Since the installation of an ITER-like wall, the JET programme has focused on the consolidation of ITER design choices and the preparation for ITER operation, with a specific emphasis given to the bulk tungsten melt experiment, which has been crucial for the final decision on the material choice for the day-one tungsten divertor in ITER. Integrated scenarios have been progressed with the re-establishment of long-pulse, high-confinement H-modes by optimizing the magnetic configuration and the use of ICRH to avoid tungsten impurity accumulation. Stationary discharges with detached divertor conditions and small edge localized modes have been demonstrated by nitrogen seeding. The differences in confinement and pedestal behaviour before and after the ITER-like wall installation have been better characterized towards the development of high fusion yield scenarios in DT. Post-mortem analyses of the plasma-facing components have confirmed the previously reported low fuel retention obtained by gas balance and shown that the pattern of deposition within the divertor has changed significantly with respect to the JET carbon wall campaigns due to the absence of thermally activated chemical erosion of beryllium in contrast to carbon. Transport to remote areas is almost absent and two orders of magnitude less material is found in the divertor.
The chemical bonding, extent, and evolution of metal-oxide semiconductor interface regions have been probed with soft-x-ray photoemission spectroscopy following room-temperature, in situ metallization. We identify strong atomic rearrangement and charge transfer at metal-SiO2 interfaces. The quantitatively different processes found for Au and Al suggest new structural models. For Al-SiO2, Al first clusters about each surface O and then grows Al2O3 by reducing SiOx (X < 2) and leaving excess Si at the interface. In contrast, Au forms islands on SiO2 with evidence of Au–Si bonding, causing an SiOx layer beneath the contact.
Ten substituted pyridinium-pyridine systems were studied in the middle and far infrared region as binary systems and as acetonitrile solutions. Furthermore, quantum chemical calculations of these systems were performed. All systems show an intense infrared continuum. The continuum does not change with the pK, of the protonated N-base in the pK, range 2.5-6.5. The hydrogen bond vibration vu in the far infrared region was found in all systems, and its wavenumber changes are caused by the change of the mass of the N-base. Almost no change in the harmonic force constant of the hydrogen bond vibration is found. Quantum chemical calculations yield a double minimum proton potential with no change of the barrier height of the well. Therefore, all systems show almost the same proton polarizability, resulting in continua with the same intensity distribution. For the systems, effective hydrogen bond vibration masses are calculated with various methods, and the obtained results are compared.
We present experimental evidence of a unique, ordered chemisorption phase in the initial interaction of oxygen with the Al(lll) surface. At high oxygen exposure or high temperature, this phase is shown to transform irreversibly to a bulklike aluminum oxide. The measured temperature dependence, as well as the low-energy electron diffraction, suggests a threefold, centered bonding site. A comparison between calculated and experimental valence-band density of states for the oxygen-covered Al(lll) surface is made for the estimated oxygen-atom-substrate-surface distance.Experimental evidence is presented showing that the initial interaction of oxygen with the (111) crystal face of aluminum is a two-step process. Oxygen atoms are shown to chemisorb first at equivalent sites on the surface in an ordered overlayer. Upon increasing the oxygen exposure or the temperature above 170°C, the chemisorbed oxygen is irreversibly transformed into a bulklike oxide film. The chemisorption phase in the aluminum-oxygen interaction was first observed for "polycrystalline" films. 1 The present work shows that the two-step oxidation process is unique to the closepacked (111) face of aluminum and reveals for the first time the presence of an ordered overlayer with oxygen on a simple fee metalc The other two faces investigated, (100) and (110), form bulklike oxide films for the lowest observable coverages. 2 The existence of a well-defined chemisorption phase on a free-electron-like metal such as aluminum is of great interest since a number of theoretical calculations using different techniques treat chemisorption of oxygen atoms on aluminum as a model system. 3 " 5 Because of the relatively simple bulk electronic structure of this system, calculations have been made self-consistent and have been performed for different adsorbate-substrate distances. Some calculations explicitly assume a specific adsorption site, but comparisons of the calculated valence-band density of states with experimental valence-band photoemission spectra have been hindered by uncertainty about the actual Al-O configurations. In the present work we deduce a specific position and estimate an adsorbate-substrate distance for oxygen atoms on the (111) surface of aluminum. Valence-band spectra obtained for the oxygen-exposed surfaces are compared with a theoretical calculation. 3 ' 6 Discussion of the valence-band spectra for the clean faces is presented elsewhere. 7 The experiments reported were performed using the monochromatized radiation from the 4° beam line at Stanford Synchrotron Radiation Laboratory (SSRL) as the excitation source. Photons at two energies were used to excite electrons: 50-eV photons to excite the valence-band region and 130-eV photons to excite the 2p core of aluminum. Incoming light illuminated the sample at 5°-10° away from grazing incidence. The photoelectrons were energy analyzed in a doublepass, cylindrical mirror analyzer having its optical axis 5°-10° off the sample surface normal; the joint energy resolution (photon plus electron) was 0....
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