High resolution X-ray diffraction studies of epitaxial ZnO nanorods grown by reactive sputtering

Vertically aligned and highly c-axis oriented ZnO nanorods were epitaxially grown on c-sapphire by dc reactive sputtering of zinc target in argon-oxygen atmosphere. Scanning electron microscopy shows that substrate temperature critically controls the morphology of sputtered ZnO films, eventually causing the formation of laterally oriented ZnO nanorods at higher temperatures (700 degrees C-750 degrees C), as confirmed by phi-scan measurements. High resolution X-ray diffraction was used to obtain the micro-structural parameters of ZnO columnar films/nanorods from Williamson-Hall plots of omega and omega-2 theta scans, and rocking curves of asymmetric reflections. These results show that epitaxially grown ZnO nanorods exhibit substantially superior micro-structural parameters, namely, tilt (0.4 degrees), twist (0.5 degrees), and microstrain (4 x 10(-4)), compared to columnar ZnO films grown at 500 degrees C-600 degrees C. The reciprocal space maps of (0002), (0004), (10 (1) over bar1), (10 (1) over bar4); and (11 (2) over bar0) planes of ZnO nanorods were carried out to obtain the lattice parameters of epitaxial ZnO nanorods and calculate lattice strain (9 x 10(-4), for both "a" and "c"), which indicates the absence of biaxial strain. Room temperature photoluminescence of epitaxial ZnO nanorods shows a strong near-band-edge emission along with negligible defect emission, owing to their high crystalline quality and micro-structural parameters. Published by AIP Publishing.