Initial growth stages of CeO 2 nanosystems by Plasma-Enhanced Chemical Vapor Deposition
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Initial growth stages of CeO2 nanosystems by Plasma-Enhanced Chemical Vapor Deposition Davide Barreca1, Alberto Gasparotto1, Eugenio Tondello1, Stefano Polizzi2, Alvise Benedetti2, Cinzia Sada3, Giovanni Bruno4, Maria Losurdo4 1 ISTM-CNR and CIMA Department, Padova University, Via Marzolo, 1 - 35131 Padova, Italy. 2 Physical Chemistry Department, Ca' Foscari Venice University, Via Torino, 155/B - 30170 Venezia-Mestre, Italy. 3 INFM and Physics Department, Padova University, Via Marzolo, 8 - 35131 Padova, Italy. 4 IMIP-CNR, via Orabona, 4 - 70126 Bari, Italy.
ABSTRACT Nanocrystalline CeO2 thin films were synthesized by Plasma-Enhanced Chemical Vapor Deposition using Ce(dpm)4 as precursor. Film growth was accomplished at 150-300°C either in Ar or in Ar-O2 plasmas on SiO2 and Si(100) with the aim of studying the effects of substrate temperature and O2 content on coating characteristics. Film microstructure as a function of the synthesis conditions was investigated by Glancing Incidence X-Ray Diffraction (GIXRD) and Transmission Electron Microscopy (TEM), while surface morphology was analyzed by Atomic Force Microscopy (AFM). Surface and in-depth chemical composition was studied by X-ray Photoelectron Spectroscopy (XPS) and Secondary Ion Mass Spectrometry (SIMS).
INTRODUCTION Cerium dioxide (CeO2) thin films are interesting candidates for different technological applications [1], the most important being the preparation of Three-Way Catalysts (TWCs) [2]. In particular, the interest has been recently focused on oxygen-deficient ceria-based nanosystems [3]. As a matter of fact, the synergy between the peculiar nanosystem properties and the copresence of Ce(III)/Ce(IV) might eventually allow the preparation of TWCs without noble metals, thus reducing their environmental impact [2]. In order to fully exploit the nanosystem potential, a major concern regards the possibility of tailoring their composition, microstructure and morphology. In this context, Plasma-Enhanced Chemical Vapor Deposition (PE-CVD) offers important advantages over other preparation techniques, allowing the synthesis of nanosystems under non-equilibrium conditions, where nucleation is predominant over the subsequent aggregate growth. The present work is focused on the synthesis of nanocrystalline CeO2-based thin films by PE-CVD, with particular attention to the first nucleation stages. Ce(dpm)4 (Hdpm = 2,2-6,6tetramethyl-3,5-heptanedione) was chosen as precursor compound and its fragmentation behavior was preliminarily investigated by Electron Impact Mass Spectrometry (EI-MS). The films were deposited on SiO2 and Si(100) in Ar and Ar-O2 plasmas. The most relevant results concerning the sample properties and their dependence on synthesis conditions are presented and discussed.
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EXPERIMENTAL DETAILS Ceria films were deposited by a custom-built PE-CVD reactor described elsewhere [4]. RF power (13.56 MHz) was delivered to one electrode, while the substrates were placed on a second grounded electrode. The precursor (Ce(dpm)4, Strem Chemi
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