Functionalisation of CdSe and GaAs Quantum Dots
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169 Mat. Res. Soc. Symp. Proc. Vol. 581 ©2000 Materials Research Society
EXPERIMENTAL UV/Vis Absorption and IR Spectroscopy The optical measurements of the nanoparticles were carried out on a Philips PU 8710 spectrophotometer. The sample solutions were placed in silica cuvettes (path length = 1 cm). The samples were pyridine solutions and pyridine was used as the reference. Infra-red spectra were carried out using a Matteson Polaris FT-IR spectrometer as nujol mulls. Photoluminescence Spectroscopy (PL) PL measurements were obtained using a Spex FluoroMax instrument with a xenon lamp (150W) and a 152 P photomultiplier tube as a detector. Silica cuvettes of 1 cm path length were used. Solutions were made using pyridine. Scanninm/Transmission Electron Microscopy (SEM, TEM) A JOEL 2000 FX MK1 electron microscope operating at 200 kV with an Oxford Instrument AN 10000 EDS analyser was used for the conventional TEM micrographs. The samples for TEM were prepared by placing a drop of a dilute solution of sample in toluene on a copper grid (400 mesh, Agar). The excess solvent was wicked away with a paper tip and the sample allowed to dry completely at room temperature. Syntheses Preparation of CdSe nanocrystals in TOPO The precursor [Cd{Se 2 CN(CH 3)(C6 H13 )} 2] was prepared by the literature method [14]. The precursor (0.5 g, 0.73 mmol) was then dissolved in TOP (5 ml, 2.8 mmol) and then injected into TOPO (20 g, 51 mmol, degassed at 100 TC for 30 mins prior to use) at 200 TC. The colour of the mixture changed to red. This mixture was allowed to stir for ca. 30 mins where upon the heat was removed. At approximately 60 TC methanol (40 ml) was added to precipitate the nanoparticles. The nanoparticles were centrifuged and would readily redissolve in toluene. Preparation of functionalised CdSe nanoparticles, method 1 The already prepared CdSe/TOPO nanoparticles were taken and washed with methanol to remove most of the capping TOPO. These were then added to the desired ligand and heated whilst stirring for several hours. The nanoparticles were then collected by centrifugation following the addition of a non-solvent. Nonanedithiol capped CdSe nanoparticles were prepared by the same method but using CdSe/C12 H25SH instead of CdSe/TOPO.
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Preparation of functionalised CdSe nanoparticles, method 2 The precursor [Cd{Se 2CN(CH 3)(C6HI 3)}2] (0.22 g, 0.32 mmol) was dissolved in TOP (2.5 ml, 5.6 mmol) and injected into C12H25SH (10 ml, 41.7 mmol) stabilised at 190 'C. The mixture was heated for 20 min and then left to cool. The particles were isolated by centrifugation after addition of a mixture of MeOH and HCCI3 . These were readily redispersed in C12H25SH or toluene. Preparation of GaAs nanocrystals Gallium chloride, (GaCI 3, 0.8 g, 4.6 mmol), was dissolved in 4'ethylpyridine (25 ml, xmol) and to it was added tris(dimethylamino)arsenide, ( [As(NMe 2)3], 0.95 ml, 4.6 mol). This mixture was then slowly heated to 167 TC and allowed to reflux for 5 days at. The solution was allowed to cool and 40 - 60 petroleum spirit was added t
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