Synthesis of Self-Capped Metal Sulfide Nanoparticles
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reported the use of single source precursors to prepare several II/VI chalcogenides [12-14]. These nanocrystals are organically capped with tri-n-octylphosphine oxide (TOPO). Other capping groups such as 4-ethylpyridine have also been used to solubilise nanocrystals, for example, InP [15]. We have also recently reported the use of trioctylphosphine sulfide as an air/moisture stable sulfiding precursor [16] for cadmium or zinc sulfide. However, to date there has only been one paper [17] describing the synthesis of nanocrystals in a process in which the particle is capped by a ligand transferred from the precursor; we term this process 'self-capping'. Finely divided silver has been prepared from the salts of fatty acids by a bulk pyrolysis. Here we report the first synthesis of self-capped CdS and ZnS nanocrystals from the thermolysis at 150 - 300 °C, in a dynamic vacuum, of the novel asymmetric metal dithiocarbamates, bis(N-methyloctadecyldithiocarbamato) cadmium(II) or zinc(II) [M {S2CN(C 18H 37)(CH 3)}2]. 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). 175 Mat. Res. Soc. Symp. Proc. Vol. 581 © 2000 Materials Research Society
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. Nuclear Magnetic Resonance spectroscopy (NMR) The 1H and 13C solution NMR spectra were recorded on a Bruker AM 500 or a DRX 400 in deuterated chloroform. X-ray Powder Diffraction (XRD) X-ray powder diffraction patterns were measured using a Siemens D500 series automated powder diffractometer using Cu-K0 radiation at 40kV/4OmA with a secondary graphite crystal 2 monochromator. Samples were supported on glass slides (5cm ).
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. Energy Dispersive Analysis by X-rays (EDAX) EDAX was performed on samples deposited by evaporation on glass substrates by using a JEOL JSM35CF scanning electron microscope. Scanning/Transmission Electron Microscopy (SEM, TEM) A JOEL 2000 FX MKI 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. X-ray Photoelectron Spectroscopy (XPS) The XPS measurements were performed in the ultra-high vacuum chamber (base pressure 10.8 Pa) of a VG ESCALAB-Mk II (VG Scientific) using Al Kct excitation (analyser pass energy of 50 eV). The energy scale was calibrated using C1
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