Search results for "PHOTOELECTRON"
showing 10 items of 458 documents
Electronic and magnetic properties of Mn 12 molecular magnets on sulfonate and carboxylic acid prefunctionalized gold surfaces
2012
Structural, electronic, and magnetic properties of [Mn 12O 12(bet) 16(EtOH) 4](PF 6) 14·4CH 3CN·H 2O (in short Mn 12bet, bet = betaine = +N(CH 3) 3-CH 2-COO -) single-molecule magnets (SMMs) deposited on previously functionalized gold surfaces have been investigated. Self-assembled monolayers (SAMs) either of sodium mercaptoethanesulfonate (MES) or mercaptopropionic acid (MPA) are used as functionalization to avoid the direct interaction between the Mn 12bet molecules and the Au surface with the aim of preserving the main functional properties of the molecules. Scanning tunneling microscopy (STM) and X-ray photoemission spectroscopy (XPS) analysis show deposited Mn 12bet SMMs well-isolated …
Interfacial reaction between deposited molybdenum and TiO2(110) surface: role of the substrate bulk stoichiometry
2004
Abstract The interfacial reaction between deposited molybdenum and three different TiO2(1 1 0) substrates (a bulk and surface stoichiometric TiO2; a bulk stoichiometric and surface reduced crystal; a bulk and surface slightly reduced crystal) was investigated by means of X-ray photoelectron spectroscopy (XPS) and X-ray absorption near edge spectroscopy (XANES). While the interfacial reaction is not a function of the substrate at room temperature (in any case, molybdenum layers grow with oxygen dissolved in), this study clearly reveals a strong effect of the substrate bulk stoichiometry on the chemical state of the deposit after annealing up to 750 °C whereas the substrate surface stoichiome…
Study of the structural phase transformation of iron oxide nanoparticles from an Fe2+ ion source by precipitation under various synthesis parameters …
2015
Abstract Magnetite nanoparticles were precipitated from a pure aqueous ferrous salt solution in an air atmosphere. The influence of the solution molarity, the rate of precipitator agent addition, stirring time and annealing temperature was studied. The morphology, crystalline phase purity and magnetic properties of the obtained powders were studied by X-Ray powder diffraction (XRD), Scanning electron microscopy (SEM), Differential thermal analysis (DTA), X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS) and Vibrating sample magnetometer (VSM). The synthesis conditions were seen to have an effect on phase composition. It was possible to obtain near stoichiometric Fe…
Co doped ZnO nanowires as visible light photocatalysts
2016
Abstract High aspect ratio cobalt doped ZnO nanowires showing strong photocatalytic activity and moderate ferromagnetic behaviour were successfully synthesized using a solvothermal method and characterized by scanning electron microscopy (SEM), X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), vibrating sample magnetometry (VSM) and UV–visible absorption spectroscopy. The photocatalytic activities evaluated for visible light driven degradation of an aqueous methylene orange (MO) solution were higher than for Co doped ZnO nanoparticles at the same doping level and synthesized by the same synthesis route. The rate constant for MO visi…
Support effects on NiO-based catalysts for the oxidative dehydrogenation (ODH) of ethane
2019
[EN] We report on the effect of NiO-support interactions on the chemical nature of Ni species in a series of supported NiO catalysts for the ODH of ethane. SiO2, TiO2-anatase, a high surface area TiO2 and a porous clay hetero-structure (PCH) with TiO2 and SiO2 pillars were used as supports, which led to a selectivity to ethylene in the range 30-90% over supported NiO catalysts. The catalysts were characterized by means of XRD, N-2-Adsorption, H-2-TPR, XPS and in situ (under H-2 reductive atmosphere) and ex situ XAS spectroscopy. The catalytic performance of supported materials is discussed in terms of their reducibility and specific reduction kinetics, but also taking into account the speci…
Structure and composition of sputter-deposited nickel-tungsten oxide films
2011
Films of mixed nickel-tungsten oxide, denoted NixW1-x oxide, were prepared by reactive DC magnetron co-sputtering from metallic targets and were characterized by Rutherford backscattering spectrometry. X-ray photoelectron spectroscopy, X-ray diffractometry and Raman spectroscopy. A consistent picture of the structure and composition emerged, and at x<0.50 the films comprised a mixture of amorphous WO3 and nanosized NiWO4, at x = 0.50 the nanosized NiWO4 phase was dominating, and at x>0.50 the films contained nanosized NiO and NiWO4.
X‐Ray Photoelectron Spectroscopy
2021
X-ray photoelectron spectroscopy (XPS) is a spectroscopic technique in the family of electron spectroscopies, that is, those methods whose probe consists of electrons instead of photons. In the case of XPS, a soft, usually monochromatic X-ray causes the emission of electrons by means of the photoelectric effect. Differences in chemical potential and/or polarizability of the molecules can cause an alteration of the binding energy; in addition to photoelectrons, an ordinary XPS spectrum may also contain Auger electrons. In an XPS system, an electron gun is used to deliver a low-energy electron flux with a low current over the illuminated spot. In an XPS instrument, an ion gun may be used with…
The polarization dependence of x‐ray photoelectron yield of a Au photocathode
1994
We report a measurement of the total photoelectron yield of gold as a function of the incident x‐ray polarization. Polarized x rays with energies of 2.5, 2.7, and 4.0 keV were used to excite a gold photocathode at a glancing incidence angle between 5° and 50°. Contrary to a previous report, we found no measurable polarization dependence for all three x‐ray energies. We conclude that the modulation factor, i.e., the fractional change of the total yield when the polarization state is varied, is less than 4%.
Local Structure of Supported Keggin and Wells-Dawson Heteropolyacids and Its Influence on the Catalytic Activity
2019
[EN] Keggin [PW12O40]3– and Wells–Dawson [P2W18O62]6– heteropolyanions are nanosized transition-metal-oxygen clusters belonging to the heteropolyacids (HPAs) family. They are widely used as catalysts due to their high Brønsted acidity, and their dispersion on solid supports favors the accessibility to their acid sites generally increasing the catalytic activity. A series of binary materials composed of Keggin or Wells–Dawson HPAs and SiO2, TiO2, and ZrO2 have been prepared by impregnation or solvothermal methods. Remarkable differences have been found in the catalytic activities among the unsupported and supported HPAs. These differences have been correlated in the past to the structural ch…
Using photoelectron emission microscopy with hard-X-rays
2001
We present several successful test cases of using photoelectron emission microscopy (PEEM) for photon energy up to 25 keV. First, the full extended X-ray absorption fine structure analysis was implemented in areas as small as 100 mum(2) for transition-metal K edge absorption spectra and, therefore, demonstrated the feasibility of combining structural and chemical analysis with hard-X-ray absorption spectroscopy with high lateral resolution. We also show that PEEM can be used in a transmission (radiography) mode as an imaging detector for hard-X-ray, This approach again leads to the unprecedented 0.3 mum lateral resolution, particularly critical for the use of coherence-based phase contrast …