Nasr-Eddine Mekkakia-Maaza

Black silicon (BSi) is an important texturized form of a semiconducting material used in photovoltaic solar cell technology. It is characterized by surface structuration of silicon with very low reflectance. In this paper, we study the optical properties of black silicon in the visible-near infrared wavelength range. Our work focuses on texturing the silicon surface using cryogenic etching in an inductively coupled plasma (ICP) system. The surface structure of black silicon is formed by varying several parameters of the cryo-etching process, like wafer temperature, / ratio and bias voltage. The microstructure surfaces of BSi can be formed in various shapes (Pyramids, Columns, and Cones forms). The optical properties of the micro-structures were studied by spectrophotometer measurements. The results obtained show that columnar microstructures (CMS) exhibit different texturing shapes under different plasma etching process conditions. The CMS obtained without HF chemical treatment process have a reflectance value as high as about 14%. However, the surface reflectance is reduced to less than 2% in the VIS-NIR range by processing the samples in HF solution.

Due to the development of microfluidic systems biomedical microelectromechanical systems (BioMEMS) for magnetic labelling detection by magnetic microbeads circling in microfluidic channels, we used the magnetic field created by microcoils. The magnetic field associated with the electric current, but with negatively affects if its value increases too much. Handling bio-species in the microfluidic chip requires that the temperature maintained to keep the cells to prevent their destruction. In this paper we have described the spiral square coil design of different structures to produce an effective magnetic flux density. The simulation of the magnetic flux density is carried out with the help of the COMSOL software. We have presented an optimization of the geometric parameters of the microcoil for a better performance and a miniaturization of the structure with copper wire section S=25 µm2 and inter-wire space a=5 µm. We have also developed this microcoil by adding a ferromagnetic core to the inner center, the results obtained in this work shown that the magnetic flux density increases around 1.07 times in Bx and 1.45 times in Bz. This new approach in designing a microcoil allows to obtaining a fast trapping of the microbeads and a highly sensitive biological element detection and avoiding increase heat ratio in microfluidic systems.