Siming Dong

Research Interests

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. TiN_x/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.

Publications

• S. Dong, M. Watanabe, R.H. Dauskardt, Conductive Transparent TiNx/TiO2 Hybrid Films Deposited on Plastics in Air using Atmospheric Plasma Processing, Advanced Functional Materials, 24, 3075-3081, 2014.
• S. Dong, Z. Zhao, R. H. Dauskardt, Highly Transparent Bilayer Organosilicate Multifunctional Coatings on Plastics Deposited by Atmospheric Plasma Deposition with Dual Organic and Inorganic Precursors in Air,  ACS Applied Materials & Interfaces, 7, 17929-17934, 2015 . 
• S. Dong, Z. Zhao, R. H. Dauskardt, Role of Carbon Bridge length in Organosilicate Precursors on the Atmospheric Plasma Deposition of Transparent Bilayer Protective Coatings on Plastics, submitted.
• Contamination and moisture absorption effects on the mechanical properties of catalyst coated membranes in PEM fuel cells, International journal of hydrogen energy, 37 (2012) 6790-6797.
• Membrane-based electrolyte sheets for facile fabrication of flexible dye-sensitized solar cells, Electrochimica Acta, Vol 56, Issue 17(2011).
• Copper iron bimetal modified PAN fiber complexes as novel heterogeneous Fenton Catalysts for degradation of organic dye under visible light irradiation, Journal of Hazardous Material, 189 (2011) 241–248.

Conference Proceedings and Presentations

• R.Jia, S. Dong, R.H. Dauskardt, Durability of Platinum-Based Catalysts in Fuel Cell Membranes, MRS Spring Meeting, Apr. 10, 2012
• S. Dong, L. Cui, M. Watanabe, R.H. Dauskardt, Atmospheric Plasma Deposition and Durability of Transparent Functional Coatings, CIS AdCom Meeting, Stanford, November 12, 2013. 
• S. Dong, M. Watanabe, R.H. Dauskardt, Conductive Transparent TiNx/TiO2 Hybrid Films Deposited on Plastics in Air using Atmospheric Plasma Processing, MRS Spring Meeting, San Francisco, CA, April 2, 2014.
• S. Dong, Z. Zhao, R. H. Dauskardt, Atmospheric Plasma Deposition of Transparent Organosilicate Multifunctional Coatings on Plastics in Air, MRS Spring Meeting, San Francisco, CA, April 9, 2015.
• S. Dong, L.Cui, Z. Zhao, R.H. Dauskardt, Atmospheric Plasma Deposition of Transparent Organosilicate Multifunctional Coatings on Plastics in Air, E-MRS Meeting, Lille, France, May 11, 2015.
• S. Dong, Z. Zhao, R. H. Dauskardt, Atmospheric Plasma Deposition of Transparent Organosilicate Multifunctional Coatings on Plastics in Air, AVS 62 meeting, San Jose, CA, Oct 23, 2015.
• S. Dong, Z. Zhao, Y. Ding, L. Cui, R.H. Dauskardt, Atmospheric Plasma Deposition and Durability of Transparent Functional Coatings, SystemX Conference, Stanford, November 18, 2015. 

Awards

• The Enlight Foundation Engineering Fellowship Fund (2012)