We have used a combination of dynamical low-energy-electron diffraction and density functional fo... more We have used a combination of dynamical low-energy-electron diffraction and density functional formalism calculations to find a structural model for two-dimensional ͑2D͒ YSi 2 layers epitaxially grown on Si͑111͒. Both techniques show that the geometric structure of the yttrium silicide is quite similar to other 2D rare-earth silicides. The surface termination consists of a relaxed Si-bilayer and underlying Y atoms on T 4 sites ͓with respect to the Si͑111͒ interface͔. The low-energy electron diffraction study shows several occurrences of minima in the R factor. The analysis of diffracted beams measured at non-normal incidence allows us to discriminate the spurious minima.
How magnetism emerges in low-dimensional materials such as transition metal dichalcogenides at th... more How magnetism emerges in low-dimensional materials such as transition metal dichalcogenides at the monolayer limit is still an open question. Herein, we present a comprehensive study of the magnetic properties of single crystal and monolayer VSe2, both experimentally and ab initio. Magnetometry, X-ray magnetic circular dichrosim (XMCD) and ab initio calculations demonstrate that the charge density wave in bulk stoichiometric VSe2.0 causes a structural distortion with a strong reduction in the density of sates at the Fermi level, prompting the system towards a nonmagnetic state but on the verge of a ferromagnetic instability. In the monolayer limit, the structural rearrangement induces a Peierls distortion with the opening of an energy gap at the Fermi level and the absence of magnetic order. Control experiments on defect-induced VSe 2−δ single crystals show a breakdown of magnetism, discarding vacancies as a possible origin of magnetic order in VSe2.
The high reactivity of magnetic substrates toward molecular overlayers has so far inhibited the r... more The high reactivity of magnetic substrates toward molecular overlayers has so far inhibited the realization of more sophisticated on-surface reactions, thereby depriving these interfaces of a significant class of chemically tailored organics such as graphene nanoribbons, oligonuclear spin-chains, and metal-organic networks. Here, we present a multitechnique characterization of the polymerization of 4,4″-dibromo-p-terphenyl precursors into ordered poly(p-phenylene) arrays on top of the bimetallic GdAu2 surface alloy. The activation temperatures for bromine scission and subsequent homocoupling of molecular precursors were followed by temperature-dependent X-ray photoelectron spectroscopy. The structural characterizations of supramolecular and polymeric phases, performed by low-energy electron diffraction and scanning tunneling microscopy, establish an extraordinary degree of order extending into the mesoscale. Taking advantage of the high homogeneity, the electronic structure of the v...
A combined scanning tunneling microscopy, x-ray photoelectron spectroscopy, angle-resolved photoe... more A combined scanning tunneling microscopy, x-ray photoelectron spectroscopy, angle-resolved photoemission spectroscopy, and density functional theory study of graphene on a Fe-Ir(111) alloy with variable Ir concentration is presented. Starting from an intercalated Fe layer between the graphene and Ir(111) surface we find that graphene-substrate interaction can be fine-tuned by Fe-Ir alloying at the interface. When a critical Ir-concentration close to 0.25 is reached in the Fe layer, the Dirac cone of graphene is largely restored and can thereafter be tuned across the Fermi level by further increasing the Ir content. Indeed, our study reveals an abrupt transition between a chemisorbed phase at small Ir concentrations and a physisorbed phase above the critical concentration. The latter phase is highly reminiscent of the graphene on the clean Ir(111) surface. Furthermore, the transition is accompanied by an inversion of the graphene's induced magnetization due to the coupling with the Fe atoms from antiferromagnetic when chemisorbed to weakly ferromagnetic in the physisorption regime, with spin polarizations whose magnitude may be tuned with the amount of Fe content.
We report measurements of a new type of magnetoresistance in Pt and Ta thin films. The spin accum... more We report measurements of a new type of magnetoresistance in Pt and Ta thin films. The spin accumulation created at the surfaces of the film by the spin Hall effect decreases in a magnetic field because of the Hanle effect, resulting in an increase of the electrical resistance as predicted by Dyakonov [PRL 99, 126601 (2007)]. The angular dependence of this magnetoresistance resembles the recently discovered spin Hall magnetoresistance in Pt/Y 3 Fe 5 O 12 bilayers, although the presence of a ferromagnetic insulator is not required. We show that this Hanle magnetoresistance is an alternative, simple way to quantitatively study the coupling between charge and spin currents in metals with strong spin-orbit coupling. Spin-orbit interaction is an essential ingredient in materials and interfaces, offering the possibility to exploit the coupling between spin and orbital degrees of freedom of electrons in spintronic devices [1,2]. Of utmost importance are the spin Hall (SHE) and inverse spin Hall (ISHE) effects, which convert charge currents into transverse spin currents and vice versa, allowing us to create and detect spin currents in materials with strong spin-orbit coupling (SOC) [3-8]. In this framework, a new type of magnetoresistance (MR), spin Hall magnetoresistance (SMR), was discovered in nonmagnetic (NM) metal/ferromagnetic insulator
Codeposition of two molecular species [CuPc (donor) and PFP (acceptor)] on noble metal (111) surf... more Codeposition of two molecular species [CuPc (donor) and PFP (acceptor)] on noble metal (111) surfaces leads to the self-assembly of an ordered mixed layer with maximized donor-acceptor contact area. The main driving force behind this arrangement is assumed to be the intermolecular C-F ••• H-C hydrogen-bond interactions. Such interactions would be maximized for a coplanar molecular arrangement. However, precise measurement of molecule-substrate distances in the molecular mixture reveals significantly larger adsorption heights for PFP than for CuPc. Most surprisingly, instead of leveling to increase hydrogen bond interactions, the height difference is enhanced in mixed layers as compared to the heights found in single component CuPc and PFP layers, resulting in an overall reduced interaction with the underlying substrate. The influence of the increased height of PFP on the interface dipole is investigated through work function measurements.
The electronic character of a -conjugated molecular overlayer on a metal surface can change from... more The electronic character of a -conjugated molecular overlayer on a metal surface can change from semiconducting to metallic, depending on how molecular orbitals arrange with respect to the electrode's Fermi level. Molecular level alignment is thus a key property that strongly influences the performance of organic-based devices. In this work we report how the electronic level alignment of copper-phthalocyanines on metal surfaces can be tailored by controlling the substrate work function. We even show the way of finely tuning it for one fixed phthalocyaninemetal combination, such that charge transfer into empty molecular levels can be triggered across the metal-organic interface. These intriguing observations are the outcome of a powerful combination of surface-sensitive electron spectroscopies, which reveal a number of characteristic spectroscopic fingerprints that provide a fully coherent picture of the physical chemistry phenomena occurring at these relevant interfaces.
Surface Patterson Functions have been derived by direct inversion of experimental Low-Energy Elec... more Surface Patterson Functions have been derived by direct inversion of experimental Low-Energy Electron Diffraction I-V spectra measured at multiple incident angles. The direct inversion is computationally simple and can be used to discriminate between different structural models. (1×1) YSi2 epitaxial layers grown on Si(111) have been used to illustrate the analysis. We introduce a suitable R-factor for the Patterson Function to make the structural discrimination as objective as possible. From six competing models needed to complete the geometrical search, four could easily be discarded, achieving a very significant and useful reduction in the parameter space to be explored by standard dynamical LEED methods. The amount and quality of data needed for this analysis is discussed.
Highly doped diamond films are new candidates for electrodes in reactive environments, such as el... more Highly doped diamond films are new candidates for electrodes in reactive environments, such as electrocatalytic interfaces. Here the electronic structure of such films is investigated by X-ray absorption spectroscopy at the C 1s and B 1s edges, combined with X-ray and ultraviolet photoelectron spectroscopy, as well as optical measurements. A diamond surface functionalized covalently with Ru(tpy) 2 , a model complex similar to ruthenium-based molecules used in photocatalysis and photovoltaics, is compared to a hydrogenterminated diamond surface as a reference. Bulk-sensitive absorption spectra with photon detection reveal diamond gap states, while surface-sensitive spectra with electron detection reveal the adsorbate states and π-bonding at the diamond surface. The positions of the frontier orbitals of the dye relative to the band edges of diamond are inferred from the spectroscopic data. The implications of using diamond films as inert electron donors in photocatalysis and dye-sensitized solar cells are discussed.
The attachment of H 2-and metal (Co-and Zn-) protoporphyrin IX molecules to ZnO nanorods and sing... more The attachment of H 2-and metal (Co-and Zn-) protoporphyrin IX molecules to ZnO nanorods and single-crystal surfaces is investigated by Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy. The carboxyl groups of the protoporphyrin are found to be essential for anchoring the molecules to ZnO surfaces. The crystallographic orientation of the exposed ZnO face has an influence on the dye immobilization, with the highest uptake observed for the oxygen-terminated ZnO (000-1) surface. The preparation conditions are crucial for the dye immobilization. Under certain preparation conditions, there is a Zn atom exchange between the H 2-protoporphyrin and the ZnO surface, i.e., a metalation of H 2protoporphyrin IX to form Zn-protoporphyrin. Moreover, in the presence of chenodeoxycholic acid as coabsorber, the ZnO single-crystal surfaces are etched, as indicated by the loss of the orientation-dependent spectral features. These results help to pinpoint the chemical reactions that are responsible for the poor efficiency of ZnO-based dyesensitized solar cells, especially those built from ZnO nanorod arrays.
To discover how molecular changes affect the electronic structure of dye molecules for solar cell... more To discover how molecular changes affect the electronic structure of dye molecules for solar cells, we have investigated four titanium phthalocyanines customized by axial and peripheral ligands (monodentate oxo versus bidentate catechol and tert-butyl versus tert-butylphenoxy, respectively). X-ray absorption spectroscopy and photoelectron spectroscopy were combined with density functional theory (DFT) and crystal-field multiplet calculations to characterize the Ti 3d and N 2p valence electrons that form the frontier orbitals. When a monodentate oxo axial ligand was replaced by a bidentate catechol ligand, the multiplet structure of the Ti 2p-to-3d transitions was found to change systematically. The most noticeable change was an additional transition into the low-lying 3d xy level, which is attributed to a reduction in local symmetry from 4-fold to 2-fold at the Ti center. An increase of the Ti 2p core-level binding energy was observed in the bidentate complex and compared to a calculated core-level stabilization. DFT predicts a change of the LUMO from the inner phthalocyanine ring to the Ti d xy orbital and a reversal of the high-lying d x 2 −y 2 and d z 2 orbitals. The N 1s edge was calculated using time-dependent density functional theory (TDDFT) and compared to experiment.
We develop an effective potential approach for assessing the flow of charge within a twodimension... more We develop an effective potential approach for assessing the flow of charge within a twodimensional donor-acceptor/metal network based on core-level shifts. To do so, we perform both density functional theory (DFT) calculations and x-ray photoemission spectroscopy (XPS) measurements of the core-level shifts for three different monolayers adsorbed on a Ag substrate. Specifically, we consider perfluorinated pentacene (PFP), copper phthalocyanine ε F E vac
The atomic structure of two-dimensional yttrium silicide epitaxially grown on Si(1 1 1) was inves... more The atomic structure of two-dimensional yttrium silicide epitaxially grown on Si(1 1 1) was investigated by means of density functional theory calculations and angle-resolved photoemission experiments. The obtained accuracy of the calculations allowed to discriminate different surface arrangements in a quantitative way via comparing their theoretical band structure to the experimental result. Theoretically we find significant changes in the dispersion of a surface localized band upon varying the thickness of the topmost silicon bilayer. For a thickness of 0.4 A of the topmost silicon bilayer a strong asymmetry of the surface localized band with respect to C is found, while a thickness of 0.8 A yields a more symmetric dispersion of the band. By comparison with the experimental photoemission results, which show a rather symmetric band around C, we can conclude that the topmost bilayer has a thickness of 0.8 A.
The dispersion of quantum-well resonances in ultrathin epitaxial Al films on Si(111) reveals ener... more The dispersion of quantum-well resonances in ultrathin epitaxial Al films on Si(111) reveals energyand wave vector-dependent reflection properties at the Al͞Si interface. The substrate electronic structure strongly influences the phase shift of the electron waves upon reflection at the interface. Thus the details of the substrate electronic structure need to be taken into account for a complete analysis of metallic quantum-well resonances. Furthermore, the assumption of loss of parallel wave vector information upon reflection or transmission through a lattice-mismatched interface is challenged. The changes induced in the electronic structure of the overlayer can be used to probe the ground-state substrate band edges.
Combining STM, LEED, and density functional theory, we determine the atomic surface structure of ... more Combining STM, LEED, and density functional theory, we determine the atomic surface structure of rutile TiO 2 110-1 2: nonstoichiometric Ti 2 O 3 stripes along the 001 direction. LEED patterns are sharp and free of streaks, while STM images show monatomic steps, wide terraces, and no cross-links. At room temperature, atoms in the Ti 2 O 3 group have large amplitudes of vibration. The long quasi-1D chains display metallic character, show no interaction between them, and cannot couple to bulk or surface states in the gap region, forming good atomic wires.
Publisher’s Note: Self-Assembly of Bicomponent Molecular Monolayers: Adsorption Height Changes and Their Consequences [Phys. Rev. Lett. 112, 117602 (2014)]
We have used a combination of dynamical low-energy-electron diffraction and density functional fo... more We have used a combination of dynamical low-energy-electron diffraction and density functional formalism calculations to find a structural model for two-dimensional ͑2D͒ YSi 2 layers epitaxially grown on Si͑111͒. Both techniques show that the geometric structure of the yttrium silicide is quite similar to other 2D rare-earth silicides. The surface termination consists of a relaxed Si-bilayer and underlying Y atoms on T 4 sites ͓with respect to the Si͑111͒ interface͔. The low-energy electron diffraction study shows several occurrences of minima in the R factor. The analysis of diffracted beams measured at non-normal incidence allows us to discriminate the spurious minima.
How magnetism emerges in low-dimensional materials such as transition metal dichalcogenides at th... more How magnetism emerges in low-dimensional materials such as transition metal dichalcogenides at the monolayer limit is still an open question. Herein, we present a comprehensive study of the magnetic properties of single crystal and monolayer VSe2, both experimentally and ab initio. Magnetometry, X-ray magnetic circular dichrosim (XMCD) and ab initio calculations demonstrate that the charge density wave in bulk stoichiometric VSe2.0 causes a structural distortion with a strong reduction in the density of sates at the Fermi level, prompting the system towards a nonmagnetic state but on the verge of a ferromagnetic instability. In the monolayer limit, the structural rearrangement induces a Peierls distortion with the opening of an energy gap at the Fermi level and the absence of magnetic order. Control experiments on defect-induced VSe 2−δ single crystals show a breakdown of magnetism, discarding vacancies as a possible origin of magnetic order in VSe2.
The high reactivity of magnetic substrates toward molecular overlayers has so far inhibited the r... more The high reactivity of magnetic substrates toward molecular overlayers has so far inhibited the realization of more sophisticated on-surface reactions, thereby depriving these interfaces of a significant class of chemically tailored organics such as graphene nanoribbons, oligonuclear spin-chains, and metal-organic networks. Here, we present a multitechnique characterization of the polymerization of 4,4″-dibromo-p-terphenyl precursors into ordered poly(p-phenylene) arrays on top of the bimetallic GdAu2 surface alloy. The activation temperatures for bromine scission and subsequent homocoupling of molecular precursors were followed by temperature-dependent X-ray photoelectron spectroscopy. The structural characterizations of supramolecular and polymeric phases, performed by low-energy electron diffraction and scanning tunneling microscopy, establish an extraordinary degree of order extending into the mesoscale. Taking advantage of the high homogeneity, the electronic structure of the v...
A combined scanning tunneling microscopy, x-ray photoelectron spectroscopy, angle-resolved photoe... more A combined scanning tunneling microscopy, x-ray photoelectron spectroscopy, angle-resolved photoemission spectroscopy, and density functional theory study of graphene on a Fe-Ir(111) alloy with variable Ir concentration is presented. Starting from an intercalated Fe layer between the graphene and Ir(111) surface we find that graphene-substrate interaction can be fine-tuned by Fe-Ir alloying at the interface. When a critical Ir-concentration close to 0.25 is reached in the Fe layer, the Dirac cone of graphene is largely restored and can thereafter be tuned across the Fermi level by further increasing the Ir content. Indeed, our study reveals an abrupt transition between a chemisorbed phase at small Ir concentrations and a physisorbed phase above the critical concentration. The latter phase is highly reminiscent of the graphene on the clean Ir(111) surface. Furthermore, the transition is accompanied by an inversion of the graphene's induced magnetization due to the coupling with the Fe atoms from antiferromagnetic when chemisorbed to weakly ferromagnetic in the physisorption regime, with spin polarizations whose magnitude may be tuned with the amount of Fe content.
We report measurements of a new type of magnetoresistance in Pt and Ta thin films. The spin accum... more We report measurements of a new type of magnetoresistance in Pt and Ta thin films. The spin accumulation created at the surfaces of the film by the spin Hall effect decreases in a magnetic field because of the Hanle effect, resulting in an increase of the electrical resistance as predicted by Dyakonov [PRL 99, 126601 (2007)]. The angular dependence of this magnetoresistance resembles the recently discovered spin Hall magnetoresistance in Pt/Y 3 Fe 5 O 12 bilayers, although the presence of a ferromagnetic insulator is not required. We show that this Hanle magnetoresistance is an alternative, simple way to quantitatively study the coupling between charge and spin currents in metals with strong spin-orbit coupling. Spin-orbit interaction is an essential ingredient in materials and interfaces, offering the possibility to exploit the coupling between spin and orbital degrees of freedom of electrons in spintronic devices [1,2]. Of utmost importance are the spin Hall (SHE) and inverse spin Hall (ISHE) effects, which convert charge currents into transverse spin currents and vice versa, allowing us to create and detect spin currents in materials with strong spin-orbit coupling (SOC) [3-8]. In this framework, a new type of magnetoresistance (MR), spin Hall magnetoresistance (SMR), was discovered in nonmagnetic (NM) metal/ferromagnetic insulator
Codeposition of two molecular species [CuPc (donor) and PFP (acceptor)] on noble metal (111) surf... more Codeposition of two molecular species [CuPc (donor) and PFP (acceptor)] on noble metal (111) surfaces leads to the self-assembly of an ordered mixed layer with maximized donor-acceptor contact area. The main driving force behind this arrangement is assumed to be the intermolecular C-F ••• H-C hydrogen-bond interactions. Such interactions would be maximized for a coplanar molecular arrangement. However, precise measurement of molecule-substrate distances in the molecular mixture reveals significantly larger adsorption heights for PFP than for CuPc. Most surprisingly, instead of leveling to increase hydrogen bond interactions, the height difference is enhanced in mixed layers as compared to the heights found in single component CuPc and PFP layers, resulting in an overall reduced interaction with the underlying substrate. The influence of the increased height of PFP on the interface dipole is investigated through work function measurements.
The electronic character of a -conjugated molecular overlayer on a metal surface can change from... more The electronic character of a -conjugated molecular overlayer on a metal surface can change from semiconducting to metallic, depending on how molecular orbitals arrange with respect to the electrode's Fermi level. Molecular level alignment is thus a key property that strongly influences the performance of organic-based devices. In this work we report how the electronic level alignment of copper-phthalocyanines on metal surfaces can be tailored by controlling the substrate work function. We even show the way of finely tuning it for one fixed phthalocyaninemetal combination, such that charge transfer into empty molecular levels can be triggered across the metal-organic interface. These intriguing observations are the outcome of a powerful combination of surface-sensitive electron spectroscopies, which reveal a number of characteristic spectroscopic fingerprints that provide a fully coherent picture of the physical chemistry phenomena occurring at these relevant interfaces.
Surface Patterson Functions have been derived by direct inversion of experimental Low-Energy Elec... more Surface Patterson Functions have been derived by direct inversion of experimental Low-Energy Electron Diffraction I-V spectra measured at multiple incident angles. The direct inversion is computationally simple and can be used to discriminate between different structural models. (1×1) YSi2 epitaxial layers grown on Si(111) have been used to illustrate the analysis. We introduce a suitable R-factor for the Patterson Function to make the structural discrimination as objective as possible. From six competing models needed to complete the geometrical search, four could easily be discarded, achieving a very significant and useful reduction in the parameter space to be explored by standard dynamical LEED methods. The amount and quality of data needed for this analysis is discussed.
Highly doped diamond films are new candidates for electrodes in reactive environments, such as el... more Highly doped diamond films are new candidates for electrodes in reactive environments, such as electrocatalytic interfaces. Here the electronic structure of such films is investigated by X-ray absorption spectroscopy at the C 1s and B 1s edges, combined with X-ray and ultraviolet photoelectron spectroscopy, as well as optical measurements. A diamond surface functionalized covalently with Ru(tpy) 2 , a model complex similar to ruthenium-based molecules used in photocatalysis and photovoltaics, is compared to a hydrogenterminated diamond surface as a reference. Bulk-sensitive absorption spectra with photon detection reveal diamond gap states, while surface-sensitive spectra with electron detection reveal the adsorbate states and π-bonding at the diamond surface. The positions of the frontier orbitals of the dye relative to the band edges of diamond are inferred from the spectroscopic data. The implications of using diamond films as inert electron donors in photocatalysis and dye-sensitized solar cells are discussed.
The attachment of H 2-and metal (Co-and Zn-) protoporphyrin IX molecules to ZnO nanorods and sing... more The attachment of H 2-and metal (Co-and Zn-) protoporphyrin IX molecules to ZnO nanorods and single-crystal surfaces is investigated by Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy. The carboxyl groups of the protoporphyrin are found to be essential for anchoring the molecules to ZnO surfaces. The crystallographic orientation of the exposed ZnO face has an influence on the dye immobilization, with the highest uptake observed for the oxygen-terminated ZnO (000-1) surface. The preparation conditions are crucial for the dye immobilization. Under certain preparation conditions, there is a Zn atom exchange between the H 2-protoporphyrin and the ZnO surface, i.e., a metalation of H 2protoporphyrin IX to form Zn-protoporphyrin. Moreover, in the presence of chenodeoxycholic acid as coabsorber, the ZnO single-crystal surfaces are etched, as indicated by the loss of the orientation-dependent spectral features. These results help to pinpoint the chemical reactions that are responsible for the poor efficiency of ZnO-based dyesensitized solar cells, especially those built from ZnO nanorod arrays.
To discover how molecular changes affect the electronic structure of dye molecules for solar cell... more To discover how molecular changes affect the electronic structure of dye molecules for solar cells, we have investigated four titanium phthalocyanines customized by axial and peripheral ligands (monodentate oxo versus bidentate catechol and tert-butyl versus tert-butylphenoxy, respectively). X-ray absorption spectroscopy and photoelectron spectroscopy were combined with density functional theory (DFT) and crystal-field multiplet calculations to characterize the Ti 3d and N 2p valence electrons that form the frontier orbitals. When a monodentate oxo axial ligand was replaced by a bidentate catechol ligand, the multiplet structure of the Ti 2p-to-3d transitions was found to change systematically. The most noticeable change was an additional transition into the low-lying 3d xy level, which is attributed to a reduction in local symmetry from 4-fold to 2-fold at the Ti center. An increase of the Ti 2p core-level binding energy was observed in the bidentate complex and compared to a calculated core-level stabilization. DFT predicts a change of the LUMO from the inner phthalocyanine ring to the Ti d xy orbital and a reversal of the high-lying d x 2 −y 2 and d z 2 orbitals. The N 1s edge was calculated using time-dependent density functional theory (TDDFT) and compared to experiment.
We develop an effective potential approach for assessing the flow of charge within a twodimension... more We develop an effective potential approach for assessing the flow of charge within a twodimensional donor-acceptor/metal network based on core-level shifts. To do so, we perform both density functional theory (DFT) calculations and x-ray photoemission spectroscopy (XPS) measurements of the core-level shifts for three different monolayers adsorbed on a Ag substrate. Specifically, we consider perfluorinated pentacene (PFP), copper phthalocyanine ε F E vac
The atomic structure of two-dimensional yttrium silicide epitaxially grown on Si(1 1 1) was inves... more The atomic structure of two-dimensional yttrium silicide epitaxially grown on Si(1 1 1) was investigated by means of density functional theory calculations and angle-resolved photoemission experiments. The obtained accuracy of the calculations allowed to discriminate different surface arrangements in a quantitative way via comparing their theoretical band structure to the experimental result. Theoretically we find significant changes in the dispersion of a surface localized band upon varying the thickness of the topmost silicon bilayer. For a thickness of 0.4 A of the topmost silicon bilayer a strong asymmetry of the surface localized band with respect to C is found, while a thickness of 0.8 A yields a more symmetric dispersion of the band. By comparison with the experimental photoemission results, which show a rather symmetric band around C, we can conclude that the topmost bilayer has a thickness of 0.8 A.
The dispersion of quantum-well resonances in ultrathin epitaxial Al films on Si(111) reveals ener... more The dispersion of quantum-well resonances in ultrathin epitaxial Al films on Si(111) reveals energyand wave vector-dependent reflection properties at the Al͞Si interface. The substrate electronic structure strongly influences the phase shift of the electron waves upon reflection at the interface. Thus the details of the substrate electronic structure need to be taken into account for a complete analysis of metallic quantum-well resonances. Furthermore, the assumption of loss of parallel wave vector information upon reflection or transmission through a lattice-mismatched interface is challenged. The changes induced in the electronic structure of the overlayer can be used to probe the ground-state substrate band edges.
Combining STM, LEED, and density functional theory, we determine the atomic surface structure of ... more Combining STM, LEED, and density functional theory, we determine the atomic surface structure of rutile TiO 2 110-1 2: nonstoichiometric Ti 2 O 3 stripes along the 001 direction. LEED patterns are sharp and free of streaks, while STM images show monatomic steps, wide terraces, and no cross-links. At room temperature, atoms in the Ti 2 O 3 group have large amplitudes of vibration. The long quasi-1D chains display metallic character, show no interaction between them, and cannot couple to bulk or surface states in the gap region, forming good atomic wires.
Publisher’s Note: Self-Assembly of Bicomponent Molecular Monolayers: Adsorption Height Changes and Their Consequences [Phys. Rev. Lett. 112, 117602 (2014)]
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Papers by Celia Rogero