Interfacing Quantum Dots and Graphitic Surfaces with Chlorine Atomic Ligands

Abstract

The performance of devices based on semiconductor nanocrystals (NCs) improves both with stronger interface interactions among NCs and between NCs and solid electrode surfaces. The combination of X-ray photoelectron spectroscopy (XPS) and solid 31P CP/MAS NMR (cross-polarization/magic angle spinning nuclear magnetic resonance) shows that the selective substitution of long organic chains by chlorine atomic ligands during the colloidal synthesis by the hot injection method promotes the adsorption of CdSe NCs to carbon sp2 surfaces, leading to the formation of well-ordered NC monolayers on graphitic materials.

The Role of Halogens in the Synthesis of Semiconductor Nanocrystals

“…This was firstly observed in 2007, when including carbon nanotubes dispersed in DCE during the synthesis of CdSe rods, pyramidal NCs attached to the nanotubes were obtained [7,33]. Since then, several works have evidenced the possibility to decorate any carbon sp 2 lattice (also other wurtzite NCs types such as ZnO) [47] following the same procedure, which guaranties a monolayer of NCs on the graphene surface [29,33]. As explained before, the original shell combining ODPA 2− and anhydrides for CdSe is modified by the presence of chloride anions, which displace the anhydrides selectively and promotes the interaction with C-sp 2 surfaces.…”

“…As explained before, the original shell combining ODPA 2− and anhydrides for CdSe is modified by the presence of chloride anions, which displace the anhydrides selectively and promotes the interaction with C-sp 2 surfaces. This incorporation of chloride strengthens the interaction, as demonstrated by the fact that NCs with larger amounts of Cl on their surface (determined by XPS) decorate the C-sp 2 surfaces more efficiently than particles with a lower amount [29].…”

“…This trend is inverse for high Cd/Se values (Cd/Se > 1). The fact that the Cl/Cd and P/Cd ratios follow opposite trends as a function of the Cd/Se precursor molar ratio sup- [29]. The shift in the whole spectrum could be attributed to the influence of adjacent chlorine atoms in the capping shell.…”

“…It is worth mentioning that, in contrast to the labile interaction of NCs monolayers covered with long alkyl chains obtained by means of techniques such as Langmuir-Blodgett, the monolayers obtained by this method (named pot-deposition) [29] are relatively strong and do not detach from the carbon sp 2 lattice by washing the substrates in toluene or under mild sonication conditions. High Angle Annular Dark Field (HAADF) Scanning Transmission Electron Microscopy (STEM) tomography studies were performed to ascertain the three di- mensional geometry of the attached NCs.…”

Size and Aspect Ratio Control of Pd2Sn Nanorods and Their Water Denitration Properties

“…Schematic illustration of the influence of the TOP and chloride ions on the shape and size of the Pd 2 Sn NRs.Several theories have been proposed to explain the influence of halide ions on the shape control of Pd, 30 Ag,[31][32] Au,[33][34][35] and CdSe[36][37][38][39] NPs. Halides may modify the reduction potential of the metal ions, passivate specific NP surfaces or control surface passivation by modulating the concentration of surface ligands [31][32][33][34][40][41].…”