Self-enhanced plasma discharge effect in the deposition of diamond-like carbon films on the inner surface of slender tube

Industrial demand for internal plasma processing of slender halls and tubes is on the rise. This has motivated research aimed at establishing new ways of producing these structures. Theoretical and empirical studies have been conducted on the emerging technique of inner surface films deposition, on enhanced glow-discharge plasma immersion ion implantation and deposition process, with the aim of proving that it can be highly effective in inner surface film disposition process.

A team of researchers led by Professor Liuhe Li from Beihang University in China investigated the self-enhanced plasma discharge effect in the deposition of diamond-like carbon films on the interior surface of slender tube with an aim to establish the sufficiency of this process. Their work is now published in the journal Applied Surface Science.

Foremost, the team conducted the emerging technique on internal surface films deposition, enhanced glow discharge plasma immersion ion implantation and deposition (EGD-PIII&D) procedure using a special hardware arrangement. The system was set up in a vacuum chamber. Insulating tube was then pre-cleaned ultrasonically in deionization water bath and rinsed in ethanol. Two experiments were then to be carried out.  First, one blending acetylene gas into the chamber through the insulating tube with internal material of quartz glass whose main component was silicon (iv) oxide. The second experiment utilized two tubes one similar to the previous experiment and the other made of lucalox of aluminum oxide. For this experiment argon gas was used.

Large tabular cathode and small pointed hollow anode were used. Diamond like carbon films(DLC) were adopted for disposition on interior surface of the quartz tube with minor internal diameter and notable length-diameter ratio, due to their high rate of efficiency.

Implantation current was linearly increased during the whole process which led to the introduction of the EGD-PIII&D technique ten times faster than previous methods in depositing diamond like carbon films. During this deposition process, the electron mean free path inside the tube was much less in length of the tube but still way larger than the interior diameter of the tube. This contributed to high electron-neutral collision which led to high frequency of electron internal surface impact.

To shed more light on the effect of internal surface materials of the slender insulating tube on the plasma discharge, the implementation currents in the EGD-PIII&D with tubes developed from varying materials had to be measured. Subsequently, numerical simulations were conducted so as to obtain the pressure gradient distribution and ion density in the empirical region. The electron free mean path was then introduced so as to determine how the inner surface materials affected the plasma discharge.

From these simulative, theoretical and empirical studies, self-enhanced plasma discharge effect is discovered. It is also clear that the inner surface material contributes vitally on the film disposition. The research team also discovered that secondary electrons generated from the internal surface material or the diamond like carbon surface can dramatically improve the plasma discharge to promote the diamond like carbon deposition rate.