Roll-to-Roll Deposition of Thin Graphitic Films and Dependence on Discharge Modes in Radio Frequency Capacitively Coupled Plasma

Abstract

We report the deposition of nanocrystalline graph- itic films on Cu foil in a roll-to-roll (R2R) plasma-enhanced chemical vapor deposition (PECVD) system. The influence of discharge modes on the graphitic film synthesis is studied in radio frequency (RF) capacitively coupled Ar/H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /CH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> plasma. First, electrical and spectroscopic characterizations supported with modeling are carried out to study the properties of hybrid and gamma modes in Ar plasma at an excitation frequency of 80 kHz. A hybrid mode, which exhibits both alpha and gamma characteristics, exists at 950 Pa for Ar plasma at powers up to 1100 W. However, Ar plasma transitions at 1380 Pa from hybrid to gamma mode when the power is greater than 750 W. Second, the quality of the nanocrystalline graphitic films, which is assessed with Raman spectroscopy, is correlated with the characteristics of hybrid and gamma modes in Ar/H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /CH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> plasma. The hybrid mode in Ar/H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /CH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> plasma has relatively less ion bombardment. However, the gamma mode in Ar/H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /CH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> plasma provides abundant intermediate carbon species and heats the Cu substrate directly to around 1193 K. Hence, thin films of nanocrystalline graphite with different qualities can be produced at a web feed rate of 30 mm/min without supplemental heating by adjusting the discharge modes.