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Colloidal Two-Dimensional Nanosheets as Functional Inks for Printable Electronic Thin-Films


Thin-films deposited through scalable printing techniques is key to next generation large-area electronics, such as displays, sensors, and soft electronics. The typical thin film deposition approaches such as chemical vapor deposition and high vacuum physical vapor deposition are energy intensive, or require high temperatures that limit the diversity of substrates, and are generally too costly for the next generations of cheap wearable electronics. Solution-processable thin-films can be prepared at ambient pressures and temperatures allowing electronics to be made on soft plastic substrates for flexible devices. To this end, solution processable inorganic nanomaterials have superior stability and electronic performance when compared to currently researched organic semiconducting materials. In particular, two-dimensional nanosheets represent an attractive candidate for solution-processed thin-film electronics. Their ultrathin wide-area structure offers the perfect geometry to form electronic thin-films with complete coverage, and the natural flexibility of such 2D nanosheets suits well for the needs of soft electronics. To enable robust application of colloidal nanosheets for solution-processed electronics, an essential task is to develop functional 2D inks with controllable thickness, size and electronic properties. Additionally, new printing and processing techniques need to be investigated to produce uniform films. This thesis will look at both bottom-up synthesis and top-down intercalation exfoliation methods of producing colloidal nanosheets which can then be further processed into inks. For synthetic methods, we investigate the preparation of InSe and SnSe nanoplates using long chain amines as a surfactant. For top-down strategy, we focus on using electrochemistry to intercalate and then further exfoliating with gentle bath sonication. Initially MoS2 is investigated by cathodically intercalating large organic quaternary ammonium ions using a simply electrochemical cell setup. This produces MoS2 that remains in its 2H state with electron mobilities of 10 cm2�V-1�s-1. The produced nanosheets of MoS2 shows promising semiconducting thin-film applications with superior electronic performance. Finally, by utilizing home-grown layered crystals, we show a large family colloidal nanosheets (InSe, In2Se3, Bi2Se3, Bi2Te3, SnSe2, SnS2, etc) may be prepared using a similar intercalation and exfoliation approach.

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