Formation of ordered arrays of gold particles by nanoindentation templating

Ordered arrays of gold‐rich particles, with diameters ranging from 50 nm to 180 nm, have been formed on a silicon (100) surface through pre‐patterning by nanoindentation. Indentation and gold deposition of the sample is followed by thermal processing, causing the gold to become trapped at the indentation sites. We suggest that gold trapping is via an alloying process with the underlying Si substrate where the native oxide is structurally compromised by the indentation process. The final size for a given particle is directly dependent on the size of the indentation site. It has also been demonstrated that excess gold found on the surface outside of these indentation sites can be readily removed via simple mechanical abrasion without affecting the particles within the indent. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

NMR evidence for a two-step phase separation in Nd1.85Ce0.15CuO4-delta

By Cu NMR we studied the spin and charge structure in Nd(2-x)Ce(x)CuO(4-delta). For x=0.15, starting from a superconducting sample, the low temperature magnetic order in the sample reoxygenated under 1 bar oxygen at 900 degrees C reveals a peculiar modulation of the internal field, indicative of a phase characterized by large charge droplets ("blob" phase). By prolonged reoxygenation at 4 bars the blobs break up and the spin structure changes to that of an ordered antiferromagnet. We conclude that the superconductivity in the n-type systems competes with a genuine type I Mott-insulating state.     

Pyrolysis of dimethyl peroxide

By using isobutane (t-BuH) as a radical trapit has been possible to study the initial step in the decomposition of dimethyl peroxide (DMP) over the temperature range of 110–140°C in a static system. For low concentrations of DMP (2.5 × 10^?5?10^?4M) and high pressures of t?BuH (～0.9 atm) the first-order homogeneous rate of formation of methanol (MeOH) is a direct measure of reaction (1): \documentclass{article}\pagestyle{empty}\begin{document}${\rm DMP}\mathop \to \limits^1 2{\rm Me}\mathop {\rm O}\limits^{\rm .},{\rm Me}\mathop {\rm O}\limits^{\rm .} + t{\rm - BuH}\mathop \to \limits^4 {\rm MeOH} + t{\rm -}\mathop {\rm B}\limits^{\rm .} {\rm u}$\end{document}. For complete decomposition of DMP in t-BuH, virtually all of the DMP is converted to MeOH. Thus DMP is a clean thermal source of Me\documentclass{article}\pagestyle{empty}\begin{document}$\mathop {\rm O}\limits^{\rm .}$\end{document}. In the decomposition of pure DMP complications arise due to the H-abstraction reactions of Me\documentclass{article}\pagestyle{empty}\begin{document}$\mathop {\rm O}\limits^{\rm .}$\end{document} from DMP and the product CH₂O. The rate constant for reaction (1) is given by k₁ = 10^15.5?37.0/θ sec^?1, very similar to other dialkyl peroxides. The thermochemistry leads to the result D(MeO? OMe) = 37.6 ± 0.2 kcal/mole and /H(Me\documentclass{article}\pagestyle{empty}\begin{document}$\mathop {\rm O}\limits^{\rm .}$\end{document}) = 3.8 ± 0.2 kcal/mole. It is concluded that D(RO? OR) and D(RO? H) are unaffected by the nature of R. From ΔS and A₁, k₂ is calculated to be 10^10.3±0.5 M^?1· sec^?1: \documentclass{article}\pagestyle{empty}\begin{document}$2{\rm Me}\mathop {\rm O}\limits^{\rm .} \mathop \to \limits^2 {\rm DMP}$\end{document}. For complete reaction, trace amounts of t-BuOMe lead to the result k₂ ～ 10⁹ M^?1 ·sec^?1: \documentclass{article}\pagestyle{empty}\begin{document}$2t{\rm - Bu}\mathop \to \limits^5$\end{document} products. From the relationship k₆ = 2(k₂k_5a)^1/2 and with k_5a = 10^8.4 M^?1 · sec^?1, we arrive at the result k₆ = 10^9.7 M^?1 · sec^?1: \documentclass{article}\pagestyle{empty}\begin{document}$2t{\rm - u}\mathop {\rm B}\limits^{\rm .} \to (t{\rm - Bu)}_{\rm 2}{\rm,}t{\rm -}\mathop {\rm B}\limits^{\rm .} {\rm u} + {\rm Me}\mathop {\rm O}\limits^{\rm .} \mathop \to \limits^6 t{\rm - BuOMe}$\end{document}.     

Dynamic NMR studies of ferrocenylsulphide-palladium(II) and -platinum(II) complexes

The stereodynamics of ferrocenylsulphide-palladium(II) and -platinum(II) complexes, Fe(C₅H₄SR)₂MX₂, (M = Pd^II, Pt^II; X = Cl, Br; R = Ph, i-Pr and i-Bu), have been examined by variable temperature NMR. At temperatures down to ca. ?100° C, the pyramidal inversion of the S atoms could be slowed down sufficiently to yield accurate energy data, while the reversal of the ferrocenophane ring remained fast on the NMR time scale. ΔG^≠ data for the S inversion process were in the range 47 to 65 kJ mol^?1 and were influenced to varying extents by the nature of the transition metal, the halogen, and the R substituent on the sulphur.     

An ab initio study of structural properties and single vacancy defects in Wurtzite AlN

The cell parameters, bulk moduli and electronic densities-of-states (DOS) of pure and vacancy defect AlN were computed using generalized-gradient approximation (GGA) and hybrid functional (B3LYP) computational methods within both plane wave-pseudopotential and localized Gaussian basis set approaches. All of the methods studied yielded cell parameters and bulk moduli in reasonable agreement with experiment. The B3LYP functional was also found to predict an optical band gap in excellent agreement with experiment. These methods were subsequently applied to the calculation of the geometry, defect state positions and formation energies of the cation (V(Al)) and anion (V(N)) single vacancy defects. For the V(Al) defect, the plane wave-pseudopotential predicted a significant retraction of the neighboring N away from the vacancy, while for the V(N) defect, only slight relaxations of the surrounding Al atoms towards the vacancy were predicted. For the computed DOS of both vacancy defects, the GGA methods yielded similar features and defect level positions relative to the valence band maximum, while the B3LYP method predicted higher separations between the defect levels and the valence and conduction bands, leading to higher energy occupied defect levels.     

Organic field-effect transistors of poly(2,5-bis(3-dodecylthiophen-2-yl)thieno[2,3-b]thiophene) deposited on five different silane self-assembled monolayers

Depositing a fused-ring thieno-thiophene polymer on different self-assembled monolayers indicates that varying the SAM surface energy changes the FET mobility and turn-on voltage by varying polymer crystallinity at the buried interface.     

Hafnium oxide thin films deposited from a filtered cathodic vacuum arc

The electrical and structural characteristics of hafnium oxide thin films reactively deposited from a filtered cathodic vacuum arc have been investigated. X-ray photoelectron spectroscopy was used to determine the deposition conditions (Ar/O₂ ratio) which produced stoichiometric HfO₂ films. Cross-sectional transmission electron microscopy showed that the micro-structure of the films was highly disordered with electron-diffraction analysis providing evidence for the presence of sub-nano-metre crystallites of the monoclinic HfO₂ (P2₁/c) phase. Further evidence for the presence of this phase was provided by measuring the O k-edge using electron energy loss spectroscopy and comparing it with calculations performed using FEFF8.2, a multiple scattering code. Surface imaging revealed that local film damage occurred in films deposited with substrate bias voltages exceeding −200 V. The current-leakage characteristics of the HfO₂ films deposited with a bias of approximately −100 V suggest that device grade HfO₂ films can be produced from a filtered cathodic vacuum arc.