The formation of a novel spin-polarized 2D electron gas at the LaMnO$_3$ monolayer embedded in SrMnO$_3$ is predicted from the first-principles density-functional calculations. The La (d) electrons become confined in the direction normal to the interface in the potential well of the La layer, serving as a positively-charged layer of electron donors. These electrons mediate a ferromagnetic alignment of the Mn t$_{2g}$ spins near the interface via the Anderson-Hasegawa double exchange and become, in turn, spin-polarized due to the internal magnetic fields of the Mn moments.
The main obstacles in realizing diluted magnetic oxide (DMO) in spintronics are the unknown electronic structures associated with its high TC ferromagnetism and spin polarized current and how to manipulate desired electronic structures by fabrication techniques. We demonstrate that fine-tuned electronic structures and band structures can be modified to initiate DMO properties. Interestingly, in the semiconducting state, the doped Co ions and oxygen vacancies contribute non-negligible magnetic moments; and the magnetic coupling between these moments is mediated by the localized carriers via hig…
A number of electronic devices involve metal/oxide interfaces in their structure where the oxide layer plays the role of electrical insulator. As the downscaling of devices continues, the oxide thickness can spread over only a few atomic layers, making the role of interfaces prominent on its insulating properties. The prototypical Al/SiO2 metal/oxide interface is investigated using first principle calculations, and the effect of the interfacial atomic bonding is evidenced. It is shown that the interface bonding configuration critically dictates the mechanical and electronic properties of the i…
The paper reviews methods used to study the electronic and structural properties of silicon/insulator interfaces. Methodological approaches to study the interface states and charge trapping in the oxide are considered. An overview of archetypical structural defects of the Si/SiO2 interface is given.
We report on the Dzyaloshinskii-Moriya (DMI) interaction at the interface between a ferromagnet and an oxide. We demonstrate experimentally that oxides can give rise to DMI. By comparison of systems comprised of Pt/Co90Fe10/Oxide and Cu/Co90Fe10/Oxide, we also show how oxidation of one interface can enhance and add to the total DMI of that generated by the Pt interface. This is due to the fact that the DMI on both interfaces promotes left-handed chirality. Finally, by use of ferromagnetic resonance spectroscopy, we show that the DMI and the spectroscopic splitting factor, which is a measure of…
In strongly correlated oxides, heterointerfaces, manipulating the interaction, frustration, and discontinuity of lattice, charge, orbital, and spin degrees of freedom, generate new possibilities for next generation devices. In this study, we went back to examine the existing oxide heterostructures and found the local conduction at the BiFeO3-CoFe2O4 vertical interface. In such hetero-nanostructure, the tubular interface, surrounding BiFeO3-CoFe2O4 vertical interface, can not only be the medium to the coupling between phases, but also be a new state of the matter. Our study demonstrates a novel…
In the framework of the modern theory of polarization, we rigorously establish the microscopic nature of the electric displacement field D. In particular, we show that the longitudinal component of D is preserved at a coherent and insulating interface. To motivate and elucidate our derivation, we use the example of LAO/STO interfaces and superlattices, where the validity of the above conservation law is not immediately obvious. Our results generalize the "locality principle" of constrained-D density functional theory to the first-principles modeling of charge-mismatched systems.
Polarization control of terahertz wave is a challenging subject in terahertz science and technology. Here, we report a simple method to control polarization state of the terahertz wave in terahertz generation process. At room temperature, terahertz radiation from a noncentrosymmetric and chiral oxide, sillenite Bi$_{12}$GeO$_{20}$, is observed by the irradiation of linearly polarized femtosecond laser pulses at 800 nm. The polarization state of the emitted terahertz wave is found to be elliptic with an ellipticity of $\sim$0.37$\pm$0.10. Furthermore, the ellipticity was altered to a nearly zer…
Amorphous insulating oxides play a significant role in the contemporary electronic industry. Understanding the band alignment of heterogeneous interfaces containing amorphous structures helps to better control the carrier transport property at the interface. Classical band offset methods developed previously line-up eigenlevels with respect to an ideal bulk reference or vacuum level. However, the local disorder of amorphous structures makes the bulk reference ambiguous. Therefore, classical methods cannot be applied. In this study, we introduce a new approach based on the Linear Combination of…
We report on the polarized neutron reflectometry investigation of monolayer of magnetic iron oxide nanoparticles assembled by the Langmuir-Schaefer method. After deposition onto a solid substrate the polarized neutron reflectometry measurements in the external magnetic field were carried out. Thickness, density, roughness and in-depth resolved magnetization profile of the resulted layer were obtained from accurate fitting routine.
The dielectric breakdown at metal-oxide interfaces is a critical electronic device failure mechanism. Electronic tunneling through dielectric layers is a well-accepted explanation for this phenomenon. Theoretical band alignment studies, providing information about tunneling, have already been conducted in the literature for metal-oxide interfaces. However, most of the time materials were assumed defect free. Oxygen vacancies being very common in oxides, their effect on band lineup is of prime importance in understanding electron tunneling in realistic materials and devices. This work explores …
The ability to follow Moore's Law has been the basis of the tremendous success of the semiconductor industry in the past decades. To date, the greatest challenge for device scaling is the required replacement of silicon dioxide-based gate oxides by high-k oxides in transistors. Around 2010 high-k oxides are required to have an atomically defined interface with silicon without any interfacial SiO2 layer. The first clean interface between silicon and a high-K oxide has been demonstrated by McKee et al. Nevertheless, the interfacial structure is still under debate. Here we report on first-princip…
Three driving forces control the energy level alignment between transition-metal oxides and organic materials: the chemical interaction between the two materials, the organic electronegativity and the possible space charge layer formed in the oxide. This is illustrated in this letter by analyzing experimentally and theoretically a paradigmatic case, the TiO2(110) / TCNQ interface: due to the chemical interaction between the two materials, the organic electron affinity level is located below the Fermi energy of the n-doped TiO2. Then, one electron is transferred from the oxide to this level and…
Oxide interfaces provide an opportunity for electronics. However, patterning of electron gases at complex oxide interfaces is challenging. In particular, patterning of complex oxides while preserving a high electron mobility remains underexplored and inhibits the study of quantum mechanical effects where extended electron mean free paths are paramount. This letter presents an effective patterning strategy of both the amorphous-LaAlO$_3$/SrTiO$_3$ (a-LAO/STO) and modulation-doped amorphous- LaAlO$_3$/La$_{7/8}$Sr$_{1/8}$MnO$_3$/SrTiO$_3$ (a-LAO/LSM/STO) oxide interfaces. Our patterning is based…
We report layer-resolved measurements of the \textit{unoccupied} electronic structure of ultrathin MgO films grown on Ag(001). The metal-induced gap states at the metal/oxide interface, the oxide band gap as well as a surface core exciton involving an image-potential state of the vacuum are revealed through resonant Auger spectroscopy of the Mg $KL_{23}L_{23}$ Auger transition. Our results demonstrate how to obtain new insights on \textit{empty} states at interfaces of metal-supported ultrathin oxide films.
Well-controlled sub-unit-cell layer-by-layer epitaxial growth of spinel alumina is achieved at room temperature on the TiO2-terminated SrTiO3 single crystalline substrate. By tailoring the interface redox reaction, two-dimensional electron gases with mobilities exceeding 3000 cm2V-1s-1 are achieved at this novel oxide interface.
We use \textit{ab initio} calculations to estimate formation energies of cation (transition metal) antisite defects at oxide interfaces and to understand the basic physical effects that drive or suppress the formation of these defects. Antisite defects are found to be favored in systems with substantial charge transfer across the interface, while Jahn-Teller distortions and itinerant ferromagnetism can prevent antisite defects and help stabilize atomically sharp interfaces. Our results enable identification of classes of systems that may be more and less susceptible to the formation of antisit…
2D electron gases (2DEGs) formed at oxide interfaces provide a rich testbed for fundamental physics and device applications. While the discussion of the physical origins of this phenomenon continues, the recent discovery of oxide 2DEGs at non-epitaxial interfaces between amorphous and crystalline oxides provides useful insight onto this debate. Furthermore, using amorphous oxides offers a low-cost route towards realizing 2DEGs for device applications. In this work, the band offsets of a simple model system of amorphous-crystalline oxide interface are investigated. The model system consists of …
The discovery of two-dimensional electron gas (2DEG) at well-defined interfaces between insulating complex oxides provides the opportunity for a new generation of all-oxide electronics. Particularly, the 2DEG at the interface between two perovskite insulators represented by the formula of ABO3, such as LaAlO3 and SrTiO3, has attracted significant attention. In recent years, progresses have been made to decipher the puzzle of the origin of interface conduction, to design new types of oxide interfaces, and to improve the interfacial carrier mobility significantly. These achievements open the doo…
Order-disorder processes fundamentally determine the structure and properties of many important oxide systems for energy and computing applications. While these processes have been intensively studied in bulk materials, they are less investigated and understood for nanostructured oxides in highly non-equilibrium conditions. These systems can now be realized through a range of deposition techniques and probed at exceptional spatial and chemical resolution, leading to a greater focus on interface dynamics. Here we survey a selection of recent studies of order-disorder behavior at thin film oxide…
We demonstrate generation of linearly polarized pulses from a passively Q-switched Erbium-doped fiber laser. The cavity was designed using only polarization maintaining (PM) fibers and components, resulting in linearly polarized output beam with degree of polarization (DOP) at the level of 97.6%. Reduced graphene oxide (rGO) was used as a saturable absorber for Q-switched operation. The laser was capable of delivering 1.85us pulses with 125nJ pulse energy at 115kHz repetition rate.
Polar discontinuities and redox reactions provide alternative paths to create two-dimensional electron liquids (2DELs) at oxide interfaces. Herein, we report high mobility 2DELs at interfaces involving SrTiO3 (STO) achieved using polar La7/8Sr1/8MnO3 (LSMO) buffer layers to manipulate both polarities and redox reactions from disordered overlayers grown at room temperature. Using resonant x-ray reflectometry experiments, we quantify redox reactions from oxide overlayers on STO as well as polarity induced electronic reconstruction at epitaxial LSMO/STO interfaces. The analysis reveals how these …
The oxygen vacancy is a crucial intrinsic defect in metal-ultrathin oxide semiconductor heterostructures, and its formation at an interface is of great importance in determining the device performance and degradation. This paper presents an ab initio thermodynamic study of oxygen vacancies at metal/oxide interfaces. Electronic energies and entropies are calculated for defective interface systems, as a function of interface-vacancy distance. The study indicates that oxygen vacancies near the interface modify its bonding structure, and significantly change the thermodynamic properties of the sys…
In order to determine the key parameters that control the resistive switching mechanism in metal-complex oxides interfaces, we have studied the electrical properties of metal / YBa2Cu3O7-d (YBCO) interfaces using metals with different oxidation energy and work function (Au, Pt, Ag) deposited by sputtering on the surface of a YBCO ceramic sample. By analyzing the IV characteristics of the contact interfaces and the temperature dependence of their resistance, we inferred that ion migration may generate or cancel conducting filaments, which modify the resistance near the interface, in accordance …
A modulation-doping approach to control the carrier density of the high-density electron gas at a prototype polar/non-polar oxide interface is presented. It is shown that the carrier density of the electron gas at a GdTiO3/SrTiO3 interface can be reduced by up to 20% from its maximum value (~ 3x10^14 cm^-2) by alloying the GdTiO3 layer with Sr. The Seebeck coefficient of the two-dimensional electron gas increases concurrently with the decrease in its carrier density. The experimental results provide insight into the origin of charge carriers at oxide interfaces exhibiting a polar discontinuity…
The complex oxide heterostructures such as LaAlO3/SrTiO3 (LAO/STO) interface are paradigmatic platforms to explore emerging multi-degrees of freedom coupling and the associated exotic phenomena. In this study, we reveal the effects of multiorbital and magnetic ordering on Rashba spin-orbit coupling (SOC) at the LAO/STO (001) interface. Based on first-principles calculations, we show that the Rashba spin splitting near the conduction band edge can be tuned substantially by the interfacial insulator-metal transition due to the multiorbital effect of the lowest t_2g bands. We further unravel a co…
Spin polarized current is the main ingredient of diluted magnetic oxides due to its potential manipulation in spintronic devices. However, most research has focused on ferromagnetic properties rather than polarization of electric current, because direct measurements were difficult and the origin of spin polarized currents has yet to be fully understood. The method to increase the spin polarized current percentage is beyond practical consideration at the present status. To target this problem, we focus on the role of oxygen vacancies and nano grain size on the spin polarized current, which are …
Band offsets at semiconductor-oxide interfaces are determined through a scheme based on hybrid density functionals, which incorporate a fraction $α$ of Hartree-Fock exchange. For each bulk component, the fraction $α$ is tuned to reproduce the experimental band gap, and the conduction and valence band edges are then located with respect to a reference level. The lineup of the bulk reference levels is determined through an interface calculation, and shown to be almost independent of the fraction $α$. Application of this scheme to the Si-SiO$_2$, SiC-SiO$_2$, and Si-HfO$_2$ interfaces yields exce…
We report a study on the interface between polar high-k materials and the Si(001)-(2X1) reconstructed surface with LaAlO3 taken as a prototype material. The construction of the interface is based on the prior growth of metal lines followed by oxidation, whose stability against oxygen coverage is studied. Electronic structure calculations within the Density Functional Theory framework help in building the interface and understanding its bonding structure. Moreover, we computed a conduction band offset of 1.9 eV, in agreement with electronic applications requirement. The results may provide a gu…
The conductance confined at the interface of complex oxide heterostructures provides new opportunities to explore nanoelectronic as well as nanoionic devices. Herein we show that metallic interfaces can be realized in SrTiO3-based heterostructures with various insulating overlayers of amorphous LaAlO3, SrTiO3 and yttria-stabilized zirconia films. On the other hand, samples of amorphous La7/8Sr1/8MnO3 films on SrTiO3 substrates remain insulating. The interfacial conductivity results from the formation of oxygen vacancies near the interface, suggesting that the redox reactions on the surface of …
The discovery of conducting two-dimensional electron gas (2DEG) and magnetism at the interface between insulating nonmagnetic oxides, as exemplified by the polar LaAlO3 and nonpolar SrTiO3 has raised prospects for attaining interfacial functionalities absent in the component materials. Yet, the microscopic origin of such emergent phenomena remains unclear, posing obstacles to design of improved functionalities. Using first principles defect calculations, we reveal a unifying polarity-induced defect mechanism for both conductivity and magnetism at polar-nonpolar interfaces of nonmagnetic insula…
Graphene Oxide and reduced Graphene Oxide are intriguing materials for photonics and electronic devices both for intrinsic characteristics and as precursors for the synthesis of graphene. Whatever the application and the engineering purpose, a fine control of the chemical and physical properties is required since the performances of graphene based systems depend on the reduction state of Graphene Oxide and can be strongly affected by interfaces interactions and neighboring effects. Then, a method for a local control of electric, electronic and chemical properties is required. The synergic appl…
The Anode Hydrogen Release (AHR) mechanism at interfaces is responsible for the generation of defects, that traps charge carriers and can induce dielectric breakdown in Metal-Oxide-Semiconductor Field Effect Transistors. The AHR has been extensively studied at Si/SiO$_2$ interfaces but its characteristics at metal-silica interfaces remain unclear. In this study, we performed Density Functional Theory (DFT) calculations to study the hydrogen release mechanism at the typical Al/SiO$_2$ metal-oxide interface. We found that interstitial hydrogen atoms can break interfacial Al-Si bonds, passivating…
Interfaces between (110) and (111)SrTiO3 (STO) single crystalline substrates and amorphous oxide layers, LaAlO3 (a-LAO), Y:ZrO2 (a-YSZ), and SrTiO3 (a-STO) become conducting above a critical thickness tc. Here we show that tc for a-LAO is not depending on the substrate orientation, i.e. tc (a-LAO/(110)STO) ~ tc(a-LAO/(111)STO) interfaces, whereas it strongly depends on the composition of the amorphous oxide: tc(a-LAO/(110)STO) < tc(a-YSZ/(110)STO) < tc(a-STO/(110)STO). It is concluded that the formation of oxygen vacancies in amorphous-type interfaces is mainly determined by the oxygen affinit…
The replacement of SiO2 by so-called high-k oxides is one of the major challenges for the semiconductor industry to date. Based on electronic structure calculations and ab-initio molecular dynamics simulations, we are able to provide a consistent picture of the growth process of a class of epitaxial oxides around SrO and SrTiO3. The detailed understanding of the interfacial binding principles has also allowed us to propose a way to engineer the band-offsets between the oxide and the silicon substrate.
In this paper, density functional theory calculations are used to explore the electronic and atomic reconstruction at interfaces between III-III/I-V oxides. In particular, at these interfaces, two dimensional electron gases (2DEGs) with twice the interfacial charge densities of the prototypical LaTiO3/SrTiO3 heterostructure are observed. Furthermore, a significant decrease in the band effective masses of the conduction electrons is shown, suggesting that possible enhancements in electron mobilities may be achievable. These findings represent a framework for chemically modulating 2DEGs, thereby…
Control of order-disorder phase transitions is a fundamental materials science challenge, underpinning the development of energy storage technologies such as solid oxide fuel cells and batteries, ultra-high temperature ceramics, and durable nuclear waste forms. At present, the development of promising complex oxides for these applications is hindered by a poor understanding of how interfaces affect lattice disordering processes and defect transport. Here we explore the evolution of local disorder in ion-irradiated La$_2$Ti$_2$O$_7$ / SrTiO$_3$ thin film heterostructures using a combination of …
The structural and electronic properties of the LaAlO3/Si(001) interface are determined using state-of-the-art electronic structure calculations. The atomic structure differs from previous proposals, but is reminiscent of La adsorption structures on silicon. A phase diagram of the interface stability is calculated as a function of oxygen and Al chemical potentials. We find that an electronically saturated interface is obtained only if dopant atoms segregate to the interface. These findings raise serious doubts whether LaAlO3 can be used as an epitaxial gate dielectric.
Molybdenum disulfide (MoS$_2$) attracts attention as a high efficient and low cost photocatalyst for hydrogen production, but suffers from low conductance and high recombination rate of photo-generated charge carriers. In this work, we investigate the MoS$_2$ heterostructures with graphene variants (GVs), including graphene, graphene oxide, and their boron- and nitrogen-doped variants, by using first-principles calculations. Systematic comparison between graphene and graphene oxide composites is performed, and contrary effect of B and N doping on interface function and hydrogen evolution is cl…
Despite widespread interest, a detailed understanding of the dynamics of proton transfer at interfaces is lacking. Here we use ab initio molecular dynamics to unravel the connection between interfacial water structure and proton transfer for the widely studied and experimentally well-characterized water-ZnO$(10\bar{1}0)$ interface. We find that upon going from a single layer of adsorbed water to a liquid multilayer changes in the structure are accompanied by a dramatic increase in the proton transfer rate at the surface. We show how hydrogen bonding and rather specific hydrogen bond fluctuatio…
Oxygen vacancies are increasingly recognized to play a role in phenomena observed at transition-metal oxide interfaces. Here we report a study of SrRuO3/La0.7Sr0.3MnO3 (SRO/LSMO) interfaces using a combination of quantitative aberration-corrected scanning transmission electron microscopy, electron energy loss spectroscopy, and density-functional calculations. Cation displacements are observed at the interface, indicative of a dipole-like electric field even though both materials are nominally metallic. The observed displacements are reproduced by theory if O vacancies are present in the near-i…
The epitaxial growth of crystalline oxides on semiconductors provides a pathway to introduce new functionalities to semiconductor devices. Key to electrically coupling crystalline oxides with semiconductors to realize functional behavior is controlling the manner in which their bands align at interfaces. Here we apply principles of band gap engineering traditionally used at heterojunctions between conventional semiconductors to control the band offset between a single crystalline oxide and a semiconductor. Reactive molecular beam epitaxy is used to realize atomically abrupt and structurally co…
The deposition of a thin oxide layer at metal/semiconductor interfaces has been previously reported as a means of reducing contact resistance in 2D electronics. Using X-ray photoelectron spectroscopy with in-situ Ti deposition, we fabricate Au/Ti/TiOx/MoS2 samples as well as Au/Ti/MoS2 and Au/TiOx/MoS2 for comparison. Elemental titanium reacts strongly with MoS2 whereas no interface reactions are observed in the two types of samples containing TiOx/MoS2 interfaces. Using time domain thermoreflectance for the measurement of thermal boundary conductance, we find that samples contacted with Ti an…
The introduction of manganite buffer layers, La7/8Sr1/8MnO3 (LSMO) in particular, at the metallic interface between SrTiO3 (STO) and another band insulator suppresses the carrier density of the interfacial two-dimensional electron gas (2DEG) and improves significantly the electron mobility. However, the mechanisms underlying the extreme mobility enhancement remain elusive. Herein, we used 18O isotope exchanged SrTi18O3 as substrates to create 2DEG at room temperature with and without the LSMO buffer layer. By mapping the oxygen profile across the interface between STO18 and disordered LaAlO3 o…
The conducting quasi-two dimensional electron system (q2DES) formed at the interface between LaAlO3 and SrTiO3 band insulators is confronting the condensed matter physics community with new paradigms. While the mechanism for the formation of the q2DES is debated, new conducting interfaces have been discovered paving the way to possible applications in electronics, spintronics and optoelectronics. This chapter is an overview of the research on the LAO/STO sys-tem, presenting some of the most important results obtained in the last decade to clarify the mechanism of formation of the q2DES at the …
A giant tunneling electroresistance effect may be achieved in a ferroelectric tunnel junction by exploiting the magnetoelectric effect at the interface between a ferroelectric barrier and magnetic La1-xSrxMnO3 electrode. Using first-principles density functional theory we demonstrate that a few magnetic monolayers of La1-xSrxMnO3 near the interface act, in response to ferroelectric polarization reversal, as an atomic scale spin-valve by filtering spin-dependent current. This effect produces more than an order of magnitude change in conductance, and thus constitutes a giant resistive switching …
The discovery of two-dimensional electron gases (2DEGs) at the heterointerface between two insulating perovskite-type oxides, such as LaAlO3 and SrTiO3, provides opportunities for a new generation of all-oxide electronic and photonic devices. However, significant improvement of the interfacial electron mobility beyond the current value of approximately 1,000 cm2V-1s-1 (at low temperatures), remains a key challenge for fundamental as well as applied research of complex oxides. Here, we present a new type of 2DEG created at the heterointerface between SrTiO3 and a spinel γ-Al2O3 epitaxial film w…
Mastery of order-disorder processes in highly non-equilibrium nanostructured oxides has significant implications for the development of emerging energy technologies. However, we are presently limited in our ability to quantify and harness these processes at high spatial, chemical, and temporal resolution, particularly in extreme environments. Here we describe the percolation of disorder at the model oxide interface LaMnO$_3$ / SrTiO$_3$, which we visualize during in situ ion irradiation in the transmission electron microscope. We observe the formation of a network of disorder during the initia…
The predictions of the polar catastrophe scenario to explain the occurrence of a metallic interface in heterostructures of the solid solution(LaAlO$_3$)$_{x}$(SrTiO$_3$)$_{1-x}$ (LASTO:x) grown on (001) SrTiO$_3$ were investigated as a function of film thickness and $x$. The films are insulating for the thinnest layers, but above a critical thickness, $t_c$, the interface exhibits a constant finite conductivity which depends in a predictable manner on $x$. It is shown that $t_c$ scales with the strength of the built-in electric field of the polar material, and is immediately understandable in …
Heterostructures and crystal interfaces play a major role in state-of-the-art semiconductor devices and play a central role in the field of oxide electronics. In oxides the link between the microscopic properties of the interfaces and bulk properties of the resulting heterostructures challenge our fundamental understanding. Insights on the early growth stage of interfaces and its influence on resulting physical properties are scarce -- typically the information is inferred from post growth characterization. Here, we report on real time measurements of the transport properties of SrTiO3-based h…
Atomic-Scale Characterization of Oxide Interfaces and Superlattices Using Scanning Transmission Electron Microscopy
National Laboratory of the Rockies（落基山国家实验室）；Metallurgical and Materials Engineering Department, Colorado School of Mines（科罗拉多矿业学院冶金与材料工程系）；Renewable and Sustainable Energy Institute, University of Colorado Boulder（科罗拉多大学博尔德分校可再生与可持续能源研究所）
Performing an analysis within density functional theory, we develop insight into the structural and electronic properties of the oxide heterostructure LaAlO3/SrTiO3. Electrostatic surface effects are decomposed from the internal lattice distortion in order to clarify their interplay. We first study the interface relaxation by a multi-layer system without surface, and the surface effects, separately, by a substrate-film system. While elongation of the TiO6 octahedra at the interface enhances the metallicity, reduction of the film thickness has the opposite effect due to a growing charge depleti…
The discovery of two-dimensional electron gases (2DEGs) in SrTiO3-based heterostructures provides new opportunities for nanoelectronics. Herein, we create a new type of oxide 2DEG by the epitaxial-strain-induced polarization at an otherwise nonpolar perovskite-type interface of CaZrO3/SrTiO3. Remarkably, this heterointerface is atomically sharp, and exhibits a high electron mobility exceeding 60,000 cm2V-1s-1 at low temperatures. The 2DEG carrier density exhibits a critical dependence on the film thickness, in good agreement with the polarization induced 2DEG scheme.
Tantalum, tantalum oxide and their hetero-interfaces are of tremendous technological interest in several applications spanning electronics, thermal management, catalysis and biochemistry. For example, local oxygen stoichiometry variation in TaOx memristors comprising of metallic (Ta) and insulating oxide (Ta2O5) have been shown to result in fast switching on the sub-nanosecond timescale over a billion cycles, relevant to neuromorphic computation. Despite its broad importance, an atomistic scale understanding of oxygen stoichiometry variation across Ta/TaOx hetero-interfaces, such as during ear…
By performing first-principles calculations on four capacitor structures based on BaTiO3 and PbTiO3, we determine the intrinsic interfacial effects that are responsible for the destabilization of the polar state in thin-film ferroelectric devices. We show that, contrary to the established interpretation, the interfacial capacitance depends crucially on the local chemical environment of the interface through the force constants of the metal-oxide bonds, and is not necessarily related to the bulk screening properties of the electrode material. In particular, in the case of interfaces between AO-…
Emergent phases in the two-dimensional electron gas (2DEG) formed at the interface between two insulating oxides have attracted great attention in the past decade. We present ab-initio electronic structure calculations for the interface between a Mott insulator GdTiO$_3$ (GTO) and a band insulator SrTiO$_3$ (STO) and compare our results with those for the widely studied LaAlO$_3$/SrTiO$_3$ (LAO/STO) interface between two band insulators. Our GTO/STO results are in excellent agreement with experiments, but qualitatively different from LAO/STO. We find an interface carrier density of 0.5$e^{-}$/…
