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Title: Synthesis of Ce(IV) and Ti(IV) alkoxides for use as precursors for MOCVD and ALD
Author: Wrench, Jacqueline Samantha
ISNI:       0000 0004 2734 7768
Awarding Body: University of Liverpool
Current Institution: University of Liverpool
Date of Award: 2011
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A synthetic route for the general synthesis of Ce(IV) alkoxides is described utilising a reaction with eerie ammonium nitrate and tert-butoxide 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. [Cetdmae)»] was shown to decompose over time and gave a crystal structure of the cluster [Ce14(dmae)22(N03)2O14(OH)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 β-diketonate ligand (thd, dbm) with the complexes [Ce(rnmp)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)(L)2] (L=dbm, dmom, dmomp) and [Ce(dmap)2(dbm)2]. The reaction between [Ce(mmp)4] and 2 equivalents of dmop gave the dimer [Ce2(mmp)2(dmop)4O] 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 Ce02 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 QC for MOCVD. [Ce(dmap)4] showed growth at temperatures as low as 100 QC in ALD though was susceptible to decomposition via CVD processes at 250 QC. [Ce(mmp)4] was self-limiting over the temperature range of 150-350 QC. A range of heteroleptic Ti(IV) alkoxide complexes were also synthesised by reaction of either [Ti(OBut)4] or [Ti(OPri)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 = But, Pri, L = dmae, mmp, dmop, dmom). [Ti(OPri)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(OPri)2( dmae )2] provided the optimum conditions of growth on both substrates at 450 QC for 180 minutes giving full coverage and uniform nanostructures. The precursor also interestingly grew nanorods at 600 QC on Si(100).
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral