We have experimentally studied the pump-probe Kerr rotation dynamics in WSe2 monolayers. This yields a direct measurement of the exciton valley depolarization time τv. At T = 4 K, we find τv ≈ 6 ps, a fast relaxation time resulting from the strong electron-hole Coulomb exchange interaction in bright excitons. The exciton valley depolarization time decreases significantly when the lattice temperature increases with τv being as short as 1.5 ps at 125 K. The temperature dependence is well explained by the developed theory taking into account exchange interaction and fast exciton scattering time on short-range potential.

Cr-Ti-N films are deposited on the surface of Ti6Al4V alloy by unbalanced multi-targets reactive magnetron sputtering. In this study, the effect of the Ti content on microstructure, hardness, modulus and tribological behaviours of Cr-Ti-N films are systematically investigated. The XRD shows that with the increasing of Ti content, the phase structure evolves from Cr + Cr 2 N + TiN → amorphous → FCC solid solution. The hardness and modulus of Cr-Ti-N films are increased by improving Ti content in the films and Cr 32.5 Ti 24.6 N 42.9 film reaches maximum values of 25.8 and 362.7 GPa, respectively. The wear rate of the Cr-Ti-N films is gradually decreased with increasing Ti content and the Cr 32.5 Ti 24.6 N 42.9 film decreases five times and 25 times than Cr 50.7 Ti 10.1 N 39.2 and substrate, respectively.

Periodic nano-ripples structures were fabricated by femtosecond laser scanning on WC/Co based TiAlN coatings. The surface morphology, ripples dimension and changes in the element content of samples irradiated with different processing parameters were analysed. The results show that the formation and quality of ripples are largely determined by pulse energy, scanning speed and scanning spacings. The 3 mJ pulse energy, 500 mm s 21 scanning speed and 5 mm scanning spacing induce best quality ripples on TiAlN films among all experimental conditions. The period of ripples formed on TiAlN films gradually increases with increasing pulse energy, scanning speed and scanning spacing, which is smaller than the laser wavelength. With the high pulse energy and low scanning speed, TiAlN films could be removed, and ripples with period of 480-600 nm are formed on cemented carbide substrates. Concentration and distribution of all constitutive elements in the irradiated area are gradually changed with increasing pulse energy.