| 1. |
- Ataman, Evren, et al.
(författare)
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Adsorption of L-cysteine on rutile TiO2(110)
- 2011
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028. ; 605:1-2, s. 179-186
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Tidskriftsartikel (refereegranskat)abstract
- We have used X-ray photoelectron spectroscopy to study the adsorption of L-cysteine on a rutile TiO2(110) surface at room temperature and -65 degrees C. For the molecules in direct contact with the surface our results suggest that the molecules bind dissociatively to the fivefold-coordinated Ti atoms of the surface through their deprotonated carboxylic groups. A second, dissociative interaction occurs between the molecular thiol groups and the surface. It is attributed to a dissociative bond to the bridging oxygen vacancies. Most likely, the thiol groups are deprotonated and a bond is formed between the thiolates and defects. In an alternative scenario, the C-S bond is cleaved and atomic sulfur binds to the defects. With regard to the molecular amino groups, they remain neutral at the lowest investigated coverages (0.3-0.5 ML), but already starting from around 0.7 ML nominal coverage protons are being transferred to them. The fraction of protonated amino groups increases with coverage and becomes dominating in multilayers prepared at room temperature and -65 degrees C. In these multilayers the carboxylic groups are deprotonated. (C) 2010 Elsevier B.V. All tights reserved.
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| 2. |
- Ataman, Evren, et al.
(författare)
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Modification of the Size of Supported Clusters by Coadsorption of an Organic Compound: Gold and l-Cysteine on Rutile TiO(2)(110).
- 2011
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 27:18, s. 11466-11474
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Tidskriftsartikel (refereegranskat)abstract
- Using X-ray photoelectron spectroscopy we studied the coadsorption of the amino acid l-cysteine and gold on a rutile TiO(2)(110) surface under ultrahigh vacuum conditions. Irrespective of the deposition order, i.e., irrespective of whether l-cysteine or gold is deposited first, the primary interaction between l-cysteine and the gold clusters formed at the surface takes place through the deprotonated thiol group of the molecule. The deposition order, however, has a profound influence on the size of the gold clusters as well as their location on the surface. If l-cysteine is deposited first the clusters are smaller by a factor two to three compared to gold deposited onto the pristine TiO(2)(110) surface and then covered by l-cysteine. Further, in the former case the clusters cover the molecules and thus form the outermost layer of the sample. We also find that above a minimum gold cluster size the gold cluster/l-cysteine bond is stronger than the l-cysteine/surface bridging oxygen vacancy bond, which, in turn, is stronger than the gold cluster/vacancy bond.
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| 3. |
- Ataman, Evren, et al.
(författare)
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Unconventional Zwitterionic State of L-Cysteine
- 2011
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Ingår i: The Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 2:14, s. 1677-1681
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Tidskriftsartikel (refereegranskat)abstract
- We report the signature of an unconventional zwitterion in thick (>40 angstrom) L-cysteine films grown at low temperature (100 K) by means of sublimation in ultrahigh vacuum. Using X-ray photoelectron spectroscopy (XPS) we find that protonated amino groups (57%) are less prevalent than in films grown at higher temperatures. A large majority of the protonated amino groups receive the hydrogen through deprotonation of the thiol group (45%) and, in contrast, only a small fraction of the carboxylic groups (13%) is deprotonated. This shows, for the first time, the unconventional zwitterion to be the dominant species in L-cysteine. We believe the unusual growth parameters are responsible for this novel observation.
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| 4. |
- Chaudhary, Shilpi, et al.
(författare)
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Controlled short-linkage assembly of functional nano-objects
- 2014
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Ingår i: Applied Surface Science. - : Elsevier BV. - 1873-5584 .- 0169-4332. ; 300, s. 22-28
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Tidskriftsartikel (refereegranskat)abstract
- In this work, we report a method that allows the deterministic, photo-controlled covalent assembly of nanoparticles directly on surface. As a model system, we study the conjugation of molecularly imprinted polymer (MIP) nanoparticles on a glass surface and confirm that the immobilized nanoparticles maintain their molecular recognition functionality. The glass slide was first modified with perfluorophenylazide and then used to bind MIP nanoparticles under UV irradiation. After each step the surface was analyzed by water contact angle measurement, fluorescence microscopy, scanning electron microscopy, and/or synchrotron-based X-ray photoelectron spectroscopy. The MIP nanoparticles immobilized on the glass surface remained stable and maintained specific binding for the template molecule, propranolol. The method developed in this work allows MIP nanoparticles to be directly coupled to a flat surface, offering a straightforward means to construct robust chemical sensors. Using the reported photo conjugation method, it is possible to generate patterned assembly of nanoparticles using a photomask. Since perfluorophenylazide-based photochemistry works with all kinds of organic material, the method developed in this work is expected to enable immobilization of not only MIPs but also other kinds of organic and inorganic-organic core-shell particles for various applications involving photon or electron transfer. (C) 2014 The Authors. Published by Elsevier B.V. All rights reserved.
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| 5. |
- Faraggi, M. N., et al.
(författare)
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Role of Deprotonation and Cu Adatom Migration in Determining the Reaction Pathways of Oxalic Acid Adsorption on Cu(111)
- 2011
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 115:43, s. 21177-21182
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Tidskriftsartikel (refereegranskat)abstract
- Scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and first principles theoretical calculations have been used to gain insight into the fundamental processes involved in the adsorption and self-assembly of oxalic acid on Cu(111). The experimental data demonstrate that several reaction pathways are involved in the chemisorption of oxalic acid on Cu(111), one of which leads to deprotonation of the acid into oxalate molecules that form ordered structures on the surface. Theoretical calculations indicate that the adsorption of oxalate molecules is not stable on the surface unless copper adatoms are taken into consideration. Coordination with copper adatoms prevents oxalate molecules from getting closer to the substrate, precluding the expected decomposition of oxalate into carbon dioxide. Our results, thus, suggest that the 2D gas of diffusing copper adatoms might play a very important role in the self-assembly of the molecules not only by catalyzing the deprotonation of oxalic acid but also by decreasing the surface reactivity.
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| 6. |
- Grizolli, Walan, et al.
(författare)
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Use of astigmatic re-focusing at HP-XPS end-station
- 2013
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Ingår i: 11th International Conference on Synchrotron Radiation Instrumentation (SRI 2012). - : IOP Publishing. - 1742-6596 .- 1742-6588. ; 425
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Konferensbidrag (refereegranskat)abstract
- In this paper we present the refocusing optics for the new high pressure photoelectron spectroscopy (HP-XPS) branch line at MAX-lab, based on a plane grating monochromator with vertically collimated beam. For the HP-XPS instrument, the required spot size is dictated by the small geometric acceptance of the HP-XPS electron energy analyzer. Whereas a pair of bendable mirrors in a KB configuration has some advantages as refocusing elements, we have studied whether similar performance can be achieved with a single non-bendable mirror. In this solution, however, the need for strong horizontal magnification results in a strong vertical magnification and into a very asymmetric image, the height being just a fraction of the width. We have studied through an analytical geometrical model and ray tracing simulations the use of astigmatism to increase the vertical beam size up to the geometric acceptance of the detector. As a result the vertical beam size at sample plane is mostly determined by the photon angular distribution and is not dependent on the exit slit aperture size. In addition the vertical beam size can be controlled by the grating c(ff) parameter, making possible to adjust the photon density and minimize sample damage by the radiation.
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| 7. |
- Grånäs, Elin, et al.
(författare)
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CO Intercalation of Graphene on Ir(111) in the Millibar Regime
- 2013
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 117:32, s. 16438-16447
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Tidskriftsartikel (refereegranskat)abstract
- Here we show that it is possible to intercalate CO under graphene grown on Ir(111) already at room temperature when CO pressures in the millibar regime are used. From the interplay of X-ray photoelectron spectroscopy and scanning tunneling microscopy we conclude that the intercalated CO adsorption structure is similar to the (3 root 3 X 3 root 3)R30 degrees) adsorption structure that is formed on Ir(111) upon exposure to similar to 1 mbar of CO. Further, density functional theory calculations reveal that the structural and electronic properties of CO-intercalated graphene are similar to p-doped freestanding graphene. Finally we characterize nonintercalated stripes and islands that we always observe in the CO-intercalated graphene. We observe these nonintercalated areas predominately in HCP and FCC areas near step edges and suggest that stress release in graphene is the driving force for their formation, while the weak chemical bonds in HCP and FCC areas are the reason for their area selectivity.
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| 8. |
- Isvoranu, Cristina, et al.
(författare)
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Adsorption of ammonia on multilayer iron phthalocyanine.
- 2011
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 134:11
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Tidskriftsartikel (refereegranskat)abstract
- The adsorption of ammonia on multilayers of well-ordered, flat-lying iron phthalocyanine (FePc) molecules on a Au(111) support was investigated by x-ray photoelectron spectroscopy. We find that the electron-donating ammonia molecules coordinate to the metal centers of iron phthlalocyanine. The coordination of ammonia induces changes of the electronic structure of the iron phthalocyanine layer, which, in particular, lead to a modification of the FePc valence electron spin.
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| 9. |
- Isvoranu, Cristina, et al.
(författare)
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Ammonia adsorption on iron phthalocyanine on Au(111): Influence on adsorbate-substrate coupling and molecular spin.
- 2011
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 134:11
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Tidskriftsartikel (refereegranskat)abstract
- The adsorption of ammonia on Au(111)-supported monolayers of iron phthalocyanine has been investigated by x-ray photoelectron spectroscopy, x-ray absorption spectroscopy, and density functional theory calculations. The ammonia-induced changes of the x-ray photoemission lines show that a dative bond is formed between ammonia and the iron center of the phthalocyanine molecules, and that the local spin on the iron atom is quenched. This is confirmed by density functional theory, which also shows that the bond between the iron center of the metalorganic complex and the Au(111) substrate is weakened upon adsorption of ammonia. The experimental results further show that additional adsorption sites exist for ammonia on the iron phthalocyanine monolayer.
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| 10. |
- Isvoranu, Cristina, et al.
(författare)
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Comparison of the Carbonyl and Nitrosyl Complexes Formed by Adsorption of CO and NO on Mono layers of Iron Phthalocyanine on Au(111)
- 2011
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 115:50, s. 24718-24727
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Tidskriftsartikel (refereegranskat)abstract
- The interaction between monolayers of iron phthalocyanine on a Au(111) support and carbon monoxide and nitric oxide is studied by X-ray photoelectron spectroscopy and density functional theory calculations. We find several carbon monoxide and nitric oxide adsorbate species, and in particular species that bind to the iron ions of the phthalocyanine compound. The formation of phthalocyanine carbonyl and nitrosyl complexes leads to a redistribution of the electrons in the iron 3d levels resulting in a change of the spin state. Further, the adsorption results in an electronic decoupling of the iron phthalocyanine adsorbates from the substrate. The extent of the spin change and adsorbate substrate decoupling depends on which ligand is used. The X-ray photoelectron spectroscopy results suggest that a covalent bond is formed between the NO and CO adsorbates and the FePc iron ion, and that the NO and CO valence states hybridize with metal ion d states. The density functional theory calculations show that CO adsorbs in a linear configuration, while NO adsorption assumes a tilted geometry.
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