| 1. |
- Kahk, J. Matthias, et al.
(författare)
-
A study of the pressure profiles near the first pumping aperture in a high pressure photoelectron spectrometer
- 2015
-
Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048 .- 1873-2526. ; 205, s. 57-65
-
Tidskriftsartikel (refereegranskat)abstract
- In a high-pressure photoelectron spectrometer, the sample is positioned close to a differential pumping aperture, behind which the pressure is several orders of magnitude lower than the pressure in the analysis chamber. To find the optimal sample position, where the path length of the photoelectrons through the high pressure region is minimized as far as possible without compromising knowledge of the actual pressure at the sample surface, an understanding of the pressure variations near the sample and the aperture is required. A computational fluid dynamics study has been carried out to examine the pressure profiles, and the results are compared against experimental spectra whose intensities are analyzed using the Beer-Lambert law. The resultant pressure profiles are broadly similar to the one previously derived from a simplistic molecular flow model, but indicate that as the pressure in the analysis chamber is raised, the region over which the pressure drop occurs becomes progressively narrower.
|
|
| 2. |
- Schnadt, J, et al.
(författare)
-
Excited-state charge transfer dynamics in systems of aromatic adsorbates on TiO2 studied with resonant core techniques
- 2003
-
Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 119:23, s. 12462-12472
-
Tidskriftsartikel (refereegranskat)abstract
- Resonant core spectroscopies are applied to a study of the excited electron transfer dynamics on a low-femtosecond time scale in systems of aromatic molecules (isonicotinic acid and bi-isonicotinic acid) adsorbed on a rutile TiO2(110) semiconductor surface. Depending on which adsorbate state is excited, the electron is either localized on the adsorbate in an excitonic effect, or delocalizes rapidly into the substrate in less than 5 fs (3 fs) for isonicotinic acid (bi-isonicotinic acid). The results are obtained by the application of a variant of resonant photoemission spectroscopy. (C) 2003 American Institute of Physics.
|
|
| 3. |
- Schnadt, Joachim, et al.
(författare)
-
Structural study of adsorption of isonicotinic acid and related molecules on rutile TiO2(110) I: XAS and STM
- 2003
-
Ingår i: Surface Science. - 0039-6028. ; 540:1, s. 39-54
-
Tidskriftsartikel (refereegranskat)abstract
- X-ray absorption spectroscopy (XAS) and scanning tunneling microscopy (STM) have been used to study the absorption of monolayers of the pyridinecarboxylic acid monomers (isonicotinic acid, nicotinic acid, and picolinic acid) and benzoic acid on a rutile TiO2(1 1 0) surface. We find that the pyridine and phenyl rings are oriented with their planes largely perpendicular to the surface. The azimuthal orientations are strongly influenced by adsorbate-adsorbate interactions, which in each case leads to at least two different molecular species. In order to reach this conclusion a detailed strategy has been developed for the interpretation of angle-dependent XAS data, which does not rely on any curve fitting procedures. (C) 2003 Elsevier B.V. All rights reserved.
|
|
| 4. |
- Eriksson, Susanna K, et al.
(författare)
-
A versatile photoelectron spectrometer for pressures up to 30 mbar
- 2014
-
Ingår i: Review of Scientific Instruments. - : American Institute of Physics (AIP). - 0034-6748 .- 1089-7623. ; 85:7, s. 075119-
-
Tidskriftsartikel (refereegranskat)abstract
- High-pressure photoelectron spectroscopy is a rapidly developing technique with applications in a wide range of fields ranging from fundamental surface science and catalysis to energy materials, environmental science, and biology. At present the majority of the high-pressure photoelectron spectrometers are situated at synchrotron end stations, but recently a small number of laboratory-based setups have also emerged. In this paper we discuss the design and performance of a new laboratory based high pressure photoelectron spectrometer equipped with an Al Ka X-ray anode and a hemispherical electron energy analyzer combined with a differentially pumped electrostatic lens. The instrument is demonstrated to be capable of measuring core level spectra at pressures up to 30 mbar. Moreover, valence band spectra of a silver sample as well as a carbon-coated surface (graphene) recorded under a 2 mbar nitrogen atmosphere are presented, demonstrating the versatility of this laboratory-based spectrometer.
|
|
| 5. |
- Alfredsson, Y, et al.
(författare)
-
Phase and molecular orientation in metal-free phthalocyanine films on conducting glass: Characterization of two deposition methods
- 2005
-
Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090. ; 493:1-2, s. 13-19
-
Tidskriftsartikel (refereegranskat)abstract
- in this study, metal-free phthalocyanine has been deposited on a conducting glass surface by two methods: by spreading the molecular powder directly on the substrate in air and by vapor sublimation under ultra-high vacuum conditions (evaporation). The films have been characterized by means of core level X-ray Photoemission Spectroscopy, X-ray Absorption Spectroscopy (XAS) and Ultra Violet and Visible absorption spectroscopy (UV-Vis). Our results show that the two deposition methods produce molecular overlayers in different polymorphic phases; the UV-Vis measurements indicate that the film obtained by powder deposition is of x-phase type whereas sublimation leads to an a-polymorph structure. The XAS results show that in the powder deposited film the molecules are mainly oriented parallel to the surface. This is opposite to the case of the vapor deposited film, where the molecules mainly are oriented orthogonal to the surface.
|
|
| 6. |
- Edwards, Marten O. M., et al.
(författare)
-
Increased photoelectron transmission in High-pressure photoelectron spectrometers using "swift acceleration"
- 2015
-
Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 785, s. 191-196
-
Tidskriftsartikel (refereegranskat)abstract
- A new operation mode of a HPXPS (high-pressure X-ray photoelectron spectroscopy) analyzer is evaluated on a HPXPS system fitted with an Al K alpha X-ray source. A variety of metal foil samples (gold, silver and copper) were measured in different sample gas environments (N-2 and H2O), and a front aperture diameter of 0.8 mm. The new design concept is based upon "swiftly" accelerating the photoelectrons to kinetic energies of several keV after they pass the analyzer front aperture. Compared to the standard mode, in which the front section between the two first apertures is field-free, this gives a wider angular collection and a lower tendency for electron losses in collisions with gas molecules within the analyzer. With the swift-acceleration mode we attain, depending on the experimental conditions, up to about 3 times higher peak intensities in vacuum and about 10 to 20 times higher peak intensities in the 6-9 mbar regime, depending on kinetic energy. These experimental findings agree well with simulated transmission functions for the analyzer. The new mode of operation enables faster data acquisition than the standard mode of operation, particularly valuable in a home laboratory environment. Further demonstrations of performance are highlighted by measurements of the valence band structure in dye sensitized solar cell photoelectrodes under a 2 mbar H2O atmosphere, a molecularly modified surface of interest in photoelectrochemical devices.
|
|
