Chemical Vapor Deposition

In this communication we report the synthesis and characterization of the vanadium (III) alkoxide [V(OCMe₂CH₂OMe)₃], which presents an appreciable volatility (55°C/1.5Torr), its successful use as MOCVD precursor for the deposition of pure VO₂ and V₂O₅ films and the characterization of the films by means of Rutherford Backscattering Spectroscopy (RBS), X-Ray Diffraction (XRD) and Cyclic Voltammetry.

Few-layered sheets of graphene were synthesized on polycrystalline thin Co and Ni films by low pressure chemical vapor deposition. On average, thinner layers of graphene were synthesized on Co than on the conventional Ni at the same process conditions, but slightly higher defects were detected on Co-grown graphene layers than on Ni-grown ones. Possible explanations for this are suggested.

Methylated [(benzene)(1,3-butadiene)Ru(0)] derivatives 1–3 have been designed and prepared as novel metal organic chemical vapor deposition (MOCVD) precursor complexes. They can be evaporated without decomposition below 100°C, and thin Ru films can be obtained from 200°C substrate temperature on. Purity of the films is granted by the inherent properties of both the precursor complexes and the catalytically active freshly formed ruthenium film surfaces.

The degradation of as-deposited CVD BPSG films was investigated. Different mechanisms of boron out-gassing at room temperature were discussed. A new proposed mechanism is based on the effect of boric oxide charging, which was studied by the surface photo-voltage technique. The role of the undoped SiO₂ layer deposited below or/and above BPSG film in terms of stability enhancement of the latter was studied and discussed.

Titanium dioxide thin films were synthesised using aerosol assisted chemical vapour deposition (AACVD) of titanum (IV) isopropoxide (TTIP) in methanol. Deposition was carried out on glass, steel and titanium substrates at 400–550°C. The films produced morphologies that were radically different to that from typical aerosol assisted processes and from the use of TTIP in low or atmospheric pressure CVD.

The growth of ultrathin Ta-N films at the initial stages of atomic layer deposition was investigated by in situ X-ray photo-electron spectroscopy (XPS) starting from the first precursor pulse. The chemical composition, the growth mode and the film thickness are derived in dependence on the cycle number and the substrate chemistry.

Vertically aligned ZnO nanowires have been grown by liquid injection MOCVD using the dimethylzinc-bidentate ether adducts [Me₂Zn(L)] (L=1,4-dioxane, 1,2-dimethoxyethane, 1,4-thioxane). The crystal structures of the complexes have also been determined.

The decomposition kinetics of Cyclopentadienyl-allyl-Pd [Cp(allyl)Pd] on silica and titania substrates were investigated by continuous MO-CVD at atmospheric pressure. While the initially decomposition of precursor molecules on the OH groups depends strongly on process conditions like precursor concentration or decomposition temperature, the autocatalytic decomposition is very rapid on very small Pd clusters, but comes to a standstill at a Pd particle size around 2nm, regardless of process parameters.

New support was used for ALD growth: the fibre of Curauá (Ananas erectifolius). This promising lignocellulosic material was studied insufficiently. SEM imaging of fibres revealed dense structure and nanoveinlets of cellulose agglomerates. Thin Al₂O₃ and Ta₂O₅ coatings of thicknesses 30nm ÷ 130nm were grown by ALD. They are continuous, resistant and homogeneous. Both coatings and nanowalled microtubes, obtained by oxidative annealing replicate well the irregular fibre relief.

Cu(hfac)₂(TEA) (hfac=1,1,1,5,5,5-hexafluoroacetylacetonate, TEA (triethylamine)) is a new liquid Cu(II) precursor. Using Cu(hfac)₂(TEA), we successfully deposited Cu thin films as a seed layer even at low the deposition temperature of 373K. To explain this behavior, the bonding status of Cu(hfac)₂ in the presence of TEA was determined by density-functional theory. The theoretical bond length of Cu-O in Cu(hfac)₂ was significantly greater (by 0.06 Å) than that without an adduct ligand.