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Ashraf S.,University of Liverpool | Jones A.C.,University of Liverpool | Bacsa J.,University of Liverpool | Steiner A.,University of Liverpool | And 6 more authors.
Chemical Vapor Deposition | Year: 2011

The dimethylzinc-bidentate ether adducts [Me2Zn(1,4-dioxane)] (1), [Me2Zn(1,2-dimethoxyethane)] (2) and [Me2Zn(1,4- thioxane)] (3) are used as precursors for the growth of vertically aligned zinc oxide (ZnO) nanowires (NWs) by liquid-injection, metal-organic (MO)CVD. The ZnO NWs are deposited on Si(111) and F-doped SnO2/glass substrates in the absence of a seed catalyst. The precursors (1) and (2) are used to deposit ZnO NWs at substrate temperatures of 450°C and 500°C, whilst higher deposition temperatures of 550-600°C are necessary to obtain ZnO NWs using (3). X-ray diffraction (XRD) data show that the NWs grown from all three adduct precursors are deposited in the wurtzitic ZnO phase. Room-temperature photoluminescence (PL) data for the ZnO NWs grown using (1) and (2) show an intense peak at 3.28eV due to near band-edge emission with a very low intensity of defect-related green luminescence at 2.42eV. In contrast, room-temperature PL data for the ZnO NWs deposited using (3) is dominated by deep centre, defect-related emission at 2.42eV. Auger electron spectroscopy (AES) shows that the ZnO films deposited from (1) and (2) are high purity with no detectable carbon, but the ZnO films grown from (3) are contaminated with sulfur (1at.-%). Single-crystal X-ray structures show that (1) is polymeric containing bridging 1,4-dioxane ligands while (2) is a monomeric complex featuring a chelating 1,2-dimethoxyethane ligand. The wide [Me-Zn-Me] bond angles in (1) and (2) (152.0(3)° and 154.5(2)°, respectively) suggest moderately weak [Me 2Zn]-ligand interactions. Complex (3) is polymeric and exhibits nearly linear [Me-Zn-Me] bond angles, indicative of much weaker [Me 2Zn]-ligand interactions. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Werner M.,University of Liverpool | King P.J.,University of Liverpool | Hindley S.,University of Liverpool | Romani S.,University of Liverpool | And 4 more authors.
Journal of Vacuum Science and Technology A: Vacuum, Surfaces and Films | Year: 2013

Titanium-doped hafnium oxide films, TixHf1-xO 2-δ, have been deposited with a Ti content of x = 0.1 and x = 0.5, by atomic layer deposition. The TixHf1-xO 2-δ growth rate is lower compared with the growth rates of the individual binary oxides; however, the composition of the films is unaffected by the reduced growth rate. An 850 °C spike anneal and a 500 °C 30 min furnace anneal were performed, and the resulting film composition and structure was determined using medium energy ion scattering, x-ray diffraction, and transmission electron microscopy. The Ti0.1Hf0.9O 2-δ films readily crystallize into a monoclinic phase during both types of annealing. By contrast, the Ti0.5Hf0.5O 2-δ films remain amorphous during both annealing processes. Electrical characterization of the as-deposited Ti0.1Hf 0.9O2-δ films yielded a dielectric constant of 20, which is slightly higher than undoped HfO2 films. The as-deposited Ti0.5Hf0.5O2-δ films showed a significant increase in dielectric constant up to 35. After a 500 °C 30 min anneal, the dielectric constant reduced slightly to 27. The leakage current density of the amorphous film remains relatively unaffected at 8.7×10-7 A/cm2 at -1 MV/cm, suggesting this composition/heat treatment is a candidate for future device dielectrics. © 2013 American Vacuum Society.

King P.J.,University of Liverpool | Werner M.,University of Liverpool | Chalker P.R.,University of Liverpool | Jones A.C.,University of Liverpool | And 6 more authors.
Thin Solid Films | Year: 2011

Cerium oxide dielectric thin films have been grown on n-type silicon by atomic layer deposition using a monomeric homoleptic CeIV alkoxide precursor with water vapour. Herein we report the dielectric properties of CeO2 films deposited from tetrakis(1-methoxy-2-methyl-2-propanolate) cerium. The resulting films exhibit permittivities in the range 25-42 at 1 MHz with a strong dependency on the deposition temperature. The microstructural origin of this behaviour has been investigated. The as-deposited films were found to be crystalline and they exhibited the cubic fluorite structure for deposition temperatures in the range 150 °C to 350 °C. Variations in the crystallite sizes are governed by the deposition temperature and have been estimated using a Debye-Scherrer analysis of the X-ray diffraction patterns. The changing crystallite size correlates with changes seen in the triply-degenerate F2g first-order Raman line half-width at 465 cm- 1. It is concluded that the frequency dependency of the film dielectric properties is strongly influenced by the crystallite size which in turn is governed by the growth temperature. © 2011 Elsevier B.V.

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