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The nature of structural changes of nanosecond laser modification inside silicon is investigated. Raman spectroscopy and transmission electron microscopy measurements of cross sections of the modified channels reveal highly localized crystal deformation. Raman spectroscopy measurements prove the existence of amorphous silicon inside nanosecond laser induced modifications, and the percentage of amorphous silicon is calculated based on the Raman spectrum. For the first time, the high-resolution transmission electron microscopy images directly show the appearance of amorphous silicon inside nanosecond laser induced modifications, which corroborates the indirect measurements from Raman spectroscopy. The laser modified channel consists of a small amount of amorphous silicon embedded in a disturbed crystal structure accompanied by strain. This finding may explain the origin of the positive refractive index change associated with the written channels that may serve as optical waveguides. 

Refractory materials hold great promise to develop functional multilayer coating for extreme environments and temperature applications but require high temperature and complex synthesis to overcome their strong atomic bonding and form a multilayer structure. Here, a spontaneous reaction producing sophisticated multilayer refractory carbide coatings on carbon fiber (CF) is reported. This approach utilizes a relatively low-temperature (950 °C) moltensalt process for forming refractory carbides. The reaction of titanium (Ti), chromium (Cr), and CF yields a complex, high-quality multilayer carbide coating composed of 1) Cr carbide (Cr3C2), 2) Ti carbide, and 3) Cr3C2 layers. The layered sequence arises from a difference in metal dissolutions, reactions, and diffusion rates in the salt media. The multilayer-coated CFs act as a permeable oxidation barrier with no crystalline degradation of the CFs after extreme temperature (1,200 °C) and environment (oxyacetylene flame) exposure. The synthesis of high-quality multilayer refractory coating in a fast, efficient, easy, and clean manner may answer the need for industrial applications that develop cheap and reliable extreme environment protection barriers. 

The concept for fabrication of waveguides by an in‐volume laser direct writing in single‐crystal silicon is explored using a nanosecond pulse laser. The key innovation of this technology relies on the generation of amorphous silicon, which has a higher refractive index than that of crystalline silicon. Herein, transmission electron microscopy (TEM) together with selected area electron diffraction (SAED) and high‐resolution TEM (HRTEM) characterizations are used to better understand the microstructural evolutions. TEM images reveal the core‐shell structures, while SAED patterns and HRTEM directly observe the presence of amorphous silicon in the core surrounded by a crystalline silicon shell. With a lower laser scanning speed, a higher density of defects yet less amorphous silicon is formed by laser direct writing. 

Abstract A novel high‐temperature laser shock peening (HT‐LSP) process was applied to polycrystalline α‐SiC to improve the mechanical performance. HT‐LSP prevents microcrack formation on the surface while induces plastic deformation in the form of dislocation slip on the basal planes, which may be caused by the combination of high shock pressure and a lower critical resolved shear stress at 1000℃. A maximum compressive residual stress of 650 MPa, measured with Raman spectroscopy, was introduced into the surface of α‐SiC by HT‐LSP, which can increase the nanohardness and in‐plane fracture toughness of α‐SiC by 8% and 36%, respectively. This work presents a fundamental base for the promising applications of HT‐LSP to brittle ceramics to increase their plasticity and mechanical properties.