dc.description.abstract | Two-dimensional (2D) materials are one of the promising candidates for future optoelectronics due to their superior properties, including high field-effect mobility within atomic thickness, flexibility, and layered structure, which have benefits of scaling and hetero-integration. Although lots of 2D semiconductors have been widely explored, such as transition metal dichalcogenide (TMDC), each 2D materials have unique characteristics and are readily applied to various applications; for instance, black phosphorus (BP) is one of the 2D materials having thickness-dependent direct bandgap (0.3 eV~2 eV) and high hole mobility up to 103 cm2V-1s-1 in BP-based field-effect transistor (FET), but suffering from its great weakness of instability, which limits its practical applications on nanodevices.
In the first part of this study, an effective and scalable pathway was introduced to protect few-layer BP with the hydrophobic fluorinated compound, achieving long-term stability over five months because of two key factors: (1) A condensed passivation layer which isolates the oxygen and water molecules in air. (2) Fluorination of BP which stabilizes the surface of BP to inhibit oxidation. Moreover, the selectively fluorinated BP was demonstrated through further ultrasonication process, and then fabricated for fluorinated BP FET with the reliable transistor applications in ambient conditions, presenting stabilized properties over one week and the enhanced output current larger than ten times compared to the pristine BP FET.
For the second part, the solution-processed BP nanosheets were explored and applied to the emerging memory, namely resistive random-access memory (RRAM) and memristor. The RRAM exhibited the non-volatile property and high on/off ratio of 102, as well as long retention time up to 1500 s. In addition, the novel method to exfoliate highly crystalline BP by melamine-assisted liquid-phase exfoliation (LPE) was introduced, and BP nanosheets together with supramolecular assembly could be directly extracted. Afterward, the incorporated BP nanosheets with supramolecules were integrated into the memristor and unidirectional selector, where the memristor presented analog resistive switching behaviors as well as potentiation and depression by applying both voltage sweeping and pulse. The threshold switching (TS) selector constructed by different structures was also investigated, displaying the nonlinearity of 30 mV/dec, high on/off resistance ratio up to 104, and long retention time over 4000 s. Most importantly, the transport mechanisms of the memories were unveiled through fitting data and material identification where BP nanosheets served as conducting paths for the transport of charge carriers in the active layer. | en_US |