Single-crystal trigonal (t) Se nanobelts have been synthesized on a large scale by reducing SeO 2 with glucose at 160 °C. Electron microscopy images show that the nanobelts are ∼80 nm in diameter, ∼25 nm in thickness, and up to several hundreds of micrometers in length. HRTEM images prove that the nanobelts are single crystals and preferentially grow along the [001] direction. The time-dependent TEM images revealed that the formation and growth of t-Se nanobelts were governed by a solidsolution-solid growth mechanism. The redox reaction directly produced amorphous (R) Se nanoparticles under hydrothermal conditions. t-Se nanobelts were formed by dissolution and recrystallization of the initial R-Se nanoparticles under the functional capping of poly(vinylpyrrolidone) (PVP). The nanobelts obtained exhibit a quantum size effect in optical properties, showing a blue shift of the band gap and direct transitions relative to the values of bulk t-Se.

Chemical mechanical polishing (CMP), as a widely used planarization technology, requires high removal rate and low surface roughness generally. However, it is difficult to meet these requirements in a single-step polishing process. To get an ultrasmooth surface of the sapphire substrate, we investigated a two-step CMP of the sapphire substrate using ultrafine α-alumina-based slurry and nanoscale silica-based slurry. Also, in situ coefficient of friction (COF) measurements were conducted. The results show that during the first-step polishing in the alumina-based slurry, the COF decreases with polishing time first and then tends to be a constant; a relatively high material removal rate was reached, and the root-mean-square (rms) roughness value of the polished surface can be decreased from 968.9–21.98 Å. In the second-step CMP, the nanoscale silica slurry was adopted; the COF increased in the first minute of polishing and then became stable too, and the rms roughness of the sapphire substrate surfaces can be further reduced to 6.83 Å by using the optimized process parameters. In addition, the CMP mechanism of sapphire using the above two slurries was deduced and documented preliminarily.

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