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Title: Synthesis and evaluation of new molecular precursors for the chemical vapour deposition of electronic materials
Author: Hawken, Samantha Louise
ISNI:       0000 0004 7234 251X
Awarding Body: University of Southampton
Current Institution: University of Southampton
Date of Award: 2018
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MCl3 (M = Sb, Bi) react with EnBu2 (E = Se, Te) to form [MCl3(EnBu2)3], which are effective single source precursors for the low pressure chemical vapour deposition (LPCVD) of metal chalcogenide, M2E3, thin films. The precursors are extensively dissociated in solution. Flash evaporation of the precursor led to polycrystalline (by XRD), stoichiometric (EDX) M2E3 films, and their electrical properties have been established by Hall and van de Pauw measurements. It is possible to selectively deposit the p-type Sb2Te3 onto TiN over SiO2 using [SbCl3(TenBu2)3], Combining [SbCl3(TenBu2)3] and [BiCl3(TenBu2)3] in various ratios allows the deposition of the ternary phase, (SbxBi1-x)2Te3, where x varies mainly with deposition temperature. The synthesis of the germanium tellurolate compound, [Ge(TenBu)4], has been developed by reacting GeCl4 with nBuTeLi and optimised by the alternative reaction of activated Ge with nBu2Te2. It has been demonstrated that using [Ge(TenBu)4] leads to the deposition of thin stoichiometric and polycrystalline GeTe films by LPCVD at 723 K at 0.02 mmHg. Deposition conditions were varied to reduce the co-deposition of crystalline tellurium in these films. These films were characterised by XRD, Raman spectroscopy, SEM and EDX analysis. The distorted octahedral coordination complexes [SnCl4{nBuS(CH2)3SnBu}] and [SnCl4(SnBu2)2] are effective precursors for the deposition of SnS2 at 559 and 645 K respectively, and 0.02 mm Hg whilst SnSe2 can be deposited via LPCVD between 598 K and 743 K and 0.02 mm Hg using the selenoether analogue, [SnCl4(SenBu2)2]. By optimising the conditions, it is also possible to produce polycrystalline SnS and SnSe thin films, as determined by XRD, Raman spectroscopy and EDX analysis, using the dichalcogenoether precursors, [SnCl4{nBuS(CH2)3SnBu}] and [SnCl4{nBuSe(CH2)3SenBu}] at higher temperature (831 K and 861 K, respectively). The electrical properties of these films were also measured by Hall and van de Pauw measurements. [SnCl4{nBuSe(CH2)3SenBu}] has also been used to grow SnSe2 nanowires (~100 nm) using a liquid injection CVD and vapour liquid solid (VLS) method and a silicon substrate with Au nanoparticles or a 3 nm Au film. The density and morphology of the nanowires can be controlled by the carrier gas flow rate and concentration of precursor. The nanowires produced were stoichiometric by EDX. Preliminary experiments using this method have also produced M2Se3 (M = Bi, Sb) nanowires from [BiCl3(SenBu2)3] and [SbCl3(SenBu2)3], respectively, though further optimisation is required. Nanowires were also characterised by SEM, TEM, XRD and Raman spectroscopy. Films of TiSe2 can be deposited via LPCVD from [TiCl4{nBuSe(CH2)nSenBu}] (n = 2, 3) between 723 and 873 K. XRD analysis of the films grown from ~ 5 mg of precursor showed a high degree of preferred orientation of the c axis perpendicular to the substrate. A series of hybrid amine-selenoether and telluroether ligands were prepared in an effort to tether the soft donor to the Ti(IV) ion more securely. However, this approach did not prove successful and was not pursued further.
Supervisor: Reid, Gillian Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available