Band gap engineering of CdTe nanocrystals through chemical surface modification

Journal of the American Chemical Society

Volumn 127, Issue 6, 2005, Pages 1634-1635

  Akamatsu, Kensuke ^a   Tsuruoka, Takaaki ^a   Nawafune, Hidemi ^a  

^a KONAN UNIVERSITY   (Japan)

Author keywords

[No Author keywords available]

Indexed keywords

1 DECANETHIOL; ACETONITRILE; BROMINE DERIVATIVE; CARBOXYLIC ACID; DODECANETHIOL; TETRA N OCTYLAMMONIUM BROMIDE; THIOL DERIVATIVE; TOLUENE; UNCLASSIFIED DRUG;

ARTICLE; BIOENGINEERING; CHEMICAL MODIFICATION; CRYSTAL STRUCTURE; HIGH TEMPERATURE; SEMICONDUCTOR; STOICHIOMETRY; SURFACE PROPERTY; SYNTHESIS;

EID: 13644264060     PISSN: 00027863     EISSN: None     Source Type: Journal    
DOI: 10.1021/ja044150b     Document Type: Article

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23. 1/2 = 0.64 h). These results imply that the reaction does not depend on initial nanocrystal size (and therefore relative surface area) because the reaction is performed with an excess of DT relative to CdTe nanocrystals in the solution.
24. To characterize single nanocrystals, we performed nanobeam EDX analysis using a 3-nm electron beam spot for TEM observation. The composition of single nanocrystals was broadly consistent with the average composition obtained by EDX analysis in FESEM observation (Table 1). These results also gave direct evidence of Te dissociation from the nanocrystals and S incorporation into the nanocrystals.
25. 3). The initial 3.3-nm CdTe nanocrystal has ca. 276 Te atoms. EDX analysis reveals that ca. 57% Te is dissociated after reaction for 5 h (Table 1), which indicates that ca. 117 Te atoms remain in the CdTe core. This implies formation of CdTe cores with a diameter of 2.5 nm, which reasonably accounts for the emission peak wavelength of the nanocrystals obtained 5 h after reaction (520 nm). Since the estimated core size indicates a shell thickness of ca. 4 Å and the lattice constant of cubic CdTe is 6.5 Å, it is considered that only the outermost Te ions dissociate to achieve the final core size of 2.5 nm. When the outermost Te species are almost completely exchanged with DT, the DT layers thus formed may prevent further dissociation of Te from the core so that the reaction is terminated, resulting in saturation of the spectral blue shift.
26. This reaction did not work for CdSe nanocrystals. This may be due to the relative stability of Se towards oxidation. We believe that the present process is due to the inherent instability of Te anions, which can be readily oxidized by dissolved oxygen (ref 6).