Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session G32: Functional Oxides: Surfaces, Modification and Growth |
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Sponsoring Units: DCMP Chair: Marcel Meyer, Delft University of Technology Room: Room 224 |
Tuesday, March 7, 2023 11:30AM - 11:42AM |
G32.00001: Switching dynamics and transient negative capacitance in improper ferroelectric h-YbFeO3 film Xin Li, Yu Yun, Xiaoshan Xu The transient negative capacitance (NC) effect in ferroelectric thin film, serving as the touchstone for the nature of transient polarization states and related ferroelectric switching dynamics, has received wide attentions. To date, all known NC effects are limited to proper ferroelectrics, limiting the general applicability and interpretation of NC in ferroelectric materials. In this work, we report, for the first time, the transient NC effects and the underlying switching dynamics in improper ferroelectric h-YbFeO3 films. The transient NC range was dominated by inhomogeneous nucleation and the subsequent concave trend of electric responses imply the effect of negative curvature of energy potential, providing the reconciliation to the existing controversy for the physical origins of transient NC. The processes including transient NC are simulated with high consistency basing on phenomenological theory of switching dynamics. The frequency-dependent effective modulation of transient NC reveals the dominant role of initial multidomain states, providing the insights for controlling transient NC effects beyond extrinsic factors. |
Tuesday, March 7, 2023 11:42AM - 11:54AM |
G32.00002: Synthesis and characterization of KTO membranes using a sacrificial layer Yan Li, Xi Yan, Jill K Wenderott, Qianheng Du, Junyi Yang, Hanu Arava, Hua Zhou, Anand Bhattacharya, Dillon D Fong The KTaO3 (KTO) superconductivity with a transition temperature of 2.2 K have been discovered in interfaces formed by two-dimensional electron gases (2DEGs) [1]. Interestingly, the interface superconductivity isn’t observed in all 2DEGs through a series of research. Here, to further investigate its interface properties, we present results of crystal structures and electric properties in KTO/Sr3Al2O6 (SAO)/KTO (111) using a water-dissolvable sacrificial layer with two different interfaces [2]. The SAO water-sacrificial films are grown by pulsed laser deposition from polycrystalline SAO target on KTO (111) followed by KTO films. We will first discuss the synthesis of the epitaxial SAO (111) layers on KTO (111) substrate and its evolution of time-dependent interfacial electric properties. Then we will report its interfacial performance between SAO and amorphous KTO. This work provides much structural and electrical insight into the SAO/KTO heterostructures to understand the similarities and differences with STO, and offers a possibility to explore recyclable electronics. |
Tuesday, March 7, 2023 11:54AM - 12:06PM |
G32.00003: Optical constants and lattice vibrations of bulk SrTiO3 and BaSnO3 on SrTiO3 using spectroscopic ellipsometry from 0.03 to 6.6 eV. Yoshitha Hettige, Stefan Zollner, Suyeong Jang, Alexander A Demkov, Wente Li We measured the ellipsometric angles Ψ and Δ for bulk SrTiO3 (STO) before and after cleaning (first isopropyl cleaning and then ozone cleaning at 150°C for 20 minutes) on a J. A. Woollam Variable Angle Spectroscopic Ellipsometer from 0.5 to 6.6 eV with 0.01 eV steps at four different angles of incidence from 60° to 75° with a step size of 5°. We found that ozone cleaning is a better cleaning method than isopropyl cleaning. We calculated the thickness of the surface layer considering the <ε2> below the band gap of STO as 19.7 Å. Then we measured the ellipsometric angles Ψ and Δ for ozone cleaned bulk STO on J. A. Woollam IR VASE MARK II Ellipsometer from 250 to 8000 cm-1 at four different angles of incidence from 60° to 75° with a step size of 5° at 8 cm-1 resolution. Lattice vibrations of STO was descrided by Lorentz and Gaussian oscillators. We developed a VASE model for bulk STO using the obtained oxide layer thickness to describe the optical constants of STO and IR VASE model to describe the lattice vibrations of STO. Then BaSnO3/STO sample was ozone cleaned (after isopropyl cleaning) and we measured Ψ and Δ under the same conditions on both ellipsometers. Ozone cleaning removes most of the water and chemical molecules attached to BaSnO3 (BSO) surface. This VASE model was used to find the surface layer thickness and optical constants of BSO (band gap of ∼ 3.1 eV) using the thin film layer thickness (136 Å) from XRR measurement and IR VASE model was used to describe the lattice vibrations of BSO/STO using two Lorentz oscillators. |
Tuesday, March 7, 2023 12:06PM - 12:18PM |
G32.00004: Strontium Titanium Oxysulfide (STO-S) and its Photoelectrochemical properties Young Jun Chang, Hyuk Jin Kim, Taekjib Choi, Eunjip Choi, Ayoung Cho, Hu Young Jeong, Min-Hyoung Jung, Hyun Don Kim, Kyeong Jun Lee, Jin Eun Heo, Seo Hyoung Chang Photoelectrochemical property of oxysulfide is of great interest for water splitting and hydrogen production applications due to its tunability of bandgap from ultraviolet to visible-light region and high reactivity for redox reaction [1,2]. Understanding the interaction between oxysulfide surface and water is essential to enhance photoelectrochemical performance. However, fundamental understanding during catalytic reactions at the interface have not been remained in its infancy yet. Ambient pressure X-ray photoemission spectroscopy (AP-XPS) is useful to investigate chemical bonding characteristics of the solid surfaces exposed with various gas environments, such as water (H2O), up to a few millibar pressure [3]. Here, we examined surface bonding characteristics of both SrTiO3 (STO) and sulfur-doped SrTiO3 (STO-S) in H2O gas environment using the AP-XPS. We revealed that surface oxygen states (O2-) is a dominant constituent at STO-S surface when H2O gas is adsorbed on the surface. Our results suggest that the active surface states are largely enhanced in the STO-S compared to the STO and propose potential application of STO-S for the photocatalytic applications. |
Tuesday, March 7, 2023 12:18PM - 12:30PM |
G32.00005: Modulation of Conductivity and Metallic Properties in Perovskite Metal Oxide Thin Films by Fluorination Treatment Ryan S Paxson, Benjamin A Moore, Taylor Pettaway, Joseph Kromer, Richard Seabrease, Marcus Rose, Ravinder Kumar, Ramesh C Budhani, David Schaefer, Vera Smolyaninova, Rajeswari M Kolagani We have studied the effects of ‘fluorination’ treatment on the structural, magnetic and electrical properties of La0.67 Ca0.33MnO 3-y thin films. Fluorination treatment involves coating the films with a fluorine containing polymer Poly-Vinyl Difluoride (PVDF) followed by an ex-situ heat treatment. The films grown in 400 mTorr show properties very close to that of the fully oxygenated bulk material. Fluorination treatment of these films results in a marginal increase in resistivity and no change in in insulator-metal transition, or lattice parameters. Films grown in lower oxygen pressures show orders of magnitude higher resistivity and no insulator-metal transition in the as-grown state. Fluorination treatment of these films decrease the resistivity by several orders of magnitude and induces the insulator-metal transition. XRD shows an additional phase which corresponds to a shortened c-lattice parameter. Identical control samples subject to the same thermal treatment without the PVDF coating do not show any significant changes. The drastic decrease in resistivity and the occurrence of the insulator-to-metal transition indicate that the fluorination promotes an increase in the charge carrier concentration. Incorporation of fluorine at oxygen vacancy sites can lead to increase in the hole doping thus promoting a higher Mn4+ to Mn3+ ratio. We are pursuing X-ray photoelectron spectroscopy studies to verify changes in valence states and investigating fluorination effects in SrTiO3. |
Tuesday, March 7, 2023 12:30PM - 12:42PM |
G32.00006: Solid-phase epitaxy of CuAlO2 as a template layer for growth of delafossite films Amanda Huon, Jong Mok Ok, Sangmoon Yoon, Andrew R Lupini, Ho Nyung Lee Thin film growth of ABO2 delafossites has garnered significant attention due to its attractive properties and potential applications. However, achieving high quality thin films is still an obstacle. A fundamental requirement for achieving high quality thin films relies on chemical compatibility and lattice matching substrates. Here, we report a process to engineer a template ABO2 delafossite structure by solid-phase epitaxy of CuAlO2 on the surface of a commercial sapphire substrate. This approach offers a promising route to growing high quality epitaxial thin films. In this talk, we will discuss the process and optimization parameters used to prepare CuAlO2 samples and show an example of a successful epitaxial growth of highly conducting PdCrO2 by using a CuAlO2 template. This method provides an essential stepping-stone toward the approachability of a lattice matching template for ABO2 heterostructures. |
Tuesday, March 7, 2023 12:42PM - 12:54PM |
G32.00007: Stoichiometric control and optical properties of BaTiO3 thin films grown by hybrid MBE Benazir Fazlioglu Yalcin, Albert C Suceava, Tatiana A Kuznetsova, Venkatraman Gopalan, Roman Engel-Herbert BaTiO3 is an appealing class of ferroelectric perovskite materials that has room-temperature ferroelectricity with a Curie temperature, Tc, of ∼120 °C. It has been extensively studied due to its superior dielectric, ferroelectric, piezoelectric, pyroelectric, and electro-optical properties. It has emerged as an excellent candidate for applications such as ferroelectric random-access memory, lead-free capacitors, photonic devices, ferroelectric energy conversion, and electro-optical devices.[1] Furthermore, strained BaTiO3 exhibits both enhanced Tc and increased remanent polarization when compared to bulk BaTiO3. However, while strain engineering through heteroepitaxial growth has proven to be a powerful strategy for obtaining new functionalities in complex oxides, achieving controlled and uniform stoichiometry in thin films is equally important, as defects can destroy ferroelectric behavior in materials.[2] Although conventional ultrahigh vacuum thin film growth techniques such as pulsed laser deposition and molecular beam epitaxy (MBE) are capable of producing high-quality oxide films, precise control over stoichiometry still remains challenging. Therefore, hMBE which has been demonstrated to provide superior control over cation stoichiometry was used in this study to grow BaTiO3 thin films. |
Tuesday, March 7, 2023 12:54PM - 1:06PM |
G32.00008: The kinetic inductance of superconducting electron gas formed at KTaO3 interfaces Qianheng Du, Xianjing Zhou, Junyi Yang, Xinhao Li, Changjiang Liu, John Pearson, Dafei Jin, Anand Bhattacharya The discovery of superconducting two-dimensional electron gases (2-DEG) in (111)-and (110)-oriented KTaO3 (KTO)-based heterostructures has attracted new interest in the field of oxide interfaces. The kinetic inductance of the superfluid in KTO 2DEGs can be used to probe fundamental properties of the superconducting state, including the orientation selectivity of superconductivity at KTO interfaces and its tunability with external fields. We use coplanar waveguide resonators (SCWRs) made using superconducting KTO 2DEGs to probe their kinetic inductance, which is a direct measure of superfluid density. We will present our results on the temperature and gating-voltage dependent the kinetic inductance and discuss the implications of our results for the superconducting state in KTaO3-based 2-DEGs, as well as their use as a platform for resonant structures in applications. |
Tuesday, March 7, 2023 1:06PM - 1:18PM |
G32.00009: Oxide Thin films for various Electronic, Optical and Heath Applications Wilfrid Prellier Metal oxides often having a perovskite structure form a wide and technologically important class of compounds. In these systems, ferroelectric, ferromagnetic, ferroelastic, or even orbital and charge orderings can develop and eventually coexist. These orderings can be tuned by external electric, magnetic, or stress field, and the cross-couplings between them enable important multifunctional properties, such as piezoelectricity, or magneto-elasticity. Here, we will present how oxide thins films can be grown on different types of substrates including polycrystalline substrates, and glass templates. Examples will given to show different applications that can be utilized for medical, optical or electronic. |
Tuesday, March 7, 2023 1:18PM - 1:30PM |
G32.00010: In situ x-ray nano-imaging of polarization evolution in epitaxial 0.7PbMg1/3Nb2/3O3-0.3PbTiO3 thin film heterostructures Aileen Luo, Tony Chiang, Tao Zhou, Martin Holt, John T Heron, Andrej Singer High electromechanical coupling in relaxor ferroelectrics such as 0.7PbMg1/3Nb2/3O3-0.3PbTiO3 (PMN-PT) have nanoscale polar structures, which are believed to facilitate polarization rotation. In this study, we utilize hard x-ray nanodiffraction to simultaneously measure real and reciprocal space of epitaxial thin film FeGa/PMN-PT/Ba0.5Sr0.5RuO3/GdScO3 (110) devices under applied DC electric field. Dark-field imaging by the x-ray nanoprobe allows us to attribute strain and lattice rotation information from multiple Bragg reflections over the same spatial region of a device. We observe different localized changes to the crystal structure of PMN-PT, and provide a discussion on the distribution of phase coexistence throughout the device. |
Tuesday, March 7, 2023 1:30PM - 1:42PM |
G32.00011: Epitaxial growth and experimental study of Cr2O3 Thin Films Josiah Keagy, Haoyu Liu, Weilun Tan, Jing Shi Antiferromagnetic thin films hold much promise for the future of spintronics, not only as media to enhance spin transport but as sources of spin current in nano-devices as well. Synthesis of antiferromagnetic thin films and obtaining near perfect crystalline quality is essential to understanding and controlling spin related phenomena. In this work, we have explored the epitaxial growth of Cr2O3 antiferromagnetic thin films on Al2O3 substrates using pulsed laser deposition under various growth and post-growth annealing conditions with different crystal orientations. The Cr2O3 thin films are characterized by both in-situ (e.g., RHEED) and ex-situ (e.g., HRXRD, XPS, AFM). Under the optimal conditions, we have obtained atomically smooth surface in (11-20)-oriented epitaxial films with well-defined Neel temperature ~ 305 K. Spin Seebeck effect (SSE) responses seem to show correlation with the film structural quality. |
Tuesday, March 7, 2023 1:42PM - 1:54PM |
G32.00012: Synergistic Effect of Thermal Activation and Plasma: Low-Temperature, Universal Synthetic Approach for Crystalline Mesoporous Metal Oxide keon-woo kim Crystalline mesoporous metal oxides have received much attention due to various applications in catalysis, sensors, and energy storage materials. The soft-templating method, which combine molecular self-assembly with sol-gel chemistry, is an effective way for synthesis of mesoporous metal oxide with crystalline phase. However, conventional soft-templating method should use high-temperature calcination for template removal and inorganic crystallization, which restrict the integration on a plastic substrate for flexible electronics. Here, we introduce an innovative low-temperature synthetic approach for crystalline mesoporous metal oxide by utilizing the synergistic effect of thermal activation and plasma. Thermal activation-assisted plasma (TAP) induces the crystallization of inorganic precursors in addition to effective template removal at low temperature (150 °C). We synthesized various metal oxides with crystalline mesoporous phase on flexible polyimide substrate. |
Tuesday, March 7, 2023 1:54PM - 2:06PM |
G32.00013: Synthesis of (111) oriented films of rare-earth pyrochlore titanates with sub-unit cell precision Fangdi Wen, Jak Chakhalian, Mikhail Kareev, Tsung-Chi Wu, Michael Terilli, Qinghua Zhang, Lin Gu, Xiaoran Liu Frustrated rare-earth pyrochlore titanates have been introduced as promising candidates to realize quantum spin ice (QSI) with a 2-in-2-out magnetic ordering as its ground state. The realization of this class of materials in the thin-film form, especially as heterostructures, has been predicted to result in the unusual magnetic states stemming from the interfacial magnetism combined with the oriented Kagome-triangular frustrated lattice. Here, we report the successful layer-by-layer growth of high-quality thin films of the frustrated quantum pyrochlores, R2Ti2O7 (R = Er, Yb, and Tb), along the (111) direction. We confirmed their high crystallinity and proper chemical composition, discovered a robust mode of growth, and observed a pressure-sensitive growth for Tb2Ti2O7. The availability of large area (111)-oriented QSI structures with planar geometry offers a new complementary to the bulk platform. |
Tuesday, March 7, 2023 2:06PM - 2:18PM |
G32.00014: Buffer Layer Selection for the Fabrication of Freestanding Oxide Membranes Yu-Jung Wu, Varun Harbola, Sander Smink, Sarah C Parks, Jochen D Mannhart Epitaxial films of complex oxides have gained interest due to their wide-ranging physical properties, including high-temperature superconductivity, magnetism, ferroelectricity, and multiferroicity. Conventionally grown single-crystalline oxide thin films are usually bound to their substrates, which imposes constraints on their properties and usage. Therefore, growth techniques have recently been developed that enable lifting-off freestanding complex oxide membranes by wet etching of oxide buffer layers. To achieve the transfer of large-area oxide films, we have systematically studied the transfer of a variety of thin films grown on aluminate and manganite buffer layers. We found that for a chosen material of the freestanding membrane, the choice of required buffer layer typically is not universal. Various materials of oxide membranes were successfully transferred with good quality and up to 3x 2 mm2 area with minimal cracking. This work is expected to enable a wide range of oxide films to be transferred in high quality for fundamental studies and applications in oxide electronic devices. |
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