Brian Cockayne

Liquid injection metal organic chemical vapour deposition of nickel zinc ferrite thin films

Abstract Liquid injection metal organic chemical vapour deposition has been used to grow thin films of the single metal oxides of nickel, zinc and iron, the binary ferrites of nickel ferrite and zinc ferrite and the ternary nickel zinc ferrite. The precursor chemicals used for the deposition of the metal oxide layers were solutions of the metal thd compounds (thd=2,2,6,6-tetramethyl-3,5-heptanedionato) dissolved in tetrahydrofuran. The growth rates of the single metal oxide layers have been systematically determined as a function of substrate temperature in the temperature range 300–650°C and the ferrite layers were deposited at a substrate temperature of 500°C. The ferrite layers were polycrystalline with well-defined spinel crystal structures.

Vapour-phase transport of barium β-diketonates in the deposition of oxides and the isolation and structural characterization of a novel hexameric cluster of 2,2,6,6-tetramethylheptane-3,5-dionatobarium(II)

Studies of the growth of BaCO3 by using the evaporative transport of Ba(thd)2(the = 2,2,6,6-tetramethylheptane-3,5-dionate) in triethylamine (NEt3) are reported. The novel ionic compound [Ba6(thd)10(H2O)4(OH)2O2][HNEt3]2(I) has been isolated from solutions used in this work. Characterization of I, by X-ray single-crystal diffraction, shows that the molecule comprises an anionic hexameric cluster of Ba, thd, water and hydroxide ions centred on a bridging peroxide with charge balancing [HNEt3]+ cations in the lattice.

Carbonyl sulfide (OCS) as a sulfur-containing precursor in MOCVD: a study of mixtures of Me2Cd and OCS in the gas and solid phases and their use in MOCVD

Mixtures of dimethylcadmium (Me2Cd) and carbonyl sulfide (OCS) have been examined in the gas and solid phases over a wide range of temperatures. No interaction is observed between Me2Cd and OCS in a 1:1 molar ratio at room temperature in the gas phase, nor is any interaction detected in the solid phase at liquid-nitrogen temperature. On heating the 1:1 mixtures of Me2Cd and OCS to 250 °C in a sealed vessel, gaseous products are formed. These consist of methane, carbon monoxide and ethane in an approximately 12:2:1 molar ratio, although a large excess of unreacted OCS is also present showing that this compound does not react fully with Me2Cd at 250 °C. In a flow system at 300 °C only methane and carbon monoxide are formed, in the molar ratio 6:1, although the amount of reaction of the OCS is much less (as evidenced by a higher proportion of unreacted OCS). When the flow reaction is repeated at 450 °C more of the OCS reacts and the proportion of carbon monoxide in the gaseous reaction products is much higher. Using a commercial MOCVD apparatus, high-quality layers of cadmium sulfide are obtained from Me2Cd–OCS mixtures. Temperatures in the range 350–450 °C lead to somewhat slow growth rates which only reach 1 µm h–1 when a 200-fold molar excess of OCS over Me2Cd is used. A small amount of prereaction is observed, but only when H2 is used as the carrier gas. This is attributed to the formation of very small concentrations of H2S by reaction of OCS with H2. The resulting epitaxial layers have good thickness and electrical uniformity. These experiments confirm that OCS may be used as a precursor for the growth of thin layers of CdS by MOCVD. However, the large excess of OCS required here suggests that the compound might be more useful for doping than for the growth of pure layers of CdS.

Magnetic and electrical characteristics of MnAs films grown by metalorganic chemical vapour deposition

Abstract The magnetic and electrical property of changes associated with the phase transition in MnAs have been measured in uncracked material by using thin films grown on to sapphire substrates by metal organic chemical vapour deposition. The films exhibited a first-order transition with Curie points in the range 35–47±1°C. An increase of approximately 60% in the electrical resistivity of the films was measured on heating through the phase transition. The Curie temperature of the films increased with an applied magnetic field by approximately 1.2°C in a field of 600 kA m −1 . This shift in Curie temperature with applied magnetic field also produced a magnetoresistance effect with a maximum value of 2.24% at 600 kA m −1 . The values of these parameters are shown to be dependent upon the growth conditions of the films.

Precipitate identification in Ti-doped YAlO3 single crystals

Abstract Precipitates which form during the growth by the Czochralski technique of Ti-doped YAlO 3 have been identified as Y 2 Ti 2 O 7 .

Propylene sulfide as a sulfur-containing precursor in MOCVD: study of mixtures of Me2Cd and propylene sulfide in the gas, liquid and solid phases and their use in MOCVD

Mixtures of dimethylcadmium (Me2Cd) and propylene sulfide have been examined in the gas and liquid phases over a range of temperatures. No interaction is observed between Me2Cd and propylene sulfide in a 1:1 molar ratio at room temperature in the gas or liquid phases, although a weak interaction is detected in the solid phase at liquid-nitrogen temperature. On heating the 1:1 mixtures of Me2Cd and propylene sulfide to 85–250 °C, in sealed vessels, gaseous products are formed. These are principally propene and methane, in an approximately 2:1 molar ratio, while in a flow system not only are propene and methane found as the major gaseous products at 300 °C, but also a layer of solid CdS is deposited.Using a commercial metal–organic chemical vapour deposition (MOCVD) apparatus high-quality layers of cadmium sulfide are obtained from Me2Cd–propylene sulfide mixtures. Temperatures in the range 300–450 °C lead to growth rates in excess of 1 p µm h–1. The unwanted pre-reaction, observed when hydrogen sulfide is used as the sulfur source in CdS deposition, is eliminated and the resulting epitaxial layers have good thickness and electrical uniformity. These experiments confirm the usefulness of propylene sulfide for the growth of CdS by MOCVD.