| 1. |
- Fairclough, Simon M., et al.
(author)
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Growth and Characterization of Strained and Alloyed Type-II ZnTe/ZnSe Core-Shell Nanocrystals
- 2012
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In: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 116:51, s. 26898-26907
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Journal article (peer-reviewed)abstract
- We investigate the growth and the physical and optical properties of type-II heterostructured ZnTe/ZnSe colloidal nanocrystals, focusing on the role of the 7% lattice mismatch between the two materials in determining growth homogeneity and band structure. We find that the lattice mismatch between the two materials places limitations on the range of structures that can be grown, and for those in which coherent growth is achieved we present clear evidence that the low bulk modulus ZnTe cores are compressed by the higher modulus ZnSe shells, accentuating the red-shift of the excitonic state with increasing shell thickness. By employing a variety of characterization tools we build a clear picture of the core-shell architecture. We show how strain is manifested in structures with sharp core-shell interfaces and how intentional alloying of the interface can influence the growth and exciton energies. We show that a (2,6)-band effective mass model is able to distinguish between the as-grown "sharp" and "alloyed" interfaces, indicating that the alloyed structures incorporate reduced strain.
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| 2. |
- Ahola-Tuomi, M., et al.
(author)
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Properties of self-assembled Bi nanolines on InAs(100) studied by core-level and valence-band photoemission, and first-principles calculations
- 2011
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 83:24, s. 245401-
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Journal article (peer-reviewed)abstract
- We have studied self-assembled bismuth (Bi) nanolines on the Bi-terminated InAs(100) surface by core-level and valence-band photoelectron spectroscopy, and ab initio first-principles calculations. A structural model for this intriguing surface is suggested based on the comparison of the measured and calculated core-level shifts. Also, the atomic origins for the core-level shifts are proposed based on the calculations. A clear peak related to this surface was observed in the valence band 0.34 eV below the Fermi level, which can be used as a "fingerprint" of a well-ordered Bi/InAs(100) nanoline surface.
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| 3. |
- Bournel, F., et al.
(author)
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Hydrosilylation of Styrene on Water-Saturated Si(001)-2 x 1 at Room Temperature
- 2011
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In: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 115:30, s. 14827-14833
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Journal article (peer-reviewed)abstract
- The Si(001)-2 x 1 surface saturated by water is characterized by the passivation of nearly all of the dimerized atoms by H/OH terminations, except isolated dangling bonds, whose areal density is in the range of 1.5 +/- 0.2 x 10(-2) defects per Si atom. Therefore the water-saturated Si(001)-2 x 1 surface presents similarities with the defective H-terminated Si(001)2 x I. surface (presence of monohydrides and isolated dangling bonds), on which alkene molecules are known to be grafted via a radical-based hydrosilylation mechanism initiated at silicon dangling bonds. These common features stimulated the present study devoted to the reactivity of the water-saturated surface (n(+)-doped substrate) with styrene (H2C alpha=C beta H-C6H5) at room temperature. Using synchrotron radiation X-ray photoemission spectroscopy (XPS), our aim was to estimate the extent of styrene growth and to characterize the chemistry of the adsorbed molecule. XPS showed that styrene does react with the surface: after an exposure of 6.7 L (900 s x 0.75 x 10(-8) Torr), we estimate that about 0.2 molecules per Si dimer (similar to 0.1 molecule per Si atom) are grafted on the surface. The C is XPS spectrum is consistent with a hydrosilylation product, Si-C alpha H2-C beta H2-C6H5. Indeed we found that the C Is spectral shape of styrene mono-a bonded to the water-covered surface is markedly different from that of styrene di-sigma bonded to the clean Si(001)-2 x 1 surface, confirming the specificity of the reaction product formed on the former surface. Mechanistically, a radical-based hydrosilylation reaction is the most plausible, as theoretical works indicate that the activation barrier. of the latter mechanism is much lower than that of a direct, concerted mechanism. The C is spectral shape also excludes a reaction of the molecule with surface hydroxyls, leading to the formation of monohydroxyls C beta OH(H) (radical-based reaction) or of Si-O-C linkages (Markovnikov or anti-Markovnikov addition).
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| 4. |
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| 5. |
- Laukkanen, P., et al.
(author)
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Core-level shifts of the c(8 x 2)-reconstructed InAs(100) and InSb(100) surfaces
- 2010
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In: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048 .- 1873-2526. ; 177:1, s. 52-57
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Journal article (peer-reviewed)abstract
- We have studied In-stabilized c(8 2)-reconstructed InAs(1 0 0) and InSb(1 0 0) semiconductor surfaces, which play a key role in growing improved III-V interfaces for electronics devices, by core-level photoelectron spectroscopy and first-principles calculations. The calculated surface core-level shifts (SCLSs) for the zeta and zeta a models, which have been previously established to describe the atomic structures of the III-V(1 00)c(8 x 2) surfaces, yield hitherto not reported interpretation for the As 3d, In 4d, and Sb 4d core-level spectra of the III-V(1 00)c(8 x 2) surfaces, concerning the number and origins of SCLSs. The fitting analysis of the measured spectra with the calculated zeta and zeta a SCLS values shows that the InSb spectra are reproduced by the zeta SCLSs better than by the zeta a SCLSs. Interestingly, the zeta a fits agree better with the InAs spectra than the zeta fits do, indicating that the zeta a model describes the InAs surface better than the InSb surface. These results are in agreement with previous X-ray diffraction data. Furthermore, an introduction of the complete-screening model, which includes both the initial and final state effects, does not improve the fitting of the InSb spectra, proposing the suitability of the initial-state model for the SCLSs of the III-V(1 0 0)c(8 x 2) surfaces. The found SCLSs are discussed with the ab initio on-site charges.
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| 6. |
- Schindler, L, et al.
(author)
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Development of a Neurotensin-Derived 68Ga-Labeled PET Ligand with High In Vivo Stability for Imaging of NTS1 Receptor-Expressing Tumors
- 2022
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In: Cancers. - : MDPI AG. - 2072-6694. ; 14:19
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Journal article (peer-reviewed)abstract
- Overexpression of the neurotensin receptor type 1 (NTS1R), a peptide receptor located at the plasma membrane, has been reported for a variety of malignant tumors. Thus, targeting the NTS1R with 18F- or 68Ga-labeled ligands is considered a straightforward approach towards in vivo imaging of NTS1R-expressing tumors via positron emission tomography (PET). The development of suitable peptidic NTS1R PET ligands derived from neurotensin is challenging due to proteolytic degradation. In this study, we prepared a series of NTS1R PET ligands based on the C-terminal fragment of neurotensin (NT(8–13), Arg8-Arg9-Pro10-Tyr11-Ile12-Leu13) by attachment of the chelator 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) via an Nω-carbamoylated arginine side chain. Insertion of Ga3+ in the DOTA chelator gave potential PET ligands that were evaluated concerning NTS1R affinity (range of Ki values: 1.2–21 nM) and plasma stability. Four candidates were labeled with 68Ga3+ and used for biodistribution studies in HT-29 tumor-bearing mice. [68Ga]UR-LS130 ([68Ga]56), containing an N-terminal methyl group and a β,β-dimethylated tyrosine instead of Tyr11, showed the highest in vivo stability and afforded a tumor-to-muscle ratio of 16 at 45 min p.i. Likewise, dynamic PET scans enabled a clear tumor visualization. The accumulation of [68Ga]56 in the tumor was NTS1R-mediated, as proven by blocking studies.
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| 7. |
- Schlenk, T., et al.
(author)
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Controllable Magnetic Doping of the Surface State of a Topological Insulator
- 2013
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In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 110:12, s. 126804-
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Journal article (peer-reviewed)abstract
- A combined experimental and theoretical study of doping individual Fe atoms into Bi2Se3 is presented. It is shown through a scanning tunneling microscopy study that single Fe atoms initially located at hollow sites on top of the surface (adatoms) can be incorporated into subsurface layers by thermally activated diffusion. Angle-resolved photoemission spectroscopy in combination with ab initio calculations suggest that the doping behavior changes from electron donation for the Fe adatom to neutral or electron acceptance for Fe incorporated into substitutional Bi sites. According to first principles calculations within density functional theory, these Fe substitutional impurities retain a large magnetic moment, thus presenting an alternative scheme for magnetically doping the topological surface state. For both types of Fe doping, we see no indication of a gap at the Dirac point. DOI: 10.1103/PhysRevLett.110.126804
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| 8. |
- Davila, M. E., et al.
(author)
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Comparative structural and electronic studies of hydrogen interaction with isolated versus ordered silicon nanoribbons grown on Ag(110)
- 2012
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In: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 23:38
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Journal article (peer-reviewed)abstract
- We have investigated the geometry and electronic structure of two different types of self-aligned silicon nanoribbons (SiNRs), forming either isolated SiNRs or a self-assembled 5 x 2/5 x 4 grating on an Ag(110) substrate, by scanning tunnelling microscopy and high resolution x-ray photoelectron spectroscopy. At room temperature we further adsorb on these SiNRs either atomic or molecular hydrogen. The hydrogen absorption process and hydrogenation mechanism are similar for isolated or 5 x 2/5 x 4 ordered SiNRs and are not site selective; the main difference arises from the fact that the isolated SiNRs are more easily attacked and destroyed faster. In fact, atomic hydrogen strongly interacts with any Si atoms, modifying their structural and electronic properties, while molecular hydrogen has first to dissociate. Hydrogen finally etches the Si nanoribbons and their complete removal from the Ag(110) surface could eventually be expected.
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| 9. |
- Eckert, Sebastian, et al.
(author)
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From the Free Ligand to the Transition Metal Complex : FeEDTA- Formation Seen at Ligand K-Edges
- 2022
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In: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 61:27, s. 10321-10328
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Journal article (peer-reviewed)abstract
- Chelating agents are an integral part of transition metal complex chemistry with broad biological and industrial relevance. The hexadentate chelating agent ethylenediaminetetraacetic acid (EDTA) has the capability to bind to metal ions at its two nitrogen and four of its carboxylate oxygen sites. We use resonant inelastic X-ray scattering at the 1s absorption edge of the aforementioned elements in EDTA and the iron(III)-EDTA complex to investigate the impact of the metal-ligand bond formation on the electronic structure of EDTA. Frontier orbital distortions, occupation changes, and energy shifts through metal- ligand bond formation are probed through distinct spectroscopic signatures.
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| 10. |
- Jay, Raphael, et al.
(author)
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Following Metal-to-Ligand Charge-Transfer Dynamics with Ligand and Spin Specificity Using Femtosecond Resonant Inelastic X-ray Scattering at the Nitrogen K-Edge
- 2021
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In: The Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 12:28, s. 6676-6683
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Journal article (peer-reviewed)abstract
- We demonstrate for the case of photoexcited [Ru(2,2'-bipyridine)(3)](2+) how femtosecond resonant inelastic X-ray scattering (RIXS) at the ligand K-edge allows one to uniquely probe changes in the valence electronic structure following a metal-to-ligand charge-transfer (MLCT) excitation. Metal-ligand hybridization is probed by nitrogen-1s resonances providing information on both the electron-accepting ligand in the MLCT state and the hole density of the metal center. By comparing to spectrum calculations based on density functional theory, we are able to distinguish the electronic structure of the electron-accepting ligand and the other ligands and determine a temporal upper limit of (250 +/- 40) fs for electron localization following the charge-transfer excitation. The spin of the localized electron is deduced from the selection rules of the RIXS process establishing new experimental capabilities for probing transient charge and spin densities.
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