Title
Pyramidal growth of ceria nanostructures by pulsed laser deposition
Author
E.S.Bârcă, M.Filipescu, C.Luculescu, R.Birjega, V.Ion, M.Dumitru, L.C.Nistor, G.Stanciu, M.Abrudeanu, C.Munteanu, M.Dinescu
Year
2016
Journal
Applied Surface Science
Abstract
We report in this paper on the deposition and characterization of CeO2 nanostructured thin films with hierarchical morphology. Micro-sized ceria powder (CeO2, 99.9% purity) was pressed to obtain a ceramic target. An ArF laser working at 193 nm irradiated the target in controlled oxygen gas flow at constant pressure (0.1 mbar). Silicon wafers used as substrates for thin films were heated at different temperatures, up to 773 K.
The influence of substrate temperature on the structure and surface morphology of ceria thin films was studied by X-ray diffraction (XRD), transmission electron microscopy (TEM), Raman spectroscopy and scanning electron microscopy (SEM). The refractive indices and information about roughness and thickness were revealed by spectroellipsometry.
Crystalline cubic ceria thin films exhibiting a hierarchical structure that combines columnar and dendritic growth were obtained at temperatures above 473 K. For the samples obtained at 773 K, columns ending in pyramidal formations with sharp edges and sizes of hundreds of nanometers were observed, indicating a high crystallinity of the layer. XRD analysis reveals a consistent increase of the X-ray coherence length/crystallite size along the [111] direction with increasing temperature. Using a semi-empirical formula, Raman crystallites sizes were calculated and it was found that size increases with the temperature increasing. The spectroellipsometry investigations evidenced the increasing of refractive index with the substrate temperature increase. High surface roughness and pyramidal structures were noticed from the atomic force microscopy images for layers deposited at substrate temperature above 473 K.
Instrument
NRS-7200
Keywords
Raman imaging microscopy, Ceria thin film, Pulsed laser deposition, Pyramidal growth, Crystalline cubic structure