Abstract
Post-annealing treatment is a necessary process to create/eliminate/repair defects in self–assembly (SA) metal oxide by providing enough thermal energy to the O atoms to overcome the migration energy barrier in ZnO. The height of migration energy barrier is dependent on the depth from the surface, which is hard to be estimated by theoretical calculations, as well as the optical analyses. SA ZnO nanorods (ZNRs) have high surface-to-volume ratio to provide complete picture between the optical and surface properties obtained by photoluminescence (PL) and ultraviolet/X-ray photoemission spectroscopy (UPS/XPS), which is used to investigate the evolution of structure and chemical states of the surface layers to reveal mutual agreement on all observations in PL, XPS, and UPS. We demonstrate variation of the surface structure of SA-ZNRs by scanning over a range of annealing temperatures and time to regulate the structure variation of SA-ZNRs, and their optical analyses agrees well with PL, XPS and UPS, which indicates the dependence of migration energy barriers on the depth from the surface of ZNR. The results reveal the well ZNRs formed at 570 °C and the further oxidation process and the formation of hydroperoxide on the Zn-rich surface of ZNRs at 640 °C.
Highlights
Metal oxides and their nanostructures are popular subjects because of their applications in photoelectric [1], photo-catalytic [2], and gas/bio sensing [3,4] because of high surface-to-volume ratio that gives rise to typical surface effects
The evolution of structure and deficiencies would occur as annealing temperature crossover the threshold of migration energy barrier which is dependent on the depth from the surface
Nanomaterials 2018, 8, 811 generated at the higher annealing temperature (660 ◦C) and broaden the FWHM of X-ray photoemission spectroscopy (XPS) pattern, which caused by the migration/adsorption of oxygen atoms over the surface layer [23]
Summary
Metal oxides and their nanostructures are popular subjects because of their applications in photoelectric [1], photo-catalytic [2], and gas/bio sensing [3,4] because of high surface-to-volume ratio that gives rise to typical surface effects. The proper annealing temperature and its related treatment on the post-annealing process is not well determined since the energy barriers for eliminating defects on nanostructure should be dependent on the depth from the surface [9]. Based on the correlated response of PL and XPS analyses on ZNRs, it is possible to study the activation energy of ZNR surface by using the annealing treatment with variation in temperature and time. The evolution of structure and deficiencies would occur as annealing temperature crossover the threshold of migration energy barrier which is dependent on the depth from the surface. Tahte BpLh2o4toAn, eNnSeRrgRyCf.oTrhOe1pshXoPtoSnaennderZgny2fporXOPS1swXePrSe a6n25d aZnnd2p11X0P0SeVw,erreesp62e5ctaivnedly1,1a0n0detVh,ererespsuelcttsivoeflyX,PaSndwethre creasliublrtasteodf XwPitShwtheerepcealkiborfaCte1ds w(2i8th4.8theeVp).eTahkeopf hCo1tson(2e8n4e.8rgeyVf)o. rTUhePSphiso4to0neVenaenrdgythfoerreUsuPlStsisof40UePVS wanedrethcaelirbersautletsdoafgUaiPnSstwAeur4efc7a/li2br(a8t3e.9d eaVga).inst Au4f 7/2 (83.9 eV)
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