MgO Layer Research Articles

Interface engineering of LDH-based material as efficient anti-corrosive system via synergetic performance of host, interlayers, and morphological features of nature-mimic architectures

High-performance hybrid materials with special features are desired to meet the requirements of more complex cutting-edge applications. However, the self-assembly of layered double hydroxides (LDH) with organic frameworks is hampered by a lack of understanding of the formation mechanism and the effects of the self-assembled architecture on anticorrosion activity remain a major challenge. Herein, we put forward how the honeycomb-like network would architecturally upgraded on the pre-existing hierarchical floral structure with Trimesic acid (TMA) compound resulting in a promising layer-by-layer (LBL) material. This nature-inspired network is realized to offer an ideal approach not only endows with excellent properties but also exploits the power of layered coating materials as a bastion in the fields of nanotechnology, without limiting conditions, taking advantage of the synergy beneficial effects of the self-assembled honeycomb-like TMA and the anion-exchange ability of the layered coating material. In this work, a three-dimensional assembly with an architecture closely resembling interconnected micro-petals was successfully deposited on the defective surface obtained via plasma electrolytic oxidation (PEO) of Mg alloy, where TMA compound was used for supramolecular self-assembly. The MgO layer was first formed on AZ31Mg alloy via PEO treatment and the Mg-Al LDH micro-petals were synthesized on the MgO surface in the presence of a chelating agent [diethylenetriaminepentaacetic acid (DTPA)]. In a typical synthesis, TMA compound was used as an appropriate linker for the formation of well-organized multidimensional layered materials taking advantage of the synergy beneficial effects of the self-assembled honeycomb-like TMA and the anion-exchange ability of the Mg-Al LDH coating. The results indicate that Mg alloy coated with the self-assembled TMA@LDH-MgO materials presents excellent anti-corrosion performance as compared to the bare Mg. The use of such system would open a brand-new possibility to correct, in a targeted way, the inevitable defects of the layered coating morphology while retaining its exceptional potential. First-principles calculations, quantitative molecular surface analyses and independent gradient model framework further verify the self-assembly and adsorption behavior of TMA over the Mg-Al LDH layer. The improved performance of the TMA@Mg-Al LDH film is attributed to the synergistic effects of different interactions that occurred around active sites in the hierarchical network.

ZTO/MgO-Based Optoelectronic Synaptic Memristor for Neuromorphic Computing

Synapse having good linearity plays a vital role in the memory and computing of human brain. Therefore, the achievement of efficient learning process in neuromorphic computing by the implementation of the synaptic functions, such as long-term potentiation/ depression (LTP/LTD) and spike time-dependent plasticity (STDP) of two-terminal optoelectronic memristor device, is critical for the next-generation artificial intelligence. In this work, we improve the resistive switching and synaptic characteristics of a Zn2SnO4 (ZTO)-based optoelectronic synaptic memristor (OSM) by the insertion of an ultrathin MgO layer. For this bilayer (BL) structured OSM, the nonlinearities of LTP and LTD curves are improved to 1.96 and 0.33, respectively. Asymmetrical STDP response demonstrates the suitability of device toward the Hebbian learning. In addition, a Hopfield neural network (HNN) is successfully trained to recognize a 10 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times10$ </tex-math></inline-formula> pixel input image with an accuracy of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim 100$ </tex-math></inline-formula> % after 15 iterations. Under blue light (405 nm) illumination, OSM emulates the synaptic functions, such as paired pulse facilitation, learning experience behavior, and short- to long-term memory transition. The photoresponse and relaxation characteristics of the device depend on the ionization and neutralization of oxygen vacancies. This highly transparent ZTO/MgO-based OSM with the convergence of “nonvolatile electronic memory and visible light sensor” is suitable as an artificial synapse for neuromorphic computing applications.

A Study of Al2O3/MgO Composite Films Deposited by FCVA for Thin-Film Encapsulation.

Al2O3 and MgO composite (Al2O3/MgO) films were rapidly deposited at low temperatures using filtered cathode vacuum arc (FCVA) technology, aiming to achieve good barrier properties for flexible organic light emitting diodes (OLED) thin-film encapsulation (TFE). As the thickness of the MgO layer decreases, the degree of crystallinity decreases gradually. The 3:2 Al2O3:MgO layer alternation type has the best water vapor shielding performance, and the water vapor transmittance (WVTR) is 3.26 × 10-4 g·m-2·day-1 at 85 °C and 85% R.H, which is about 1/3 of that of a single layer of Al2O3 film. Under the action of ion deposition, too many layers will cause internal defects in the film, resulting in decreased shielding ability. The surface roughness of the composite film is very low, which is about 0.3-0.5 nm depending on its structure. In addition, the visible light transmittance of the composite film is lower than that of a single film and increases with the increase in the number of layers.

Interface-resolved study of magnetism in MgO/FeCoB/MgO trilayers using x-ray standing wave techniques

Interfaces in the MgO-FeCoB-MgO trilayer have been studied with grazing incident nuclear resonance scattering (GINRS) using the x-ray standing waves (XSW) technique. High depth selectivity of the present method allows one to measure magnetism and structure at the two interfaces of FeCoB, namely, FeCoB-on-MgO and MgO-on-FeCoB, independently, yielding an intriguing result that both interfaces are not symmetric. A high-density layer with an increased magnetic hyperfine field at the FeCoB-on-MgO interface suggests different growth mechanisms at the two interfaces. The azimuthal angle-dependent magneto-optic Kerr effect measurements reveal the presence of unusual uniaxial magnetic anisotropy (UMA) in the trilayer. An in-situ temperature-dependent study discovered that this UMA systematically reduces with temperature. The trilayer becomes isotropic at 450C with an order-of-magnitude increase in coercivity. The asymmetry at the interfaces is, in turn, explained by boron diffusion from the FeCoB interface layer into the nearby MgO layer. Stress-induced UMA is observed in the boron-deficient FeCoB layer, superimposed with the bulk FeCoB layer, and found to be responsible for unusual UMA. The temperature-dependent variation in the UMA and coercivity can be understood in terms of variations in the internal stresses and coupling between FeCoB bulk and the interface layer.

Interface-Mediated YIG/Ce:YIG Bilayers Structure with Enhanced Magneto-optical Properties via Pulsed Laser Deposition

For the realization of integrated nonreciprocal photonic devices for optical communication, on-chip monolithic integration of magneto-optical materials onto silicon remains a challenge. Implemented with pulsed laser deposition (PLD), a MgO interfacial layer is introduced to overcome the material incompatibilities between a silicon substrate and magneto-optical thin films of yttrium iron garnet (YIG). With a thickness of ∼40 nm, the amorphous interfacial layer of MgO can effectively inhibit interdiffusion across YIG/Si and promote the growth of a high-density, high-phase-purity polycrystalline garnet structure in the bilayer of YIG/Ce:YIG. Such modified chemistry and microstructure in YIG/Ce:YIG lead to enhanced magneto-optical properties, including an ∼38% increase in Faraday rotation and an ∼15% increase in saturation magnetization, as well as an ∼20% increase in infrared (IR) transmission. Offering dual functions of diffusion barrier and structure template, the MgO layer demonstrated herein suggests a new remedy solution to heterogeneous interfaces in advanced thin film devices.

First-principles study of origin of perpendicular magnetic anisotropy in MgO|CoFeB|Ta structures

Using fist-principles calculations, we study the B atom of diffusion process and the origin of the perpendicular magnetic anisotropy in MgO|CoFe|Ta structures with boron. It is found that B atoms are more likely to enter the Ta layer than FeCo layer and MgO layer. This result is in good agreement with that of the experimental and theoretical results. Furthermore, we elucidate the physical origin of the interfacial PMA Ta|CoFe|MgO structure with B element. We find that interfacial PAM come from both the MgO|CoFe and CoFe|Ta layer interfaces. These findings provide a comprehensive understanding of the PMA and point towards the possibility to achieve the advanced-node STT-MRAM with high thermal stability.

Evaluation of MR ratio and reliability of MTJ device having SiN sidewall by modifying reference layer thickness

For high-performance magnetic tunnel junction devices, the ion beam etching (IBE) process is improved by including the fabrication of a SiN sidewall around the MgO tunnel barrier layer. This sidewall prevents the redeposition from lower metal layers on the edge of the MgO layer. The magnetoresistance (MR) ratio at an IBE angle of 20° is larger than that at 60°. Edge current by the redeposition is suppressed by the SiN sidewall, and etching damage is reduced by decreasing the IBE angle. The dependence of the MR ratio on the reference layer thickness is investigated using an FeB reference layer with thicknesses of 0.7, 0.9 and 1.05 nm. The MR ratio increases with the reference layer thickness, and an MR ratio of 180% is achieved at a layer thickness of 1.05 nm. A resistance variability of under 0.5% confirms the high resistance stability of the tested device.

Controlling interface anisotropy in CoFeB/MgO/HfO2 using dusting layers and magneto-ionic gating

In this work, we present the magneto-ionic response to ionic liquid gating in Ta/CoFeB/MgO/HfO2 stacks, where heavy metal dusting layers of Ta, W, and Pt are inserted at the Ta/CoFeB and CoFeB/MgO interfaces. Dusting layers of W inserted at the Ta/CoFeB interface increase perpendicular magnetic anisotropy (PMA) by more than 50%, while no significant changes are seen for Pt. In these samples, gating cannot break the PMA seeded at the CoFeB/MgO interface, only relatively small changes in the coercivity can be induced, about 20% for Ta and Pt and 6% for W. At the CoFeB/MgO interface, a significant quenching of the magnetization is seen when W and Ta dusting layers are inserted, which remains unchanged after gating, suggesting a critical deterioration of the CoFeB. In contrast, Pt dusting layers result in an in-plane anisotropy that can be reversibly converted to PMA through magneto-ionic gating while preserving the polycrystalline structure of the MgO layer. This shows that dusting layers can be effectively used not only to engineer magnetic properties in multilayers but also to strongly modify their magneto-ionic performance.

Sizable spin-to-charge conversion in PLD-grown amorphous (Mo, W)Te2−x films

We report on the spin-to-charge conversion (SCC) in Mo0.25W0.75Te2−x (MWT)/Y3Fe5O12 (YIG) heterostructures at room temperature. The centimeter-scale amorphous MWT films are deposited on liquid-phase-epitaxial YIG by pulsed laser deposition technique. The significant SCC voltage is measured in the MWT layer with a sizable spin Hall angle of ∼0.021 by spin pumping experiments. The control experiments by inserting MgO or Ag layer between MWT and YIG show that the SCC is mainly attributed to the inverse spin Hall effect rather than the thermal or interfacial Rashba effect. Our work provides a novel spin-source material for energy-efficient topological spintronic devices.

Development of a Mg/O ReaxFF Potential to describe the Passivation Processes in Magnesium-Ion Batteries.

One of the key challenges preventing the breakthrough of magnesium-ion batteries (MIB) is the formation of a passivating boundary layer at the Mg anode. To describe the initial steps of Mg anode degradation by O2 impurities, a Mg/O ReaxFF (force field for reactive systems) parameter set was developed capable of accurately modeling the bulk, surface, adsorption, and diffusion properties of metallic Mg and the salt MgO. It is shown that O2 immediately dissociates upon first contact with the Mg anode (modeled as Mg(0001), Mg(10 0)A, and Mg(10 1)), heating the surface to several 1000 K. The high temperature assists the further oxidation and forms a rock salt interphase intersected by several grain boundaries. Among the Mg surface terminations, Mg(10 0)A is the most reactive, forming an MgO layer with a thickness of up to 25 Å. The trained force field can be used to model the ongoing reactions in Mg-air batteries but also to study the oxidation of magnesium metal in general.

The influence of interface effects on the switching behavior in ultra-scaled MRAM cells

The development of advanced magnetic tunnel junctions with a single-digit nanometer footprint can be achieved using an elongated multilayered ferromagnetic free layer structure. In this work, we demonstrate the switching of a composite free layer consisting of two ferromagnets separated by an MgO layer and an additional capping MgO layer to boost perpendicular anisotropy. This serially connected MTJs form a multi-state memory cell. Because of the ability to store data in more than one bit (0 or 1), the memory density can be increased, making the memory more efficient and cost-effective. A proper design of the free layer and its interface-induced perpendicular anisotropy helps to achieve reliable switching.

The effect of time dependent native oxide surface conditions on the electrochemical corrosion resistance of Mg and Mg-Al-Ca alloys

The time dependent native oxide surface conditions of Mg and Mg-Al-Ca alloys under moderate atmospheric conditions were continuously analysed via in situ SKPFM, in situ XRR and ex situ XPS measurements. The progressive hydration of the MgO layer appears to be the dominant surface reaction for all investigated alloys during the investigated time period up to 24 h. Subsequent electrochemical measurements revealed a reduced corrosion resistance of all Mg alloys under short-term immersion conditions with a higher hydration degree of the native oxide.

Pressure-dependent bandgap study of MBE grown {CdO/MgO} short period SLs using diamond anvil cell

Semiconductor superlattices (SLs) have found widespread applications in electronic industries. In this work, a short-period SL structure composed of CdO and MgO layers was grown using a plasma-assisted molecular beam epitaxy technique. The optical property of the SLs was investigated by absorption measurement at room temperature. The ambient-pressure direct bandgap was found to be 2.76 eV. The pressure dependence of fundamental bandgap has been studied using a diamond anvil cell technique. It has been found that the band-to-band transition shifts toward higher energy with an applied pressure. The bandgap of SLs was varied from 2.76 to 2.87 eV with applied pressure varied from 0 to 5.9 GPa. The pressure coefficient for the direct bandgap of SLs was found to be 26 meV/GPa. The obtained experimental result was supported by theoretical results obtained using density functional theory calculations. The volume deformation potential was estimated using the empirical rule. We believe that our findings may provide valuable insight for a better understanding of {CdO/MgO} SLs toward their future applications in optoelectronics.

Long-Term in Vitro Corrosion of Biodegradable WE43 Magnesium Alloy in DMEM

The biodegradable WE43 magnesium alloy is an attractive biomedical material for orthopaedic implants due to its relatively high strength and corrosion resistance. Understanding the long-term corrosion behaviour in the human body plays a crucial role in the biomedical development and application of WE43 alloy for orthopaedic implants. In this work, the corrosion of an extruded WE43 magnesium alloy was investigated in a physiological environment using Dulbecco’s Modified Eagle Medium’s (DMEM) over a period of up to 10 weeks. To assess the in vitro corrosion process, we analysed the corrosion pits of the specimens’ cross sections and the composition of the corrosion layer by scanning electron microscopy. The experimental results indicated that the long-term corrosion process of WE43 magnesium alloy consists of three stages: (1) The rapid corrosion stage within the first 7 days, (2) the steady corrosion stage between 7 and 28 days, (3) the accelerated corrosion stage between 28 and 70 days. The microchemical analysis revealed a heterogeneous three-layer corrosion product with varying thicknesses of 10 to 130 µm on the surfaces of the samples for all corrosion times. It is composed of an inner layer of Mg-O, an intermediate layer of Mg-O-Ca-P, and an outer layer of Mg-O-Ca-P-C. The corrosion layers have many microcracks that allow limited contact between the liquid medium and the surface of the alloy. In addition, microgalvanic corrosion was observed to cause corrosion pits between the intermetallic rare earth element-rich phases and the Mg matrix.

New insights into the aggregation and disaggregation between serpentine and pyrite in the xanthate flotation system

Hypothesis: In xanthate flotation system, the aggregation of serpentine on sulfide minerals significantly weakened their floatability. And it was generally assumed that the electrostatic attraction was of the dominant driver for coating of serpentine slimes. In this paper, the hydrophobic interaction between the “talc-like” cleavage plane of serpentine and the xanthate-hydrophobized surface of sulfide minerals was proposed as the dominated driver.Experiments: To evaluate the aggregation of serpentine on pyrite surface, a novel experimental protocol was designed, and the aggregation behavior and mechanism in the absence and presence of sodium isobutyl xanthate (SIBX) were explored through in situ optical microscope, micro-flotation, contact angle, zeta potential and FT-IR. Afterwards, the disaggregation mechanism of 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP) to the aggregates of serpentine on pyrite surface was revealed.Findings: The electrostatic attraction facilitated the slight aggregation of serpentine slimes on bare pyrite surface. The hydrophobic interaction between the “talc-like” plane of serpentine and SIBX-covered pyrite significantly promoted the aggregation between them, which remarkably weakened the floatability of pyrite. The attendance of HEDP anions reversed the surface potential of the octahedral Mg-O layers of serpentine from the positive into the negative, thus to prevent the aggregation of the HEDP-anchored serpentine with the SIBX-covered pyrite via the strong electrostatic repulsion between them. As a result, the disaggregation as well as SIBX flotation separation of pyrite from serpentine was realized. This investigation also provided new insights into the aggregation and disaggregation between serpentine and sulfide minerals during froth flotation.

Role of ZnO and MgO interfaces on the growth and optoelectronic properties of atomic layer deposited Zn1−xMgxO films

Zn1−xMgxO films with very precise Mg content are of strong interest for the development of buffer layers on copper-indium-gallium-sulfide solar cells. Atomic layer deposition (ALD) has been successfully used for buffer layers with appropriate electronic properties; however, a good understanding of the growth properties of the ternary oxide is still lacking. Here, we investigate the role of the ZnO/MgO interface on the growth and resulting optoelectronic properties by varying the supercycle parameters (pulse ratio and bilayer period) of the ALD process. We demonstrate that the growth of the MgO layer is enhanced by the ZnO surface, describing the interplay between ZnO and MgO interfaces on the growth of Zn1−xMgxO films. The optical properties of the film not only depend on the Mg content but also on the bilayer period at a given Mg content. More specifically, the bandgap for a given Mg composition is high for the smallest bilayer period 5, starts decreasing slightly for bilayer periods between 10 and 20 due to the increase in thickness of the ZnO layer and confinement effects, and falls to a bandgap of ZnO as the bilayer period increases further &amp;gt;40. With the change in Zn1−xMgxO films from well-mixed to multilayer material as the bilayer period is varied, we illustrate that the optical properties of Zn1−xMgxO can be tuned effectively without largely altering the composition. Probing the effect of the bilayer period on the ternary oxides by ALD is a useful tool in understanding the mixing and interplay of binary materials that can be applied for many other materials.

Origin of enhanced interfacial perpendicular magnetic anisotropy in LiF-inserted Fe/MgO interface

The Fe/MgO interface is an essential ingredient in spintronics as it shows giant tunneling magnetoresistance and strong perpendicular magnetic anisotropy (PMA). A recent study demonstrated that the insertion of an ultra-thin LiF layer between the Fe and MgO layers enhances PMA significantly. In this study, we perform x-ray magnetic circular dichroism measurements on Fe/LiF/MgO multilayers to reveal the origin of the PMA enhancement. We find that the LiF insertion increases the orbital-magnetic-moment anisotropy and thus the magnetic anisotropy energy. We attribute the origin of this orbital-magnetic-moment-anisotropy enhancement to the stronger electron localization and electron-electron correlation or the better interface quality with fewer defects.

Two-dimensional heterostructures formed by graphenelike ZnO and MgO monolayers for optoelectronic applications

Two-dimensional heterostructures are an emerging class of materials for novel applications because of extensive engineering potential by tailoring intriguing properties of different layers as well as the ones arising from their interface. A systematic investigation of mechanical, electronic, and optical properties of possible heterostructures formed by bilayer structures graphenelike ZnO and MgO monolayers is presented. Different functionality of each layer makes these heterostructures very appealing for device applications. ZnO layer is convenient for electron transport in these structures, while MgO layer improves electron collection. At the outset, all of the four possible stacking configurations across the heterostructure are mechanically stable. In addition, stability analysis using phonon dispersion reveals that the AB stacking formed by placing the Mg atom on top of the O atom of the ZnO layer is also dynamically stable at zero temperature. Henceforth, we have investigated the optical properties of these stable heterostructures by applying many-body perturbation theory within the framework of GW approximation and solving the Bethe-Salpeter equation. It is demonstrated that strong excitonic effects reduce the optical band gap to the visible light spectrum range. These results show that this new two-dimensional form of ZnO/MgO heterostructures open an avenue for novel optoelectronic device applications.

The Influence of Plasma Treatment on the Corrosion and Biocompatibility of Magnesium.

In our study, plasma surface modification was employed to tailor the surface properties of magnesium in terms of surface chemistry, topography, and wettability. For two sets of samples, the plasma treatment involved two steps using two different gases (hydrogen and oxygen), while one set of samples was treated with one step only using oxygen. X-ray photoelectron spectroscopy (XPS) was applied to determine the surface composition, oxidation state of the elements, and the thickness of the surface oxide layer on the Mg samples after different plasma treatments. The surface morphology was characterised using atomic force microscopy (AFM) and scanning electron microscopy (SEM). The wettability was analysed by measuring the static water-contact angles and the corrosion was evaluated using potentiodynamic measurements. The interaction of the live cells with the differently modified Mg surfaces was evaluated in terms of biocompatibility using MG-63 cells (human bone osteosarcoma cells). We have shown that a plasma surface treatment significantly decreased the carbon content and the formation of a 15–20-nm-thick MgO layer was observed. This improves the corrosion resistance, while the biocompatibility was retained, compared to the untreated Mg. A plasma surface treatment is therefore an important step in the development of novel surfaces with improved corrosion resistance for magnesium in biomedical applications.

Plasma-enhanced atomic layer deposition of amorphous Ga2O3 for solar-blind photodetection

Wide-bandgap gallium oxide (Ga2O3) is one of the most promising semiconductor materials for solar-blind (200 ​nm–280 ​nm) photodetection. In its amorphous form, a-Ga2O3 maintains its intrinsic optoelectronic properties while can be prepared at a low growth temperature, thus it is compatible with Si integrated circuits (ICs) technology. Herein, the a-Ga2O3 film is directly deposited on pre-fabricated Au interdigital electrodes by plasma enhanced atomic layer deposition (PE-ALD) at a growth temperature of 250 ​°C. The stoichiometric a-Ga2O3 thin film with a low defect density is achieved owing to the mild PE-ALD condition. As a result, the fabricated Au/a-Ga2O3/Au photodetector shows a fast time response, high responsivity, and excellent wavelength selectivity for solar-blind photodetection. Furthermore, an ultra-thin MgO layer is deposited by PE-ALD to passivate the Au/a-Ga2O3/Au interface, resulting in the responsivity of 788 A/W (under 254 ​nm at 10 ​V), a 250-nm-to-400-nm rejection ratio of 9.2 ​× ​103, and the rise time and the decay time of 32 ​ms and 6 ​ms, respectively. These results demonstrate that the a-Ga2O3 film grown by PE-ALD is a promising candidate for high-performance solar-blind photodetection and potentially can be integrated with Si ICs for commercial production.