Surface Functionalization of Polyethylene by Silicon Nitride Laser Cladding

Functional coatings are commonly applied to biomaterials in order to improve their properties. In this work, polyethylene was coated with a silicon nitride (Si3N4) powder using a pulsed laser source in a nitrogen gas atmosphere. Several analytical techniques were used to characterize the functionalized surface of the polymer, including Raman spectroscopy, laser microscopy, scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS). Antibacterial properties were tested in vitro against Staphylococcus epidermidis. The Si3N4 coating sensibly reduced the amount of living bacteria when compared to the uncoated polymer. Osteoconductivity was also tested in vitro using SaOS-2 osteosarcoma cells. The presence of Si3N4 coating resulted in an increased amount of hydroxyapatite. Coating of polyethylene with silicon nitride may lead to improved performance of indwelling orthopaedic or less invasive medical devices.

Influence of InGaN waveguide on injection efficiency in III-nitride laser diodes

The influence of using InGaN waveguides on blue laser diodes was theoretically studied using 1D drift diffusion model and 2D optical mode calculation. Despite of the known effect of increased confinement of an optical mode, especially for long wavelengths, an unexpected influence on the efficiency of carrier injection into the active region is discussed. It is found that InGaN-AlGaN interface is crucial to achieving high injection efficiency. A numerical model is created, which describes the influence of InGaN waveguide and Mg doping of electron blocking layer on basic properties of laser diodes. It is found that an increase of injection efficiency allows to reduce the doping level in an electron blocking layer and take advantage of decreased optical losses.