Liquid Gating Research Articles

Detection and tuning of spin-orbit interactions on inclined-grown Bi2O2Se nanoplates

Inclined semiconductor Bi2O2Se nanoplates of a high crystal quality were prepared via chemical vapor deposition, and a circular photogalvanic effect (CPGE) current was detected in them. The CPGE current in the Bi2O2Se nanoplate reached 100 nA/W, which is far beyond what has been found in other two-dimensional (2D) materials, e.g., Bi2Se3, WSe2, and Sb2Te3, as well as some 2D electron systems such as AlxGa1-xN/GaN heterostructures, indicating the large spin–orbit coupling (SOC) in inclined Bi2O2Se. To tune the strength of the SOC, an ionic liquid gate was applied to the Bi2O2Se nanoplate. The significant increase in the CPGE current that appeared with the application of the positive gate voltage indicates that the gate can further break spatial inversion symmetry, leading to enhanced SOC. Unlike the in-plane Bi2O2Se, the bottom surface of which has electrostatic interactions with the mica substrate and hence is naturally asymmetric with the top surface, the inclined-grown nanoplate has two Bi2O2Se-air interfaces. Therefore, the large CPGE current in the inclined Bi2O2Se shows that strong SOC is intrinsic to the Bi2O2Se lattice instead of the interfaces, and Bi2O2Se is a prospective material in the application of spintronic devices.

Performance prediction of magnetorheological fluid‐based liquid gating membrane by kriging machine learning method

AbstractA smart liquid gating membrane is a responsive structural material as a pressure‐driven system that consists of solid membrane and dynamic liquid, responding to the external field. An accurate prediction of rheological and mechanical properties is important for the designs of liquid gating membranes for various applications. However, high predicted accuracy by the traditional sequential method requires a large amount of experimental data, which is not practical in some situations. To conquer these problems, artificial intelligence has promoted the rapid development of material science in recent years, bringing hope to solve these challenges. Here we propose a Kriging machine learning model with an active candidate region, which can be smartly updated by an expected improvement probability method to increase the local accuracy near the most sensitive search region, to predict the mechanical and rheological performance of liquid gating system with an active minimal size of experimental data. Besides this, this new machine learning model can instruct our experiments with optimal size. The methods are then verified by liquid gating membrane with magnetorheological fluids, which would be of wide interest for the design of potential liquid gating applications in drug release, microfluidic logic, dynamic fluid control, and beyond.

Outside Front Cover: Volume 1 Issue 1

Interdisciplinary MaterialsVolume 1, Issue 1 p. i-i COVER IMAGEOpen Access Outside Front Cover: Volume 1 Issue 1 First published: 31 January 2022 https://doi.org/10.1002/idm2.12015AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Abstract Outside Front Cover: Liquid gating membrane is a new kind of structural materials, response to an applied force as a pressure-driven system. To address the long-term high consumption caused by traditional “experimental trial method”, a machine learning algorithm is trained to effectively integrate material structure, composition and performance. This cover shows machine learning technology, offers a promising approach to exchange negligible machine resources for valuable researcher time, thus accelerating and optimizing the development of liquid gating technology. Volume1, Issue1January 2022Pages i-i RelatedInformation

Liquid Gating Meniscus‐Shaped Deformable Magnetoelastic Membranes with Self‐Driven Regulation of Gas/Liquid Release (Adv. Mater. 3/2022)

Liquid Gating Liquid-gating technology is attracting increasing attention for the delivery of some brand-new properties for real-world applications. In article number 2107327, Xu Hou and co-workers report a self-driven smart liquid-gating system, developed by designing a liquid-gating magnetoelastic porous membrane with reversible meniscus-shaped deformations. This system provides a universal and convenient way to realize active regulation of gas/liquid release. The illustrated visible gas/liquid-mixture content monitoring showcases one example of the application of the reported material.

Electrostatic Fermi level tuning in large-scale self-assembled monolayers of oligo(phenylene-ethynylene) derivatives.

Understanding and controlling the orbital alignment of molecules placed between electrodes is essential in the design of practically-applicable molecular and nanoscale electronic devices. The orbital alignment is highly determined by the molecule-electrode interface. Dependence of orbital alignment on the molecular anchor group for single molecular junctions has been intensively studied; however, when scaling-up single molecules to large parallel molecular arrays (like self-assembled monolayers (SAMs)), two challenges need to be addressed: 1. Most desired anchor groups do not form high quality SAMs. 2. It is much harder to tune the frontier molecular orbitals via a gate voltage in SAM junctions than in single molecular junctions. In this work, we studied the effect of the molecule-electrode interface in SAMs with a micro-pore device, using a recently developed tetrapodal anchor to overcome challenge 1, and the combination of a single layered graphene top electrode with an ionic liquid gate to solve challenge 2. The zero-bias orbital alignment of different molecules was signalled by a shift in conductance minimum vs. gate voltage for molecules with different anchoring groups. Molecules with the same backbone, but a different molecule-electrode interface, were shown experimentally to have conductances that differ by a factor of 5 near zero bias. Theoretical calculations using density functional theory support the trends observed in the experimental data. This work sheds light on how to control electron transport within the HOMO-LUMO energy gap in molecular junctions and will be applicable in scaling up molecular electronic systems for future device applications.

Manipulating the optical and electronic properties of MoO3 films through electric-field-induced ion migration

The intercalation of hydrogen ions and lithium ions in MoO3 films is realized by acidic ionic liquid gating, which modifies the electronic and optical properties of MoO3 films, is promising for designing multifunctional devices.

Ionic-Liquid Gating in Two-Dimensional TMDs: The Operation Principles and Spectroscopic Capabilities.

Ionic-liquid gating (ILG) is able to enhance carrier densities well above the achievable values in traditional field-effect transistors (FETs), revealing it to be a promising technique for exploring the electronic phases of materials in extreme doping regimes. Due to their chemical stability, transition metal dichalcogenides (TMDs) are ideal candidates to produce ionic-liquid-gated FETs. Furthermore, as recently discovered, ILG can be used to obtain the band gap of two-dimensional semiconductors directly from the simple transfer characteristics. In this work, we present an overview of the operation principles of ionic liquid gating in TMD-based transistors, establishing the importance of the reference voltage to obtain hysteresis-free transfer characteristics, and hence, precisely determine the band gap. We produced ILG-based bilayer WSe2 FETs and demonstrated their ambipolar behavior. We estimated the band gap directly from the transfer characteristics, demonstrating the potential of ILG as a spectroscopy technique.

Liquid Gating Meniscus-Shaped Deformable Magnetoelastic Membranes with Self-Driven Regulation of Gas/Liquid Release.

Liquid gating membranes have been demonstrated to show unprecedented properties of dynamicity, stability, adaptivity, and stimulus-responsiveness. Most recently, smart liquid gating membranes have attracted increasing attention to bring some brand-new properties for real-world applications, and various environment-driven systems have been created. Here, a self-driven system of a smart liquid gating membrane is further developed by designing a new sytem based on a liquid gating magnetoelastic porous membrane with reversible meniscus-shaped deformations, and it is not subject to the complex gating liquid restriction of magnetorheological fluids. Compared with other systems, this magnetic-responsive self-driven system has the advantage that it provides a universal and convenient way to realize active regulation of gas/liquid release. Experiments and theoretical calculations demonstrate the stability, the nonfouling behavior, and the tunability of the system. In addition, this system can be used to perfectly open and close gas transport, and the gating pressure threshold for the liquid release can be reduced under the same conditions. Based on the above capabilities, combined with the fast and 3D contactless operation, it will be of benefit in fields ranging from visible gas/liquid mixture content monitoring and energy-saving multiphase separation, remote fluid release, and beyond.

Detection of H2 facilitated by ionic liquid gating of tungsten oxide films

Molecular hydrogen (H2) shows promise as a future renewable energy carrier. However, due to safety concerns, its reliable detection in different atmospheres is an important issue. Here, we propose a hydrogen sensor based on ion-gated transistors exploiting the interface between tungsten oxide and ionic liquids. Two different approaches to gas sensors (metal oxide gas sensor and ionic liquid-based electrochemical sensor) are integrated in a single device. We demonstrate that ionic liquid gating enhances the effect of H2 on the tungsten oxide transistor channel. The transistor current response permits the detection of H2 in an O2-free environment with the device operating in room temperature. After H2 sensing, the initial properties of the tungsten oxide channel can be recovered by exposure to O2.

Suspended MoTe2 field effect transistors with ionic liquid gate

The electrical performance of suspended few-layer MoTe2 field-effect-transistors with ionic liquid gating has been investigated. The suspended structure not only enhances the mobility of MoTe2 by removing the influence of the substrate but also allows ions to accumulate on both the top and the bottom surface of MoTe2. The consequent increase in the gate capacitance resulted in an improved subthreshold swing (∼73 mV/dec) and on–off ratio (106) at room temperature for suspended MoTe2 compared to substrate-supported devices. Suspended transistors with ionic liquid gating enable a larger charge density compared to ionic liquid gated supported devices and may provide a useful platform to study screening physics in 2D materials.

Granular metallicity as a minimal normal state for superconductivity

We report the evolution of electrical transport properties in insulating FeSe films with electron doping induced by the ionic liquid gating technique. Superconductivity never emerges in the strong insulators with variable-range hopping behavior but is shown to arise once the resistance of the normal state varies as $ln(1/T)$, indicating that this behavior corresponds to the minimal conducting character for developing superconductivity. Our work points toward granular metallicity for the $ln(1/T)$ behavior, suggesting that the emergence of superconductivity requires at least an insulating state containing metallic granules. Moreover, it unravels an electronic segregation in proximity to superconductor-insulator transition, which calls for a comprehensive understanding of this segregated phase.

Rapid SARS-CoV-2 Nucleic Acid Testing and Pooled Assay by Tetrahedral DNA Nanostructure Transistor.

Direct SARS-CoV-2 nucleic acid testing with fast speed and high frequency is crucial for controlling the COVID-19 pandemic. Here, direct testing of SARS-CoV-2 nucleic acid is realized by field-effect transistors (FETs) with an electro-enrichable liquid gate (LG) anchored by tetrahedral DNA nanostructures (TDNs). The applied gate bias electrostatically preconcentrates nucleic acids, while the liquid gate with TDNs provides efficient analyte recognition and signal transduction. The average diagnosis time is ∼80 s, and the limit of detection approaches 1-2 copies in 100 μL of clinical samples without nucleic acid extraction and amplification. As such, TDN-LG FETs solve the dilemma of COVID-19 testing on mass scale that diagnosis accuracy and speed undergo trade-off. In addition, TDN-LG FETs achieve unamplified 10-in-1 pooled nucleic acid testing for the first time, and the results are consistent with PCR. Thus, this technology promises on-site and wide population COVID-19 screening and ensures safe world-reopening.

Quantized critical supercurrent in SrTiO 3 -based quantum point contacts

Superconductivity in SrTiO3 occurs at remarkably low carrier densities and therefore, unlike conventional superconductors, can be controlled by electrostatic gates. Here, we demonstrate nanoscale weak links connecting superconducting leads, all within a single material, SrTiO3. Ionic liquid gating accumulates carriers in the leads, and local electrostatic gates are tuned to open the weak link. These devices behave as superconducting quantum point contacts with a quantized critical supercurrent. This is a milestone toward establishing SrTiO3 as a single-material platform for mesoscopic superconducting transport experiments that also intrinsically contains the necessary ingredients to engineer topological superconductivity.

Preparation of polyethylene oxide single crystals via liquid gating technology and morphology design strategy

A novel type of liquid gating technology has been developed to prepare a polyethylene oxide (PEO) single-crystal film, and the crystal growth was observed via atomic force microscopy. The self-seeding method has been widely used in the preparation of polymer single crystals, but the mechanism through which single polymer crystals are formed via the combination of liquid gating technology and the self-seeding method remains unclear. To elucidate the mechanism of this process, a series of experiments were conducted in which a dilute polymer solution was sprayed onto a mica substrate to form a single-crystal film through liquid gating technology to study the effect of the crystallization time on the morphology of a thiol PEO (mPEO-SH) crystal. Based on this research, it was found that liquid gating helps to prevent twinning during crystal growth. The combination of liquid gating and self-seeding technology thus provides a new strategy for polymer single-crystal growth.

Investigation of phonon modes in 2H-TaX2 (X = S/Se) flakes with electrostatic doping

Electrostatic doping-assisted phonon softening has been intensively investigated in semiconducting transition metal dichalcogenides (TMDCs), in which strong electron–phonon interactions can be achieved in thin layers. Though electron–phonon coupling plays an important role in structure phase transitions for metallic 2H-TaX2 (X = S, Se), it has been rarely studied under electrostatic doping. Here, the effect of electrostatic doping on the vibrational phonon modes of 2H-TaSe2 and 2H-TaS2 thin films is studied with ionic liquid gating by the electric-double-layer gating technique. Under a gate bias (VG) of 1.5 V, 2H-TaSe2 has a blue shift of 7 cm−1 and a red shift of 3 cm−1 for the in-plane (E2g) and out-of-plane vibration (A1g) modes, respectively, indicating a strong electron–phonon interaction in both intralayer and interlayer. By varying the thickness of the flakes, it has been found that there exists a threshold VG value for the stiffening of the E2g mode and the softening of the A1g mode because of the strong electrostatic screening effect at lower doping density. As the intensity of the E2g mode decreases with VG, an anomalous enhancement of the A1g phonons can be achieved, which is further convinced in TaS2. The asymmetric phonon evolution behavior is very different with that in the semiconducting TMDCs, which may provide useful information for understanding electron–phonon interplay in metallic layer materials.

Total solution processable and low-cost DNA methylation sensor

DNA methylation sensor is an emerging demand of modern medical for laboratory, though lots of efforts have been contributed in this discipline, the easy-to-operate and efficient sensing terminal is still in deficiency. In this work, a total solution processable printing technology is proposed to fabricate the DNA methylation sensor, which is based on the liquid gate graphene field effect transistor (Lg-GFET). Meanwhile, the graphene ink (G-ink) was prepared by using the modified liquid-exfoliation method, to facilitate printing production. Then, five kinds of tested single strand DNA (ssDNA) which have 0 to 4 5-methylcytosine (5mC) sites were covalently anchored on the graphene channel. X-ray photoelectron spectroscopy (XPS) was conducted to demonstrate the analyte ssDNA was successfully fixed. Thirdly, the 5mC sites were identified by their antibody of 5mC (5mCab) and transduced as the changed current between the source and drain electrodes ( I ds). It is found the proposed sensor has good linear sensitivity (about -1.68% for per 5mC) to the amount of 5mC sites on the tested ssDNAs with Pearson correlation coefficient -0.98 and excellent anti-interference to unmethylated ssDNAs. Besides, the cost is estimated to be about $ 1.5 for each of the proposed DNA methylation sensor. Conclusively, the proposed low-cost component may be an efficient candidate for promoting the instant DNA methylation determination.

Electrochemically and Mechanically Regulated Liquid Metal Gate via Giant Surface Tension Alteration

AbstractLiquid gates can provide an effective method to control the release of substances. However, the size of liquid gates and the control methods limit their broad applications. The controllable large deformation of liquid metals (LMs) makes it possible to be used in liquid gate design with simple actuation methods. Here an LM gate that can be easily driven under moderate conditions is proposed, on demand opening at mild electrical voltage (2–5 V) and closing at an oscillating mechanical force (≈0.05 N) in a wide range of pH (2–12). The gating mechanism relies on the large surface tension alteration at these conditions, which directly changes the shape of the LM from a flat film to a contracted meniscus to one side of the copper gate‐frame. As demonstrated, this gate can be applied to release substances such as liquid (ink), biomolecule (insulin) by free diffusion. Moreover, single‐channel and multichannel gates can be realized for high throughput control. The biocompatibility of the whole gate is also proved by cytotoxicity assays. Above all, a novel LM gate is offered with simple structure and easy control, which may bring inspiration to applications in controlled substance release and separation.

Photothermally induced liquid gate with navigation control of the fluid transport

The ability to control multiphase flows is essential for applications such as microvalves, chemical analyses, microreactors, and multiphase separators. Furthermore, more specific controls, including the positional navigation control of fluids under steady-state pressures, will improve the development of these applications. Here, we present a fundamentally new photothermally induced liquid gating system that allows light-controlled contactless fluid transport and gas/liquid separations at designated locations, with seconds response times, under constant pressures. Experiments and theoretical calculations demonstrate the stability of our system and its novel regulation mechanism, which is based on a photothermally induced liquid-reconfigurable gate with a change in the surface/interfacial tension and Marangoni flow redistribution of the gating liquid at the illuminated location. This regulation mechanism with positional navigation properties requires neither mechanical parts nor complex accessories and can further enable the miniaturization and integration of various engineering processes. Our application demonstrations confirm the potential of this system in fields of smart valves, multiphase separations, multiphase microreactors, and beyond.

Ionitronic manipulation of current-induced domain wall motion in synthetic antiferromagnets

The current induced motion of domain walls forms the basis of several advanced spintronic technologies. The most efficient domain wall motion is found in synthetic antiferromagnetic (SAF) structures that are composed of an upper and a lower ferromagnetic layer coupled antiferromagnetically via a thin ruthenium layer. The antiferromagnetic coupling gives rise to a giant exchange torque with which current moves domain walls at maximum velocities when the magnetic moments of the two layers are matched. Here we show that the velocity of domain walls in SAF nanowires can be reversibly tuned by several hundred m/s in a non-volatile manner by ionic liquid gating. Ionic liquid gating results in reversible changes in oxidation of the upper magnetic layer in the SAF over a wide gate-voltage window. This changes the delicate balance in the magnetic properties of the SAF and, thereby, results in large changes in the exchange coupling torque and the current-induced domain wall velocity. Furthermore, we demonstrate an example of an ionitronic-based spintronic switch as a component of a potential logic technology towards energy-efficient, all electrical, memory-in-logic.

Light Controllable Electronic Phase Transition in Ionic Liquid Gated Monolayer Transition Metal Dichalcogenides.

Ionic liquid gating has proved to be effective in inducing emergent quantum phenomena such as superconductivity, ferromagnetism, and topological states. The electrostatic doping at two-dimensional interfaces relies on ionic motion, which thus is operated at sufficiently high temperature. Here, we report the in situ tuning of quantum phases by shining light on an ionic liquid-gated interface at cryogenic temperatures. The light illumination enables flexible switching of the quantum transition in monolayer WS2 from an insulator to a superconductor. In contrast to the prevailing picture of photoinduced carriers, we find that in the presence of a strong interfacial electric field conducting electrons could escape from the surface confinement by absorbing photons, mimicking the field emission. Such an optical tuning tool in conjunction with ionic liquid gating greatly facilitates continuous modulation of carrier densities and hence electronic phases, which would help to unveil novel quantum phenomena and device functionality in various materials.