
Zuhuang ChenHarbin Institute of Technology | HIT · School of Materials Science and Engineering
Zuhuang Chen
Doctor of Philosophy
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126
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January 2013 - June 2014
Publications
Publications (126)
Researchers pursuing advanced photoelectric devices have discovered near room-temperature metal–insulator transitions (MIT) in nonvolatile VO2. Despite theoretical investigations suggesting that polaron dynamics mediate the MIT, direct experimental evidence remains scarce. In this study, we present direct evidence of the polaron state in insulating...
Due to traits of CMOS compatibility and scalability, HfO2-based ferroelectrics are promising candidates for next-generation memory devices. However, their commercialization has been greatly hindered by reliability issues, with fatigue being a major impediment. We report the fatigue-free behavior in interface-designed Hf0.5Zr0.5O2-based heterostruct...
Perovskite oxides have a wide variety of physical properties that make them promising candidates for versatile technological applications including nonvolatile memory and logic devices. Chemical tuning of those properties has been achieved, to the greatest extent, by cation-site substitution, while anion substitution is much less explored due to th...
The antiferroelectric-to-ferroelectric (AFE-FE) phase transition has attracted considerable attention due to its potential applications in high-strain transducers, thermal switching, and pulsed-power devices. To deepen our understanding of this transition and enable its functionalities, ultrafast dynamics, especially lattice dynamics of antiferroel...
Anti-ferroelectric thin films are renowned for their signature double hysteresis loops and sheds light on the distinguished energy storage capabilities of dielectric capacitors in modern electronic devices. However, anti-ferroelectric capacitors are still facing the dual challenges of low energy density and efficiency to achieve state-of-the-art pe...
Efforts to combine the advantages of multiple systems to enhance functionlities through solid solution design present a great challenge due to the constraint imposed by the classical Vegard law. Here, we successfully navigate this trade off by leveraging the synergistic effect of chemical doping and strain engineering in solid solution system of Bi...
The bulk and surface electronic structures of Sn-doped β−Ga2O3 thin films have been studied by soft and hard x-ray photoemission spectroscopy (soft PES at 1486.6 eV and HAXPES at 5920 eV). The experimental spectra are compared with density functional theory calculated density of states in the valence band and conduction band. Excellent agreement wa...
In the realm of ferroelectric memories, HfO2-based ferroelectrics stand out because of their exceptional CMOS compatibility and scalability. Nevertheless, their switchable polarization and switching speed are not on par with those of perovskite ferroelectrics. It is widely acknowledged that defects play a crucial role in stabilizing the metastable...
Effective control of heat transfer is vital for energy saving and carbon emission reduction. In contrast to achievements in electrical conduction, active control of heat transfer is much more challenging. Ferroelectrics are promising candidates for thermal switching as a result of their tunable domain structures. However, switching ratios in ferroe...
Dielectric capacitors are desired for electronics and electrical power systems because of their fast charge–discharge speed and high‐power density. Nevertheless, dielectric capacitors typically exhibit lower energy densities in comparison to other energy storage systems like batteries or fuel cells. Among dielectrics, antiferroelectrics have shown...
Electrocaloric cooling, with the advantages of zero global warming potential, high efficiency, smart size, etc., is regarded as a promising next-generation technology for green refrigeration. The exotic negative electrocaloric effect (ECE) in antiferroelectric materials forms the basis to improve the caloric cooling power density, but the underlyin...
The origin of insulating ferromagnetism in epitaxial LaCoO3 films under tensile strain remains elusive despite extensive research efforts are devoted. Surprisingly, the spin state of its Co ions, the main parameter of its ferromagnetism, is still to be determined. Here, the spin state in epitaxial LaCoO3 thin films is systematically investigated to...
Thin ferroelectric layers are capable of generating large dielectric and electromechanical responses at relatively low voltages, thus can be utilized in various applications including energy storage, energy harvesting, sensors, and actuators. Among ferroelectrics, relaxor ferroelectrics (1 − x)Pb(Mg1/3Nb2/3)O3 − xPbTiO3 are particularly interesting...
The origin of insulating ferromagnetism in epitaxial LaCoO3 films under tensile strain remains elusive despite extensive research efforts have been devoted. Surprisingly, the spin state of its Co ions, the main parameter of its ferromagnetism, is still to be determined. Here, we have systematically investigated the spin state in epitaxial LaCoO3 th...
It has been nearly 70 years since the first discovery of anti-ferroelectric. The unique electric field induced phase transition behaviors show great potential in the field of energy storage, electrocaloric, negative capacitance, thermal switching, etc. With the development of advanced synthesis technology and the trend of miniaturization and integr...
Antiferroelectric PbZrO3 has attracted renewed interest in recent years because of its unique properties and wide range of potential applications. However, the nature of antiferroelectricity and its evolution with the electric field and temperature remain controversial, mostly due to the difficulty of obtaining high-quality single-crystal samples....
One major challenge in heterogeneous catalysis is to reduce the usage of noble metals while maintaining the overall catalytic stability and efficiency in various chemical environments. In this work, a series of high‐entropy catalysts are synthesized by a chemical dealloying method and find the increased entropy effect and non‐noble metal contents w...
With the combination of the advantages of both Zn-Ag and Zn-air batteries, hybrid Zn-Ag/Zn-air batteries nevertheless suffer greatly from structural instability and activity degradation of the catalysts at the air electrodes. Herein, we introduce a scalable chemical dealloying procedure to synthesize mutually interacting and stable bifunctional cat...
Designing and fabricating bifunctional electrocatalysts for both the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is crucial to high-performance rechargeable metal–air batteries. Herein, we introduce a generic dealloying procedure to fabricate nanoporous spinel high-entropy oxides (HEO) (AlCoFeMoCr)3O4 as the OER catalysts, i...
Although epitaxial strain imparted by lattice mismatch between a film and the underlying substrate has led to distinct structures and emergent functionalities, the discrete lattice parameters of limited substrates, combined with strain relaxations driven by film thickness, result in severe obstructions to subtly regulate electro‐elastic coupling pr...
Controlling magnetization dynamics is imperative for developing ultrafast spintronics and tunable microwave devices. However, the previous research has demonstrated limited electric-field modulation of the effective magnetic damping, a parameter that governs the magnetization dynamics. Here, we propose an approach to manipulate the damping by using...
Topological spin/polarization structures in ferroic materials continue to draw great attention as a result of their fascinating physical behaviors and promising applications in the field of high‐density nonvolatile memories as well as future energy‐efficient nanoelectronic and spintronic devices. Such developments have been made, in part, based on...
Spintronic elements based on spin transfer torque have emerged with potential for on‐chip memory, but they suffer from large energy dissipation due to the large current densities required. In contrast, an electric‐field‐driven magneto‐electric storage element can operate with capacitive displacement charge and potentially reach 1–10 µJ cm−2 switchi...
Nanoscale phase mixtures in transition metal oxides (TMOs) often render these materials susceptible to external stimuli (electric field, mechanical stress, etc.), which can lead to rich functional properties and device applications. Here, direct observation and multi-field manipulation of a nanoscale mixture of brownmillerite SrFeO2.5 (BM-SFO) and...
Multiferroic materials with multifunctional characteristics play a critical role in the field of microelectronics. In a perovskite oxide, ferroelectric polarization and ferromagnetism usually cannot coexist in a single-phase material at the same time. In this work, we design a superlattice structure composed of alternating BiFeO3 and BiMnO3 layers...
A room temperature amorphous ferromagnetic oxide semiconductor can substantially reduce the cost and complexity associated with utilizing crystalline materials for spintronic devices. We report a new material (Fe0.66Dy0.24Tb0.1)3O7-x (FDTO), which shows semiconducting behavior with reasonable electrical conductivity (~500 mOhm-cm), an optical band-...
Negative and near-zero Poisson's ratio materials are mechanical metamaterials that host an improved strain energy absorption property in respect of conventional materials. By using first-principles calculations, we report the negative and near-zero Poisson's ratios in van der Waals (vdW) heterostructures, such as graphene/hexagonal molybdenum disul...
Low‐dimensional magnetism has been boosted by the recent discovery of the ferromagnetism in layered two‐dimensional (2D) semiconductors. Although the macroscopic magnetic moments of 2D ferromagnets are weak, the anomalous Hall effect (AHE) can serve as a versatile electric probe to their magnetic properties. Here, the nonvolatile electric‐field man...
Multi-component high-entropy alloys (HEAs) and their corresponding high-entropy oxides (HEOs) provide great flexibility in modulating the electronic properties and catalytic activities due to the interaction of five or more different metal species. Herein, a top-down dealloying strategy is used to fabricate various noble-metal-free nanoprous HEAs c...
The stability of a purely tetragonal phase relative to the nominal rhombohedral phase in ultrathin BiFeO3 films is investigated using thermodynamics and phase-field simulations. The thermodynamic analysis demonstrates the possible presence of a purely tetragonal state primarily due to the interfacial effect from the constraint of the adjacent layer...
Ir‐based binary and ternary alloys are effective catalysts for the electrochemical oxygen evolution reaction (OER) in acidic solutions. Nevertheless, decreasing the Ir content to less than 50 at% while maintaining or even enhancing the overall electrocatalytic activity and durability remains a grand challenge. Herein, by dealloying predesigned Al‐b...
The ability to tailor a new crystalline structure and associated functionalities with a variety of stimuli is one of the key issues in material design. Developing synthetic routes to functional materials with partially absorbed nonmetallic elements (i.e., hydrogen and nitrogen) can open up more possibilities for preparing novel families of electron...
We have studied low-energy configurations in two-dimensional arrays consisting of Ising-type dipolar coupled nanomagnets lithographically defined onto a two-dimensional Cairo lattice, thus dubbed the dipolar Cairo lattice. Employing synchrotron-based photoemission electron microscopy (PEEM), we perform real-space imaging of moment configurations ac...
The drastic change of properties near the percolation threshold usually limits the practical applications of percolative composite materials. In this work, a tri-phase system, i.e. a BaTiO3 (BTO)/Ni0.5Zn0.5Fe2O4 (NZFO)/BaFe12O19 (BFO) ceramic composite, is proposed and investigated in detail. The BFO phase was in situ formed during a hybrid process...
Ferroelastic switching in ferroelectric/multiferroic oxides plays a crucial role in determining their dielectric, piezoelectric, and magnetoelectric properties. In thin films of these materials, however, substrate clamping is generally thought to limit the electric-field- or mechanical-force-driven responses to the local scale. Here, we report mech...
Above-band-gap optical illumination of compressively strained
BiFeO3 induces a transient reversible transformation from a state of coexisting tilted tetragonal-like and rhombohedral-like phases to an untilted tetragonal-like phase. Time-resolved synchrotron x-ray diffraction reveals that the transformation is induced by an ultrafast optically indu...
Above-band-gap optical illumination of compressively strained BiFeO3 induces a transient reversible transformation from a state of coexisting tilted tetragonal-like and rhombohedral-like phases to an untilted tetragonal-like phase. Time-resolved synchrotron x-ray diffraction reveals that the transformation is induced by an ultrafast optically induc...
[111]‐Oriented perovskite oxide films exhibit unique interfacial and symmetry breaking effects, which are promising for novel quantum materials as topological insulators and polar metals. However, due to strong polar mismatch and complex structural reconstructions on (111) surfaces/interfaces, it is still challenging to grow high quality [111] pero...
We explore the thermodynamics in two-dimensional arrays consisting of Ising-type nanomagnets lithographically arranged onto random sites and angular orientations. Introducing these basic spin-glass ingredients, we study the characteristic features of the low-energy states achieved, following thermal-annealing protocols. From direct visualization of...
Achieving high voltage and safety simultaneously in energy storage devices can greatly advance the development of flexible and wearable electronics. Thus, flexible aqueous asymmetric lithium ion supercapacitors with high voltage attract the interest of many researchers. Here, a new flexible aqueous asymmetric lithium ion supercapacitor with high vo...
We report the pulsed‐laser deposition of epitaxial double‐perovskite Bi2FeCrO6 (BFCO) films on the (001)‐, (110), and (111)‐oriented single‐crystal SrTiO3 substrates. All of the BFCO films with various orientations show the 1/21/21/2 and 3/23/23/2 superlattice‐diffraction peaks. The intensity ratios between the 1/21/21/2‐superlattice and the main 1...
Understanding and controlling the domain evolution under external stimuli in multiferroic thin films is critical to realizing nanoelectronic devices, including for non-volatile memory, data storage, sensors, and optoelectronics. In this article, we studied the shear-strain effect on the domain evolution with temperature in highly strained BiFeO 3 t...
Ferroelectric and ferroelastic 109° domain structure has great potentialities in ferroelectric and magnetoelectric devices. Understanding their structure is crucial to control the domain configurations for potential applications. In this work, a series of BiFeO 3 (BFO) thin films with various thicknesses are investigated by piezoelectric force micr...
Magnetic monopoles, proposed as elementary particles that act as isolated magnetic south and north poles, have long attracted research interest as magnetic analogs to electric charge. In solid-state physics, a classical analog to these elusive particles has emerged as topological excitations within pyrochlore spin ice systems. We present the first...
Spintronic devices based on antiferromagnetic (AFM) materials hold the promise of fast switching speeds and robustness against magnetic fields. Different device concepts have been predicted and experimentally demonstrated, such as low-temperature AFM tunnel junctions that operate as spin-valves, or room-temperature AFM memory, for which either ther...
Spintronic devices based on antiferromagnetic (AFM) materials hold the promise of fast switching speeds and robustness against magnetic fields. Different device concepts have been predicted and experimentally demonstrated, such as low-temperature AFM tunnel junctions that operate as spin-valves, or room-temperature AFM memory, for which either ther...
Electric-field control of magnetism requires deterministic control of the magnetic order and understanding of the magnetoelectric coupling in multiferroics like BiFeO3 and EuTiO3. Despite this critical need, there are few studies on the strain evolution of magnetic order in BiFeO3 films. Here, in (110)-oriented BiFeO3 films, we reveal that while th...
Complex-oxide materials tuned to be near phase-boundaries via chemistry/composition, temperature, pressure, etc. are known to exhibit large susceptibilities. Here, we observe a strain-driven, nanoscale phase competition in epitaxially-constrained Bi0.7La0.3FeO3 thin films near the antipolar-nonpolar phase boundary and explore the evolution of the s...
The desire for low-power/voltage operation of devices is driving renewed interest in understanding scaling effects in ferroelectric thin films. As the dimensions of ferroelectrics are reduced, the properties can vary dramatically, including the robust scaling relationship between coercive field (E_c) and thickness (d), also referred to as the Janov...
The potential application of artificial spin ice in magnetic nanodevices provides a strong drive to investigate different lattice geometries. Here, we combine components of a recently investigated artificial spin ratchet with components of the prototypical square lattice to form a geometrically frustrated artificial spin ice system where Ising-type...
Demonstration of ultra-low energy switching mechanisms is an imperative for continued improvements in computing devices. Ferroelectric (FE) and multiferroic (MF) orders and their manipulation promises an ideal combination of state variables to reach atto-Joule range for logic and memory (i.e., ~ 30X lower switching energy than nanoelectronics). In...
Demonstration of ultra-low energy switching mechanisms is an imperative for continued improvements in computing devices. Ferroelectric (FE) and multiferroic (MF) orders and their manipulation promises an ideal combination of state variables to reach atto-Joule range for logic and memory (i.e., ~ 30X lower switching energy than nanoelectronics). In...
Ferroelectricity is generally deteriorated or even vanishes when the ferroelectric films are downsized to unit cell scale. To maintain and enhance the polarization in nanoscale ferroelectrics are of scientific and technological importance. Here, giant polarization sustainability is reported in a series of ultrathin PbTiO3 films scaled down to three...
Emergent phenomena at polar-nonpolar oxide interfaces have been studied intensely in pursuit of next-generation oxide electronics and spintronics. Here we report the disentanglement of critical thicknesses for electron reconstruction and the emergence of ferromagnetism in polar-mismatched LaMnO3/SrTiO3 (001) heterostructures. Using a combination of...
Emergent phenomena at polar-nonpolar oxide interfaces have been studied intensely in pursuit of next-generation oxide electronics and spintronics. Here we report the disentanglement of critical thicknesses for electron reconstruction and the emergence of ferromagnetism in polar-mismatched LaMnO3/SrTiO3 (001) heterostructures. Using a combination of...
A strain driven orthorhombic (O) to rhombohedral (R) phase transition is reported in La-doped BiFeO3 thin films on silicon substrates. Biaxial compressive epitaxial strain is found to stabilize the rhombohedral phase at La concentrations beyond the morphotropic phase boundary (MPB). By tailoring the residual strain with film thickness we demonstrat...
Antiferroelectric PbZrO3 is being considered for a wide range of applications where the competition between centrosymmetric and non-centrosymmetric phases is important to the response. Here, we focus on the epitaxial growth of PbZrO3 thin films and understanding the chemistry-structure coupling in Pb1+δZrO3 (δ = 0, 0.1, 0.2). High-quality, single-p...