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Intensive research on optoelectronic memory (OEM) devices based on two-dimensional (2D) van der Waals heterostructures (vdWhs) is being conducted due to their distinctive advantages for electrical–optical writing and multilevel storage. These features make OEM a promising candidate for the logic of reconfigurable operations. However, the realization of nonvolatile OEM with broadband absorption (from visible to infrared) and a high switching ratio remains challenging. Herein, we report a nonvolatile OEM based on a heterostructure consisting of rhenium disulfide (ReS2), hexagonal boron nitride (hBN) and tellurene (2D Te). The 2D Te-based floating-gate (FG) device exhibits excellent performance metrics, including a high switching on/off ratio (∼106), significant endurance (>1000 cycles) and impressive retention (>104s). In addition, the narrow band gap of 2D Te endows the device with broadband optical programmability from the visible to near-infrared regions at room temperature. Moreover, by applying different gate voltages, light wavelengths, and laser powers, multiple bits can be successfully generated. Additionally, the device is specifically designed to enable reconfigurable inverter logic circuits (including AND and OR gates) through controlled electrical and optical inputs. These significant findings demonstrate that the 2D vdWhs with a 2D Te FG are a valuable approach in the development of high-performance OEM devices.

Transition metal dichalcogenides (TMDCs), such as MoS2, MoSe2, WS2, and WSe2,have attracted enormous attention owing to their unique electrical and optical properties. A type of material known as TMDC has the MX2formula with a direct bandgap in ultra-thin layers and indirect bandgap properties in the bulk. TMDCs have attracted significant research interest due to their use in nano-devices, opto-electronics, and next-generation electronics. In the study, two different MoS2devices, Au–bulk MoS2–Au and Au–monolayer MoS2–Au, were fabricated, and their photon-induced current–voltage characteristics at different wavelengths (red ≈ 650 nm, green ≈ 532 nm and blue ≈ 450 nm) and values were compared. Additionally, the time-dependent photoresponses of these devices under red light irradiation (wavelength, λex= 650 nm) were analyzed. The Au–monolayer MoS2–Au device had a higher current response compared with the Au–bulk MoS2–Au device. These results suggest that single-layer MoS2devices could be more efficient and responsive than bulk MoS2devices for a variety of applications.

When a magnetic moment is embedded in a metal, it captures nearby itinerant electrons to form a so-called Kondo cloud. When magnetic impurities are sufficiently dense that their individual clouds overlap with each other they are expected to form a correlated electronic ground state. This is known as Kondo condensation and can be considered a magnetic version of Bardeen–Cooper–Schrieffer pair formation. Here, we examine this phenomenon by performing electrical transport and high-precision tunnelling density-of-states spectroscopy measurements in a highly P-doped crystalline silicon metal in which disorder-induced localized magnetic moments exist. We detect the Kondo effect in the resistivity of the Si metal at temperatures below 2 K and an unusual pseudogap in the density of states with gap edge peaks below 100 mK. The pseudogap and peaks are tuned by applying an external magnetic field and transformed into a metallic Altshuler–Aronov gap associated with a paramagnetic disordered Fermi liquid phase. We interpret these observations as evidence of Kondo condensation followed by a transition to a disordered Fermi liquid.

Dense and long-chain ligands on the surface of lead halide perovskite quantum dots (PQDs) hinder charge transport. Thus, it is extremely challenging to achieve environmentally stable PQDs with an appropriate ligand, optimal density, and successful charge transfer to charge acceptors. Through comprehensive material development and photophysical experiments, rapid crystallization of CsPbBr3PQDs encapsulated in crude silica shells at room temperature was achieved using (3-aminopropyl)triethoxysilane as the key coordinating ligand. Following the control post-annealing treatment, highly stable PQDs wrapped in robust insulating silica shells were obtained; they exhibited phenomenal electron transfer characteristics beyond silica shell coverage. Based on the electron transfer phenomenon from the core–shell PQDs to the electron transport media, the formation of photoinduced superoxide ions was demonstrated. These ions triggered the photocatalytic degradation of 2-mercaptobenzothiazole. This study presents advanced insights into core–shell CsPbBr3PQDs covered in silica shells and their detailed photochemistry for renewable energy applications.

Solid-state spintronic devices are energy-efficient for data storage and energy harvesting. This field is revolutionized by the discovery of giant magnetoresistance. Recently, Qian et al. fabricated an intercalated chiral-molecular two-dimensional superlattice that exhibits highly efficient chiral-induced spin selectivity. They demonstrated a tunneling magnetoresistance ratio of >300% and a spin polarization ratio of >60%, which opens up promising future applications in spintronic devices.

The use of electrodes capable of functioning as both electrochromic windows and energy storage devices has been extended from green building development to various electronics and displays to promote more efficient energy consumption. Herein, we report the electrochromic energy storage of bimetallic NiV oxide (NiVO) thin films fabricated using chemical bath deposition. The best optimized NiVO electrode with a Ni/V ratio of 3 exhibits superior electronic conductivity and a large electrochemical surface area, which are beneficial for enhancing electrochemical performance. The color switches between semitransparent (a discharged state) and dark brown (a charged state) with excellent reproducibility because of the intercalation and deintercalation of OH–ions in an alkaline KOH electrolyte. A specific capacity of 2403 F g–1, a coloration efficiency of 63.18 cm2C–1, and an outstanding optical modulation of 68% are achieved. The NiVO electrode also demonstrates ultrafast coloration and bleaching behavior (1.52 and 4.79 s, respectively), which are considerably faster than those demonstrated by the NiO electrode (9.03 and 38.87 s). It retains 91.95% capacity after 2000 charge–discharge cycles, much higher than that of the NiO electrode (83.47%), indicating that it has significant potential for use in smart energy storage applications. The superior electrochemical performance of the best NiVO compound electrode with an optimum Ni/V compositional ratio is due to the synergetic effect between the high electrochemically active surface area induced by V-doping-improved redox kinetics (low charge-transfer resistance) and fast ion diffusion, which provides a facile charge transport pathway at the electrolyte/electrode interface.

Scintillation is a flash of light produced in a material by the passage of a high-energy particle or photon. Desirable properties of scintillators, such as high quantum yield, low afterglow, and radiation hardness, are determined by their physical and optoelectronic properties. Metal halide perovskite (CsPbX3, X = Cl, Br, I) nanocrystals (NCs) have gained increasing attention as materials for optical and X-ray scintillators across a wide range of incident photon energies owing to their outstanding luminescent properties. In this study, we demonstrate the dependence of scintillation yield (SY) on incident photon energy ranging from ultraviolet (UV) light to X-rays in colloidal CsPbBr3NCs hybridized with organic molecules (2,5-diphenyloxazole: PPO). The measured SY varied with the changing concentration ratio of NCs and PPO molecules. Experimental and theoretical analyses suggested that the SY is associated with the competition between photoluminescence quenching (reabsorption) and photoelectric effect enhanced by X-ray photon induced charge transfer from the organic molecules to the NCs. The optimally engineered hybrid nanomaterial scintillator exhibits excellent X-ray imaging with sharp image contrast (i.e., super-resolved edge spread function (ESF)), under X-ray irradiation commonly used for diagnosis.

The ability to fabricate monodisperse reduced-dimensional perovskite (RDP) films would enable researchers to further understand and apply RDP films in various optoelectronic applications. Naturerecently published a study by Ma et al. where monodisperse RDP was fabricated using a bifunctional molecular additive. The monodisperse-RDP-based LED achieved an external quantum efficiency of 25.6% with an exceptional half-life at an initial luminance of 7,200 cd m−2.

Efficient harvesting of triplet excitons in organic molecules is crucial for developing high-performance X-ray scintillators and X-ray imagers. High-performance organic scintillators based on thermally activated delayed fluorescence (TADF) have been recently demonstrated, allowing the triplet excitons to generate a high light yield under X-ray illumination. These TADF organic molecules outperformed the benchmark anthracene-based scintillators.

Herein a method is proposed for engineering the electronic properties (including the band structure) of diamond viasurface hybridization with graphene. Graphene layers (5–50 nm in thickness) were grown vertically onto a polished 〈110〉 textured polycrystalline diamond plate (1 × 1 cm2) (vGr-diamond) at ∼1300 °C viahydrogen plasma etching in a chemical vapor deposition (CVD) chamber. Due to the crystallographic relationship, the graphene layers embed at an angle of 30° to the diamond surface comprising the (110) planes. The epitaxial relationship is demonstrated vialow angle X-ray diffraction (XRD), the XRD rocking curve, Raman and scanning electron microscopy. With hybridization, the diamond sample reveals a strong photoluminescent (PL) signal at ∼2.78 eV (∼450 nm). The peak was assigned to the ‘interface defects’ of the vGr-diamond hybrid structure, which are a type of ‘surface defect’ of the CVD diamond that generates a peak at ∼2.69 eV. The blue shift (∼90 meV) of the interface defects is due to the compressive strain of ∼3% applied to the interface atoms. Simulations indicate that the hybrid structures possess a finite band gap of 1.85–0.25 eV, which decreases upon increasing the thickness of the graphene layers to ∼1.4 nm. The appearance of a small band gap was attributed to the compressive strain. These findings may provide a route for diamond to become a platform for next generation and extreme electronic devices.

Developing multicomponent superlattices (SLs) using lead halide perovskite nanocrystals (NCs) is challenging due to weak ionic bonding and the high ionic mobility of halide ions. Recently, Kovalenko et al. developed multicomponent SLs, including binary cubic SLs, binary perovskite-like SLs, ternary perovskite-like SLs, and columnar binary SLs.

Phototransistors that are based on a hybrid vertical heterojunction structure of two-dimensional (2D)/quantum dots (QDs) have recently attracted attention as a promising device architecture for enhancing the quantum efficiency of photodetectors. However, to optimize the device structure to allow for more efficient charge separation and transfer to the electrodes, a better understanding of the photophysical mechanisms that take place in these architectures is required. Here, we employ a novel concept involving the modulation of the built-in potential within the QD layers for creating a new hybrid MoS2/PbS QDs phototransistor with consecutive type II junctions. The effects of the built-in potential across the depletion region near the type II junction interface in the QD layers are found to improve the photoresponse as well as decrease the response times to 950 μs, which is the faster response time (by orders of magnitude) than that recorded for previously reported 2D/QD phototransistors. Also, by implementing an electric-field modulation of the MoS2channel, our experimental results reveal that the detectivity can be as large as 1 × 1011jones. This work demonstrates an important pathway toward designing hybrid phototransistors and mixed-dimensional van der Waals heterostructures.

Two-dimensional tellurium (2D Te) is a promising material for functional optoelectronic applications due to its narrow band gap and high carrier mobility. However, its light−matter interactions typically induce positive photoconductivity (PPC), leading to low photoresponsivity in 2D Te-based photodetectors due to their high dark current and the indirect 2D Te band gap. Here, we report novel tunable negative photoconductivity (NPC) in an Al2O3-encapsulated ambipolar 2D Te device, with excellent photoresponsivity of up to 6.9 × 104AW−1, outperforming most previously reported 2D single-element chalcogen-based photodetectors. The NPC is attributed to the lower carrier mobility due to phonon scattering induced by the enhanced photothermal effect in the encapsulated Te layer. The threshold voltage can be tuned in the encapsulated 2D Te transistor under high-energy laser irradiation, demonstrating a new strategy for controlled 2D Te doping. Well-controlled gate-tunable negative and positive persistent photocurrents are achieved in the encapsulated 2D Te transistor, thus emulating biological synapse activity. An encapsulated 2D Te device with a flexible substrate also exhibits stable NPC after 1000 bending cycles, highlighting its potential use in wearable optoelectronic devices. The construction of ambipolar 2D Te phototransistors may pave the way for the development of novel functional optoelectronic devices.

We report an efficient method for growing NiO nanostructures by oblique angle deposition (OAD) technique in an e-beam evaporator for supercapacitor applications. This facile physical vapor deposition technique combined with OAD presents a unique, direct, and economical route for obtaining high width-to-height ratio nanorods for supercapacitor electrodes. The NiO nanostructure essentially consists of nanorods with varying dimensions. The sample deposited at OAD 75° showed highest supercapacitance value of 344 F/g. NiO nanorod electrodes exhibits excellent electrochemical stability with no degradation in capacitance after 5000 charge–discharge cycles. The nanostructured film adhered well to the substrate and had 131% capacity retention. Peak energy density and power density of the NiO nanorods were 8.78 Wh/kg and 2.5 kW/kg, respectively. This technique has potential to be expanded for growing nanostructured films of other interesting metal/metal oxide candidates for supercapacitor applications.

A molybdenum disulfide (MoS2) nanosheet film was grown directly on a stainless-steel substrate by using an in-situ hydrothermal growth technique at 200 °C. The formation of an MoS2hexagonal structure with a nanosheet-like morphology was confirmed by using X-ray diffraction (XRD) and field-emission scanning electron microscopy (FE-SEM) while a layered MoS2nanosheet structure was observed under an energy-filtering transmission electron microscope (EF-TEM). The electrochemical supercapacitor properties of the MoS2nanosheet electrode were measured in 1-M aqueous Na2SO4electrolyte by using cyclic voltammetry (CV) and charge/discharge technique, and the electrode’s specific capacitances were 91.29 F/g and 146.15 F/g, respectively. The concurrent double-layer capacitance and pseudo-capacitance behaviors of the electrode manifested themselves in the rectangular shape and redox peaks of the CV curve. The mesoporous MoS2nanosheets were electrochemically stable for up to 1000 charge/discharge cycles.

This study investigates the transport and switching time of nonvolatile tungsten oxide based resistive-switching (RS) memory devices. These devices consist of a highly resistive tungsten oxide film sandwiched between metal electrodes, and their RS characteristics are bipolar in the counterclockwise direction. The switching voltage, retention, endurance, and switching time are strongly dependent on the type of electrodes used, and we also find quantitative and qualitative evidence that the electronegativity (χ) of the electrodes plays a key role in determining the RS properties and switching time. We also propose an RS model based on the role of the electronegativity at the interface.

We have investigated the electrical transport in symmetric metal-bulk MoS2-metal junction devices as a function of the temperature in the bias-voltage range between −0.5 V and +0.5 V. Three different types of MoS2were: pristine, N2-annealed and H2-annealed MoS2. Metal/MoS2contacts were formed by evaporating various metals (Al, Au, Ti and Ni) with different work functions on the surface of MoS2. The two-terminal current-voltage characteristics were measured in the temperature range from 100 K to 300 K, and the thermal activation energies at the metal-bulk MoS2interface were also estimated. The Au/MoS2and Ni/MoS2junctions exhibit Ohmic behavior (linear current-voltage characteristics) over the entire temperature range, regardless of whether N2- or H2-annealing was applied. Al/N2annealed MoS2and Ti/N2annealed MoS2junction devices exhibited Schottky behavior (nonlinear current-voltage characteristics) as the temperature was decreased below 150 K. We attribute the different electrical transport properties that were observed to the dissimilar natures of the junction interfaces and to the annealing-induced modification in the Fermi level of MoS2.

GaN:Mn epilayers were grown on Al2O3 substrate by using molecular beam epitaxy (MBE). Xray diffraction (XRD) data showed intrinsic GaMnN and precipitates including MnGa and MnN. PL transitions (e, Mn) and (D, Mn) related to Mn were remarkably activated. Clear ferromagnetic hysteresis loops were obtained in both samples, which means a good formation of ferromagnetic coupling. The M-T curves revealed a curie temperature (Tc) of 140 ~ 170 K which is intrinsic to GaMnN and a Tc of above 300 K which is due to the MnGa and the MnN precipitates. The samples clearly displayed a magnetic resonance at a field of around 200 - 400 mT. Electron spin resonance (ESR) data showed that the shift of (Hcenter) (i.e., Hcenter= 337 - Hcenter[mT]) were greater than 20 mT for samples, and the appearance of a Hcenter with a positive Hcenteris indicative of the samples having obvious ferromagnetism. The incorporated Mn ions are in a 2+ ionic state (i.e., Mn2+) because Mn2+ with a spin state of S= 5/2 typically exhibits a magnetic resonance with g≈ 2 when Mn is doped into semiconductors.

Multi-wall carbon nanotube/polyaniline (CNT/PANI) nanocomposite thin films for electrochemical electrode applications are synthesized on flexible graphene-coated indium-tin-oxide (ITO) substrates by using a drop-casting technique. Graphene serves as an adhesion layer between the CNT/PANI nanocomposite film and the flexible ITO substrate. A nanoscale vermicular morphology of PANI films containing well-dispersed CNTs is formed on the surface of graphene. The electrochemical characteristics of the nanocomposite films are investigated in a 0.5-M LiClO4+ PC electrolyte. The electrical conduction of the CNT/PANI/graphene/ITO film is considerably superior to that of a PANI/ITO film. The cyclic voltammogram measurements indicate that the specific capacitance of the CNT/PANI film is ~134 F/g which is ~11% higher than that (~120 F/g) of the pure PANI film. Most importantly, the nominal capacitance loss of the PANI/CNT film (~1.2%) is significantly improved relative to that of the pure PANI film (~18.1%) after 100 charge-discharge cycles. We attribute the considerably improved capacity retention of the flexible CNT/PANI electrode to the graphene adhesion layer.

We have investigated an effective method to control the diameter and the density of carbon nanotubes (CNTs) by introducing a catalyst-embedded supporting layer (CSL) prepared by using rf-magnetron sputtering with a mixed target consisting of Fe and Al2O3. The type of CNTs was changed from single-walled CNTs with a diameter of 0.85 ~ 1.55 nm to multi-walled CNTs with increasing rf-magnetron sputtering power. The controllability of the diameter and the density of the CNTs was confirmed to have been improved by using the rf power during the sputtering of the CSL and the concentration of Fe in the mixed target, respectively.

The PANI (polyaniline) thin films are synthesized on flexible ITO/PET (indium tin oxide/polyethylene terephthalate) substrates by using the drop-casting method. The amount of the PANI for the drop casting varies from 0.04 to 0.16 g. The morphology of the drop-casted PANI films shows a porous vermicular shape. The electrochemical supercapacitor properties of the PANI films are examined in a 0.5-M LiClO4+ PC electrolyte. The PANI films with 0.08 g of PANI show higher current density and considerably higher specific capacitance and capacity retention, compared with other PANI films. The highest specific capacitance of the films with 0.08 g of PANI is found to be ∼120 F/g, and the capacity retention is found to be as high as 70.51% after 100 charge-discharge cycles.

TiOX-polyaniline (PANI) nano-composite thin films are synthesized using an electrochemical deposition technique for supercapacitor applications. The PANI-TiOXcomposite films show granular porous morphologies along with PANI nanofibers. The electrochemical supercapacitor properties of the PANI and the composite PANI-TiOXfilms are examined in a 0.5-M LiClO4electrolyte. The pure PANI film shows a comparatively higher specific capacitance whereas the PANI-TiOXcomposite films are more stable with high power and energy densities. Negligible capacitance loss is obtained for the PANI-TiOXcomposite films over 1000 charge-discharge cycles. The composite films show considerably improved power-density and energy-density values of ∼31.2 kW/kg and ∼35.2 Wh/kg, respectively.

The multi-valued resistive switching (RS) characteristics and mechanism in a WOx/AlOyheterojunction-based nonvolatile memory have been investigated. Although Al/WOx/Pt and Al/AlOy/Pt show different RS characteristics, bipolar and unipolar modes, respectively, the Al/WOx/AlOy/Pt structure shows both bipolar and unipolar RS characteristics, depending on the magnitude of the applied voltage. Three resistance states, which are defined as the low-resistance state (LRS), the mid-high-resistance state (mid-HRS) and the high-resistance state (HRS), are observed. A model combining two different RS mechanisms, oxygen ions involving the redox process at the interface and filamentary conduction, is proposed, and provides a simple physical concept to understand the multi-valued RS behavior. Our findings will be useful to design and optimize oxide heterojunction-based non-volatile RS memory devices.

Although lab-scale organic light-emitting diode (OLED) efficiencies continue to increase, most systems use halogenated solvents to dissolve the emitting layer. Halogenated solvents achieve better film morphologies and efficiencies due to their better solubility for organic semiconductors, but they often have negative environmental impacts. Therefore, we have designed and synthesized three highly efficient new host materials for solution processable green phosphorescent OLEDs (PHOLEDs) using non-halogenated solvents. We utilized environmentally friendly high energy ball milling, with strong mechanical forces producing desired host materials with high reactivity. Impaction and friction followed by mechanical forces also heat the reactants during synthesis. All three materials exhibited excellent photoluminescence quantum yields and high triplet energy for efficient energy transfer to guest molecules. Optimized PHOLEDs by solution processing using halogenated solvent exhibited highest external quantum efficiency (EQE) and current efficiency (CE) of 25.20% and 96.85 cd A−1with highest illumination of 65931 cd m−2, correspondingly. PHOLEDs utilizing non-halogenated solvents also achieved high EQE and CE (24.70% and 93.07 cd A−1, respectively), currently the highest reported amongst solution processed PHOLEDs utilizing both halogenated and non-halogenated solvents.

Abstract: Surfactant-mediated polyaniline (PANI) samples were fabricated using an electrodeposition technique for electrochemical supercapacitor applications. We investigated the effect of surfactants such as sodium dodecyl sulfate (SDS), polyvinyl alcohol (PVA), ethylenediaminetetraacetic acid (EDTA) on the PANI morphologies. The surfactants act as a template for PANI deposition during the electrodeposition, modifying the PANI morphology. Scanning electron microscope (SEM) images of the pure PANI samples showed a uniform nanocrystalline structure whilst the surfactant-mediated samples showed overgrown cauliflower-like structures. The electrochemical supercapacitive properties (charge-discharge) were studied in a 0.5 M LiClO4 electrolyte. While the capacitance of the pure PANI sample was 240 Fg−1 at a scan rate of 20 mVs−1, it was 199 Fg−1, 106 Fg−1, and 42 Fg−1 for the PANI-SDS, PANI-PVA and PANI-EDTA samples, respectively. The electrochemical stability of the samples was investigated for 1000 charge-discharge cycles by using cyclic voltammetry measurements.

Abstract: The effects of rapid thermal annealing on the optical and the electrical properties in GaN epilayers grown on Si substrates were investigated by using cathodoluminescence (CL) and Hall effect measurements. From the two-dimensional CL image measurements, the distribution of defects embedded in the films was investigated before and after rapid thermal annealing. The penetration depth dependence of the CL spectrum demonstrated that the defect density become large in the deeper region away from the GaN surface.

Abstract: Cu2ZnSnS4 (CZTS) thin films (absorber layers) were successfully synthesized on glass substrates by using a RF magnetron sputtering system. The films were rapidly thermally annealed in a nitrogen atmosphere for 20 minutes to improve the crytallinity. The formation of kesterite structures (JCPDS-26-0575) in the film was confirmed using X-ray diffraction (XRD) measurements. The improved crytallinity of the CZTS with a (112) orientation was observed with increasing annealing temperature. The band gaps of all the as-deposited and annealed films were found to be in the range from 1.97 to 1.55 eV. The films’ stoichiometry and morphologies were investigated using scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDAX) measurements. The sample annealed at 500 °C showed a uniform granular structure with an elemental composition near stoichiometric CZTS. Next, a buffer layer of ZnS for a heterojuntion solar cell was fabricated using a chemical bath deposition (CBD) technique. The films adhered well, were optically transparent and had band gap energy of 3.6 eV.

Abstract: We investigated the effects of sulfuric acid and silver particles on the carbonization of natural cellulose from Halocynthia. We carried out thermogravimetry and used transmission electron microscopy measurements to study the yield of carbon and the structure of the carbonized nano-fiber. We found that the addition of sulfuric acid and silver particles to the cellulose fiber enhanced the yield of carbon while keeping the original structure of the carbon nano-fiber.

Abstract: Nanocrystalline and nanocolumnar aluminum thin films were deposited on glass and Ti/glass substrates at normal and oblique angles of incidence in vacuum (1.0 × 10−6 Torr) by using an electron-beam evaporator. The average grain size of the Al thin films produced at a normal angle of incidence increased from 25 nm to 50 nm when the substrate was changed from glass to Ti/glass. The average aspect ratio of the aluminum nanocolumns (Al nanorods) grown on the glass substrate increased from 1.65 to 3.65 as the deposition angle increased from 65° to 85° while the aspect ratio of Al nanorods grown on Ti/glass substrates increased from 1.80 to 4.00 as the deposition angle increased from 65° to 85°. The X-ray diffraction pattern showed a broad baseline in nanocrystalline and nanocolumnar thin films. In the case of Al thin films on glass, the full width at half maximum (FWHM) was observed to be 14.34 for all depositions while in the case of Al thin films on Ti/glass, the FWHM was decreased from 17.66 to 14.02 as the deposition angle increased from 0° to 85°. The X-ray photoelectron spectroscopy analysis confirmed that the peak for Al nanorods was observed at a binding energy of 74.44 eV.

We have investigated the 2D → 2D resonant tunneling in coupled X-band double quantum well structures, which can be achieved in GaAs/AlAs heterostructures by using high hydrostatic pressure. Until recently, there has been clear observation of 2D → 2D resonant tunneling between confined transverse XX,Y states but not between longitudinal XZ states. In this paper, we demonstrate the existence of such resonant tunneling in samples with very thin well and barrier layers. The existence of detectable 2D → 2D resonant tunneling between XZ states, even in a structure with a barrier thickness of 40 Å, is striking. However, by modelling the transport in terms of quantum beats between symmetric and anti-symmetric double well states, we show that Γ–XZ mixing can produce enhancements of up to 102.

Ruddlesden–Popper (RP) phases (An+1BnO3n+1, n= 1, 2,···) have attracted intensive research with diverse functionalities for device applications. However, the realization of a high-quality RP-phase film is hindered by the formation of out-of-phase boundaries (OPBs) that occur at terrace edges, originating from lattice mismatch in the c-axis direction with the A′B′O3(n= ∞) substrate. Here, using strontium ruthenate RP-phase Sr2RuO4(n= 1) as a model system, an experimental approach for suppressing OPBs was developed. By tuning the growth parameters, the Sr3Ru2O7(n= 2) phase was formed in a controlled manner near the film–substrate interface. This higher-order RP-phase then blocked the subsequent formation of OPBs, resulting in nearly defect-free Sr2RuO4layer at the upper region of the film. Consequently, the Sr2RuO4thin films exhibited superconductivity up to 1.15 K, which is the highest among Sr2RuO4films grown by pulsed laser deposition. This work paves the way for synthesizing pristine RP-phase heterostructures and exploring their unique physical properties.

The oxygen evolution reaction (OER) plays a key role in determining the performance of overall water splitting, while a core technological consideration is the development of cost-effective, efficient, and durable catalysts. Here, we demonstrate a robust reduced Fe-oxide@NiCo2O4bilayered non-precious-metal oxide composite as a highly efficient OER catalyst in an alkaline medium. A bilayered oxide composite film with an interconnected nanoflake morphology (Fe2O3@NiCo2O4) is reduced in an aqueous NaBH4solution, which results in a mosslike Fe3O4@NiCo2O4(reduced Fe-oxide@NiCo2O4; rFNCO) nanostructured film with an enhanced electrochemical surface area. The rFNCO film demonstrates an outstanding OER activity with an extraordinary low overpotential of 189 mV at 10 mA cm–2(246 mV at 100 mA cm–2) and a remarkably small Tafel slope of 32 mV dec–1. The film also shows excellent durability for more than 50 h of continuous operation, even at 100 mA cm–2. Furthermore, density functional theory calculations suggest that the unintentionally in situ doped Ni during the reduction reaction possibly improves the OER performance of the rFNCO catalyst shifting d-band centers of both Fe and Ni active sites.

Nonvolatile conductance switching phenomena in a nickel-titanium oxide compound thin film were investigated for memory device applications. On/off switching ratios as high as ${\sim}10^{4}$ were observed. Whereas the low-resistance state (LRS) showed good retention and endurance properties, the high resistance state (HRS) showed unstable switching properties. The temperature dependence of the LRS and HRS revealed that the switching mechanism is fundamentally based on the repeated process of the electroforming and the rupture of conducting filaments. The authors suggest that relatively weaker chemical binding between the Ti and O causes the unstable electrical conduction in the HRS.

The time resolved bipolar resistance switching in a Pt/Cr-doped SrZrO3/SrRuO3device has been investigated using pulse voltage. The required switching time between the high and low resistance states (HRS and LRS) is studied as a function of the pulse height and width. The resistance switching is found to be less dependent on the pulse height in the short pulse region. For $\mathrm{LRS}\rightarrow\mathrm{HRS}$ and $\mathrm{HRS}\rightarrow\mathrm{LRS}$ switching minimum switching times of ${\sim}500$ and ${\sim}100$ ns are required respectively, at a pulse height above the dc switching voltage. The authors attribute the distinction in the switching time to different switching mechanisms.

The electrochemical kinetics and output capacity of active electrode materials are significantly influenced by their surface structure. Herein, the template‐free morphological evolution of CuCo2O4is reported, which is achieved by controlling the nucleation and growth rate during the hydrothermal process and evaluating its anode performance. The charge‐transfer resistance and specific surface area of the fabricated CuCo2O4anode films are influenced by the viscosity of the solvent used. The optimized mesoporous nanosheet anode exhibits a high specific discharge capacity (1547 mAh g–1) at 0.1 A g–1and an excellent restoring capability (≈91%); it retains 88% of the initial capacity with a coulombic efficiency of ≈99% even after 250 discharge–charge cycles. The superior lithium‐ion energy storage performance of this anode is due to its electrochemically favorable porous 2D morphology with large Brunauer–Emmett–Teller (BET) specific surface area and pore volume, resulting in enhanced Li+storage and intercalation property. One‐step template‐free growth of CuCo2O4on Ni foam via a hydrothermal technique with different morphologies of 2D mesoporous nanosheet, cubic, compact‐granular, or agglomerated‐embossing structures, using various solvents followed by air annealing treatment is reported. The better electrochemical performance of the CuCo2O4nanosheet is a result of electrochemically favorable 2D morphology, which leads to the formation of a very large specific surface area.

A novel synthetic strategy was employed to fabricate a Cu2ZnSnS4 (CZTS) absorber layer using a quaternary compound target which has similar properties to that of copper indium gallium selenide (CIGS). A conventional R-F magnetron sputtering system was used to fabricate the CZTS absorber layers on glass substrates. The films were rapidly thermally annealed at 500 °C in a nitrogen atmosphere for 20 minutes to improve their crytallinity. The formation of a kesterite structure was confirmed using X-ray diffraction measurements. The improved crytallinity of the CZTS was observed with (112) oriented phase. The band gap of the as-deposited and annealed films was found to be 1.97 and 1.55 eV respectively. The films stoichiometry and morphology were observed using scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDAX) measurements. In addition; buffer layer of ZnS which was doped with metal elements; was fabricated by using a chemical bath deposition (CBD) technique.

We prepared resistive switching Al-AlOxmultilayered junctions and observed considerably improved endurance properties. The mechanism of the observed resistance switching basically reflects the filament model. The temperature dependence of the transport in each resistance state revealed additional features, that is a well-defined thermal activation behavior in the high-resistance state is not observed in the layered device and the metallic conduction in the low-resistance state is not affected. The improved endurance properties are discussed in terms of the increased effective number of active regions, where the Reset and Set processes probably occur before a permanent dielectric breakdown.

Specific heat was used to study the magnetic phase transition in GaMnAs. Two types of samples were investigated. The sample with a Mn concentration of 1.6% shows an insulating behavior whereas the sample with a Mn concentration of 2.6% is metallic. The temperature dependence of the specific heat for both samples reveals a lambda-shaped peak near the Curie temperature, which indicates a second-order phase transition is occuring in these samples. The critical behavior of the specific heat for the GaMnAs samples is consistent with the mean-field behavior with Gaussian fluctuations of the magnetization in the vicinity of TC.