Atmospheric plasma deposition is an emerging technique that enables plasma deposition of coatings on large and/or complex geometry substrates in ambient air without the need of a chamber. It has the advantage of minimal chemical waste throughout the process and is solvent-free compared, for example, to sol-gel techniques. The deposition temperature is usually below 100 oC which opens up the possibility to treat a variety of substrates including plastics and biological tissues.
The successful deposition of conductive transparent TiNx/TiO2 hybrid thin films on Si wafer and polycarbonate (PC) from titanium ethoxide was demonstrated by using atmospheric plasma process with high-temperature precursor delivery system. The hybrid films chemical composition, deposition rate, optical and electrical properties as well as adhesion energy with the polycarbonate substrate were investigated as a function of plasma power and nitrogen flow rate. The film was a hybrid of amorphous TiNx and Rutile phase TiO2, and the TiNx content increased with higher plasma power and nitrogen flow rate. The visible transmittance increased from 71% to 83% with decreasing plasma power and nitrogen flow rate. The film resistivity was in the range of 8.5×101 ohm cm to 2.4×105 ohm cm. The adhesion energy on the polycarbonate ranged from 1.2 J/m2 to 8.5 J/m2 with increasing plasma power and decreasing nitrogen flow rate. Finally, it is found that annealing the film or adding H2 to the primary plasma gas significantly affected the composition and decreased thin film resistivity.
Figure 1. TiNx/TiO2 hybrid films on polycarbonate substrates is deposited in air using atmospheric plasma processing.
We demonstrate a dual organic and inorganic precursor method to deposit transparent organosilicate protective bilayer coatings on poly methyl methacrylate (PMMA) substrates with atmospheric plasma deposition in ambient air. The bottom layer was a hybrid organosilicate adhesive layer deposited with dual organic 1, 5-cyclooctadiene (CYC) and widely used inorganic Tetraethoxysiline (TEOS) precursors. The selection of the organic CYC precursor allowed incorporation of carbon chain in the organosilicate adhesive layer, which resulted in improved adhesion. The top layer was a dense silica coating with high Young’s modulus and hardness deposited with TEOS. The deposited bilayer structure showed ~100% transparency in the visible light wavelength region, twice the adhesion energy and five times the Young’s modulus of commercial polysiloxane sol-gel coatings.
Figure 2. Relation between Young’s modulus and adhesion energy to PMMA for top, bottom, bi-layer deposited by atmospheric plasma deposition, and the commercial sol-gel polysiloxane coatings.