Wang Hongshui

In-situ growth of Ca/P salt on Ti surface induced by femtosecond lasers in hydroxyapatite suspension

Pure Ti plate surfaces are micro-ablated by femtosecond lasers in the ambience of hydroxyapatite suspension. It is found that three-stage hierarchical surface structures are produced with various laser energies. When the laser energy is 150 μJ, a lava-like structure with a distribution of nanoholes is dispersed evenly on the laser ablated surface. While in the case of 300 μJ, the grooves-and-islands micro-patterns covered with nanoparticles are generated on the surface. Remarkably, Ca/P based substances are revealed to firmly deposit on the micro-structured surfaces. More phosphate growth is seen for the higher laser energy. Discussions suggest that the additional elements deposition could be attributed to the chemical reaction of plasma related ions in the suspension and their subsequent crystallisation on the fresh surfaces of Ti plate due to the femtosecond laser ablation.

Controllable synthesis of high aspect ratio Mg2B2O5 nanowires and their applications in reinforced polyhydroxyalkanoate composites

Highly pure magnesium borate (Mg2B2O5) nanowires with an average diameter of ~ 30 nm, an average length of ~ 15 μm, and a high aspect ratio of ~ 500 have been synthesized on a large scale via a two-step method. MgBO2(OH) nanowires with high aspect ratios were first prepared via a PVP-assisted hydrothermal technique. Using these nanowires as precursors, single crystalline Mg2B2O5 nanowires were synthesized by post-annealing treatment at a relatively low temperature of 700 °C. The important effect of the MgBO2(OH)—Mg2B2O5 conversion process on the morphology of the Mg2B2O5 nanowires was investigated and it was indicated that the recrystallization process plays an important role in the protection of the one-dimensional (1D) nanostructure. Moreover, the rigidity and the toughness of the Mg2B2O5 nanowire-reinforced PHA composites were tremendously improved compared to those of the pure PHA. Our results demonstrate the effectiveness of Mg2B2O5 nanowires for reinforcement applications in polymer composites.

Femtosecond laser ablation of silicon wafers in air and water

In this paper, we investigate laser ablation of silicon wafers in air and water through using Ti:sapphire femtosecond laser with central wavelength of 800 nm and pulse duration of 50 fs—24 ps at a repetition rate of 1 kHz. Unique concentric rings are observed on the sample surfaces during the laser ablation in ambient air. Formation mechanisms of the inner and outer ablative structures are attributed to the thermal melting and Coulomb explosion, respectively. The influence of laser parameters, such as the laser energy, the number of pulses and the pulse duration on the radius of the ablation ring is observed experimentally. It is found that drilling a blind hole with large aspect ratio usually requires multiple laser shots with relatively small pulse energy. In the water surroundings, femtosecond laser ablation results in porous microstructure formation in the irradiated area. However, laser pulses with picosecond duration lead to large material removal by evidently nonthermal processes. Theoretical analysis suggests that this phenomenon could be explained by the photo-mechanical stress and bubble cavitation, which are strengthened with increasing pulse duration. The critical pulse width separating the two different ablation processes in the water ambience is determined experimentally for the first time.