Applications In Multifunctional Devices Research Articles

Strong Upconversion Photoluminescence and Large Ferroelectric Polarization in Er3+–Yb3+–W6+ Triply Substituted Bismuth Titanate Thin Films Prepared by Chemical Solution Deposition

Strong upconversion photoluminescence and large ferroelectric polarization were observed for the first time in layered structure Er3+–Yb3+–W6+ triply substituted bismuth titanate thin films. The thin films were prepared on fused silica and Pt(111)/Ti/SiO2/Si substrates by chemical solution deposition. Two green emission bands and a red one were observed in the upconversion photoluminescence spectra for all the films pumped by a 980 nm laser diode, which correspond to 2H11/2, 4S3/2, and 4F9/2 to 4I15/2 transitions of Er3+ ions, respectively. A two‐photon energy‐transfer process was confirmed by the power dependence of emission intensity. Compared with that of Er3+–Yb3+‐substituted bismuth titanate thin films, the improved photoluminescence is related to the reduced defects such as oxygen vacancies due to B‐site (Ti4+) substitution by W6+ ions, while the large ferroelectric remnant polarization can be attributed to the increased structure distortion and the reduced oxygen vacancies due to cosubstitution of A‐site (Bi3+) and B‐site (Ti4+) by Er3+, Yb3+, and W6+ ions, respectively. The combination of the strong upconversion photoluminescence and the good ferroelectric properties in the thin films would open the possibility of realizing novel multifunctional optoelectronic integration device applications.

ChemInform Abstract: Recent Progress in Multiferroic Magnetoelectric Composites: From Bulk to Thin Films

AbstractReview: 233 refs.

Combination of Strong Blue Up-Conversion Photoluminescence and Greatly Enhanced Ferroelectric Polarization in Tm3+-Yb3+-W6+- Doped Bi4Ti3O12 Thin Films

A strong blue up-conversion photoluminescence and a greatly enhanced ferroelectric polarization were observed in Tm3+-Yb3+-W6+-triply-doped bismuth titanate thin films. The thin films were prepared on fused silica and Pt/Ti/SiO2/Si (111) substrates by chemical solution deposition and annealed at 700°C. The strong blue up-conversion emission centered at 478 nm, corresponding to 1G4 → 3H6 transitions of Tm3+ ions, was confirmed to be a three-photon energy-transfer process by pumping laser power dependence of emission intensity. The enhanced ferroelectricity with a high remnant polarization (Pr) value of about 32 μC/cm2 is attributed to the weakened domain pinning due to the reduced oxygen vacancies by W6+ substitution for Ti4+ ions. The thin films combining the strong blue up-conversion photoluminescence with the good ferroelectric properties would provide possibility of realizing novel multifunctional optoelectronic integration device applications.

Recent Progress in Multiferroic Magnetoelectric Composites: from Bulk to Thin Films (Adv. Mater. 9/2011)

AbstractMultiferroic magnetoelectric composite systems such as ferromagnetic‐ferroelectric heterostructures have recently attracted an ever‐increasing interest and provoked a great number of research activities, driven by profound physics from coupling between ferroelectric and magnetic orders, as well as potential applications in novel multifunctional devices, such as sensors, transducers, memories, and spintronics. In this Review, we try to summarize what remarkable progress in multiferroic magnetoelectric composite systems has been achieved in most recent few years, with emphasis on thin films; and to describe unsolved issues and new device applications which can be controlled both electrically and magnetically.

Tunable Tunneling Electroresistance in Ferroelectric Tunnel Junctions by Mechanical Loads

Combining nonequilibrium Green function's approach with density functional theory, effects of the applied mechanical loads on polarization, electrostatic potential, and tunneling conductance of a ferroelectric tunneling junction (FTJ) have been investigated. Using the first principle calculations, we show that compressive strains can induce and enhance the polarization in ferroelectric tunnel barriers, and practically achieve ferroelectricity in two unit cell thickness under a -2.2% compressive strain. More importantly, mechanical strains can significantly change the effective electrostatic potential in FTJ and thus control its tunneling conductance, which is defined as giant piezoelectric resistance (GPR) effect. Our calculations indicate that GPR effect is particularly significant near the paraelectric/ferroelectric phase transition, and increases exponentially with the barrier thickness. Furthermore, it is also found that defects of oxygen vacancies and nitrogen doping have little impact on GPR ratio of strained FTJ. Because of its high-sensitivity to external mechanical loads, FTJ with GPR effect should be adequate for applications in agile mechanical sensors, transducers, and other multifunctional devices.

Recent Progress in Multiferroic Magnetoelectric Composites: from Bulk to Thin Films

Multiferroic magnetoelectric composite systems such as ferromagnetic-ferroelectric heterostructures have recently attracted an ever-increasing interest and provoked a great number of research activities, driven by profound physics from coupling between ferroelectric and magnetic orders, as well as potential applications in novel multifunctional devices, such as sensors, transducers, memories, and spintronics. In this Review, we try to summarize what remarkable progress in multiferroic magnetoelectric composite systems has been achieved in most recent few years, with emphasis on thin films; and to describe unsolved issues and new device applications which can be controlled both electrically and magnetically.

Multilevel, Multicomponent Microarchitectures of Vertically-Aligned Carbon Nanotubes for Diverse Applications

A simple multiple contact transfer technique has been developed for controllable fabrication of multilevel, multicomponent microarchitectures of vertically aligned carbon nanotubes (VA-CNTs). Three dimensional (3-D) multicomponent micropatterns of aligned single-walled carbon nanotubes (SWNTs) and multiwalled carbon nanotubes (MWNTs) have been fabricated, which can be used to develop a newly designed touch sensor with reversible electrical responses for potential applications in electronic devices, as demonstrated in this study. The demonstrated dependence of light diffraction on structural transfiguration of the resultant CNT micropattern also indicates their potential for optical devices. Further introduction of various components with specific properties (e.g., ZnO nanorods) into the CNT micropatterns enabled us to tailor such surface characteristics as wettability and light response. Owing to the highly generic nature of the multiple contact transfer strategy, the methodology developed here could provide a general approach for interposing a large variety of multicomponent elements (e.g., nanotubes, nanorods/wires, photonic crystals, etc.) onto a single chip for multifunctional device applications.

Highly dispersed ultrafine Pt and PtRu nanoparticles on graphene: formation mechanism and electrocatalytic activity

We demonstrate a robust strategy for obtaining a high dispersion of ultrafine Pt and PtRu nanoparticles on graphene by exploiting the nucleation of a metal precursor phase on graphite oxide surfaces. Our method opens up new possibilities to engineer graphene-based hybrids for applications in multifunctional nanoscale devices.

ZnO nanostructures with controlled morphologies on a glass substrate

We report morphology-controlled selective growth of ZnO nanostructures on glasssubstrates by using catalyst-free metal-organic chemical vapor deposition. For themorphology-controlled selective growth, a microheating method using a series ofmicroheaters was developed, which provided well-controlled local heating based on themicroheater geometry and spatial arrangement. ZnO nanostructure morphology dependedon the local growth temperature, so various nanostructure morphologies were obtainedselectively at specific positions on glass substrates by using local microheating. Themonolithic integration of nanostructures with different morphologies will have greatpotential for applications in multifunctional devices.

Large magnetoelectric effect in negative magnetostrictive/piezoelectric/positive magnetostrictive laminate composites with two resonance frequencies

A magnetoelectric (ME) Ni–PZT–TbFe 2 trilayer with negative magnetostrictive/piezoelectric/positive magnetostrictive layers has been prepared. The influence of the bias magnetic field and the magnetic field frequency on ME coupling is discussed. The ME coefficient behavior of the Ni–PZT–TbFe 2 trilayer is different from that of Ni–PZT–Ni and TbFe 2 –PZT–TbFe 2 trilayers. Two remarkable resonance peaks have been observed in the dependence of the ME voltage coefficient on the magnetic field frequency, which makes these Ni–PZT–TbFe 2 trilayers suitable for applications in multifunctional devices with multifrequency operation.

Continuous Rotation of Magnetization Controlled by Electric Field in Multiferroic State Originated from Conical Spin Order

The mutual control of magnetism and ferroelectricity is a longstanding goal of the investigation on multiferroicity, which offers the potential applications in multifunctional magnetoelectric devices. It has been observed in a variety of materials that the ferroelectric behavior can be controlled by magnetic field effectively, but the magnetic behavior is hard to be tuned by electric field ( E ) in most cases. The present work predicts that the magnetization ( M ) can be well controlled by E in conical spin structure. When E rotates in the plane normal to the magnetic modulation vector, M is driven by E to rotate continuously without any noticeable decay. This magnetoelectric tunability is attributed to the flexible rotation of conical spin structure.

Impact of postgrowth annealing on spin-glass ordering and exchange bias in SrMn3O6−δ nanoribbons

The magnetic properties of as-grown single-crystal SrMn3O6−δ nanoribbons synthesized by a simple molten-salt method can be significantly improved by a heat-treatment procedure, which enhances the ferromagnetism and spin-glass behavior. These enhanced properties might originate from a spin structure modulated by the thermodynamical equilibrium nonuniform oxygen distribution. Measurements of ac susceptibility prove the existence of a spin-glass phase in the postgrowth annealing SrMn3O6−δ nanoribbons, which differs from the only antiferromagnetic phase in the corresponding bulk material. Asymmetric magnetization hysteresis loops observed in applied magnetic fields H≤5 T are attributed to an exchange coupling between the spin-glass shell and the antiferromagnetic core of postgrowth annealing SrMn3O6−δ nanoribbons. Results suggest that the intrinsic phase inhomogeneity due to the surface effects of the nanostructural manganites may induce exchange anisotropy, which is of special interests for potential application in multifunctional spintronic devices.

Comparison of room-temperature multiferroics in Bi 4Fe 2TiO 12 film and bulk

It was reported that both dielectricity and magnetism at room temperature were appreciably improved in Bi 4Fe 2TiO 12 film compared with Bi 4Fe 2TiO 12 bulk. X-ray diffraction profiles reveal similar crystalline nature and random orientation of the two, but X-ray photoelectron spectroscopy (XPS) experiments indicate that it is 1.4 eV lower binding energy of core-state O1s in the film relative to that of the bulk, so the improvement of multiferroics in the film is attributed to oxygen vacancies and high fraction of interface. The results have promising applications in multifunctional integrated devices.

Electrically Tunable Polypyrrole Inverse Opals with Switchable Stopband, Conductivity, and Wettability

An electrically tunable Ppy inverse opal was fabricated by electropolymerization. The stopband, conductivity, and wettablity of the inverse opal could be reversibly modulated by electroredox. These properties endowed the material with promising applications in multifunctional optoelectronic devices.

Magnetic control of dielectric properties of Ba0.6Sr0.4TiO3 in a trilayer system

Dielectric properties of Ba0.6Sr0.4TiO3 (BST) in a layered terfenol-D/BST/terfenol-D system were investigated. Dielectric properties of the BST layer can be adjusted by magnetostrictive strain of terfenol-D layers under applied magnetic fields. Our results show that the small-signal dielectric constant of BST can be tuned ranging from about 2300 to 4000 by a small magnetic field. By adjusting the relative layer thickness ratio, a more broad adjustable dielectric constant and tunability of BST layer can be designed, which may have potential applications in sensitive multifunctional devices and microwave devices.

Synthesis, characterization and photoluminescence of well-ordered ZnO micropillars grown on ZnO buffer layers

Using ZnO buffer layers prepared by simply thermal oxidation of ion beam sputtered Zn films, highly oriented and uniformly aligned single-crystalline ZnO micropillars arrays have been synthesized by thermal evaporation of Zn powder with free catalysts at low temperature of 430 °C. The ZnO micropillars show sharp hexagonal umbrella-like tips with thin ZnO nanowire grown on the tips. The umbrella-like tips grow in a layer-by-layer mode along the direction of [001]. The growth mechanism has been discussed. The formation of the micropillars basically depends on the gradually decreasing Zn vapor pressure and subsequently cooling process. The photoluminescence (PL) spectrum indicates a moderately good crystal quality of the ZnO micropillars. Our results may reinforce the understanding of the formation mechanism of different ZnO nano/microstructures. This kind of complex microstructures may find potential applications in multifunctional microdevices, optoelectronic and field emission devices.

Magnetoelectric properties of multiferroic composites with pseudo-1-3-type structure

A pseudo-1-3-type multiferroic composite consisting of Pb(Zr,Ti)O3 (PZT) rod array (with base) and Terfenol-D/epoxy matrix was prepared by the dice-and-fill technique. Simple series and parallel mixture rules well described the measured dielectric and piezoelectric constants. Large magnetoelectric coefficients were observed in the pseudo-1-3-type composite, e.g., over 300mV∕cmOe below 40kHz and over 4500mV∕cmOe at resonant frequency. The magnetoelectric response strongly depends on the magnetostrictive behavior of the matrix and the volume fraction of PZT rods, which gives us two convenient ways to modify their magnetoelectric response. For this pseudo 1-3-type multiferroic composite, the remarkable magnetoelectric response and well-developed fabrication technique are advantageous for their practical applications in piezoelectric-magnetoelectric multifunctional devices and large bandwidth magnetic sensors.

Magnetoelectric Properties of Multiferroic Composites with Pseudo 1-3 Type Structure

ABSTRACTA pseudo 1-3 type multiferroic composite consisting of Pb(Zr,Ti)O3 (PZT) rod array (with base) and Terfenol-D/Epoxy matrix was prepared by the dice-and-fill technique. Simple series and parallel mixture rules well described the measured dielectric and piezoelectric constants. Large magnetoelectric coefficients were observed in the pseudo 1-3 type composite, e.g., over 300 mV/cmi×Oe below 40 kHz and over 4500 mV/ cm×Oe at resonant frequency. The ME response strongly depends on the magnetostrictive behavior of the matrix and the volume fraction of PZT rods, which gives us two convenient way to modify their magnetoelectric response. For this pseudo 1-3 type multiferroic composite, the remarkable magnetoelectric response and well-developed fabrication technique are advantageous for their practical applications in piezoelectric-magnetoelectric multifunctional devices and large bandwidth magnetic sensors.

Electro‐Mechano‐Optical Conversions in Pr3+‐Doped BaTiO3–CaTiO3 Ceramics

A new class of praseodymium-doped ceramics simultaneously displays electrostriction (the conversion of electrical energy into mechanical energy), mechanoluminescence, and electroluminescence. For example, red-light emission is produced upon compression (see Figure). These environmentally friendly materials may find application in multifunctional sensors or devices.

DNA-Directed Self-Assembling of Carbon Nanotubes

Multicomponent structures were constructed by DNA-directed self-assembling of multiple carbon nanotubes and gold nanoparticles. The work presented here represents an important advance in constructing many multicomponent nanotube structures for multifunctional material and device applications.