In this study, DLC films were coated on oxynitriding-treated Vanadis 10 tool steel using the DC-pulsed plasma CVD technique. The experimental parameters included different duty cycles (9, 13, 17, and 21 %) with asymmetric bipolar-pulsed voltages of -3 kV, a gas flow of CH4 maintained at 15 sccm, and a deposition time of 90 min. Meanwhile, the properties of DLC films were measured by Raman spectroscopy, Rockwell indentation, wear tests, FT-IR, corrosion tests, water contact angle tests, and four-point probes analysis. The experimental results showed that the optimum properties of DLC films occurred at a duty cycle of 17 %. It had the lowest wear volume loss for loads 2 N and 5 N were 3.49 × 10 −3 mm 3 and 4.08 × 10 −3 mm 3 , respectively. Moreover, the optimal DLC films possessed the lowest corrosion current (Icorr = 7.91 × 10 −5 A cm −2 ) and highest polarization resistance (Rp = 1185.21 Ω cm 2 ) in 3.5 wt.% NaCl solutions. The FT-IR spectrum analysis also found that the characteristic peaks of DLC films were generated at positions of 2852 and 2921 cm −1 , and the water contact angle tests showed that the DLC films had great hydrophobicity (78.33 • ). Consequently, the results confirmed that the duplex surface treatment effectively improved the coating properties of Vanadis 10 tool steel. K e y w o r d s : diamond-like carbon (DLC), oxynitriding, Vanadis 10 tool steel, DC-pulsed plasma-enhanced CVD, wear, corrosion, water contact angle
The optical emissive transitions from the ground and excited states of the self-assembled In x Ga 1Àx As/GaAs quantum dots (QDs) at room temperature were experimentally measured as a function of the external hydrostatic pressure by means of the confocal micro-photoluminescence technique. The ground state transition is very weak under zero external pressure and the photoluminescence is dominant by the excited state transition. However, the intensity of the ground state transition monotonically increases with increasing the external pressure and eventually become the dominant transition. Their pressure coefficients (PCs) were determined to be 6.8 and 7.1 meV/kbar, respectively, which were astonishingly smaller than those of GaAs bulk and the InGaAs/GaAs reference quantum well. The emission peak from the higher order excited states had a much smaller PC ($0.5 meV/kbar). The influence of the built-in strain and external hydrostatic pressure on the electronic structures and optical transitions of various In x Ga 1Àx As/ GaAs QDs was theoretically investigated by using the eight-band kÁp method. Good agreement between the theoretical and experimental results was achieved, firmly revealing that the internal built-in strain in the dot system is mainly responsible for the experimental findings. V C 2012 American Institute of Physics. [http://dx.
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