M. Azad Malik

The crystal and molecular structure of N,N-diethyldiselenocarbamatocadmium(II): Cadmium and zinc diethyldiselenocarbamates as precursors for selenides

Abstract The X-ray crystal structure of N,N-diethyldiselenocarbamatocadmium(II) has been determined and contains centrosymmetric, dimeric molecular units Of [Cd2(Se2 CNEt2)4] with five-coordinated distorted square pyramidal cadmium. Preliminary studies of the pyrolysis of both cadmium and zinc diethyldiselenocarbamates show that these complexes may be useful precursors for the deposition of ZnSe and CdSe.

Growth of ZnO by MOCVD using alkylzinc alkoxides as single-source precursors

Thin films of ZnO have been grown by low-pressure MOCVD using methylzinc isopropoxide, MeZn(OPri), and methylzinc tert-butoxide, MeZn(OBut), in the absence of an added oxygen source. The films were grown on to glass substrates in the temperature range 250–400 °C with growth rates of between 0.2 and 4.4 µm h–1.

Single-source molecular precursors for the deposition of zinc selenide quantum dots

TOPO (tri-n-octylphosphine oxide)-capped ZnSe (in the form of close to mono-dispersed nanoparticles) has been prepared by a single source route using ethyl(diethyldiselenocarbamato)zinc(ii) as a precursor. The nanoparticles obtained show quantum size effects in their optical spectra and exhibit near band-edge luminescence. A blue shift of 0.25eV in relation to the bulk material is observed. The selected area electron diffraction (SAED) and X-ray diffraction (XRD) patterns show the material to be hexagonal. The crystallinity of the material was also evident from high-resolution transmission electron microscopy (HRTEM) which gave well defined images of nanosize particles with clear lattice fringes.

Deposition of zinc sulfide quantum dots from a single-source molecular precursor

Nanoparticles of ZnS capped with tri-n-octylphosphineoxide (TOPO) and close to monodispersed have been prepared by a single-source route using ethyl(di-ethyldithiocarbamato)zinc(II) as a precursor. The nanoparticles obtained showed quantum size effects in their optical spectra, and the photoluminescence spectrum showed a broad emission that could be attributed to the surface traps. A blue shift of 0.31 eV in relation to the bulk material was observed. The selected area electron diffraction, x-ray diffraction pattern and transmission electron microscopy showed the material to be of the zinc blend structure. The crystallinity of the material was also evident from high-resolution transmission electron microscopy, which gave well-defined images of nano-sized particles with clear lattice fringes and a spacing of approximately 3 A, corresponding to the (111) planes of the cubic crystalline ZnS phase and in the size range of 3.9–4.9 nm. The presence of strong phosphorus peak in the energy dispersion analytical x-ray pattern, together with a shift in infrared band for P = O of TOPO showed that the particles were TOPO capped.

Studies of the thermal decomposition of some diselenocarbamato complexes of cadmium or zinc : molecular design for the deposition of MSe films by CVD

The compounds M(Se 2 CNEt 2 ) 2 , M = Zn 1 or Cd 2, M(Se 2 CNMe n Hex) 2 , M = Zn 3 or Cd 4, and ZnEt(Se 2 CNEt 2 ) 5 have been investigated by GC-MS and EI-MS in an attempt to determine why 1 and 2 often deposit films containing an excess of selenium by metal organic chemical vapour deposition (MOCVD) whereas 3, 4 and 5 give MSe (M = Zn or Cd). The EI-MS of all five selenium compounds revealed similar decomposition pathways, which start with loss of an alkyl group. However, studies of compounds 1–5 by pyrolysis GC-MS showed that selenium clusters Se n , n = 1–7, are formed in the vapour phase from 1 and 2. Compounds 1, 2 and 5 also form significant quantities of diethyl diselenide (EtSe 2 Et) in the ratio of 1∶0.9∶0.2 respectively, as detected by GC-MS, whereas 3 and 4 do not.

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.

Synthesis and characterization of some mixed alkyl selenocarbamates of zinc and cadmium: novel precursors for II/VI materials

A series of new compounds [RMSe2CNEt2](R = Et, M = Zn; M = Zn or Zn0.5Cd0.5 or Cd, R = Me) have been synthesized and characterized by X-ray crystallography. The compounds have potential as single-molecule precursors for the deposition of the corresponding binary and ternary materials.

Synthesis of pyrite thin films and transition metal doped pyrite thin films by aerosol-assisted chemical vapour deposition†‡

Diethyldithiocarbamato-metal complexes of the general formula [M(S2CN(Et)2)n] (M = Fe(III), Co(III), Ni(II), Cu(II), Zn(II) and n = 2, 3) have been synthesized and used as precursors for the deposition of iron pyrite (FeS2) and transition metal doped iron pyrite (MxFe1−xS2) thin films on glass and indium tin oxide (ITO) coated glass substrates by aerosol assisted chemical vapour deposition (AACVD). Thermogravimetric analysis (TGA) confirmed that all the five complexes decompose into their corresponding metal sulfides. The iron complex [Fe(S2CNEt2)3] (1) deposited pure cubic pyrite (FeS2) films with granular crystallites at 350 °C, whereas at 450 °C pyrite and marcasite were deposited. MxFe1−xS2 (where M = Co, Ni, Cu, or Zn) films were deposited by varying the relative concentration of complexes [Fe(S2CNEt2)3] (1) and [Co(S2CNEt2)3] (2), [Ni(S2CNEt2)2] (3), [Cu(S2CNEt2)2] (4) and [Zn(S2CNEt2)2] (5) at 350 °C. The formation of a solid solution was confirmed by powder X-ray diffraction (p-XRD). The surface morphology of the films was studied by scanning electron microscopy (SEM) whilst the height profiles of the films were revealed by atomic force microscopy (AFM). The elemental compositions of the films were confirmed by energy-dispersive X-ray (EDX) spectroscopy. To the best of our knowledge, these complexes are the first in their class to be used as single source precursors to deposit MxFe1−xS2 thin films.

X-ray crystal structures of bis-2,2,6,6-tetramethylheptane-3,5-dionatolead(II) and bis-2,2-dimethyl-6,6,7,7,8,8,8-heptafluorooctane-3,5-dionatolead(II): compounds important in the metalorganic chemical vapour deposition (MOCVD) of lead-containing films

Abstract Bis-2,2,6,6-tetramethylheptane-3,5-dionatolead (1), bis-2,2-dimethyl-6,6,7,7,8,8,8-heptafluorooctane-3,5-dionatolead (2) and bis-1,1,1,5,5,5-hexafluoropentane-2,4-dionatolead (3) have been prepared and characterised. X-ray single crystal structures for (1) and (2) have been determined. Compound (1) has a monomeric structure with the chelating thd (2,2,6,6-tetramethyl-3,5-heptanedione) units distorted away from a stereochemically active lone pair of electrons at the lead (II) centre. The structure of compound (2) is based on unusual dimers. Seven co-ordinate lead units are bridged by the fluorine atoms of the ligand. All three compounds are useful precursors in the deposition of lead-containing materials and their structures are useful in understanding their behaviour in materials deposition.

A simple route to synthesise nanodimensional CdSe–CdS core–shell structures from single molecule precursors

Highly mono-dispersed CdSe–CdS core–shell nanoparticles have been prepared by a novel method in which [Cd{Se2CNMe(nHex)}2] (250 °C for 30 min) and [Cd{S2CNMe(nHex)}2] (250 °C for a further 30 min) are thermolysed in tri-n-octylphosphine oxide (TOPO) in a ‘one pot’ synthesis; the core–shell structure has been characterized by electronic spectroscopy, photoluminescence, X-ray diffraction and electron microscopy (SAED, SEM and TEM).