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 K41: Ferroics in Two Dimensional Materials, Films, and HeterostructuresFocus
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Sponsoring Units: DMP Chair: Lingfang Lin, University of Tennessee Room: Room 319 |
Tuesday, March 7, 2023 3:00PM - 3:36PM |
K41.00001: A type-II multiferroic in two dimensions Invited Speaker: Riccardo Comin Multiferroic materials have garnered wide interest for their exceptional static and dynamical magnetoelectric properties [1]. In particular, type-II multiferroics exhibit an inversion-symmetry-breaking magnetic order which directly induces a ferroelectric polarization through various mechanisms, such as the spin-current or the inverse Dzyaloshinskii-Moriya effect. This intrinsic coupling between the magnetic and dipolar order parameters results in record-strength magnetoelectric effects [2]. In this context, there has been a recent surge of interest in 2D materials possessing such intrinsic multiferroic properties, enabling the integration and control of magnetoelectric effects in artificial heterostructures and nanoelectronic devices [3,4]. |
Tuesday, March 7, 2023 3:36PM - 3:48PM |
K41.00002: Operando hard X-ray photoemission characterization of oxygen vacancies and correlation with the performance of ferroelectric, hafnia-based, non-volatile memories Nicholas Barrett, Wassim Hamouda, Christophe Lubin, Furqan Mehmood, Uwe Schroeder, Thomas Mikolajick, Olivier Renault, Shinegori Ueda, Yoshiyuki Yamashita The successful integration of ferroelectric hafnia into high performance, ultra-low power CMOS compatible memory and logic depends not only on suitable material properties but also on engineering these properties in order to optimize device performance. Key performance indicators are imprint, wake-up, fatigue and leakage all intimately linked to the material and device responses to field cycling and more generally to environmental and processing conditions. |
Tuesday, March 7, 2023 3:48PM - 4:00PM |
K41.00003: In Situ Observation of Thin Film Ferroelectric HZO with STEM EBIC Ho L Chan, Shelby S Fields, Tristan O'Neill, Yueyun Chen, William Hubbard, Jon Ihlefeld, Brian C Regan Ferroelectric thin film hafnium oxide (HfO2) is an especially promising candidate for next generation non-volatile memory applications because of its compatibility with complementary metal-oxide-semiconductor (CMOS) technology. Although the metastable polar orthorhombic Pca21 phase is generally thought to be responsible for ferroelectricity in thin film HfO2, this identification is not absolutely certain because multiple structurally similar phases are present in the polycrystalline films. Moreover, the mechanism stabilizing the relevant crystal phases is not fully understood. Scanning transmission electron microscopy (STEM) can identify crystal phases, but usually is insensitive to polarization. Electron-beam induced current (EBIC) imaging can map electric fields directly. Using STEM EBIC imaging along with the positive-up-negative-down (PUND) method, we map the polarization state and measure the global polarization, respectively, on a TaN/HZO/TaN capacitor. We compare the global polarization determined via transport with detailed maps showing which ferroelectric domains are switching. By varying the applied field, we identify the threshold switching fields for different domain populations. |
Tuesday, March 7, 2023 4:00PM - 4:12PM |
K41.00004: Direct imaging of grain and domain structure in nanocrystalline ferroelectric thin films Daniel B Durham, Khandker Akif Aabrar, Suman Datta, Nestor J Zaluzec, Supratik Guha, Charudatta Phatak Ultrathin doped HfO2 ferroelectric films are gaining increasing interest for next-generation computing technologies such as field-effect transistors, memories, and neuromorphic devices thanks to their high performance, reliability, and CMOS compatibility. However, when grown by atomic layer deposition on silicon, these polycrystalline films contain a distribution of grain sizes and multiple structural phases, and the relationship between these structural features and the electrical response is not fully understood. We will present our work towards correlative imaging of the grain and domain structure in Zr-doped HfO2 (HZO) films and superlattices with nm-scale resolution using advanced electron microscopy approaches, including off-axis electron holography and scanning electron nanodiffraction with in-situ electrical biasing. We will discuss links observed so far between grain structure, including size, orientation, and phase, and the electrostatic potential distribution in the film. Finally, we will discuss opportunities for further development of these approaches as well as how our initial observations can inform pathways to improve device performance and scalability. |
Tuesday, March 7, 2023 4:12PM - 4:24PM |
K41.00005: Exquisite control of the Landau energy landscape in ferroelectric HZO Raul A Flores, Sinead M Griffin HZO – (Hf,Zr)O2 -- has emerged as a promising ferroelectric material for low-power microelectronics with robust polarization switching in films as thin as 10 nm. As such, it is highly desirable to further improve the performance of HZO through engineering of its chemical and physical properties. To date, the polarization switching behavior has eluded theoretical description, with polarization barriers predicted by Density Functional Theory (DFT) being much larger than experimental measurements. |
Tuesday, March 7, 2023 4:24PM - 4:36PM |
K41.00006: Structures and photoelectric properties of superdomains in epitaxial (110)-PZT films Sheng-Zhu Ho, Meng-Xun Xie, Yu-Chen Liu, Yu-Huai Li, Li-Chieh Huang, Ying-Chih Pu, Jan-Chi Yang, Yi-Chun Chen Nano-domains with multiple ferroic orders have received increasing attention for their potential applications in next-generation electronics, including non-volatile memories, sensors, and phototronic devices etc. In this work, we construct a broad picture of ferroelectric properties, photoelectric behaviors, and multiple manipulating pathways on a strained (110)-oriented epitaxial Pb(ZrxTi1-x)O3 (PZT) film. The in-plane strain from SrTiO3 (110) substrate breaks the uniaxial symmetry of the tetragonal PZT, and with suitable strain energy, superdomains can be formed in local areas. Piezoresponse force microscopy (PFM) and conductive atomic force microscopy (cAFM) are used to determine the three-dimensional polarization orientations of the superdomain structures and reveal the nature of the conductive domain walls. The enhanced photoactivity is shown in the head-to-head charged domain walls, which is due the bandgap reduction led by the band bending effect, and the superdomains exhibit enhanced photoelectrochemical (PEC) performance compared to that of typical c/a domains in PZT. Finally, we utilized time-varying pulsed voltages to measure the dynamic current switching within one millisecond and achieve direct/multi-step switching for different polarization state manipulation. The understanding of the photoelectrical mechanisms and the multiple pathways to control the intermediate state make the superdomain PZT a candidate for functional photoelectronic devices. |
Tuesday, March 7, 2023 4:36PM - 4:48PM |
K41.00007: Thickness dependence and strain effects in NaNbO3 thin films Aarushi Khandelwal, Kevin J Crust, Harikrishnan K.P., Yu-Tsun Shao, David A Muller, Ruijuan Xu, Harold Hwang NaNbO3 is one of the most complex perovskite oxides, with room-temperature antiferroelectricity and several temperature-dependent phase transitions in bulk1,2. Despite extensive studies in bulk3,4, relatively little is known about the evolution of structure and properties in NaNbO3 thin films. Here, we explore the effects of thickness and misfit strain on the structure and electrical properties of NaNbO3 thin-film heterostructures. Using pulsed laser deposition, we synthesize epitaxially-strained NaNbO3 thin films on SrTiO3 (001) and DyScO3 (110) substrates. Using X-ray diffraction and scanning transmission electron microscopy, we characterize the crystal structures and compute polarization via atomic displacements. We observe strain-induced ferroelectricity and characterize this via electrical measurements and piezoresponse force microscopy to measure the polarization-electric field hysteresis loops and ferroelectric domain structures. This work provides new insights into the structure and electrical property evolution of these lead-free ferroelectric thin films. |
Tuesday, March 7, 2023 4:48PM - 5:00PM |
K41.00008: Hyper-efficient mechanical switching of ferroelectric polarization on metastable perovskite ferroelectric thin films Ji Hye Lee Feasibility of domain switching through mechanical force (i.e. in the absence of electric field) by scanning-probe-induced strain gradient suggests an alternative way to switching the ferroelectric polarization, attracting much interest in the application for ferreoelectric-based devices. Therefore, ultra-low mechanical switching load can lead to a new strategy for realizing of low energy electronics because it could reduce the energy costs for information storage in nanoscale mechanoelectric devices. |
Tuesday, March 7, 2023 5:00PM - 5:12PM |
K41.00009: Direct electrical control of a single-layer multiferroic Jiaruo Li, Qian Song, Riccardo Comin Two-dimensional (2D) magnetic van der Waals materials can exhibit novel phases that are not present in bulk materials due to reduced dimensionality. Among them, type-II 2D multiferroics are of unique interest because of the coexistence of a helical magnetic ground state, a magnetism-induced ferroelectric order, and a record-strength magnetoelectric coupling. Following the recent discovery of single-layer multiferroic in NiI2 system, here we study the magnetic ground state of single-layer NiI2 as a function of electrostatic doping and electric field in a dual gate device architecture. The evolution of magnetic and ferroelectric orders is investigated using magneto-optical Kerr effect microscopy, circularly dichroic Raman spectroscopy, and second-harmonic generation. Specifically, we investigated the helimagnetic transition temperature, the spin helix chirality, and the propagation direction and periodicity of the spin helical vector as a function of electrostatic doping and electric field. This work aimed for the piloting attempt of direct electrical control of a single-layer multiferroic system. These observations provide a new platform for studying 2D magnetism, chiral magnetic textures, and magnetoelectric coupling, yielding transformative technological potentials such as low-power nanoelectronic devices. |
Tuesday, March 7, 2023 5:12PM - 5:24PM |
K41.00010: Probe of Multifunctionality in BaTiO3-BiFeO3 Films and Nanorod Arrays Nicholas W Smith, Rathsara R Herath Mudiyanselage, Min Gyu Kang, Shuang Wu, Satoru Emori, Brenden A Magill, Shashank Priya, Giti A Khodaparast Multifunctional materials are ushering a new era of revolutionary advances in optoelectronics, spintronics, and in quantum sensing due to their enhanced coupling between electronic, vibrational, and spin degrees of freedom. In this talk, we present several less explored properties of BaTiO3-BiFeO3 (BTO-BFO) films and nanorod arrays, including second harmonic generation (SHG) and ferromagnetic resonance (FMR). Aiming for miniaturization and integration on Si chips, beyond commonly used nonlinear materials, we explored SHG using excitation wavelengths ranging from 1000-1050 nm on BTO-BFO films and nano-rod arrays, with different film thicknesses and heights. In addition, we report FMR on the same structures (from 5 to 30 GHz) where the effective Gilbert damping parameter, in the range of 4-7x10-3, was extracted. The observation of low effective damping indicates that these BTO-BFO systems could be promising for enabling low-loss spin dynamics. |
Tuesday, March 7, 2023 5:24PM - 5:36PM |
K41.00011: Terahertz Acoustics in a Ferroelectric/Dielectric Superlattice Deepankar Sri Gyan, Hyeonjun Lee, Youngjun Ahn, Samuel D Marks, Mohammed H. Yusuf, Matthew Dawber, Diling Zhu, Takahiro Sato, Sanghoon Song, Haidan Wen, Paul G Evans The THz-frequency regime acoustic excitations of ferroelectric thin-film heterostructures underpin optical, electronic, and phase-transformation phenomena. Ferroelectric/dielectric superlattice (SL) heterostructures, in particular, can have atomic-scale periodicity and novel polarization configurations that pose a challenge to the prediction of the modes and frequencies of excitations and can be expected to produce previously unknown modes. We report an optical pump x-ray probe study using a free-electron laser x-ray diffraction to probe the wavevector-frequency dispersion in a ferroelectric/dielectric SL. The thin-film heterostructure consisted of a 100 nm-thick 8 unit-cell PbTiO3/3 unit-cell SrTiO3 SL deposited on a 20 nm SrRuO3 layer on SrTiO3 (001). The time-dependence of the intensity distribution of x-rays scattered from the SL was measured with high dynamic range and converted to a frequency-wavevector dispersion spectrum using a time-domain Fourier transform. The dispersion reveals folded longitudinal acoustic modes and frequency gaps at the centers and boundaries of the SL mini-Brillouin zones (BZs). The distribution of Fourier-transformed intensity indicates that novel modes at angular frequencies of 5 THz and 10 THz may arise at the BZ boundary. |
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