A possibility to treat surfaces of various materials by bombardment with neutral atomic oxygen excited to the metastable state 2s22p4(S10), (4.1891 V from the ground) is described. The oxygen dissociation and excitation was developed in plasmas generated in reactors of capacitively coupled dielectric barrier discharge configurations comprised of a quartz or ceramic tube passing throughout two annular electrodes and containing a gas mixture of ∼98% Ar with ∼2% O2 ionized at the atmospheric pressure by the radio frequency discharge at 13.56 MHz and flowing at about 6 m/s. As shown in the experiments, the transition 2s22p4(S10)−2s22p4(D12) with a high degree of probability is responsible for the yellow color of afterglow products, and the lifetime of the metastable state can be as long as 5.4 ms in certain cases, allowing one to separate the excited atomic medium from plasma that it produced. It has been shown that the cleaning process included significant Van der Waals bonds liberation to the depth of several hundred angstroms of surfaces treated, which drastically reduced the percentage of carbon-containing contaminants and changed, to some degree, the chemical structure of surfaces containing chemically bonded oxygen.

This paper describes the increase in surface energy of substrates by their treatment with gas composition generated in plasmas of DBD (Dielectric Barrier Discharge) in O2 admixed with N2. Operating gas dissociation and excitation was occurred in plasmas developed in two types of reactors of capacitively-coupled dielectric barrier configurations: coaxial cylindrical, and flat rectangular. The coaxial cylindrical type comprised an inner cylindrical electrode encapsulated in a ceramic sheath installed coaxially inside a cylindrical ceramic (quartz) tube passing through an annular outer electrode. Components of the flat rectangular type were a flat ceramic tube of a narrow rectangular cross section supplied with two flat electrodes mounted against one another outside of the long parallel walls of this tube. The operating gas, mixture of N2 and O2, was flowing in a completely insulated discharge gap formed between insulated electrodes of the devices with an average velocity of gas inlet of about 7 to 9 m/s. Dielectric barrier discharge plasma was excited in the operating gaps with a bipolar pulse voltage of about 6 kV for 2 ms at 50 kHz repetition rate applied to the electrodes of the coaxial device, and of about 14 kV for 7 ms at 30 kHz repetition rate for the flat linear device. A lifetime of excited to the 2s22p4(1S0) state in DBD plasma and streaming to the surfaces with a gas flow atomic oxygen, responsible presumably for treating surfaces, exceeded 10 ms in certain cases, that simplified its separation from DBD plasma and delivery to substrates. As it was found in particular, surfaces of glass and some of polymers revealed significant enhancement in wettability after treatment.

Solenoid coils with grounded ends positioned on the dielectric window were proposed and numerically studied to reduce the capacitive coupling in conventional inductively coupled plasma (ICP) sources. The capacitive coupling between the plasma and the coils was subsequently suppressed, leading to a significant reduction of the window erosion. To understand the plasma characteristics and the advantages of this configuration, the discharges by the solenoid coil were modeled and compared with a conventional planar coil ICP discharge. The solenoid coil could generate a plasma with higher density than the planar coil under the same absorbed power. The ratio of inductive to capacitive heating power of the solenoid coil was more than one magnitude higher than that of the planar ICP source. The voltage drop on the dielectric window under the solenoid coil was significantly reduced, which was attributed to a potential shielding effect of the grounded end of the radio frequency coil.

No abstract

An influence of different procedures and conditions of cleaning the Langmuir probe surface on its current-voltage characteristic in a plasma is experimentally studied. It is shown that the electronic bombardment of the probe surface and its ohmic warm-up lead to a very effective cleaning of the surface.