High-density Information Storage Research Articles

Six-Coordinated CoII Single-Molecule Magnets: Synthetic Strategy, Structure and Magnetic Properties.

The pursuit of molecule-based magnetic memory materials contributes significantly to high-density information storage research in the frame of the ongoing information technologies revolution. Remarkable progress has been achieved in both transition metal (TM) and lanthanide based single-molecule magnets (SMMs). Notably, six-coordinated CoII SMMs hold particular research significance owing to the economic and abundant nature of 3d TM ions compared to lanthanide ions, the substantial spin-orbit coupling of CoII ions, the potential for precise control over coordination geometry, and the air-stability of coordination-saturated structures. In this review, we will summarize the progress made in six-coordinated CoII SMMs, organized by their coordination geometry and molecular structure similarity. Valuable insights, principles, and new mechanism gleaned from this research and remaining issues that need to be addressed will also be discussed to guide future optimization.

Narrowband Organic/Inorganic Hybrid Afterglow Materials.

Narrowband afterglow materials display interesting functions in high-quality anti-counterfeiting and multiplexed bioimaging. However, there is still a limited exploration of these afterglow materials, especially for those with a full width at half maxima (FWHM) around 30 nm. Here, we report the fabrication of narrowband organic/inorganic hybrid afterglow materials via energy transfer technology. Coronene (Cor) with a long phosphorescence feature and broad phosphorescence band is selected as the donor for energy transfer, and inorganic quantum dots (QDs) of CdSe/ZnS with a narrowband emission are used as acceptors. Upon doping into the organic matrix, the resultant three-component materials exhibit a narrowband afterglow with an afterglow lifetime of approximately 3.4 s and an FWHM of 31 nm. The afterglow wavelength of the afterglow materials can be controlled by the QDs. This work based on organic/inorganic hybrids provides a facile approach for developing multicolor and narrowband afterglow materials, as well as opens a new way for expanding the features of organic afterglow for multifunctional applications. It is expected to rely on narrowband afterglow emitters to solve the "spectrum congestion" problem of high-density information storage in optical anti-counterfeiting and information encryption.

Catalyst-regulated conversion of p-phenylenediamine-based carbon dots from red to deep-blue emission

Deep-blue emission (＜450 nm) is significant in high-density information storage, solid-state lighting, and vivid displays. However, the carbon dots (CDs) obtained from p-phenylenediamine (pPD) have only red fluorescence, which greatly limits the application and development of pPD-based CDs. As we all know, a catalyst is a substance that can change the rate and pathway of a chemical reaction. Herein, we designed to add a catalyst to realize the conversion of pPD-based CDs from red to deep-blue fluorescence. The emission peak of obtained deep-blue CDs was 440 nm, and the full-width at half-maximum (FWHM) was only 58 nm, with a high color purity. In addition, through in-depth analysis of microstructure and photoluminescence (PL) properties, it is found that the decrease of the sp2-conjugated domain and the graphite N content and the increase in pyridinic N content were the main reasons for the blue shift of the spectra. Based on this, the formation process and mechanism of red and deep-blue CDs were further elucidated. This work not only efficiently realized the design of the deep-blue CDs but also provided a new idea for the luminescence regulation of CDs without changing the raw materials and reaction conditions.

Boosting the Curie temperature of GaN monolayer through van der Waals heterostructures

The pursuit of van der Waals (vdW) heterostructures with high Curie temperature and strong perpendicular magnetic anisotropy (PMA) is vital to the advancement of next generation spintronic devices. First-principles calculations are used to study the electronic structures and magnetic characteristics of GaN/VS2 vdW heterostructure under biaxial strain and electrostatic doping. Our findings show that a ferromagnetic ground state with a remarkable Curie temperature (477 K), much above room temperature, exists in GaN/VS2 vdW heterostructure and 100% spin polarization efficiency. Additionally, GaN/VS2 vdW heterostructure still maintains PMA under biaxial strain, which is indispensable for high-density information storage. We further explore the electron, magnetic, and transport properties of VS2/GaN/VS2 vdW sandwich heterostructure, where the magnetoresistivity can reach as high as 40%. Our research indicates that the heterostructure constructed by combining the ferromagnet VS2 and the non-magnetic semiconductor GaN is a promising material for vdW spin valve devices at room temperature.

Multilevel Information Encryption Based on Thermochromic Perovskite Microcapsules via Orthogonal Photic and Thermal Stimuli Responses.

Increasing modal variations of stimulus-responsive materials ensure the high capacity and confidentiality of information storage and encryption systems that are crucial to information security. Herein, thermochromic perovskite microcapsules (TPMs) with dual-variable and quadruple-modal reversible properties are designed and prepared on the original oil-in-fluorine (O/F) emulsion system. The TPMs respond to the orthogonal variations of external UV and thermal stimuli in four reversible switchable modes and exhibit excellent thermal, air, and water stability due to the protection of perovskites by the core-shell structure. Benefiting from the high-density information storage TPMs, multiple information encryptions and decryptions are demonstrated. Moreover, a set of devices are assembled for a multilevel information encryption system. By taking advantage of TPMs as a "private key" for decryption, the signal can be identified as the corresponding binary ASCII code and converted to the real message. The results demonstrate a breakthrough in high-density information storage materials as well as a multilevel information encryption system based on switchable quadruple-modal TPMs.

Nonvolatile behavior of resistive switching memory in Ag/WOx/TiOy/ITO device based on WOx/TiOy heterojunction

Two-terminal structure memristors are the most promising electronic devices that could play a significant role in artificial intelligence applications of the next generation and the post-Moore era. In this work, we fabricated the memristive device by depositing a heterojunction WOx/TiOy functional layer onto an indium tin oxide substrate using magnetron sputtering. The Ag/WOx/TiOy/ITO device exhibits improved memory behavior of bipolar resistive switching (RS) nonvolatile compared to TiOy-based single-layer memristors, enabling it to meet high-density information storage requirements. Moreover, our device exhibited the coexistence of the negative differential resistance effect and the behavior of the RS memory. Through a comprehensive analysis of conductivity on the curve of current–voltage (I–V), a physical model based on the mechanism of space charge-limited current, ohmic conduction, and Schottky emission was suggested to explain the behavior device RS memory. This study's findings demonstrate that including a heterojunction bilayer WOx/TiOy as a functional layer can significantly improve the performance of memristive devices. This advancement expands the potential application of ferroelectric metallic oxide heterojunctions within the field of memristors.

Recent Developments of Nontraditional Single-Molecule Toroics.

Single-molecule toroics (SMTs), defined as a type of molecules with toroidal arrangement of magnetic moment associated with bi-stable non-magnetic ground states, are promising candidates for high-density information storage and the development of molecule based multiferroic materials with linear magneto-electric coupling and multiferroic behavior. The design and synthesis of SMTs by arranging the magnetic anisotropy axis in a circular pattern at the molecular level have been of great interest to scientists for last two decades since the first detection of the SMT behavior in the seminal Dy3 molecules. DyIII ion has long been the ideal candidate for constructing SMTs due to its Kramer ion nature as well as high anisotropy. Nevertheless, other LnIII ions such as TbIII and HoIII ions, as well as some paramagnetic transition metal ions, have also been used to construct many nontraditional SMTs. Therefore, we review the progress in the studies of SMTs based on the nontraditional perspective, ranging from the 3D topological to 1D&2D&3D polymeric SMTs, and 3d-4f to non Dy-based SMTs. We hope the understanding we provide about nontraditional SMTs will be helpful in designing novel SMTs.

Endohedral metallofullerene molecular nanomagnets.

Magnetic lanthanide (Ln) metal complexes exhibiting magnetic bistability can behave as molecular nanomagnets, also known as single-molecule magnets (SMMs), suitable for storing magnetic information at the molecular level, thus attracting extensive interest in the quest for high-density information storage and quantum information technologies. Upon encapsulating Ln ion(s) into fullerene cages, endohedral metallofullerenes (EMFs) have been proven as a promising and versatile platform to realize chemically robust SMMs, in which the magnetic properties are able to be readily tailored by altering the configurations of the encapsulated species and the host cages. In this review, we present critical discussions on the molecular structures and magnetic characterizations of EMF-SMMs, with the focus on their peculiar molecular and electronic structures and on the intriguing molecular magnetism arising from such structural uniqueness. In this context, different families of magnetic EMFs are summarized, including mononuclear EMF-SMMs wherein single-ion anisotropy is decisive, dinuclear clusterfullerenes whose magnetism is governed by intramolecular magnetic interaction, and radical-bridged dimetallic EMFs with high-spin ground states that arise from the strong ferromagnetic coupling. We then discuss how molecular assemblies of SMMs can be constructed, in a way that the original SMM behavior is either retained or altered in a controlled manner, thanks to the chemical robustness of EMFs. Finally, on the basis of understanding the structure-magnetic property correlation, we propose design strategies for high-performance EMF-SMMs by engineering ligand fields, electronic structures, magnetic interactions, and molecular vibrations that can couple to the spin states.

Sliding ferroelectricity and the moiré effect in Janus bilayer MoSSe.

Two-dimensional van der Waals layered materials have attracted extensive attention in the field of low-dimensional ferroelectricity, on account of their readily delaminated structure and high-density information storage advantages. Here, we report the sliding ferroelectricity and moiré effects on the ferroelectricity in Janus bilayer MoSSe based on first-principles calculations. We focus on the changes of in-plane and out-of-plane polarizations due to sliding, and the calculations demonstrate that the in-plane and out-of-plane polarizations can be switched simultaneously by sliding. In addition, in moiré-twisted bilayer MoSSe, the complex stacking pattern and significant interlayer distance suppress the interlayer charge transfer, and the ferroelectric polarization is effectively suppressed. The polarization in the large-angle twisted structure is small but its direction can be adjusted by changing the twist angle. Our results emphasize the importance of low-dimensional ferroelectrics in van der Waals structures and pave a way for the search of sliding ferroelectric materials, as well as enriching the research on the ferroelectricity of large-angle twisted structures.

Above-Room-Temperature Ferromagnetism in Copper-Doped Two-Dimensional Chromium-Based Nanosheets.

Two-dimensional ferromagnetic materials (2D-FMs) are expected to become ideal candidates for low-power, high-density information storage in next-generation spintronics devices due to their atomically ultrathin and intriguing magnetic properties. However, 2D-FMs with room-temperature Curie temperatures (Tc) are still rarely reported, which greatly hinders their research progress and practical applications. Herein, ultrathin Cu-doped Cr7Te8 FMs were successfully prepared and can achieve above-room-temperature ferromagnetism with perpendicular magnetic anisotropy via a facile chemical vapor deposition (CVD) method, which can be controlled down to an atomic thin layer of ∼3.4 nm. STEM-EDX quantitative analysis shows that the proportion of Cu to metal atoms is ∼5%. Moreover, based on the anomalous Hall effect (AHE) measurements in a six-terminal Hall bar device without any encapsulation as well as an out-of-plane magnetic field, the maximum Tc achieved ∼315 K when the thickness of the sample is ∼28.8 nm; even the ultrathin 7.6 nm sample possessed a near-room-temperature Tc of ∼275 K. Meanwhile, theoretical calculations elucidated the mechanism of the ferromagnetic enhancement of Cu-doped Cr7Te8 nanosheets. More importantly, the ferromagnetism of CVD-synthesized Cu-doped CrSe nanosheets can also be maintained above room temperature. Our work broadens the scope on room-temperature ferromagnets and their heterojunctions, promoting fundamental research and practical applications in next-generation spintronics.

A Multiconfigurational Wave Function Theoretical Study on Electronic Structure and Magnetic Susceptibility of Dilanthanide Single Molecule Magnet.

Single molecule magnets (SMMs) have been a promising material for next-generation high-density information storage and molecular spintronics. N23--bridged dilanthanide complexes, {[(Me3Si)2N]2Ln(THF)(μ-η2:η2-N2)(THF)Ln[(Me3Si)2N]2}1-, exhibit high blocking temperatures and have been one of the promising candidates for future application. Rational understanding should be established between the magnetic properties and electronic structure. However, the theoretical study is still challenging due to the complexities in their electronic structures. Here, we theoretically studied the magnetic susceptibility of dilanthanide SMMs based on the state-of-the-art multistate-complete active space self-consistent field and perturbation theory at the second order and restricted active space state interaction with spin-orbit coupling calculations. Temperature dependence of the magnetic susceptibility (χmT-T curve) was quantitatively reproduced by the theoretical calculations. The complexities in the electronic states of these dilanthanide complexes originate from significantly strong static electron correlations in the lanthanide 4f and N2 π* orbitals and the SOC effect. The temperature dependence of the magnetic susceptibility results from the energy levels and magnetic properties of the low-lying excited state. The χmT values below 50 K are dominated by the ground state, while thermal distribution in the low-lying excited state affects the χmT values over 50 K. Saturation magnetization at low temperatures was also evaluated, and the result agrees with the experimental observation.

The polarization-modulated electronic structure and giant tunneling-electroresistance effect of a one-dimensional ferroelectric Ta4OTe9I4 nanowire

Low-dimensional ferroelectrics have a great deal of potential for use in electronic memory devices. However, intrinsic one-dimensional (1D) ferroelectricity is very rare. Using first-principles calculations, we present the discovery of an inborn 1D Ta4OTe9I4 ferroelectric (FE) nanowire. Its distinctive geometry can cause spontaneous electric polarization along the z-axis and allow it to maintain a certain temperature and strain. In addition to its sizable spontaneous polarization and appropriate Curie temperature, the 1D Ta4OTe9I4 nanowire exhibits an energy barrier comparable to those of other ferroelectrics. With polarization reversal, the energy gap can be modulated in the range of 0.38–1.33 eV, corresponding to an apparent peak shift phenomenon in the optical response. We use this nanowire as an exemplary material for building a FE tunnel junction composed of Hf0.5Ta3.5OTe9I4/Ta4OTe9I4/W0.5Ta3.5OTe9I4 with a giant tunneling electroresistance ratio at zero and low bias. Our calculations suggest that this 1D intrinsically FE material obtained from van der Waals crystals can be used in miniaturized and advanced high-density information storage.

Ferrocenyl-Substituted Triazatruxenes: Synthesis, Electronic Properties, and the Impact of Ferrocenyl Residues on Directional On-Surface Switching on Ag(111).

We report on seven new ferrocenyl-(1, 3)- and ferrocenylethynyl-modified N,N',N″-triethyltriazatruxenes (EtTATs) 4-7 as well as the dodecyl counterpart 2 of compound 1 and their use as molecular switching units when deposited on a Ag(111) surface. Such functional units may constitute a new approach to molecule-based high-density information storage and processing. Besides the five compounds 1-3, 6, and 7, where the 3-fold rotational symmetry of the triazatruxene (TAT) template is preserved, we also included 2-ethynylferrocenyl-TAT 4 and 2,2'-di(ethynylferrocenyl)-TAT 5, whose mono- and disubstitution patterns break the 3-fold symmetry of the TAT core. Voltammetric studies indicate that the ferrocenyl residues of compounds 1-7 oxidize prior to the oxidation of the TAT core. We have noted strong electrostatic effects on TAT oxidation in the 2,2',2″-triferrocenyl-TAT derivatives 1 and 2 and the 3,3',3″-isomer 3. The oxidized complexes feature multiple electronic excitations in the near-infrared and the visible spectra, which are assigned to dδ/δ* transitions of the ferrocenium (Fc+) moieties, as well as TAT → Fc+ charge-transfer transitions. The latter are augmented by intervalence charge-transfer contributions Fc → Fc+ in mixed-valent states, where only a part of the available ferrocenyl residues is oxidized. EtTAT was previously identified as a directional three-level switching unit when deposited on Ag(111) and constitutes a trinary-digit unit for on-surface information storage. The symmetrically trisubstituted compound 6 retains this property, albeit at somewhat reduced switching rates due to the additional interaction between the ferrocenyl residues and the Ag surface. In particular, the high directionality at low bias and the inversion of the preferred sense of the on-surface rocking motion with either a clockwise or counterclockwise switching sense, depending on the identity of the surface enantiomer, are preserved. Unsymmetrical substitution in mono- and diferrocenylated 4 and 5 alters the underlying ratchet potential in a manner such that a two-state switching between the two degenerate surface conformations of 4 or a pronounced suppression of switching (5) is observed.

BO-DNA: Biologically optimized encoding model for a highly-reliable DNA data storage

DNA data storage is a promising technology that utilizes computer simulation, and synthetic biology, offering high-density and reliable digital information storage. It is challenging to store massive data in a small amount of DNA without losing the original data since nonspecific hybridization errors occur frequently and severely affect the reliability of stored data. This study proposes a novel biologically optimized encoding model for DNA data storage (BO-DNA) to overcome the reliability problem. BO-DNA model is developed by a new rule-based mapping method to avoid data drop during the transcoding of binary data to premier nucleotides. A customized optimization algorithm based on a tent chaotic map is applied to maximize the lower bounds that help to minimize the nonspecific hybridization errors. The robustness of BO-DNA is computed by four bio-constraints to confirm the reliability of newly generated DNA sequences. Experimentally, different medical images are encoded and decoded successfully with 12%–59% improved lower bounds and optimally constrained-based DNA sequences reported with 1.77bit/nt average density. BO-DNA's results demonstrate substantial advantages in constructing reliable DNA data storage.

Toward highly effective loading of DNA in hydrogels for high-density and long-term information storage

Digital information, when converted into a DNA sequence, provides dense, stable, energy-efficient, and sustainable data storage. The most stable method for encapsulating DNA has been in an inorganic matrix of silica, iron oxide, or both, but are limited by low DNA uptake and complex recovery techniques. This study investigated a rationally designed thermally responsive functionally graded (TRFG) hydrogel as a simple and cost-effective method for storing DNA. The TRFG hydrogel shows high DNA uptake, long-term protection, and reusability due to nondestructive DNA extraction. The high loading capacity was achieved by directly absorbing DNA from the solution, which is then retained because of its interaction with a hyperbranched cationic polymer loaded into a negatively charged hydrogel matrix used as a support and because of its thermoresponsive nature, which allows DNA concentration within the hydrogel through multiple swelling/deswelling cycles. We were able to achieve a high DNA data density of 7.0 × 109 gigabytes per gram using a hydrogel-based system.

Effect of Proton Irradiation Fluence on the Linearity and Symmetry of Conductance Tuning of a HfO x /TiO x Heterojunction-Based Memristor

Binary metal oxide memristor-based artificial neural synapses offer the advantages of high-density information storage, high-efficiency computing, low power consumption and strong antiradiation damage and are therefore promising aerospace electronic devices. However, the unclear damage trends and mechanisms causing nonlinearity and asymmetry during conductance tuning under irradiation have restricted further development. Here, the damage trends and mechanisms caused by proton irradiation in Au/HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>x</i></sub> /TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>x</i></sub> /Ti memristors were studied. Results show that when the fluence of proton (25 MeV) irradiation increases to 2×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sup> p/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , the Au/HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>x</i></sub> /TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>x</i></sub> /Ti memristor cannot return to its original high-resistance state upon conductance reduction, making the conductance tuning less linear and symmetric. X-ray photoelectron spectroscopy analysis revealed that the mechanism underlying the decrease in the linearity and symmetry of the conductance tuning is proton irradiation increasing oxygen vacancies in the heterojunction. These results can guide better design of metal oxide memristive devices suitable for aerospace devices and better modeling of devices with nonideal properties under irradiation.

Polarization-Sensitive Structural Colors Based on Anisotropic Silicon Metasurfaces

Structural colors based on all-dielectric metasurfaces hold great promise for a wide range of applications, including high-density optical storage, ultra-high-resolution 3D displays, imaging security certification, and so on. However, achieving dynamic tunable structural color with a compact and simple Si platform remains a great challenge. Here, we propose a dynamic tunable structural coloration with polarization-sensitive metasurfaces consisting of arrays of Si elliptical nanopillars, enabling full-colored images to be displayed and switched through the control of the polarization of incident light. A distinct feature of our design is that the color phase is independent of the viewing angle, which is fundamental for real applications. Moreover, we demonstrated that dual and multiple colors can be obtained by varying the angle of either the polarizer or the analyzer. Our scheme provides a simple yet general approach for potential applications in the fields of virtual reality, ultra-high-resolution 3D displays, and high-density information storage.

Application of a flexible memristor in self-color electronics and its depth mechanism analysis

Memristor has a high-density information storage capability and can manipulate a large amount of data computing in parallel, so it can be applied in neuromorphic computing. The advanced intelligent applications are one of the major breakthroughs made in the past decade based on the memristor's research. In this work, amorphous Nb2O5 film as functional layers on flexible niobium (Nb) foil were fabricated by anodic oxidation in oxalic acid aqueous solution. A broad spectrum of well-defined color was acquired by varying the anodic voltage during oxidation of the Nb foil. The results of spectroscopic ellipsometry (SE) tests show that the Nb2O5 layers with various colors have different thickness. The willow yellow Nb2O5 film with a thickness of ∼85 nm based memristor show an excellent memristive memory behavior. Finally, it was proposed that the potential well of the ionization center tilts under the external electric field, which causes the probability of charge to escape along and against the direction of the external electric field to explain the memristive effect of the device. This work opens up a new method for fabricating the flexible memristor, which provides the potential applications for next generation self-color electronics.

A magnetic field controlled memristor towards the design of an implantable detector

Memristors, which combine the behaviors of memory and resistive switching (RS), have a wide application prospect in information processing and artificial neural networks. The RS memory behaviors of memristors are primarily determined by the functional layer materials, device structure, and working conditions. Herein, a CuMnO2 nanomaterial with the manganese copper ore structure was prepared on a Ti substrate by hydrothermal method, and a memristor with the Ag/CuMnO2/Ti sandwich structure was developed. The RS memory behavior of the as-prepared memristor can be regulated through a low magnetic field (MF), and thus the resistance value of device shows a multi-level resistance states. Compared with other regulation factors, the MF can remotely adjust and control the RS characteristics of memristor, which is a non-invasive and non-destructive regulatory means. The MF regulated memristor can not only be used for multi-level high-density information storage, but also it can protect the health of special populations by identifying the MF intensity of the surrounding environment. When the device is operated in an MF environment, the change of resistance value of the device in both high resistance state (HRS) and low resistance state (LRS) is mainly attributed to the influence of Loren magnetic force on conductive ions.

Highly reliable and efficient encoding systems for hexadecimal polypeptide-based data storage.

Polypeptides consisting of amino acid (AA) sequences are suitable for high-density information storage. However, the lack of suitable encoding systems, which accommodate the characteristics of polypeptide synthesis, storage and sequencing, impedes the application of polypeptides for large-scale digital data storage. To address this, two reliable and highly efficient encoding systems, i.e. RaptorQ-Arithmetic-Base64-Shuffle-RS (RABSR) and RaptorQ-Arithmetic-Huffman-Rotary-Shuffle-RS (RAHRSR) systems, are developed for polypeptide data storage. The two encoding systems realized the advantages of compressing data, correcting errors of AA chain loss, correcting errors within AA chains, eliminating homopolymers, and pseudo-randomized encrypting. The coding efficiency without arithmetic compression and error correction of audios, pictures and texts by the RABSR system was 3.20, 3.12 and 3.53 Bits/AA, respectively. While that using the RAHRSR system reached 4.89, 4.80 and 6.84 Bits/AA, respectively. When implemented with redundancy for error correction and arithmetic compression to reduce redundancy, the coding efficiency of audios, pictures and texts by the RABSR system was 4.43, 4.36 and 5.22 Bits/AA, respectively. This efficiency further increased to 7.24, 7.11 and 9.82 Bits/AA by the RAHRSR system, respectively. Therefore, the developed hexadecimal polypeptide-based systems may provide a new scenario for highly reliable and highly efficient data storage.