Incoherent partial superposition modeling for single-shot angle-resolved ellipsometry measurement of thin films on transparent substrates.

Ellipsometric measurement of transparent samples suffers from substrate backside reflection challenges, including incoherent and partial superposition issues. The recently developed angle-resolved ellipsometry (ARE) can naturally eliminate the backside reflections of substrates with a micro-spot equivalent thickness or thicker; however, for thinner substrates, ARE working with general incoherent backside reflection models shows significant inaccuracy or measurement failure. In this paper, an incoherent partial superposition (IPS) model is proposed to characterize the optical superposition effect between the frontside and uncertain backside reflections from an unknown substrate. IPS introduces a cosine-like correction of the backside reflection, corresponding to the overlapping-area change of backside and frontside reflections along with incident angles. Benefiting from ARE's wide-angle spectral imaging capability, IPS achieves single-shot measurement of thin film thicknesses on transparent substrates of unknown thickness. An ARE system was built and calibrated regarding the linear relationship between the cosine-corrected angular frequencies and substrate thicknesses. Then, commercial ITO films on glasses of different thicknesses ranging from 200 to 1000 µm were measured. Experimental results show that IPS-ARE results in a root-mean-square accuracy error of ∼1 nm in film thickness measurement and provides a ∼77% error reduction from general incoherent backside reflection models.

Recent Progress on Wear-Resistant Materials: Designs, Properties, and Applications.

There has been tremendous interest in the development of different innovative wear-resistant materials, which can help to reduce energy losses resulted from friction and wear by ≈40% over the next 10-15 years. This paper provides a comprehensive review of the recent progress on designs, properties, and applications of wear-resistant materials, starting with an introduction of various advanced technologies for the fabrication of wear-resistant materials and anti-wear structures with their wear mechanisms. Typical strategies of surface engineering and matrix strengthening for the development of wear-resistant materials are then analyzed, focusing on the development of coatings, surface texturing, surface hardening, architecture, and the exploration of matrix compositions, microstructures, and reinforcements. Afterward, the relationship between the wear resistance of a material and its intrinsic properties including hardness, stiffness, strength, and cyclic plasticity is discussed with underlying mechanisms, such as the lattice distortion effect, bonding strength effect, grain size effect, precipitation effect, grain boundary effect, dislocation or twinning effect. A wide range of fundamental applications, specifically in aerospace components, automobile parts, wind turbines, micro-/nano-electromechanical systems, atomic force microscopes, and biomedical devices are highlighted. This review is concluded with prospects on challenges and future directions in this critical field.