Production and Electrical Characterisation of Phosphorene Nanoribbons (PNRs)

In our fast-paced technological world, the demand for more powerful yet smaller devices has fueled the need for nanomaterial innovation. To meet this demand, precise chemical doping techniques can be employed to tailor the properties of low-dimensional materials and facilitate their integration into functional films, electrodes, and spin-based electronics.<br/><br/>Phosphorene nanoribbons (PNRs), a nanomaterial synthesized by our research group at UCL [1], are predicted to exhibit exotic properties, including the Seebeck effect, tunable layer-dependent electronic, optical and ionic transport properties. Recent experiments have demonstrated room-temperature magnetism [2] in PNRs and their ability to enhance hole mobility in solar cells [3]. By combining the flexibility and unidirectional properties of nanoribbons with the high surface area and anisotropic properties of 2D phosphorene sheets, PNRs are expected to exhibit high conductivity due to the 2D confinement of electronic movements and edge effects.<br/><br/>This work focuses on the synthesis of PNRs using a two-step method. Firstly, black phosphorus is intercalated with alkali metal ions, followed by exfoliation to form stable liquid dispersions of PNRs with few-layer thicknesses and 4-50 nm widths uniform along their lengths [4]. This scalable approach allows us to isolate high quality individual PNRs from bulk black phosphorus. In collaboration with Bristol Nanodynamics Ltd., I am using a recently developed high-speed scanning probe microscope, <i>Vector Dynamic SPM</i>, to characterise the local charge distribution of PNRs [5][6].<br/><br/>Vector is an advanced characterization instrument specialising in rapid, high-resolution mapping and nanoscale surface characterisation. This technique enables simultaneous topography and conductivity measurements, providing valuable insights into the spatial maps of conductivity. By analyzing these maps, we can derive insights on how the electronic band structure of PNRs varies with their dimension and number of layers.<br/> <br/>[1] Watts, M. C. <i>et al. </i>Production of phosphorene nanoribbons. <i>Nature </i><b>568</b>, 216–220 (2019).<br/>[2] Ashoka, A. <i>et al. </i>Room Temperature Optically and Magnetically Active Edges in Phosphorene Nanoribbons. <i>Under Rev. </i>(2022).<br/>[3] Macdonald, T. J. <i>et al. </i>Phosphorene Nanoribbon-Augmented Optoelectronics for Enhanced Hole Extraction. <i>Cite This J. Am. Chem. Soc </i><b>143</b>, 21549–21559 (2021).<br/>[4] Cullen, P. L. <i>et al. </i>Ionic solutions of two-dimensional materials. <i>Nat. Chem. </i><b>9</b>, 244–249 (2017).<br/>[5] Payton, O. D., Picco, L. & Scott, T. B. High-speed atomic force microscopy for materials science. <i>Int. Mater. Rev. </i><b>61</b>, 473–494 (2016).<br/>[6] Bristol Nano Dynamics Ltd. <i>Vector Dynamic SPM</i>. Available at: https://nanodynamics.co.uk/vector-dynamic-spm (2024).