Neerish Revaprasadu

Cadmium ethylxanthate: A novel single-source precursor for the preparation of CdS nanoparticles

CdS nanoparticles capped with tri-n-octylphosphine oxide (TOPO) have been synthesised by a single-source route using cadmium ethylxanthate as a precursor. The nanoparticles obtained show quantum size effects in the optical absorption spectra and the photoluminescence shows an emission maximum that is characteristically red shifted in relation to the band edge. The X-ray diffraction (XRD) pattern shows the material to be hexagonal with a calculated particle size (from the Scherrer equation) of 3.9 nm. The size of the particles is confirmed by the transmission electron microscope (TEM) image, which shows well-defined, spherical particles with an average size of 4.2 nm ± 10%.

Preparation of CdS nanoparticles using the cadmium(II) complex of N,N′-bis(thiocarbamoyl)hydrazine as a simple single-source precursor

CdS nanoparticles have been synthesised by thermolysing Cd(SCNHNH2)2Cl2 in tri-n-octylphosphine oxide (TOPO) at 230°C. The optical properties and structural characteristics of the particles are reported.

Heterocyclic dithiocarbamates: precursors for shape controlled growth of CdS nanoparticles

We report the synthesis of hexadecylamine (HDA) and tri-n-octylphosphine oxide (TOPO) capped CdS nanoparticles using cadmium piperidine dithiocarbamate (DTC) and cadmium tetrahydroquinoline dithiocarbamate complexes as single source precursors. These complexes are easy to prepare, air stable for long periods and pyrolyze to give high quality nanoparticles. The nanoparticles obtained showed quantum confinement with near band edge luminescence. The reaction conditions such as the amount of capping group and reaction temperature were varied to study their influence on the properties and morphology of the nanoparticles. Elongated CdS particles in the form of rods, bipods and tripods were obtained for the HDA capped CdS whereas spherical particles were observed when TOPO was used as the capping material. The X-ray diffraction studies revealed the hexagonal phase to be dominant. Details on the particle crystallinity, size and size distribution were investigated by transmission electron microscopy (TEM) and high resolution TEM.

Cd(NH2CSNHNHCSNH2)Cl2: a new single-source precursor for the preparation of CdS nanoparticles

Abstract The complex of cadmium with dithiobiurea, [Cd(NH 2 CSNHNHCSNH 2 )Cl 2 ], has been used as a precursor for the synthesis of CdS nanoparticles. The precursor was decomposed in tri- n -octylphosphine oxide to give CdS nanoparticles that show quantum confinement effects with characteristic close to band edge luminescence. The broad diffraction in the XRD pattern and diffused diffraction rings of the SAED pattern are typical of nanometer-sized particles. The particle morphology was found to depend on the temperature of injection of the precursor. Transmission electron microscopy shows irregular non-spherical particles prepared by injection at 150 °C, whilst with injection at 240 °C the particles are formed as spherical aggregates of relatively uniform size (50 nm).

Characterization of polystyrene filled with HgS nanoparticles

A polystyrene (PS)–HgS nanocomposite has been synthesized by first preparing a copolymer of styrene and mercury–acrylamide (5% by weight) and further reaction of it with H2S in chloroform solution. The effect of the HgS nanoparticles on the physical properties of the composite has been studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The glass transition temperature of the composite is 20 jC higher than that of polystyrene. The thermal stability of the composite is higher than that of polystyrene as evidenced by the shift of onset temperature of degradation by 12 jC as measured by TGA. D 2003 Elsevier B.V. All rights reserved.

Bis(piperidinedithiocarbamato)pyridinecadmium(II) as a single-source precursor for the synthesis of CdS nanoparticles and aerosol-assisted chemical vapour deposition (AACVD) of CdS thin films

The synthesis and single-crystal X-ray structure of bis(piperidinedithiocarbamato)pyridinecadmium(II), [Cd(S2C(NC5H10))2(NC5H5)] are reported and its use as a precursor for the synthesis of hexagonal CdS nanoparticles and CdS thin films is presented. Thermogravimetric analysis (TGA) of this complex showed clean decomposition in two steps to give CdS. Thermolysis of the complex in hexadecylamine at different temperatures in the range 190–270 °C gave CdS nanostructures including nanorods and oval shaped particles. The band gap of the as-synthesized CdS nanoparticles varied as the temperature was increased. CdS thin films with optical direct band gaps of ca. 2.4 eV were deposited by aerosol-assisted chemical vapour deposition (AACVD) in the temperature range 350 to 450 °C using the same precursor. Powder X-ray diffraction (p-XRD) patterns of CdS nanoparticles and thin films confirmed the hexagonal phase of CdS.

N-alkylthioureacadmium (II) complexes as novel precursors for the synthesis of CdS nanoparticles

The cadmium(II) complexes of thiourea and N-alkylthioureas (with alkyl group methyl or ethyl) have been used as precursors for the preparation of TOPO-capped CdS nanoparticles. The precursors are air-stable, easy to prepare and inexpensive. These compounds decompose cleanly to give good quality crystalline materials. The nanoparticles obtained showed quantum confinement effects in their optical spectra and close-to-band-edge emission in luminescence experiments. The broad diffraction patterns and the diffuse rings observed in the SAED patterns are typical of nanometric particles. The TEM images showed agglomerates of needle-like plates of particles. The presence of a strong phosphorus peak in the EDAX spectra is indicative of TOPO bound to the surface.

The synthesis of HgS nanoparticles in polystyrene matrix

A composite of nanodimensional HgS and polystyrene has been prepared by reacting a solution of the copolymer formed from mercury acrylamide and styrene in chloroform solution with H2S. The product shows different colours depending on the amount of H2S used. The composite material has been characterised by UV, PL, TEM, and XRD techniques. The TEM images show particle sizes of less than 12 nm. The band gaps calculated from the optical spectra are higher than that for bulk material as expected for quantum confined materials.

Precursor Routes to Semiconductor Quantum Dots

Abstract Quantum Dots are unique for two very important reasons both of which can potentially be commercially exploited: • The electronic and optical properties of Quantum Dots are dependent on the particle size. • As the Quantum Dot nanoparticle becomes smaller the ratio of the number of surface atoms to those in the interior increase. For example in very small particles greater than a third of all atoms reside on the surface. Such a high surface area is useful for catalysis. The solutions to the right all contain the same semiconductor material (cadmium selenide, CdSe) but are different colours because unlike the bulk material, which is black, we have controlled the size and therefore the electronic and optical properties (colour) of the Quantum Dots. This property alone can be exploited for the use in a number of technologies such as security tagging and biological probes. These small particles are one of the inventions spearheading a drive to control of materials with dimensions of the order of nanometres. The potential of the area of nanotechnology as being opened up by interactions between molecular biologists, chemists physisists and almost every type of engineer will be discussed. Applications of such technologies will range from computer chips through display screens to security printing. These new technologies will impact on all of our daily lives. Nanotechnology is attracting attention from all quarters from academia, venture capitalists to the general public. This lecture will explain why the area is both so topical and important.

Phase-pure fabrication and shape evolution studies of SnS nanosheets

Phase pure SnS nanosheets were synthesized by a hot injection method from a new single molecular precursor (SMP), dibutyl-bis(piperidinedithiocarbamato)tin(IV) in oleylamine at 230 °C. The tin complex was characterized by single crystal X-ray crystallography, nuclear magnetic resonance, thermogravimetry and microelemental analysis. The complex is thermally stable up to 260 °C, after which it decomposes in a single step with a major mass loss between 260 °C and 300 °C. The thermolysis of the as-prepared precursor was carried out in oleylamine between 190 and 230 °C. The formation and shape evolution of SnS was investigated using high resolution electron microscopy. The mechanism of the time dependent growth of SnS from spherical particles into nanosheets is proposed.