Thin film growth and microstructure analysis of CeO₂ prepared by MOCVD

Abstract

CeOz thin films were prepared by metal-organic chemical vapor deposition (MOCVD) using tetrakis(2,2,6,6-tetramethyl-3,5-heptanedionato)cerium(iv), [Ce(thd)4], as the precursor. The films were grown in a horizontal cold-wall reactor at low pressure and temperatures of 400-900 "C in an atmosphere of argonloxygen. SrTi03, yttria stabilized zirconia (YSZ), and MgO were used as substrates. Films were prepared on single crystalline substrates with a (100) orientation as well as on polycrystalline YSZ. The film microstructure was investigated by X-ray diffraction and the surface morphology was studied by scanning electron microscopy (SEM). The growth rate was determined using data obtained by profilometry and cross-section SEM. The films are polycrystalline with a (100) preferential orientation with respect to the substrate orientation. Low oxygen partial pressures deteriorated the crystalline quality. The SEM images of the surface and the cross sections demonstrated a columnar microstructure. The growth rates in the range of 25-250 nmlh were strongly dependent on the precursor feeding rate but less affected by the deposition temperature and substrate material.

Gadolinia Doped Ceria Thin Films Prepared by Aerosol Assisted Chemical Vapor Deposition and Applications in Intermediate‐Temperature Solid Oxide Fuel Cells

“…According to X-ray diffraction, amorphous thin films were deposited on sapphire substrates at 400 C, while polycrystalline cubic Gd 2 O 3 films with a preferred (100) orientation were obtained between 450 and 550 C. However, no signs of thin film growth were detected for deposition from Ce(acac) 4 at temperatures between 400 and 500 C after 1 h. This is in contrast to literature reports on the deposition of ceria thin films by ultrasonic spray pyrolysis from the same precursor at growth rates of up to 40 nm min ±1 at 425 C [29,30]. Most other studies on chemical vapor deposition of ceria [19,22,23,31,32] and gadolinia [33], however, are based on tetramethylheptanedionate precursors. To avoid complications by ligand exchange reactions in the precursor solution, both Gd(tmhd) 3 and Ce(tmhd) 4 were applied in the following.…”

“…While a thermally activated regime is observed for the growth rates of GDC in Figure 2, a clear transition from surface reaction limited to mass transport (gas phase diffusion) limited deposition as reported for AA-CVD of yttria stabilized zirconia in a previous study [24] is not evident. The decreasing growth rates at temperatures above 450 C may indicate the instability of the volatile metal precursors at these temperatures [19] or competing reactions like particle formation in the gas phase [20,35]. Film thicknesses were also derived using Rutherford Backscattering (RBS), which resulted in approximately 30% lower values than determined from SEM cross-sections.…”

Nucleation and Growth of Nanophasic CeO2 Thin Films by Plasma‐Enhanced CVD

“…[6,10,11] Further interest in CeO 2 -based materials is related to their use in the fields of optics and optoelectronics, [5,12±14] and in the preparation of solid electrolytes for fuel cells operating at moderate temperatures (400±600 C). [3] The most remarkable application of CeO 2 systems is in the preparation of three-way catalysts (TWCs), used in the control of automotive exhaust emissions.…”

“…Thanks to their chemical and physical characteristics, [6] ceria thin films have many successful technological applications such as silicon on insulator (SOI) structures, [7,8] high storage capacitor devices, [9] and buffer layers for high-T c superconducting (HTS) films on oxide substrates. [6,10,11] Further interest in CeO 2 -based materials is related to their use in the fields of optics and optoelectronics, [5,12±14] and in the preparation of solid electrolytes for fuel cells operating at moderate temperatures (400±600 C).…”

Preparation of (100)-oriented CeO2 film on (100) MgO single crystal substrate by laser chemical vapor deposition using solid precursor

“…Ceria (CeO 2 ) film is a potential candidate because it has a fluorite structure (a ¼ 5.411 Å) with a small lattice mismatch of 1% between CeO 2 (100) and YBCO (110) planes. For preparation of CeO 2 film, various approaches such as pulsed laser deposition [3], magnetron sputtering [4], electron-beam evaporation [5], and metalorganic chemical vapor deposition (MOCVD) [6][7][8][9][10][11] have been developed, among which MOCVD is a promising approach due to the conformal coverage, deposition of complex shape and controllability of the preferred orientation [6][7][8][9][10][11]. Recently, a novel approach of laser enhanced MOCVD (termed laser CVD) has been developed to prepare the CeO 2 film.…”