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We report observations of microstructural changes in {100} and {110} oriented silicon wafers during initial lithiation under relatively high current densities. Evolution of the microstructure during lithiation was found to depend on the crystallographic orientation of the silicon wafers. In {110} silicon wafers, the phase boundary between silicon and LixSi remained flat and parallel to the surface. In contrast, lithiation of the {100} oriented substrate resulted in a complex vein-like microstructure of LixSi in a crystalline silicon matrix. A simple calculation demonstrates that the formation of such structures is energetically unfavorable in the absence of defects due to the large hydrostatic stresses that develop. However, TEM observations revealed micro-cracks in the {100} silicon wafer, which can create fast diffusion paths for lithium and contribute to the formation of a complex vein-like LixSi network. This defect-induced microstructure can significantly affect the subsequent delithiation and following cycles, resulting in degradation of the electrode., Engineering and Applied Sciences

The frequency response of all oxide field-effect transistors with amorphous LaAlO3 on a crystalline SrTiO3 substrate is reported. The intrinsic cut-off frequencies of 4 μm gate-length devices are found to be approximately 17 MHz indicating that with gate length scaling gigahertz cut-off frequency is possible. The low cut-off frequency is primarily limited by the low effective mobility. The estimated effective mobility value determined from the S-parameter measurement is 3.8 cm2/Vs, which is consistent with previous reports. Small-signal equivalent circuit model parameters are extracted by fitting to on-wafer measured S-parameters. Good agreement is obtained between measured and simulated S-parameters based on the equivalent circuit model., Chemistry and Chemical Biology