Alex Demkov, The University of Texas
Jean Fompeyrine, IBM Research
Joerg Osten, Leibniz Universit Hannover
Fred Walker, Yale University
Symposium Support DCA Instruments OY
IBM T.J. Watson Research Center
Raytheon Integrated Defense Systems
Staib Instruments, Inc.
The University of Texas at Austin, Institute for Computational Engineering amp; Sciences
Universitat Politegrave;cnica de Valegrave;ncia, Nanophotonics Technology Center
Yale University, The Center for Research on Interface Structures and Phenomena (CRISP)
FF2: Perovskite Materials II
Monday PM, November 30, 2015
Hynes, Level 2, Room 201
2:30 AM - *FF2.01
Electrically Coupling Crystalline Oxides to Semiconductors: A Route to Novel Material Functionalities
Joseph Ngai 1
1Univ of Texas-Arlington Arlington United StatesShow Abstract
Crystalline oxides and semiconductors exhibit distinct yet complementary properties owing to their respective ionic and covalent natures. By electrically coupling oxides to semiconductors within epitaxial heterostructures, enhanced or novel functionalities beyond those of the constituent materials alone can potentially be realized. Key to electrically coupling crystalline oxides to semiconductors is controlling the physical and electronic structure at interfaces between the two materials. In this talk, we will discuss how stoichiometry can be exploited to control both physical and electronic structure at interfaces. Two prototypical interfaces, namely Ba1-xSrxTiO3/ Ge and SrZrxTi1-xO3/Ge, will be presented. In the case of Ba1-xSrxTiO3/ Ge, we will discuss how strain can be engineered through stoichiometry to enable the re-orientable ferroelectric polarization of the former to be coupled to carriers in the latter . In the case of SrZrxTi1-xO3/Ge we will discuss how stoichiometry can be exploited to control the band offset at the interface . Analogous to heterojunctions between III-V semiconducting materials, control of band offset, i.e. band-gap engineering, provides a pathway to electrically couple crystalline oxides to semiconductors to realize a host of material functionalities  J.H. Ngai et al. Appl. Phys. Lett. 104, 062905 (2014);  J. Moghadam et al. Adv. Mater. Interfaces 2, 1400497 (2015).
3:00 AM - FF2.02
Theoretical Modeling and Experimental Observations of the Atomic Layer Deposition of SrO Using a Sr Cyclopentadienyl Precursor
Kurt Fredrickson 1 Martin McDaniel 1 John G. Ekerdt 1 Alex Demkov 1
1Univ of Texas-Austin Austin United StatesShow Abstract
We use first principles calculations to model the surface adsorption and hydration of strontium bis(cyclopentadienyl) [Sr(Cp)2] for the deposition of strontium oxide, SrO, by atomic layer deposition (ALD). For initial calculations, we study the Sr(Cp)2 adsorption on a TiO2-terminted STO surface. The Sr(Cp)2 precursor is shown to adsorb on the TiO2-terminated surface, with the Sr atom sitting essentially where it should be in a bulk STO cell. Calculations show that the TiOnot;2 surface does not need to be hydrogenated precursor adsorption. We simulate a pulse of water by incrementally adding H and O atoms to the surface. The two H atoms bond to the Cp rings and cause them to detach from the surface. O placed on the surface prefers to be closest to the adsorbed Sr atom. The first principle calculations are compared with experimental observations for a Sr cyclopendienyl precursor, Sr(iPr3Cp)2 adsorbed onto the TiO2-terminated STO. High-resolution x-ray photoelectron spectroscopy shows adsorption of the Sr precursor on the TiO2-terminated STO after a single precursor dose. The adsorption of Sr on the TiO2-terminated STO surface is further confirmed by low-energy ion scattering spectroscopy (LEISS). This study suggests that Sr(Cp)2 precursors may be used for ALD growth on non-hydroxylated surfaces.
3:15 AM - FF2.03
Giant Conductivity Switching of Perovskite Heterointerfaces Governed by Surface Protonation
Keith A. Brown 1 Shu He 1 Daniel J. Eichelsdoerfer 1 Mengchen Huang 2 3 Ishan Levy 2 3 Hyungwoo Lee 4 Sangwoo Ryu 4 Patrick Irvin 2 3 Jose Mendez-Arroyo 1 Chang-Beom Eom 4 Chad A. Mirkin 1 Jeremy Levy 2 3
1Northwestern University Evanston United States2University of Pittsburgh Pittsburgh United States3Pittsburgh Quantum Institute Pittsburgh United States4University of Wisconsin-Madison Madison United StatesShow Abstract
The interface between the band insulators SrTiO3 (STO) and LaAlO3 (LAO) is host to diverse phenomena including a quasi-two dimensional electron liquid (2DEL) with gate-tunable superconductivity, magnetism, and spin-orbit coupling. However, many basic questions remain about the mechanisms regulating conductivity switching and the role of the surface chemistry in dictating these properties. Here we report the observation of a fully reversible, >4 order of magnitude change in LAO/STO interface conductance in which nominally conductive interfaces are rendered insulating by solvent immersion and returned to a conductive state through exposure to light. Through coordinated electrical measurements and X-ray photoelectron spectroscopy, we determine that the metal-to-insulator transition is consistent with deprotonation of the hydroxylated LAO surface while reprotonation occurs via photocatalytic oxidation of adsorbed water. These observations suggest a strong connection between surface chemistry and 2DEL formation and point to a future route toward large-scale patterning of interfacial electronic devices.
3:30 AM - FF2.04
Thermodynamics and Electronic Structure of SrTiO3 Ionic and Electronic Defects
Mostafa Youssef 1 Bilge Yildiz 1 Krystyn J. Van Vliet 1
1MIT Cambridge United StatesShow Abstract
SrTiO3 is an archetypal functional metal oxide with defects that give rise to emergent properties that cannot be explained by the underlying perfect crystal. Electric conductivity, ferroelectricity, blue luminescence, and magnetism are all functional properties that can be tuned by generating and controlling ionic and electronic defects in SrTiO3. In spite of the extensive theoretical and experimental work on the defects of this material, a comprehensive picture for its defect equilibria in a wide range of thermodynamic conditions spanned by temperature and anion and cation activities is still missing. In this work we provide a detailed study for all ionic and electronic defects of SrTiO3. The formation energy of anion and cation vacancies, antisites on all sublattices, and small polarons are computed using density functional theory with an on-site Coulomb interaction term (DFT+U approach). In addition, using density functional perturbation theory (DFPT) and statistical thermodynamics, we account for the contribution of lattice vibrations (phonons) to the formation free energies of all defects. By imposing the charge neutrality condition, we construct defect equilibria diagrams that depict defect concentrations as a function of a thermodynamic force (temperature and/or chemical potential). The charged defects which deemed to be predominant under certain conditions, were selected for further examination of their electronic structure. In particular, we examine their local magnetic and electric dipole moments and relate these defect properties to the macroscopic properties of defective SrTiO3. There has been several phenomenological observations related to SrTiO3 that have been attributed tentatively to its defects. The framework we introduce in this study can be invoked to link each defect to the property that it causes.
4:15 AM - *FF2.05
Integration of Ferroelectric Thin Films on Silicon and Silicon Germanium
Catherine A. Dubourdieu 1
1CNRS-ECL-INL Ecully FranceShow Abstract
The extraordinary wealth of physical properties in complex oxides offers a promising potential for developing new functionalities in devices that can address societal needs related to health, energy or information and communication technologies. Ferroelectrics are particularly attractive for their applications in nanoelectronics, communication devices, electro-mechanical systems and integrated photonics provided that they can be integrated on semiconductors. In this presentation, we will review our recent work on the molecular beam epitaxy of BaTiO3 heterostructures on Si and strained-SiGe/Si substrates. Effects of process parameters on the microstructure, cationic composition, crystalline orientation and ferroelectricity will be discussed. The growth of nanostructures on patterned Si substrates will be presented. Finally, perspectives on integrating ferroelectric BaTiO3 thin films in field-effect devices using a damascene scheme will be discussed.
4:45 AM - FF2.06
Intrinsic Space Charge Layers and Field Enhancement in Ferroelectric Nanojunctions
Ye Cao 4 1 Anton V. Ievlev 4 1 Anna Morozovska 2 Long-Qing Chen 3 Sergei V. Kalinin 4 1 Petro Maksymovych 4 1
1Oak Ridge National Laboratory Oak Ridge United States2National Academy of Science of Ukraine Kiev Ukraine3The Pennsylvania State University University Park United States4Oak Ridge National Laboratory Oak Ridge United StatesShow Abstract
Conducting characteristics of topological defects in ferroelectric materials, such as charged domain walls, engendered a broad interest on their scientific merit and the possibility of novel applications utilizing domain engineering.  At the same time, the problem of electron transport in ferroelectrics still remains full of unanswered questions, and becomes yet more relevant over the growing interest in ferroelectric semiconductors and new improper ferroelectric materials. We have employed self-consistent phase-field modeling to investigate the physical properties of a local metal-ferroelectric (Pb(Zr0.2Ti0.8)O3) junction in applied electric field. We revealed an up to 10-fold local enhancement of electric field realized by large polarization gradient and over-polarization effects due to inherent non-linear dielectric properties of PZT. The effect is independent of bias polarity and maintains its strength prior, during and after ferroelectric switching. The observed field enhancement can be considered on similar grounds as increased doping level, giving rise to reduced switching bias and threshold voltage for charge injection, electrochemical and photoelectrochemical processes.
This research was sponsored by the Division of Materials Sciences and Engineering, Basic Energy Sciences, Department of Energy (YC, SVK, PM). Research was conducted at the Center for Nanophase Materials Sciences, which also provided support (AVI) and which is a DOE Office of Science User Facility. The phase-field simulation was performed in collaboration with Prof. Long-Qing Chen at Penn State, which is supported by the U.S. Department of Energy, Of#64257;ce of Basic Energy Sciences, Division of Materials Sciences and Engineering under Award No. DE-FG02-07ER46417(Chen). We thank Pu Yu and Ramamoorthy Ramesh for providing the PZT sample on which the I-V curves were recorded.
 J. Seidel, L. W. Martin, Q. He, Q. Zhan, Y. H. Chu, A. Rother, M. E. Hawkridge, P. Maksymovych, P. Yu, M. Gajek, N. Balke, S. V. Kalinin, S. Gemming, F. Wang, G. Catalan, J. F. Scott, N. A. Spaldin, J. Orenstein, and R. Ramesh, Nature Materials 8, 229 (2009)
5:00 AM - FF2.07
Plentiful Magnetic Moments in Oxygen Deficient SrTiO3
Alejandro Lopez-Bezanilla 1 Peter Littlewood 1 2
1Argonne National Laboratory Lemont United States2James Franck Institute, University of Chicago Chicago United StatesShow Abstract
Correlated band theory calculations based on the DFT+U approach are employed to investigate oxygen-deficient SrTiO3. We show that the appearance of magnetism in oxygen vacancies is not determined solely by the presence of a single oxygen vacancy, but by the density of free carriers and the relative proximity of the vacant sites. While an isolated vacancy behaves as a non-magnetic double donor, manipulation of the doping conditions allows the stability of a single donor state with emergent local moments. For clusters of vacancies, different kinds of Ti atomic orbital hybridization are described as a function of the doping level and defect geometry. Our description of the charged clusters widens the previous descriptions of mono and multi-vacancies and points out the importance of the controlled formation of defects for the realization of transition metal oxide based devices with a desirable magnetic performance.
5:15 AM - FF2.08
Weak Ferromagnetism in Ferroelectric Ba0.4Sr0.6TiO3 Integrated with Semiconductors
Srinivasa Rao Singamaneni 1 John T. Prater 1 Jagdish Narayan 1
1North Carolina State Univ Raleigh United StatesShow Abstract
Ba0.4Sr0.6TiO3 (BST) is a good ferroelectric material characterized by high (>6000) dielectric constant, has been used for tunable microwave devices. Our interest is whether we could identify possible processing routes that would introduce a coexisting magnetic component, i.e produce of multiferroics. In this work, we have epitaxially integrated ferroelectric BST thin films on MgO/TiN buffered Si (100) substrates using PLD. The phase formation was confirmed by XRD, TEM, XPS and Raman measurements. As deposited films show weak-ferromagnetic nature measured through SQUID magnetometry and electron spin resonance spectroscopy. We found that the magnetic moment decreased upon laser and oxygen annealing. Our study confirmed that the weak ferromagnetism originates from oxygen vacancies, not from external (unwanted) magnetic impurities. BST-based devices fabricated on silicon substrates are being tested for their ferroelectric and multiferroic properties as a function of temperature and magnetic field using our QUANTUM DESIGN PPMS coupled with Radiant technologies ferroelectric tester. We present and discuss the salient experimental findings.
5:30 AM - FF2.09
Conductivity Noise Studies on Epitaxial Ultrathin Films of NdNiO3
Ali M. A. Alsaqqa 1 Sujay Kumar Singh 1 Srimanta Middey 2 Michael Kareev 2 Jak Chakhalian 2 Ganapathy Sambandamurthy 1
1University at Buffalo Buffalo United States2University of Arkansas Fayetteville United StatesShow Abstract
Oxide thin films possess a great potential for technological applications, from synaptic transistors to diodes to catalysts, due to the high degree of tunability in their transport properties using simple parameters like temperature, magnetic field, strain, etc. Recent advances in layer-by-layer epitaxial growth techniques and engineering of the heterointerfaces have led to the realization of stoichiometric, single-crystalline, ultrathin oxides films with a plethora of exciting properties. NdNiO3 thin films (15 u.c. thick) exhibit two phase transitions, upon cooling, from a paramagnetic metal (PM) to a paramagnetic insulator (PI) and from that to an antiferromagnetic insulator (AFI). While standard transport measurements can probe the average behavior, noise spectroscopy can provide valuable, complementary information about the microscopic charge carrier transport, structural defects, phase transitions, etc. From our noise studies on NdNiO3 thin films, we find that the magnitude of 1/f noise at room temperature is 3-5 orders of magnitude higher than in typical disordered metallic films of similar resistivity. Results from noise studies across both the phase transitions in a set of NdNiO3 thin films with varying strain values at the interface will be presented. We observe an intriguing time dependence in the noise characteristics in the AFI phase, where the probability density function fluctuates between a single-peak Gaussian behavior and a two-peak non-Gaussian behavior. The implications of these results will be presented. This work is supported by NSF-DMR 0847324.
FF1: Perovskite Materials I
Monday AM, November 30, 2015
Hynes, Level 2, Room 201
9:30 AM - *FF1.01
Si-Based Virtual Substrates for Functional Perovskite Oxide
Roman Engel-Herbert 1 Lei Zhang 1
1Pennsylvania State Univ University Park United StatesShow Abstract
Furnishing semiconductor materials with useful properties alien to them but inherent to functional oxides has been a main driving factor to develop materials integration strategies of crystalline oxides on semiconductors. Conversely, the epitaxial integration of high quality crystalline oxides on Si would enable a much faster dissemination of these materials into marketable technologies, lowering their costs by providing an affordable wafer scale platform. In this regard the combination of Si, being the most widely used commercial substrates, and SrTiO3, serving as a substrate for the growth of many functional perovskite oxides, including superconducting, ferroelectric, pyroelectric, piezoelectric and (anti)ferromagnetic and multiferroic thin films, make the monolithic integration of SrTiO3 on Si (001) highly desirable.
In this talk we will discuss how the challenges towards the development of a wafer scale virtual substrate can be addressed. By combining the advantages of molecular beam epitaxy and chemical beam epitaxy the requirements for the growth of a high quality template are met in an ideal way. We will show how carbonization of Si surfaces is avoided and discuss how structural quality and surface morphology of the films are affected by growth condition, film thickness and post growth anneals. The self-regulated growth of atomically smooth SrTiO3 films at high growth rates is demonstrated, forming an ideal buffer layer for subsequent epitaxial growth. We will propose strategies, how the large thermal expansion mismatch of Si and SrTiO3 can be utilized to create growth templates with continuously variable lattice parameter, key to empower strain-enabled functionality engineering of perovskite thin films on Si-based virtual substrates.
This work was supported by the Office of Naval Research through Grant No. N00014-11-1-0665.
10:00 AM - FF1.02
Electronic and Optical Properties of MBE-Grown p-SrxLa1-xCrO3/n-Si(001) Heterojunctions
Scott A. Chambers 1 Kelvin Zhang 2 Yingge Du 1 Oliver Bierwagen 3 Shawn Sallis 4 Louis Frederick Piper 4 Mark E Bowden 1 Shutta Shutthanandan 1 Peter V Sushko 1
1Pacific Northwest National Laboratory Richland United States2Cambridge University Cambridge United Kingdom3Paul Drude Institute Berlin Germany4Binghamton University Binghamton United StatesShow Abstract
The ability to effectively harvest visible sunlight for the purpose of photovoltaics, photoelectrochemistry and photochemical organics destruction is of clear importance in the energy and environmental landscapes. Several different classes of materials are under consideration for this purpose. Perovskite oxide semiconductors are of interest because of their superior stability in aqueous environments compared to that of traditional semiconductors. It is thus of interest to combine perovskite oxides with traditional low-gap semiconductors with the goal of utilizing the best properties of both classes of materials. To this end, we are investigating the MBE growth and properties of p-SrxLa1-xCrO3/n-Si(001). LaCrO3 is an insulator. However, replacing La with Sr in LaCrO3 dopes holes into the Cr 3dt2g-derived top of the valence band, resulting in significantly enhanced p-type conductivity of a polaronic nature. X-ray based spectroscopies (XPS and XAS) and first-principles modeling reveal that Sr doping results in a split-off, unoccupied Cr 3dt2g-derived band above the Fermi level which shifts in energy with increasing x. The material becomes metallic above x = ~0.5, but only when grown without large (~1%) in-plane tensile strain. In the semiconducting regime (x le; ~0.5), SrxLa1-xCrO3 exhibits the characteristics of a p-type transparent semiconducting oxide. p-Sr0.1La0.9CrO3/n-Si(001) thus constitutes an attractive low-gap p-n junction with substantially more stability in aqueous media than Si based heterostructures without an oxide surface layer. In this talk, I will present our results on this material system.
10:15 AM - FF1.03
Sr on Si (001): The Path to Oxidation Resistance?
Alex Demkov 1 Kurt Fredrickson 1 Hosung Seo 1
1Univ of Texas