Optimization of fluid characteristics of 2D materials for inkjet printing
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Optimization of fluid characteristics of 2D materials for inkjet printing Monica Michel1, Jay A. Desai1, Alberto Delgado1, Chandan Biswas1,2, Anupama B. Kaul1,2* 1 Department of Metallurgical, Materials and Biomedical Engineering 2 Department of Electrical and Computer Engineering University of Texas at El Paso, El Paso, TX 79968, USA. *Email: [email protected] ABSTRACT 2D materials have shown to be the next step in semiconductor use and device manufacturing that can allow us to reduce the size of most electronics. One of the novel ways to obtain 2D materials is through liquid exfoliation, in which these materials can be obtained by dispersing the smallest possible particles in different solvents. Once obtained, the solutions can be used to manufacture devices via different processes, one of which is inkjet printing. This process relies in selecting “jettable” fluids, which need to have the necessary combination of viscosity and surface energy or “wettability”. In this work we have modified the viscosities and surface energies of five solvents: IPA (Isopropanol), NMP (N-methyl – 2 pyrrolidone), DMA (Dimethylacetamide), DMF (Dimethylformamide) and a mixture of Cyclohexanone / Terpineol 7:3. We have found an avenue to tailor the viscosity of these solvents though the addition of Ethyl Cellulose (EC), where the viscosity has been increased by up to 15 times at an EC concentration of 6%. For inkjet printing, ideally a viscosity of 4 – 10 cP is recommended, which we have been able to achieve with all of the solvents studied. It has been found that the different solvents present different susceptibilities to the EC addition, with DMA and DMF being the least sensitive to the EC addition. We have also studied the change in the drop dynamics and interactions of the 2D solutions with the substrate. Through this analysis we have found solvents that appear to be attractive for inkjet printing of MoS2 and graphite. INTRODUCTION 2D materials, also called single layer materials are the next platform of electronics, especially when it comes to more lightweight, flexible and transparent devices. Different synthesizing and manufacturing techniques exist, and liquid exfoliation has emerged as a promising way of obtaining single and few layer 2D materials as dispersions that can be later used in larger scale [1] [2] [3] [4]. One of the manufacturing techniques that has shown to be of promise is inkjet printing [5], which is an additive manufacturing technique that relies on the purposeful deposition of pico liter size drops of ink on different substrates. Useful inks however, are not readily available, and even after the bulk material has been exfoliated, the actual printing of the dispersions require the inks to have certain properties in order for the inkjet printing process to be successful [6] [7] [8]. The most impactful properties of the ink on the final printing are viscosity, surface tension, and the concentration and characteristics of the dispersed nano particles [9] [10]. In this study, we have tuned the viscosities of five solv
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