Special Issue on Low Temperature Plasma Jets

Low temperature plasma jets are unique plasma sources capable of delivering plasma outside of the confinement of electrodes and away from gas enclosures/chambers. With these jets plasma can be easily delivered to a target located at some distance from the plasma generation region [1]. Various power driving methods have been used to ignite and sustain low temperature plasma jets. These include direct current (DC), pulsed DC, Radio Frequency (RF), and microwave power [1]. In particular, low temperature plasma jets that are generated at atmospheric pressure are playing an ever increasing role in many plasma processing applications, including surface treatment and in biomedicine. This is because they provide interesting reactive chemistry that can be exploited in various processing applications. Reactive oxygen and nitrogen species (RONS), such as O, OH, O₂⁻, ¹O₂, H₂O₂, NO, NO₂, which are generated by these plasma jets, have been shown to play a central role in their interactions with solids surfaces, liquids, and soft matter (including cells and tissues).

The discovery that atmospheric pressure, low temperature plasma jets are in fact not continuous plasma plumes but fast propagating discrete small volumes of plasma (known as “plasma bullets”) makes the physics of these jets particularly interesting [2,3]. This led to numerous experimental and modeling works which aimed at elucidating their mechanisms of ignition and propagation [4,5,6,7,8]. Today, it is well established that these jets are enabled by guided ionization waves where photoionization and the electric field at the head of the ionization front play important roles [9]. The magnitude of the electric field was measured by several investigators and was found to be in the 10–30 kV/cm range [10,11,12,13].

Low temperature plasma jets have been used in various applications. For example, in material processing, using various operating conditions and gases, they were found to increase the wettability of Polypropylene (PP) and Polyethylene terephthalate (PET) films [14], degrade aromatic rings of dies such methyl violet [15], etch silicon, Si (100), ash photoresist at a rate greater than 1.2 μm/min [16], deposit silicon dioxide, SiO₂, films on various substrates at deposition rates greater than 10 nm/s, etc. However, and by far, the most interesting and emerging applications of low temperature plasma jets are in biomedicine. In this field of research, intense investigations of their various biomedical applications surged ever since the first “bio-tolerant” plasma jets were reported in the mid-2000s [17,18]. Today these plasma jets are being extensively researched for medical applications ranging from wound healing, to dentistry, and to cancer therapy [19,20,21].

This special issue contains articles discussing the latest works which cover both fundamental studies and applications of low temperature plasma jets. The guest editor would like to thank the authors for their valuable contributions and the reviewers for their time and efforts.