Growth and characterization of well-aligned densely-packed rutile TiO ₂ nanocrystals on sapphire substrates via metal-organic chemical vapor deposition

Well-aligned densely-packed rutile TiO₂ nanocrystals (NCs) have been grown on sapphire (SA) (100) and (012) substrates via metal-organic chemical vapor deposition (MOCVD), using titanium-tetraisopropoxide (TTIP, Ti(OC₃H₇)₄) as a source reagent. The surface morphology as well as structural and spectroscopic properties of the as-deposited NCs were characterized using field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), selected-area electron diffractometry (SAED), x-ray diffraction (XRD) and micro-Raman spectroscopy. FESEM micrographs reveal that vertically aligned NCs were grown on SA(100), whereas the NCs on the SA(012) were grown with a tilt angle of ∼33° from the normal to substrates. TEM and SAED measurements showed that the TiO₂ NCs on SA(100) with square cross section have their long axis directed along the [001] direction. The XRD results reveal TiO ₂ NCs with either (002) orientation on SA(100) substrate or (101) orientation on SA(012) substrate. A strong substrate effect on the alignment of the growth of TiO₂ NCs has been demonstrated and the probable mechanism for the formation of these NCs has been discussed.