Thin film AC ZnSxSe1-x:Mn EL
Conventional ZnS:Mn electroluminescence (EL) device has a good level of brightness but needs a high operating voltage. The best way to lower the operating voltage seemed to be by reducing the band gap of the host material and to achieve this, ZnSe had been proposed before. However, our experiments showed that when the ZnSe:Mn EL was operated at low voltages the brightness level and contrast ratio decreased, due to the yellowish coloration of the ZnSe film. The authors have developed a host material which combines both advantages; the high brightness level of ZnS, and the low operating voltage of ZnSe. A material with a band gap between those of ZnS (3.7 eV) and ZnSe (2.7 eV) was tested. By coevaporation of ZnS and ZnSe, a solid solution ZnSxSe1-xwas found in an evaporated film. By measuring the absorption edge and using X-ray techniques, we found that the band gap varied in proportion to the concentration of selenium. A thin film of ZnS0.4Se0.6EL sandwiched between Y2O3insulating layers can operate at a low voltage (120 V) with a high level of brightness (>100 fL at 1 KHz), with a very small upward voltage shift (10 V) during aging.
ac electroluminescence in thin‐film ZnSe : Mn
ac electroluminescence from thin films of Mn‐doped ZnSe, sandwiched between two insulating films, shows a hysteresis in light output versus applied voltage, similar to that observed in ZnS : Mn. We also find that the threshold voltage for light emission is approximately a factor of 2 smaller for ZnSe structures than for similarly prepared ZnS structures of identical dimensions.
Determination of Optimal Ball-Burnishing Parameters for Plastic Injection Moulding Steel
The objective of this study is to determine the optimal plane ball-burnishing parameters for plastic injection moulding steel PDS5 on a machining centre by utilising the Taguchi’s orthogonal array method. The design and manufacture of a burnishing tool are described. Four burnishing parameters, namely the ball material, burnishing speed, burnishing force and feed, were selected as the experimental factors in Taguchi’s design of experiments to determine the optimal burnishing parameters which have the dominant influence on surface roughness. The optimal burnishing parameters were found after carrying out the experiments specified by Taguchi’s L18 orthogonal table, by the analysis of variation, and by a full factorial experiment. The optimal plane burnishing parameters for the plastic injection moulding steel PDS5 were a combination of a tungsten carbide ball, a burnishing speed of 200 mm/min, a burnishing force of 300 N and a feed of 40 μm. The surface roughness Ra of the specimen can be improved from about 1 μm to 0.07 μm by using the optimal burnishing parameters for plane burnishing.