Information Storage Applications Research Articles

Enhanced ferroelectric and piezoelectric properties of BCT-BZT at the morphotropic phase boundary driven by the coexistence of phases with different symmetries

The discovery of lead-free piezoelectric materials is crucial for future information and energy storage applications. Enhanced piezoelectric and other physical properties are commonly observed near the morphotropic phase boundary (MPB) composition of ferroelectric solid solutions. The $(1\ensuremath{-}x)\mathrm{Ba}({\mathrm{Zr}}_{0.2}{\mathrm{Ti}}_{0.8}){\mathrm{O}}_{3}\text{\ensuremath{-}}x({\mathrm{Ba}}_{0.7}{\mathrm{Ca}}_{0.3}){\mathrm{TiO}}_{3}$ $(\mathrm{BZT}\text{\ensuremath{-}}x\mathrm{BCT})$ system exhibits a large electromechanical response around its MPB region at $x=0.5$. We report experimental and theoretical results of $\mathrm{BZT}\text{\ensuremath{-}}x\mathrm{BCT}$ over a wide composition range $(0.3\ensuremath{\le}x\ensuremath{\le}1.0)$. X-ray diffraction and Raman spectroscopy studies indicate a composition-induced structural phase transition from a rhombohedral $(R3m)$ phase at $x\ensuremath{\le}0.4$ to a tetragonal $(P4mm)$ phase at $x\ensuremath{\ge}0.6$ through a multiphase coexistence region at 0.45 \ensuremath{\le} $x\ensuremath{\le}0.55$ involving orthorhombic + tetragonal (Amm2 + $P4mm$) phases. First-principles calculations elucidate the phase competition in the coexistence region. The critical composition $(x=0.5)$ displays enhanced dielectric, ferroelectric, and piezoelectric properties, where notably ${d}_{33}\ensuremath{\sim}320$ pC/N. This paper provides clear evidence of Amm2 + $P4mm$ crystallographic phases in the MPB region, which is responsible for the improved functional properties.

Giant tunneling electroresistance in epitaxial ferroelectric ultrathin films directly integrated on Si

Retaining information with the least loss of energy is of interest for ubiquitous mobile devices. Various forms of nonvolatile memory have been pursued based on the resistance change in the memory architecture. The nonvolatility of spontaneous polarization in a ferroelectric material also has been considered a promising ingredient for information storage applications, including traditional nonvolatile memory applications and emerging neuromorphic synaptic devices. Here, we demonstrate a colossal resistance change in the ferroelectric tunnel junction with an On/Off ratio of 106 in a ferroelectric HfO2 thin film integrated directly on a silicon wafer, which is inevitable for practical application. To achieve this large On/Off ratio, we integrated the epitaxial fluorite-structure HfO2 thin film on the silicon substrate. The polarization direction in the metal-ferroelectric-semiconductor junction altered the depletion width, leaving behind the change in the tunnel barrier. Industry-relevant HfO2 with high CMOS compatibility could lead to fast adoption of a ferroelectric tunnel barrier with newly observed ferroelectricity in fluorite-structured HfO2 films.

Reversible Mechanically Induced On–Off Photoluminescence in Hybrid Metal Halides

AbstractStimulus‐responsive photoluminescent materials have attracted extensive research attention in recent years owing to their potential application in information storage and switch devices. It is important to further explore such bistable materials as well as the underlying transformation mechanisms. Herein, the syntheses and mechanically tunable “on–off” photoluminescence (PL) of two organic–inorganic hybrid metal halides, (Bmpip)9Pb3Zn2Br19 and (Bmpip)9Pb3Cd2Br19 (Bmpip+ = 1‐butyl‐1‐methyl‐piperidinium, C10H22N+), are reported. Both as‐obtained compounds are nonemissive under UV light at ambient conditions but exhibit bright PL upon grinding or under hydrostatic pressure. Interestingly, the PL is quenchable by short‐time annealing or storage in air for 1 week, and the process is repeatable. Through a combination of extensive structural and spectral analyses, the crucial role of the organic cations interacting with inorganic chromophores in the “on–off” PL behavior of the title compounds is revealed. Moreover, pressure‐induced PL and PL‐enhancement phenomena are observed in both compounds, which are similar to but slightly different than the above‐mentioned mechano‐PL. Finally, proof‐of‐concept devices are fabricated to demonstrate the potential applications of the title compounds in message recording and force sensing.

Low temperature magnetic study and first principle calculation in ‘Mo’ doped CoFe2O4 for magnetic information storage applications

Structural and low temperature magnetic properties of CoFe2−xMoxO4 (x = 0.01, 0.03 and 0.05) were studied in the present work. Rietveld refinement of XRD patterns of CoFe2−xMoxO4 (x = 0.01, 0.03 and 0.05) confirm the pure phase cubic crystal structure in Fd3m space group. The decrease in lattice parameters (a contraction of the lattice) has been observed with doping, which confirms the probability of substitution of ‘Mo’ at the octahedral site of parental CoFe2O4 (CFO). The micro-strain via W-H plots was found to be enhanced for CoFe1.95Mo0.05O4 (CMFO5) sample which confirms the incorporation of ‘Mo’ atoms at Fe-site and subsequently reducing impurities as observed from refined patterns. The low temperature (2K) magnetic parameters were found to be greatly enhanced with ‘Mo’ substitution. We observed the decrease in anisotropy constant of Co2+ ions with ‘Mo’ doping and Mo6+ ions concentration at the tetrahedral site of CFO, increases the magnetization of the samples. Both M-H and ZFC-FC measurements confirm the ferrimagnetic behavior of all the samples. The maximum value of information storage parameter ‘S’ achieved around 0.442 for x = 0.03 sample at 2K. The structural parameters, electronic (density of states and band structure) and magnetic properties of pure CFO have also been investigated via computational first principle based density functional theory (DFT) calculations. The computational results are in good agreement with the experimental outputs.

Electrically Tunable and Dramatically Enhanced Valley-Polarized Emission of Monolayer WS2 at Room Temperature with Plasmonic Archimedes Spiral Nanostructures.

Monolayer transition metal dichalcogenides (TMDs) have intrinsic valley degrees of freedom, making them appealing for exploiting valleytronic applications in information storage and processing. WS2 monolayer possesses two inequivalent valleys in the Brillouin zone, each valley coupling selectively with a circular polarization of light. The degree of valley polarization (DVP) under the excitation of circularly polarized light (CPL) is a parameter that determines the purity of valley polarized photoluminescence (PL) of monolayer WS2 . Here efficient tailoring of valley-polarized PL from monolayer WS2 at room temperature (RT) through surface plasmon-exciton interactions with plasmonic Archimedes spiral (PAS) nanostructures is reported. The DVP of WS2 at RT can be enhanced from <5% to 40% and 50% by using 2 turns (2T) and 4 turns (4T) of PAS, respectively. Further enhancement and control of excitonic valley polarization is demonstrated by electrostatically doping monolayer WS2 . For CPL on WS2 -2TPAS heterostructures, the 40% valley polarization is enhanced to 70% by modulating the carrier doping via a backgate, which may be attributed to the screening of momentum-dependent long-range electron-hole exchange interactions. The manifestation of electrically tunable valley-polarized emission from WS2 -PAS heterostructures presents a new strategy toward harnessing valley excitons for application in ultrathin valleytronic devices.

Polarized Emission of Lanthanide Metal–Organic Framework (Ln‐MOF) Crystals for High‐Capacity Photonic Barcodes

AbstractPhotonic barcodes hold great promise for applications in information storage and data encryption. However, the spectroscopic encoding of lanthanide‐based photonic barcodes reported thus far is exclusively manipulated by sophisticated external stimuli or spatially resolved lanthanide heterostructures, and still suffers from small coding space and low coding capacity. Herein, a facile approach to design high‐capacity photonic barcodes through manipulating the polarized emission of Eu3+ metal–organic framework is proposed. Thanks to the highly anisotropic crystal structure and low‐symmetry energy level splitting of Eu3+, the large degree of polarization (≈0.96) enables not only color‐tunable emission but also abundant well‐resolved sub‐barcodes. Such polarization‐sensitive emission of the crystals provides a smart encoding strategy to realize polarization‐covert sub‐barcodes, which can be further integrated into a large coding library of photonic barcodes toward high‐capacity data storage and advanced anti‐counterfeiting applications.

Enhanced crystallinity and photoluminescence properties of Yb2+ doped SrSi2O2N2 phosphor for image storage applications

A series of Yb2+ and Dy3+ doped SrSi2O2N2 phosphors with enhanced crystallinity and photoluminescence properties have been successfully synthesized by two-step method using Sr2SiO4 as precursor. It is clearly indicated from XRD results that Yb2+ ions can substitute Sr sites in SrSi2O2N2 crystal and exhibit pure phase and well-crystalline in comparison with the samples prepared by traditional solid-state reaction. The excessive amount of Si3N4 in the reactants promoted the formation of pure SrSi2O2N2 phosphors phase. SrSi2O2N2: Yb2+ phosphors show emission band at 583 nm and the broad excitation peaks located at 308 nm, 384 nm and 447 nm, covering the emission wavelength of NUV and blue chips. Compared with the sample prepared by traditional one-step solid-state reaction method, a dramatic enhancement of photoluminescence emission intensity (∼1.75 times) can be observed for SrSi2O2N2: 0.01 Yb2+ phosphor synthesized by two-step method. Due to the concentration quenching, the luminescence intensity reaches the maximum when doping concentration of Yb2+ ions is 1 mol%, which is identified as the electric dipole-electric dipole interaction. Notably, Yb2+ and Dy3+ co-doped SrSi2O2N2 phosphors with pure phase exhibit a unique thermal-stimulated luminescence property under NUV excitation, indicating the potential application in optical information storage. Furthermore, the mechanism of thermal-stimulated luminescence has been proposed.

Near‐Infrared Persistent Luminescence and Trap Reshuffling in Mn4+ Doped Alkali‐Earth Metal Tungstates

AbstractNear‐infrared persistent luminescent materials have great potential for in vivo bioimaging and night‐vision surveillance due to their long‐lasting autofluorescence‐free emission through deep tissues and multicycle photostimulated luminescence by releasing energy from captured traps using high‐intensity 808 or 980 nm lasers. However, phosphors combining both near‐infrared persistent luminescence and photostimulated luminescence are found mostly in chromium doped gallates hosts, other emitters are rarely reported. Herein, a new material system with near‐infrared persistent luminescence is achieved in tetravalent manganese doped double‐perovskite alkali‐earth metal tungstates via the aliovalent substitution of calcium ions with lanthanum ions. Persistent luminescence can be generated via X‐ray irradiation, providing great promise in long‐term deep‐tissue ultrasensitive imaging, information storage, and X‐ray detection. Photostimulated detrapping is successfully demonstrated using a common 420 nm light emitting diode instead of a high‐intensity 808 or 980 nm laser. The traps distribution is proved to be reshuffled upon this laser‐free visible light stimulation. Reshuffling of trap distributions upon visible light stimulation may be promising for optical information storage applications. This work is expected to broaden the range of near‐infrared persistent material systems and provides new insights into manipulating photostimulated traps via laser‐free light stimulation.

Smart screen-printed photochromic fabrics with fast color switching performance and high fatigue resistance for energy storage applications

Photochromic materials have great potential in various novel optoelectronic devices such as adaptive regulation, smart detection, information storage, and camouflage anti-counterfeiting displays. However, the problems of high sensitivity and not to be influenced by external factors are urgent to be solved. Here, we have successfully prepared smart photochromic fabrics for stimulus-responsive applications with high-sensitive spiropyran (SP) and a phase change material of butyl stearate as core materials and encapsulated by a highly translucent poly(methyl methacrylate) (PMMA) shell. And then, they are coated on the fabrics with water-based polyurethane (WPU) by a facile method of screen printing. The preparation of photochromic materials as the form of microcapusles aims at reducing external factors’ disturb and achieving a rapid response when in use. The phase change material of microcapusles acts as a thermal regulation effect on the whole system, providing energy storage and temperature regulation. The resultant reversible photochromic fabrics prepared by this method has the potential applications of tangible information storage (QR codes), anti-counterfeit printing and rewritable patterns due to their fast response and reusability under UV light.

Structure and luminescence properties of Ce3+-activated BaLu2Al2Ga2SiO12 persistent phosphors for optical information storage

A novel BaLu2Al2Ga2SiO12:Ce3+ persistent phosphor was designed and synthesized through hetero-valence substituting Ba2+-Si4+ ion pair for Lu3+-Al3+ one in the Lu3Al3Ga2O12. XRD and Rietveld refinement results confirm the garnet typed crystal structure. SEM information shows that the constituent elements are uniformly distributed on the irregular particles. Under 360 or 430 nm excitation, the samples exhibit broad emission bands peaking at 510 nm. The luminescence intensity reaches to the maximum at 6 mol% Ce3+ doping content, and an internal quantum efficiency of 51.2% is achieved. The concentration quenching between Ce3+ ions is mainly originated from exchange interaction. Moreover, the phosphors exhibit bright cyan afterglow for minutes after removing the blue-light excitation source. The persistent luminescence decay process is studied by thermoluminescence spectra. The persistent luminescence mechanism and optical information writing and reading process are also discussed to explore the application in optical information storage.

Recognition of printed small texture modules based on dictionary learning

Quick Response (QR) codes are designed for information storage and high-speed reading applications. To store additional information, Two-Level QR (2LQR) codes replace black modules in standard QR codes with specific texture patterns. When the 2LQR code is printed, texture patterns are blurred and their sizes are smaller than0.5{mathrm{cm}}^{2}. Recognizing small-sized blurred texture patterns is challenging. In original 2LQR literature, recognition of texture patterns is based on maximizing the correlation between print-and-scanned texture patterns and the original digital ones. When employing desktop printers with large pixel extensions and low-resolution capture devices, the recognition accuracy of texture patterns greatly reduces. To improve the recognition accuracy under this situation, our work presents a dictionary learning based scheme to recognize printed texture patterns. To our best knowledge, it is the first attempt to use dictionary learning to promote the recognition accuracy of printed texture patterns. In our scheme, dictionaries for all kinds of texture patterns are learned from print-and-scanned texture modules in the training stage. And these learned dictionaries are employed to represent each texture module in the testing stage (extracting process) to recognize their texture pattern. Experimental results show that our proposed algorithm significantly reduces the recognition error of small-sized printed texture patterns.

Construction of dendrimer-induced quantum dots loaded colloids towards fluorescent photonic crystal patterns via direct writing

A facile strategy is developed to construct fluorescent photonic crystals (PCs) patterns composed of hybrid microspheres by direct writing. These microspheres are fabricated by grafting fluorescent Cu-In-S/ZnS quantum dots (QDs) on the surface of SiO2 microspheres by using generation 3 polyamindoamine (G3 PAMAM) dendrimers as bridges. In virtue of the strong interaction of dendrimers with QDs and SiO2 microspheres through amidation reaction, the hybrid microspheres exhibit remarkable structural stability and fluorescent stability. Accordingly, the as-prepared PCs patterns display stable structural color and fluorescence. This work brings a unique viewpoint in patterned photonic crystal, which are highly versatile for information storage and anti-counterfeiting applications.

Imprint phenomenon of ferroelectric switching characteristics in BaTiO3/PbTiO3 multilayer thin films

Materialsin which ferroelectric polarization can be locally controlled have potential for high-density information storage applications. Herein, we investigated the ferroelectric polarization switching characteristics of epitaxial BaTiO3/PbTiO3 (BTO/PTO) multilayer thin films by using piezoresponse force microscopy. Pulsed laser deposition was used to form an epitaxial BTO layer on an epitaxial ferroelectric PTO single thin film. This epitaxial BTO/PTO multilayer thin film exhibited an imprint phenomenon, in which the internal electric field was asymmetrically induced and the ferroelectric hysteresis loop was shifted. Owing to this imprint phenomenon, a large difference occurred between the two coercive electric fields of the ferroelectric hysteresis loop. Because the coercive electric field was reduced in one direction, a relatively small switching voltage was required to form ferroelectric polarization nanobits in a local region and the size of the switched nanobits was minimized. This behavior can be utilized as the basis for developing high-density ferroelectric-based storage media.

Steering Nonlinear Twisted Valley Photons of Monolayer WS2 by Vector Beams.

Monolayer transition metal dichalcogenides have intrinsic spin-valley degrees of freedom, drawing broad interests due to their potential applications in information storage and processing. Here, we demonstrate the possibility of using cylindrical vector pumped beams, which are nonseparable in their polarization and spatial modes, to manipulate nonlinear valley-locked twisted-vortex emissions in monolayer tungsten disulfide (WS2). The second-harmonic (SH) photons from K and K' valleys are encoded with opposite optical vortices, thus allowing the SH beams to emerge as cylindrical vector beams with doubled topological orders compared to the fundamental beams. The conically refracted pumped beams allow us to generate the first-order SH cylindrical vector and full Poincaré beams via tuning the valley-locked emitted light field profiles. With fanshaped WS2 films breaking the axial symmetry of SH beams, the SH valley photons are routed to opposite directions. Our results pave the way to develop atomically thin nonlinear photonic devices and valleytronic nanodevices.

Metal Cation-Responsive and Excitation-Dependent Nontraditional Multicolor Fluorescent Hydrogels for Multidimensional Information Encryption.

Fluorescent polymeric hydrogels especially multicolor fluorescent polymeric hydrogels (MFPHs) have important applications in information storage, encryption, and encoding. MFPHs are generally prepared by incorporating multiple traditional fluorescent materials into hydrogels. In recent years, nontraditional luminescent polymers without any traditional π-conjugated chromophores have received increasing attention. Here, we report a novel type of nontraditional MFPHs prepared by in situ polymerization of acrylamide (AAm) in the presence of poly(itaconic acid) (PITAc). The hydrogen-bonded mechanically strong PAAm/PITAc hydrogels show strong intrinsic fluorescence, and the fluorescence emission is excitation-dependent and metal cation-responsive. More impressively, the hydrogels treated with metal cations also possess excitation-dependent fluorescence. We developed a multi-ion inkjet printing (MIIP) technique to print texts or designed patterns onto the hydrogel surface using different metal cation solutions as inks, and then variable texts or patterns appear under the irradiation of UV, violet, and blue lights. Patterns can be further changed by selective printing, erasing, or reprinting on some regions. Therefore, multidimensional information encryption is achieved. This work provides a new strategy for preparing MFPHs for wide applications.

Controllable enormous valley splitting in Janus WSSe on CrN monolayer

Manipulation of valley polarization in low-dimensional systems is desirable for future applications in information process and storage. Here, we design two-dimensional WSSe/CrN van der Waals heterostructures and control the valley degree of freedom based on the first-principles calculations. Combining the internal electric field and magnetic proximity effect, the interfacial interaction and the valley splitting are efficiently modulated in the system. Intrinsic enormous valley splitting of 103 meV and 144 meV are generated in S- and Se-terminated WSSe/CrN heterostructures, which corresponds to the effective Zeeman magnetic field of 1280 and 1574 T, respectively. A prominent anomalous Hall conductivity at K valley is induced by time-reversal symmetry breaking and sizable Berry curvature. Furthermore, valley splitting can be manipulated continually by the in-plane strain and interlayer distance. The largest valley splitting of 272 (240) meV and the effective Zeeman magnetic field of 2560 (2275) T are achieved for S (Se)-terminated WSSe/CrN heterostructures, respectively, under the compressive interlayer distance. It is found that the changes of induced spin charges around S and W atom are responsible for the modulated valley splitting. This work opens new vistas for the design of valleytronic devices.

Phase-field simulations of surface charge-induced ferroelectric vortex

Ferroelectric vortices are characterized by their small size and exotic physical properties, which have great potential for application in high-density information storage. However, the influence of the shape of the external field on such topological vortex domain morphology and domain percentage is still lacking research. Here, the ferroelectric domain evolution induced by a circular-, square-, and triangular-shaped surface charge are investigated in BiFeO3 thin films by phase-field simulations. The shape symmetry of the surface charge distribution determines the 4R domain percentage in one single vortex. Triangle-shaped surface charge distribution with odd number symmetry axes has the greatest influence on the percentage of 4R domain, while that of circular- and square-shaped with even number symmetry axes have almost no influence on the 4R domain ratio. Compared to the triangle, an antivortex can be observed around the vortex domain in the circular- and square-shaped surface charge. The rotating triangle affects the domain percentage of the vortex and the emergence of an antivortex. Here, the difference of domain percentage is determined by the choice of nucleation position and the domain switching mechanism. It was found that the percentage of domain along the edge is greater than the corner of the triangle. Among them, 71° domain switching is more likely to happen than 109° and 180° domain switching. These findings provide a fundamental understanding for ferroelectric domain manipulation in a single vortex from an external field with different shapes.

Magnetic energy product and magnetocaloric effect in [formula omitted] anti-perovskite nitride material

Anti-perovskite nitride material Fe3AlN is studied by using the density functional theory with generalized gradient approximation (GGA+U) approaches and the Monte Carlo simulation in the framework of the Ising model. The parameter of the unit cell has been optimized, the electronic band structure, the electronic density of states and the magnetic moments of the compound are discussed. Based on the energy calculations, the exchange interactions and the magnetic anisotropy are calculated in order to perform the Monte Carlo simulation. Therefore the obtained Curie temperature Tc=780 (K) of the compound is in agreement with the experimental one Tc=770 (K). The magnetic and magnetocaloric properties are also investigated, the maximum entropy change and the RCP values are 3.355 J/Kg.K and 638 J/Kg for h=5T, respectively. Based on the hysteresis loops, the energy product BH was calculated. The obtained BHmax is equal to 1.26 (MGOe) above the ambient temperature. These results show that the Fe3AlN compound can be a good candidate for both information storage applications and magnetic refrigeration.

Designing Photochromic Materials with Large Luminescence Modulation and Strong Photochromic Efficiency for Dual‐Mode Rewritable Optical Storage

AbstractInorganic materials combining photochromism and luminescence modulation characteristics have great potential in dual‐mode rewritable optical storage due to their unique optical features and excellent thermal stability. However, the failure of achieving a large luminescence modulation and a strong photochromic efficiency in photostimulated inorganic photochromic materials limits their applications. Herein, a new strategy for realizing an overlap between the photochromic absorption peak and the photoluminescent emission/excitation peak is proposed for designing high‐performance photochromic materials. The obtained BaMgSiO4: M (M = Ce3+, Mn2+, or Nd3+) ceramics exhibit a reversible white‐pink color change upon alternate 310 nm and 590 nm illumination (or thermal stimulus) accompanied by a high photochromic efficiency (&gt;50%). Benefiting from a perfectly matched photochromic absorption peak and Mn2+ emission peak, a record luminescence modulation of 96.3% with excellent fatigue resistance is obtained in BaMgSiO4: Mn2+ ceramics. These properties are superior to all photochromic materials reported to date, demonstrating great potential in optical information storage applications. The trap‐related photochromic and regulated luminescence behavior is investigated together with a prototype of a dual‐mode information display. This work is expected to promote the practical application of photochromic materials in various optical devices and provides an effective strategy to develop other photochromic materials.

Self-accelerating photocharge separation in BiOBr ultrathin nanosheets for boosting photoreversible color switching

Photoreversible color switching materials (PCSMs) are promising for applications in optical information storage and security features. However, conventional inorganic PCSMs such as semiconductor oxides generally suffer from slow color switching speed and limited reversibility. Here we report a fast light-responsive color switching and high reversible inorganic PCSM based on oxygen vacancies BiOBr ultrathin nanosheets. Owing to the unique 2D ultrathin structure and oxygen vacancies, the BiOBr ultrathin nanosheets possess high photoreductive activity and fast charge separation and transfer efficiency under ultraviolet (UV) illumination to initiate color changing from light yellow to brown black. Importantly, UV illumination induced oxygen vacancies during color switching process act as self-accelerating charge separation centers to further boost the photoreversible color switching. By integrating BiOBr ultrathin nanosheets with agarose as matrix, the freestanding BiOBr ultrathin nanosheets/agarose nanocomposite film exhibit outstanding photoreversible color switching properties, including coloration in 1 min under UV illumination, decoloration in 15 min in ambient air, and high reversibility (≥100 cycles). Moreover, we demonstrate the application of nanocomposite films in time-sensitive, self-erasing rewritable paper with long-awaited positive imaging mode and black color. This work presents the possibility of developing high-efficient inorganic PCSMs that could be significantly broad their practical applications.