Indentation-induced phase transformation processes were studied by in situ Raman microspectroscopy of the deformed contact region of silicon on sapphire samples during contact loading and unloading. During loading, the formation of Si-II and another phase, indentified as the bct5 structure, was observed, thus providing experimental evidence for both the existence of the bct5 phase and the possibility of generating this phase under indentation conditions. The pressure dependence of the Raman phonon frequencies for the bct5 modes was determined. During unloading, the transformation of the bct5 phase into the metastable bc8 (Si-III) and r8 (Si-XII) structures was observed. The measurements indicated that bc8 can form simultaneously with the r8 structure in indentation tests rather than subsequently from r8 in a separate process as previously assumed.

In this work, we describe a facile approach to improve the robustness of conductive mesoporous carbon-based thin films by the addition of silica to the matrix through the triconstituent organic–inorganic–organic co-assembly of resol (carbon precursor) and tetraethylorthosilicate (silica precursor) with triblock-copolymer Pluronic F127. The pyrolysis of the resol–silica–pluronic F127 film yields a porous composite thin film with well-defined mesostructure. X-Ray diffraction (XRD), grazing incidence small angle X-ray scattering (GISAXS), and electron microscopy measurements indicate that the obtained carbon-based thin films have a highly ordered orthorhombic mesostructure (Fmmm) with uniform large pore size (∼3 nm). The orthorhombic mesostructure is oriented and the (010) plane is parallel to the silicon wafer substrate. The addition of silica to the matrix impacts the pore size, surface area, porosity, modulus and conductivity. For composite films with approximately 40 wt% silica, the conductivity is decreased by approximately an order of magnitude in comparison to a pure carbon mesoporous film, but the conductivity is comparable to typical printed carbon inks used in electrochemical sensing, ∼10 S cm⁻¹. The mechanical properties of these mesoporous silica–carbon hybrid films are similar to the pure carbon analogs with a Young's modulus between 10 GPa and 15 GPa, but the material is significantly more porous. Moreover, the addition of silica to the matrix appears to improve the adhesion of the mesoporous film to a silicon wafer. These mesoporous silica–carbon composite films have appropriate characteristics for use in sensing applications.