Applications In Memory Devices Research Articles

Theoretical expolartion of site selective Perovskites for the application of electronic and optoresponsive memory devices

Now a days, the advent of energy efficient artificial neuromorphic hardware is facing variability and uniformity related state of art issues. DFT deals with this plethora at the atomistic level by introducing innovative composites of improved neuromorphic performance. In this theoretical study unprecedented potential of non-toxic and high dielectric strength of BaHfO 3 is investigated for storage devices. For improving the variability and uniformity related state of art issues, the influence of substitutional doping ofsingle rare earth metal cation at “A” (Ba atom) and “B” (Hf atom) sites of the studied cubic ABO 3 supercell is explored in formation of conducting filaments (CFs). Formation of strongly confined CFs in BaHf 1-x SmO 3 will provide an intriguing roadmap for practical application by resolving the variability and uniformity issues in electronic and optoresponsive memory devices. Alterations of structural and electronic properties by single rare earth dopants will assist in understanding the filamentary based resistive switching in BaHfO 3 . Change in resistance state caused by incident photon stimuli based extrinsic trigger revealed the intriguing neuromorphic nature of BaHfO 3 . The findings of this study will enrich the research exploring the perovskite based resistive switching materials for low power consuming resistive random access memory devices in neuromorphic applications. • The electronic modification subsequently with the creation of the rare earth metal (REM) ion dopant in cubic BaHfO 3 using Perdew-Burke-Ernzerhof Generalized gradient approximation (PBE-GGA) in addition to Hubbered parameter (GGA + U) are performed to investigate the A (Ba atom) and B (Hf atom) site impact of REM (Ce, La, Sm) dopant for switching process and application of optoelectronic devices. • Electronic properties showed sensitivity towards A and B site doping. • Integrated charge density plots depicted charge transfer mechanism. • The conductivity of the phases increased with substitutional replacement of A and B site atom by REM; and eventually resulted that the considered phase opted for low resistance state. • BaHf (1-x) Sm x O 3 is found to be composite with better optoelectronic properties.

Tri-level resistive switching characteristics and conductive mechanism of HfO<sub>2</sub>/NiO<sub><i>x</i></sub>/HfO<sub>2</sub> stacks

<sec>With the extensive integration of portable computers and smartphones with “Internet of Things” technology, further miniaturization, high reading/writing speed and big storage capacity are required for the new-generation non-volatile memory devices. Compared with traditional charge memory and magnetoresistive memory, resistive random access memory (RRAM) based on transition metal oxides is one of the promising candidates due to its low power consumption, small footprint, high stack ability, fast switching speed and multi-level storage capacity.</sec><sec>Inspired by the excellent resistive switching characteristics of NiO and HfO<sub>2</sub>, NiO<sub><i>x</i></sub> films are deposited by magnetron sputtering on the Pt<inline-formula><tex-math id="Z-20230629144836">\begin{document}$\langle111\rangle $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20230331_Z-20230629144836.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20230331_Z-20230629144836.png"/></alternatives></inline-formula> layer and the polycrystalline HfO<sub>2</sub> film, respectively. Their microstructures, resistive switching characteristics and conductive mechanisms are studied. X-ray diffractometer data show the <inline-formula><tex-math id="Z-20230629144852">\begin{document}$\langle111\rangle $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20230331_Z-20230629144852.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20230331_Z-20230629144852.png"/></alternatives></inline-formula> preferred orientation for the NiO<sub><i>x</i></sub> film deposited on the Pt<inline-formula><tex-math id="Z-20230629144904">\begin{document}$\langle111\rangle $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20230331_Z-20230629144904.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20230331_Z-20230629144904.png"/></alternatives></inline-formula> layer but the <inline-formula><tex-math id="Z-20230629144913">\begin{document}$\langle100\rangle $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20230331_Z-20230629144913.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20230331_Z-20230629144913.png"/></alternatives></inline-formula> preferred one for the film deposited on the polycrystalline HfO<sub>2</sub> layer. X-ray photoelectron depth profile of Ni 2p core level reveals that the NiO<sub><i>x</i></sub> film is the mixture of oxygen-deficient NiO and Ni<sub>2</sub>O<sub>3</sub>. NiO<sub><i>x</i></sub>(111) films show bipolar resistive switching (RS) characteristics with a clockwise current-voltage (<i>I-V</i>) loop, but its ratio of the high resistance to the low resistance (<i>R</i><sub>H</sub>/<i>R</i><sub>L</sub>) is only ~10, and its endurance is also poor. The NiO<sub><i>x</i></sub>(200)/HfO<sub>2</sub> stack exhibits bipolar RS characteristics with a counterclockwise <i>I-V</i> loop. The <i>R</i><sub>H</sub>/<i>R</i><sub>L</sub> is greater than 10<sup>4</sup>, the endurance is about 10<sup>4</sup> cycles, and the retention time exceeds 10<sup>4</sup> s. In the initial stage, the HfO<sub>2</sub>/NiO<sub><i>x</i></sub>(200)/HfO<sub>2</sub> stack shows similar bi-level RS characteristics to the NiO<sub><i>x</i></sub>(200)/HfO<sub>2</sub> stack. However, in the middle and the last stages, its <i>I-V</i> curves gradually evolve into tri-level RS characteristics with a “two-step Setting process” in the positive voltage region, showing potential applications in multilevel nonvolatile memory devices and brain-like neural synapses. Its <i>I-V</i> curves in the high and the low resistance state follow the relationship of ohmic conduction (<inline-formula><tex-math id="Z-20230714031758-1">\begin{document}$ I \propto V $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20230331_Z-20230714031758-1.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20230331_Z-20230714031758-1.png"/></alternatives></inline-formula>), while the <i>I-V</i> curves in the intermediate resistance state are dominated by the space-charge-limited-current mechanism (<inline-formula><tex-math id="Z-20230714031758-2">\begin{document}$ I \propto V^2 $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20230331_Z-20230714031758-2.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20230331_Z-20230714031758-2.png"/></alternatives></inline-formula>). The tri-level RS phenomena are attributed to the coexistence of the oxygen-vacancy conductive filaments in the NiO<sub><i>x</i></sub>(200) film and the space charge limited current in the upper HfO<sub>2</sub> film.</sec>

Fast switching of spontaneous polarization in a microporous molecular rotor ferroelectric

A microporous structural molecular rotor ferroelectric with fast polarization switching (25 kHz) originates from the unique mechanism of fast static–rotating–static motional process showing potential application in non-volatile memory devices.

Temporal dynamic photochromic materials for advanced anticounterfeiting

The intriguing optical phenomena of photochromism and photoluminescence, when integrated into a solitary material, can offer innovative applications in optical memory devices and multimode anti-counterfeiting.

Giant tunneling electroresistance in a 2D bilayer-In2Se3-based out-of-plane ferroelectric tunnel junction.

Ferroelectric tunnel junctions (FTJs) have great potential in nonvolatile memory devices and have been extensively studied in recent years. Compared with conventional FTJs based on perovskite-type oxide materials as the barrier layer, two-dimensional (2D) van der Waals ferroelectric materials are advantageous in improving the performance of FTJs and achieving miniaturization of FTJ devices due to the features such as atomic thickness and ideal interfaces. In this work, we present a 2D out-of-plane ferroelectric tunnel junction (FTJ) constructed using graphene and bilayer-In2Se3. Using density functional calculations combined with the nonequilibrium Green's function technique, we investigate the electron transport properties in the graphene/bilayer-In2Se3 (BIS) vdW FTJ. Our calculations show that the FTJ we constructed can be switched from ferroelectric to antiferroelectric by changing the relative dipole arrangement of the BIS to form multiple nonvolatile resistance states. Since the charge transfer between the layers varies for the four different polarization states, the TER ratios range from 103% to 1010%. The giant tunneling electroresistance and multiple resistance states in the 2D BIS-based FTJ suggest that it has great potential for application in nanoscale nonvolatile ferroelectric memory devices.

Temperature-dependent magnetic properties of the room-temperature ferromagnetic Janus monolayer Fe2XY (X, Y = I, Br, Cl; X ≠ Y).

Excellent magnetic properties at room temperature are crucial for the application of ferromagnets in spintronic and topological quantum devices. Using first-principles calculations and atomistic spin model simulations, we investigate the temperature-dependent magnetic properties of the Janus monolayer Fe2XY (X, Y = I, Br, Cl; X ≠ Y), as well as the effects of different magnetic interactions within the next-nearest-neighbor shell on the Curie temperature (TC). A large isotropic exchange interaction between one Fe atom and its next-nearest-neighbor counterparts can significantly increase the TC, while an antisymmetric exchange interaction decreases it. More importantly, we employ the temperature rescaling method, which can obtain temperature-dependent magnetic properties quantitatively consistent with experimental values, and find that the effective uniaxial anisotropy constant and coercive field decrease with increasing temperature. Moreover, at room temperature, Fe2IY is a rectangular-loop magnetic material with a giant coercive field up to ∼8 T, demonstrating its potential for application in room-temperature memory devices. Our findings can advance the application of these Janus monolayers in room-temperature spintronic devices and through heat-assisted techniques.

Anisotropy and thermal properties in GeTe semiconductor by Raman analysis.

Low-symmetric GeTe semiconductors have attracted wide-ranging attention due to their excellent optical and thermal properties, but only a few research studies are available on their in-plane optical anisotropic nature that is crucial for their applications in optoelectronic and thermoelectric devices. Here, we investigate the optical interactions of anisotropy in GeTe using polarization-resolved Raman spectroscopy and first-principles calculations. After determining both armchair and zigzag directions in GeTe crystals by transmission electron microscopy, we found that the Raman intensity of the two main vibrational modes had a strong in-plane anisotropic nature; the one at ∼88.1 cm-1 can be used to determine the crystal orientation, and the other at ∼124.6 cm-1 can reveal a series of temperature-dependent phase transitions. These results provide a general approach for the investigation of the anisotropy of light-matter interactions in low-symmetric layered materials, benefiting the design and application of optoelectronic, anisotropic thermoelectric, and phase-transition memory devices based on bulk GeTe.

Magnetic Anisotropy of Yttrium Iron Garnet from Density Functional Theory

For applications in magnetic memory and spintronic devices, ferrimagnetic insulators (FMIs) with perpendicular magnetic anisotropy (PMA) are of special interest. Because of its low magnetic losses, yttrium iron garnet (Y3Fe5O12, also known as YIG) is frequently regarded as the most promising FMI film. However, YIG films typically have an in-plane easy axis, which limits their potential applications. In YIG films, several strategies are suggested to obtain PMA. In YIG and doped YIG films, the epitaxial strain brought on by lattice mismatch has proven to be a successful method for achieving PMA. The investigation on the theoretical mechanism of PMA induction has not yet been reported, even though PMA has been successfully induced in YIG and other FMIs films. In this study, density functional theory has been used to systematically examine the effects of mechanical strain, including in-plane biaxial strain and out-of-plane strain, on magnetic anisotropy energy (MAE) in YIG and bismuth-doped YIG (BiYIG). The findings demonstrate that unstrained YIG has no magnetic anisotropy. Additionally, it has been found that the easy axis of the YIG may be changed from being in-plane to being out-of-plane by an out-of-plane compressive strain or a modest tensile in-plane biaxial strain. From the examination of the electronic structure, it has been observed that the local density of states close to the Fermi energy is mostly responsible for the shift in MAE. It is anticipated that the modulation of PMA in YIG and the design of spin wave devices based on YIG will both benefit from these results.

Motion of a magnetic skyrmionium driven by acoustic wave

A magnetic skyrmionium does not exhibit skyrmion Hall effect due to its special structure with zero topological charge, which has an advantage over a skyrmion in the application of tracetrack memory. With the development of straintronics, acoustic waves could remotely control the topological magnetic structures, including skyrmionium. In this work, the acoustic wave induced dynamics of a skyrmionium on a strip film is studied by means of micromagnetic simulations. The results show that the motion of a skyrmionium is significantly influenced by the magnetic damping, the amplitude, and the frequency of the acoustic wave. The skyrmionium tends to acquire higher velocity at larger amplitude of the acoustic wave and smaller magnetic damping. With the increase in the acoustic wave amplitude, the skyrmionium deforms and moves faster due to stronger magnetoelastic interaction. When the frequency increases from 1 to 15 GHz, the velocity of skyrmionium generally increases except for the velocity fluctuation caused by magnetization resonance at a few frequencies. This work suggests a mechanical way to drive the motion of magnetic skyrmioniums by acoustic waves, offering potential applications in future information memory devices.

Construction of a novel self-bleaching photochromic hydrogel embraced within the Zn-MOF@WO3 junction for assembling UV-irradiated smart rewritable device

Photochromic hydrogels, which are dynamic in response to external light stimuli, have aroused increasing attentions due to their potential applications in intelligent devices. However, achieving excellent photochromic activity with fast photoresponse and self-bleaching rates still remains a huge challenge. Herein, a novel photochromic junction of zinc-based metal–organic framework (Zn-MOF) and tungsten oxide (WO3) was established as photochromic unit and embraced within hydrogel of poly(acrylic acid-co-polyethylene glycol) [P(AA/PEG)] via the interaction of ionic and hydrogen bonding (denoted as P(AA/PEG)-Zn-MOF@WO3), following by exploiting as self-bleaching photochromic agent for assembling UV-irradiated smart rewritable device. The photoinduced electrons can be efficiently separated and migrated from Zn-MOF to WO3 in the Zn-MOF@WO3 junction after UV irradiation, thereby increasing the coloration degree. Due to the enhanced fast response to light stimuli, the P(AA/PEG)-Zn-MOF@WO3-3 hydrogel prepared using 200 mg Zn-MOF demonstrated the fast responsive photochromic behavior of 10 s under UV lamp illumination and the self-fading process could be easily performed in room condition (within 20 min). Moreover, the coloration degree of P(AA/PEG)-Zn-MOF@WO3-3 photochromic hydrogel was precisely controlled and repeated by changing the UV irradiation time. Consequently, the fast photochromic and self-fading properties of P(AA/PEG)-Zn-MOF@WO3-3 afforded rapid and easy ‘‘writing’’ and “erasing” abilities. The present work proposes a new way for the construction of the reversibly responsive photochromic hydrogel with smart optical materials, further broadening their applications in intelligence sensors, smart windows, and flexible memory devices.

New Room-Temperature Molecular Ferroelectric (C6H16N2O)CdBr4·H2O with Preferable Luminescent Properties

Organic–inorganic hybrid materials are easy to modify, which makes it possible to construct multifunctional ferroelectrics directionally and apply the built-in electric field and switching properties of ferroelectrics to multidisciplinary fields. Particularly, the coupling of photoluminescence and ferroelectricity in a single hybrid material facilitates its novel applications in lighting sensors, memory devices, and other multifunctional applications. Based on the photoluminescent molecule 4-(2-aminoethyl) morpholine (AEM), here, a room-temperature ferroelectric (C6H16N2O)CdBr4·H2O (AEM-CdBr4) is designed and obtained, which crystallizes in a polar orthorhombic space group of Pca21. A reversible ferroelectric–paraelectric phase transition was confirmed at 353 K through experimental results, such as differential scanning calorimetry (DSC) curves, variable-temperature Raman spectroscopy, and photoluminescence (PL) spectroscopy. The crystal exhibits ferroelectricity at room temperature with a saturation polarization of approximately 8 μC/cm2. The photoluminescence of compound AEM-CdBr4 is mainly derived from the monomeric fluorescence emission of the AEM molecule and is not directly related to the energy band structure of the crystal. This room-temperature molecular-type ferroelectric AEM-CdBr4 with photoluminescence will provide new ideas for the design of new multifunctional ferroelectrics.

Competing Easy-Axis Anisotropies Impacting Magnetic Tunnel Junction-Based Molecular Spintronics Devices (MTJMSDs).

Molecular spintronics devices (MSDs) attempt to harness molecules' quantum state, size, and configurable attributes for application in computer devices-a quest that began more than 70 years ago. In the vast number of theoretical studies and limited experimental attempts, MSDs have been found to be suitable for application in memory devices and futuristic quantum computers. MSDs have recently also exhibited intriguing spin photovoltaic-like phenomena, signaling their potential application in cost-effective and novel solar cell technologies. The molecular spintronics field's major challenge is the lack of mass-fabrication methods producing robust magnetic molecule connections with magnetic electrodes of different anisotropies. Another main challenge is the limitations of conventional theoretical methods for understanding experimental results and designing new devices. Magnetic tunnel junction-based molecular spintronics devices (MTJMSDs) are designed by covalently connecting paramagnetic molecules across an insulating tunneling barrier. The insulating tunneling barrier serves as a mechanical spacer between two ferromagnetic (FM) electrodes of tailorable magnetic anisotropies to allow molecules to undergo many intriguing phenomena. Our experimental studies showed that the paramagnetic molecules could produce strong antiferromagnetic coupling between two FM electrodes, leading to a dramatic large-scale impact on the magnetic electrode itself. Recently, we showed that the Monte Carlo Simulation (MCS) was effective in providing plausible insights into the observation of unusual magnetic domains based on the role of single easy-axis magnetic anisotropy. Here, we experimentally show that the response of a paramagnetic molecule is dramatically different when connected to FM electrodes of different easy-axis anisotropies. Motivated by our experimental studies, here, we report on an MCS study investigating the impact of the simultaneous presence of two easy-axis anisotropies on MTJMSD equilibrium properties. In-plane easy-axis anisotropy produced multiple magnetic phases of opposite spins. The multiple magnetic phases vanished at higher thermal energy, but the MTJMSD still maintained a higher magnetic moment because of anisotropy. The out-of-plane easy-axis anisotropy caused a dominant magnetic phase in the FM electrode rather than multiple magnetic phases. The simultaneous application of equal-magnitude in-plane and out-of-plane easy-axis anisotropies on the same electrode negated the anisotropy effect. Our experimental and MCS study provides insights for designing and understanding new spintronics-based devices.

Strain- and thickness-dependent magnetic properties of epitaxial La0.67Sr0.33CoO3/La0.67Sr0.33MnO3 bilayers

Magnetic properties and interfacial phenomena of epitaxial perovskite oxides depend sensitively on parameters such as film thickness and strain state. In this work, epitaxial La0.67Sr0.33CoO3 (LSCO)/La0.67Sr0.33MnO3 (LSMO) bilayers were grown on NdGaO3 (NGO) and LaAlO3 (LAO) substrates with a fixed LSMO thickness of 6 nm, and LSCO thickness (tLSCO) varying from 2 to 10 nm. Soft x-ray magnetic spectroscopy revealed that magnetically active Co2+ ions that strongly coupled to the LSMO layer were observed below a critical tLSCO for bilayers grown on both substrates. On LAO substrates, this critical thickness was 2 nm, above which the formation of Co2+ ions was quickly suppressed leaving only a soft LSCO layer with mixed valence Co3+/Co4+ ions. The magnetic properties of both LSCO and LSMO layers displayed strong tLSCO dependence. This critical tLSCO increased to 4 nm on NGO substrates, and the magnetic properties of only the LSCO layer displayed tLSCO dependence. A non-magnetic layer characterized by Co3+ ions and with a thickness below 2 nm exists at the LSCO/substrate interface for both substrates. The results contribute to the understanding of interfacial exchange spring behavior needed for applications in next generation spintronic and magnetic memory devices.

Regulating WORM/Flash electrical memory behavior of metallopolymers through varying metal centers

To study the influence of metal atoms on the performance of organic polymer memory devices, four new metallopolymers P0, P1, P2 and P3 were designed and synthesized for organic resistive random-access memory (RRAM) applications. Among them, the device based on P1 shows nonvolatile binary write-once-read-many-times (WORM) memory behavior, while the devices based on P2 and P3 show vastly different nonvolatile binary Flash-type memory behavior. The charge transfer (CT) effect between the platinum (Pt) ligand and porphyrin moieties of metallopolymers is determined to be the origin of the electrical switching behavior of P1, which is proved by the electrochemical and DFT calculations. While the reason of the Flash type memory characteristic of P2 and P3 is ascribed to the formation of metal filaments because of the introduction of metal ions (Co and Ni) into the porphyrin ring. It is suggested that the metal ions can form an internal electrode and act as a bridge during the CT process, which contributes to both the CT and back CT, consequently regulating the WORM/Flash conversion. The results indicate the feasibility of modulating the memory behavior of metallopolymers by varying the central metal ions, manifesting the significance of metal complexes in the application of organic memory devices and will attract wide research interest of scientists. The as-fabricated device based on P3 was also successfully applied to memory logic gates and display function, which offers great application prospect as smart sensor in artificial intelligence (AI) network.

Enhancement of perpendicularly magnetized τ-phase in Mn/Al bilayer thin films by swift heavy ion irradiation

This paper reports the swift heavy ion irradiation-induced tailoring of the structural and magnetic properties of the Mn/Al bilayer thin films. Mn/Al bilayer thin films were deposited on Si substrates by the evaporation technique, and as-deposited films were irradiated by a 100 MeV Ag ion beam with two distinct fluences. The molar fraction of τ- phase was enhanced at higher irradiation fluence, as revealed by the XRD and magnetic results. The average crystallite size was increased with the increase in irradiation fluence and obtained in a range of 11 to 14 nm. The magnetic hysteresis curves measured at 300 K confirmed the improvement in the ferromagnetic properties and the perpendicular magnetic anisotropy in these films. The enriched ferromagnetic properties were obtained in the perpendicular direction for the film irradiated at higher fluence, with the saturation magnetization ∼ 44 emu/cc, and coercivity ∼ 1590 Oe measured at the low temperature (5 K). These modified magnetic properties in Mn-Al alloy thin films are advantageous for their applications in spintronics and high-density magnetic memory devices.

Influence of La3+ substitutions on structural, dielectric and electrical properties of spinel cobalt ferrite

La3+ doped cobalt ferrites with composition CoLaxFe2−xO4 (0.00 ≤ x ≤ 0.20) were synthesized by a co-precipitation method. X-ray diffraction (XRD) analysis confirm the formation of single-phased spinel structure for all synthesized samples. The result of La3+ doping on dielectric and electrical properties of cobalt ferrites was investigated. Dielectric constant and dielectric loss decrease with increasing frequency whereas alternating current (AC) electrical conductivity increases with increasing frequency. The AC electrical conductivities were effectively modeled by employing the Jonscher’s power law. Role of grain and grain boundary on impedance has been explored from nyquist plots and equivalent electrical circuits were proposed to clarify the impedance spectroscopy results. The Direct Current (DC) electrical resistivities were estimated by two probe method within the temperature range of 303K–700K. DC electrical resistivity decreases with increasing temperature and explained by hopping mechanism. DC electrical resistivity and drift mobility decreases with La3+ doping. Activation energies were calculated by employing the Arrhenius plot. Activation energy found to increases with La3+ substitutions. Maximum value of DC electrical resistivity achieved was 9.26 x 10+8 (Ω-cm) with crystallite size 17 nm. Current-Voltage (I–V) measurements were carried out within 0→6V→0V→ –6V→0V voltage range. It is worth mentioning that all doped sample exhibited remarkable and improved nonlinear hysteresis loop-type behavior than pour sample. Variation in resistance, in current-voltage loops, is clarified by considering space charge limited conduction (SCLC) model and oxygen vacancies migration across the metal-semiconductor interface. Out study suggest that La3+ doped cobalt ferrites may be tested as an active material for possible applications in non-volatile memory devices and neuromorphic applications.

Ultrathin Al1−xScxN for Low‐Voltage‐Driven Ferroelectric‐Based Devices

Thickness scaling of ferroelectricity in Al1−x Sc x N is a determining factor for its potential application in neuromorphic computing and memory devices. In this letter, ultrathin (10 nm) Al0.72Sc0.28N films that are ferroelectrically switchable at room temperature are reported on. All‐epitaxial Al0.72Sc0.28N/Pt heterostructures are grown by magnetron sputtering onto GaN/sapphire substrates followed by an in situ Pt capping approach to avoid oxidation of the Al0.72Sc0.28N film surface. Structural characterization by X‐Ray diffraction and transmission electron microscopy reveals the established epitaxy. The thus‐obtained high‐quality films in combination with in situ capping facilitate ferroelectric switching of Al1−x Sc x N in the ultrathin regime. The analysis of the relative permittivity and coercive field dependence on Al0.72Sc0.28N film thicknesses in the range from 100 nm down to 10 nm indicates only moderate scaling effects, suggesting that the critical thickness for ferroelectricity is not yet approached. Furthermore, the deposited layer stack demonstrates the possibility of including ultrathin ferroelectric Al1−x Sc x N into all‐epitaxial GaN‐based devices using sputter deposition techniques. Thus, the integration and scaling potential of all‐epitaxial ultrathin Al1−x Sc x N offering high storage density paired with low‐voltage operation desired for state‐of‐the‐art ferroelectric memory devices are highlighted.

High-Efficiency Ion Enrichment inside Ultra-Short Carbon Nanotubes.

The ion-enrichment inside carbon nanotubes (CNTs) offers the possibility of applications in water purification, ion batteries, memory devices, supercapacitors, field emission and functional hybrid nanostructures. However, the low filling capacity of CNTs in salt solutions due to end caps and blockages remains a barrier to the practical use of such applications. In this study, we fabricated ultra-short CNTs that were free from end caps and blockages using ball milling and acid pickling. We then compared their ion-enrichment capacity with that of long CNTs. The results showed that the ion-enrichment capacity of ultra-short CNTs was much higher than that of long CNTs. Furthermore, a broad range of ions could be enriched in the ultra-short CNTs including alkali-metal ions (e.g., K+), alkaline-earth-metal ions (e.g., Ca2+) and heavy-metal ions (e.g., Pb2+). The ultra-short CNTs were much more unobstructed than the raw long CNTs, which was due to the increased orifice number per unit mass of CNTs and the decreased difficulty in removing the blockages in the middle section inside the CNTs. Under the hydrated-cation–π interactions, the ultra-short CNTs with few end caps and blockages could highly efficiently enrich ions.

Effect of variation in glancing angle deposition on resistive switching property of WO3 thin films for RRAM devices

In this paper, nanostructured tungsten oxide (WO3) thin films are deposited using the RF-magnetron sputtering technique in Glancing Angle (GLAD) arrangement. Variation in the structural, morphological, optical, and resistive switching (RS) characteristics of nanostructured WO3 film is investigated as a function of GLAD angle (60°–80°). Electrical studies on nanostructured WO3 films deposited at room temperature are found to exhibit enhanced bipolar resistive-switching properties in metal–insulator–metal pattern [Au/WO3/ITO]. The RON/ROFF ratio between high and low resistance states was noted to be about 190 besides a minimum set voltage of ∼2.22 V in the case of the WO3 thin film deposited at the 70° glancing angle. A detailed current transport mechanism analysis indicates the existence of ohmic-behavior and trap-assisted space charge limited conduction as the governing mechanisms at the state of low and high applied bias, respectively. Good data-retention characteristics coupled with reproducible and fast RS capabilities obtained with Au/WO3/ITO device structure promise scope of rapid development in future RS-based novel memory device applications.

Spin pumping in nanolayers of WS2/Co2FeAl heterostructures: Large spin mixing conductance and spin transparency

Materials with high spin–orbit coupling (SOC) are a prerequisite for the realization of spin–orbit torque-based magnetic memories. Transition metal dichalcogenides (TMDs) are an apt choice for such applications due to their high SOC strength. In this work, we have investigated the spin pumping phenomenon at the interface between thin tungsten disulphide (WS2) films and Co2FeAl (CFA) Heusler alloy films by performing ferromagnetic resonance (FMR) measurements on WS2/CFA heterostructures capped with the 4 nm thin Al film. While Raman spectroscopy conclusively proves the number of monolayers in the WS2 films, atomic force microscopy and x-ray reflectivity measurements were used to quantify the smoothness of the grown interfaces (<0.4 nm) as well as the individual layer thicknesses in the heterostructure stacks. Here, we vary the WS2 layer numbers and CFA thicknesses to quantify the spin pumping parameters such as spin mixing conductance, and spin transparency. FMR measurements revealed that damping enhancement reached ∼41% with a monolayer of WS2. Interfacial effective spin mixing conductance and spin transparency of the WS2/CFA interface are found to be 7.47 ± 0.97 nm−2 and 73.35 ± 9.52%, respectively. Thus, high-quality TMDs can be used as efficient materials for magnetic memory device applications.