| 1. |
- Alfredsson, Ylfi, et al.
(författare)
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Phase and molecular orientation in H2Pc on conducting glass : characterization of two deposition methods
- 2005
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Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 493:1-2, s. 13-19
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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 α-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.
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| 2. |
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| 3. |
- Alfredsson, Y, et al.
(författare)
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Phase and molecular orientation in metal-free phthalocyanine films on conducting glass: Characterization of two deposition methods
- 2005
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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.
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| 4. |
- Carabineiro, S A C, et al.
(författare)
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Resonant photoemission of N2O on Ir(110)
- 2004
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Ingår i: Surface Review and Letters. - 0218-625X. ; 11:4-5, s. 385-389
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Tidskriftsartikel (refereegranskat)abstract
- The adsorption of N2O on Ir(110) was investigated with high-resolution resonant photoemission at 135 K. The results obtained show evidence of molecular adsorption of N2O, along with some dissociation. It is found that the nitrogen photoemission spectra measured at the terminal and central nitrogen energy positions of the N2O/Ir(110) system are equivalent to those of N2O in the gas phase. In contrast, the oxygen spectrum shows little resemblance to the gas phase oxygen spectrum of N2O. In the nitrogen resonant photoemission spectra one can only discover resonant behavior with constant binding energy peaks. In contrast, the oxygen resonant photoemission spectra shows dominantly Auger behavior with peaks at constant kinetic energies. Both observations reveal that the oxygen is bonded to the Ir surface. A systematic study as a function of coverage and temperature and a comparison with other surfaces differing in structure and composition is needed to understand the variations in the adsorption behavior of N2O On metal surfaces.
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| 5. |
- Chao, Yimin, et al.
(författare)
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Evaporation and deposition of alkyl-capped silicon nanocrystals in ultrahigh vacuum
- 2007
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Ingår i: Nature Nanotechnology. - : Springer Science and Business Media LLC. - 1748-3395 .- 1748-3387. ; 2:8, s. 486-489
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Tidskriftsartikel (refereegranskat)abstract
- Nanocrystals are under active investigation because of their interesting size- dependent properties(1,2) and potential applications(3-5). Silicon nanocrystals have been studied for possible uses in optoelectronics(6), and may be relevant to the understanding of natural processes such as lightning strikes(7). Gas-phase methods can be used to prepare nanocrystals, and mass spectrometric techniques have been used to analyse Au-8,(9) and CdSe clusters(10). However, it is difficult to study nanocrystals by such methods unless they are synthesized in the gas phase(11). In particular, pre-prepared nanocrystals are generally difficult to sublime without decomposition. Here we report the observation that films of alkyl-capped silicon nanocrystals evaporate upon heating in ultrahigh vacuum at 200 degrees C, and the vapour of intact nanocrystals can be collected on a variety of solid substrates. This effect may be useful for the controlled preparation of new quantum-confined silicon structures and could facilitate their mass spectroscopic study and size- selection(12).
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| 6. |
- Chao, Y, et al.
(författare)
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Reactions and luminescence in passivated Si nanocrystallites induced by vacuum ultraviolet and soft-x-ray photons
- 2005
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Ingår i: Applied Physics Reviews. - : AIP Publishing. - 1931-9401. ; 98:4
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Tidskriftsartikel (refereegranskat)abstract
- Alkyl-modified silicon nanocrystallites are efficient fluorophores which are of interest for fundamental spectroscopic studies and as luminescent probes in biology because of their stability in aqueous media. In this work we have investigated these particles using scanning tunneling microscopy, synchrotron-radiation excited photoemission, and x-ray excited optical luminescence (XEOL). During the course of illumination with 145-eV photons we have monitored the evolution of the Si2p core level and, in samples which have suffered prolonged atmospheric exposure, observed in real time the growth of an extra Si2p component attributed to in situ photoinduced oxidation of the Si nanocrystallites. XEOL reveals that two emission bands are active upon soft-x-ray photon excitation and that photoluminescence intensity decreases with photon exposure, which is attributed to charge trapping within the film.
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| 7. |
- Glover, C. J., et al.
(författare)
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Stationary and dispersive features in resonant inelastic soft X-ray scattering at the Ge 3p resonances
- 2009
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Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048 .- 1873-2526. ; 173:2-3, s. 103-107
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Tidskriftsartikel (refereegranskat)abstract
- Resonant inelastic soft X-ray scattering at the 3p resonances in crystalline Ge is presented. Both stationary and dispersive features are observed in a wide energy range above as well as below the ionization limits. These observations are in agreement with theoretical predictions based on a two-step model where the initially excited electron has no influence on the emission step. Excess population of states in the conduction band is found, and discussed in terms of attosecond electron dynamics. (c) 2009 Elsevier B.V. All rights reserved.
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| 8. |
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| 9. |
- Kjeldgaard, Lisbeth, et al.
(författare)
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Intramolecular vibronic dynamics in molecular solids: C60
- 2005
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 72:20
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Tidskriftsartikel (refereegranskat)abstract
- Vibronic coupling in solid C60 has been investigated with a combination of resonant photoemission spectroscopy (RPES) and resonant inelastic x-ray scattering (RIXS). Excitation as a function of energy within the lowest unoccupied molecular orbital resonance yielded strong oscillations in intensity and dispersion in RPES, and a strong inelastic component in RIXS. Reconciling these two observations establishes that vibronic coupling in this core hole excitation leads to predominantly inelastic scattering and localization of the excited vibrations on the molecule on a femtosecond time scale. The coupling extends throughout the widths of the frontier valence bands.
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| 10. |
- Käämbre, Tanel, et al.
(författare)
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Bulk electronic structure of K3C60 as revealed by soft x-rays
- 2007
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 75:19, s. 195432-
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Tidskriftsartikel (refereegranskat)abstract
- We present C 1s x- ray absorption, x- ray emission, and resonant inelastic x- ray scattering (RIXS ) spectra of single- phase crystalline K3C60. The comparison to valence- band photoelectron spectra from the same sample facilitates identification of the contribution from surface and bulk electronic states in the latter. Bulk- sensitive techniques show that the valence bands of K3C60 and pure C-60 are characterized by spectral features of similar width, in agreement with the predictions of band- structure calculations. Symmetry selectivity in the RIXS process allows us to assign peaks in the C 1s absorption spectrum, demonstrating a close correspondence with pure C-60 also in the conduction band. The symmetry selectivity is as pronounced in K3C60 as in pure C-60, indicating that the local C-60 symmetry is not appreciably affected by the K doping, either in the ground state or intermediate state, on the time scale of 6 fs.
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