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The significance of ultrafast laser-induced energy and mass transfer at interfaces has been growing in the field of nanoscience and technology. Nevertheless, the complexity arising from non-linear and non-equilibrium optical-thermal-mechanical interactions results in intricate transitional behaviors. This complexity presents challenges when attempting to analyze these phenomena exclusively through modeling or experimentation. In this study, we conduct time-resolved reflective pump-probe imaging and molecular-dynamics coupled two-temperature model (MD-TTM) simulations to investigate the ultrafast dynamics and ablation mechanism of Au/Ti bilayer systems. The calculated energy absorption curves indicate that Au film reduces the energy deposition in the underlying Ti layer, resulting in reduced melting and evaporation rate of Ti. The phase transition process induces different mechanical responses. The potential energy patterns indicate that the expansion of vapor Ti extrudes the surface Au layer outward. In simulated stress distribution images, the Au layer can hamper the expansion of the vapor-phase Ti and brings dynamic compressive stress to the residual Ti layer. When the compressive stress transforms into tensile stress, the material is removed through mechanical damage. Therefore, both Au and Ti in the 20 nm Au-covered Ti are completely removed. Our approach elucidates the ablation mechanism within the Au/Ti bilayer system and offers fresh insights into managing thermo-mechanical responses within analogous systems.

Holograms hidden inside transparent materials are important for information encryption storage because of their advantages of secrecy, and could completely avoid information loss caused by surface wear. Inside the transparent material, the modified filaments array was need for hologram fabrication to change the optical phase or amplitude of incident laser, which is sensitive to the change of refractive index. Then the uniformity of modified filaments inside transparent materials is highly required. In this study, by tuning the interval time of the double-pulse processing, holograms with improved imaging quality were fabricated by double-pulse femtosecond laser and the effect and mechanism of self-trapped excitons (STEs) on the ablation have been systematically studied. The imaging quality of the hologram fabricated with double-pulse laser was superior to that of the one fabricated with the single-pulse laser and 350 fs was verified to be the best time interval for double-pulse processing. The evolution of the electrons dynamics was investigated by using the pump-probe technology. With the double-pulse time interval increasing, the residual electrons, excitons, STEs, and defects caused by the first sub-pulse would become dominated sequentially. The results demonstrated the controllability of STEs and quality improvement of final structures by double-pulse femtosecond laser processing.

The normal operation of critical infrastructure is related to the stability of society and a country's development. Based on game theory and network science, this paper analyzes the attack–defense issues of critical infrastructure, proposing a network attack–defense game model based on virtual flow. Five coupling methods are established according to the complex interdependent characteristics and important evaluation indicators (the degree value and betweenness value) in the network. Considering the network's information transmission, redistribution, and cascading failures, a cascading failure model based on betweenness virtual flow is established. A two-player game is adopted, in which the attacker and the defender act simultaneously. The scale-free, small-world, and random networks are related using these five coupling methods. Simulation and theoretical analyses are carried out on the interdependent network game scenario under different coupling modes. The game equilibrium under different network coupling conditions and coupling methods is simulated, and the preferences of the game participants are determined. In addition, a sensitivity analysis of the game parameters is conducted, facilitating the identification of certain effective strategies that can support decision-makers. Critical infrastructure networks play an important role in maintaining social stability. Based on game theory and network science, this paper analyzed the attack–defense problems of critical infrastructures and proposed an attacker–defender game model based on the betweenness virtual flow. The attack–defense game in the interdependent network is analyzed in terms of coupling modes, network types, and tolerance coefficient. A sensitivity analysis of the game parameters is also conducted. The results show that the interdependent networks under random coupling and reverse coupling strategies are more vulnerable to attack. In addition, the cost-sensitive parameter is a key factor affecting the game equilibrium. Even if the two subnetworks in the interdependent network are the same, the payoffs and the robustness will be different when the order of removing nodes is different. This paper provides decision support for actual infrastructure protection. [ABSTRACT FROM AUTHOR]

The study investigates the two different underlying ablation mechanisms of WS2 processed by femtosecond (fs) laser with different fluences. With increasing fluence, the saturable expansion of craters and the transformation of three distinct crater morphologies are found. The material response and the transfer and deposition of laser energy are tracked by using a plasma model based on the classical single rate equation model and the Drude model. The results of the numerical simulation and time-resolved transient reflectivity reveal the two different ablation mechanisms, which are coulomb explosion and phase explosion. The mechanism of material removal is distinguished by the critical threshold of 0.85 J/cm2. In addition, the internal ablation region exhibits a high concentration of defects and WO3 according to the results of Raman spectra, X-ray photoelectron spectra, and morphology-dependent photoluminescence mapping. Due to the high concentration with high fluence, the device of WS2/Si p-n junction exhibits a 2.6 times enhancement on the current under forward bias. The findings would be of value to engineer structures to tailor the optoelectronic response of WS2 and to develop potential future optoelectronic devices. [ABSTRACT FROM AUTHOR]

Ni catalysts decorated with trace Rh supported on γ-Al2O3 were prepared by the co-impregnation method. To obtain the Ni–Rh nanoparticles with different nanostructures and chemical compositions, bimetallic catalysts with varied Ni/Rh molar ratios were prepared. For comparison, monometallic Ni/γ-Al2O3 and Rh/γ-Al2O3 catalysts were also prepared by the impregnation method. The selective gas phase catalytic hydrodechlorination of 1,2-dichloroethane to ethylene was used to evaluate catalytic performances of the catalysts. The catalysts were characterized by X-ray diffraction, N2 adsorption, X-ray photoelectron spectroscopy, H2 temperature-programmed reduction, transmission electron microscopy–energy-dispersive X-ray, and CO chemisorption. It was found that the introduction of Rh to Ni catalyst facilitated the generation of spillover hydrogen which could enhance the ability of the Ni catalyst for H2 activation. In bimetallic catalysts, there was an intimate interaction between Ni and Rh, and isolated Rh sites were formed due to the dilution effect of Ni. Accordingly, compared with the monometallic Ni catalyst for gas phase catalytic hydrodechlorination of 1,2-dichloroethane, the bimetallic Ni–Rh(800)/γ-Al2O3 catalyst exhibited markedly higher 1,2-dichloroethane conversion (37%) and comparable selectivity to ethylene (95%). The findings in this study indicate that Ni–Rh/γ-Al2O3 with trace Rh can be used as a promising catalyst for highly effective and selective catalytic hydrodechlorination of chlorinated hydrocarbons. [ABSTRACT FROM AUTHOR]