Ferroelectric Substrate Research Articles

Nonvolatile control of valley related properties and valley-contrasting transport in multiferroic van der Waals heterostructures

It is highly desirable to tune valley-related property through reversible and electrically nonvolatile methods. Taking the VSiGeP4/Al2S3 heterostructure as an example, we demonstrate that the valley splitting and valley-contrasting transport in VSiGeP4 monolayer are significantly enhanced by using a ferroelectric Al2S3 substrate. The vertical strain and electric field can modulate valley splitting, magnetic anisotropy, and magnetic ground state. The valley splitting is mainly governed by charge transfer between the two sublayers. The valley splitting and valley-contrasting transport are highly tunable when the ferroelectric polarization state of the Al2S3 substrate is the upward direction. In contrast, the valley splitting is rather robust when the ferroelectric polarization state is switched to the opposite direction. Furthermore, we propose to use electrical conversion between two opposite ferroelectric polarization states to obtain nonvolatile control of valley-related properties. Our research provides a proof-of-concept scheme to achieve electrical control based on multiferroic van der Waals heterostructures.

Optical imaging of ferroelectric domains in periodically poled lithium niobate using ferroelectric liquid crystals

Ferroelectric liquid crystals exhibiting a chiral smectic C* phase are deposited on z cut periodically poled lithium niobate substrates and investigated by polarized optical microscopy. While the pure substrates placed between crossed polarizers and observed in transmission appear dark, uniformly aligned liquid crystal films deposited on these substrates show alternating domains with varying brightness. This effect can be attributed to the well-known coupling between the direction of the spontaneous polarization and the optical axis in the birefringent ferroelectric smectic C* phase. Quantitative measurements of the tilt angle between the local optical axis and the smectic layer normal confirm antiparallel orientations of spontaneous polarization of the liquid crystal from domain to domain, as expected by the periodic poling of the lithium niobate substrate. This effect provides a valuable non-destructive method of optical inspection of the quality of periodically poled ferroelectric substrates, which plays an important role in achieving quasi-phase-matching in non-linear optical applications.

Ferroelastic strain control of multiple nonvolatile resistance tuning in Cr:In2O3/PMN-PT(111) multiferroic heterostructures

Strain can significantly affect the electronic structure and functional properties of dilute magnetic semiconductors. As a wide bandgap transparent semiconductor, doped In2O3 has also received extensive attention for the modulation of physical properties by lattice strain due to its excellent functional properties. Here, we epitaxially grew the Cr:In2O3 thin film on the (111)-oriented 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 (PMN–PT) ferroelectric single-crystal substrate. By applying an electric field to PMN–PT, multiple reversible and nonvolatile resistance states can be achieved at room temperature. Utilizing in situ XRD, different strain states corresponding to different resistance states induced by the ferroelastic domain switching of the PMN–PT were characterized. Based on first-principles calculations, the influence of lattice strain on the resistivity of the Cr:In2O3 was discussed. These results offer a route for the design of multiple-valued nonvolatile memory devices and multiple functional magneto-electric devices based on dilute magnetic semiconductors.

Wide-Range and Multistate Work Functions of Organometallic Halide Perovskite Films Regulated by Ferroelectric Substrates.

Work function of organometallic halide perovskite (OHP) films is one of the most crucial photoelectric properties, which dominates the carrier dynamics in OHP-based devices. Despite surface treatments by additives being widely used to promote crystallization and passivate defects in OHP films, these chemical strategies for modulation of work functions face two trade-offs: homogeneity on the surface versus along the thickness; the range versus the accuracy of modulation. Herein, by using ferroelectric substrates of uniform polarization and subnanometer roughness, homogeneous CH3NH3PbI3 films are fabricated with five states of work functions with large spanning (∼0.8 eV) and high precision (sd ∼ 0.01 eV). We reveal that the ferroelectric polarizations and the smooth surfaces regulate CH3NH3+ orientations and suppress distortions of PbI6 octahedrons. The wide-range and multistate work functions originate from the ordered CH3NH3+ orientations and PbI6 octahedrons, which result in intensity enhancements and wavelength shifts in photoluminescence with a 30-fold increase of photoexcited carrier lifetime.

Ultrasensitive Graphene Field-Effect Biosensors Based on Ferroelectric Polarization of Lithium Niobate for Breast Cancer Marker Detection.

Herein, we present a novel ultrasensitive graphene field-effect transistor (GFET) biosensor based on lithium niobate (LiNbO3) ferroelectric substrate for the application of breast cancer marker detection. The electrical properties of graphene are varied under the electrostatic field, which is generated through the spontaneous polarization of the ferroelectric substrate. It is demonstrated that the properties of interface between graphene and solution are also altered due to the interaction between the electrostatic field and ions. Compared with the graphene field-effect biosensor based on the conventional Si/SiO2 gate structure, our biosensor achieves a higher sensitivity to 64.7 mV/decade and shows a limit of detection down to 1.7 fM (equivalent to 12 fg·mL-1) on the detection of microRNA21 (a breast cancer marker). This innovative design combining GFETs with ferroelectric substrates holds great promise for developing an ultrahigh-sensitivity biosensing platform based on graphene that enables rapid and early disease diagnosis.

Polarization Coupling between Ferroelectric Liquids and Ferroelectric Solids: Effects of the Fringing Field Profile

Recent experiments devoted to characterizing the behavior of sessile ferroelectric liquid droplets on ferroelectric solid substrates have shown the existence of a droplet electromechanical Rayleigh-like instability. The instability is induced by the bulk polarization of the ferroelectric fluid, which couples to the polarization of the underlying substrate through its fringing field and solid–fluid interface coupling. With the aim of characterizing this phenomenon, namely the coupling between the polarizations of a fluid and a solid material, we studied the behavior of ferroelectric liquid droplets confined between two solid substrates, arranged in different configurations, realized to generate fringing fields with different profiles. The results show that the features of the droplets instability are indeed affected by the specific fringing field shape in a way dominated by the minimization of the electrostatic energy associated with the bulk polarization of the ferroelectric fluid.

Microwave heterostructures in the form of submicron Y<sub>3</sub>Fe<sub>5</sub>O<sub>12</sub> films on non-oriented ferroelectric ceramic substrates: synthesis, properties, and prospects for applications

In the work monolithic structures of yttrium iron garnet (YIG, Y3Fe5O12) with a thickness of about 2 μm were obtained on ferroelectric ceramic substrates based on PbZr0.45Ti0.55O3 (PZT) and Ba0.4Sr0.6TiO3 (BST). The Y3Fe5O12 layer was deposited by ion beam sputtering deposition on substrates 400 μm thick by sputtering a polycrystalline Y3Fe5O12 target with with argon ions. The heterostructures were crystallized by annealing in air at a temperature of 820 °C for 5 min. The results of the characteristic X-ray radiation method showed that the elemental composition of the monolithic heterostructure corresponds to the specified one. During X-ray studies, it was found that the YIG crystallization process is completed and the resulting structure is single-phase. The results of magnetic and ferromagnetic resonance studies indicate the possibility of using the obtained heterostructures in logic circuits based on spin waves with low scattering, in memory elements, as well as in electrically controlled microwave devices.

Two-dimensional 1T′ α -VXY (X = S, Se, Te; Y = Cl, Br, I): A multifunctional vanadium chalcohalide family with room-temperature ferromagnetism and sliding ferroelectricity

Two-dimensional (2D) ferromagnetic materials with Curie temperature (Tc) above room temperature have great potential ranging from spintronics to information processing and storage. Here, we computationally design a series of 1T′α-VXY (X = S, Se, Te; Y = Cl, Br, I) monolayers with the X and Y atoms arranged alternately in the 2D plane. VXY monolayers are ferromagnetic semiconductors with Tc much higher than room temperature. Furthermore, the symmetry breaking of VXY bilayers leads to sliding ferroelectricity with large reversible out-of-plane electric polarization and moderate interlayer sliding barriers. We further show that half-metal-to-semiconductor nonvolatile field-effect switching can be achieved in multiferroic van der Waals heterostructures composed of VXY and In2S3 ferroelectric substrates due to the synergistic effect between the polarization field-induced band edge shifting and the selective charge transfer at the interface. These findings reveal a promising role of 2D Janus 1T′α-VXY in spintronics, ferroelectric, and multiferroic device applications.

Real-time tunable notched waveguide based on voltage controllable ferroelectric resonator.

In the present study, we have devised and conducted an investigation into a real-time tunable notched waveguide, employing a voltage-controllable plasmonic resonator. This plasmonic resonator is meticulously engineered from a ferroelectric substrate featuring a compound multilayer structure, thereby conferring it with the remarkable capability of flexible permittivity control. Furthermore, we have implemented two non-intersecting Archimedean spiral electrodes on the surface of the ferroelectric substrate, dedicated to applying the bias field onto the controllable plasmonic ferroelectric resonator (CPFR). Notably, our system affords the capability to finely tune both the magnetic and electric modes, achieving precise adjustments of 8.7% and 11%, respectively. The performance is complemented by minimal insertion loss, rapid response times, and a broad range of potential applications, positioning it as a candidate for a diverse array of notched waveguide scenarios.

Multiple factors of regulation for transient negative capacitance in PbZr(1−x)Ti(x)O3 ferroelectric thin films

The negative capacitance (NC) of ferroelectric (FE) materials can effectively break the ‘Boltzmann tyranny’ and drive the continuation scaling of Moore’s law. In this work, to find a novel way for amplifying the transient NC, a series network of external resistors and PbZr(1−x)Ti(x)O3 (PZT) FE capacitors was constructed. Uniform modeling and simulation were performed using Kirchhoff’s current law, electrostatics equations, and Landau–Khalatnikov equations. The derived results revealed that the mismatch of switching rate between free charge and polarization during FE domain switching is responsible for the transient NC generation. Some interesting results were obtained for the regulation of the transient NC by various factors such as the strain between the FE film and substrate, the viscosity coefficient, the ratio of Ti components, the external resistance magnitude, and the operating temperature. This work provides considerable insight into the control of FE transient NC, and offers guidance for obtaining larger and longer transient NC in the widely used PZT thin films.

Controllable Modulation of the Electronic Properties of a Two-Dimensional Ambipolar Semiconductor by Interface Ferroelectric Polarization.

Precise control of charge carrier type and density of two-dimensional (2D) ambipolar semiconductors is the prerequisite for their applications in next-generation integrated circuits and electronic devices. Here, by fabricating a heterointerface between a 2D ambipolar semiconductor (hydrogenated germanene, GeH) and a ferroelectric substrate (PbMg1/3Nb2/3O3-PbTiO3, PMN-PT), fine-tuning of charge carrier type and density of GeH is achieved. Due to ambipolar properties, proper band gap, and high carrier mobility of GeH, by applying the opposite local bias (±8 V), a lateral polarization in GeH is constructed with a change of work function by 0.6 eV. Besides, the built-in polarization in GeH nanoflake could promote the separation of photoexcited electron-hole pairs, which lead to 4 times enhancement of the photoconductivity after poling by 200 V. In addition, a gradient regulation of the work function of GeH from 4.94 to 5.21 eV by adjusting the local substrate polarization is demonstrated, which could be used for data storage at the micrometer size by forming p-n homojunctions. This work of constructing such heterointerfaces provides a pathway for applying 2D ambipolar semiconductors in nonvolatile memory devices, photoelectronic devices, and next-generation integrated circuit.

Fluid jets and polar domains, on the relationship between electromechanical instability and topology in ferroelectric nematic liquid crystal droplets.

Ferroelectric nematic liquid crystals are a class of recently discovered fluid materials formed by highly polar molecules that spontaneously align along a common direction, giving rise to a macroscopic polarization P. Since the polarization vector is locally collinear to the optical axis n, the study of the spatial patterns of n enables deducing the structure of P. We have carried on such topological study on ferroelectric nematic droplets confined between two solid ferroelectric substrates both when the droplet is in equilibrium and during a jet-emission phase that takes place when the solid surfaces become sufficiently charged. We find that in equilibrium the droplet splits in striped domains in which P has alternating directions. When these domains extend close to the droplets' perimeter, P adopts a π-twisted structure to minimize accumulation of polarization charges. As the substrate surface charge is increased above threshold, fluid jets are emitted with a quasi-periodic pattern, a behaviour suggesting that their location is governed by an electrofluidic instability on the droplets' rim, in turn indicating the absence of specific trigger points. Soon after their emission, the jet periodicity is lost; some jets retract while other markedly grow. In this second regime, jets that grow are those that more easily connect to polar domains with P along the jet axis. Occasionally, ejection of isolated spikes also occurs, revealing locations where polarization charges have accumulated because of topological patterns extending on length scales smaller than the typical domain size.

Electric field control of the ferromagnetic resonance linewidth in synthetic antiferromagnetic heterostructure

In this study, we present a novel approach to control the microwave properties of a Co/Ru/FeNi film, characterized by strong antiferromagnetic coupling and in plane uniaxial anisotropy. The film is fabricated on a Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) ferroelectric substrate using the magnetron oblique sputtering. Our experimental results demonstrate a remarkable non-volatile mediation of the ferromagnetic resonance (FMR) field and linewidth by applying the perpendicular-bias electric field. The observed asymmetric butterfly curve indicates the existence of electric mediation dominated by strain effect. Moreover, we investigate the angular dependence of FMR under different electric field, which reveals changes in magnetic anisotropy including FMR field. Notably, the FMR linewidth exhibits a distinctive four-fold anisotropy. Through microstructure analysis of the film surface, we identify that the origin of this FMR linewidth anisotropy is attributed to the two-magnon scattering induced by the oblique sputtering.

Giant room-temperature modulation of magnetic anisotropy by electric fields in CoFeB/(011)-PMN-PT multiferroic heterostructures with two distinct initial magnetic anisotropies

This paper reports that the in situ growth magnetic field (Hg) during magnetic-phase CoFeB deposition impacts the electric-field control of magnetic anisotropy in Co40Fe40B20/(011)-Pb(Mg1/3Nb2/3)0.7Ti0.3O3 [CoFeB/(011)-PMN-PT] composite multiferroic heterostructures at room temperature. In the Hg1 mode (in situ Hg along the [011¯] direction of the ferroelectric PMN-PT substrate), the electric-field-controlled modulation ratios of the magnetic coercivity HC and saturation magnetic field HS are approximately −47% and +156%, respectively. However, in the Hg2 mode (in situ Hg along the [100] direction of the ferroelectric PMN-PT substrate) of the CoFeB/(011)-PMN-PT multiferroic heterostructure, the electric-field-controlled modulation ratios of the magnetic coercivity HC and saturation magnetic field HS can reach as high as +162% and +393%, respectively. Moreover, the electric-field-controlled magnetic coercive field HC exhibits a butterfly shape when plotted versus the applied electric fields in both modes, which matches the in-plane butterfly strain loop of the ferroelectric PMN-PT substrate. However, the electric-field-controlled saturation magnetic field HS presents a square loop, which is very consistent with the ferroelectric loop of the PMN-PT substrate. This result may be ascribed to the distinct pathway of the ferroelastic domain switching in the (011)-oriented PMN-PT substrate. This study provides a new idea for the design of spintronic devices based on multiferroic heterostructures.

Ab Initio Characterization of Magnetoelectric Coupling in Fe/BaTiO3, Fe/SrTiO3, Co/BaTiO3 and Co/SrTiO3 Heterostructures

Magneto-electric coupling is a desirable property for a material used in modern electronic devices to possess due to the favorable possibilities of tuning the electronic properties using a magnetic field and vice versa. However, such materials are rare in nature. That is why the so-called superlattice approach to creating such materials is receiving so much attention. In the superlattice approach, the functionality of a combined heterostructure depends on the interacting components and can be adjusted depending on the desired property. In the present paper, we present supercells of ferromagnetic thin films of Fe and Co deposited on ferroelectric and piezoelectric substrates of BaTiO3 and SrTiO3 that exhibit magnetism, ferroelectric polarization and piezoelectric effects. Within the structures under investigation, magnetic moments can be tuned by an external electric field via the ferroelectric dipoles. We investigate the effect of magnetoelectric coupling by means of ab initio spin-polarized and spin–orbit calculations. We study the structural, electronic and magnetic properties of heterostructures, and show that electrostriction can reduce the magnitude of the magnetization vector of a ferromagnet. This approach can become the basis for controlling the properties of one of the ferromagnetic layers of a superconducting spin valve, and thus the superconducting properties of the valve.

Application the Ion Beam Sputtering Deposition Technique for the Development of Spin-Wave Structures on Ferroelectric Substrates

The microwave properties of structures in the form of the 2 μm iron-yttrium garnet (YIG) films, grown by the ion beam sputtering deposition method on epitaxially mismatched substrates of ferroelectric ceramics based on lead zirconate titanate (PZT, PbZr0.45Ti0.55O3), are discussed. The obtained structures were formed and pre-smoothed by the ion beam planarization substrates with the use of an anti-diffusion layer of titanium dioxide TiO2. The atomic force microscopy showed that the planarization of the substrates allows for reaching a nanoscale level of roughness (up to 10 nm). The presence of smooth plane–parallel interfaces of YIG/TiO2 and TiO2/PZT is evidenced by scanning electron microscopy performed in focused gallium ion beams. Ferromagnetic resonance spectroscopy revealed a broadening in the absorption line of the ferrite garnet layers in the resonance ≈ 100 Oe. This broadening is associated with the presence of defects caused by the of the ceramic substrate non-ideality. The estimated damping coefficient of spin waves turned out to be ~10−3, which is two orders of magnitude higher than in an ideal YIG single crystal. The YIG/TiO2/PZT structures obtained can be used for the study of spin waves.

Optical control of mass ejection from ferroelectric liquid droplets: A possible tool for the actuation of complex fluids

We report on the optical control of the recently observed electromechanical instability of ferroelectric liquid droplets exposed to the photovoltaic field of a lithium niobate ferroelectric crystal substrate. The ferroelectric liquid is a nematic liquid crystal in which almost complete polar ordering of the molecular dipoles generates an internal macroscopic polarization locally collinear to the mean molecular long axis. Upon entering the ferroelectric phase, droplets irradiated by unfocused beam undergo an electromechanical instability and disintegrate by the explosive emission of fluid jets. We show here that the regions of jets emission can be controlled by focusing the light beam in areas close to the droplet’s edge. Once emitted, the fluid jets can be walked by moving the beam up to millimeter distance from the mother droplet. Reverting the lithium niobate substrate, jets become thinner and show the tendency of being repelled by the beam instead of being attracted, thus offering an additional tool for their optical manipulation. These observations may pave the way to intriguing applications of ferroelectric nematic fluids related to manipulation, actuation, and control of soft, flexible materials.

Ferroelectric control of magnetic anisotropy of 5d transition metal monolayers

Electric field control of magnetism using ferroelectric materials offers promising applications in low-power spintronics. We have conducted systematic density functional theory calculations to investigate the magnetic properties of epitaxial $5d$ transition metal monolayers on a ferroelectric substrate: $\mathrm{PbTi}{\mathrm{O}}_{3}$ (PTO). Our study reveals that the magnetocrystalline anisotropy energy of the osmium monolayer is significantly enhanced to 18.1 meV/Os in the upward polarization state and, moreover, the anomalous Hall coefficient of osmium/PTO film is tunable by reversing the electric polarization of the PTO substrate. Additionally, the electric polarization reversal in PTO rotates the easy magnetization axis of the iridium and platinum monolayers by ${90}^{\ensuremath{\circ}}$, which is attributed to the rearrangement of interfacial charges. Our findings suggest an efficient approach to control the magnetization direction of monoatomic layers and provide valuable insights for the development of low-energy spintronics devices.

Walking Ferroelectric Liquid Droplets with Light.

The motion of ferroelectric liquid sessile droplets deposited on a ferroelectric lithium niobate substrate can be controlled by a light beam of moderate intensity irradiating the substrate at a distance of several droplet diameters from the droplet itself. The ferroelectric liquid is a nematic liquid crystal, in which almost complete polar ordering of the molecular dipoles generates an internal macroscopic polarization locally collinear to the mean molecular long axis. Upon entering the ferroelectric phase, droplets are either attracted toward the center of the beam or repelled, depending on the side of the lithium niobate exposed to light irradiation. Moreover, moving the beam results in walking the ferroelectric droplet over long distances on the substrate. This behavior is understood as due to the coupling between the polarization of the ferroelectric droplet and the polarization photoinduced in the irradiated region of the lithium niobate substrate. Indeed, the effect is not observed in the conventional nematic phase, suggesting the crucial role of the ferroelectric liquid crystal polarization.

Light-Controlled Magnetoelastic Effects in Ni/BaTiO3 Heterostructures

Magnetoelastic and magnetoelectric coupling in the artificial multiferroic heterostructures facilitate valuable features for device applications such as magnetic field sensors and electric-write magnetic-read memory devices. In ferromagnetic/ferroelectric heterostructures, the intertwined physical properties can be manipulated by an external perturbation, such as an electric field, temperature, or a magnetic field. Here, we demonstrate the remote-controlled tunability of these effects under visible, coherent, and polarized light. The combined surface and bulk magnetic study of domain-correlated Ni/BaTiO3 heterostructures reveals that the system shows strong sensitivity to the light illumination via the combined effect of piezoelectricity, ferroelectric polarization, spin imbalance, magnetostriction, and magnetoelectric coupling. A well-defined ferroelastic domain structure is fully transferred from a ferroelectric substrate to the magnetostrictive layer via interface strain transfer. The visible light illumination is used to manipulate the original ferromagnetic microstructure by the light-induced domain wall motion in ferroelectric substrates and consequently the domain wall motion in the ferromagnetic layer. Our findings mimic the attractive remote-controlled ferroelectric random-access memory write and magnetic random-access memory read application scenarios, hence facilitating a perspective for room temperature spintronic device applications.