Expression of concern: Enhanced electrical and magnetic properties of (Co, Yb) co-doped ZnO memristor for neuromorphic computing.

Expression of concern for 'Enhanced electrical and magnetic properties of (Co, Yb) co-doped ZnO memristor for neuromorphic computing' by Noureddine Elboughdiri et al., RSC Adv., 2023, 13, 35993-36008, https://doi.org/10.1039/D3RA06853F.

A band gap and photoluminescence properties engineering in BaO semiconductor for ultraviolet (UV) photodetector applications: A comprehensive role of co-doping.

We report on ultra-violet (UV) photodetectors based on BaO nanoparticles by the detailed investigation of band gap and photoluminescence properties. The BaO nanomaterials were fabricated by the modified sol-gel technique. The innovation of co-doping can modulate the photoluminescence or sensing properties by narrowing the band gap related to enhancing the high carrier concentration, higher electronic lifetime, and low carriers recombination. It is investigated that the BaO nanoparticles with co-doping reveals a highly reduced band gap and exceptional photoluminescence properties as compared to the pristine BaO nanoparticles due to hindering carrier,s recombination for Ultra-violet (UV) photodetectors. The optical studies revealed that the addition of co-dopants in BaO host material creates new energy sites, so the band gap declines up to 1.31 eV as compared to that of pristine BaO (1.36 eV). The photoluminescence properties recorded with photoluminescence (PL) spectroscopy were recorded which revealed the decrease in PL intensity due to the hindering of carriers recombination with the addition of co-dopant metal ions. Furthermore, the inclusion of co-dopant metals results in an improvement in electrical conductivity because of a decline in carrier recombination, according to an I-V characteristic study. This factor contributes to enhance the photoluminescence properties of BaO which, in turn, contributes to enhance the sensing capability of the photodetector device. These obtained features modify optoelectronic properties are far superior as compared to that of previously reported literature on BaO nanomaterials, and the synthesized BaO semiconductor material becomes a potential candidate for efficient use in the ultraviolet (UV) photodetectors device applications.

Cobalt-doped zinc oxide based memristors with nociceptor characteristics for bio-inspired technology.

Neuromorphic computing is a new field of information technology, which is inspired by the biomimetic properties of the memristor as an electronic synapse and neuron. If there are electronic receptors that can transmit exterior impulses to the internal nervous system, then the use of memristors can be expanded to artificial nerves. In this study, a layer type memristor is used to build an artificial nociceptor in a very feasible and straightforward manner. An artificial nociceptor is demonstrated here through the fabrication and characterization of a cobalt-doped zinc oxide (CZO)/Au based memristor. In order to increase threshold switching performance, the surface effects of the CZO layer are eliminated by adding cobalt cobalt-doped zinc oxide (CZO) layer between the P++-Si and Au electrodes. Allodynia, hyperalgesia, threshold, and relaxation are the four distinct nociceptive behaviours that the device displays based on the strength, rate of relapse, and duration of the external stimuli. The electrons that are trapped in or released from the CZO layer's traps are responsible for these nociceptive behaviours. A multipurpose nociceptor performance is produced by this type of CZO-based device, which is crucial for artificial intelligence system applications such as neural integrated devices with nanometer-sized characteristics.

Enhanced electrical and magnetic properties of (Co, Yb) co-doped ZnO memristor for neuromorphic computing.

We investigate the morphological, electrical, magnetic, and resistive switching properties of (Co, Yb) co-ZnO for neuromorphic computing. By using hydrothermal synthesized nanoparticles and their corresponding sputtering target, we introduce Co and Yb into the ZnO structure, leading to increased oxygen vacancies and grain volume, indicating grain growth. This growth reduces grain boundaries, enhancing electrical conductivity and room-temperature ferromagnetism in Co and Yb-doped ZnO nanoparticles. We present a sputter-grown memristor with a (Co, Yb) co-ZnO layer between Au electrodes. Characterization confirms the ZnO layer's presence and 100 nm-thick Au electrodes. The memristor exhibits repeatable analog resistance switching, allowing manipulation of conductance between low and high resistance states. Statistical endurance tests show stable resistive switching with minimal dispersion over 100 pulse cycles at room temperature. Retention properties of the current states are maintained for up to 1000 seconds, demonstrating excellent thermal stability. A physical model explains the switching mechanism, involving Au ion migration during "set" and filament disruption during "reset." Current-voltage curves suggest space-charge limited current, emphasizing conductive filament formation. All these results shows good electronic devices and systems towards neuromorphic computing.

Threshold switching in nickel-doped zinc oxide based memristor for artificial sensory applications.

Electronic devices featuring biomimetic behaviour as electronic synapses and neurons have motivated the emergence of a new era in information and humanoid robotics technologies. In the human body, a nociceptor is a unique sensory neuron receptor that is capable of detecting harmful signals, leading to the central nervous system initiating a motor response. Herein, a nickel-doped zinc oxide (NZO)/Au based memristor is fabricated for the first time and characterized for artificial nociceptor application. For this, the introduction of a nickel-doped zinc oxide (NZO) layer between P++-Si and Au electrodes is used to eliminate the surface effects of the NZO layer, resulting in improved volatile threshold switching performance. Depending on the intensity, duration, and repetition rate of the external stimuli, this newly created memristor exhibits various critical nociceptive functions, including threshold, relaxation, allodynia, and hyperalgesia. The electron trapping/detrapping to/from the traps in the NZO layer is responsible for these nociceptive properties. This kind of NZO-based device produces a multifunctional nociceptor performance that is essential for applications in artificial intelligence systems, such as neural integrated devices with nanometer-sized features.

Structural Evolution and Microwave Dielectric Properties of Ba1-x Sr x Ti4O9, (0.0 ≤ x ≤ 0.06) Ceramics.

The structural, microstructural, and microwave dielectric properties of Ba1-x Sr x Ti4O9, (0.0 ≤ x ≤ 0.06) ceramics samples synthesized by a conventional route were investigated. These structural, microstructural, and dielectric properties were recorded using X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared (FTIR) and impedance analyzer spectroscopies. Ti-O octahedral distortion was observed due to Sr2+ addition. The microwave dielectric properties were interrelated with various Sr2+ concentrations. Excellent microwave dielectric properties, i.e., high relative permittivity (ϵr = 71.50) and low dielectric loss (tan δ = 0.0006), were obtained.

First-principal investigations of electronic, structural, elastic and optical properties of the fluoroperovskite TlLF3 (L = Ca, Cd) compounds for optoelectronic applications.

In this research work, the Tl-based fluoroperovskite compounds TlLF3 (L = Ca, Cd) were investigated computationally using density functional theory (DFT) to comprehend their structural, elastic, optical, and electronic properties. Computation of the tolerance factor and Birch-Murnaghan curve indicated that the compounds are cubic and structurally stable. The structurally optimized lattice constants and the optimum volume corresponding to the optimum energy were measured. Elastic properties were predicted using the IRelast package, and the results showed that the compounds of interest are mechanically stable, ductile, and anisotropic in nature. The electronic properties (band structures and density of states) show that TlCaF3 and TlCdF3 possess a wide direct bandgap from (X-X) symmetry points of 5.7 eV and 5.6 eV, respectively. The contributions of different elemental states to the valence and conduction bands are evaluated from the total and partial density of states (TDOS & PDOS). Analysis of the optical properties showed that these compounds possess a high refractive index, absorption coefficient, and reflectivity at high energy ranges. The values of the direct bandgap indicated that these compounds are expected to be semiconducting in nature, and their use is primarily considered to be in the semiconductor industries and optoelectronic devices. These compounds are new and have been investigated for the first time using the computational approach, which provides comprehensive insight into their different properties; based on the results, they are recommended as industrial candidates.

Synthesis and Characterization of Sn/SnO2/C Nano-Composite Structure: High-Performance Negative Electrode for Lithium-Ion Batteries.

Tin oxide (SnO2) and tin-based composites along with carbon have attracted significant interest as negative electrodes for lithium-ion batteries (LIBs). However, tin-based composite electrodes have some critical drawbacks, such as high volume expansion, low capacity at high current density due to low ionic conductivity, and poor cycle stability. Moreover, complex preparation methods and high-cost carbon coating procedures are considered main challenges in the commercialization of tin-based electrodes for LIBs. In this study, we prepared a Sn/SnO2/C nano-composite structure by employing a low-cost hydrothermal method, where Sn nanoparticles were oxidized in glucose and carboxymethyl cellulose CMC was introduced into the solution. Scanning electron microscope (SEM) and transmission electron microscope revealed the irregular structure of Sn nanoparticles and SnO2 phases in the conductive carbon matrix. The as-prepared Sn/SnO2/C nano-composite showed high first-cycle reversible discharge capacity (2248 mAhg-1) at 100 mAg-1 with a first coulombic efficiency of 70%, and also displayed 474.64 mAhg-1 at the relatively high current density of about 500 mAg-1 after 100 cycles. A low-cost Sn/SnO2/C nano-composite with significant electrochemical performance could be the next generation of high-performance negative electrodes for LIBs.

Hydrothermal Extraction of Amorphous Silica from Locally Available Slate.

Slate is a naturally available aluminous silicate based material and can be used as a good source for silica extraction. In the current investigation, the slate sample was passed through calcination and acid leaching processes to decrease alumina contents and other major constituents. Silica extraction was performed by alkaline hydrothermal treatment of a given slate sample followed by acidic precipitation. Different steps, including the effect of concentration of sodium hydroxide solution, reaction time, the ratio of the mass of sample to volume of alkaline solution, the temperature of dispersion, and pH of the filtrate, were investigated to extract the maximum amount of pure amorphous silica. The extracted silica was physicochemically analyzed through XRF, XRD, FT-IR spectroscopy, and SEM techniques. The amorphous nature of the extracted silica is evident from XRD and SEM studies, while FT-IR studies support its purity, showing peaks of only Si-O-Si bonds. The purity of the extracted silica was further confirmed via XRF spectroscopic analysis and a hydrofluoric acid test.

Effects of Vacuum and Air Annealing on Structural, Morphological, Optical, and Electrical Properties of Multilayer CdZnS Thin Films for Photovoltaic and Optoelectronic Applications.

Multilayer CdZnS (CZS) thin film was deposited on soda lime glass substrates. After deposition, the films were vacuum and air annealed at 100 °C, 200 °C, 300 and 400 °C for 1 h. Effects of vacuum and air annealing on structural, morphological, optical, and electrical properties of multilayer CZS films with increasing annealing temperature (IAT) were studied. The structural analysis revealed that the films were polycrystalline with hexagonal structure having a prominent/intensive peak along the (002) plane at 300 and 400 °C. The crystallite size of nanoparticles increased from 18.4 to 20.5 nm under air annealing and from 18.4 to 26.9 nm under vacuum annealing, showing the significance of annealing on nanoparticle grain growth. According to morphological analysis, the multilayer technique provides homogeneous film distribution over the substrate. The transmittance graphs of films revealed that it increased up to 92% in the visible and NIR regions under vacuum annealing and up to 52% under air annealing. Vacuum annealing enhanced the band gap energies more significantly than air annealing. The electrical resistivity increased with IAT, showing that structural, morphological, optical, and electrical properties of the multilayer thin films of CZS were strongly dependent on vacuum and air annealing.

Room temperature dilute magnetic semiconductor response in (Gd, Co) co-doped ZnO for efficient spintronics applications.

The co-precipitation approach was utilized to experimentally synthesize ZnO, Zn0.96Gd0.04O and Zn0.96-x Gd0.04Co x O (Co = 0, 0.01, 0.03, 0.04) diluted magnetic semiconductor nanotubes. The influence of gadolinium and cobalt doping on the microstructure, morphology, and optical characteristics of ZnO was investigated, and the Gd doping and Co co-doping of the host ZnO was verified by XRD and EDX. The structural investigation revealed that the addition of gadolinium and cobalt to ZnO reduced crystallinity while maintaining the preferred orientation. The SEM study uncovered that the gadolinium and cobalt dopants did not affect the morphology of the produced nanotubes, which is further confirmed through TEM. In the UV-vis spectra, no defect-related absorption peaks were found. By raising the co-doping content, the crystalline phase of the doped samples was enhanced. It was discovered that the dielectric response and the a.c. electrical conductivity display a significant dependent relationship. With the decreasing frequency and increasing Co co-dopant concentration, the ε r and ε'' values decreased. It was also discovered that the ε r, ε'', and a.c. electrical conductivity increased when doping was present. Above room temperature, co-doped ZnO nanotubes exhibited ferromagnetic properties. The ferromagnetic behaviour increased as Gd (0.03) doping increased. Increasing the Co content decreased the ferromagnetic behaviour. It was observed that Zn0.96-x Gd0.04Co x O (x = 0.03) nanotubes exhibit superior electrical conductivity, magnetic and dielectric characteristics compared to pure ZnO. This high ferromagnetism is typically a result of a magnetic semiconductor that has been diluted. In addition, these nanoparticles are utilized to design spintronic-based applications in the form of thin-films.

Enhancing the physical properties and photocatalytic activity of TiO2 nanoparticles via cobalt doping.

Cobalt-doped TiO2-based diluted magnetic semiconductors were successfully synthesized using a co-precipitation method. The X-ray diffraction study of all the samples showed good crystallinity, matching the standard tetragonal anatase phase. The X-ray diffraction peaks of the cobalt-doped sample slightly shifted towards a lower angle showing the decrease in particle size and distortion in the unit cell due to cobalt incorporation in the lattice of TiO2. Transmission electron microscopy showed the spherical morphology of the TiO2 nanoparticles, which decreased with Co-doping. The optical characteristics and band gap investigation revealed that defects and oxygen vacancies resulted in lower band gap energy and maximum absorption in the visible region. Dielectric measurements showed enhancement in the dielectric constant and AC conductivity, while the dielectric loss decreased. The enhancement in the dielectric properties was attributed to interfacial polarization and charge carrier hopping between Co and Ti ions. The magnetic properties displayed that pure TiO2 was diamagnetic, while Co-doped TiO2 showed a ferromagnetic response at 300 K. The visible light-driven photocatalytic activity showed an improvement for Co-doped TiO2. Our results demonstrate that Co-doping can be used to tune the physical properties and photocatalytic activity of TiO2 for possible spin-based electronics, optoelectronics, and photo-degradation applications.

Diluted magnetic semiconductor properties in TM doped ZnO nanoparticles.

The hydrothermal method was used to create dilute magnetic semiconductor nanoparticles of Zn1-x Co x O (x = 0, 0.01, 0.05, 0.09). The effect of cobalt doping on the microstructure, morphological and optical properties of Zn1-x Co x O was also studied and the Co doping to host ZnO was confirmed from XRD and EDX analysis. The structural analysis showed that doping of cobalt into ZnO decreased the crystallinity, but the preferred orientation didn't change. SEM analysis revealed that the cobalt dopant did not have a strong influence on the shape of the synthesized nanoparticles. No defect-related absorption peaks were observed in the UV-Vis spectra. The crystallinity of the doped samples was improved by high growth temperature and long growth time. Ferromagnetic behavior above room temperature was detected in co-doped ZnO nanoparticles. The ferromagnetic behavior increased with increasing Co (up to x = 0.05) doping. The ferromagnetic behavior declined when the Co content was further increased. Related research shows that doped ZnO nanoparticles have better dielectric, electrical conductivity, and magnetic properties than pure ZnO. This high ferromagnetism is usually a response reported for dilute magnetic semiconductors. These semiconductor nanoparticles were further used to designed spintronic based applications.

Electrocatalytic hydrogen generation using tripod containing pyrazolylborate-based copper(ii), nickel(ii), and iron(iii) complexes loaded on a glassy carbon electrode.

Three transition metal complexes (MC) namely, [TpMeMeCuCl(H2O)] (CuC), [TpMeMeNiCl] (NiC), and [TpMeMeFeCl2(H2O)] (FeC) {TpMeMe = tris(3,5-dimethylpyrazolyl)borate} were synthesized and structurally characterized. The three complexes CuC, NiC, and FeC-modified glassy carbon (GC) were examined as molecular electrocatalysts for the hydrogen evolution reaction (HER) in alkaline solution (0.1 M KOH). Various GC-MC electrodes were prepared by loading different amounts (ca. 0.2-0.8 mg cm-2) of each metal complex on GC electrodes. These electrodes were used as cathodes in aqueous alkaline solutions (0.1 M KOH) to efficiently generate H2 employing various electrochemical techniques. The three metal complexes' HER catalytic activity was assessed using cathodic polarization studies. The charge-transfer kinetics of the HER at the (GC-MC)/OH- interface at a given overpotential were also studied using the electrochemical impedance spectroscopy (EIS) technique. The electrocatalyst's stability and long-term durability tests were performed employing cyclic voltammetry (repetitive cycling up to 5000 cycles) and 48 h of chronoamperometry measurements. The catalytic evolution of hydrogen on the three studied MC surfaces was further assessed using density functional theory (DFT) simulations. The GC-CuC catalysts revealed the highest HER electrocatalytic activity, which increased with the catalyst loading density. With a low HER onset potential (E HER) of -25 mV vs. RHE and a high exchange current density of 0.7 mA cm-2, the best performing electrocatalyst, GC-CuC (0.8 mg cm-2), showed significant HER catalytic performance. Furthermore, the best performing electrocatalyst required an overpotential value of 120 mV to generate a current density of 10 mA cm-2 and featured a Tafel slope value of -112 mV dec-1. These HER electrochemical kinetic parameters were comparable to those measured here for the commercial Pt/C under the same operating conditions (-10 mV vs. RHE, 0.88 mA cm-2, 108 mV dec-1, and 110 mV to yield a current density of 10 mA cm-2), as well as the most active molecular electrocatalysts for H2 generation from aqueous alkaline electrolytes. Density functional theory (DFT) simulations were used to investigate the nature of metal complex activities in relation to hydrogen adsorption. The molecular electrostatic surface potential (MESP) of the metal complexes was determined to assess the putative binding sites of the H atoms to the metal complex.

The effect of Mn and Co dual-doping on the structural, optical, dielectric and magnetic properties of ZnO nanostructures.

This paper addresses the effect of Mn (2%, fixed) and Co (2, 4, and 6%, varied) substitution on the structural, optical, dielectric and magnetic responses of ZnO nanoparticles synthesized by the co-precipitation chemical route. The X-ray diffraction analysis confirms the hexagonal wurtzite structure of ZnO. The incorporation of co-doping in the ZnO host, indicated by peak shifting in the XRD patterns, enhanced the crystallite size of the Mn/Co dual-doped ZnO nanoparticles. The FTIR spectra show a characteristic peak around 875 cm-1 assigned to Zn-O stretching, this validates the formation of the wurtzite structure of ZnO. Raman spectroscopy reveals the characteristic band of the wurtzite structure of ZnO nanoparticles along with coupled vibration modes of Mn/Co with the donor defect states in the doped samples. Enhanced optical absorption in the visible region and a significant red-shift in the absorption band edge were found due to doping. The optical band gap is found to decrease from 3.45 eV to 3.15 eV when Co doping increases up to 6%. The dielectric properties, strongly frequency-dependent, decrease with increasing Co doping while the electrical conductivity increases. Ferromagnetism is observed in all the doped samples, and its origin is attributed to an increase in oxygen vacancies which form bound magnetic polarons. It can be inferred that the doping of Mn and Co can be an effective tool to tune the physical properties of ZnO nanoparticles for potential spintronics and high-frequency applications.

Correction: Electrocatalytic hydrogen generation using tripod containing pyrazolylborate-based copper(ii), nickel(ii), and iron(iii) complexes loaded on a glassy carbon electrode.

[This corrects the article DOI: 10.1039/D1RA08530A.].

Structural Elucidation, Electronic and Microwave Dielectric Properties of Ca(Sn x Ti1-x )O3, (0 ≤ x ≤ 0.8) Lead-Free Ceramics.

The lead-free Ca(Sn x Ti1-x )O3, (0 ≤ x ≤ 0.8) sample has been successfully prepared through the ball milling process, sintered at 1200 °C for 3 h. The structural, morphological, vibrational, and microwave dielectric properties of synthesized samples were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), and impedance analysis. All the samples have an orthorhombic phase structure with a space group of Pbnm formation, and the crystalline size and strain changes with respect to Sn4+ doping were observed in the XRD analysis. From a morphological point of view, on increasing the content "x", the grain size reduces from 3.29 to 1.37 µm. The existence of vibrations and the bridging stretching mode of Ti-O-Ti and Ti-O-Sn both are associated with the broadband in the region below 800 cm-1 verified by FT-IR. The variation in electrons hopping off the host compound with respect to Sn4+ ions was analyzed in AC conductivity. The changes of dielectric properties such as complex permittivity, modulus spectroscopy, and dielectric loss at room temperature with a different frequency range of 1.00-2.00 GHz are discussed.

Structural, optical and microwave dielectric properties of Ba(Ti1-xSnx)4O9, 0 ≤ x ≤ 0.7 ceramics.

Sn-doped BaTi4O9 (BT4) dielectric ceramics were prepared by a mixed oxide route. Preliminary X-ray diffraction (XRD) structural study shows that the ceramic samples have orthorhombic symmetry with space group (Pnmm). Scanning electron microscopy (SEM) shows that the grain size of the samples decreases with an increase in Sn4+ content. The presence of the metal oxide efficient group was revealed by Fourier transform infrared (FTIR) spectroscopy. The photoluminescence spectra of the ceramic samples reported red color ~ 603, 604, 606.5 and 605 nm with excitation energy ~ 2.06, 2.05, 2.04 and 2.05 eV for Sn4+ content with x = 0.0, 0.3, 0.5, and 0.7, respectively. The microwave dielectric properties of these ceramic samples were investigated by an impedance analyzer. The excellent microwave dielectric properties i.e. high dielectric constant (εr = 57.29), high-quality factor (Qf = 11,852), or low-dielectric loss (3.007) has been observed.

Transformation of Oil Palm Waste-Derived Cellulose into Solid Polymer Electrolytes: Investigating the Crucial Role of Plasticizers.

This study explores the possibility of transforming lignocellulose-rich agricultural waste materials into value-added products. Cellulose was extracted from an empty fruit bunch of oil palm and further modified into carboxymethyl cellulose (CMC), a water-soluble cellulose derivative. The CMC was then employed as the polymeric content in fabrication of solid polymer electrolyte (SPE) films incorporated with lithium iodide. To enhance the ionic conductivity of the solid polymer electrolytes, the compositions were optimized with different amounts of glycerol as a plasticizing agent. The chemical and physical effects of plasticizer content on the film composition were studied by Fourier transform infrared (FTIR) and X-ray diffraction (XRD) analysis. FTIR and XRD analysis confirmed the interaction plasticizer with the polymer matrix and the amorphous nature of fabricated SPEs. The highest ionic conductivity of 6.26 × 10-2 S/cm was obtained with the addition of 25 wt % of glycerol. By fabricating solid polymer electrolytes from oil palm waste-derived cellulose, the sustainability of the materials can be retained while reducing the dependence on fossil fuel-derived materials in electrochemical devices.

An innovative approach towards the simultaneous enhancement of the oxygen reduction and evolution reactions using a redox mediator in polymer based Li-O2 batteries.

For safety concerns, polymer-based Li-O2 batteries have received more attention than traditional non-aqueous Li-O2 batteries. However, poor cycling stability, low round trip efficiency, and over charge potential during cycling are the major shortcomings for their future applications. In this work, a soluble redox mediator integrated into a polymer electrolyte provides immediate access to the solid discharged product, lowering the energy barrier for reversible Li2O2 generation and disintegration. Moreover, introducing a redox mediator to the polymer electrolyte boosts the ORR during discharge and the OER during the recharge process. The synergistic redox mediator pBQ (1,4 benzoquinone) dramatically reduces the over-potential. A small proportion of pBQ in the polymer electrolyte allows Li2O2 to develop in a thin film-like morphology on the cathode surface, resulting in a high reversible capacity of ∼12 000 mA h g-1 and an extended cycling stability of 100 cycles at 200 mA g-1 with a cut-off capacity of 1000 mA h g-1. The remarkable cell performance is attributed to the fast kinetics of para benzoquinone for the ORR and OER in Li-O2 batteries. The use of a redox mediator in a polymer electrolyte opens a new avenue for practical Li-O2 battery applications in achieving low charge potential and excellent energy efficiency.