Sarah L. Stoll

Controlled growth of HfO2 thin films by atomic layer deposition from cyclopentadienyl-type precursor and water

HfO2 thin films have been deposited onto p-Si(100) substrates by atomic layer deposition (ALD) using Cp2Hf(CH3)2 (Cp = cyclopentadienyl) and water as precursors at 300–500 °C. Processing parameters were optimised and the ALD type growth mode corroborated at 350 °C where a deposition rate of 0.42 A cycle−1 was obtained. The crystallinity, morphology and chemical composition of the deposited films were characterised. Films deposited at 300–450 °C were polycrystalline with monoclinic (−111) as the preferred orientation. Impurity levels of the stoichiometric HfO2 films deposited at 350 and 400 °C were very low, or below 0.4 and 0.25 atom% for carbon and hydrogen, respectively. In addition, ultrathin HfO2 films showed good dielectric properties such as low hysteresis and nearly ideal flatband voltage.

Gadolinium Doped Europium Sulfide

We have prepared gadolinium doped europium sulfides, Eu(1-x)Gd(x)S for a doping range of 0 ≤ x ≤ 0.1 by thermal decomposition of the precursors Eu(S(2)CNEt(2))(3)Phen/Gd(S(2)CNEt(2))(3)Phen with respective ratios. Electron doping provides indirect evidence for the magnetic coupling through carrier electrons in magnetic semiconductors. Based on the magnetic properties, we determined that the paramagnetic Curie temperature, Θp, varies with doping level, in a similar way to Eu(1-x)Gd(x)O exhibiting a significant increase at low doping levels. All materials have been characterized by X-ray powder diffraction, magnetic measurements, ICP-MS, and TEM.

Magnetic nanobeads as potential contrast agents for magnetic resonance imaging.

Metal-oxo clusters have been used as building blocks to form hybrid nanomaterials and evaluated as potential MRI contrast agents. We have synthesized a biocompatible copolymer based on a water stable, nontoxic, mixed-metal-oxo cluster, Mn8Fe4O12(L)16(H2O)4, where L is acetate or vinyl benzoic acid, and styrene. The cluster alone was screened by NMR for relaxivity and was found to be a promising T2 contrast agent, with r1 = 2.3 mM(-1) s(-1) and r2 = 29.5 mM(-1) s(-1). Initial cell studies on two human prostate cancer cell lines, DU-145 and LNCap, reveal that the cluster has low cytotoxicity and may be potentially used in vivo. The metal-oxo cluster Mn8Fe4(VBA)16 (VBA = vinyl benzoic acid) can be copolymerized with styrene under miniemulsion conditions. Miniemulsion allows for the formation of nanometer-sized paramagnetic beads (~80 nm diameter), which were also evaluated as a contrast agent for MRI. These highly monodispersed, hybrid nanoparticles have enhanced properties, with the option for surface functionalization, making them a promising tool for biomedicine. Interestingly, both relaxivity measurements and MRI studies show that embedding the Mn8Fe4 core within a polymer matrix decreases r2 effects with little effect on r1, resulting in a positive T1 contrast enhancement.

Surface attached manganese-oxo clusters as potential contrast agents.

Surface attachment of the manganese-oxo cluster known as Mn-12 provided aqueous solution stabilization that allowed investigation of the use of the cluster as an MRI contrast agent.

Miniemulsion Synthesis of Metal–Oxo Cluster Containing Copolymer Nanobeads

Hybrid nanobeads containing either a manganese-oxo or manganese-iron-oxo cluster have been prepared via the miniemulsion polymerization technique. Two new ligand substituted oxo clusters, Mn(12)O(12)(VBA)(16)(H(2)O)(4) and Mn(8)Fe(4)O(12)(VBA)(16)(H(2)O)(4) (where VBA = 4-vinylbenzoate), have been prepared and characterized. Polymerization of the functionalized metal-oxo clusters with styrene under miniemulsion conditions produced monodispersed polymer nanoparticles as small as ~60 nm in diameter. The metal-oxo polymer nanobeads were fully characterized in terms of synthetic parameters, composition, structure, and magnetic properties.

Selenide and selenolate compounds of indium: a comparative study of In–Se bond-forming reactions

A range of In–Se bond-forming reactions have been investigated, including insertion of selenium into either an In–C or In–S bond, reaction of an indium halide with a magnesium selenolate and via chlorosilane elimination. The reaction of InBu t 3 with Se yielded [Bu t 2 In(µ-SeBu t )] 2 and [Bu t In(µ 3 -Se)] 4 . In contrast, In(CMe 2 Et) 3 and InBu n 3 with Se preferentially formed [(Me 2 EtC)In(µ 3 -Se)] 4 and [Bu n In(µ 3 -Se)] 4 , respectively. The reaction of In(CMe 2 Et) 3 with Te yielded [(Me 2 EtC)In(µ 3 -Te)] 4 ]. The compound [Bu t In(µ 3 -Se)] 4 is also formed from the reaction of [Bu t 2 In(µ-SBu t )] 2 with either Se or SePPh 3 , while both it and [Bu t In(µ-SeBu t )] 2 may be prepared from [Bu t 2 In(µ-Cl)] n and (Bu t Se)MgCl. Similarly, [Bu n 2 In(µ-SeBu t )] 2 may be prepared from [Bu n 2 In(µ-Cl)] 2 . However, the reaction of [(Me 2 EtC) 2 In(µ-Cl)] 2 with (Bu t E)MgCl (E = S, Se or Te) yielded [(Me 2 EtC)In(µ 3 -E) 4 ]. Reaction of [Bu t 2 M(µ-Cl)] n (M = In or Ga) with Se(SiMe 3 ) 2 yielded the silylselenolate compounds [Bu t 2 M(µ-SeSiMe 3 )] 2 . The various In–Se bond-forming reactions are compared. The molecular structures of [Bu t 2 In(µ-EBu t )] 2 (E = S or Se) have been determined by X-ray crystallography.

Solid-state structure of [(But)2In(μ-Cl)]∞: an unusual saw-tooth polymeric chain

Abstract The solid-state structure of di- tert -butyl indium chloride, [(Bu t ) 2 In(μ-Cl)], has been determined by X-ray diffraction and consists of polymeric [33-In-Cl—] ∞ chains arranged in an unusual saw-tooth pattern motif. The indium atom is in a severely distorted coordination environment approximated as a capped trigonalplanar geometry. The structure of [(Bu t ) 2 In(μ-Cl)] ∞ is compared with [(Me) 2 In(μ-Cl)] ∞ .