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An oxidizable metal diffusion barrier inserted between the active metal electrode and the switching layer decreases the electroforming voltage and enhances the switching stability and synaptic performances in TaOx-based conducting bridge memristor devices. The TiW barrier layer avoids an excessive metal ion diffusion into the switching layer, while the TiWOx interfacial layer is formed between the barrier and the switching layer. It modulates the oxygen vacancy distribution at the top interface and contributes to the formation and rupture of the metal ion-oxygen vacancy hybrid conducting bridge. We observe that the device that relies upon non-hybrid (metal ions only) conducting bridge suffers from poor analogous performance. Meanwhile, the device made with the barrier layer is capable of providing 2-bit memory and robust 50 stable epochs. TaOx also acts as resistance for suppressing and a thermal enhancement layer, which helps to minimize overshooting current. The enhanced analog device with high linear weight update shows multilevel cell characteristics and stable 50 epochs. To validate the neuromorphic characteristic of the devices, a simulated neural network of 100 synapses is used to recognize 10 × 10 pixel images.

The unbalanced carrier injection is a key factor that deteriorates the performance of blue InP quantum dot light-emitting diodes (QLEDs). Therefore, to achieve efficient blue InP QLEDs, an effective strategy that balances carrier injection through enhancing the hole injection and transport is in demand. In this study, we introduced an ultrathin MoO3 electric dipole layer between the hole injection layer and the hole transport layer (HTL) to form a pair of dipole-induced built-in electric fields with forward resultant direction to enhance hole injection and facilitate the balance of carrier injection. Meanwhile, the p-doping effect by MoO3 leads to increased carrier concentration and decreased trap density of interfacial HTL, therefore improved its effective hole mobility. Consequently, the maximal external quantum efficiency of blue InP QLEDs was enhanced from 1.0% to 2.1%. This work provides an effective method to balance carrier injection by modulating hole injection and transport, indicating the feasibility to realize high-efficiency QLEDs.

The use of the compact hole-transporting layer (HTL) with strong hole extraction ability is vital to prepare high-efficiency solar cells. Here, we report the application of 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ) doped copper phthalocyanine (CuPc) as the hole-transporting layer for the Sb2(S,Se)3 solar cells. We find that the diffusion of gold atoms into the copper phthalocyanine film is able to heal the cracks and pinholes of the CuPc film, which enables the morphology to become more flat and denser, along with enhanced hole mobility. Benefitting from these results, the F4-TCNQ doped CuPc-based Sb2(S,Se)3 solar cells achieved best power conversion efficiency of 8.57%. More importantly, the device based on F4-TCNQ doped CuPc HTL showed essentially improved operational stability under the condition of 85% humidity and 85 °C. This research provides a suitable method for improving the morphology and transport properties of the CuPc based hole-transporting layer for solar cell and other optoelectronic device applications.

High-field-effect-mobility InSnZnO thin-film transistors (TFTs) are prepared through Al-induced microstructure regularization (AIMR) at an annealing temperature lower to 400 °C. Spherical crystalline particles are distributed throughout the back channel near the Al layer, while an amorphous phase still represents the front channel but with enhanced microstructure ordering. Especially, the packing density is distinctly increased, and oxygen vacancies are largely reduced. The optimized TFT exhibits excellent performance with a steep sub-threshold swing of 0.18 V/dec, a high on/off current ratio of 2.5 × 108, a threshold voltage of −0.21 V, and a small threshold voltage shift of −0.24 V under negative bias stress (−20 V, 3600 s), especially a remarkable field-effect mobility boosted to 53.2 cm2/V s compared to 19.1 cm2/V s for the TFT without the Al layer. After Al removal, the TFT performance shows no obvious degradation, implying good compatibility of the AIMR technique to the current device process.

Limited nonrenewable resources on earth motivate people to use natural polymer materials in the development of environment-friendly devices for flexible electronics. In this work, a biocompatible and biodegradable organic memristor based on regenerated cellulose is prepared by a facile and green route. Here, cellulose, the key functional layer material, is used as not only the resistive switching layer but also a substrate to construct a flexible self-supporting memristor. Both volatile and nonvolatile resistive switching can be achieved by controlling the compliance current in the SET process. Moreover, this cellulose-based memristor performs competitive environmental and temperature stability compared with other organic memristors. This research provides a facile strategy for constructing an environment-friendly memristor based on natural polymer-based materials.

HfO2 has many favorable characteristics for use in energy conversion devices including high thermodynamic stability, good chemical stability in corrosive electrolytes, high refractive index, and wide bandgap. Here, we report surface passivation of a c-Si photocathode by ultrathin HfO2 prepared using atomic layer deposition as an effective approach for enhancing its photoelectrochemical (PEC) performance. The effect of the thickness of HfO2, deposition temperature, and annealing in forming gas on the passivation performance are systematically investigated. We demonstrate that the Si photocathode with a p+/n/n+ structure decorated with a Ni3N/Ni cocatalyst and an HfO2 interlayer follows a metal–insulator–semiconductor mechanism with thicker HfO2 films proving detrimental to the PEC performance. The Si photocathode passivated with a 1 nm HfO2 layer exhibits an enhancement in the onset potential by 100 mV, an applied-bias photon-to-current efficiency of 9%, and improved operational stability. This work provides insights into the application of HfO2 as a passivating layer for Si photoelectrodes for solar hydrogen production.

Hf0.5Zr0.5O2 (HZO) has become one of the most popular HfO2 based ferroelectric thin films due to its huge potential to integrate low-cost high-density nonvolatile ferroelectric memory. Most researchers sandwiched the HZO between metals, such as TiN, and then adopted post-deposition high temperature anneal to improve the ferroelectricity and reliability of the film. In this work, the effect of a thin dielectric Al2O3 layer with different thicknesses to replace a metallic capping layer on the ferroelectric properties of a HZO (10 nm) thin film is evaluated, and we also compared the effects of TiN and W bottom electrodes on the properties of a capacitor. The results showed that the TiN/Al2O3 (1 nm)/HZO/W capacitor performed the best with a maximum 2Pr as high as 31.4 μC/cm2 at an electric field of ±3 MV/cm and very low leakage currents. In addition, the fatigue studies demonstrated the capacitor's excellent endurance properties with continuous cycling up to 1010 cycles. The use of an ultra-thin Al2O3 layer with excellent capping effects would significantly simplify the integration process of HfO2-based ferroelectric memory.

Nonvolatile memory technology is a necessary component in many electronic devices. With the scaling down of memory devices to achieve high density and low power consumption, floating gate devices encounter various challenges like high leakage current, which leads to reliability issues and a decrease in charge density. Therefore, the use of metal nanoparticles (NPs) as charge storage centers is becoming a promising candidate due to their excellent scalability and favorable reliability. In this work, we demonstrate the charge storage dependency on the size of a gold-nanoparticle (Au-NP) by using a contact mode atomic force microscope. The individually dispersed Au-NPs are sandwiched between a thin layer (3 nm) of TiO2 blocking layer and SiO2 (2 nm) tunneling layer thin films. The consecutive I–V sweeps on a pristine device of stacking TiO2/Au-NP/SiO2/n-Si show that the threshold voltage (ΔV) increases with the increase in the Au-NP size, whereas the retention shows much more stability time with smaller size NPs, in the range of 10 nm.

We have investigated the correlations between the in-plane uniaxial magnetic anisotropy (Ku) and spin–orbit torque (SOT) of Ni80Fe20 (Py)/Pt thin films sputtered on a single-crystal 128° Y-Cut LiNbO3 (LNO) substrate by performing second-harmonic voltage measurements. The results show that the value of the damping-like (DL) SOT torque varies with the angle χ between Ku and the applied current and increases with χ from 0° to 90°. The effective spin Hall angle θSH, Pteff = 0.073 and 0.123 for χ = 0 and 90°, respectively, indicate a difference of approximately 1.7 times. The θSH,Pteff at χ = 90° is greater because the direction of the DL-SOT on the magnetization is the same as the Ku direction. This result implies that the effective spin Hall angle can be controlled by the Ku direction of the ferromagnetic metal layer induced on the LNO substrate, thereby providing valuable insight for the development of spin devices using SOT.

We investigated interlayer exchange coupling through Pt/Ru/Pt and Pt/Ru multilayers as candidates of nonmagnetic spacer layers in the synthetic antiferromagnetic (AF) layer, which is available for studying AF spintronics using current-induced spin–orbit torque (SOT) switching originating from the spin Hall effect. The AF interlayer exchange coupling with the oscillation period of Λ2 ∼ 1.05 nm was observed even for the face-centered cubic (fcc) Pt (tPt)/hexagonal Ru/fcc Pt (tPt) nonmagnetic spacer layer structures in the wide range of both Pt and total nonmagnetic spacer layer thicknesses (0 ≤ tPt ≤ 0.8 nm, 1.0 ≤ ttotal ≤ 2.3 nm), which would be useful for the systematic investigation of the SOT on the AF structure. Moreover, we observed the disappearance of the one oscillation period (Λ1 ∼ 1.65 nm) in the case of Pt(111)/Ru(0001) and Pt(111)/Ru(0001)/Pt(111) spacer layers, whereas the existence of two oscillation periods of AF interlayer exchange coupling (Λ1 ∼ 1.65 nm and Λ2 ∼ 1.05 nm) in the case of Ru spacer layer was observed. We expect that the Pt/Ru/Pt spacer layer with the oscillation period of Λ2 ∼ 1.05 nm will pave a way to the AF spintronics based on the multilayer systems.

Multi-dimensional perovskite (MDP) interface consisting of a lower-dimensional (2D) perovskite phase sandwiched between a bulk (3D) perovskite layer and a charge transporting layer is being propounded as a feasible solution for enhancing the stability of perovskite solar cells (PSCs). Here, using first principles-based density functional theory calculations, we study the effect of interface anion engineering on the stability and electronic property of the MDP interfaces. We find that 2D–3D perovskite interfaces are highly stable and are immune to interfacial defect formation. Furthermore, interface chlorination helps in mitigating the deleterious effect of charge localization for antisite defects at these interfaces. For an interface between 2D-perovskite and a charge-extracting TiO2 layer, we find that interfacial anion engineering is instrumental in alleviating the lattice mismatch induced instability. We propose that opposed to interfacial defects, the hole localization arising due to the presence of interfacial halide at the pristine 2D-TiO2 interface is the major obstacle that needs to be overcome for achieving a defect immune MDP for realizing a PSC with ultrahigh stability and performance.

Feedback-controlled electric breakdown of graphene in air or vacuum is a well-established way of fabricating tunnel junctions, nanogaps, and quantum dots. We show that the method is equally applicable to encapsulated graphene constrictions fabricated using hydrogen silsesquioxane. The silica-like layer left by hydrogen silsesquioxane resist after electron-beam exposure remains intact after electric breakdown of the graphene. We explore the conductance switching behavior that is common in graphene nanostructures fabricated via feedback-controlled breakdown and show that it can be attributed to atomic-scale fluctuations of graphene below the encapsulating layer. Our findings open up routes for fabricating encapsulated room-temperature single-electron nanodevices and shed light on the underlying physical mechanism of conductance switching in these graphene nanodevices.

A low-cost, small molecular monomer, 5′-bis(9–(4-vinylbenzyl)-2-carbazol)-2,2′-bithiophene, termed VB-CB, is designed, synthesized, and polymerized to form a uniform film as the hole-transporting material for the fabrication of inverted planar perovskite solar cells with high performance. The presence of a suitable energy level in the polymerized VB-CB layer can effectively promote the transport of holes and block electrons from the perovskite layer, thus decreasing photon energy loss due to charge recombination. Designing perovskite solar cells with polymerized VB-CB as the hole-transporting material helps us to obtain a high power conversion efficiency of 17.58% with small hysteresis effect, which is higher than that with poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as the hole-transporting material. Additionally, as compared to PEDOT:PSS, the devices with polymerized VB-CB exhibit better stability under one sun illumination at maximum power point tracking, such that the T80 of the champion devices could exceed 1000 h. The results suggest that the polymerized VB-CB is a suitable hole-transporting material for commercial applications in planar perovskite solar cells, given its low-cost, high efficiency, and good stability.

A highly relaxed InGaN buffer layer was demonstrated over a full two-inch c-plane sapphire substrate by metalorganic chemical vapor deposition. The InGaN buffer layer was grown on a 100 nm GaN decomposition stop layer with a 3 nm thick high indium composition InGaN underlayer. After thermal decomposition of the underlayer at 1000 °C, a 200 nm thick In0.04Ga0.96N buffer showed 85% biaxial relaxation measured by a high resolution x-ray diffraction reciprocal space map. When used as a pseudo-substrate for the regrowth of InGaN/InGaN multi-quantum wells, the sample showed a 75 nm red-shift in room temperature photoluminescence when compared to a co-loaded GaN template reference. The longer emission wavelength is associated with higher indium incorporation in the InGaN layers from the lessening of the compositional pulling effect caused by compressive strain. Using this technique, a simple red light emitting diode was demonstrated with an active layer growth temperature of 825 °C and a peak wavelength of 622 nm at a current density of 20 A cm−2. This work represents a unique method to relax a III-nitride based layer over a full substrate.

Metal-insulator transitions (MIT),an intriguing correlated phenomenon induced by the subtle competition of the electrons' repulsive Coulomb interaction and kinetic energy, is of great potential use for electronic applications due to the dramatic change in resistivity. Here, we demonstrate a reversible control of MIT in VO2 films via oxygen stoichiometry engineering. By facilely depositing and dissolving a water-soluble yet oxygen-active Sr3Al2O6 capping layer atop the VO2 at room temperature, oxygen ions can reversibly migrate between VO2 and Sr3Al2O6, resulting in a gradual suppression and a complete recovery of MIT in VO2. The migration of the oxygen ions is evidenced in a combination of transport measurement, structural characterization and first-principles calculations. This approach of chemically-induced oxygen migration using a water-dissolvable adjacent layer could be useful for advanced electronic and iontronic devices and studying oxygen stoichiometry effects on the MIT., 16 pages, 4 figures

In this study, the influence of the HfOxNy interfacial layer (IL), interposed between the atomic layer deposited ferroelectric (FE) Hf0.5Zr0.5O2 thin film and TiN top electrode, on the FE properties of such a film was examined. The HfOxNy IL decreased the relative proportion of the non-FE monoclinic phase, possibly due to the N-doping effect. Furthermore, the oxidation of the TiN top electrode was also suppressed by the sacrificial oxidation of the HfOxNy IL during the rapid thermal process. As a result, the double remanent polarization of a Hf0.5Zr0.5O2 thin film could be enhanced from 40.2 to 48.2 μC/cm2 by the positive-up-negative-down test, and its degradation by fatigue during the endurance test can also be decreased. This result demonstrates the significance of interfacial engineering to optimize the FE properties of Hf0.5Zr0.5O2 films.

Chalcopyrites could fill the gap between the low-cost, poor-efficiency single junction metal oxide photoelectrochemical (PEC) water splitting cells and the high efficiency, yet costly III–V tandems. In this Perspective, we first review the key barriers that must be addressed by the community to enable economical chalcopyrite-based PEC water splitting. Then, we highlight how theoretical modeling can be used to identify promising ordered vacancy compound absorbers with improved energetics compared to their chalcopyrite parents. Finally, we describe how advanced spectroscopic analysis performed on chalcopyrite photocathodes after PEC testing uncovered a new passivation layer candidate for prolonged durability.

We study the interlayer charge transfer dynamics across the heterojunction of graphene and chemical-vapor-deposition grown MoS2, using ultrafast optical spectroscopy. Electron–hole pairs are generated only in the graphene layer by a 100-fs pump pulse, and the presence of carriers in the MoS2 layer is observed via a probe pulse tuned to the MoS2 bandgap. Due to the band lineup, there is an initial rapid transfer of electrons from the graphene into the MoS2 layer, which cannot be well resolved within the 100-fs resolution of the experiment. This work focuses instead on the transfer of thermalized electrons back from the MoS2 to the graphene layer, as the system returns to equilibrium. The dynamics of the back transfer are found to be nonexponential and, for times after carrier cooling is complete (≳5 ps), can only be fit using a Porter-Thomas distribution of the charge transfer rates, indicating that the MoS2 states are localized by disorder and that the interlayer transfer process is dominated by random coupling.

By exploiting NbOx, we demonstrate its hybrid memory characteristics, indicating that resistive switching is unified with selector behavior. First, we identify that the 50-nm-thick amorphous NbOx inherently shows volatile threshold switching (TS). To enable memory switching (MS) in NbOx, device environments are configured that can supply oxygen vacancies or cations constituting a conductive filament (CF). In the Al/NbOx/TiN stack, oxygen vacancies can be internally generated from an interfacial oxide layer formed by the chemical reaction between a highly reactive Al electrode and NbOx, which is confirmed via multiple physical analyses. When the effect of the extrinsic vacancies becomes comparable to the intrinsic properties of the NbOx, the hybrid memory characteristics are observed. While the TS prevents leakage current, the MS is driven by oxygen vacancy CF, allowing multilevel cell operation. Furthermore, hybrid switching can be obtained using the Cu/NbOx/TiN stack. However, the effect of a Cu CF is dominant, because the Cu electrode can externally provide ions infinitely in this case; therefore, hybrid memory behavior is achieved after MS is performed.

Hematite (α-Fe2O3) is a promising photoanode material for photoelectrochemical (PEC) water splitting due to its appropriate bandgap, good stability, and earth-abundance. However, the poor charge transfer property and sluggish kinetics of water oxidation limit the PEC performance of α-Fe2O3 photoanodes. Herein, a thin NiOx buffer layer was introduced between the Ti doped α-Fe2O3 (Fe2O3-Ti) layer and the fluorine-doped tin oxide (FTO) substrate without affecting the nanowire morphology and light absorption property of Fe2O3-Ti. This buffer layer can apparently suppress the charge recombination by mitigating the lattice mismatching between the Fe2O3-Ti film and the FTO substrate. In addition, the good conductivity of the NiOx film from the non-stoichiometric composition is also beneficial to the charge transfer. As a consequence, the photocurrent density was greatly improved by adding the NiOx layer in the Fe2O3-Ti photoanode, reaching 1.32 mA·cm−2 at 1.23 VRHE without any co-catalyst and sacrificial agent. This work gives a detailed analysis of the back contact in the hematite-based photoanode and provides an effective strategy for underlayer interface optimization.

Perovskite emitters have attracted great attention in recent years owing to their excellent photoelectric performance with low-cost potential. Some very recent studies have revealed that perovskites not only have narrow emitting peak with high purity but also have multi-color or broad spectrum in entire visible light, even some single emissive layer-based white perovskite light-emitting diodes (SEL-WPeLEDs) have been confirmed, showing promise in lighting and display. In this Perspective, we summarized the issues and challenges faced by these perovskite-based SEL-WLEDs and proposed some feasible suggestions in improving their light-emitting performance, hoping to promote their applications in lighting and other optoelectronic devices.

Photoelectrochemical activity for water reduction (H2 liberation) over a co-evaporated CuGaSe2 compact thin film modified with a CdS layer and Pt deposits under simulated sunlight (AM 1.5G) radiation was evaluated, specifically focusing on the impact of a Cu-deficient layer (CDL) loaded on the top part of the CuGaSe2 film. It was found that the intentional loading of the CDL with an appropriate thickness was effective for achieving a large current flow and relatively positive photocurrent onset. The half-cell solar-to-hydrogen efficiency reached 6.6% over the best photocathode used. Moreover, the highest photocurrent onset potential of more than 0.9 V vs reversible hydrogen electrode was achieved over the photocathode based on the CuGaSe2 film having an extremely thick CDL (200 nm) with a relatively thick CdS layer (90 nm) due to efficient spatial separation of photogenerated carriers.

A large cross-polarization (CP) rotation of light is found on the graphene surface experimentally and applied to measuring the layer number of graphene. First, a general propagation model for the polarization of light reflected on the graphene is established. By using this model, it is found that the CP effect rotates remarkably with the incident polarization near the pseudo-Brewster angle. More importantly, such a rotation differs noticeably for graphene surfaces with distinct layers, thereby providing a simple and efficient approach to detect the graphene layer number. Finally, the CP rotation is shown to be accompanied by the rotation of the spin Hall effect of light. Further experiments are performed to validate the theoretical results.

Transparent conductive electrodes are one of the important components of organic optoelectronic devices. Mg:Ag alloys have been widely used as a semi-transparent cathode for top-emitting organic light-emitting diodes (OLEDs) or transparent OLEDs (TrOLEDs) due to their high conductivity and relatively low work function. However, their low transmittance makes the light-extraction efficiency to be comparatively low. In this study, a highly transparent (84.6% in the visible light range), conductive, laminated cathode with the structure of ZnO/Mg:Ag/ZnO was fabricated via atomic layer deposition (ALD). ALD-deposited ZnO is used to protect the vulnerable ultrathin Mg:Ag-alloy layer, while preserving its low work function for the entire structure. In particular, the bottom ZnO layer is used as an ETL, which can provide reasonable energy alignment between the cathode layer and the emission layer and prevent metal particles from penetrating into the underlying organic layer. The top-emission OLED, which is prepared in this study by using the laminated cathode, showed an 85.8% increase in brightness, with a current density of 11.2 mA/cm3 at 4.0 V, which is an ultra-low voltage compared with devices made with Mg:Ag cathodes. In addition, the total luminance of TrOLEDs increases 34.4% compared with devices using Mg:Ag cathodes. Furthermore, the average transmittance of the device was still as high as 77.19% for visible light.

An analogous change in lateral channel current from source to drain in three-terminal synaptic devices actuated by mobile ions vertically provided from a gate can enhance neuromorphic computing performances. We demonstrate a gradually tuned channel current in a fully complementary metal–oxide–semiconductor compatible HfOx/WOx stack with Cu ions. By examining each layer in the three-terminal device, such as the channel, electrolyte, and mobile ion supplier, we identify which device structure can modulate the channel current effectively using mobile ions. Our findings reveal that the gate-tunable channel current response can be solely achieved when the Cu ions are not locally formed but migrate throughout the HfOx electrolyte. The linear dependence of the analog current operation on the channel width further proves the area-switching mechanism. The importance of ion movement can be indirectly verified from the uncontrollable channel currents using either Ag ions with faster mobility than Cu ions or a local path is created because of the thinned HfOx electrolyte.

The surface of the p-GaN layer in Schottky-type p-GaN gate high-electron-mobility transistors (HEMTs) can be reinforced with enhanced immunity to hot electron bombardment by reconstructing the surface region of p-GaN into GaON. The surface region of p-GaN is treated by remote oxygen plasma and subsequently annealed at 800 °C, thereby becoming a thin crystalline gallium oxynitride (GaON) layer that will be in direct contact with the Schottky metal. The GaON exhibits a lower valence band maximum energy than that of the p-GaN, which leads to a higher Schottky barrier at the metal/GaON interface to holes and, thus, greatly suppresses the forward gate leakage. More importantly, with higher thermodynamic stability and a larger bandgap of ∼4.1 eV, the GaON reinforces the susceptible metal/p-GaN interface against the hot electrons and, thus, substantially enhances the long-term gate reliability of p-GaN gate HEMTs under forward bias stress. The high-temperature thermal process is indispensable for the surface reconstruction, without which the plasma oxidation only reduces the gate leakage but fails to prolong the time-dependent gate breakdown lifetime.

The low growth rate of mist chemical vapor deposition normally requires a long growth time to achieve coalescence in the epitaxial lateral overgrowth of α-Ga2O3 thin films on sapphire substrates. To address this issue, sub-μm features were patterned using laser interference lithography. Periodical stripes with a ∼590-nm pitch allowed the overgrowth of crack-free, void-free, and continuous thin films, while typical growth conditions using a low carrier gas flow rate and a low Ga precursor concentration were maintained. Coalescence was achieved even with a short growth time of

Organic-inorganic hybrid perovskite materials are excellent candidates as light absorbers in tandem solar cells with advantages of tunable bandgaps, high absorption coefficients, and facile and low-cost fabrication processes. As the key component of a tandem structure, the interconnecting layer (ICL) requires optical transparency, efficient carrier recombination, and facile up-scalability. To demonstrate the feasibility of an efficient TCO-free ICL in all-perovskite tandem solar cell devices, we have performed a comprehensive computational analysis using the transfer matrix method. The results suggest that varying the silver recombination layers up to 3 nm does not present a significant effect on the maximum achievable photocurrent (MAPC) of the cell. Moreover, the highest MAPC from the tandem cell with the lowest sensitivity to electron and hole transport layer thicknesses can be obtained by the transport layers with refractive indices within the range of 1.9-2.6. The findings are of direct practical relevance, i.e., with meeting our optical framework, a fabrication procedure can be merely directed toward the electrical optimization of the ICL. The presented methodology can serve as an introduction to benchmark ICL design for multi-junction excitonic solar cells. Published under an exclusive license by AIP Publishing.

Few-layer films of transition metal dichalcogenides have emerged as promising candidates for applications in electronics. Within this group of 2D materials, platinum diselenide (PtSe2) was predicted to be a compound with one of the highest charge carrier mobility. Recently, the successful integration of group III–V nitride semiconductors with NbNx-based superconductors was reported with a semiconductor transistor grown directly on a crystalline superconductor. This opens up the possibility of combining the macroscopic quantum effects of superconductors with the electronic, photonic, and piezoelectric properties of the semiconducting material. Here, we report on the fabrication of a few-layer PtSe2 film on top of an NbN substrate layer by selenization of pre-deposited 3 nm thick Pt layers. We found the selenization parameters preserving the chemical and structural integrity of both the PtSe2 and NbN films. The PtSe2 film alignment can be tuned by varying the nitrogen flow rate through the reaction chamber. The superconducting critical temperature of NbN is only slightly reduced in the optimized samples compared to pristine NbN. The carrier mobility in PtSe2 layers determined from Hall measurements is below 1 cm2/V s.

Contact resonance atomic force microscopy (CR-AFM) was used to spatially map variations in the out-of-plane elastic modulus of graphene covered surfaces of a silicon wafer having a native oxide. A modulus of 0.973 ± 0.001 TPa was measured for one layer of graphene covering the silicon substrate, consistent with many experimental and theoretical studies. A monotonic decrease in the measured contact resonance frequency with increasing layers of graphene covering the silicon substrate was observed, resulting in a decrease in the measured modulus by 4.95% with four layers of graphene covering the substrate. The interplay between the hydrophobic graphene layers covering the hydrophilic silicon substrate, the interlayer spacing of graphene, and the range of adhesion from the substrate are proposed to influence the stiffness of the graphene–graphene interaction, which was probed with the sub-Angstrom displacements with CR-AFM measurements.

Write once read many times (WORM) memory devices based on the resistive switching mechanism of a sputtered amorphous BaTiO3 (am-BTO) thin film in a metal–insulator–metal structure is fabricated on a FTO coated glass substrate with a silver top contact. Fabricated devices show the switching from a low-conductance state to a high-conductance state with the formation of conductive filament(s) in the am-BTO layer. The memory characteristics are investigated as a function of thickness of am-BTO layer, which is determined by varying the deposition time. Devices with all deposited thicknesses show data retention for more than 4000 s and 300 reading cycle. Devices with 180 nm thickness show a high on-off ratio on the order of 106. The fabricated WORM devices exhibit good reading-endurance and data-retention characteristics.

In this work, we demonstrated the high switching uniformity and 50 fJ/bit energy consumption in an amorphous silicon-based resistive switching (RS) device by inserting the AgInSbTe (AIST) layer between the silicon insulating layer and Ag top electrodes. The improved RS performance is attributed to the introduction of an Ag ion reservoir layer, which helps to suppress conducting filament overgrowth. After insertion of the AIST layer, the cumulative probability of low/high resistance states decreased from 176.8%/46.2% to 3.1%/11.9%, respectively. The advantages of promoting Ag dissolution enable the realization of fast switching speed (

The regulation in the magnetic anisotropy of magnetic films is crucial for developing the magnetic storage and logic devices. The traditional work achieved an effective tunability of the magnetic anisotropy by a subsequent processing of the as-deposited film, such as a post-annealing treatment or electric field application. Here, we proposed an effective method to achieve a direct and broad tunability of the magnetic anisotropy in the as-prepared film by adjusting electronic coordination. Nitrogen (N) atoms were doped in the Co layer of Pt/Co/MgO multilayers to effectively control the electronic coordination of Co and enhance the 3dz2–r2 orbital occupancy of Co for modulating the Co–O orbital hybridization. Consequently, the magnetic anisotropy of the as-deposited film changed from in-plane to perpendicular direction with the N doping, resulting in a significant increment in the magnetic anisotropy energy by 2.48 × 106 erg/cm3. Furthermore, the critical Co thickness with maintaining the perpendicular magnetic anisotropy was enlarged from 1 to 3 nm, which is beneficial for enhancing the stability of nanodevices. These findings provide an effective strategy to tune the magnetic anisotropy of magnetic films toward the applications of various magnetic storage and logic devices.

Recently, a spontaneous exchange bias (SEB) driven by the isothermal crystallization of the antiferromagnetic IrMn layer has been reported in IrMn/FeCo bilayer. However, the key factors to determine the magnitude of SEB have not been clearly understood yet. Here, we investigate the effect of isothermal crystallization in IrMn layer on the formation of SEB in IrMn/CoFeB bilayer through preparing the samples with different degrees of isothermal crystallization in IrMn layer. The SEB is negligible in the sample with more structure-stable IrMn layer, confirming that the isothermal crystallization of IrMn plays a crucial role in the formation of SEB. However, the SEB field does not change significantly with the free-relaxation time of IrMn/CoFeB bilayers or IrMn layer. These results indicate that a slight degree of isothermal crystallization in IrMn layer is sufficient to induce a large SEB in IrMn/CoFeB bilayer. Our results not only confirm the newly reported SEB driven by the isothermal crystallization in IrMn layer but also clarify the key factor to control the magnitude of SEB.

The current work aims at investigating the detailed spatial structure of the thin plasma column of a gliding arc (GA) discharge extended in N2-CH4 gas mixtures, using visualization techniques. The GA discharge was operated at up to 5 atm in a high-pressure vessel with extensive optical access. The results show that the emission intensity from the plasma column increased tenfold with the addition of 0.1% CH4 in nitrogen, compared to that in pure N2. Furthermore, an additional layer located around the GA discharge column is detected. Imaging through spectral filters and spectral analysis of the emitted signal indicate that the emissions of this outer layer are mostly from the CN A-X and CH A-X transitions. This outer layer can propagate and extinguish dynamically, similar to the flame front in combustion. Besides, the separation of this outer layer to the plasma core decreases with pressure. The layered structure and its dynamical behaviors can be explained by a plasma-sustained radical propagation mechanism. The high-power plasma column can produce a high-temperature zone with rich atomic species, surrounded by the relatively cold N2-CH4 mixture. At the mixing layer between the high-temperature zone and the N2-CH4 mixture, some highly exothermic reactions occur to produce excited CN and CH species, which emit their specific spectra. As the high-temperature zone expands with time, the outer layer propagates outward. However, with the propagation continuing, the radical species involved in the outer layer formation are rapidly consumed, and thus, this layer disappears when it propagates too far away from the plasma column.

We report on the design of highly absorptive thermostable composite materials for microwave applications. Ceramics comprising the thermostable phosphate host and silicon carbide particles or whiskers were studied in a wide frequency range from several Hertz up to microwaves. It was demonstrated that a thin layer of ceramics placed on the back-reflector absorbs perfectly at the 30 GHz frequency. In the case of a free-standing ceramic composite layer being 1 mm thick, it provides more than 50% of absorption.

Reducing the energy loss in output voltage is critically important for further enhancing the efficiency of organic solar cells (OSCs). Here, we report that OSCs with high mobility and highly crystalline donor (D) and acceptor (A) materials were able to reduce an open-circuit voltage (VOC) loss. The crystallinity of the acceptor layer could be altered by appropriate selection of the three molecules with different alkyl side chain lengths. The VOC was found to increase as the crystallinity of the acceptor layer increased. The origin of the high VOC was that the highly crystalline D/A interface reduced the energy loss in the output voltage by realizing ideal band-to-band recombination. Especially, the high crystallinity of the several molecular layers (less than 6 nm) in the vicinity of the D/A interface was important for realizing the high VOC. Our results demonstrate that the careful design of the D/A interface enables high power conversion efficiencies to be achieved in OSCs by reducing open-circuit voltage loss.

In this Letter, a Ti/HfOx/Pt memristor with a modified Ti electrode created by inserting polydopamine (PDA)/Ag nanoparticles (AgNPs) between the Ti electrode and functional layer is reported. This memristor exhibits a significant improvement in the uniformity of device parameters [including set voltage, reset voltage, high resistance state (HRS) resistances, low resistance state (LRS) resistances, endurance, and retention] compared to conventional memristors. The AgNPs embedded in PDA renders a reduced variability in HRS and LRS resistances from 47% to 7%, and 46% to 11%, respectively. By fitting Poole–Frenkel and Ohmic behavior models, the consistency of the conductive mechanism of the devices before and after modification has been proven, which is further enhanced through variable temperature tests and the simulation of electric field distribution. It is believed that AgNPs play a lightning rod role in guiding the growth of conductive paths; thus, by growing AgNPs in situ on PDA film on the Ti electrode, it reduces the parameter variability.

We have investigated the interaction between carbon impurities and threading dislocations and their impact on the transport properties of GaN grown on Si substrates. The incorporation of carbon impurity was found to be associated with dislocation density, with a linear dependence. It indicates that the carbon may accumulate around the dislocations. The temperature-dependent Hall-effect measurement further confirmed that those carbon-decorated dislocations can act as acceptor-like traps, existing at every c-lattice spacing along a threading dislocation. The acceptor-like traps are important scattering centers and, thus, cannot be neglected. By reducing the density of the carbon-decorated dislocation via introducing a thick dislocation filtering layer to reduce the dislocation-related acceptor-like trap scattering, a record room-temperature electron mobility of 1090 cm2/V s with a carrier concentration of ∼2 × 1016 cm−3 for n--GaN on Si was achieved. Our results provide an effective approach to obtain high-quality n−-GaN on Si for vertical GaN based devices.

Transparent conductive films are important components of organic optoelectronic devices. However, current organic light-emitting devices (OLEDs) used in flexible wearable applications are severely restricted by the fragility and poor conductivity of composing ultra-thin electrodes. In this study, poly(methyl methacrylate) (PMMA)/trimethylaluminum (TMA) was prepared through an atomic layer half-reaction and used as a self-encapsulating nucleation layer. The study suggested coordination between the Au atoms with the functional methyl groups of PMMA/TMA to yield an entire substrate surface. The Au nuclei were evenly and densely distributed on the substrate surface, and island growth of Au film was prevented, leading to good flexibility and photoelectric properties of the Au film deposited on the nucleation layer. For instance, a 7 nm thick layer resulted in a sheet resistance of 18.19 ± 0.44 Ω/◻ at 85.89% transmittance. Furthermore, the use of the as-obtained high-performance electrode in flexible organic optoelectronic devices led to repeated bending over 1000 cycles to a radius of 1 mm without significant reduction in the optoelectronic performances. The nucleation induction layer could also function as a bottom encapsulation with a water vapor transmission rate as low as 2.123 × 10−3 g/cm2/day (60 °C/80% relative humidity). Additionally, the nucleation induction layer exhibited excellent performances in fully transparent devices (75.72% transmittance). In sum, these findings look promising for future flexible wearable applications.

Two-dimensional (2D) GaInS3 nanosheets are found to exhibit thermal and structural stabilities, good oxidation resistance, and tunable and layer-dependent electronic properties from first-principles calculations. Remarkably, the nanosheets with arbitrary thickness possess robust in-plane piezoelectricity without the odd-even effect commonly observed in other 2D piezoelectric materials, which is attributed to the retention of noncentrosymmetry resulting from their homogeneous and direct stacking patterns. The piezoelectric stress coefficient e 11 3 D of the nanosheets is about 0.23 C/m2, almost independent of the numbers of atomic layers of 2D GaInS3. The stability in piezoelectricity and the high carrier mobility of 2D GaInS3 nanosheets could endow them with promising application prospects in nanoelectronic and nanoelectromechanical devices.

A unipolar charge device was utilized to gain information of the charge balance in organic optoelectronic devices to enhance efficiency and operational stability. Usually, a unipolar charge device is designed as a multilayer structure to improve charge transport and block injection of counter charges from electrodes. In this paper, the correlation between charge transport across the interlayer and corresponding bulk electrical parameters from quasi-static analysis was investigated. Although only the interlayer material was modified, the charge carrier mobility and drift charge carrier density of the light-emitting layer were totally changed, which originated from large series resistance due to charge accumulation at the interface. This result indicates that quantitative analysis of electrical properties from unipolar charge devices should be performed as background analysis to ensure efficient interface charge transport during operation.

We report on the extended infrared single photon response of niobium nitride supercon- ducting nanowires deposited by atomic layer deposition. The superconducting nanowire single-photon detectors are based on 4.65 nm thick NbN, patterned into 100 nm meanders and characterized at 2.5 K. We verify single-photon sensitivity from 1310 nm to 2006 nm with saturated response at shorter wavelengths.

Plasmonic nanopores are extensively investigated as single molecules detectors. The main limitations in plasmonic nanopore technology are the too fast translocation velocity of the molecule through the pore and the consequent very short analysis times, as well as the possible instabilities due to local heating. An interesting approach to enable longer acquisition times is represented by the ability to stably trap the nanoparticles used to tag molecules close to the nanopore. Here, we theoretically investigate the performance of a magneto-plasmonic nanopore prepared with a thin layer of cobalt sandwiched between two gold layers. A nanopore is then coupled with a bifunctional (magnetic and plasmonic) core–shell nanoparticle made of magnetite (core) covered with a thin layer of gold (shell). By setting the magnetic configuration of the cobalt layer around the pore by an external magnetic field, it is possible to generate a nanoscale magnetic tweezer to trap the nanoparticle at a specific point. Considering a ∼10 nm diameter magnetite nanoparticle, we calculate a trapping force up to 28 pN, an order of magnitude above the force that can be obtained with standard optical or plasmonic trapping approaches. Moreover, the magnetic force pulls the nanoparticle in close contact with the plasmonic nanopore's wall, thus enabling the formation of a nanocavity enclosing a sub-10 nm3 confined electromagnetic field with an average field intensity enhancement up to 230 at near-infrared wavelengths. The presented hybrid magneto-plasmonic system points toward a strategy to improve nanopore-based biosensors for single-molecule detection and potentially for the analysis of various biomolecules.

High-efficiency, four-terminal tandem solar cells composed of thin GaAs films mechanically stacked onto interdigitated back contact silicon solar cells with a glass interlayer are demonstrated. The optimal thickness of the absorber layer of a rear heterojunction GaAs subcell for use in four terminal tandem solar cells was studied. GaAs top cells with absorber layer thicknesses of 1.5, 1.9, 2.3, 2.8, and 3.5 μm were fabricated on glass and mechanically stacked onto interdigitated back-contact Si bottom cells. All tandem cells were found to have efficiencies above 30% under the AM1.5 G spectrum demonstrating a relatively weak sensitivity to thickness in the four-terminal configuration. We found the 2.8 μm absorber layer cell to have the highest top cell and tandem cell efficiency at 26.38% and 32.57%, respectively. Optical modeling with transfer matrix method for the planar top cell and Lambertian light trapping in the textured Si subcell, along with drift-diffusion Hovel equations, were used to show photon recycling enhancement to the effective diffusion length and VOC of the top cell as a result of the low-index glass interlayer.

Killer defects are responsible for leakage current and breakdown in β-gallium oxide (β-Ga2O3) Schottky barrier diodes, which are crucial for power device applications. We have found that stacking faults in the halide vapor phase epitaxial (HVPE) (001) layer are killer defects. One type of defect is found to consist of (111) and (1 1 ¯1) stacking faults. The leakage current is 50 nA/defect at −200 V. This defect appears as a heart-shaped etch pit. Another type of defect is found to be a sequence of stacking faults from microparticles, which are formed at low gas flow rate during HVPE growth. The leakage current is 0.11–0.49 μA/defect at −200 V. This defect appears as a group of bullet-shaped etch pits.

Sb2Se3 has drawn wide attention in thin-film solar cells in recent years because of its advantages of low-cost, low-toxic, and physicochemically stable properties. The most efficient Sb2Se3 solar cells are based on a CdS/Sb2Se3 heterojunction, but the cliff-like conduction band offset at the CdS/Sb2Se3 interface causes detrimental interface recombination. In this Letter, we apply the ZnxCd1-xS to tune the interface band alignment. When x is equal to 0.163, the flatband results in an optimal efficiency of 7.02%, which is absolutely 0.6% higher than the control device with pure CdS.

We report on the highest two-terminal magnetoresistance (MR) ratio at room temperature in semiconductor-based lateral spin-valve devices. From first-principles calculations, we predict energetically stable ferromagnet–semiconductor heterointerfaces consisting of Co2MnSi (CMS) and Ge(111) upon insertion of Fe atomic layers. Using low-temperature molecular beam epitaxy, we demonstrate L21-ordered CMS epilayers at 80 °C on Ge(111), where the CMS layer can be utilized as a spin injector and detector. Two-terminal MR ratios as high as 0.1% are achieved in n-Ge-based lateral spin-valve devices with CMS/Fe/Ge Schottky tunnel contacts annealed at 200 °C. This study will open a path for semiconductor-based spintronic devices with a large MR ratio at room temperature.

To reduce the threshold current density (Jth) of ultraviolet (UV)-B AlGaN-based laser diodes, we investigated the critical parameters aiming to increase the injection efficiency ηi and the optical confinement factor Γ. Optimization of the thickness of the waveguide layer, the average Al content of the p-type AlGaN cladding layer, and the film thickness of the cladding layer demonstrated that the device characteristics can be improved. This optimization achieved a reduction in Jth to 13.3 kA cm−2 at a lasing wavelength of 300 nm, thus offering the lowest Jth value yet achieved for a UV-B laser diode.