Information Storage Applications Research Articles

Evolution and modulation of Ag filament dynamics within memristive devices based on necklace-like Ag@TiO2 nanowire networks

Random nanowire networks (NWNs) are regarded as promising memristive materials for applications in information storage, selectors, and neuromorphic computing. The further insight to understand their resistive switching properties and conduction mechanisms is crucial to realize the full potential of random NWNs. Here, a novel planar memristive device based on necklace-like structure Ag@TiO2 NWN is reported, in which a strategy only using water to tailor the TiO2 shell on Ag core for necklace-like core–shell structure is developed to achieve uniform topology connectivity. With analyzing the influence of compliance current on resistive switching characteristics and further tracing evolution trends of resistance state during the repetitive switching cycles, two distinctive evolution trends of low resistance state failure and high resistance state failure are revealed, which bear resemblance to memory loss and consolidation in biological systems. The underlying conduction mechanisms are related to the modulation of the Ag accumulation dynamics inside the filaments at cross-point junctions within conductive paths of NWNs. An optimizing principle is then proposed to design reproducible and reliable threshold switching devices by tuning the NWN density and electrical stimulation. The optimized threshold switching devices have a high ON/OFF ratio of ∼107 with threshold voltage as low as 0.35 V. This work will provide insights into engineering random NWNs for diverse functions by modulating external excitation and optimizing NWN parameters to satisfy specific applications, transforming from neuromorphic systems to threshold switching devices as selectors.

Blue Phase III: Topological Fluid of Skyrmions

Optical microscopy reveals that blue phases---molecularly ordered liquids---consist of filaments with vortexlike cross sections known as skyrmions, whirls in a material, with possible information-storage applications.

Single charge control of localized excitons in heterostructures with ferroelectric thin films and two-dimensional transition metal dichalcogenides.

Single charge control of localized excitons (LXs) in two-dimensional transition metal dichalcogenides (TMDCs) is crucial for potential applications in quantum information processing and storage. However, traditional electrostatic doping method by applying metallic gates onto TMDCs may cause inhomogeneous charge distribution, optical quenching, and energy loss. Herein, by locally controlling the ferroelectric polarization of the ferroelectric thin film BiFeO3 (BFO) with a scanning probe, we can deterministically manipulate the doping type of monolayer WSe2 to achieve p-type and n-type doping. This nonvolatile approach can maintain the doping type and hold the localized excitonic charges for a long time without applied voltage. Our work demonstrated that the ferroelectric polarization of BFO can control the charges of LXs effectively. Neutral and charged LXs have been observed in different ferroelectric polarization regions, confirmed by magnetic optical measurement. Highly circular polarization degree with 90% photon emission from these quantum emitters was achieved in high magnetic fields. Controlling the single charge of LXs in a non-volatile way shows a great potential for deterministic photon emission with desired charge states for photonic long-term memory.

ONE-POT SYNTHESIS OF CARBON QUANTUM DOTS AND THEIR APPLICATION AS A FLUORESCENT INKS

A facile, low cost, and one-pot hydrothermal reaction method is utilized to synthesized highly stable and durable carbon quantum dots (CQDs) by using laurus nobilis leaves as a carbon source. Laurus nobilis leaves were subjected to hydrothermal reaction at 175 °C for 10 h. The color of obtained CQDs under UV-light is bright blue fluorescence. The excitation dependent fluorescent emission of the prepared CQDs was observed and the obtained CQDs gives maximum emission at 425 nm when excited at 344 nm. The absorption peak of the CQDs is located at 279 nm. Furthermore, the synthesized CQDs can be consumed as a fluorescent ink for security, encryption and information storage applications. Combining with good stability and water solubility, unique fluorescence properties and its low-cost, CQDs can also be used as a next generation fluorescent ink alternative to traditional fluorescent ink for anti-counterfeiting.

Fabry-Perot Mode-Limited High-Purcell-Enhanced Spontaneous Emission from In Situ Laser-Induced CsPbBr3 Quantum Dots in CsPb2Br5 Microcavities.

The patterned metal halide perovskites exhibit novel photophysical properties and high performance in photonic applications. Here, we show that a UV continuous wave laser can induce in situ crystallization of individual and patterned CsPbBr3 quantum dots (QDs) inside the CsPb2Br5 microplatelets. The microplatelet acts as a natural Fabry-Perot cavity and causes the high-Purcell-effect-enhanced (by 287 times) cavity mode spontaneous emission of the embedded CsPbBr3 QDs. The luminescence exhibits a superlinear emission intensity-excitation intensity relation I(p) ∝ p2.83, and the exponent is much bigger than that of the free-space exciton spontaneous emission, suggesting arising of stimulated emission at higher photon concentrations. These laser-driven crystallized and patterned cavity mode luminescent perovskite QDs in a waterproof wider-bandgap perovskite microcavity act as an ideal platform for studying the cavity quantum electrodynamics phenomena and for applications in information storage and encryption, anticounterfeiting, and low-threshold lasers.

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.