Ultra-stable nanoparticles of CdSe revealed from mass spectrometry

Abstract

Nanoparticles under a few nanometres in size have structures and material functions that differ from the bulk because of their distinct geometrical shapes and strong quantum confinement. These qualities could lead to unique device applications. Our mass spectral analysis of CdSe nanoparticles reveals that (CdSe)(33) and (CdSe)(34) are extremely stable: with a simple solution method, they grow in preference to any other chemical compositions to produce macroscopic quantities. First-principles calculations predict that these are puckered (CdSe)(28)-cages, with four- and six-membered rings based on the highly symmetric octahedral analogues of fullerenes, accommodating either (CdSe)(5) or (CdSe)(6) inside to form a three-dimensional network with essentially heteropolar sp(3)-bonding. This is in accordance with our X-ray and optical analyses. We have found similar mass spectra and atomic structures in CdS, CdTe, ZnS and ZnSe, demonstrating that mass-specified and macroscopically produced nanoparticles, which have been practically limited so far to elemental carbon, can now be extended to a vast variety of compound systems.

Mechanistic Study of the Formation of Bright White Light-Emitting Ultrasmall CdSe Nanocrystals: Role of Phosphine Free Selenium Precursors

“…This lack could be due to their relatively low stability in comparison to other magic-sized nanocrystals such as (CdSe)13 and (CdSe)33/34. 60,63 It should be mentioned that the broadness of the LDI-MS peak (covering 5.5-7.5 kDa) could be due to formation of other MSNs during the laser ablation as had earlier been reported. 60 Until now the literature have reported that exclusive formation of single-sized MSNs such as (CdSe)13, (CdSe)34, or (CdSe)56 has only been observed at room temperature.…”

“…60 Until now the literature have reported that exclusive formation of single-sized MSNs such as (CdSe)13, (CdSe)34, or (CdSe)56 has only been observed at room temperature. 41,60,63 Upon heating these nanocrystals at moderately high temperature (>100 0 C), RNCs were formed, which is due to destabilization of MSNs by overcoming the energy barrier. Figure 2B shows the UV-vis spectra of the our reaction mixture containing (CdSe)19 nanocrystals at 60 0 C. Interestingly, with time not only did the band-edge peak red-shift but also the peak intensity decrease.…”

“…This controversy arises because of the identical mass distribution and fragmentation pattern from both ultrasmall semiconductor nanocrystals and bulk semiconductor that had been observed in LDI-MS analysis. 63 To further confirm our experimental data that the sample contained (CdSe)n [n = 29-36] and to distinguish the fragmented species from the original nanocrystal cores, LDI-MS analysis was conducted with variable laser power levels. This approach is very useful in the context of determining the parent core and the fragmented species as was demonstrated for ultrasmall gold nanoparticles 87 and CdSe nanocrystals.…”

Effect of chemical composition on luminescence of thiol-stabilized CdTe nanocrystals

“…The magic numbers for the (CdSe) n clusters (n = 13, 33, and 34) were revealed by mass spectroscopy [7]. These building blocks play a role in constructing the NCs of interest.…”

Effect of size-selective photoetching on the absorption and photoluminescence spectra of CdSe nanoparticles

“…CdSe nanoparticles were prepared by a wet chemical method in reverse micelles put in toluene [12,13] following injection of toluene. Once the toluene is added to this solution, the micelles move up into the toluene and transform into reverse micelles, in which nucleation and further growth of nanoparticles takes place at the temperatures higher than 45˚C.…”