Fabrication of high quality lead-free double perovskite Cs2AgBiBr6thin film and its application in memristor with ultralow operation voltage.

Recently, the lead-free double perovskite Cs2AgBiBr6has been considered as a promising candidate for next-generation nonvolatile memory and artificial synapse devices due to its high stability and low toxicity compared to its lead-based counterparts. In this work, we developed a simple and effective method to produce high-quality lead-free double perovskite Cs2AgBiBr6thin films without pinholes and particles by applying a low-pressure assisted method under ambient condition with a relative humidity (RH) of about 45%. The formation of pinholes and Ag precipitation in the perovskite Cs2AgBiBr6 films is effectively suppressed by the proper ratio of N,N-dimenthylformamide (DMF) mixed in dimethyl sulfoxide (DMSO) solvents. Furthermore, the grain size of the Cs2AgBiBr6films can be significantly increased by increasing the post-annealing temperature. Finally, a sandwiched structure memristor with an ITO/Cs2AgBiBr6/Ta configuration was successfully demonstrated, featuring ultralow operation voltage (VSet∼ 57 ± 23 mV,VReset∼ -692 ± 68 mV) and satisfactory memory window (the ratio ofRHRS/RLRS∼ 10 times), which makes it suitable for low-power consumption information storage devices.

Silicon-Nanomembrane-Based Broadband Synaptic Phototransistors for Neuromorphic Vision.

Neuromorphic vision has been attracting much attention due to its advantages over conventional machine vision (e.g., lower data redundancy and lower power consumption). Here we develop synaptic phototransistors based on the silicon nanomembrane (Si NM), which are coupled with lead sulfide quantum dots (PbS QDs) and poly(3-hexylthiophene) (P3HT) to form a heterostructure with distinct photogating. Synaptic phototransistors with optical stimulation have outstanding synaptic functionalities ranging from ultraviolet (UV) to near-infrared (NIR). The broadband synaptic functionalities enable an array of synaptic phototransistors to achieve the perception of brightness and color. In addition, an array of synaptic phototransistors is capable of simultaneous sensing, processing, and memory, which well mimics human vision.

Highly efficient electroluminescence from SnO2 nanocrystals and Er3+ co-doped silica thin film via introducing Ca2.

Efficient and stable near-infrared silicon-based light source is a challenge for future optoelectronic integration and interconnection. In this paper, alkaline earth metal Ca2+ doped SiO2-SnO2: Er3+ films were prepared by sol-gel method. The oxygen vacancies introduced by the doped Ca2+ significantly increase the near-infrared luminescence intensity of Er3+ ions. It was found that the doping concentration of Sn precursors not only modulate the crystallinity of SnO2 nanocrystals but also enhance the luminescence performance of Er3+ ions. The stable electroluminescent devices based on SiO2-SnO2: Er3+/Ca2+ films exhibit the power efficiency as high as 1.04×10-2 with the external quantum efficiency exceeding 10%.

Experimental observations on metal-like carrier transport and Mott hopping conduction behaviours in boron-doped Si nanocrystal multilayers.

Studies on the carrier transport characteristics of semiconductor nanomaterials are the important and interesting issues which are helpful for developing the next generation of optoelectronic devices. In this work, we fabricate B-doped Si nanocrystals/SiO2multilayers by plasma enhanced chemical vapor deposition with subsequent high temperature annealing. The electronic transport behaviors are studied via Hall measurements within a wide temperature range (30-660 K). It is found that when the temperature is above 300 K, all the B-doped Si nanocrystals with the size near 4.0 nm exhibit the semiconductor-like conduction characteristics, while the conduction of Si nanocrystals with large size near 7.0 nm transforms from semiconductor-like to metal-like at high B-doping ratios. The critical carrier concentration of conduction transition can reach as high as 2.2 × 1020cm-3, which is significantly higher than that of bulk counterpart and may be even higher for the smaller Si nanocrystals. Meanwhile, the Mott variable-range hopping dominates the carrier transport when the temperature is below 100 K. The localization radius of carriers can be regulated by the B-doping ratios and Si NCs size, which is contributed to the metallic insulator transition.

Alkaline earth metal ion doping to enhance the light emission from Er3+:SnO2 nanocrystal Co-doped silica films.

Alkaline earth metal ions (Mg2+, Ca2+, Sr2+) have been introduced into Er3+:SnO2 nanocrystal co-doped silica thin films fabricated by a sol-gel method combined with a spin-coating technique. It is found that the incorporation of alkaline earth metal ions can enhance the light emission from Er3+ at the wavelength around 1540 nm and the strongest enhancement is observed in samples doped with 5 mol% Sr2+ ions. Based on X-ray diffraction, X-ray photoelectron spectroscopy and other spectroscopic measurements, the improved light emission can be attributed to more oxygen vacancies, better crystallinity and a stronger cross-relaxation process with the introduction of alkaline earth metal ions.

Enhanced subband light emission from Si quantum dots/SiO2 multilayers via phosphorus and boron co-doping.

Seeking light sources from Si-based materials with an emission wavelength meeting the requirements of optical telecommunication is a challenge nowadays. It was found that the subband emission centered near 1200 nm can be achieved in phosphorus-doped Si quantum dots/SiO2 multilayers. In this work, we propose the phosphorus/boron co-doping in Si quantum dots/SiO2 multilayers to enhance the subband light emission. By increasing the B co-doping ratio, the emission intensity is first increased and then decreased, while the strongest integrated emission intensity is almost two orders of magnitude stronger than that of P solely-doped sample. The enhanced subband light emission in co-doped samples can be attributed to the passivation of surface dangling bonds by B dopants. At high B co-doping ratios, the samples transfer to p-type and the subband light emission from phosphorus-related deep level is suppressed but the emission centered around 1400 nm is appeared.

Multiple channels to enhance near-infrared emission from SiO2-SnO2:Er3+ films by Ba2+ ion doping.

Ba2+ ions co-doped SiO2-SnO2:Er3+ thin films are prepared using a sol-gel method combined with a spin-coating technique and post-annealing treatment. The influence of Ba2+ ion doping on the photoluminescence properties of thin films is carefully investigated. The enhancement of near-infrared (NIR) emission of Er3+ ions by as much as 12 times is obtained via co-doping with Ba2+ ions. To illustrate the relevant mechanisms, X-ray diffraction, X-ray photoelectron spectroscopy and comprehensive spectroscopic measurements are carried out. The enhanced NIR emission induced by Ba2+ co-doping can be explained by more oxygen vacancies, improved crystallinity and strong cross-relaxation processes between Er3+ ions. The incorporation of Ba2+ ions into SiO2-SnO2:Er3+ thin films results in a considerable enhancement in the NIR emission, making the thin films more suitable for Si-based optical lasers and amplifiers.

Low power consumption light emitting device containing TiO2:Er3+ thin film prepared by sol-gel method.

Er3+ ions doped titanium dioxide (TiO2) thin films have been prepared by sol-gel method. The photoluminescence both in visible light range (510-580 nm and 640-690 nm) and near infrared light range (1400-1700nm) have been observed. The photoluminescence excitation spectra demonstrate that energy transfer from wide band-gap TiO2 to Er3+ ions causes the infrared light emission. It is also found that the post annealing temperature can influence the luminescence intensity significantly. Based on sol-gel prepared TiO2:Er3+ thin films, we fabricate light emitting device containing ITO/TiO2:Er3+/SiO2/n+-Si/Al structure. Both the visible and near infrared electroluminescence (EL) can be detected under the operation voltage as low as 5.6 V and the working current of 0.66 mA, which shows the lower power consumption compared with the conventional EL devices.

Plasmon-enhanced upconversion luminescence in pyrochlore phase Yb x Er2-x Ti2O7 thin film.

Pyrochlore phase Yb x Er2-x Ti2O7 (YETO) thin films have been prepared by employing a facile sol-gel method combining with spin-coating technique and post-annealing treatment at 700 °C. High concentration of Yb3+ ions can promote the transformation from Yb3+/Er3+ co-doped anatase phase TiO2 to pyrochlore phase YETO at 700 °C temperature. We find that the YETO thin film with 30 mol% Yb3+ ions exhibits the brightest upconversion (UC) emission. Moreover, the introduction of Au nanorods (Au NRs) in the YETO thin film can further enhance the UC fluorescence. By adjusting the density of Au NRs, the UC emission intensity is increased by about 2.8-fold due to the excitation field enhancement caused by the localized surface plasmon resonance effect.

Modulation of surface states by phosphorus to improve the optical properties of ultra-small Si nanocrystals.

Here, we report the enhanced luminescence and optical gain by appropriate P-doping in Si nanocrystals (NCs)/SiO2 multilayers with ultra-small size of ∼1.9 nm. The luminescence intensity is enhanced by 19.4% compared to that of an un-doped NC and the optical gain is as high as 171.8 cm-1, which can be attributed to the reduction of surface defect states by the passivation of P impurities as revealed by electron spin resonance spectra. Further increasing the P-doping ratios results in the increase of conduction electrons due to the substitutional doping of phosphorus in the Si NCs, which favors the Auger recombination process. Consequently, both the luminescence intensity and the optical gain decrease rapidly. It is demonstrated that introduction of the suitable impurities can effectively modulate the surface chemical environment of Si NCs, which provides a new way to control the physical properties of Si NCs.

Enhanced Electroluminescence from a Silicon Nanocrystal/Silicon Carbide Multilayer Light-Emitting Diode.

Developing high-performance Si-based light-emitting devices is the key step to realizing all-Si-based optical telecommunication. Usually, silica (SiO2) as the host matrix is used to passivate silicon nanocrystals, and a strong quantum confinement effect can be observed due to the large band offset between Si and SiO2 (~8.9 eV). Here, for further development of device properties, we fabricate Si nanocrystals (NCs)/SiC multilayers and study the changes in photoelectric properties of the LEDs induced by P dopants. PL peaks centered at 500 nm, 650 nm and 800 nm can be detected, which are attributed to surface states between SiC and Si NCs, amorphous SiC and Si NCs, respectively. PL intensities are first enhanced and then decreased after introducing P dopants. It is believed that the enhancement is due to passivation of the Si dangling bonds at the surface of Si NCs, while the suppression is ascribed to enhanced Auger recombination and new defects induced by excessive P dopants. Un-doped and P-doped LEDs based on Si NCs/SiC multilayers are fabricated and the performance is enhanced greatly after doping. As fitted, emission peaks near 500 nm and 750 nm can be detected. The current density-voltage properties indicate that the carrier transport process is dominated by FN tunneling mechanisms, while the linear relationship between the integrated EL intensity and injection current illustrates that the EL mechanism is attributed to recombination of electron-hole pairs at Si NCs induced by bipolar injection. After doping, the integrated EL intensities are enhanced by about an order of magnitude, indicating that EQE is greatly improved.

A semiconducting hybrid of RhOx/GaN@InGaN for simultaneous activation of methane and water toward syngas by photocatalysis.

Prior to the eventual arrival of carbon neutrality, solar-driven syngas production from methane steam reforming presents a promising approach to produce transportation fuels and chemicals. Simultaneous activation of the two reactants, i.e. methane and water, with notable geometric and polar discrepancy is at the crux of this important subject yet greatly challenging. This work explores an exceptional semiconducting hybrid of RhOx/GaN@InGaN nanowires for overcoming this critical challenge to achieve efficient syngas generation from methane steam reforming by photocatalysis. By coordinating density functional theoretical calculations and microscopic characterizations, with in situ spectroscopic measurements, it is found that the multifunctional RhOx/GaN interface is effective for simultaneously activating both CH4 and H2O by stretching the C-H and O-H bonds because of its unique Lewis acid/base attribute. With the aid of energetic charge carriers, the stretched C-H and O-H bonds of reactants are favorably cleaved, resulting in the key intermediates, i.e. *CH3, *OH, and *H, to sit on Rh sites, Rh sites, and N sites, respectively. Syngas is subsequently produced via energetically favored pathway without additional energy inputs except for light. As a result, a benchmarking syngas formation rate of 8.1 mol·gcat-1·h-1 is achieved with varied H2/CO ratios from 2.4 to 0.8 under concentrated light illumination of 6.3 W·cm-2, enabling the achievement of a superior turnover number of 10,493 mol syngas per mol Rh species over 300 min of long-term operation. This work presents a promising strategy for green syngas production from methane steam reforming by utilizing unlimited solar energy.

Gallium Oxide for Gas Sensor Applications: A Comprehensive Review.

Ga2O3 has emerged as a promising ultrawide bandgap semiconductor for numerous device applications owing to its excellent material properties. In this paper, we present a comprehensive review on major advances achieved over the past thirty years in the field of Ga2O3-based gas sensors. We begin with a brief introduction of the polymorphs and basic electric properties of Ga2O3. Next, we provide an overview of the typical preparation methods for the fabrication of Ga2O3-sensing material developed so far. Then, we will concentrate our discussion on the state-of-the-art Ga2O3-based gas sensor devices and put an emphasis on seven sophisticated strategies to improve their gas-sensing performance in terms of material engineering and device optimization. Finally, we give some concluding remarks and put forward some suggestions, including (i) construction of hybrid structures with two-dimensional materials and organic polymers, (ii) combination with density functional theoretical calculations and machine learning, and (iii) development of optical sensors using the characteristic optical spectra for the future development of novel Ga2O3-based gas sensors.

Variation on the Microstructure and Mechanical Properties of Ti-Al-N Films Induced by RF-ICP Ion Source Enhanced Reactive Nitrogen Plasma Atmosphere.

Acquiring the optimum growth conditions of Ti-Al-N films, the effects of gas atmosphere, especially the reactive plasma on the material microstructures, and mechanical properties are still a fundamental and important issue. In this study, Ti-Al-N films are reactively deposited by radio frequency inductively coupled plasma ion source (RF-ICPIS) enhanced sputtering system. Different nitrogen gas flow rates in letting into the ion source are adopted to obtain nitrogen plasma densities and alter deposition atmosphere. It is found the nitrogen element contents in the films are quite influenced by the nitrogen plasma density, and the maximum value can reach as high as 67.8% at high gas flow circumstance. XRD spectra and FESEM images indicate that low plasma density is benefit for the film crystallization and dense microstructure. Moreover, the mechanical properties like hardness and tribological performance are mutually enhanced by adjusting the nitrogen atmosphere.

Transition of Carrier Transport Behaviors with Temperature in Phosphorus-Doped Si Nanocrystals/SiO2 Multilayers.

High-conductive phosphorus-doped Si nanocrystals/SiO2(nc-Si/SiO2) multilayers are obtained, and the formation of Si nanocrystals with the average crystal size of 6 nm is confirmed by high-resolution transmission electron microscopy and Raman spectra. The temperature-dependent carrier transport behaviors of the nc-Si/SiO2 films are systematically studied by which we find the shift of Fermi level on account of the changing P doping concentration. By controlling the P doping concentration in the films, the room temperature conductivity can be enhanced by seven orders of magnitude than the un-doped sample, reaching values up to 110 S/cm for heavily doped sample. The changes from Mott variable-range hopping process to thermally activation conduction process with the temperature are identified and discussed.

Arc-melting to narrow the bandgap of oxide semiconductors.

The bandgap of a series of oxide semiconductors is narrowed by a quick and facile arc-melting method. A defective structure is formed in the fast melting and cooling process without changing its phase structure. Enhanced optical and electrical properties are found in the arc-melted oxide, such as enhanced photocatalytic properties of the arc-melted ZnO under visible light.