Deposition of CNx thin films by plasma-activated chemical vapour deposition using various precursors as carbon source

CNx-thin films have been deposited by plasma-activated chemical vapour deposition with capacitively or inductively coupled r.f. plasma. Acetylene, methane, carbon monoxide and tetracyanoethylene have been used as carbon precursor. A strong dependence of the layer properties on the precursor was found. In some films the nitrogen to carbon ratio was close to that of C3N4. The highest nitrogen content was observed in films made from carbon monoxide as precursor in an inductively coupled argon/nitrogen plasma. The nitrogen was mainly incorporated with covalent nitrogen–carbon single bonds. X-ray diffraction measurements showed no reflections indicating crystallinity. In small grains (length ∼10 μm) found on the layer surface the stoichiometry corresponded nearly to that of C3N4, the oxygen content is very low. Further characterizations by TEM are intended. This revised version was published online in November 2006 with corrections to the Cover Date.     

Hybrid chemical vapour and nanoceramic aerosol assisted deposition for multifunctional nanocomposite thin films

Hybrid atmospheric pressure chemical vapour and aerosol assisted deposition via the reaction of vanadium acetylacetonate and a suspension of preformed titanium dioxide or cerium dioxide nanoparticles, led to the production of vanadium dioxide nanocomposite thin films on glass substrates. The preformed nanoparticle oxides used for the aerosol were synthesised using a continuous hydrothermal flow synthesis route involving the rapid reaction of a metal salt solution with a flow of supercritical water in a flow reactor. Multifunctional nanocomposite thin films from the hybrid deposition process were characterised using scanning electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The functional properties of the films were evaluated using variable temperature optical measurements to assess thermochromic behaviour and methylene blue photodecolourisation experiments to assess photocatalytic activity. The tests show that the films are multifunctional in that they are thermochromic (having a large change in infra-red reflectivity upon exceeding the thermochromic transition temperature) and have significant photocatalytic activity under irradiation with 254 nm light.     

The incorporation of preformed metal nanoparticles in zinc oxide thin films using aerosol assisted chemical vapour deposition

The feasibility of Aerosol Assisted Chemical Vapour Deposition (AA-CVD) has been investigated for the growth of zinc oxide (ZnO) films containing preformed metal nanoparticles. The deposition parameters were first established for ZnO thin films, by varying the heating configuration, substrate temperature and deposition time. Films were characterised using Scanning Electron Microscopy and X-Ray Diffraction. As-deposited films, grown at 250 °C, were mostly amorphous and transformed to highly crystalline Wurtzite ZnO at higher substrate temperatures (400-450 °C). A change in the preferential orientation of the films was observed upon changing (i), the substrate temperature or (ii), the heating configuration. Following this, the applicability of the AA-CVD process for the incorporation of preformed nanoparticles (platinum and gold) in ZnO thin films was investigated. It was found that surface agglomeration occurred, such that the ZnO films were capped with an inhomogeneous coverage of the metal. These layers were characterised using Transmission Electron Microscopy and Electron Diffraction. A possible mechanism for the formation of these metal surface clusters is presented.     

Growth of diamond thin films by chemical vapour deposition

Deposition of diamond thin films on non-diamond substrates at low pressures (<760 torr) and low temperatures (<2000°C) by chemical vapour deposition (CVD) has been the subject of intense research in the last few years. The structural and the electrical properties of CVD diamond films grown on p-type 〈111〉 and high-resistivity (>100 kΩ-cm) 〈100〉 oriented silicon substrates by hot filament chemical vapour deposition technique are described in this review paper.     

Aerosol assisted chemical vapour deposition control parameters for selective deposition of tungsten oxide nanostructures

Tungsten oxide films were deposited via Aerosol Assisted Chemical Vapour Deposition (AACVD) from the single-source precursor W(OPh)6. Film morphology and optimum deposition temperatures for formation of quasi-one-dimensional structures is influenced by the solvent 'carrier' used for deposition of the films with bulk porous films and nanostructured needles, hollow tubes and fibres obtained dependent on the solvent used and the deposition temperature. This influence of solvent could be exploited for the synthesis of other nanomaterials, and so provide a new and versatile route to develop and integrate nanostructured materials for device applications.     

Growth of PbS and CdS thin films by low-pressure chemical vapour deposition using dithiocarbamates

Thin films of cadmium and lead sulphides grown by chemical vapour deposition (CVD) and remote plasma enhanced chemical vapour deposition (RPECVD) using dithiocarbamates as precursors were prepared on fused silica, sapphire, (111)Si and (111)InP substrates. These films were deposited in the temperature range 473–873 K. It was established that the activation energy of the CVD process is 191.5±1.5 kJ mol⁻¹. The structure of polycrystalline films was halenide for PbS and wurtzite for CdS. It was also found that r.f.-plasma activation of the gas phase decreases remarkably the growth temperature and orders the film structure. RPECVD sulphide films had a high degree of preferred orientation.     

Nickel thin films prepared by chemical vapour deposition from nickel acetylacetonate

Nickel thin films were prepared by a low-temperature atmospheric-pressure chemical vapour deposition method. The raw material was nickel acetylacetonate. At a reaction temperature above 250 °C, polycrystalline nickel films can be obtained by hydrogen reduction of the raw material. The resistivity (8.1–13.3 cm) of the film was close to that of bulk nickel.     

Copper thin films prepared by chemical vapour deposition from copper dipivalylmethanate

Copper thin films were prepared by a low-temperature atmospheric-pressure chemical vapour deposition method. The raw material was copper dipivalylmethanate which is volatile and thermally stable. At a reaction temperature above 220°C, polycrystalline copper films can be obtained by hydrogen reduction of the raw material. The resistivity of the film was in the range 1.7–2.7 cm.     

Defects in nickel ferrite thin films grown by chemical vapour deposition

Thin single-crystal films of nickel ferrite have been grown on magnesia substrates. The structure of the films has been examined using X-ray diffraction, scanning electron microscopy and transmission electron microscopy and diffraction. The films are characterized by arrays of planar faults on {110} due to faults in cation arrangements in the nickel ferrite spinel lattice. The origin of these defects is discussed.     

Preparation and properties of ZnS thin films by low-pressure metalorganic chemical vapour deposition

Low-pressure metalorganic chemical vapour deposition of ZnS thin films on silicon, oxidized silicon and glass substrates using Zn (C₂H₅)₂ and C₄H₄S as source chemicals was investigated. The growth process and the film properties were characterized as functions of process parameters including substrate temperature, reactant ratio and reaction pressure. In general, growth rates as a function of substrate temperature were found to reach a maximum at a much lower temperature than that for growth at atmospheric pressure. In addition, growth rates increased with reaction pressure and thiophene flow rate depending on the temperature condition. The microstructure indicated that growths above 250°C possess a cubic (zincblende) structure, while growths below 150°C are polycrystalline of wurtzite structure. The resistivity varies from 10⁴ cm to a maximum of about 3×10⁵ cm for growth at 250°C, depending on the reactant ratio. The details are discussed in the text.     

A simple chemical vapour deposition method for depositing thin TiO2 films

Thin films of TiO₂ were produced at 130–250°C by chemical vapour deposition (CVD) involving the hydrolysis of TiCl₄. An apparatus was developed which gives good control and reproducibility. The reaction takes place on a heated disc that rotates the silicon substrate. Premature reaction between the gases, TiCl₄ and water vapour is prevented by appropriate temperature control and careful design of the gas delivery system. With this apparatus the thickness of the TiO₂ films is controlled to within ±5% of the target value. Attention is also directed to reducing the pinhole density of the resulting films. The refractive index of the TiO₂ films was found to increase with increasing deposition temperature, from 2.1 at around 130°C to 2.4 at 250°C. From capacitance-voltage measurements the surface charge at the TiO₂-Si interface of films deposited at 200°C was found to be negative. Hence these TiO₂ films are good antireflection coatings for n-type metal/insulator/semiconductor inversionlayer solar cells.     

Study of magnetic properties of thin cobalt films deposited by chemical vapour deposition

Chemical Vapour Deposition (CVD) of cobalt was deposited from a liquid source precursor of cobalt tricarbonyl nitrosyl (Co(CO)₃NO) on to oxidised < 100 > silicon wafers. The cobalt layers were deposited at 450∘C at 1.5 torr chamber pressure of hydrogen for 15 min processing time with various precursor flow rates. X-ray diffraction studies of the cobalt films reveal both hcp and fcc peaks. The vibrating sample magnetometer (VSM) yields coercivity (Hc) 167 Oe and 364 Oe for 46 nm and 30 nm thickness layers respectively at room temperature and squareness (S) M_r/M_s (remanence/saturation of magnetisation) value of ∼ 1. The study of magnetic properties of the cobalt suggests that magnetisation is dependent on grain size and therefore thickness. The grain size was observed by atomic force microscopy (AFM). Magnetic images were observed by magnetic force microscopy (MFM) and analyzed in terms of domain structure. The surface domain structure was recorded with the tip lift height 100 nm so that the magnetic interactions arising produced the topography effect. Where there is repulsive interaction the intensity is recorded as a bright region and where the interaction is attractive the intensity is recorded as a dark region.     

Preparation of ferroelectric BaTiO3 thin films by metal organic chemical vapour deposition

Polycrystalline BaTiO₃ thin films have been successfully prepared on (100) silicon substrates at temperatures under 600° C by metal organic chemical vapour deposition using barium acetylacetonate and diisopropoxy-titanium-bis-(acetylacetonate). To vaporize the barium acetylacetonate, which is nonvolatile under 300° C and thermally unstable, an ultrasonic spraying technique was used. The substrate temperature had a great influence on the structure and composition of films and the single-phase BaTiO₃ films could be prepared at 500° C. At temperatures above 550° C the reaction between the film and the silicon substrate occurred to a large extent. The polarization-electric field (P-E) hysteresis loops and counter-clockwise direction of hysteresis in the high-frequency (1 MHz)C-V characteristics indicate that the BaTiO₃ films deposited on silicon using the present method are ferroelectric.     

The crystallographic properties of PbTiO3 thin films fabricated by chemical vapour deposition

Lead titanate, PbTiO₃, is a well-known material having remarkable ferroelectric, piezoelectric and pyroelectric properties. Thin films of lead titanate have been successfully fabricated by chemical vapour deposition on a titanium substrate. Layers deposited on the titanium substrate using PbO vapour and O₂ gas grow along the (1 0 1) preferred orientation. The maximum dielectric constant and loss tangent of PbTiO₃ thin film deposited on a titanium substrate are about 90 and 0.02, respectively. The electrical resistivity of the PbTiO₃ is about 10⁹cm. The deposition rates of PbTiO₃ deposited on the titanium substrate were 10 to 15 mh^–1. A titanium dioxide interlayer formed between the PbTi0₃ film and titanium substrate materials. It might improve the adhesion of the film.     

Electric fields in the chemical vapour deposition growth of vanadium dioxide thin films

Thin films of thermochromic vanadium dioxide have been the subject of intensive research in recent years year due to their postulated use as "intelligent" window coatings. The usefulness of such technology depends on a semi-conducting to metal transition with an associated change in infra-red optical properties. This exact nature of this transition depends on a large number of factors such as doping, crystallite size, strain, crystallographic orientation etc. In this paper we discuss the nature of these factors with a particular focus on how the application of electric fields in the deposition affects crystallite size and film strain with reference to recent results.