Applications In Multifunctional Devices Research Articles

Mechanically durable superhydrophobic PDMS-candle soot composite coatings with high biocompatibility

To realize practical applications, the development of superhydrophobic coatings with high durability against harsh environmental conditions has been of interest, especially coatings that are susceptible to mechanical damage. Herein, we present mechanically durable superhydrophobic polydimethylsiloxane (PDMS)-candle soot (CS)-based composite coatings through simple and rapid casting and soot processes, which can be fabricated on various substrates, such as glass, woods, stainless steel meshes, and plastics. The reported extremely water-repellent coatings consist of a PDMS basic binding layer, candle soot clusters (CSC), and an outside CS layer, which has exhibited long-lived superwettability and resistance against mechanical damage in multi-cycle abrasion tests and ultrasonication treatments over a long duration. The resulting mechanical durability was mainly a result of three-dimensional topography-protected and carbon nanoparticle-mixed structures, which decreased the contact area and created highly hydrophobic bulk coatings. Moreover, the durable performances of the three types of CS-based superhydrophobic coatings to resist mechanical damage, involving CS, PDMS-CS, and PDMS-CSC-CS coatings, were compared on a glass substrate, and the results indicated higher robustness of the present PDMS-CSC-CS coatings. In addition, it showed higher biocompatibility than a PDMS film surface, and can therefore be employed as a promising material for further modification for applications in prospective multifunctional biomedical devices.

Structural, ferroelectric, and optical properties of Pr-NBT-xCTO relaxor ferroelectric thin films

Sol-gel method was used to prepare the Pr3+ ions-doped (1-x)Na0.5Bi0.5TiO3-xCaTiO3 (Pr-NBT-xCTO) (x = 0, 0.04, 0.06, 0.08, 0.1, 0.12, and 0.16) thin films on Pt/Ti/SiO2/Si and fused silicon substrates. The structure phase of thin films was evolving from rhombohedral (R3c) to orthorhombic (Pnma) with increasing CTO content. Owing to the morphotropic phase boundary (MPB), the improved ferroelectric and dielectric properties were obtained at x = 0.06–0.1. The MPB was formed from the concomitant phase of rhombohedral (R3c) and orthorhombic (Pnma). The Pr-NBT-0.08CTO thin film showed the best ferroelectric and dielectric properties, as well as strong relaxor behavior (the diffusion factor is γ = 1.79). In addition, all the films exhibited strong red emission as excited by UV light, and wide optical band-gap (3.44–3.47 eV), which might be influenced by grain size and structural variation. Our results indicate that Pr-NBT-xCTO thin films may have potential applications in ferroelectric-luminescence multifunctional optoelectronic devices.

Intense piezoluminescence in LiTaO3 phosphors doped with Pr3+ ions

A novel piezoluminescent (PZL) phosphor was prepared by doping Pr3+ ions into ferroelectric LiTaO3 matrices, and their crystal structure and multi-luminescent performance were investigated. A slightly Li-rich nonstoichiometric design gave the phosphors optimized PZL behavior with favorable recoverability. Excited by 240 nm radiation, two strong photoluminescent (PL) emission bands lay around 511 and 615 nm, which corresponded to Pr3+ transitions of 3P0 to 3H4 and 1D2 to 3H4, respectively. Nevertheless, the 3P0 to 3H4 transition was detectably suppressed in AG/PZL spectra with 1D2 to 3H4 becoming dominant, which was possibly owing to the effect of trap level distribution on direct tunneling possibilities. In this context, a probable mechanism was proposed to explain the multi-luminescent process in LiTaO3:Pr3+. This study was aimed at exploring novel PZL materials for fundamental research and applications in multifunctional devices.

Optimization of room temperature multiferroic properties and magnetoelectric coupling effect in MnO2 doped BiFeO3−Bi0.5K0.5TiO3 ceramics

Abstract The 0.6BiFeO3–0.4Bi0.5K0.5TiO3 + x mol% MnO2 ceramics (BFKT–xMn, x = 0, 2.5, 5, 7.5 and 10) have been successfully synthesized via a conventional solid-state reaction method. All the ceramics possess a morphotropic phase boundary formed by rhombohedral and tetragonal phases. A room temperature magnetoelectric (ME) coupling coefficient of 30.12 mV cm−1 Oe−1 is observed for the first time in the undoped BFKT ceramic. The appropriate addition of MnO2 can optimize the electrical insulation and ferroelectricity of BFKT ceramic due to the decreased densities of impurity and grain boundary, and thus enhance the magnetoelectric coupling effect significantly. The BFKT–2.5Mn ceramic exhibits a high remanent polarization of 36.2 μC/cm2 at a maximum electric field of 70 kV/cm and a high ME coupling coefficient of 42.56 mV cm−1 Oe−1 as well. Meanwhile, the leakage current density of the BFKT–2.5Mn ceramic maintains at a low value of 1.83 × 10−8 A/cm2 (at a maximum electric field of 45 kV/cm). These characteristics indicate the BFKT–2.5Mn ceramic has potential applications in multifunctional devices as lead-free multiferroic materials.

Transmissive to Dark Electrochromic and Fluorescent Device Based on Poly(fluorene-bisthiophene) Derivative

Films of a poly(fluorene-bisthiophene) derivative, named PFBT, were electrodeposited onto indium tin oxide (ITO) electrodes and their electrochromic and fluorescence properties were investigated. Such films displayed color variation from yellow, in the neutral state, to green, in the oxidized state, as shown by tracking of the CIE (Commission Internationale de l’Eclairage) 1931 xy chromaticity coordinates. PFBT films are fluorescent in the neutral state (E = 0.0 V vs. Ag/Ag+) with emission at 532 nm; however, upon oxidation at 0.85 V the photoluminescence intensity is significantly decreased. A solid-state electrochromic device was assembled using PFBT and poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonate) (PEDOT-PSS) films and a polymer electrolyte. The device presented color variation from transmissive greenish-yellow to blue and reversible fluorescent properties upon switching between -1.5 to 1.5 V vs. PEDOT. Thus, the high contrast and stability both in electrochromism and electrofluorescence of the PFBT film and its device make them suitable for application in multifunctional optical devices.

Magnetoelectric multiferroicity and quantum paraelectricity in hexaferrites

Multiferroic materials with coexisting ferroelectric and magnetic orders have attracted tremendous research interests because of their intriguing fundamental physics as well as potential applications in the next-generation multifunctional devices. Hexaferrites with conical magnetic structures are among the most promising single-phase multiferroics because strong magnetoelectric effects can be achieved in them from low temperatures up to room temperature in low magnetic fields. In this review, after briefly introducing the background on multiferroics and classification of hexaferrites, we summarize recent progress in multiferroic hexaferrites, including the mechanisms of spin-induced ferroelectricity, the magnetoelectric phase diagram, giant direct and converse magnetoelectric effects. Furthermore, we present a new mechanism of magnetic-ion-induced displacive polarization in hexaferrites, which leads to quantum paraelectricity and quantum electric-dipole liquid in M-type hexaferrites.

Electrical heating behavior of flexible thermoplastic polyurethane/Super-P nanoparticle composite films for advanced wearable heaters

A rationally designed flexible electrothermal film is composed of Super-P (SP, nanoparticle), thermoplastic polyurethane (TPU) and silica. The electric heating behavior of electrothermal films can be facilely adjusted by SP contents and applied voltages. TPU/SP composite with 25wt.% SP presents robust structural stability, fast response feature and superior electrothermal reproducibility. The conductive network formed by SP nanoparticles not only could quickly convert the electric energy to heat, but also is stable under stepwise periodic and long-term electric heating–cooling conditions. Finally, a smart wrist band integrated electric heater and temperature indicator is verified the high potential in multifunctional wearable device applications.

Photo-induced negative differential resistance in a resistive switching memory device based on BiFeO3/ZnO heterojunctions

Photo-induced novel effect in a material with multiple physical properties has highly important potential applications in the photo-electric multifunctional electronic devices. In this work, the BiFeO3/ZnO bilayer films were sequentially prepared by magnetron sputtering method, which displays an obvious photo-modulated conversion between resistive switching (RS) memory and negative differential resistance (NDR) effect. Through theoretical analysis and simulation calculation, suggesting the NDR effect can be attributed to the inner electric field and the efficiently separated photogenerated electrons and holes under light-irradiation in the interface of the BiFeO3/ZnO p–n heterojunctions, while the RS memory behavior can be attributed to the formation of oxygen vacancies assisted Ag conductive filaments. This work opens up a new way to preparation a multifunction electronic device with photo-modulated conversion between RS memory and NDR effect for potential applications in optical electrical bifunctional devices, electronic information and optical quantum computers, and so on.

Light-Tunable 1T-TaS2 Charge-Density-Wave Oscillators.

External stimuli-controlled phase transitions are essential for fundamental physics and design of functional devices. Charge density wave (CDW) is a metastable collective electronic phase featured by the periodic lattice distortion. Much attention has been attracted to study the external control of CDW phases. Although much work has been done in the electric-field-induced CDW transition, the study of the role of Joule heating in the phase transition is insufficient. Here, using the Raman spectroscopy, the electric-field-driven phase transition is in situ observed in the ultrathin 1T-TaS2. By quantitative evaluation of the Joule heating effect in the electric-field-induced CDW transition, it is shown that Joule heating plays a secondary role in the nearly commensurate (NC) to incommensurate (IC) CDW transition, while it dominants the IC-NC CDW transition, providing a better understanding of the electric field-induced phase transition. More importantly, at room temperature, light illumination can modulate the CDW phase and thus tune the frequency of the ultrathin 1T-TaS2 oscillators. This light tunability of the CDW phase transition is promising for multifunctional device applications.

Negative Photoconductance in van der Waals Heterostructure-Based Floating Gate Phototransistor.

van der Waals (vdW) heterostructures made of two-dimensional materials have been demonstrated to be versatile architectures for optoelectronic applications due to strong light--matter interactions. However, most light-controlled phenomena and applications in the vdW heterostructures rely on positive photoconductance (PPC). Negative photoconductance (NPC) has not yet been reported in vdW heterostructures. Here we report the observation of the NPC in the ReS2/h-BN/MoS2 vdW heterostructure-based floating gate phototransistor. The fabricated devices exhibit excellent performance of nonvolatile memory without light illumination. More interestingly, we observe a gate-tunable transition between the PPC and the NPC under the light illumination. The observed NPC phenomenon can be attributed to charge transfer between the floating gate and the conduction channel. Furthermore, we show that control of NPC through light intensity is promising in realization of light-tunable multibit memory devices. Our results may enable potential applications in multifunctional memories and optoelectronic devices.

Synthesis, photoluminescence and ultrafast nonlinear optical properties of copper nanolayers/particles uniformly decorated ZnO nanowires

Copper (Cu) nanolayers/particles decorated zinc oxide (Cu-ZnO) nanowires have been successfully synthesized by two-step chemical vapour deposition to prepare ZnO nanowires and magnetron sputtering method to deposit Cu nanolayers/particles. The field emission scanning electron microscopy images indicated the Cu nanolayers/particles are clearly visualized on surface of ZnO nanowires. The impact of sputtering time and sputtering power was analyzed. The results show that the atomic percent of Cu was gradually increased with the sputtering time and sputtering power was increased. The photoluminescence results demonstrated two major emission peaks for the Cu-ZnO nanowires, and the visible emission peaks of Cu-ZnO nanowires stronger than that of unmodified ZnO nanowires. Moreover, the results of open-aperture Z-scan measurements that all samples show the two-photon absorption behavior, and the two-photon absorption coefficients of Cu-ZnO is higher than that of unmodified ZnO nanowires. The results of closed-aperture Z-scan results demonstrated that all samples show self-focusing optical nonlinearity. These studies promise their potential applications in multifunctional optical devices.

Spectroscopic study of phase transitions in ferroelectric Bi0.5Na0.5Ti1−xMnxO3−δ films with enhanced ferroelectricity and energy storage ability

Lead-free ferroelectric Bi0.5Na0.5TiO3 (BNT) has attracted considerable attention taking into account environment issues and applications in micro electro mechanical systems. The effects of manganese (Mn) substitution on microstructure, lattice dynamics, and optical properties of BNT films have been investigated by X-ray diffraction, Raman scattering and ellipsometric spectra. The phase transitions as a function of temperature have been systemically explored by temperature-dependent Raman and ellipsometric spectra. The anomalous temperature-dependent behavior of Raman-active modes suggests that there is an intermediate phase between ferroelectric rhombohedral and paraelectric tetragonal phase, which is confirmed by the temperature-dependent optical band gap (Eg) and extinction coefficient (κ) extracted from ellipsometric spectra analysis. And then, a phase diagram as a function of Mn composition has been proposed. Finally, we demonstrate that Mn-dopant is an effective approach to enhance ferroelectric properties, improve energy storage ability, and increase permittivity as well as suppress leakage current. Electrical dielectric responses indicate that there is a critical frequency and polarization relaxation behavior in the films. The present results will be helpful for the application of BNT-based lead-free multifunctional devices.

Co-substitution induced structural transition with enhanced magnetic and electrical properties of multiferroic BiFeO3 nanoparticles

Polycrystalline Bi1−xTbxFe1−xCoxO3 (for x = 0.05, 0.10, 0.15 and 0.20) nanoparticles were synthesized by tartaric acid assisted sol–gel route. The quantitative crystallographic phase analysis of XRD pattern demonstrates the subsequent structural phase transition from rhombohedral (R3c) to cubic (Pm $$\bar {3}$$ m) with the intermediate orthogonal (Pbnm) and orthogonal (Pnma) phase with the gradual increase in concentration of co-substituents. Raman spectroscopic analysis emphasizes that all the co-substituted samples has undergone structural phase transitions which are in good agreement with the results of Rietveld analysis. X-ray photoelectron spectroscopy (XPS) have confirmed that Fe exists predominantly in +3 state in the co-substituted sample. The enhancement in the room temperature magnetic behavior of the sample can be attributed to the co-substitution induced suppression of spatially modulated spiral spin structure of BiFeO3. All the samples exhibit dielectric anomaly at the vicinity of Neel temperature (TN) signifies the change in magnetic ordering. Moreover, all the co-substituted samples have been witnessed with reduced leakage current and improved ferroelectric behaviour, which is the desirable characteristics for multifunctional device applications of multiferroics.

Development and application of bio-inspired microfluidics

Bio-inspired microfluidic systems can be obtained through multidisciplinary approaches by using bio-inspired structural and functional designs for the microfluidic devices. This review mainly focuses on the concept of bio-inspired microfluidics to improve the properties of microfluidic systems for breaking through the bottlenecks of the current microfluidic devices, such as anti-fouling, smart, and dynamic response inside the microchannels under different environments. In addition, here, we show the current research progress of bio-inspired microfluidic systems in applications related to anti-fouling and smart devices, and biomedical research. The review discusses both physical theories and critical technologies in the bio-inspired microfluidics, from biomimetic design to real-world applications, so as to offer new ideas for the design and application of smart microfluidics, and the authors hope this review will inspire the active interest of many scientists in the area of the development and application of soft matter, and multifunctional and smart bio-inspired devices.

Effect of substrate temperature on structural and magnetic properties of c-axis oriented spinel ferrite Ni0.65Zn0.35Fe2O4 (NZFO) thin films

Varying the substrate temperature changes structural and magnetic properties of spinel ferrite Ni0.65Zn0.35Fe2O4 (NZFO) thin films. X-ray diffraction of films grown at different temperature display only (004) reflections, without any secondary peaks, showing growth orientation along the c-axis. We find an increase in crystalline quality of these thin films with the rise of substrate temperature. The surface topography of thin films grown at different growth temperatures reveal that these films are smooth with low roughness; however, the thin films grown at 800 °C exhibit lowest average and root mean square (rms) roughness among all thin films. We find iron and nickel to be more oxidized (greater Fe3+ and Ni3+ content) in films grown and annealed at 700 °C and 800 °C, compared to those films grown at lower temperatures. The magnetic moment is observed to increase with an increase of substrate temperature and all thin films possess high saturation magnetization and low coercive field at room temperature. Films grown at 800 °C exhibit a ferrimagnetic–paramagnetic phase transition well above room temperature. The observed large magnetizations with soft magnetic behavior in NZFO thin films above room temperature suggest potential applications in memory, spintronics, and multifunctional devices.

Strong magnetoelectric effect in pulse laser deposited [Ba(Zr0.2Ti0.8)O3‐0.5(Ba0.7Ca0.3)TiO3]/CoFe2O4 bilayer thin film

AbstractPolycrystalline bilayer thin film of multiferroic [Ba(Zr0.2Ti0.8)O3‐0.5(Ba0.7Ca0.3)TiO3]/CoFe2O4([BZT‐0.5BCT]/CFO) has been deposited on Pt/Si (100) substrate using a pulsed laser deposition technique. The dielectric analysis reveals a significant change in the dielectric constant (~39% at a typical frequency of 100 Hz) at room temperature when a magnetic field is applied, in addition to a substantial improvement in the saturation polarization. A low leakage current density (~ 5 × 10−7 A/cm2) and a high magnetoelectric coupling coefficient (αE) both in the transverse (~2.085 V/Oe cm) as well as in the longitudinal (~0.708 V/cm Oe) directions, indicate in‐principle usability of this system for multifunctional device applications in thin film form.

Ultrahigh-luminosity white-light-emitting devices based on edge functionalized graphene quantum dots

Graphene quantum dots (GQDs) have received considerable attention as excellent candidates for promising applications in multifunctional optoelectronic devices. The synthesis method for GQDs has been investigated in an attempt to find an optimal method for fabricating white GQDs (WGQDs) suitable for use in display systems. However, the emission wavelengths of WGQDs are still not sufficient to cover the range of wavelengths required by lighting sources, and the luminance of the light-emitting devices (LEDs) based on the WGQDs is still lower than that of white LEDs (WLEDs) fabricated utilizing organic molecular phosphors. Here, we report high-luminosity WLEDs based on edge functionalized GQDs (EF-GQDs) formed by using a simple solution method. The white light emission of the EF-GQDs originates from the various energy states between the octadecylamine functional group and the graphitic domain. The maximum luminance and the Commission Internationale de l’Enclairage coordinates for the WLEDs based on EF-GQDs are 464 cd/m2 and (0.27, 0.29), respectively. The luminosity of 464 cd/m2 is, to the best of our knowledge, the highest value ever reported for WLEDs based on GQDs. This successful demonstration of efficiency enhancement for WLEDs based on EF-GQDs can improve our understanding of the mechanisms at play in these devices and lead to their promising applications as backlights in flat panel displays and lighting sources.

Magnetic Properties and Spontaneous Polarization of La-, Mn- and N-Doped Tetragonal BiFeO3: A First-Principles Study

Multiferroic materials have been receiving attention for their potential applications in multifunctional devices. Chemical substitution is an effective method for improving the physical properties of BiFeO3 (BFO). However, different experimental results have been reported for Lanthanum- (La-) and Manganese (Mn) -doped BFO ceramics. Here, we systematically studied the magnetic properties and spontaneous polarization of La-, Mn-, and Nitrogen (N) -doped tetragonal BiFeO3 using density functional theory with the generalized gradient approximation and U-value method. The calculated results demonstrated that the systems show ferromagnetism with Mn and N doping, whereas no magnetization was found with La doping in G- and C-type antiferromagnetic orderings. Our research further revealed that the ferromagnetism is attributed to the p-d orbital hybridization. Berry-phase polarization calculations predicted a large polarization of 149.2 µC/cm2 along the [001] direction of pure tetragonal BFO. We found that La and N substitution had little influence on the spontaneous polarization, whereas Mn substitution reduced the spontaneous polarization. The reduced energy barrier heights of the doped systems indicate the reduced stability of the off-centering ferroelectricity against the thermal agitation. These findings provide greater understanding for controlling and tuning the multiferroic properties of BFO.

Resistive switching and ferroelectric properties in BiFeO3 superlattice films

Bi0.89Ho0.08Sr0.03Fe0.97−aMn0.03NiaO3/Bi0.89Ho0.08Sr0.03Fe0.97−bMn0.03NibO3 (Nia/Nib) superlattice films were prepared via a CSD method. The influences of interface effects on ferroelectric properties and resistance switching behaviors of the superlattice films were investigated. There was a weak interface effect in the superlattice films, which was caused by the misfit dislocation generated at the interfaces between Nia and Nib. The results indicate that the superlattice films show superior ferroelectric properties and good resistance switching behaviors, which is caused by the interface effect. Those superlattice films may have potential applications in multifunctional devices due to their excellent electric properties.

High-performance phototransistor based on individual high electron mobility MnWO4 nanoplate

MnWO4 nano-materials have been attracting intensive attention as a potential candidate for modern electronic and optoelectronic nanodevices. However, the availability of highly crystalline MnWO4 nanostructures with controllable geometry shapes still remains a great challenge and further hinders their technologically important applications in optoelectronic devices. Herein, large yield and crystalline MnWO4 nanoplates with regular crystal facets are synthesized on Ti substrate based on a conventional plasma electrolytic oxidation (PEO) process followed by a thermal annealing method. The phototransistor based on individual high electron mobility MnWO4 nanoplate has been fabricated and it shows a classical n-type semiconductor behavior with superior field emission transistor (FET) properties including a very low threshold voltage of 1 V and a high peak transconductance of 2.7 μS. Furthermore, the MnWO4 phototransistor also exhibits fast photoresponse time and high photoresponsivity under light illumination. All these unique characteristics of incident-light control and gate regulation from the MnWO4 nanoplate are expected to further promote its potential applications in multifunctional optoelectronic devices in the future.