Effect of the Nitrogen Incorporation on the Microstructure and Photoelectric Properties of N Type Nanocrystalline Silicon Thin Films.

N type silicon-rich nanocrystalline-SiN(x) ∶ H films were prepared by plasma enhanced chemical vapor deposition technique by changing NH3 flow rate. The effect of nitrogen incorporation on the microstructure and photoelectric properties of the thin films were characterized by Raman, Fourier transform infrared spectroscopy, ultraviolet-visible absorption spectra, and Hall effect measurement. The results indicated that with the increasing NH3, a phase transition from microcrystalline to amorphous silicon occured. Transmission electron microscope observation revealed that the size of silicon quantum dots could be adjusted by varying the flow rate of NH3. The microstructure order of the films reduced with increasing the flow rate of NH3, while the optical band gap increased, and the optical band tail became narrow. Meanwhile, Si­N bonds density increased and P doping was blocked. I-V testing results showed that with increasing NH3, the conductivity of films first decreased compared with nanocrystalline-Si and then increased. These behaviors reveal a competition in the mechanisms controlling the conductivity. However, with further increasing NH3, the conductivity decreased significantly due to rapid carrier recombination on the amorphous net structure.

Mechanical Properties and Failure Behavior of 3D-SiCf/SiC Composites with Different Interphases.

Continuous silicon carbide fiber-reinforced silicon carbide ceramic matrix composites (SiCf/SiC) are promising as thermal structural materials. In this work, the microstructure and static mechanical properties of 3D-SiCf/SiC with PyC, SiC, and PyC/SiC and without an interface prepared via polymer infiltration and pyrolysis (PIP) were investigated systematically in this paper. The results show that the microstructure and static mechanical properties of SiCf/SiC with an interphase layer were superior to the composites without an interlayer, and the interface debondings are existing in the composite without an interphase, resulting in a weak interface bonding. When the interphase is introduced, the interfacial shear strength is improved, the crack can be deflected, and the fracture energy can be absorbed. Meanwhile, the shear strength of the composites with PyC and PyC/SiC interfaces was 118 MPa and 124 MPa, respectively, and showing little difference in bending properties. This indicates that the sublayer SiC of the PyC/SiC multilayer interface limits the binding state and the plastic deformation of PyC interphase, and it is helpful to improve the mechanical properties of SiCf/SiC.