Atmospheric pressure non-equilibrium plasma jet technology: general features, specificities and applications in surface processing of materials

Atmospheric pressure non-equilibrium(cold) plasma jet technology received enormous attention in surface processing of materials in the last two decades, and still continues nowadays to attract growing interest. In addition to the advantages of the atmospheric pressure operation such as the potential cost reduction of apparatuses as well as their easier handling and maintenance, due to the distinctive remote operation, plasma jets give the unique possibility of placing the substrate outside the source boundaries. Consequently, the processing of complex three-dimensional objects and the integration into existing production lines are expected to bemuch easier. However,while appealing, plasma jet technology has the drawback that great efforts are required for process optimization, sincemany factors can affect, for instance, the physical and chemical proprieties of the so-called “plasma plume” emanating from the devices and propagating in open space towards the substrate to be treated. The aim of this paper is to provide a critical literature review on the utilization of atmospheric pressure non-equilibrium plasma jets in surface processing of materials. Starting from the description and classification of the multitude of devices used in this applicative field so far, the attention will be drawn on some very important aspects to be taken into account in process optimization. The discussion will be focused on basic concepts and peculiarities closely related to the remote operation of the plasma sources, which include the characteristics and dynamics of the plasma plume interactingwith the substrate and the surrounding atmosphere. Since the plasma jet approach allows the surface modification of small localized regions of the sample, the strategies implemented to enlarge the treated areawill be also addressed. Finally, a brief overviewwill be given of the available applications and recent developments in the field of etching, thin film deposition and treatment.