John McAleese

Developing an understanding of the processes controlling the chemical bath deposition of ZnS and CdS

The deposition of cadmium sulfide by chemical bath methods is straightforward and involves an alkaline solution of a cadmium salt, a complexant and a chalcogen source, often thiourea or thioacetamide. Supersaturation of the bath with respect to ‘Cd(OH) 2 ’ is necessary for the deposition of good quality films under a wide range of conditions. In contrast zinc sulfide is more difficult to deposit. In this paper we discuss the literature concerning the deposition of these chalcogenides and use equilibrium models to rationalise many of the observations found in the literature. Strategies for the deposition of high quality films of ZnS by CBD are discussed.

The use of Ce(fod)4 as a precursor for the growth of ceria films by metal-organic chemical vapour deposition

We report the growth of thin films of cerium oxide using the metal-organic chemical vapour deposition (MOCVD) technique. The homoleptic complex, Ce(fod)4, where fod-H is 1,1,1,2,2,3,3-heptafluoro-7,7-dimethyloctane-4,6-dione, was used as a precursor. Silicon wafers with a (100) orientation were used as substrates. This work can be considered a feasibility study of this precursor as a potential source of ceria for the eventual production of solid solutions with a stoichiometry of Ce0.9Gd0.1O1.95. These ceramic films are intended for use as electrolytes in solid oxide fuel cells (SOFCs). In this paper, the difficulties associated with CVD growth of oxide films using solid phase precursors such as Ce(fod)4 which contain fluorinated ligands are discussed as well as the methods used to eliminate such problems. The variation of important CVD parameters such as moist oxygen flow rate are discussed in terms of their effect on the growth rate and the elemental composition of the deposited films. Analysis was carried out using techniques such as scanning electron microscopy, X-ray photoelectron spectroscopy and X-ray fluorescence.

Synthesis and structural characterisation of two novel GdIIIβ-diketonates [Gd4(µ3-OH)4(µ2-H2O)2(H2O)4(hfpd)8]·2C6H6·H2O 1 and [Gd(hfpd)3(Me2CO)(H2O)] 2(hfpd–H = 1,1,1,5,5,5-hexafluoropentane-2,4-dione)

Two novel GdIII–hfpd complexes 1 and 2 have been synthesised from aqueous and non-aqueous media; the crystal structural studies reveal that 1 has a M4O6 bicapped cubane core with the metals having tricapped trigonal prismatic geometry, while 2 is a monomeric adduct with water and acetone in the coordination sphere, with the metal having square antiprismatic geometry.

Thin film growth of gadolinia by metal-organic chemical vapour deposition (MOCVD)

Abstract We report the growth of thin films of gadolinia using metal-organic chemical vapour deposition (MOCVD) under reduced pressure. The mixed ligand complex [(Gd(tmhd) 3 ) 2 (tetraglyme)], where tmhd-H is 2,2,6,6-tetramethyl-3,5-heptanedione and tetraglyme is tetraethylene glycol dimethyl ether, was used as precursor. Silicon wafers with a (100) orientation were used as substrates. The work described can be considered as a preliminary stage in the eventual manufacture of solid electrolytes with a mixed metal composition of Ce 0.9 Gd 0.1 O 1.95 and, as such, certain process parameters are restricted by limits associated with potential cerium precursors which are reported in a separate paper. The effects of the deposition conditions on the structure and composition of the resulting oxide films are presented. The dependence of growth on parameters such as the evaporation rate, moist oxygen flow rate and substrate temperature ( T sub ) is discussed. Characterization of the microstructure using scanning electron microscopy (SEM) and X-ray diffraction (XRD) confirms the first reported growth, to our knowledge, of thin, uniform layers of gadolinia by the CVD technique.

The synthesis and characterisation of some stable CeIII β-diketonate compounds; X-ray crystal structures of [Ce2(etbd)6(tetraglyme)] and [NH4][Ce(etbd)4] [etbd = 1-ethoxy-4,4,4-trifluorobutane-1,3-dionate and tetraglyme = CH3O(CH2CH2O)4CH3]

Abstract The cerium(III) β-diketonate compounds [Ce2(β-diket)6(tetraglyme)] [β-diket = etbd (1-ethoxy-4,4,4-trifluorobutane-1,3-dionate)1, hfpd (1,1,1,5,5,5-hexafluoropentane-2,5-dionate) 2 and hfod (1,1,1,2,2,3,3-heptafluoro-7,7-dimethyloctane-4,6-dionate) 3 and tetragrlyme = CH3O(CH2CH2O)4CH3] were sytnhesised from the reaction of CeCl3 · 7H2O and tetraglyme with an aqueous ethanolic solution of Na(β-diket). The unusual reaction of cerium ammonium nitrate, [Ce(NH4)2(NO3)6], and Hetbd in an ammoniacal mixture of dimethoxyethane resulted in the ammonium cerium(III) salt, [NH4][Ce(etbd)4] 4, rather than the expected cerium(IV) species. All compounds were characterised by spectroscopic methods and in the cases of 1 and 4, also by X-ray crystallography. The structure of [Ce2(etbd)6(tetraglyme)] 1 consists of two Ce(etbd)3 moieties bridged by a tetraglyme molecule. The two Ce atoms in this molecule are eight and nine coordinate respectively with distorted docahedral and monocapped square antiprismatic geometries. The crystal structure of 4 is stabilised by an extensive hydrogen bonding network involving the NH4+ cation and one oxygen atom from each of the four etbd ligands belonging to the [Ce(etbd)4]− anion, with additional NH4+…F3C(etbd) interactions. The Ce atom in the [Ce(etbd)4]− anion is eight coordinate with a distorted square antisprismatic geometry. All the complexes are air and moisture stable, and some compounds have good volatilities and thermal stabilities, as demonstrated by sublimation and TGA/DSC studies.

Unusual coordination modes of multidentate ligands; crystal structure of [{ {(tmhd)3Y} }2(hmteta)][tmhd = But COCHCOBut and hmteta = Me2N(CH2CH2NMe)2CH2CH2NMe2]

Abstract The reaction of the hydrated lanthanide metal β-diketonate complexes [Ln(tmhd)3(H2O)] (tmhd=ButCOCHCOBut) with hexamethyltriethylenetetramine (hmteta=Me2N(CH2CH2NMe)2CH2CH2 NMe2) in n-hexane at room temperature yields the anhydrous, bridged dimeric complexes, [{(tmhd)3Ln}2(hmteta)], where Ln=Gd 1 or Y 2. An X-ray study of 2 shows that only three of the four possible nitrogen atoms of the hmteta ligand are utilised in bonding to the yttrium centres. The complexes are air and moisture stable, and more importantly both have good volatility, thermal stability, and mass transport properties as demonstrated by sublimation, differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA), thus making them potential precursors for MOCVD application.

Corrosion of ferritic stainless steel during metal-organic chemical vapour deposition growth using a fluorinated precursor

The growth of Ce1−xGdxO2−x2 films, which are of interest as electrolytes in solid oxide fuel cells, by metal-organic chemical vapour deposition has been studied. The precursors [[Ce(fod)3]2(tetraglyme)]and [*lcub;Gd(tmhd)3]2(tetraglyme)](where fod-H is 1,1,1,2,2,3,3-heptanuoro-7,7-dimethyloctane-4,6-dione, tmhd-H is 2,2,6,6-tetramethyl-3,5-heptanedione and tetraglyme is tetraethylene glycol dimethyl ether) have been used. Type 430 ferritic stainless steel was used as the substrate. Although the overlayer thickness appeared to be substantial, cross-sectional analysis revealed an intermediate oxide layer had formed. This paper details the experimental work used to ascertain the conditions that caused oxidation. A corrosion mechanism based on existing theories is presented. Halogenated precursors may be incompatible with alloy metal substrates.

Metalorganic chemical vapor deposition of CuInSe{sub 2} from copper and indium diselenocarbamates for solar cell devices

Thin film(s) of chalcopyrite CulnSe 2 have been grown by low-pressure metal-organic chemical vapour deposition (LP-MOCVD) using the precursors In(Se 2 CNMe n Hexyl) 3 and precursors Cu(Se 2 CNMe n Hexyl) 2 . The precursors were prepared from carbon diselenide. Films were grown on glass between 400 – 450 °C, and characterized by X-ray diffraction, optical spectroscopy (UV/Vis), EDAX and scanning electron microscopy.