Atomic Layer Deposition of Molybdenum and Tungsten Oxide Thin Films Using Heteroleptic Imido-Amidinato Precursors : Process Development, Film Characterization, and Gas Sensing Properties

Heteroleptic bis(tert-butylimido)bis(N,N'-diisopropylacetamidinato) compounds of molybdenum and tungsten are introduced as precursors for atomic layer deposition of tungsten and molybdenum oxide thin films using ozone as the oxygen source. Both precursors have similar thermal properties but exhibit different growth behaviors. With the molybdenum precursor, high growth rates up to 2 angstrom/cycle at 300 degrees C and extremely uniform films are obtained, although the surface reactions are not completely saturative. The corresponding tungsten precursor enables saturative film growth with a lower growth rate of 0.45 angstrom/cycle at 300 degrees C. Highly pure films of both metal oxides are deposited, and their phase as well as stoichiometry can be tuned by changing the deposition conditions. The WO films the crystallize as gamma-WO3 at 300 degrees C and above, whereas films deposited at lower temperatures are amorphous. Molybdenum oxide can be deposited as either amorphous (= 325 degrees C) films. MoOr films are further characterized by synchrotron photoemission spectroscopy and temperature-dependent resistivity measurements. A suboxide MoOx film deposited at 275 degrees C is demonstrated to serve as an efficient hydrogen gas sensor at a low operating temperature of 120 degrees C.Peer reviewe

Crystal Structures of Two Titanium Phosphate-Based Proton Conductors: Ab Initio Structure Solution and Materials Properties

Transition-metal phosphates show a wide range of chemical compositions, variations of the valence states, and crystal structures. They are commercially used as solid-state catalysts, cathode materials in rechargeable batteries, or potential candidates for proton-exchange membranes in fuel cells. Here, we report on the successful ab initio structure determination of two novel titanium pyrophosphates, Ti(III)p and Ti(IV)p, from powder X-ray diffraction (PXRD) data. The low-symmetry space groups P2$_1$/c for Ti(III)p and P$\overline{1}$ for Ti(IV)p required the combination of spectroscopic and diffraction techniques for structure determination. In Ti(III)p, trivalent titanium ions occupy the center of TiO$_6$ polyhedra, coordinated by five pyrophosphate groups, one of them as a bidentate ligand. This secondary coordination causes the formation of one-dimensional six-membered ring channels with a diameter d$_{max}$ of 3.93(2) Å, which is stabilized by NH$_{4}$$^{+}$ ions. Annealing Ti(III)p in inert atmospheres results in the formation of a new compound, denoted as Ti(IV)p. The structure of this compound shows a similar three-dimensional framework consisting of [PO$_4$]3– tetrahedra and Ti$^{IV+}$O$_6$ octahedra and an empty one-dimensional channel with a diameter d$_{max}$ of 5.07(1) Å. The in situ PXRD of the transformation of Ti(III)p to Ti(IV)p reveals a two-step mechanism, i.e., the decomposition of NH$_{4}$$^{+}$ ions in a first step and subsequent structure relaxation. The specific proton conductivity and activation energy of the proton migration of Ti(III)p, governed by the Grotthus mechanism, belong to the highest and lowest, respectively, ever reported for this class of materials, which reveals its potential application in electrochemical devices like fuel cells and water electrolyzers in the intermediate temperature range

The Mechanism and Pathway of Selective Partial Oxidation of <i>n</i>‑Butane to Maleic Anhydride Studied on Titanium Phosphate Catalysts

The partial selective oxidation of n-butane to maleic anhydride with molecular oxygen is commercially well-established and strongly associated with the vanadium phosphorus oxide (VPO) catalyst. We report that also titanium phosphate (TiPO) exhibits the rare feature of accomplishing the most demanding complex selective oxidation reaction industrially applied. A facile molten salt method was used to prepare TiPO catalysts from mixtures of (NH4)2HPO4 and TiO2 (P25). In a continuous flow process under industrially relevant conditions with TiPO, conversions above 50% resulted in 20% overall selectivity for maleic anhydride with 90% oxygenate selectivity. Due to a high tendency to total oxidation (>60%), the performance of TiPO catalysts cannot yet compete with the industrial VPO catalyst. However, herein we want to highlight our studies on the reaction pathway and mechanism for the complex multistep conversion of n-butane to maleic anhydride, which is still under debate for the VPO catalyst after more than four decades of research. A complete chain of reaction intermediates was identified via online mass spectroscopy, under industrially relevant conditions, and in pulse experiments, including the consecutive formation of 2-butene, 1,3-butadiene, furan, and 2-furanone as C4 intermediates. Cyclic pulse experiments complemented with EPR measurements revealed a combined mechanism involving carbocation chemistry via Brønsted acid sites and a redox mechanism according to Mars van Krevelen

Interferon-alpha-induced TRAIL on natural killer cells is associated with control of hepatitis C virus infection.

BACKGROUND & AIMS: Pegylated interferon-alpha (PEG-IFNalpha), in combination with ribavirin, controls hepatitis C virus (HCV) infection in approximately 50% of patients by mechanisms that are not completely understood. Beside a direct antiviral effect, different immunomodulatory effects have been discussed. Natural killer (NK) cells might be associated with control of HCV infection. We examined the effects of IFNalpha on human NK cells and its relevance to HCV infection. METHODS: We performed gene expression profiling studies of NK cells following stimulation of peripheral blood mononuclear cells with IFNalpha. We evaluated IFNalpha-induced tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) expression using flow cytometry analyses of NK cells isolated from patients with acute or chronic hepatitis C that had received PEG-IFNalpha therapy. RESULTS: TRAIL was among the most up-regulated genes after IFNalpha stimulation of NK cells from healthy controls. After in vitro stimulation with IFNalpha, CD56(dim) NK cells from patients who had responded to PEG-IFNalpha therapy expressed higher levels of TRAIL than cells from patients with chronic hepatitis C. TRAIL expression, ex vivo, was inversely correlated with HCV-RNA levels during the early phase of PEG-IFNalpha therapy. In patients with acute hepatitis C, TRAIL expression on CD56(bright) NK cells increased significantly compared with cells from controls. In in vitro studies, IFNalpha-stimulated NK cells eliminated HCV-replicating hepatoma cells by a TRAIL-mediated mechanism. CONCLUSIONS: IFNalpha-induced expression of TRAIL on NK cells is associated with control of HCV infection; these observations might account for the second-phase decline in HCV-RNA levels during PEG-IFNalpha therapy

Interferon α-stimulated natural killer cells from patients with acute hepatitis C virus (HCV) infection recognize HCV-infected and uninfected hepatoma cells via DNAX accessory molecule-1.

BACKGROUND: Natural killer (NK) cells are an important component of the innate immune defense against viruses, including hepatitis C virus (HCV). The cell culture system using HCV-permissive Huh-7.5 cells make studies on interaction of NK cells and HCV-infected target cells possible. We used this system to characterize interactions of HCV-infected Huh-7.5 cells and NK cells from healthy controls and patients with acute HCV infection. METHODS: IFNα- and IL-2 stimulated NK cells were cultured with HCV-infected hepatoma cells and subsequently analyzed (for degranulation and cytokine production) via multicolour flow cytometry. Luciferase assyas have been used to study inhibition of HCV replication. Further, PBMC from patients with acute hepatitis C as well as HCV-infected Huh7.5 cells have been analyzed via flow cytometry for expression of NK cell receptors and ligands, respectively. RESULTS: After interferon (IFN) α stimulation, NK cells from healthy controls and patients with acute hepatitis C efficiently recognized both HCV-infected and uninfected hepatoma cells. Subsequent dissection of receptor-ligand interaction revealed a dominant role for DNAM-1 and a complementary contribution of NKG2D for NK cell activation in this setting. Furthermore, IFN-α-stimulated NK cells effectively inhibited HCV replication in a DNAM-1-dependent manner. CONCLUSIONS: Human NK cells recognize HCV-infected hepatoma cells after IFN-α stimulation in a DNAM-1-dependent manner. Furthermore, interaction of IFN-α-stimulated NK cells with HCV-infected hepatoma cells efficiently reduced HCV replication. This study opens up future studies of NK cell interaction with HCV-infected hepatocytes to gain further insight into the pathogenesis of human HCV infection and the therapeutic effects of IFN-α