Session: Chemistry of Materials:

Surface functionalization of two-dimensional nanosheets provides a facile path to tune their intrinsic physical, chemical, and electronic properties. However, methods to directly probe new bond formation at modified surfaces are scarce. Materials characterization techniques often cannot distinguish between intentional surface functionalization and adventitious side reactions (e.g., oxidation) with sufficient resolution, making the assignment of surface binding motifs circumstantial and challenging to distinguish.

Herein the direct observation of deliberate surface functionalization on black phosphorus is reported. Black phosphorus (bP), a 2D van der Waals material composed entirely of tricoordinate phosphorus atoms, is particularly suited to mild and highly specific surface modification protocols due to the availability of lone pairs in its basal plane. While previous efforts to covalently functionalize bP rely primarily on harsh conditions traditionally used for less reactive nanosheets, a mild, surface-specific protocol is used to functionalize few-layer black phosphorus with a family of nitrenes (RN) photolytically generated from the corresponding azides. Functional groups with embedded spectroscopic tags installed on the bP surface allow the chemical structure to be examined in detail with a multitude of characterization techniques including vibrational, X-ray (photoelectron, emission), NMR, and UV-vis spectroscopies. For the first time, the bonds between functional groups and the bP surface are directly probed using infrared spectroscopy and ¹⁵N labeling experiments in conjunction with DFT methods. Diagnostic P=N vibrational stretches are observed, allowing for conclusive identification of iminophosphorane units on the nanosheet surface.

Aaron Rossini

Iowa State University

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