Rare earth oxides, such as La2O3 and Yb2O3, deposited on Si(100) were investigated for high-k gate insulator applications. La2O3 has the largest bandgap and smallest lattice energy among the rare earth oxides, while Yb2O3 has a smaller bandgap and larger lattice energy compared to La2O3. La2O3 showed excellent electrical properties, such as small capacitance equivalent thickness and low leakage current density with smooth film surface and interface after rapid thermal annealing (RTA) at 400-600°C. On the other hand, the surface of Yb2O3 thin film was easily roughened after RTA even at 400°C, and the leakage current density was higher compared to La2O3. The difference in characteristics for the films was considered to be attributed to the difference of their properties, such as bandgap and lattice energy. La2O3 was able to keep the amorphous phase at least up to 600°C RTA, and this seems promising for future high-k gate insulator applications. © 2003 The Electrochemical Society. All rights reserved.
Nickel complexes with hydrotris(pyrazolyl)borate ( = Tp R ) ligands catalyze alkane oxidation with organic peroxide meta-Cl-C 6 H 4 C(vO)OOH (= mCPBA). The electronic and steric hindrance properties of Tp R affect the catalyses. The complex with an electron-withdrawing group containing a less-hindered ligand, that is, Tp Me2,Br , exhibits higher alcohol selectivity. Higher selectivity for secondary over tertiary alcohols upon oxidation of methylcyclohexane indicates that the oxygen atom transfer reaction proceeds within the coordination sphere of the nickel centers. A reaction of the catalyst precursor, dinuclear nickel(II)bis(μ-hydroxo) complexes, with mCPBA yields the corresponding nickel(II)-acylperoxo species, as have been characterized by spectroscopy. Thermal decomposition of the nickel(II)-acylperoxo species in CH 2 Cl 2 yields the corresponding nickel(II)-chlorido complexes through Cl atom abstraction. Employment of the brominated ligand increases the thermal stability of the acylperoxo species. Kinetic isotope effects observed on decay of the nickel(II)-acylperoxo species indicate concerted O-O breaking of the nickelbound acylperoxide and H-abstraction from the solvent molecule. † Electronic supplementary information (ESI) available. See
An alkylperoxonickel(II) complex with hydrotris(3,5-diisopropyl-4-bromo-1-pyrazolyl)borate, [Ni(II)(OOtBu)(Tp(iPr2,Br))] (3 a), is synthesized, and its chemical properties are compared with those of the prototype non-brominated ligand derivative [Ni(II)(OOtBu)(Tp(iPr2))] (3 b; Tp(iPr2)=hydrotris(3,5-diisopropyl-1-pyrazolyl)borate). Same synthetic procedures for the prototype 3 b and its precursors can be employed to the synthesis of the Tp(iPr2,Br) analogues. The dimeric nickel(II)-hydroxo complex, [(Ni(II)Tp(iPr2,Br))(2)(mu-OH)(2)] (2 a), can be synthesized by the base hydrolysis of the labile complexes [Ni(II)(Y)(Tp(iPr2,Br))] (Y=NO(3) (1 a), OAc (1 a')), which are obtained by the metathesis of NaTp(iPr2,Br) with the corresponding nickel(II) salts, and the following dehydrative condensation of 2 a with the stoichiometric amount of tert-butylhydroperoxide yields 3 a. The unique structural characteristics of the prototype 3 b, that is, highly distorted geometry of the nickel center and intermediate coordination mode of the O--O moiety between eta(1) and eta(2), are kept in the brominated ligand analogue 3 a. The introduction of the electron-withdrawing substitutents on the distal site of Tp(R) affects the thermal stability and reactivity of the nickel(II)-alkylperoxo species.
The thermal properties of crystalline complex [Cr(H(2)bim)(3)](TMA) x 23.5 H(2)O were studied by adiabatic calorimetry to clarify the structural ordering and dynamic freezing-in behaviors of the nanochannel water within the pores possessing crystalline wall structure, where H(2)bim denotes 2,2'-biimidazole and TMA is 1,3,5-benzenetricarboxylic acid. Phase and glass transitions were found to occur at 233 K with the associated entropy of Delta(trs)S = 7.96 J K(-1) mol(-1) and at T(g) = 100 K, respectively, in the hydrated sample. The phase transition was interpreted as attributed to the crystallization-like formation of the hydrogen-bond network of the channel-water molecules. The glass transition was interpreted as a freezing-in phenomenon on the way of the development of the network, and its presence indicates that the network formation achieves no completion even at 100 K. The T(g) value is similar to those found previously in other channel-water systems of [Ni(cyclam)(H(2)O)(2)](3)(TMA)(2) x 24 H(2)O and porous silica. It is noted that the channel water within silica pores with their diameter below 1.8 nm undergoes no structural phase transition while the present one does. The origins of the phase and glass transitions and the implication of their presence are discussed based on the difference in the structures of pore wall interacting with the channel-water molecules.
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