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Similar quality nanoparticles of semiconductors with an organic capping agent have also been prepared. Murray et al. first reported the preparation of TOPO (tri-n-octylphosphine oxide) capped CdE (E = S, Se and Te) in 1993, which has become a popular method of preparing robust, monodispersed high quality semiconductor quantum dots [7]. The nanoparticles, capped with a monolayer of the ligand could be incorporated into simple devices and films, and manipulated into ordered colloidal crystals [8,9]. This method has been extended to cover the preparation of III-V, IV-VI and 113-V2 materials, and the use of single molecule precursors [10-

13].

Murray also described the preparation of cobalt nanoparticles using an alteration of the original TOPO route [14]. Various Lewis base ligands were utilised as passivating agents and reaction solvents for the reduction of COC13 by superhydride. Altering the ligand could control the size of the nanoparticle. The size distribution was small (ca. 5 % - comparable to TOPO capped I-VI materials); manipulation into ordered structures was possible. Bawendi also prepared nanoparticulate cobalt by the thermolysis of Co 2(CO) 8 in TOPO, leading to a new phase of cobalt designated ECo [15]. The preparation of high quality, single domain particles can lead to high-density storage devices, an area of intense current research. Nanoparticles of metal have other potential applications, such as catalysts. Recently, Heath et al. demonstrated a metal - insulator transition in films of silver nanoparticles, which has obvious industrial applications [16]. Here we report the preparation of passivated nanoparticulate Cr, Ni and Au. The nanoparticles were prepared in 47 Mat. Res. Soc. Symp. Proc. Vol. 581 © 2000 Materials Research Society

a TOPO or modified TOPO system and investigations have been undertaken into the effects of basicity and ligand chain length on the particle morphology. In certain cases, we have been able to manipulate the particles into ordered 2D and 3D arrays. 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 dispersed in toluene. Infra-red spectra were carried out using a Matteson Polaris FT-IR spectrometer as CsI pressed discs (1% sample). Nuclear Magnetic Resonance spectroscopy (NMR) The 'H and 31p solution NMR spectra were recorded on a Bruker AM 500 or a DRX 400 in deuterated chloroform. H3PO 4 was used as a phosphorus standard. X-ray Powder Diffraction (XRD) X-ray powder diffraction patterns were measured using a Siemens D500 series automated powder diffractometer using Cu-KI radiation at 40kV/4OmA with a secondary graphite crystal monochromator. Samples were supported on glass slides (5cm 2). Transmission Electron Microscopy and Scanning electron microscopy (TEM, SEM) A JOEL 2000 FX MK1 electron microscope operating at 200 kV with an Oxford Instrument AN 10000 EDS analyser was used for