Chemical Vapor Deposition

Selective preparation of double wall carbon nanotubes (DWCNTs) is achieved by a floating iron catalyst CVD method with sufur promotion. SEM shows that the product consists of entangled nanotubes. HRTEM and Raman scattering have revealed that the smallest inner diameter of as-grown carbon nanotubes is 0.4 nm (see Figure). The smallest diameter is found to be produced at the low carbon partial pressure with low sulfur content.

Phase selective chromium oxide films are deposited from chromyl chloride by CVD in the temperature range 320–380 °C. Phase selectivity is found to be driven, in part, by a templating effect of the substrate. Thin films of metastable CrO₂ in (100), (001), and (110) orientations have been stabilized, respectively, by (100), (001), and (110) TiO₂ single crystal substrates. In contrast, thin oriented films of the more stable Cr₂O₃ in (006) orientation are formed when depositing on (0001) Al₂O₃ single crystals over the same deposition temperature range. This phase selectivity appears to be unique to the chromyl chloride precursor.

Nanocrystals of cubic (SiC) are formed by laser-assisted gas-phase CVD synthesis using silane and acetylene as precursors. The nanocrystals (see Figure) are prepared by applying a mechanically chopped infrared excitation CO₂ laser beam to the mixture. The formed SiC particles adopt the zinc blend crystal structure (β-phase) with an average primary particle size of about 12 nm. Higher chopping frequencies yield smaller crystals. Particle size is further reduced by oxidation followed by HF etching of the outer shell.

Hard hydrogen containing silicon-carbon based films have been grown at 453–853 K in a plasma assisted CVD system from tetramethylsilane (TMS). Optical emission spectroscopy (OES) and various electrical measurements are employed to understand the plasma chemistry of TMS and to establish correlations between the characteristics of the plasma discharge and deposited films. Results indicate that increasing the ion energy tends to lower the Si/C ratio regardless of the deposition temperature; ion bombardment is a key factor in controlling this ratio. Effects of species identified by OES on the deposition process are discussed.

Visible light emitting nanocomposite Si/diamond polycrystalline layers (see Figure) are prepared by means of a hybrid CVD/powder-flowing technique. Temperature-dependent changes in the nature and localization of paramagnetic centers suggest that the active centers originate from the dangling bonds induced in the sp³-coordinated C atoms by insertion of the Si nanoparticles, which have a mean diameter of 3.3 nm.

The decomposition of two potential silver precursors is investigated. [AgO₂CR] (R = CF₃, C₂F₅) and [(n-Bu₃P)₂AgO₂CR] (R = CF₃ or C₂F₅) are studied under hot-wall CVD conditions using molecular beam mass spectrometry where (n-Bu₃P) and silver-containing intermediates are identified within fragments given by the phosphine ligand. While the silver carboxylates are found not to be suitable precursors under the conditions investigated, the phosphane-stabilized silver(I) carboxylates seem to be promising candidates. Thermal stability and potential formation mechanisms for the observed Ag-containing fragments are discussed.

Copper thin films exhibiting a bulk-like resistivity of 2.16 μΩ cm have been grown on SiO2/Si substrate using copper(II) amino alkoxides as precursors (see Figure). The thermally induced deposition reaction was carried out in an inert atmosphere and the XRD analysis proved that the films were highly crystalline with a strong (111) preferred orientation. On the basis of RBS and XPS analysis, the deposits were free from carbon , oxygen, and nitrogen contamination.

Deposition of Pt–Ru alloy thin films from a single source precursor is achieved. The films are deposited on SiO₂ from [CpRu(η⁵-C₅H₃-CH₂NMe₂)Pt(hfac)] (Cp = C₅H₅) using O₂ as reactive carrier gas in the temperature range 300 to 400 °C. Analyses of the as-deposited films using EDX, SEM, XPS, and XRD methods indicate that films deposited at 300 °C consist of homogeneous Pt–Ru solid solutions. However phase separation, which includes the growth of RuO₂, occurs at 400 °C. The electrocatalytic activities of the deposited films toward methanol oxidation are investigated by cyclic voltametry.

The synthesis of a precursor Ru or RuO₂ films is reported. The prepared diruthenium pyrazolate complex is shown to be a suitable and volatile CVD precursor that cleanly deposits the metal or (101) oriented conductive oxide thin films using H₂ or O₂, respectively, as carrier gases. Smooth and well adherent films are grown in the temperature range 300–450 °C (see Figure).