CERIUM ALKOXIDES

Ce(hfip)4(TMEDA), Ce(hfip)4(diglyme) for CeO2, CeF3 CVD

Cerium tetrafluoroisopropoxide adducts with TMEDA (Ce(hfip)4(TMEDA)) and diglyme (Ce(hfip)4(diglyme)) have been synthesized and their molecular structures were established by single crystal XRD.

(Ce(hfip)4(TMEDA)) and (Ce(hfip)4(diglyme)) have been applied for the MOCVD growth of CeO2 and CeF3 films on glass substrates; the films were characterized by XPS, XRD, SEM and UV–Vis spectroscopy. [[i][]

[i] Stephane Daniele, Liliane G. Hubert-Pfalzgraf, and Monique Perrin

Polyhedron, Volume 21, Issue 20, 1 September 2002, Pages 1985-1990

Cerium tetrakis(dimethylisopropylcarbinolate) Ce(OCMe2iPr)4

Cerium tetrakis(dimethylisopropylcarbinolate) Ce(OCMe2iPr)4, a homoleptic cerium alkoxide, is liquid having a low boiling point and good thermal stability. It crystallizes as a dimer from the neat liquid (see below) when it is stored in the freezer but the crystals melt at approximately 20 °C.

Properties:

Ce(OCMe2-i-Pr)4 : yellow liquid (purification by vacuum distillation), mp. ~20°C, bp 123 °C/10-2 Torr; reported bp 132 °C/0.05 Torr)20 , typically 50-60% yield on a 10-g scale. 1H NMR (C6D6): ä 1.04 (d, 6, J ) 6.9 Hz, OCMe2CHMe2), 1.25 (s, 6, OCMe2CHMe2), 1.67 (sept, 1, J ) 6.9 Hz, OCMe2CHMe2). 13C NMR (C6D6): ä 19, 29, 41, 86.

Synthesis:

Two possible routes of preparation of Ce(OCMe2iPr)4 are known:

Alkoxide/alcohol exchange [Ce(OiPr)4(HOiPr)]2 +4 HOCMe2-i-Pr => Ce(OCMe2-i-Pr)4 [ Bradley, Chatterjee, and Wardlaw ]

Methathesis of cerium-ammonium nitrate with corresponding sodium alkoxide (NH4)2Ce(NO3)6+ 6NaOCMe2iPr => Ce(OCMe2iPr)4 + 6NaNO3+ 2NH3+2HOCMe2iPr , yield 50-60% after vacuum distillation.

[route based on method reported by Gradeff et al.21,22 as later modified by Evans et al.23 and Caulton et al.24 ].

Ce(OCMe2iPr)4 for CeO2 films by MOCVD

The precursor container was maintained at 84-85 °C, and precursor feed lines at 95 to 142 °C; 150-200sccm Ar carrier gas and dilution flow (800 sccm Ar) was used before entering the reactor; the typical deposition pressure was 1.0-1.1 Torr. Growth temperatures were typically 270-530 °C. In case of LAO and textured Ni substrates, oxygen (200 sccm) was added just before entering the reactor.

Ce(OCMe2-i-Pr)4 has been applied as single source precursor (without addition of O2) for low-pressure MOCVD of shiny CeO2 films on silicon (Si (100) or (111)), glass and quartz substrates at substrate temperatures of 330-530 °C (no films were formed at 270°C). When O2 was applied as a co-reactant, ceria film formed at 270 °C but none were grown at 230 °C. Film composition in all cases was O/Ce = 2.2 (RBS data), growth rates varied from 11 to 14 nm/min (increasing from 270 to 530°C).

Ce(OCMe2-i-Pr)4 with added O2 as co-reactant formed , formed highly oriented films on LAO (001) at substrate temperatures 500-650 °C (on the roll-textured Ni (001) substrates at the temperatures 450-900 °C) and system pressure 2.0-2.5 Torr. The grown films were annealed under Ar/O2 flow at the deposition temperature for 1 h [[i]]

[i] Seigi Suh, Jun Guan, Liliana A. Mıˆinea, Jean-Se´bastien M. Lehn, and David M. Hoffman, Chem. Mater. 2004, 16, 1667-1673, « Chemical Vapor Deposition of Cerium Oxide Films from a Cerium Alkoxide Precursor »

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