Browsing by Author "Yao, Lide"
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Item Alternating domains with uniaxial and biaxial magnetic anisotropy in epitaxial Fe films on BaTiO3(2012) Lahtinen, Tuomas H.E.; Shirahata, Yasuhiro; Yao, Lide; Franke, Kévin J.A.; Venkataiah, Gorige; Taniyama, Tomoyasu; van Dijken, Sebastiaan; Department of Applied PhysicsItem Alternating domains with uniaxial and biaxial magnetic anisotropy in epitaxial Fe films on BaTiO[sub 3](AIP Publishing, 2012) Lahtinen, Tuomas H. E.; Shirahata, Yasuhiro; Yao, Lide; Franke, Kevin J. A.; Venkataiah, Gorige; Taniyama, Tomoyasu; van Dijken, Sebastiaan; Teknillisen fysiikan laitos; Department of Applied Physics; Perustieteiden korkeakoulu; School of ScienceWe report on domain formation and magnetization reversal in epitaxial Fe films on ferroelectric BaTiO3 substrates with ferroelastica–c stripe domains. The Fe films exhibit biaxial magnetic anisotropy on top of c domains with out-of-plane polarization, whereas the in-plane lattice elongation of a domains induces uniaxial magnetoelasticanisotropy via inverse magnetostriction. The strong modulation of magnetic anisotropy symmetry results in full imprinting of the a–c domain pattern in the Fe films. Exchange and magnetostaticinteractions between neighboring magnetic stripes further influence magnetization reversal and pattern formation within the a and c domains.Item Apparent ferrimagnetism in Sr(Fe0.2Mn0.2Co0.2Ti0.2V0.2)O3 high-entropy oxide perovskite thin films(American Institute of Physics, 2024-02-01) Regmi, Balaram; Miertschin, Duncan; Cocconcelli, Maria; Stramaglia, Federico; Crater, Davis; Yao, Lide; Piamonteze, Cinthia; van Dijken, Sebastiaan; Farhan, Alan; Department of Applied Physics; OtaNano; Nanomagnetism and Spintronics; Baylor University; Paul Scherrer Institute; Polytechnic University of MilanWe present a study on the structural and magnetic properties of Sr(Fe0.2Mn0.2Co0.2Ti0.2V0.2)O3 (S5BO) high-entropy oxide perovskite thin films. We use synchrotron-based x-ray absorption spectroscopy employing x-ray magnetic circular dichroism (XMCD) and reveal an enhanced presence of high-spin Co2+, which appears to feature a magnetic response opposing that of the two other magnetic transition metal elements, Fe and Mn. This is marked by both opposite XMCD signals and an inverted XMCD hysteresis loop for Co, while Fe and Mn show regularly shaped hysteresis curves, as the picture of a ferrimagnetic ground state emerges for S5BO.Item Coherent piezoelectric strain transfer to thick epitaxial ferromagnetic films with large lattice mismatch(IOP Publishing, 2013) Kim, Jang-Yong; Yao, Lide; van Dijken, Sebastiaan; Teknillisen fysiikan laitos; Department of Applied Physics; Perustieteiden korkeakoulu; School of ScienceStrain control of epitaxial films using piezoelectric substrates has recently attracted significant scientific interest. Despite its potential as a powerful test bed for strain-related physical phenomena and strain-driven electronic, magnetic, and optical technologies, detailed studies on the efficiency and uniformity of piezoelectric strain transfer are scarce. Here, we demonstrate that full and uniform piezoelectric strain transfer to epitaxial films is not limited to systems with small lattice mismatch or limited film thickness. Detailed transmission electron microscopy (TEM) and x-ray diffraction (XRD) measurements of 100 nm thick CoFe2O4 and La2/3Sr1/3MnO3 epitaxial films on piezoelectric 0.72Pb(Mg1/3Nb2/3)O3–0.28PbTiO3 substrates (+4.3% and -3.8% lattice mismatch) indicate that misfit dislocations near the interface do not hamper the transfer of piezoelectric strain. Instead, the epitaxial magnetic oxide films and PMN-PT substrates are strained coherently and their lattice parameters change linearly as a function of applied electric field when their remnant growth-induced strain state is negligible. As a result, ferromagnetic properties such as the coercive field, saturation magnetization, and Curie temperature can be reversibly tuned by electrical means. The observation of efficient piezoelectric strain transfer in large-mismatch heteroepitaxial structures opens up new possibilities for the engineering of strain-controlled physical properties in a broad class of hybrid material systems.Item Concurrent bandgap narrowing and polarization enhancement in epitaxial ferroelectric nanofilms(2015) Tyunina, Marina; Yao, Lide; Chvostova, Dagmar; Dejneka, Alexandr; Kocourek, Tomas; Jelinek, Miroslav; Trepakov, Vladimir; van Dijken, Sebastiaan; Department of Applied Physics; Nanomagnetism and SpintronicsItem Deterministic Polymorphic Engineering of MoTe2 for Photonic and Optoelectronic Applications(Wiley-VCH Verlag, 2023-08-15) Ahmed, Faisal; Rodríguez-Fernández, Carlos; Fernandez, Henry A.; Zhang, Yi; Shafi, Abde Mayeen; Uddin, Md Gius; Cui, Xiaoqi; Yoon, Hoon Hahn; Mehmood, Naveed; Liapis, Andreas C.; Yao, Lide; Caglayan, Humeyra; Sun, Zhipei; Lipsanen, Harri; Department of Electronics and Nanoengineering; Department of Applied Physics; OtaNano; Harri Lipsanen Group; Zhipei Sun Group; Centre of Excellence in Quantum Technology, QTF; Tampere UniversityDeveloping selective and coherent polymorphic crystals at the nanoscale offers a novel strategy for designing integrated architectures for photonic and optoelectronic applications such as metasurfaces, optical gratings, photodetectors, and image sensors. Here, a direct optical writing approach is demonstrated to deterministically create polymorphic 2D materials by locally inducing metallic 1T′-MoTe2 on the semiconducting 2H-MoTe2 host layer. In the polymorphic-engineered MoTe2, 2H- and 1T′- crystalline phases exhibit strong optical contrast from near-infrared to telecom-band ranges (1–1.5 µm), due to the change in the band structure and increase in surface roughness. Sevenfold enhancement of third harmonic generation intensity is realized with conversion efficiency (susceptibility) of ≈1.7 × 10−7 (1.1 × 10−19 m2 V−2) and ≈1.7 × 10−8 (0.3 × 10−19 m2 V−2) for 1T′ and 2H-MoTe2, respectively at telecom-band ultrafast pump laser. Lastly, based on polymorphic engineering on MoTe2, a Schottky photodiode with a high photoresponsivity of 90 AW−1 is demonstrated. This study proposes facile polymorphic engineered structures that will greatly benefit realizing integrated photonics and optoelectronic circuits.Item Direct observation of oxygen vacancy-driven structural and resistive phase transitions in La2/3Sr1/3MnO3(2017-02-23) Yao, Lide; Inkinen, Sampo; Van Dijken, Sebastiaan; Department of Applied Physics; Nanomagnetism and SpintronicsResistive switching in transition metal oxides involves intricate physical and chemical behaviours with potential for non-volatile memory and memristive devices. Although oxygen vacancy migration is known to play a crucial role in resistive switching of oxides, an in-depth understanding of oxygen vacancy-driven effects requires direct imaging of atomic-scale dynamic processes and their real-time impact on resistance changes. Here we use in situ transmission electron microscopy to demonstrate reversible switching between three resistance states in epitaxial La2/3Sr1/3MnO3 films. Simultaneous high-resolution imaging and resistance probing indicate that the switching events are caused by the formation of uniform structural phases. Reversible horizontal migration of oxygen vacancies within the manganite film, driven by combined effects of Joule heating and bias voltage, predominantly triggers the structural and resistive transitions. Our findings open prospects for ionotronic devices based on dynamic control of physical properties in complex oxide nanostructures.Item Element-sensitive x-ray absorption spectroscopy and magnetometry of Lu(Fe0.2Mn0.2Co0.2Cr0.2Ni0.2) O3 high-entropy oxide perovskite thin films(American Physical Society, 2023-04) Farhan, Alan; Cocconcelli, Maria; Stramaglia, Federico; Kuznetsov, Nikolai; Flajšman, Lukáš; Wyss, Marcus; Yao, Lide; Piamonteze, Cinthia; Van Dijken, Sebastiaan; Department of Applied Physics; OtaNano; Nanomagnetism and Spintronics; Centre of Excellence in Quantum Technology, QTF; Paul Scherrer Institute; University of BaselWe present a study on the structural and magnetic properties of Lu(Fe0.2Mn0.2Co0.2Cr0.2Ni0.2)O3 (Lu5BO) high-entropy oxide perovskite thin films. We use synchrotron-based x-ray absorption spectroscopy employing x-ray magnetic circular and linear dichroism (XMCD and XMLD) to perform an element-sensitive study on single-crystal epitaxial Lu5BO thin films. Together with XMCD magnetometry, the results reveal dominant antiferromagnetic order with a transition temperature around 100 K.Item Giant anisotropic photonics in the 1D van der Waals semiconductor fibrous red phosphorus(Nature Publishing Group, 2021-08-10) Du, Luojun; Zhao, Yanchong; Wu, Linlu; Hu, Xuerong; Yao, Lide; Wang, Yadong; Bai, Xueyin; Dai, Yunyun; Qiao, Jingsi; Uddin, Md Gius; Li, Xiaomei; Lahtinen, Jouko; Bai, Xuedong; Zhang, Guangyu; Ji, Wei; Sun, Zhipei; Department of Electronics and Nanoengineering; Department of Applied Physics; Centre of Excellence in Quantum Technology, QTF; Zhipei Sun Group; Surface Science; CAS - Institute of Physics; Renmin University of ChinaA confined electronic system can host a wide variety of fascinating electronic, magnetic, valleytronic and photonic phenomena due to its reduced symmetry and quantum confinement effect. For the recently emerging one-dimensional van der Waals (1D vdW) materials with electrons confined in 1D sub-units, an enormous variety of intriguing physical properties and functionalities can be expected. Here, we demonstrate the coexistence of giant linear/nonlinear optical anisotropy and high emission yield in fibrous red phosphorus (FRP), an exotic 1D vdW semiconductor with quasi-flat bands and a sizeable bandgap in the visible spectral range. The degree of photoluminescence (third-order nonlinear) anisotropy can reach 90% (86%), comparable to the best performance achieved so far. Meanwhile, the photoluminescence (third-harmonic generation) intensity in 1D vdW FRP is strong, with quantum efficiency (third-order susceptibility) four (three) times larger than that in the most well-known 2D vdW materials (e.g., MoS2). The concurrent realization of large linear/nonlinear optical anisotropy and emission intensity in 1D vdW FRP paves the way towards transforming the landscape of technological innovations in photonics and optoelectronics.Item High Voltage Cycling Stability of LiF-Coated NMC811 Electrode(American Chemical Society, 2024-01-17) Llanos, Princess Stephanie; Ahaliabadeh, Zahra; Miikkulainen, Ville; Lahtinen, Jouko; Yao, Lide; Jiang, Hua; Kankaanpää, Timo; Kallio, Tanja; Department of Chemistry and Materials Science; Department of Applied Physics; OtaNano; Electrochemical Energy Conversion; Atomically Controlled Materials Engineering; Surface Science; NanoMaterials; Umicore Finland OyThe development of LiNi0.8Mn0.1Co0.1O2 (NMC811) as a cathode material for high-energy-density lithium–ion batteries (LIBs) intends to address the driving limitations of electric vehicles. However, the commercialization of this technology has been hindered by poor cycling stability at high cutoff voltages. The potential instability and drastic capacity fade stem from irreversible parasitic side reactions at the electrode–electrolyte interface. To address these issues, a stable nanoscale lithium fluoride (LiF) coating is deposited on the NMC811 electrode via atomic layer deposition. The nanoscale LiF coating diminishes the direct contact between NMC811 and the electrolyte, suppressing the detrimental parasitic reactions. LiF-NMC811 delivers cycling stability superior to uncoated NMC811 with high cutoff voltage for half-cell (3.0–4.6 V vs Li/Li+) and full-cell (2.8–4.5 V vs graphite) configurations. The structural, morphological, and chemical analyses of the electrodes after cycling show that capacity decline fundamentally arises from the electrode–electrolyte interface growth, irreversible phase transformation, transition metal dissolution and crossover, and particle cracking. Overall, this work demonstrates that LiF is an effective electrode coating for high-voltage cycling without compromising rate performance, even at high discharge rates. The findings of this work highlight the need to stabilize the electrode–electrolyte interface to fully utilize the high-capacity performance of NMC811.Item Imaging of short-wavelength spin waves in a nanometer-thick YIG/Co bilayer(American Institute of Physics, 2023-05-15) Talapatra, Abhishek; Qin, Huajun; Schulz, Frank; Yao, Lide; Flajšman, Lukáš; Weigand, Markus; Wintz, Sebastian; van Dijken, Sebastiaan; Department of Applied Physics; OtaNano; Nanomagnetism and Spintronics; Max Planck Institute for Intelligent Systems; Helmholtz Centre Berlin for Materials and Energy; Wuhan UniversityWe report the imaging of short-wavelength spin waves in a continuous nanometer-thick YIG film with a Co stripe patterned on top. Dynamic dipolar coupling between the YIG film and the Co stripe lowers the spin-wave wavelength when spin waves enter the YIG/Co bilayer region from the bare YIG film, causing partial reflection at the YIG/Co edge. We use time-resolved scanning transmission x-ray microscopy to image the mode conversion process down to a wavelength of 280 nm and extract the spin-wave dispersion, decay length, and magnetic damping in the YIG/Co bilayer. We also analyze spin-wave reflection from the YIG/Co edge and its dependence on the wavelength of incoming and transmitted spin waves.Item In-situ TEM study of resistive switching and oxygen vacancy migration in a perovskite complex oxide(2015-11-03) Inkinen, Sampo; Yao, Lide; Perustieteiden korkeakoulu; van Dijken, SebastiaanItem In-situ TEM study on strain-driven flexoelectricity in epitaxial SrTiO3 film(2019-05-08) Vaara, Lauri; Yao, Lide; Perustieteiden korkeakoulu; Van Dijken, SebastiaanItem Influence of intermixing at the Ta/CoFeB interface on spin Hall angle in Ta/CoFeB/MgO heterostructures(2017) Cecot, Monika; Karwacki, Łukasz; Skowroński, Witold; Kanak, Jarosław; Wrona, Jerzy; Zywczak, Antoni; Yao, Lide; van Dijken, Sebastiaan; Barnaś, Józef; Stobiecki, Tomasz; Department of Applied Physics; Nanomagnetism and Spintronics; AGH University of Science and Technology; Adam Mickiewicz University Poznan; Singulus Technologies AGWhen a current is passed through a non-magnetic metal with strong spin-orbit coupling, an orthogonal spin current is generated. This spin current can be used to switch the magnetization of an adjacent ferromagnetic layer or drive its magnetization into continuous precession. The interface, which is not necessarily sharp, and the crystallographic structure of the nonmagnetic metal can both affect the strength of current-induced spin-orbit torques. Here, we investigate the effects of interface intermixing and film microstructure on spin-orbit torques in perpendicularly magnetized Ta/Co40Fe40B20/MgO trilayers with different Ta layer thickness (5 nm, 10 nm, 15 nm), greater than the spin diffusion length. Effective spin-orbit torques are determined from harmonic Hall voltage measurements performed at temperatures ranging from 20 K to 300 K. We account for the temperature dependence of damping-like and field-like torques by including an additional contribution from the Ta/CoFeB interface in the spin diffusion model. Using this approach, the temperature variations of the spin Hall angle in the Ta underlayer and at the Ta/CoFeB interface are determined separately. Our results indicate an almost temperature-independent spin Hall angle of {{\boldsymbol{\theta }}}-{{\boldsymbol{SH}}}^{{\boldsymbol{N}}}\approx -{\bf{0}}.{\bf{2}} θ SH N ≈ - 0. 2 in Ta and a strongly temperature-dependent {{\boldsymbol{\theta }}}-{{\boldsymbol{SH}}}^{{\boldsymbol{N}}} θ SH N for the intermixed Ta/CoFeB interface.Item InSb Nanowire Direct Growth on Plastic for Monolithic Flexible Device Fabrication(AMERICAN CHEMICAL SOCIETY, 2022-01-25) Khayrudinov, Vladislav; Koskinen, Tomi; Grodecki, Kacper; Murawski, Krzysztof; Kopytko, Małgorzata; Yao, Lide; Jiang, Hua; Tittonen, Ilkka Juhani; Lipsanen, Harri; Haggren, Tuomas; Department of Electronics and Nanoengineering; Department of Applied Physics; Ilkka Tittonen Group; NanoMaterials; Harri Lipsanen Group; Military University of Technology WarsawWe report direct growth of InSb nanowires (NWs) and monolithic device fabrication on flexible plastic substrates. The nanowires were grown using metal–organic vapor-phase epitaxy (MOVPE) in self-catalyzed mode. The InSb NWs are shown to form in the zinc-blende crystal structure and to exhibit strong photoluminescence at room temperature. The NW array light-trapping properties are evidenced by reflectance that is significantly reduced compared to bulk material. Finally, the InSb NWs are used to demonstrate a metal–semiconductor–metal photoresistor directly on the flexible plastic substrate. The results are believed to advance the integration of III–V nanowires to flexible devices, and infrared photodetectors in particular.Item Jahn–Teller Distortion Induced Mn2+-Rich Cathode Enables Optimal Flexible Aqueous High-Voltage Zn-Mn Batteries(Wiley, 2021-06-23) Dai, Lixin; Wang, Yan; Sun, Lu; Ding, Yi; Yao, Yuanqing; Yao, Lide; Drewett, Nicholas E.; Zhang, Wei; Tang, Jun; Zheng, Weitao; Department of Applied Physics; Jilin University; CIC energiguneAlthough one of the most promising aqueous batteries, all Zn-Mn systems suffer from Zn dendrites and the low-capacity Mn4+/Mn3+ process (readily leading to the occurrence of Jahn–Teller distortion, which in turn causes structural collapse and voltage/capacity fading). Here, the Mn3+ reconstruction and disproportionation are exploited to prepare the stable, Mn2+-rich manganese oxides on carbon-cloth (CMOs) in a discharged state through an inverted design, which promotes reversible Mn2+/Mn4+ kinetics and mitigates oxygen-related redox activity. Such a 1.65 V Mn2+-rich cathode enable constructing a 2.2 V Zn-Mn battery, providing a high area capacity of 4.16 mA h cm–2 (25 mA h cm–2 for 10 mL electrolyte) and superior 4000-cycle stability. Moreover, a flexible hybrid 2.7 V Zn-Mn battery is constructed using 2-pH hydrogel electrolytes to demonstrate excellent practicality and stability. A further insight has been gained to the commercial application of aqueous energy storage devices toward low-cost, high safety, and excellent energy density.Item Long-term cycling behavior of Mg-doped LiCoO2 materials investigated with the help of laboratory scale X-ray absorption near-edge spectroscopy(Elsevier, 2022-07) Lahtinen, Katja; Labmayr, Maximilian; Mäkelä, Ville; Jiang, Hua; Lahtinen, Jouko; Yao, Lide; Fedorovskaya, Ekaterina O.; Räsänen, Samuli; Huotari, Simo; Kallio, Tanja; Department of Chemistry and Materials Science; Department of Applied Physics; OtaNano; Electrochemical Energy Conversion; NanoMaterials; Surface Science; Aalto University; University of Helsinki; Umicore Finland OyThe use of Li-ion batteries is increasing rapidly. Understanding the processes behind active material aging helps to enhance the materials, and therefore, development of new in situ methods for structural studies is important. In addition, understanding the effect of different synthesis methods on the active material properties is necessary to optimize the material cycle life. In this work, the performance of LiCoO2 doped with Mg during the lithiation step is compared to LiCoO2 prepared using an Mg-doped Co3O4 precursor. In situ laboratory-scale X-ray absorption near-edge spectroscopy is used to analyze the Co valence changes in LiCoO2 to understand the electrochemical behavior of the investigated materials. The maximum reachable Co valence state is found to decrease upon aging, a small decrease indicating a good cycle-life, and this is attributed to the enhanced stacking order, better Mg distribution in the lattice, and fine primary particle size in the material. In the synthesis conditions used in this study, Mg doping during the lithiation step is shown to perform better compared to the precursor doping. Overlithiation is shown to reduce the electrochemical performance of nondoped and precursor-doped LiCoO2 materials but not to affect the cyclability of lithiation-doped LiCoO2.Item Low-loss YIG-based magnonic crystals with large tunable bandgaps(2018-12-01) Qin, Huajun; Both, Gert Jan; Hämäläinen, Sampo J.; Yao, Lide; van Dijken, Sebastiaan; Department of Applied Physics; Nanomagnetism and SpintronicsControl of spin waves in magnonic crystals is essential for magnon-based computing. Crystals made of ferromagnetic metals offer versatility in band structure design, but strong magnetic damping restricts their transmission efficiency. Yttrium iron garnet (YIG) with ultralow damping is the palpable alternative, yet its small saturation magnetization limits dipolar coupling between discrete units. Here, we experimentally demonstrate low-loss spin-wave manipulation in magnonic crystals of physically separated nanometer-thick YIG stripes. We enhance the transmission of spin waves in allowed minibands by filling the gaps between YIG stripes with CoFeB. Thus-formed magnonic crystals exhibit tunable bandgaps of 50–200 MHz with nearly complete suppression of the spin-wave signal. We also show that Bragg scattering on only two units produces clear frequency gaps in spin-wave transmission spectra. The integration of strong ferromagnets in nanometer-thick YIG-based magnonic crystals provides effective spin-wave manipulation and low-loss propagation, a vital parameter combination for magnonic technologies.Item Molybdenum Disulfide/Double-Wall Carbon Nanotube Mixed-Dimensional Heterostructures(WILEY-BLACKWELL, 2022-05-04) Bai, Xueyin; Xu, Zhenyu; Zhang, Qiang; Li, Shisheng; Dai, Yunyun; Cui, Xiaoqi; Yoon, Hoon Hahn; Yao, Lide; Jiang, Hua; Du, Mingde; Zhang, Yi; Kauppinen, Esko I.; Sun, Zhipei; Department of Electronics and Nanoengineering; Department of Applied Physics; Zhipei Sun Group; Centre of Excellence in Quantum Technology, QTF; NanoMaterials; National Institute for Materials ScienceMixed-dimensional heterostructures which combine materials with different dimensions have emerged to expand the scope and functionality of van der Waals heterostructures. Here, a direct synthesis method of molybdenum disulfide/double-wall carbon nanotube (MoS2/DWCNT) mixed-dimensional heterostructures by sulfurating a molten salt, Na2MoO4, on a substrate covered with a DWCNT film is reported. The synthesized heterostructures are comprehensively characterized and their stacking order is confirmed to be MoS2 under the DWCNTs, although the DWCNT film is transferred on the substrate first. Moreover, field-effect transistors based on the heterostructure are fabricated for photodetection, and an abnormal negative photoresponse is discovered due to the strong carrier transfer in the mixed-dimensional heterostructures under light incidence. The MoS2/DWCNT heterostructure results provide a new approach for the synthesis and applications of mixed-dimensional heterostructures.Item Perpendicular magnetic anisotropy in Bi-substituted yttrium iron garnet films(American Institute of Physics, 2023-12-26) Das, Sreeveni; Mansell, Rhodri; Flajšman, Lukáš; Yao, Lide; van Dijken, Sebastiaan; Department of Applied Physics; OtaNano; Nanomagnetism and Spintronics; Aalto UniversityMagnetic garnet thin films exhibiting perpendicular magnetic anisotropy (PMA) and ultra-low damping have recently been explored for applications in magnonics and spintronics. Here, we present a systematic study of PMA and magnetic damping in bismuth-substituted yttrium iron garnet (Bi-YIG) films grown on sGGG (111) substrates by pulsed laser deposition. Films with thicknesses ranging from 5 to 160 nm are investigated. Structural characterization using x-ray diffraction and reciprocal space mapping demonstrates the pseudomorphic growth of the films. The films exhibit perpendicular magnetic anisotropy up to 160 nm thickness, with the zero-magnetic field state changing from fully saturated for low thicknesses to a dense magnetic stripe pattern for thicker films. The films show a ferromagnetic resonance (FMR) linewidth of 100-200 MHz with a Gilbert damping constant of the order of 4 × 10 − 3 . The broad FMR linewidth is caused by inhomogeneities of magnetic properties on micrometer length scales.
