Silicon nanomaterials are also popular since they can be synthesized on a large scale and inexpensively by several methods, and in various morphologies including silicon nanowires (SiNWs), nanorods, nanobelts, and nanoparticles. Quasi-one-dimensional (1D) SiNW semiconductors have attracted much attention because of their distinctive optical, electronic, and mechanical properties, suitable for modern applications in electron field emission due to their high electron mobility. Recently, there has been an increase in applications of quasi-1D SiNWs due to their compatibility with existing semiconductor technology, evidenced by the successful incorporation of SiNWs in field-effect transistors and in UHD full-color flat panel displays. This chapter shows that bare SiNWs possess good Electron Field Emitters (EFE) properties; nevertheless they can be significantly enhanced by growing ultrananocrystalline diamond (UNCD) on the SiNWs. The SiNWs were coated with UNCD by using a hot filament chemical vapor deposition (HF-CVD) process.