Growth and characterization of well-aligned densely-packed rutile TiO2 nanocrystals on sapphire (100) and (012) substrates by reactive magnetron sputtering

Well-aligned densely-packed rutile phase TiO2 nanocrystals (NCs) have been grown on sapphire (100) and (012) substrates by reactive magnetron sputtering using Ti metal target. The surface morphology, structural and spectroscopic properties of the as-deposited NCs were characterized using field-emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and micro-Raman spectroscopy. FESEM micrographs reveal the growth of vertically aligned NCs on sapphire (100), whereas the NCs on sapphire (012) were grown with a tilt angle of ∼ 33° from the normal to substrate. The XRD results reveal TiO2 NCs with either (002) orientation on sapphire (100) substrate or (101) orientation on sapphire (012) substrate. A strong substrate effect on the alignment of the TiO2 NCs growth has been demonstrated and the probable mechanism for the formation of these NCs has been discussed. XPS analyses show the oxygen vs. titanium ratio of 2.0 ± 0.1 for the as-grown TiO2 NCs. Raman spectra of NCs exhibit a slight redshift in the peak position and a small broadening in linewidth with respect to that of the bulk counterpart. The results indicate the formation of good quality of nanocrystalline rutile phase TiO2.