| 1. |
- Burmeister, Florian, et al.
(författare)
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Description and performance of an electron-ion coincidence TOF spectrometer used at the Brazilian synchrotron facility LNLS
- 2010
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Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048 .- 1873-2526. ; 180:1-3, s. 6-13
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Tidskriftsartikel (refereegranskat)abstract
- This paper reports the characteristics and performance of a Time-of-Flight Mass Spectrometer (TOF-MS) for coincidence measurements between electrons and ions that has been developed jointly in Sweden and Brazil. The spectrometer, used for studies of inner-shell photoexcitation of molecules in the gas-phase, has been optimized by implementing ion and electron lenses to allow the use of relatively small diameter detectors. Simulations were performed to understand the lens performance and they show that ions (electrons) could be collected without angular discrimination with a maximum kinetic energy up to ten (two) times higher than without the lens actions. A rotary vacuum chamber allows the spectrometer axis to be positioned at different angles relative to the polarization vector of the excitation beam. An important characteristic of the apparatus is that the acquisition setup allows a multi-hit capability with 1 ns resolution. Hereby, Photoelectron-Photoion-Photoion Coincidence (PEPIPICO) measurements can be performed on molecules containing two or more atoms of equal mass. A method to obtain experimental detection efficiencies of a single ion and one of one, two or three electrons has been developed. A systematic study of the interaction region has been performed to determine the shape of the photon and gas beams. Measurements on molecular nitrogen demonstrate the spectrometer's ability to resolve fragments with the same charge to mass ratio arriving within only a few ns. Simulations and experimental results of fragmentation of two singly charged cation nitrogen atoms agree, confirming that the spectrometer performance is well understood. (C) 2010 Elsevier B.V. All rights reserved.
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| 2. |
- Carravetta, V., et al.
(författare)
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PH-dependent X-ray Photoelectron Chemical Shifts and Surface Distribution of Cysteine in Aqueous Solution
- 2019
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 123:17, s. 3776-3785
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Tidskriftsartikel (refereegranskat)abstract
- The distribution and protonation states of amino acids in water droplets are of considerable concern in studies on the formation of clouds in the atmosphere as well as in many biological contexts. In the present work we use the amino acid cysteine as a prototypical example and explore the protonation states of this molecule in aqueous solution, which are strongly affected by the acidity of the environment and also can show different distributions between surface and bulk. We use a combination of X-ray photoelectron chemical shift measurements, density functional theory calculations of the shifts, and reactive force field molecular dynamics simulations of the underlying structural dynamics. We explore how the photoelectron spectra distinctly reflect the different protonation states that are generated by variation of the solution acidity and how the distribution of these protonation states can differ between bulk and surface regions. At specific pH values, we find that the distribution of the cysteine species at the surface is quite different from that in bulk, in particular, for the appearance in the surface region of species which do not exist in bulk. Some ramifications of this finding are discussed.
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| 3. |
- Grånäs, Oscar, 1979-, et al.
(författare)
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Femtosecond fragmentation of CS2 after sulfur 1s ionization : interplay between Auger cascade decay, charge delocalization, and nuclear motion
- 2020
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Ingår i: Journal of Physics B. - : IOP PUBLISHING LTD. - 0953-4075 .- 1361-6455. ; 53:24
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Tidskriftsartikel (refereegranskat)abstract
- We present a combined experimental and theoretical study of the fragmentation of molecular CS2 after sulfur 1s Auger cascade decay, consisting of electron-multi-ion coincidence spectra of charged fragments and theoretical simulations combining density functional theory and molecular dynamics. On the experimental side, a procedure for a complete determination of all sets of ions formed is described. For many of the fragmentation channels, we observed a higher charge in one of the sulfur atoms than the other atoms. Based on these observations and the theoretical simulations where the time scale of the nuclear motion and decay is taken into account, we propose that KLL Auger decay after the 1s core hole creation, via 2p double hole states, results in highly charged and strongly repulsive states with one localized core hole. These localized core holes are sufficiently long-lived that some will decay after fragmentation of the molecular ion, thereby efficiently impeding charge exchange between the fragments.
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| 4. |
- Le Guen, K., et al.
(författare)
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H2S ultrafast dissociation probed by energy-selected resonant Auger electron–ion coincidence measurements
- 2007
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 127:11, s. 114315-
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Tidskriftsartikel (refereegranskat)abstract
- We have studied the ultrafast dissociation of the H2S molecule upon S 2p(3/2)-> 6a(1) inner-shell excitation by combining high-resolution resonant Auger spectroscopy and energy-selected Auger electron-ion coincidence measurements. Auger final states have been correlated to the different fragmentation pathways (S+, HS+, and H2S+ ions). As an original result, we evidence a three-step mechanism to describe the resonant production of S+: the Auger recombination in the HS* fragment is followed for the A (3)Pi and c (1)Pi states by the S++H fragmentation mechanism.
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| 5. |
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| 6. |
- Alkebro, J, et al.
(författare)
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Mechanical alloying of alumina-yttria powder mixtures
- 2000
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Ingår i: Journal of the European Ceramic Society. - 0955-2219 .- 1873-619X. ; 20:12, s. 2169-2174
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Tidskriftsartikel (refereegranskat)abstract
- Mechanical alloying has been used to prepare powder mixtures of alumina and yttria as a means to create composites with a dominant matrix phase together with small particles of a dispersed second phase. The yttria-alumina system, containing five possible phases, has the potential for creating eight combinations of matrix and dispersed phases. Here compositions designed to give YAlO3(YA) dispersed in Y3Al5O12(Y3A5 i.e. YAG) or Y4Al2O9(Y2A) were studied. After milling with steel tools for times up to 8 h, the powders were subjected to thermal cycles up to 1500 °C during which the phase evolution was monitored using X-ray diffractometry (including high-temperature XRD) and differential thermal analysis. During milling the original crystal structures were quickly broken down, in some cases partially replaced by an intermediate structure after milling. Upon subsequent heating the milled mixtures crystallized to give the expected phases, YA in Y3A5 and YA in Y2A respectively, but the reaction route was seen to be different depending on the amount of amorphization of the yttria. Contamination by iron was seen to affect the phase distribution and the lattice parameters.
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| 7. |
- Alkebro, Jesper, et al.
(författare)
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Modeling high-energy ball milling in the alumina-yttria system
- 2002
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Ingår i: Journal of Solid State Chemistry. - : Elsevier BV. - 0022-4596 .- 1095-726X. ; 164:1, s. 88-97
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Tidskriftsartikel (refereegranskat)abstract
- Experimental results from high-energy ball milling of alumina-yttria powder mixtures have been analyzed with models collected from the literature. Depending on the milling conditions, either there is formation of an intermediate phase in the alumina-yttria system (yttrium aluminum perovskite, YAP), or the sample becomes mostly amorphous. Variations due to milling tool material can be accounted for by local models based on the Hertzian theory of elastic bodies, but the effects of changing mills are poorly accounted for by published models. Therefore, the concept of an impact frequency distribution over the energy spectrum is introduced as a tool for studying the characteristics of the mills. The pressure on the powder trapped between two colliding bodies has been found to be the factor deciding the outcome of the process. The threshold behavior of the system yields an amorphous structure for low pressures, and formation of YAP when impact pressures exceed the threshold value.
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| 8. |
- Alkebro, Jesper, et al.
(författare)
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Two-phase materials in the alumina-yttria system produced by mechanical alloying
- 2000
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Ingår i: Ceramic Engineering and Science Proceedings. - Hoboken, NJ, USA : John Wiley & Sons, Inc.. - 0196-6219 .- 1940-6339. ; 21:4, s. 87-94
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Tidskriftsartikel (refereegranskat)abstract
- Mechanical alloying has been used to prepare a mixture of alumina and yttria as a means to create composites with a dominant matrix phase with small particles of a dispersed second phase. A way of avoiding possible problems with the contamination from the milling tools, is to use balls and vials in a material belonging to the system. Here a mixture of 37.9 wt% alumina and 62.1 wt% yttria has been milled with steel and alumina tools for times up to 8 h. The milled powder was subjected to thermal cycles up to 1500°C during which the phase evolution was monitored using X-ray diffractometry (including high-temperature XRD) and differential thermal analysis. The results show that although the loss of mass from alumina milling tools does not move the system from the alumina-yttria binary system, the large amounts of alumina added to the system cause difficulties in controlling the process. The phase evolution of the powders, both during milling and subsequent heat treatment, can be controlled by altering parameters of the milling, such as the density of the balls, the milling time, the powder to ball mass ratio and the hardness of the milling tools.
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| 9. |
- de, Brito AN, et al.
(författare)
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Femtosecond dissociation dynamics of core-excited molecular water
- 1999
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Ingår i: CHEMICAL PHYSICS LETTERS. - : ELSEVIER SCIENCE BV. - 0009-2614. ; 309:5-6, s. 377-385
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The fragmentation of the water molecule upon resonant core excitation and subsequent Auger decay has been studied by electron-ion coincidence spectroscopy. A qualitative comparison between the fragmentation patterns for H2O and D2O reveals that the anti-b
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| 10. |
- Le Guen, K, et al.
(författare)
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Development of a four-element conical electron lens dedicated to high resolution Auger electron-ion(s) coincidence experiments
- 2002
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Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 1089-7623 .- 0034-6748. ; 73:11, s. 3885-3894
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Tidskriftsartikel (refereegranskat)abstract
- A four-element conical electron lens has been developed in view of its integration to a double toroidal electron energy analyzer (DTA) dedicated to Auger electron-ion coincidence measurements. The lens design, using electron trajectory numerical simulations, was entirely guided by the perspective of analyzing energetic electrons with high resolution in the multicoincidence regime. The design, construction, and experimental characterization stages of this electron optics system are described in this article. Emphasis is put on the importance of third generation synchrotron radiation sources when performing such multicoincidence experiments.
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| 11. |
- Mocellin, A, et al.
(författare)
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Experimental study of photoionization of ozone in the 12 to 21 eV region
- 2001
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Ingår i: JOURNAL OF CHEMICAL PHYSICS. - : AMER INST PHYSICS. - 0021-9606. ; 115:11, s. 5041-5046 Language: English
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Tidskriftsartikel (refereegranskat)abstract
- The total and partial ion yield of ozone using time-of-flight is presented. The measurements were done using multicoincidence between a photoelectron and a photoion (PEPICO). Comparison with the photoelectron spectrum and previous measurements using other
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| 12. |
- Osso, D., et al.
(författare)
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Mechanical-thermal synthesis of Al2O3-Cr composite powders
- 1995
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Ingår i: Journal of the European Ceramic Society. - : Elsevier BV. - 0955-2219 .- 1873-619X. ; 15:12, s. 1207-1212
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Tidskriftsartikel (refereegranskat)abstract
- Three different approaches have been investigated to synthesize alumina-chromium composites by displacement reactions between aluminium and chromia. The reactions have been performed either by pure mechanosynthesis or pure thermal ignition or also by a combined mechanical and thermal activation process. Differential thermal analysis, dilatometry and high temperature X-ray diffraction have been used to show the various reaction mechanisms and chemical transformations. High-energy milling of the powder modifies the reactivity of the system. A partial pre-milling treatment not only reduces the reaction temperature but can also induce a different reaction path. It has been shown that an appropriate mechanical-thermal treatment leads to the synthesis of an alumina-chromia composite by a pure solid-state process: intermediate reaction stages exhibit little if any liquid phases.
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