Growth of high-quality carbon nanotubes on free-standing diamond substrates

Carbon nanotubes (CNTs) were grown on diamond-coated Si substrates and free-standing diamond wafers to develop efficient thermal interface materials for thermal management applications. High-quality, translucent, free-standing diamond substrates were processed in a 5 kW microwave plasma chemical vapor deposition (CVD) system using CH4 as precursor. Ni and Ni–9%W–1.5%Fe catalyst islands were deposited to nucleate CNTs directly onto the diamond substrates. Randomly-oriented multi-walled CNTs forming a mat of ∼5 μm thickness and consisting of ∼20 nm diameter tubes were observed to grow in a thermal CVD system using C2H2 as precursor. Transmission electron microscopy and Raman analyses confirmed the presence of high-quality CNTs on diamond showing a D/G peak ratio of 0.2–0.3 in Raman spectra.