Synthesis of Ce(IV) and Ti(IV) alkoxides for use as precursors for MOCVD and ALD

J.S. Wrench
Abstract & Cover

A synthetic route for the general synthesis of Ce(IV) alkoxides is described utilising a reaction with ceric ammonium nitrate and fe/Abutoxide to create the in situ intermediate [Ce(OBut)4] by means of salt metathesis. A further alkoxy exchange reaction with the desired alkoxide resulted in the formation of alkoxide complexes [Ce(L)4] (L = mmp, dmae, dmap, dmop, dmomp). The compounds [Ce(mmp)4], [Ce(dmap)4] and [Ce(dmop)4] were characterised crystallographically. [Ce(dmae)4] was shown to decompose over time and gave a crystal structure of the cluster [Cei4(dmae)22(N03)20i4(0H)4]. DmomH was found to be an unsuitable ligand for the formation of a homoleptic complex. A range of heteroleptic complexes were also synthesised by reaction of 2 equivalents of an alkoxide (dmop, dmom, dmomp) or P-diketonate ligand (thd, dbm) with the complexes [Ce(mmp)4] and [Ce(dmap)4]. The thd ligand was found to be too strong a donor to make a heteroleptic complex resulting exclusively in the formation of [Ce(thd)4]. These reactions yielded the complexes [Ce(mmp)2(L)2] (L=dbm, dmom, dmomp) and [Ce(dmap)2(dbm)2]. The reaction between [Ce(mmp)4] and 2 equivalents ofdmop gave the dimer [Ce2(mmp)2(dmop)40] which was characterised crystallographically. [Ce(mmp)4] and [Ce(dmap)4] were tested for use as precursors for the liquid injection MOCVD and ALD of CeCh thin films on a Si(100) substrate. The results were compared with the known precursors [Ce(thd)4] and [Ce(OC(CH3)2Pr')4], [Ce(thd)4] being the most commonly used precursor for Ce02 thin film growth. Both new precursors were found to be more volatile and have a temperature window of 200-600 °C for MOCVD. [Ce(dmap)4] showed growth at temperatures as low as 100 °C in ALD though was susceptible to decomposition via CVD processes at 250 °C. [Ce(mmp)4] was self-limiting over the temperature range of 150-350 °C. A range of heteroleptic Ti(IV) alkoxide complexes were also synthesised by reaction of either [T^OBu^] or [Ti(OPrl)4] with 2 equivalents of the desired alkoxide in an alkoxy exchange reaction to give complexes with the formula [Ti(OR)2(L)2] (R = Bu1, Pr1, L - dmae, mmp, dmop, dmom). [Ti(OPr1)2(dmop)2] and [Ti(OBut)2(dmop)2] were characterised crystallographically. These compounds were used as precursors for the MOCVD of anatase Ti02 nanostructures on Si(100) and F-doped Sn02 substrates. [Ti(OPr1)2(dmae)2] provided the optimum conditions of growth on both substrates at 450 °C for 180 minutes giving full coverage and uniform nanostructures. The precursor also interestingly grew nanorods at 600 °C on Si(100)

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University of Liverpool
(Liverpool, United Kingdom)
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