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Silicon dioxide memristors possess multiple resistance states and can be used as a key component of memory devices and neuromorphic systems. However, their conductive mechanisms are incompletely understood, and their resistance switching (RS) variability is a major challenge for commercialization of memristors. In this work, by combining the desirable properties of silicon dioxide with those of a two-dimensional MXene material (Ti3C2), a memristor based on an MXene/SiO2 structure is fabricated. The Cu/MXene/SiO2/W memristive devices exhibit excellent switching performance compared with traditional Cu/SiO2/W devices under the same conditions. Furthermore, the role of the MXene/SiO2 structure in the SiO2-based memristors is revealed by the physical characterization of the MXene and first-principles calculation of the MXene/SiO2 structure. The results indicate that the conductive filaments (CFs) are more likely to grow along the locations of MXene nanostructures, which reduces the randomness of CFs in the Cu/MXene/SiO2/W memristors and further improves the device performance. Meanwhile, the MXene/SiO2 structure appears to greatly reduce the mobility of Cu ions in the entire RS region, as well as improve the performance of the SiO2-based memristors while maintaining the operating voltages low.

Optical properties and thermal stability of the solar selective absorber based on the metal/dielectric four-layer film structure were investigated in the variable temperature region. Numerical calculations were performed to simulate the spectral properties of multilayer stacks with different metal materials and film thickness. The typical four-layer film structure using the transition metal Cr as the thin solar absorbing layer [SiO 2 (90nm)/Cr(10nm)/SiO 2 (80nm)/Al (≥100nm)] was fabricated on the Si or K9 glass substrate by using the magnetron sputtering method. The results indicate that the metal/dielectric film structure has a good spectral selective property suitable for solar thermal applications with solar absorption efficiency higher than 95% in the 400-1200nm wavelength range and a very low thermal emittance in the infrared region. The solar selective absorber with the thin Cr layer has shown a good thermal stability up to the temperature of 873K under vacuum atmosphere. The experimental results are in good agreement with the calculated spectral results. KeywordsSolar Energy, Thermo-optical materials, Multilayers, Thin films, optical properties Abstract: Optical properties and thermal stability of the solar selective absorber based on the metal/dielectric four-layer film structure were investigated in the variable temperature region. Numerical calculations were performed to simulate the spectral properties of multilayer stacks with different metal materials and film thickness. The typical four-layer film structure using the transition metal Cr as the thin solar absorbing layer [SiO 2 (90nm)/Cr(10nm)/SiO 2 (80nm)/Al (≥100nm)] was fabricated on the Si or K9 glass substrate by using the magnetron sputtering method. The results indicate that the metal/dielectric film structure has a good spectral selective property suitable for solar thermal applications with solar absorption efficiency higher than 95% in the 400-1200nm wavelength range and a very low thermal emittance in the infrared region. The solar selective absorber with the thin Cr layer has shown a good thermal stability up to the temperature of 873K under vacuum atmosphere. The experimental results are in good agreement with the calculated spectral results.

A solar selective absorber with a multilayered SiO2 (87.0 nm)/Cr (8.3 nm)/SiO2 (96.3 nm) film structure was designed and fabricated by magnetron sputtering on a surface-roughened copper (Cu) substrate. The proposed structure can enhance solar absorption by combining both the typical solar absorption designs of the textured surface and metal–dielectric multilayer film structure. The measured solar absorptance is about 94%, which yields an enhancement of about 2% accompanied by a slightly higher thermal emittance than that observed for the surface-smoothed structure. The increasing thermal emittance of the surface-roughened film structure is expected to markedly cancel the advantage of absorptance enhancement as the temperature increases to 600 K, implying that the proposed film structure functions more efficiently at low or intermediate temperatures (<600 K).

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Utilizing electronic devices to emulate biological synapses for the construction of artificial neural networks has provided a feasible research approach for the future development of artificial intelligence systems. Until now, different kinds of electronic devices have been proposed in the realization of biological synapse functions. However, the device stability and the power consumption are major challenges for future industrialization applications. Herein, an electronic synapse of MXene/SiO2 structure-based resistive random-access memory (RRAM) devices has been designed and fabricated by taking advantage of the desirable properties of SiO2 and 2D MXene material. The proposed RRAM devices, Ag/MXene/SiO2/Pt, exhibit the resistance switching characteristics where both the volatile and nonvolatile behaviors coexist in a single device. These intriguing features of the Ag/MXene/SiO2/Pt devices make them more applicable for emulating biological synaptic plasticity. Additionally, the conductive mechanisms of the Ag/MXene/SiO2/Pt RRAM devices have been discussed on the basis of our experimental results.

A new method for measuring the dielectric functions change with the thickness of nanometal thin films was proposed. To confirm the accuracy and reliability of the method, a nano-thin wedge-shaped gold (Au) film with continuously varied thicknesses was designed and prepared on K9 glass by direct-current-sputtering (DC-sputtering). The thicknesses and the dielectric functions in the wavelength range of 300-1100 nm of the nano-thin Au films were obtained by fitting the ellipsometric parameters with the Drude and critical points model. Results show that while the real part of the dielectric function (ϵ₁) changes marginally with increasing film thickness, the imaginary part (ϵ₂) decreases drastically with the film thickness, approaching a stable value when the film thickness increases up to about 42 nm. This method is particularly useful in the study of thickness-dependent optical properties of nano-thin film.