Hafnium oxide and zirconium oxide atomic layer deposition: initial precursor and potential side-reaction product pathways with H/Si(100)-2 x 1

Hybrid density functional calculations have been carried out using cluster models of the H/Si(100)-2 x 1 surface to investigate the mechanistic details of the initial surface reactions occurring in the atomic layer deposition of hafnium and zirconium oxides (HfO2 and ZrO2). Reaction pathways involving the metal precursors ZrCl4, Zr(CH3)4, HfCl4, and Hf(CH3)4 have been examined. Pathways leading to the formation of a Zr-Si or Hf-Si linkage show a significant sensitivity to the identity of the leaving group, with chloride loss reactions being both kinetically and thermodynamically less favorable than reactions leading to the loss of a methyl group. The energetics of the Zr(CH3)4 and Hf(CH3)4 reactions are similar with an overall exothermicity of 0.3-0.4 eV and a classical barrier height of 1.1-1.2 eV. For the reaction between H2O and the H/Si(100)-2 x 1 surface, the activation energy and overall reaction enthalpy are 1.6 and -0.8 eV, respectively. Due to contamination, trace amounts of H2O may be encountered by metal precursors, leading to the formation of minor species that can lead to unanticipated side-reaction pathways. Such gas-phase reactions between the halogenated and alkylated metal precursors and H2O are exothermic with small or no reaction barriers, allowing for the possibility of metal precursor hydroxylation before the H/Si surface is encountered. Of the contaminant surface reaction pathways, the most kinetically favorable corresponds to the surface -OH deposition. Interestingly, for the hydroxylated metal precursors, a unique reaction pathway resulting in the direct formation of Si-O-Zr and Si-O-Hf linkages has been identified and found to be the most thermodynamically stable pathway available, being exothermic by approximately 1.0 eV.     

Influence of pyridine-based ligands on photostability of MAPbI3 thin films

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Favorski Type Rearrangement in the Lead Tetraacetate Oxidation of Cycloalkanones

The cycloalkanones (1a-lf) have been converted into their corresponding cycloalkane carboxylates (2a-2f) by a lead (IV) acetate promoted rearrangement in presence of perchloric acid in triethyl orthoformate.     

Spectral Measures for <Emphasis Type="Italic">G</Emphasis><Subscript>2</Subscript>

Spectral measures provide invariants for braided subfactors via fusion modules. In this paper we study joint spectral measures associated to the rank two Lie group G ₂, including the McKay graphs for the irreducible representations of G ₂ and its maximal torus, and fusion modules associated to all known G ₂ modular invariants.     

Influence of the Molecular Character and Degree of Crosslinking on the Interaction of Crosslinked Polyacrylamide-Supported Amines with Cu(Ii) Ions

Abstract

Amino groups were incorporated into polyacrylamides with 2?20 mol% of crosslinking agents by transamidation with ethylenediamine. Divinylbenzene, N,Nv′-methylene-bis-acrylamide, and tetraethyleneglycol diacrylate were used as the crosslinking agents. The complexation of these resins, which contain ligand functions in different macromolecular structural environments, was investigated with Cu(II) ions. The Cu(II) uptake of these different resins was correlated with the molecular character and degree of crosslinking in the polymer matrix. The time course and kinetics of complexation depend on the nature of the crosslinking agent in the polymer matrix. The swelling behavior of the uncomplexed and complexed resins, structural characteristics, and thermal decomposition behavior were followed by IR, EPR, and thermal analysis. The swelling characteristics of the complexed resins are lower than those of the uncomplexed resins. Complexation resulted in shifting of the IR absorptions. The EPR parameters depend on the nature of crosslinking and are in agreement with the distorted tetragonal geometry of the Cu(II) complexes. The thermal decomposition behavior also depends on the nature and the degree of crosslinking in the polymer matrix.     

Synthesis,characterisation and antibacterial applications of water-soluble,silver nanoparticle-encapsulated β-cyclodextrin

This paper describes a simple method for the synthesis of water-soluble, silver nanoparticle-encapsulated β-cyclodextrin by phase transfer of silver nanoparticles from organic to aqueous phase using β-cyclodextrin as a capping agent. β-Cyclodextrin–silver nanoparticle inclusion complex was purified, characterised by spectroscopic and microscopic analyses and tested in vitro against Pseudomonas aeruginosa, Staphylococcus aureus, Serratia marcescens, Escherichia coli and Klebsiella pneumoniae. The silver nanoparticle-encapsulated β-cyclodextrin inclusion complex displayed considerable antimicrobial activity and stability.

     

Bromine Complexes of Polyvinylpyrrolidone Supports: A Mild Reagent for the Transformation of α‐Oxoketene Dithioacetals to β‐Oxothiolesters

When α‐oxoketene dithioacetals 1a–n were treated with the bromine complex of a copolymer of 1‐vinyl‐2‐pyrrolidone and 4‐vinylpyridine, the corresponding thiolcarboxylates 2a–n were formed in excellent yields. The reaction also works with other 1‐vinyl‐2‐pyrrolidone‐derived polymers as well as commercially available polyvinylpyrrolidone–bromine complexes. The method is suitable for preparing aliphatic, aromatic, and γ,δ‐unsaturated β‐oxothiolcarboxylates.     

Synthesis of Benzofurans by the Action of Copper on Terminal Alkynes and O-Halophenols

Cuprous acetylides react with aryl halides to yield aryl acetylenes and with o-halophenols to give benzofurans.^1,2 The broad scope of this latter reaction for the synthesis of benzofuran natural products is shown by application inter alia to norlignans,³ euparinoids,⁴ phytoalexins,⁵ furanocoumarins,⁶ fomannoxin,⁷ isotubaic acid⁸ and machicendiol.     

Characterization of uranium isotopic abundances in depleted uranium metal assay standard 115

Certified reference material (CRM) 115, Uranium (Depleted) Metal (Uranium Assay Standard), was analyzed using a TRITON Thermal Ionization Mass Spectrometer to characterize the uranium isotope-amount ratios. The certified ²³⁵U/²³⁸U “major” isotope-amount ratio of 0.0020337 (12) in CRM 115 was determined using the total evaporation (TE) and the modified total evaporation (MTE) analytical techniques. In the MTE method, the total evaporation process is interrupted on a regular basis to allow correction of background from peak tailing, internal calibration of the secondary electron multiplier detector versus the Faraday cups, peak-centering, and ion source re-focusing. For the “minor” ²³⁴U/²³⁸U and ²³⁶U/²³⁸U isotope-amount ratio measurements using MTE, precision and accuracy comparable to conventional analyses are achieved, without compromising the quality of the ²³⁵U/²³⁸U isotope-amount ratios. Characterized values of the ²³⁴U/²³⁸U and ²³⁶U/²³⁸U isotope-amount ratios in CRM 115 are 0.000007545 (10) and 0.000032213 (84), respectively. The ²³³U/²³⁸U isotope-amount ratio in CRM 115 is estimated to be <5 × 10^?9. The homogeneity of the CRM 115 materials is established through the absence of any statistically significant unit-to-unit variation in the uranium isotope-amount ratios. The measurements leading to the certification of uranium isotope-amount ratios are discussed.