Low-temperature hydrogen plasma for large-area surface modification of materials
|Year of publication
|MU Faculty or unit
|We present atmospheric pressure cold plasma technology generating high power density plasma for surface modification of materials and coatings. A large area diffuse coplanar surface barrier discharge (DCSBD) was used to generate high power density (up to 2.5 W/cm2) surface plasma in hydrogen reducing gases. The surface plasma generated by proprietary, easily scalable, DCSBD discharge is macroscopically homogeneous in ambient air and other standard technical gases as N2, O2, Ar, CO2, water vapour and others. Moreover, the diffuse plasma can be generated also in pure hydrogen and H2-containing gas mixtures. The use of various gas leads to different plasma-chemical reactions on the surfaces of treated materials. The use of argon and hydrogen led to reducing and etching processes induced by plasma treatment. Besides that, we present also a hydrogen-containing plasma generation using a novel multi-hollow surface dielectric barrier discharge. Pure hydrogen plasma or H2-containing plasma was previously used for surface modification of copper oxide layers, surface cleaning and etching of silicon dioxide on top of silicon wafer, chemical modification of nanodiamonds and plasma nanostructuring of polymer substrates. In this contribution we focus on two latest application of reducing DCSBD plasma: i) reduction of thin titanium dioxide films and ii) selectivity of the etching process in pure hydrogen. We used hydrogen plasma for modification of flexible transparent metallic/polymer mesh composite substrate based on polymethyl methacrylate foil with embedded Ag-coated Cu-wires. The observed moderate etching process in pure hydrogen was found strongly selective and influenced mainly polymeric structures rather than metallic ones. In contrast, the etching in ambient air, pure N2, and N2/H2 mixtures, resulting in a strong degradation both the polymer and metal parts of the substrate. Only the etching in pure H2 plasma let to the fast (~ 1s) selective etching of the thin surface polymer film with no damage to the metallic electrodes. Titanium dioxide (TiO2) is widely investigated material for decades due to its versatile properties e.g. for photocatalysis. We studied surface reduction of TiO2 and the generation of localized Ti3+ states by means of x-ray photoelectron spectroscopy. We show that it is possible to achieve interesting results by hydrogen DCSBD plasma treatment without any high-pressure, high-temperature process taking even several hours. Low-temperature hydrogen DCSBD plasma can create a significant amount of Ti3+ defects (about 22 % Ti3+/Ti4+) even after plasma exposures only of tens of seconds or several minutes. As presented, a hydrogen DCSBD plasma technology is ready for large-area modification of flexible substrates even in roll-to-roll configuration. Integration of diffuse and stable hydrogen plasma processes in fast roll-to-roll line brings new possibilities in application of reducing plasma for high-speed and low-cost manufacturing of materials.