Mr, Bin Li is a Senior Scientist in Shanghai Institute of Technical Physics, Chinese Academy of Sciences. His research focuses into infrared coating materials and infrared-transmitting materials, including rare-earth fluorides, oxides and narrow gap semiconductors
Although some rare-earth fluorides were currently used in infrared antireflection as low-index evaporation materials in order to substitute for radioactive thorium fluoride (ThF4), the higher tensile stress presented in the layers will deteriorate the reliability and durability of the interference multilayers. Stress in the layers significantly influence not only the mechanical performance of interference multilayers such as thermal cycling life and fatigue properties but also their optical behaviors due to cracking or interfacial delamination. Most importantly, any bending or deformation of the substrate caused by stress will also affect the performance of the antireflection coatings. Therefore, the relief of the stress in the layers is a critical process. The stress in the film after the deposition process is the sum of three different types of contributions. First, there is the intrinsic stress evolving in the layer during deposition. Secondly, the thermal stress appears during the cooling process, caused by a mismatch between the coefficients of thermal expansion of the substrates and the materials deposited. Finally, the adsorptive stress occurs once the finished coating is open to air with the adsorption of moisture and impurities. The magnitude of stress can vary depending on the conditions of deposition. Since the substrate materials, deposition process, moreover, the difference between the deposition temperature and the ambient temperature, were completely controlled to be identical, only the contribution resulting from intrinsic stress is basically related to the chemical composition of the films. In our investigation, a new infrared low-index evaporation material, the admixture of praseodymium fluoride (PrF3) with barium fluoride (BaF2) was exploited. The stresses in thin films deposited on Si strips using electron beam evaporation from the sintered pellets of PrF3 admixed with a different amount of BaF2 were measured. It is disclosed that the stresses in the layers of PrF3 can be greatly reduced with the increasing amount of BaF2 in thin films.
Prof. Jing Lu has her expertise in surface modification of nano carbon materials and the corresponding application fields. After got her PHD degree in Material Science, she worked in Mechanical Engineering and focused the research on ultra-precision machining of wide bandgap semiconductor. She has developed a novel method to coat diamond core with oxide shell and significantly improve the interface bonding between the abrasive and the polymer marix. The related achievement have been published in Nano letters, Nanotechnology, Carbon, and et al.
The semi-fixed abrasive polishing film which was based on sol-gel (SG) technology exhibited favorable machining performance in processing semiconductor power device materials. Compared to the fixed diamond abrasive tool, SG semi-fixed diamond abrasive tool could easily obtain a smooth and scratch-free surface with nanometer scale roughness due to the effect of abrasive yielding. However, the strength of SG polishing film is relatively low which restrains its further development. Graphene is a two dimensional material of carbon atoms in a hexagonal arrangement with remarkable mechanical and electrical properties, high thermal conductivity, specific surface area and good compatibility. Therefore, it is widely used in a range of applications, such as electronics, solar cells and electrochemical sensors, especially as a multifunctional nanofiller. Compared with graphene, Graphene oxide (GO) has excellent mechanical properties, favorable compatibility and solubility. In this paper, graphene oxide (GO) was used to enhance the strength of the polishing film which was fabricated from sodium alginate. The dispersing stability of the GO, microstructure and tensile strength of the polishing film have been investigated by Zetasizer, three-dimension optical microscope, FTIR spectroscopy, scanning electron microscope and electronic universal testing machine. The results revealed that diamond abrasives, sodium alginate and graphene oxide could mix with each other homogeneously and the mechanical properties of the as-prepared films were improved significantly over that of the pure SG polishing film. The tensile strength of the SG film with GO increased by 52.67%, 63.13%, 28.28% compared to sheer SG film when the concentration of GO was 0.01 wt%, 0.05 wt%, 0.10 wt%, respectively. Furthermore, the addition of graphene oxide facilitated the interfacial interaction between GO sheets and polymer matrix.