Some effects of single molecule precursors on the synthesis of CdS nanoparticles P. Sreekumari Nair 1 , T. Radhakrishnan 1,2 , N. Revaprasadu 1 and P. O’Brien* 3 This paper reports the synthesis of CdS nanoparticles using bis(methylhexyldithiocarbamato)- cadmium (II), Cd(S 2 CNMeHex) 2 ; a cadmium complex of dithiobiurea, Cd(NH 2 CSNH) 2 Cl 2 cadmium ethylxanthate, Cd (C 2 H 5 OCS 2 ) 2 ; and a thiosemicarbazide complex of cadmium, Cd(NH 2 CSNHNH 2 ) 2 Cl 2 as single molecule precursors. In all cases the precursors were thermolysed in tri-n-octylphosphine oxide(TOPO) at a temperature of 250uC. A comparison of the optical properties of the particles from the various precursors are reported. Characterisation of the particles using X-ray diffraction and electron microscopy techniques is also reported. Keywords: Cadmium sulphide, Nanoparticles, Precursors Introduction During the past decade research on nanodimensional materials has been at the forefront of scientific activity. Early work focused on the designing of synthetic routes to high quality materials in the nanosize regime and to studies on the structure and photophysical properties of materials. Studies on chalcogenides have attracted interest due to their non-linear properties, luminescent properties, quantum size effects, and unique chemical and physical properties. 1–5 Currently work has shifted towards the processing of nanoparticles for use in novel applications in areas such as non-linear optics, electro- nics, photoluminescence, catalysis, biological sensors, solar cells, and optoelectronics. The efficient processing of nanoparticles requires that the particles be of high quality, monodispersed, and sufficiently surface passi- vated to have useful stability. In this regard there is still a need to find efficient routes to good quality nanoparticles for effective processing. Our group has investigated the use of single source molecular precursors to synthesise tri-n-octylphosphine (TOPO) capped nanoparticles. A series of alkylcadmium dithio-and diseleno carbamate complexes were used as precursors for the ‘one pot’ preparation of MS and MSe (where M5Cd, Zn, Pb, In) nanoparticles. 6–10 In this procedure the precursor is dissolved in tri- n- octylphosphine (TOP) and injected into TOPO at high temperatures (.200uC). Rapid nucleation occurs followed by slow growth and finally termination of growth. After a period of heating, the solution was cooled to 70uC, an excess methanol added resulting in the formation of a flocculant precipitate of the particles. The particle size and size distribution depends upon the reaction time, temperature, and ratio of capping agent to precursor used. Investigations have recently been made into the use of various precursors that have been thermolysed in TOPO to give TOPO capped CdS nanoparticles. This paper reports on a comparative study of CdS nanoparticles synthesised using the air stable single molecule precursors, bis(methylhexyldithiocarbamato)cadmium (II), 10 Cd(S 2 CNMeHex) 2 ; a cadmium complex of dithio- biurea, 11 Cd(NH 2 CSNH) 2 Cl 2 cadmium ethylxanthate, 12 Cd (C 2 H 5 OCS 2 ) 2 ; and a thiosemicarbazide complex of cadmium, 13 Cd(NH 2 CSNHNH 2 ) 2 Cl 2 . Optical and struc- tural properties of the CdS nanoparticles are compared using UV/Vis, photoluminescnce (PL), X-ray diffraction (XRD), and transmission electron microscopy (TEM) techniques. The yield, quality, size, and size distribution of CdS nanoparticles are also compared. Experimental Chemicals Cadmium acetate, N-methylhexylamine, cadmium chloride, potassium ethylxanthate, dithiobiurea, thiose- micarbazide, methanol, toluene, carbon disulphide and 1,4 dioxane used in the synthesis were analytical grade. Tri-n-octylphosphine (TOP) (Aldrich) was used as supplied. TOPO was purified by the method described in the literature. 14 Synthesis of precursors Cd(S 2 CNMeHex) 2 A mixture of Cd(OH) 2 . 2H 2 O(8?43 g, 46?2 mmol), CS 2 (4?6 mL 77?2 mmol) and N-methylhexylamine (11?6 mL, 76?3 mmol) in ethanol (50 mL) was heated at 70uC for 1 h. The mixture was filtered to remove the solid impurities and the clear filtrate was evaporated under vacuum. The yellow solid product was recrystallised from chloroform to give Cd(S 2 CNMeHex) 2 (mp 74uC; yield 14?11 g, 28?6 mmol, 75%). 1 Department of Chemistry, University of Zululand, Private Bag X1001, KwaDlangezwa, 3886, South Africa 2 Department of Chemistry, University of Kerala, Trivandrum, India 695581 3 The Manchester Materials Science Centre and Department of Chemistry, Manchester University, Oxford Road, Manchester M13 9PL, UK *Correponding author, email paul.obrien@manchester.ac.uk ß 2005 Institute of Materials, Minerals and Mining Published by Maney on behalf of the Institute Received 19 December 2003; accepted 28 November 2004 DOI 10.1179/174328405X20914 Materials Science and Technology 2005 VOL 21 NO 2 237