The Surface Structure of Semiconductor Nanoparticles Revealed

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(Top) Schematic structure of a semiconductor nanoparticle showing the crystalline core region, the surface region and capping ligands. (Lower) The impregnated powder procedure described in this work yields 9-fold better DNP NMR sensitivity than the previously described impregnated support procedure.
(Top) Schematic structure of a semiconductor nanoparticle showing the crystalline core region, the surface region and capping ligands. (Lower) The impregnated powder procedure described in this work yields 9-fold better DNP NMR sensitivity than the previously described impregnated support procedure.

Semiconductor nanoparticles (NPs) have a wide range of potential applications including, but not limited to LEDs, solar cells, batteries, catalysts and bio-sensors. The properties and functionality of semiconductor NPs are controlled and modified by altering their surface structure. Surface enhanced NMR spectroscopy (SENS) is an attractive method for surface characterization but current sample preparation protocols requires the NPs to be dispersed in porous silica. This procedure leads to sub-optimal DNP enhancements and dilution of the NPs. This work demonstrates that dispersing the NPs in hexagonal boron nitride (h-BN) improves DNP NMR sensitivity by nearly one order of magnitude. The favorable dielectric properties of h-BN improves coupling of the microwaves in the sample. The improved NMR sensitivity enabled a variety of challenging 2D homonuclear and heteronuclear correlation NMR experiments to be performed on CdS, Cd3P2and Si NPs. These 2D experiments provide detailed insight into the structure and connectivity of surface and core atomic environments in the NPs. These experiments will be used in the future studies to obtain a molecular level understanding of how post-synthetic treatments alter structure and improve the optoelectronic properties and stability of NPs.

M.P. Hanrahan, Y. Chen, F.A. R. Blome-Fernández, J.L. Stein, G.F. Pach, M.A.S. Adamson, N.R. Neale, B.M. Cossairt, J. Vela, A.J. Rossini. Probing the Surface Structure of Semiconductor Nanoparticles by DNP SENS with Dielectric Support Materials, J. Am. Chem. Soc., 2019, 141, 3915532-15546, DOI: 10.1021/jacs.9b05509.