Nitrogen-doped carbons are useful as supports for catalysts due to their low cost, low density, and enhanced metal-support interaction. We used density functional theory (DFT) to evaluate the effects of N-doping and oxidation of graphene on the adsorption and dissociation of trimethyl (methylcyclopentadienyl) platinum (MeCpPtMe₃), which is commonly used for synthesizing platinum nanoparticles and films by chemical vapor or atomic layer deposition. We confirmed that oxygen incorporation in graphene via oxidation of monovacancies is thermodynamically favorable with and without N doping and discovered that N doping elongates substrate-oxygen bonds, indicating increased reactivity of the oxygen atoms bound to the substrate. According to nudged elastic band calculations, the transfer of a Me ligand from MeCpPtMe₃ to oxidized substrates with and without N-doping displays positive enthalpies of reaction and activation energies, making Me transfer a rate determining step. However, nitrogen doping thermodynamically and kinetically drives the Me dissociation reactions by lowering the enthalpies and activation energies of the reactions. We also showed that the dissociation of MeCpPtMe₃ and subsequent adsorption of Me and MeCpPtMe₂ on identical oxidized monovacancies is endothermic but is made exothermic by pyridinic N dopants. Thus, the adsorption and dissociation of MeCpPtMe₃ is expected to occur more readily on N-doped substrates than undoped ones. We also experimentally demonstrated that elevated N and O content in mesoporous carbon supports causes MeCpPtMe₃ to deposit more platinum but only at increased temperature (300 °C).

Traditional lithography requires multiple processing steps in a resource-intensive cleanroom environment. To overcome the limitations of traditional lithographic patterning and alignment, there has been tremendous interest in developing new methods for additive manufacturing. E-jet printing is an additive manufacturing technique which allows for fast and versatile printing with high resolution. Previously, e-jet printing was used to directly deposit functional materials on the surface with solution inks. Compared to this, ALD can deposit high-quality materials with unparalleled control of film thickness and uniformity at relatively low temperatures.

Our previous work has shown that by directly printing inhibitor polymers on the surface, we can locally activate/passivate atomic layer deposition (ALD) growth for area-selective ALD (AS-ALD) [1,2]. This technique allows customizable patterns with different geometries and high resolution without the need for premade alignment masks. However, AS-ALD may suffer from defect growth and/or vapor-phase-infiltration through the inhibitor polymers which can cause undesired growth on the surface. In this study, we demonstrate the use of subtractive electrohydrodynamic jet (e-jet) printing with acid-based ink to directly pattern the metal oxides deposited with ALD.

To pattern 50 nm thick ALD ZnO that was deposited on the silicon substrate, 0.1M hydrochloric acid mixed with glycerol was used as the ink for e-jet printing. When the ink was printed, glycerol residue was left behind on the surface after ink evaporation. After soaking the sample in water, the glycerol residue was washed away with ZnO; ZnO was removed on the printed regions, exposing the underlying silicon surface. Atomic force microscopy, scanning electron microscopy, and energy dispersive spectroscopy were performed to analyze the surface topology/chemistry after patterning the ZnO layer. With e-jet, linewidth and etched depth can be precisely controlled with printing speed and the number of printed layers. This new technique can provide flexible and customizable patterning of metal oxides without the need for AS-ALD or lithography.

[1] T.H. Cho, N. Farjam, C. R. Allemang, C. P. Pannier, E. Kazyak, C. Huber, M. Rose, O. Trejo, R. L. Peterson, K. Barton, N. P. Dasgupta, ACS Nano 14, 17262 (2020)

[2] N. Farjam, T.H. Cho, N. P. Dasgupta, K. Barton, Appl. Phys. Lett.117, 133702 (2020)

[3] T. H. Cho, N. Farjam, K. Barton, N. P. Dasgupta, In preparation (2022)

In order to develop a sustainable ALD process cluster tool, it is necessary to establish a manufacturing technology for a high-productivity high-efficiency ALD process chamber that reduces the intrinsic excessive consumption of energy and materials.¹ In the present study, as the part of countermeasure to the excessive consumption, a micro-gap ALD process chamber is considered for the optimized design. The changes in the flow field of nitrogen in the process space of the process chamber with the gap sizes of 1 mm and 10 mm respectively are observed at 200 ^oC, utilizing computational fluid CFD numerical analysis. For the present nitrogen flow field with a background pressure of 1 Torr and a temperature of 200 ^oC, the Knudsen number Kn<0.1 and Reynolds number Re<<2300 are evaluated, and consequently the continuity and momentum equations of a steady-state compressible laminar flow field are considered.²

Acknowledgment

This work was supported by the Korean Ministry of SMEs and Startups, under Award no. S2960951.

References

[1] C.Y. Yuan and D.A. Dornfeld, 2010, J. of Manufacturing Science and Engineering, 132, 030918 (2010).

[2] M. R. Shaeri, T.-C. Jen, C. Y. Yuan and M. Behnia, International Journal of Heat and Mass Transfer, 89, 468 (2015).