orientation plays an important role and no conductivity would be expected for e.g., the interface between LaAlO 3 and (110)-oriented SrTiO 3 , which should not have a polarization discontinuity. In this talk, we will show the observation of conductivity at the LaAlO 3 /SrTiO 3 interface prepared on (110)-oriented SrTiO 3. The strong evidence for 2DEG at the interface of LaAlO 3 /SrTiO 3 (110) is the observed thickness dependence of insulator-metal transition at 3-4 u.c of LaAlO 3. Directional dependent electrical transport is observed in resistance versus temperature measurements. We propose some models for explaining the observed phenomena.

Through density functional calculations, we have demonstrated that ferromagnetic and metallic (FM-M) phase can be tailored in superlattices consisting of two dissimilar antiferromagnetic and insulating olivine phosphates LiMPO 4 and LiMʹPO 4 where M and Mʹ are 3d transition metals. The proposed tailored superlattices are stable and differ from the regular superlattices through broken and missing PO 4 tetrahedra. As a result, the p-d covalent bondings become reasonable and transition metal ions are forced to stabilize in fractional charge state instead of the integer-charge state observed in bulk. These result in partially occupied parabolic dispersive bands to favor the metallic phase and therefore open up the possibilities to go beyond the conventional layered perovskite polar interfaces to create metallic heterostructures out of insulating oxides. Out of all M-Mʹ combinations, we find that Cr-Mn, Cr-Co, Cr-Ni, Mn-Co and Mn-Ni combinations yield the FM-M phase as ground state in the tailored superlattices.

Oxide electronic materials provide a plethora of possible applications and offer ample opportunity for scientists to probe into some of the exciting and intriguing phenomena exhibited by oxide systems and oxide interfaces. In addition to the already diverse spectrum of properties, the nanoscale form of oxides provides a new dimension of hitherto unknown phenomena due to the increased surface-to-volume ratio. Oxide electronic materials are becoming increasingly important in a wide range of applications including transparent electronics, optoelectronics, magnetoelectronics, photonics, spintronics, thermoelectrics, piezoelectrics, power harvesting, hydrogen storage and environmental waste management. Synthesis and fabrication of these materials, as well as processing into particular device structures to suit a specific application is still a challenge. Further, characterization of these materials to understand the tunability of their properties and the novel properties that evolve due to their nanostructured nature is another facet of the challenge. The research related to the oxide electronic field is at an impressionable stage, and this has motivated us to contribute with a roadmap on 'oxide electronic materials and oxide interfaces'. This roadmap envisages the potential applications of oxide materials in cutting edge technologies and focuses on the necessary advances required to implement these materials, including both conventional and novel techniques for the synthesis, characterization, processing and fabrication of nanostructured oxides and oxide-based devices. The contents of this roadmap will highlight the functional and correlated properties of oxides in bulk, nano, thin film, multilayer and heterostructure forms, as well as the theoretical considerations behind both present and future applications in many technologically important areas as pointed out by Venkatesan. The contributions in this roadmap span several thematic groups which are represented by the following authors: novel field effect transistors and bipolar devices by Fortunato, Grundmann, Boschker, Rao, and Rogers; energy conversion and saving by Zaban, Weidenkaff, and Murakami; new opportunities of photonics by Fompeyrine, and Zuniga-Perez; multiferroic materials including novel phenomena by Ramesh, Spaldin, Mertig, Lorenz, Srinivasan, and Prellier; and concepts for topological oxide electronics by Kawasaki, Pentcheva, and Gegenwart. Finally, Miletto Granozio presents the European action 'towards oxide-based electronics' which develops an oxide electronics roadmap with emphasis on future nonvolatile memories and the required technologies. In summary, we do hope that this oxide roadmap appears as an interesting up-to-date snapshot on one of the most exciting and active areas of solid state physics, materials science, and chemistry, which even after many years of very successful development shows in short intervals novel insights and achievements.

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We have explored the effect of magnetic rare-earth dopants substitutionally incorporated on the Ba sites of BaSnO 3 in terms of electronic transport, magnetism, and optical properties. We show that for Ba 0.92 R 0.08 SnO 3 thin films (where R = La, Pr, Nd, Gd), there is a linear increase of mobility with carrier concentration across all doping schemes. La-doped films have the highest mobilities, followed by Pr-and Nd-doped films. Gddoped samples have the largest ionic size mismatch with the Ba site and correspondingly the lowest carrier concentrations and electron mobilities. However, crystallinity does not appear to be a strong predictor of transport phenomena; our results suggest that point defects more than grain boundaries are key ingredients in tuning the conduction of BaSnO 3 films grown by pulsed laser deposition. Pronounced, nonhysteretic x-ray magnetic dichroism signals are observed for Pr-, Nd-, and Gd-doped samples, indicating paramagnetism. Finally, we probe the optical constants for each of the BaSnO 3 doping schemes and note that there is little change in the transmittance across all samples. Together these results shed light on conduction mechanisms in BaSnO 3 doped with rare-earth cations.

The Anomalous Hall Effect (AHE) is an important quantity in determining the properties and understanding the behaviour of the two-dimensional electron system forming at the interface of SrTiO3-based oxide heterostructures. The occurrence of AHE is often interpreted as a signature of ferromagnetism, but it is becoming more and more clear that also paramagnets may contribute to AHE. We studied the influence of magnetic ions by measuring intermixed LaAlO3/GdTiO3/SrTiO3 at temperatures below 10 K. We find that, as function of gate voltage, the system undergoes a Lifshitz transition while at the same time an onset of AHE is observed. However, we do not observe clear signs of ferromagnetism. We argue the AHE to be due to the change in Rashba spin-orbit coupling at the Lifshitz transition and conclude that also paramagnetic moments which are easily polarizable at low temperatures and high magnetic fields lead to the presence of AHE, which needs to be taken into account when extracting carr...