Growth of self-supported diamond tubes in the hot-filament chemical vapor deposition system

A hot-filament chemical vapor deposition system fed with ethanol highly diluted in hydrogen was employed to grow self-supported diamond tubes with external diameter to wall thickness aspect ratio between ∼5 and ∼60, and 30 mm in length. Tungsten wires of diameters between 238 and 586 μm were used as substrates for the deposition, and were subsequently completely removed by etching, to leave stress-free diamond tubes, as demonstrated by micro-Raman spectroscopy. Scanning electron microscopy revealed cross-sections with diamond grains growing radially, forming well-faceted top-surface grains on the tube's external surface.