Enabling High-Performance Surfaces of Biodegradable Magnesium Alloys via Femtosecond Laser Shock Peening with Ultralow Pulse Energy

The fast degradation rate and poor wear resistance of magnesium (Mg) alloys in physiological environments have limited their potential usage as next-generation biodegradable orthopedic implant materials. In this work, femtosecond laser shock peening (fs-LSP) was successfully applied to simultaneously improve the surface mechanical, corrosion, and tribocorrosion properties of WE43 Mg alloys in blood bank buffered saline solution at body temperature. Specifically, the treated surfaces of WE43 Mg alloys via fs-LSP with ultralow pulse energy were investigated under different power densities, confining mediums, and absorbent materials. It was found that the combination of a black tape and a quartz layer gave the optimum peening effect under a power density of 28 GW/cm², which simultaneously strengthened the surface and reduced the corrosion kinetics. In addition, a rapid self-repassivation was observed in fs-LSP-treated WE43 surfaces during tribocorrosion, promising sustained corrosion resistance under mechanical loading, critical to the reliability of load-bearing implants. Finally, the subsurface microstructural evolution and residual stress development in WE43 after fs-LSP were discussed based on the results from transmission electron microscopy analysis and finite element simulations.

Graphene-Ta2O5 heterostructure enabled high performance, deep-ultraviolet to mid-infrared photodetection

Ultrafast, high sensitive, low cost photodetectors operating at room temperature sensitive from the deep-ultraviolet to mid-infrared region remain a significant challenge in optoelectronics. Achievements in traditional semiconductors using cryogenic operation and complicated growth processes prevent the cost-effective and practical application of broadband detectors. Alternative methods towards high-performance photodetectors, hybrid graphene-semiconductor colloidal quantum dots have been intensively explored. However, the operation of these photodetectors has been limited by the spectral bandwidth and response time. Here, we have demonstrated hybrid photodetectors operating from the deep-ultraviolet to the mid-infrared region with high sensitivity and ultrafast response by coupling graphene with a p-type semiconductor photosensitizer, nitrogen-doped Ta2O5 thin film. Photons with energy higher than the energy of the defect centers release holes from neutral acceptors. The holes are transferred into graphene, leaving behind ionized acceptors. Due to the advantage of two-dimensional heterostructure including homogeneous thickness, extending in a two-dimensional plane, large contact area between the N-Ta2O5 thin film and graphene, and the high mobility of carriers in graphene, holes are transferred rapidly to graphene and recirculated during the long lifetime of ionized acceptors. The photodetectors achieve a high photo-responsivity (up to 3.0 × 106 A W-1), ultrafast rise time (faster than 20 ns), and a specific detectivity (up to ∼2.2 × 1012 Jones). The work provides a method for achieving high-performance optoelectronics operating in the deep-ultraviolet to mid-infrared region.

Monte Carlo ray-trace diffraction based on the Huygens-Fresnel principle

The goal of this effort is to establish the conditions and limits under which the Huygens-Fresnel principle accurately describes diffraction in the Monte Carlo ray-trace (MCRT) environment. This goal is achieved by systematic intercomparison of dedicated experimental, theoretical, and numerical results. We evaluate the success of the Huygens-Fresnel principle by predicting and carefully measuring the diffraction fringes produced by both single slit and circular apertures. We then compare the results from the analytical and numerical approaches with each other and with dedicated experimental results. We conclude that use of the MCRT method to accurately describe diffraction requires that careful attention be paid to the interplay among the number of aperture points, the number of rays traced per aperture point, and the number of bins on the screen. This conclusion is supported by standard statistical analysis, including the adjusted coefficient of determination, Radj2, the rms deviation, and the reduced chi-square statistic, χv2.