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 S33: Physics at Interfaces |
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Sponsoring Units: DCMP Chair: Vasileios Fotopoulos, University College London Room: Room 225 |
Thursday, March 9, 2023 8:00AM - 8:12AM |
S33.00001: Near-Total-Reflection Hard X-ray Photoemission Study on Al2O3/TiO2 2-dimensional Electron Gas System Yejin Kim, Cheng-Tai Kuo, Jean-Pascal Rueff, Masato Yoshimura, Ji Hyeon Choi, Tae Joo Park, Deok-Yong Cho We investigated the electronic structure of an interfacial 2-dimensional electron gas (2DEG) formed at Al2O3/TiO2 thin films heterostructure using hard x-ray photoemission spectroscopy (HAXPES). HAXPES with a fine control of the x-ray incidence angles near the total-reflection condition (NTR) is sensitive in the depth profile of the electronic structure. The results of the NTR HAXPES analyses showed that the certain quasiparticle-like density of states indeed forms near the interface region, manifesting the 2DEG nature of the system. Meanwhile, the Ti3+ concentration deduced from the core level analyses is spread over entire the bottom TiO2 layers, suggesting it originates from the defects inherently existing in TiO2. This signifies that the detection of Ti3+, which is a frequently employed method, might not be a reliable way to substantiate the 2DEG. |
Thursday, March 9, 2023 8:12AM - 8:24AM |
S33.00002: Electronic properties of dicalcium nitride (Ca2N) nanoribbons from first principles Gunn Kim, Jinwoong Chae Electrides have confined electrons, which act as anions, in their cavities or interlayer space. They have exotic properties such as low work functions, charge transfer characteristics, and resistance anisotropy. Two-dimensional (2D) electrides, such as Ca2N, Y2C, and Gd2C, have two-dimensional electron gas on their surface. In our previous studies, we reported the electronic properties of the surfaces of electrides. [1,2] After studying the electronic structure of the bulk and few-layer systems of electrides, the next topic to be addressed is the physical properties of the edges of the electrides. It was found that even in the case of graphene, various physical properties appear depending on the width and shape of the edge of the nanoribbon. In this talk, we will present the structure and electrical properties of single-layer Ca2N nanoribbons. Two types of ribbons are considered: the Ca-terminated ribbon and the N-terminated ribbon. Interestingly, the N-terminated ribbon becomes thinner at the edge as the edge is rearranged and reorganized into a form with Ca atoms coming to the edge. In contrast, the Ca-terminated ribbon has no noticeable structural change. The Ca2N monolayer is nonmagnetic, but its nanoribbons are all antiferromagnetic. Finally, we provide scanning tunneling microscopy images. |
Thursday, March 9, 2023 8:24AM - 8:36AM |
S33.00003: Two-Photon Fluorescence and Second-Harmonic Generation at the Interface of SrTiO3 Thin Film and NdGaO3 Substrate Mojgan Dehghani, Jiandi Zhang, Louis H Haber, Zeeshan Ali, Mohammad Saghayezhian Strontium titanate SrTiO3 (STO) is a popular ferroelectric material exhibiting excellent chemical and thermal stabilities and promising electrical and physical properties for various technology applications. Studies on STO thin films revealed a dramatic difference in dielectric properties compared to the bulk. In addition, due to the mechanical coupling between STO thin film and its substrate, the cubic symmetry of the thin film breaks. We investigate this structural symmetry breaking of STO thin film by using the rotational anisotropy second harmonic generation (SHG) technique in the reflection geometry. To prepare the sample, we epitaxially grow STO (001) thin film on NdGaO3 (NGO) (110) substrate by pulsed laser deposition (PLD) technique. In the SHG experiment, we employ a femtosecond pulsed laser as a source of excitation. The polarization of the fundamental and reflected SH radiation are either parallel or perpendicular to the incident plane. The reflected two-fold SHG intensity indicates that the predominant two-fold NGO symmetry at the interface lowers the 4-fold symmetry of the STO thin film. Moreover, we observe very intense two-photon fluorescence (TPF) signals emanating from the interface which exhibits polarization and angular dependency. We determine the TPF signals originate from the interface where the inversion symmetry is broken. |
Thursday, March 9, 2023 8:36AM - 8:48AM |
S33.00004: Interplay of quasi-periodic potential and disorder in 3D Anderson model Zhengqiao LI Both random disorder and quasi-periodic potential can localize quantum mechanical wave functions. We investigate how the two factors interplay in the localization phenomenon by studying 3D Anderson model in the presence of an anisotropic quasi-periodic potential along z direction. We study the model numerically with the transfer matrix method and obtain a qualitative phase diagram. We observe that, at certain strength of the quasi-periodic potential, the model displays a two-stage phase transition as the disorder strength increases: it is localized at small disorder strength, then becomes delocalized, and eventually enters the localized phase again. Our result implies that quasiperiodic potential and disorder compete with each other in localizing wave functions in an appropriate parameter regime. |
Thursday, March 9, 2023 8:48AM - 9:00AM |
S33.00005: Photocapacitance spectroscopy on Au/TiO2 Schottky diodes Thomas Heinzel, Lukas Berg, Carlos Cesar Bof Bufon Optically transparent electrodes allow deep level transient photocapacitance spectroscopy on Au/TiO2 Schottky diodes. We report the measurement of photocapacitance transients and compare them to the corresponding conventional transient capacitance. It is demonstrated that the methods are complementary and both of them allow, via a rate equation model, the determination of the binding energy as well as the capture cross section of the dominant traps. Furthermore, information about the capture process can be extracted. |
Thursday, March 9, 2023 9:00AM - 9:12AM Author not Attending |
S33.00006: Optical properties of 30 degree twisted bilayer graphene quasicrystal Masaru Hitomi, Mikito Koshino We propose a theoretical approach to calculate the optical response function in non-periodic twisted bilayer graphene systems. It is well known that a twist bilayer with low twist angle can be approximately treated as a periodic Bloch system with a moire superlattice period. When arbitrary 2D materials are overlaid with an arbitrary rotation angle, however, |
Thursday, March 9, 2023 9:12AM - 9:24AM |
S33.00007: Depth profiling electronic structures of LaTiO3/SrTiO3 heterostructures using soft X-ray ARPES Hawoong Hong, Jessica L McChesney, Fredrike Wrobel, Xi Yan, Yan Li, Anand Bhattacharya, Dillon D Fong As with other transition-metal oxide interfaces, LaTiO3/SrTiO3 interfaces exhibit interesting electronic properties, such as a two-dimensional electron gas. While the available Mott states and multiple pathways to metallicity in LaTiO3 can lead to a variety of applications in oxide electronics, the origin of the different properties remain uncertain. Utilizing real-time, in-situ X-ray diffraction at the synchrotron, robust but thin LaTiO3/SrTiO3 heterostructures were fabricated using oxide molecular beam epitaxy. A thickness of six unit-cells was determined to be critical, at which point the LaTiO3 / SrTiO3 heterostructures begin to sustain sharp, well-defined interfaces. The layers of LaTiO3 and SrTiO3 were sufficiently thin to benefit from the finite escape length of electrons at resonant soft X-ray photoemission, and the heterostructures were transferred in vacuo after growth to another chamber for synchrotron-based X-ray photoemission spectroscopy studies. With the X-ray energy tuned to the Ti-2p resonance, the LaTiO3/SrTiO3 interfaces could be probed with enough penetration depth and selectivity. It is shown that all of the heterointerfaces exhibit the 2-dimensional electron gas. |
Thursday, March 9, 2023 9:24AM - 9:36AM |
S33.00008: Critical role of terminating layer in formation of 2DEG state at the LaInO3/BaSnO3 interface Seonghyeon Kim, Mikk Lippmaa, Jaehyeok Lee, Hyeongmin Cho, Juhan Kim, Bongju Kim, Kookrin Char Based on the interface polarization model, the two-dimensional electron gas (2DEG) at LaInO3(LIO)/BaSnO3(BSO) interfaces is understood to originate from a polarization discontinuity at the interface and the conduction band offset between LIO and BSO.[1,2] In this scenario, the direction of polarization at the interface is determined by whether the first atomic LIO layer at the interface is LaO+ or InO2−. We investigate the role of the terminating layer at the LIO/BSO interface in creating the 2DEG. Based on conductance measurements of our in-situ grown LIO/BSO heterostructures, we report in this work that the 2DEG only forms when the BSO surface is terminated mainly with a SnO2 layer. We controlled the terminating layer by additional SnO2 deposition on the BSO surface. We show that the as-grown BSO surface has a mixed terminating layer of BaO and SnO2 while the BSO surfaces prepared with additional SnO2 deposition are terminated mainly with the SnO2 layer. The terminating layer was confirmed by coaxial impact collision ion scattering spectroscopy (CAICISS). Our finding is consistent with the interface polarization model for 2DEG formation at LIO/BSO interfaces, in which the direction of the interfacial polarization in LIO is determined by the terminating layer of the BSO surface.[3] |
Thursday, March 9, 2023 9:36AM - 9:48AM |
S33.00009: Polarity-driven atomic displacements at the 2D Mg2TiO4 / MgO (001) oxide interface for hosting potential interlayer excitons Kidae Shin, Stephen Eltinge, Sangjae Lee, Hyungki Shin, Juan Jiang, Hawoong Hong, Bruce A Davidson, Ke Zou, Sohrab Ismail-Beigi, Charles H Ahn, Frederick J Walker Interlayer excitons in solid-state systems have emerged as candidates for realizing novel platforms ranging from excitonic transistors and optical qubits to exciton condensates. To date, interlayer excitons have been heavily investigated in van der Waals (vdW) heterostructures consisting of 2D transition metal dichalcogenides (TMDs). Here, an oxide system consisting of a single unit cell Mg2TiO4 on MgO (001) is proposed as a platform for hosting interlayer excitons. Using a combination of density functional theory (DFT) calculations, molecular beam epitaxy (MBE) growth and in situ crystal truncation rod (CTR) measurements, we show that the Mg2TiO4/MgO interface can be precisely controlled to yield an internal electric field suitable for hosting interlayer excitons. The atoms in the polar Mg2TiO4 layers are observed to be displaced to reduce polarity at the interface with the non-polar MgO (001) surface. Such polarity-driven atomic displacements strongly affect electrostatics of the film and the interface, resulting in localization of filled and empty band-edge states in different layers of the Mg2TiO4 film. The DFT calculations suggest that the electronic structure is favorable for localization of photoexcited electrons in the bottom layer and holes in the top layer, which may bind to form interlayer exciton states. |
Thursday, March 9, 2023 9:48AM - 10:00AM |
S33.00010: Thermodynamic analysis on the effect of H in the formation of vacancy clusters in Cu. Vasileios Fotopoulos, Ricardo Grau-Crespo, Alexander Shluger Stress-induced voiding (SIV) is amongst the most commonly reported defects in metallic systems [1]. Supersaturation of vacancies is considered an initial stage of voiding in metals [2]. It is generally known that H promotes the formation of vacancies, thus, it is anticipated that H will play a significant role in voiding phenomena [3, 4]. However, since measuring experimentally the amount of H incorporated in metals remains challenging, a theoretical analysis is needed. |
Thursday, March 9, 2023 10:00AM - 10:12AM |
S33.00011: Relating Grain Boundary Sliding to Low Friction in Metals Michael E Chandross, Nicolas Argibay Friction in metals is a direct result of the nanoscale deformation mechanisms. Previous work has demonstrated that low friction is associated with the formation/persistence of a thin layer of ultra-nanocrystalline material (10 nm) at the sliding interface. At these sizes, shear is no longer accommodated by dislocations but rather through grain boundary sliding (GBS), as in inverse Hall-Petch behavior. We present a treatment of GBS that provides qualitative and quantitative descriptions of low friction in metals. This framework -- based on materials properties with no adjustable parameters -- accurately predicts the strength of a variety of metals (FCC, BCC, and HCP), dilute alloys and metallic glasses. By directly connecting bond strengths and deformation mechanisms with the macroscale properties of metals, this work implies opportunities for optimization of alloys for low friction and high strength applications. |
Thursday, March 9, 2023 10:12AM - 10:24AM |
S33.00012: Effects of chemical randomness on strength contributors and dislocation behaviors in a BCC multi-principal element alloy Shuang Lyu, Yue Chen, Alfonso H.W. Ngan, Wei Li, Yuanhang Xia Abstract |
Thursday, March 9, 2023 10:24AM - 10:36AM |
S33.00013: Surface deformation of Nanocomposites suresh AHUJA Nanocomposites review is the modeling of the mechanical properties of polymer-based |
Thursday, March 9, 2023 10:36AM - 10:48AM |
S33.00014: Orthotropic Behavior of Aged Paper Patricia M McGuiggan, Thomas O'Connor, Jay Wallace, Molly McGath, Sophie Leheny, Thomas C Robbins, Catherine K Robbins, Fangyi Zhou, Andrea K Hall Tensile testing was used to measure the mechanical properties of paper at various orientations relative to the machine direction of paper. New, artificially aged, and naturally aged paper were shown to behave as orthotropic materials, as shown by the orientation dependence of the Young’s modulus. The Young’s modulus data could be fit to a simplified equation, indicating the shear modulus is relatively insensitive to the specific orientation. The shear modulus as measured by ultrasonic measurements was similar to that measured by fitting the modulus vs orientation data obtained by tensile testing to the orthotropic equation. The inelastic tensile strength could also be described by a simple non-linear equation, and there was more deviation of the data from this prediction for brittle papers than for non-brittle papers. The extent of fiber orientation (Ex/Ey) could be inferred by either the Young’s modulus or the tensile strength, i.e. Ex/Ey ≈ TSx/TSy. The measured strains were lowest for brittle paper. All brittle papers gave a strain to failure < 1% whereas the non-brittle papers gave a strain to failure > 1%. |
Thursday, March 9, 2023 10:48AM - 11:00AM |
S33.00015: Constitutive framework for rheologically complex interfaces with an application to elastoviscoplasticity Patrick D Anderson, Martien A Hulsen, Markus Hutter, Mick Carrozza A framework is presented for the formulation of a class of continuum constitutive models for sharp interfaces with non-linear viscoelastic behaviour due to a considerable isotropic interfacial microstructure. For the formulation of a thermodynamically consistent elastoviscoplastic interface constitutive model we adapt an approach successful in describing the behaviour of bulk polymer glasses. The model has a clear separation between dilatation and shear, and is used to predict phenomena related to the plasticity of interfaces observed in the experimental literature, which is relevant for many applications. Stress–strain predictions in standard interfacial rheological flows, i.e. shear and dilatation, are investigated numerically. A predominantly elastic response is obtained at small deformations, with a transition to primarily plastic flow at high stress levels. In interfacial shear flow, strain softening and eventually a plastic plateau occur upon further deformation beyond the yield point. The yield stress and strain and (the relative strength of) the stress overshoot in interfacial shear flow are shown to be controlled by two dimensionless groups of parameters in the model. In interfacial dilatation, the model predicts elastoviscoplastic behaviour with a stress maximum and a decreasing stress without a plateau at even larger deformations. These phenomena are studied for various choices for the parameters in the model. |
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