Synthesis and characterization of zinc oxide nanomaterials through horizontal vapor phase crystal growth

• Main Author: Ladines, Alvin Noe C.
• Format: text
• Language: English
• Published: Animo Repository 2008
• Online Access: https://animorepository.dlsu.edu.ph/etd_masteral/3737
• Institution: De La Salle University

Zinc Oxide (ZnO) nanomaterials were grown on glass substrate through the horizontal vapor phase crystal growth. ZnO powder with 99.999% purity obtained from Sigma Aldrich Singapore Pte Ltd was used as the source material. The phase transition of the ZnO powder was first examined using differential thermal analysis and from this, the growth conditions were set. Approximately 35 mg of the source material was loaded into an ultrasonically cleaned quartz tube, which is evacuated and sealed at a pressure of 10-6 Torr. The quartz tube was set in a horizontal tube furnace such that a maximum temperature gradient exists along the length of the tube. The effect of growth temperature on the synthesis of ZnO nanomaterials was investigated by adjusting the growth temperature from 600oC to 1200oC in 200oC increments. The source material was heated for 2 hours, 4 hours, 6 hours and 8 hours to determine the effect of dwell time on the growth of the nanostructures. Lastly, the ramp rate was adjusted from slow (80 minutes) to fast (20 minutes) to examine its effect on the structure of ZnO nanomaterials. The white-gray material retrieved 5-10 cm from the end of the quartz tube containing the source material was subjected to scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDX) analyses, photoluminescence (PL) measurements, and x-ray diffraction (XRD) without further treatments. The SEM images revealed that various nanostructures including nanowires, belt-like, needle-like, and blade-like structures were synthesized. ii Higher growth temperature resulted in the formation of nanostructures that have larger widths while longer dwell time corresponded in the growth of longer nanamaterials. Defects in the structure of the nanomaterials and ZnO agglomerates were observed when the ramp rate is increased. The EDX analyses confirmed that the nanomaterials were ZnO with oxygen vacancies that depended on the growth condition. A Zn:O atomic ratio of 1:1 was found in the nanomaterial synthesized at a growth temperature of 800oC, dwell time of 8 hours and slow ramp rate. The PL spectra of the samples examined revealed intense UV peaks in the range of 317-384 nm with weak emissions in the visible-light spectrum. It was found that optical properties of the synthesized nanomaterials depend on the growth parameters being investigated. The XRD investigation revealed that growth in the (001), (101) and (101) directions are prominent indicating that the grown nanomaterials are polycrystalline. This can be verified from the SEM images of the synthesized nanomaterials. It is proposed that the growth mechanism involved in the synthesis of ZnO nanomaterials through horizontal vapor phase crystal growth is vapor-solid (VS) since no catalyst was used. The growth involves two stages; nucleation of ZnO molecules on the glass substrate and growth.