Sub-micron size carbon structures synthesized using plasma enhanced CVD, without external heating and no catalyzer action

We report on the synthesis of a variety of sub-micron size carbon structures using RF, 13.6 MHz, plasma enhanced CVD, without the use of any external heater or catalyzer precursor. The plasma is generated in an asymmetric capacitively coupled discharge operated at a low power of up to 30 W, with a gas mixture of acetylene and hydrogen, at different mixing ratios. Carbon films are grown on mirror-like polished silicon (100) substrates, which are negatively biased using 4 kV, 2 μs pulses, at a 2 kHz rate, with a characteristic exposure time of around 30 min. The morphology, structure and atomic composition of the resulting carbon films are characterized using SEM, EDX, AFM and Raman spectroscopy. Carbon spheres of different diameters, of sub-micron range, are observed to grow in layers onto the Si surface. We present a detailed characterization of the resulting carbon films, in correlation with the plasma properties, as inferred from optical emission spectroscopy observations.