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AbstractPlasma-enhanced atomic layer deposition (PEALD) is gaining interest in thin films for laser applications, and post-annealing treatments are often used to improve thin film properties. However, research to improve thin film properties is often based on an expensive and time-consuming trial-and-error process. In this study, PEALD-HfO2thin film samples were deposited and treated under different annealing atmospheres and temperatures. The samples were characterized in terms of their refractive indices, layer thicknesses and O/Hf ratios. The collected data were split into training and validation sets and fed to multiple back-propagation neural networks with different hidden layers to determine the best way to construct the process–performance relationship. The results showed that the three-hidden-layer back-propagation neural network (THL-BPNN) achieved stable and accurate fitting. For the refractive index, layer thickness and O/Hf ratio, the THL-BPNN model achieved accuracy values of 0.99, 0.94 and 0.94, respectively, on the training set and 0.99, 0.91 and 0.90, respectively, on the validation set. The THL-BPNN model was further used to predict the laser-induced damage threshold of PEALD-HfO2thin films and the properties of the PEALD-SiO2thin films, both showing high accuracy. This study not only provides quantitative guidance for the improvement of thin film properties but also proposes a general model that can be applied to predict the properties of different types of laser thin films, saving experimental costs for process optimization.

High-performance thin films combining large optical bandgap Al2O3and high refractive index HfO2are excellent components for constructing the next generation of laser systems with enhanced output power. However, the growth of low-defect plasma-enhanced-atomic-layer-deposited (PEALD) Al2O3for high-power laser applications and its combination with HfO2and SiO2materials commonly used in high-power laser thin films still face challenges, such as how to minimize defects, especially interface defects. In this work, substrate-layer interface defects in Al2O3single-layer thin films, layer-layer interface defects in Al2O3-based bilayer and trilayer thin films, and their effects on the laser-induced damage threshold (LIDT) were investigated via capacitance–voltage (C–V) measurements. The experimental results show that by optimizing the deposition parameters, specifically the deposition temperature, precursor exposure time, and plasma oxygen exposure time, Al2O3thin films with low defect density and high LIDT can be obtained. Two trilayer anti-reflection (AR) thin film structures, Al2O3/HfO2/SiO2and HfO2/Al2O3/SiO2, were then prepared and compared. The trilayer AR thin film with Al2O3/HfO2/SiO2structure exhibits a lower interface defect density, better interface bonding performance, and an increase in LIDT by approximately 2.8 times. We believe these results provide guidance for the control of interface defects and the design of thin film structures and will benefit many thin film optics for laser applications.

Lithium–sulfur (Li–S) batteries are considered one of the most promising next-generation secondary batteries owing to their ultrahigh theoretical energy density. However, practical applications are hindered by the shuttle effect of soluble lithium polysulfides (LiPSs) and sluggish redox kinetics, which result in low active material utilization and poor cycling stability. Various copper-based materials have been used to inhibit the shuttle effect of LiPSs, owing to the strong anchoring effect caused by the lithiophilic/sulphilic sites and the accelerated conversion kinetics caused by excellent catalytic activity. This study briefly introduces the working principles of Li–S batteries, followed by a summary of the synthetic methods for copper-based materials. Moreover, the recent research progress in the utilization of various copper-based materials in cathodes and separators of Li–S batteries, including copper oxides, copper sulfides, copper phosphides, copper selenides, copper-based metal-organic frameworks (MOFs), and copper single-atom, are systematically summarized. Subsequently, three strategies to improve the electrochemical performance of copper-based materials through defect engineering, morphology regulation, and synergistic effect of different components are presented. Finally, our perspectives on the future development of copper-based materials are presented, highlighting the major challenges in the rational design and synthesis of high-performance Li–S batteries.