Composition Control and Localization of S²⁻ in CdSSe Quantum Dots Grown from Li₄[Cd₁₀Se₄(SPh)₁₆]

Abstract

The development of ternary nanoscale materials with controlled cross-sectional doping is an important step for the use of chemically prepared quantum dots for nanoscale engineering applications. We report cross-sectional, elemental doping with the formation of an alloyed CdSSe nanocrystal from the thermal decomposition of Li(4)[Cd(10)Se(4)(SPh)(16)]. The sulfur incorporation arises from surface-mediated phenylthiolate degradation on the growing quantum dot surface. In the alloy, we identify a pure CdSe nucleus of approximately 1.5 nm, consistent with the predictions of nucleation theory. As the particle grows, S(2-) incorporation increases until the CdSSe reaches approximately 4 nm, where a marked reduction in phenylthiolate content on the nanocrystal is observed by CP-MAS NMR spectroscopy, implying that rapid decomposition of the phenylthiolate arises with subsequent enhanced S(2-) incorporation at the level of the stoichiometry of the reaction (namely approximately 60%). The use of molecular clusters to allow controlled defect ion incorporation can open new pathways to more complex nanomaterials.

Effects of dopants on the band structure of quantum dots: A theoretical and experimental study

“…To perform the synthesis, ∼1. gested that this synthetic method can produce an alloyed material (CdS x Se 1−x ) 16 . Typically, the samples present between 1% and 3% sulfur content.…”

Studies on the Formation of CdS Nanoparticles from Solutions of (NMe4)4[Cd10S4(SPh)16]

“…The authors considered the presence of Ph 2 Se 2 in the GC/MS spectra as an indication of the presence of [M(SePh) 2 ] or [M(SePh) 3 ] -species. [19] Finally, Lovingood et al [20] proved the formation of CdSSe NPs instead of CdSe NPs [17] (SPh) 16 ] in HDA. NPs prepared at higher temperatures (230°C) had a higher S 2-proportion compared to those prepared at 120°C.…”

Specific effects in microwave chemistry explored through reactor vessel design, theory, and spectroscopy

“…The high efficiency of MW heating has led to the use of MW reactors to improve the carbon footprint in chemistry or, in effect, the ''greenness'' of preparing desired molecules, a grand challenge in synthetic chemistry. [8][9][10][11][12] In MW-enhanced nanomaterial reactions, the resultant controlled growth is more likely due to selective dielectric absorption driving nucleation by conversion of MW into thermal energy by Debye processes, as currently discussed in the literature, 13,14 than to non-thermal effects. [1][2][3][4][5] In response, a rapid growth of publications utilizing MW chemistry has occurred in the literature, including in nanoscience, following our report on MW-initiated nucleation of reactants where uniform nanocrystal growth was observed with greatly shortened reaction times.…”

“…6,7 Why such drastic MW enhancement is observed in the reaction rate is widely debated and, in the case of nanomaterials, the role of MW photon absorption by the precursors has been suggested. [8][9][10][11][12] In MW-enhanced nanomaterial reactions, the resultant controlled growth is more likely due to selective dielectric absorption driving nucleation by conversion of MW into thermal energy by Debye processes, as currently discussed in the literature, 13,14 than to non-thermal effects. 15,16 To date, MW synthesis studies show that a MW photon's energy is too low to break a chemical bond and spectroscopically excites only molecular rotations.…”