David J. Otway

Novel precursors for the growth of α-In2S3: trisdialkyldithiocarbamates of indium

Abstract Thin films of cubic α -In 2 S 3 have been deposited on glass, GaAs(100) and InP(111) by low-pressure metal-organic chemical vapour deposition (LP-MOCVD), using novel air-stable precursors of general formulae In(S 2 CNMeR) 3 [where R= n -Butyl (compound ( 1 )), n -Hexyl (compound ( 2 ))]. The predominant phase in all films grown, regardless of substrate or growth temperature, is α -In 2 S 3 , oriented in the ( h h h ) direction. The precursor compounds are considerably more volatile than known dialkyldithiocarbamates of indium.

Synthesis and characterisation of two novel titanium isopropoxides stabilised with a chelating alkoxide: their use in the liquid injection MOCVD of titanium dioxide thin films

The new precursors [Ti(OPri)3(OCH2CH2NMe2)] 1 and [Ti(OPri)2(OCH2CH2NMe2)2] 2 have been prepared and characterised. Compound 1 exists in solution at room temperature as a mixture of monomer and dimer(s), however at elevated temperatures the monomer predominates. Compound 2 exists in solution predominantly as a monomeric complex presumably with pseudo-octahedral coordination at the metal centre. Thin films of TiO2 have been deposited at 300-450C by liquid injection MOCVD using both 1 and 2. Analysis of the films by Auger electron spectroscopy failed to detect nitrogen although trace carbon was detected at levels of between 2.9 and 7.7. The potential utility of these modified compounds as precursors to TiO2 is discussed.

The growth of thin films of copper chalcogenide films by MOCVD and AACVD using novel single-molecule precursors

Highly oriented crystalline films of copper sulfide and copper selenide have been grown on glass by low-pressure metal-organic chemical vapor deposition (LP-MOCVD) and by aerosol-assisted chemical vapor deposition (AACVD), using the novel air-stable compounds Cu(E2CNMenHex)2]* (where E=S,Se). Thin films of non-stoichiometric cubic CuS and CuSe have been deposited in the temperature range 450–500 °C.

Group IIA metal β-diketonate complexes; the crystal structures of [Sr3(tmhd)6(Htmhd)]·C6H5Me·C5H12 and [Ba4(tmhd)8](Htmhd = 2,2,6,6-tetramethylheptane-3,5-dione)

Hydrocarbon-soluble Group IIA metal ethoxides [{M(OEt)2(EtOH)4}n](M = Sr or Ba) react with the β-diketonate 2,2,6,6-tetramethylheptane-3,5-dionate (Htmhd) to yield the volatile complexes [Sr3(tmhd)6(Htmhd)] and [Ba4(tmhd)8] in excellent yield. These materials have been studied by classical spectroscopic techniques, differential scanning calorimetry and thermogravimetric analysis. They have also been characterised by single-crystal X-ray diffraction at 150 K, and shown to exist as a trimer and tetramer respectively, the former also incorporating a neutral Htmhd ligand.

The importance of ternary complexes in defining basic conditions for the deposition of ZnS by aqueous chemical bath deposition

In the deposition of ZnS by chemical bath methods (CBD) at basic pH it is common to see improved deposition in the presence of a second ligand. These ternary systems (three components; two ligands one metal) are usually modelled by considering only the formation of binary species. This short paper outlines a strategy for considering the incorporation of ternary species in defining the complexes formed in solutions used for deposition. It appears that solutions which deposit ZnS are not necessarily supersaturated with respect to hydroxy-species. The relationship of these methods to deposition from acidic baths is also briefly discussed.

Novel approach to the deposition of CdS by chemical bath deposition: the deposition of crystalline thin films of CdS from acidic baths

Thin films of cadmium sulfide have been deposited from acidic solutions. The films have been characterised by electronic, photoluminescence (PL) and X-ray photoelectron (XPS) spectroscopies, scanning and transmission electron microscopy (SEM and TEM) and powder X-ray diffraction (XRD). The as-deposited polycrystalline CdS films are hexagonal, the crystallinity of the films is improved by annealing in air at 400 °C. The procedure also leads to a concentration of chloride at the surface of the films. Deposition from acidic baths may open up new simple synthetic routes towards the ternary cadmium-zinc sulfide system.

Developments in CVD delivery systems: A chemist's perspective on the chemical and physical interactions between precursors

Important factors in considering compounds for use as precursors in CVD techniques are discussed. Conventionally, volatility along with precursor purity and clean decomposition to the desired materials, are all regarded as crucial precursor properties. Recent developments in the way in which precursors are delivered into the vapor phase mean volatility is no longer such an important requirement. Less volatile precursors with better deposition routes are now routinely employed. In this review, a description of the fundamentally new approaches to CVD delivery systems developed in recent years is presented. Examples highlighting the importance of understanding both the chemical and physical interactions between different precursors, and also those between the carrier gases and precursors, are discussed.

The deposition of thin films of CuME2 by CVD techniques (M = In, Ga and E = S, Se)

Thin film(s) of chalcopyrite CuME2 (where M = In or Ga; E = S or Se) have been grown by low-pressure metal-organic chemical vapour deposition (LP-MOCVD) or aerosol-assisted chemical vapour deposition (AACVD) using the precursors M(E2CNMenHex)3 and Cu(E2CNMenHex)2. Films were grown on various substrates between 350–500 °C and characterized by X-ray diffraction, XPS, optical spectroscopy (UV/Vis), EDAX and scanning electron microscopy.

Liquid Injection MOCVD of Zirconium Dioxide Using a Novel Mixed Ligand Zirconium Precursor

Thin films of ZrO2 have been deposited by liquid injection MOCVD using tetrahydrofuran solutions of the novel mixed ligand precursor Zr2(OiPr)6(thd)2 (thd = 2,2,6,6,-tetramethyl-3,5-heptanedionate). Oxide growth was observed over an unusually wide range of temperatures from 250°C to at least 600°C. Optimized growth of ZrO2 occurred between 350°C and 550°C, which is considerably lower than the optimum temperature for deposition from the conventional Zr(thd)4 precursor. Analysis of the films by Auger electron spectroscopy showed that carbon was present at levels of between ∼2 at.-% and 11 at.-%, depending on substrate temperature and oxygen concentration in the gas phase.

Group 2/titanium heterometallic alkoxides; their reproducible syntheses and characterization. Crystal structures of the compounds [SrTi4(OEt)18] and [Sr2Ti(OPri)8(PriOH)3] · 2PriOH

Abstract The reactions of either (i) bulk metal in alcohol (EtOH or Pr i OH); or (ii) the preformed metal alkoxides, [ M ( OR ) 2 ( ROH ) x ] n with a stoichiometric amount of Ti(OPr i ) 4 at reflux yielded the novel hydrocarbon soluble molecular aggregates [ MTi 2 ( OEt ) 10 ( EtOH ) 5 ] n [ M = Sr (1) and Ba (2)]; [MTi 4 (OEt) 18 ] [ M = Sr (3) and Ba (4)]; [ M 2 Ti ( OEt ) 8 ( EtOH ) 5 ] n [ M = Sr (5) and Ba (6)]; and [Sr 2 Ti(OPr i ) 8 (Pr i OH) 3 ] · 2Pr i OH (7). All complexes have been characterized by elemental analyses and spectroscopic methods; (3) and (7) have also been characterized by X-ray crystallography. The structure of (3) is based on a “bow-tie” Ti 2 SrTi 2 unit where the strontium is coordinated to two face sharing bioctahedral Ti 2 (OEt) 9 − units, via two “terminal” and two “bridging” ethoxo ligands from each Ti 2 (OEt) 9 − unit. In (7) the Sr 2 Ti unit forms a triangle, bridged by three μ 2 - Pr i O ligands and capped by two μ 3 - Pr i O ligands, and further supported by six terminal Pr i O/Pr i OH ligands.