Revealing the Surface Structure of CdSe Nanocrystals by Dynamic Nuclear Polarization-Enhanced ⁷⁷Se and ¹¹³Cd Solid-State NMR Spectroscopy

Abstract

J( 77 Se, 113 Cd), heteronuclear 77 Se{ 113 Cd} spin echo (J-resolved) NMR experiments were then used to determine the number of Cd atoms bonded to Se atoms and vice versa.The J-resolved experiments directly confirmed that major Cd and Se surface species have CdSe2O2 and SeCd4 stoichiometries, respectively. Considering the crystal structure of zinc blende CdSe, and the similarity of the solid-state NMR data for the platelets and spheroids, we conclude that the surface of the spheroidal CdSe NCs is primarily composed of {100} facets. The methods outlined here will generally be applicable to obtain detailed surface structures of various main group semiconductors.

PbS Nanocrystals Made Using Excess Lead Chloride Have a Halide-Perovskite-Like Surface

“…60,61 While all these mechanisms introduce carboxylate moieties on the surface of the NCs, their feasibility is inherently reliant on the material's surface structure, chemistry, and thus possible binding motifs. 62 Therefore, the structure of the surface atoms must be determined to paint a complete picture of the colloidal chemistry.…”

“…It was reported that the addition of carboxylates to this surface could proceed through the concomitant displacement of an alkylammonium–chloride . Third, dissociative absorption of carboxylic acids into a proton and carboxylate has been recognized to displace amines, but has only been observed if an amphoteric surface is present, such as afforded by metal oxide NCs. , Finally, simple L-type binding of a carboxylic acid has been reported to occur without the displacement of any surface bound ligands. , While all these mechanisms introduce carboxylate moieties on the surface of the NCs, their feasibility is inherently reliant on the material’s surface structure, chemistry, and thus possible binding motifs . Therefore, the structure of the surface atoms must be determined to paint a complete picture of the colloidal chemistry.…”

Recent Advances and Prospects in Colloidal Nanomaterials

“…While the solid-state NMR (SSNMR) spectroscopy has great potential in analyzing the surface of nanocrystals, poor sensitivity precludes its regular use. Interestingly, the signal intensities can be enhanced by several folds through dynamic nuclear polarization surface enhanced NMR spectroscopy (DNP SENS). , The DNP-SSNMR was used to gain insights into the surface structure of plate- and spheroidal-shaped zinc blende CdSe nanocrystals ligated by carboxylic acids . Various Cd coordination environments, such as CdSe 3 O, CdSe 2 O 2 , and CdSeO 3 , were identified, with the oxygen atoms having originated from the carboxylate ligands.…”

“…77,78 The DNP-SSNMR was used to gain insights into the surface structure of plate-and spheroidal-shaped zinc blende CdSe nanocrystals ligated by carboxylic acids. 78 Various Cd coordination environments, such as CdSe 3 O, CdSe 2 O 2 , and CdSeO 3 , were identified, with the oxygen atoms having originated from the carboxylate ligands. The stoichiometries of the major Cd and Se surface species were established to be CdSe 2 O 2 and SeCd 4 , respectively.…”

Calibrate Ligand-ligand Interaction on Nanocrystals via the Dynamic Volume of Chain Segments

“…Nuclear magnetic resonance (NMR), with a high resolution of organic functionalities, is a preferred tool to pinpoint the ligands on NCs 39 . For instance, different NMR approaches have been used to study ligand coordination structures 17,[40][41][42] , the ligand exchange processes 21,[43][44][45] , and even the surface distributions of ligands [46][47][48] . However, no existing NMR method provides quantitative information on the ligand-ligand interaction, because weak intermolecular forces leave only minute and intractable impact on NMR energy levels, i.e., the chemical shifts.…”