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3. Interfacial Charge Transfer Enhances Transient Surface Photovoltage in Hybrid Heterojunctions.

Author

Soncini, Cristian, Costantini, Roberto, Dell'Angela, Martina, Morgante, Alberto, and Pedio, Maddalena

Abstract

The interfacial energy level alignment in the copper phthalocyanine/SiO2/p-Si(100) heterojunction has been studied in dark conditions and under illumination. The element-sensitivity of the time-resolved X-ray photoemission provides a real-time picture of the photoexcited carrier dynamics at the interface and within the film, enabling one to distinguish between substrate and molecular contributions. We observe a molecule-to-substrate charge transfer under photoexcitation, which is directly related to the transient modification of the band bending in the substrate due to the surface photovoltage effect. Our results show that charge generation in the heterojunction is driven by the molecular layer in contact with the substrate. The different molecular orientation at the interface creates a new channel for charge injection in the substrate under photoexcitation. [ABSTRACT FROM AUTHOR]

Published
2025
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5. Oxygen Promoted On‐Surface Synthesis of Polyboroxine Molecules

Author

Toffoli, Daniele, primary, Turco, Elia, additional, Stredansky, Matus, additional, Costantini, Roberto, additional, Dell’Angela, Martina, additional, Floreano, Luca, additional, Goldoni, Andrea, additional, Morgante, Alberto, additional, Kladnik, Gregor, additional, Cvetko, Dean, additional, de Oteyza, Dimas G., additional, Colazzo, Luciano, additional, Mohammed, Mohammed S. G., additional, Sala, Alessandro, additional, Comelli, Giovanni, additional, Africh, Cristina, additional, Fronzoni, Giovanna, additional, Balducci, Gabriele, additional, Stener, Mauro, additional, Ustunel, Hande, additional, and Cossaro, Albano, additional

Published
2024
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6. Co(III), Co(II), Co(I): Tuning Single Cobalt Metal Atom Oxidation States in a 2D Coordination Network.

Author

Armillotta, Francesco, Bidoggia, Davide, Baronio, Stefania, Sala, Alessandro, Costantini, Roberto, dell'Angela, Martina, Cojocariu, Iulia, Feyer, Vitaliy, Morgante, Alberto, Peressi, Maria, and Vesselli, Erik

Subjects
COBALT porphyrins, ELECTRON configuration, OXIDATION states, ELECTRONIC structure, CARBON monoxide
Abstract

It is shown that the self‐assembly of a surface‐confined metal–organic network such as cobalt porphyrins on graphene is accompanied by the evolution of coordination‐dependent observables in the electronic structure: variation of the layer's valence states within almost 1 eV range and of the metal atoms oxidation states. Coordination of cobalt porphyrins, driven by Co ad‐atoms, allows the synthesis of single metal atom centers with +3, +2, or +1 oxidation states. The electronic structure is determined by lateral interactions extending up to a few nanometers, beyond nearest‐neighbor distances. The reactivity of the single Co sites, which is strongly dependent on the local electronic configuration and, thus, on the metal‐specific oxidation state, is probed by carbon monoxide, which is found to ligate at pyridinic Co(I) at room temperature for background pressures above a fraction of a mbar. [ABSTRACT FROM AUTHOR]

Published
2024
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9. Making ARPES Measurements on Corrugated Monolayer Crystals: Suspended Exfoliated Single-Crystal Graphene

Author

Knox, Kevin R., Locatelli, Andrea, Yilmaz, Mehmet B., Cvetko, Dean, Mentes, Tevfik Onur, Nino, Miguel Angel, Kim, Philip, Morgante, Alberto, and Osgood Jr, Richard M.

Subjects
Condensed Matter - Materials Science
Abstract

Free-standing exfoliated monolayer graphene is an ultra-thin flexible membrane, which exhibits out of plane deformation or corrugation. In this paper, a technique is described to measure the band structure of such free-standing graphene by angle-resolved photoemission. Our results show that photoelectron coherence is limited by the crystal corrugation. However, by combining surface morphology measurements of the graphene roughness with angle-resolved photoemission, energy dependent quasiparticle lifetime and bandstructure measurements can be extracted. Our measurements rely on our development of an analytical formulation for relating the crystal corrugation to the photoemission linewidth. Our ARPES measurements show that, despite significant deviation from planarity of the crystal, the electronic structure of exfoliated suspended graphene is nearly that of ideal, undoped graphene; we measure the Dirac point to be within 25 meV of $E_F$ . Further, we show that suspended graphene behaves as a marginal Fermi-liquid, with a quasiparticle lifetime which scales as $(E - E_F)^{-1}$; comparison with other graphene and graphite data is discussed.

Published
2011
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10. Noncontact Layer Stabilization of Azafullerene Radicals: Route toward High-Spin-Density Surfaces

Author

Tanuma, Yuri, primary, Kladnik, Gregor, additional, Schio, Luca, additional, van Midden Mavrič, Marion, additional, Anézo, Bastien, additional, Zupanič, Erik, additional, Bavdek, Gregor, additional, Canton-Vitoria, Ruben, additional, Floreano, Luca, additional, Tagmatarchis, Nikos, additional, Wegner, Hermann A., additional, Morgante, Alberto, additional, Ewels, Christopher P., additional, Cvetko, Dean, additional, and Arčon, Denis, additional

Published
2023
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11. Spectro-microscopy of single and multi-layer graphene supported by a weakly interacting substrate

Author

Knox, Kevin R., Wang, Shancai, Morgante, Alberto, Cvetko, Dean, Locatelli, Andrea, Mentes, Tevfik Onur, Niño, Miguel Angel, Kim, Philip, and Osgood Jr, R. M.

Subjects
Condensed Matter - Materials Science
Abstract

We report measurements of the electronic structure and surface morphology of exfoliated graphene on an insulating substrate using angle-resolved photoemission and low energy electron diffraction. Our results show that although exfoliated graphene is microscopically corrugated, the valence band retains a massless fermionic dispersion, with a Fermi velocity of ~10^6 m/s. We observe a close relationship between the morphology and electronic structure, which suggests that controlling the interaction between graphene and the supporting substrate is essential for graphene device applications., Comment: 10 pages of text, 4 JPEG figures

Published
2008
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19. On-Surface Synthesis of Boroxine-Based Molecules

Author

Turco, Elia, primary, Stredansky, Matus, additional, Costantini, Roberto, additional, Martinez, Javier A., additional, Dell’Angela, Martina, additional, Zerbato, Elena, additional, Toffoli, Daniele, additional, Fronzoni, Giovanna, additional, Morgante, Alberto, additional, Floreano, Luca, additional, and Cossaro, Albano, additional

Published
2021
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20. Self‐Metalation of Porphyrins at the Solid–Gas Interface

Author

Armillotta, Francesco, primary, D'Incecco, Enrico, additional, Corva, Manuel, additional, Stredansky, Matus, additional, Gallet, Jean‐Jacques, additional, Bournel, Fabrice, additional, Goldoni, Andrea, additional, Morgante, Alberto, additional, Vesselli, Erik, additional, and Verdini, Alberto, additional

Published
2021
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23. Phase diagram of pentacene growth on Au(110)

Author

Floreano, Luca, Cossaro, Albano, Cvetko, Dean, Bavdek, Gregor, and Morgante, Alberto

Subjects
Hydrocarbons -- Chemical properties, Gold compounds -- Chemical properties, Monomolecular films -- Design and construction, Chemicals, plastics and rubber industries
Abstract

The growth of pentacene (C22H14) on the Au(110) surface is studied by means of He atom scattering and Synchrotron X-ray photoemission. The (3 cross 6) phase is shown to be formed at high temperature, where second layer molecules do not stick on the surface while a new phase with (6 cross 8) symmetry is found at a slightly higher coverage and a disordered growth is observed at a substrate temperature lower than 370 K.

Published
2006

24. Ultrahigh vacuum deposition of L-Cysteine on Au(110) studied by high-resolution

Author

Gonella, Grazia, Terreni, Silvana, Cvetko, Dean, Cossaro, Albano, Mattera, Lorenzo, Cavalleri, Ornella, Rolandi, Ranieri, Morgante, Alberto, Floreano, Luca, and Canepa, Maurizio

Subjects
Gold compounds -- Spectra, Cysteine -- Spectra, Photoemission -- Research, Chemicals, plastics and rubber industries
Abstract

High-resolution X-ray photoemission spectroscopy measurements on molecular-thick films of L-cysteine deposited at room temperature under ultrahigh vacuum conditions on an Au(110) surface are studied. The analysis of core level shifts allowed to distinguish unambiguously the states of the first-layer molecules from those of molecules belonging to the second layer.

Published
2005

26. Cyclopropenylidenes as Strong Carbene Anchoring Groups on Au Surfaces

Author

Doud, Evan A., primary, Starr, Rachel L., additional, Kladnik, Gregor, additional, Voevodin, Anastasia, additional, Montes, Enrique, additional, Arasu, Narendra P., additional, Zang, Yaping, additional, Zahl, Percy, additional, Morgante, Alberto, additional, Venkataraman, Latha, additional, Vázquez, Héctor, additional, Cvetko, Dean, additional, and Roy, Xavier, additional

Published
2020
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28. Anisotropic ordered planar growth of alpha-sexithienyl thin films

Author

Prato, Stefano, Floreano, Luca, Cvetko, Dean, De Renzi, Valentina, Morgante, Alberto, Modesti, Silvio, Biscarini, Fabio, Zamboni, Roberto, and Taliani, Carlo

Subjects
Anisotropy -- Research, Scanning tunneling microscopy -- Usage, Thin films -- Research, Chemicals, plastics and rubber industries
Abstract

Research is presented to demonstrate how spontaneous ordered planar growth of uniaxially oriented rodlike conjugated oligomers can be achieved on the substrate of the anisotropy of the (1x2) reconstructed Au(110) surface.

Published
1999

33. Tuning ultrafast electron injection dynamics at organic-graphene/metal interfaces

Author

European Commission, Slovenian Research Agency, Ministero dell'Istruzione, dell'Università e della Ricerca, Ministerio de Economía y Competitividad (España), Ravikumar, Abhilash, Kladnik, Gregor, Müller, Moritz, Cossaro, Albano, Bavdek, Gregor, Patera, Laerte L., Sánchez-Portal, Daniel, Venkataraman, Latha, Morgante, Alberto, Brivio, Gian Paolo, Cvetko, Dean, Fratesi, Guido, European Commission, Slovenian Research Agency, Ministero dell'Istruzione, dell'Università e della Ricerca, Ministerio de Economía y Competitividad (España), Ravikumar, Abhilash, Kladnik, Gregor, Müller, Moritz, Cossaro, Albano, Bavdek, Gregor, Patera, Laerte L., Sánchez-Portal, Daniel, Venkataraman, Latha, Morgante, Alberto, Brivio, Gian Paolo, Cvetko, Dean, and Fratesi, Guido

Abstract

We compare the ultrafast charge transfer dynamics of molecules on epitaxial graphene and bilayer graphene grown on Ni(111) interfaces through first principles calculations and X-ray resonant photoemission spectroscopy. We use 4,4′-bipyridine as a prototypical molecule for these explorations as the energy level alignment of core-excited molecular orbitals allows ultrafast injection of electrons from a substrate to a molecule on a femtosecond timescale. We show that the ultrafast injection of electrons from the substrate to the molecule is ∼4 times slower on weakly coupled bilayer graphene than on epitaxial graphene. Through our experiments and calculations, we can attribute this to a difference in the density of states close to the Fermi level between graphene and bilayer graphene. We therefore show how graphene coupling with the substrate influences charge transfer dynamics between organic molecules and graphene interfaces.

Published
2018

34. Mesoscopic donor-acceptor multilayer by ultrahigh-vacuum codeposition of Zn-tetraphenyl-porphyrin and [C.sub.70]

Author

Vilmercati, Paolo, Castellarin-Cudia, Carla, Gebauer, Ralph, Ghosh, Prasenjit, Lizzit, Silvano, Petaccia, Luca, Cepek, Cinzia, Larciprete, Rosanna, Verdini, Alberto, Floreano, Luca, Morgante, Alberto, and Goldoni, Andrea

Subjects
Charge transfer -- Analysis, Coating processes -- Analysis, Porphyrins -- Chemical properties, Porphyrins -- Structure, Zinc -- Chemical properties, Chemicals, plastics and rubber industries
Abstract

The nanostructured multilayer of porphyrin/fullerene pairs obtained by codeposition of Zn-tetraphenyl-porphyrin (ZnTPP) and [C.sub.70] in ultrahigh-vacuum by powder sublimation is described. The studies have shown the existence of charge-transfer interactions between the electron-rich Zn-tetraphenyl-porphyrin (ZnTPP) and the electron-deficient fullerene.

Published
2008

35. Tuning ultrafast electron injection dynamics at organic-graphene/metal interfaces

Author

Ravikumar, Abhilash, primary, Kladnik, Gregor, additional, Müller, Moritz, additional, Cossaro, Albano, additional, Bavdek, Gregor, additional, Patera, Laerte L., additional, Sánchez-Portal, Daniel, additional, Venkataraman, Latha, additional, Morgante, Alberto, additional, Brivio, Gian Paolo, additional, Cvetko, Dean, additional, and Fratesi, Guido, additional

Published
2018
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38. Pump–Probe X-ray Photoemission Reveals Light-Induced Carrier Accumulation in Organic Heterojunctions

Author

Costantini, Roberto, Grazioli, Cesare, Cossaro, Albano, Floreano, Luca, Morgante, Alberto, and Dell’Angela, Martina

Abstract

The energy level alignment in the heterojunction formed by tetracene and copper phthalocyanine grown on the Ag(111) substrate has been studied for two different sequences of layer stacking. Filled and empty molecular levels as well as charge transfer states have been characterized by combining ultraviolet and two-photon photoemission spectroscopies. It is shown that the layer in contact with the substrate determines the molecular arrangements of the whole system, thus inducing different interface dipoles at the heterojunction, depending on the stacking sequence. Such dipoles strongly influence the exciton dynamics and charge separation at the interface. The accumulation of the charge carriers in the heterojunction has been observed by measuring the transient shift of core level photoemission lines, which arises after the resonant excitation of either of the two molecular constituents.

Published
2020
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39. A Ru-Ru pair housed in ruthenium phthalocyanine : the role of a 'cage' architecture in the molecule coupling with the Ag(111) surface

Author

Alippi, Paola, Lanzilotto, Valeria, Paoletti, Anna Maria, Mattioli, Giuseppe, Zanotti, Gloria, Pennesi, Giovanna, Filippone, Francesco, Cossaro, Albano, Verdini, Alberto, Morgante, Alberto, Bonapasta, Aldo Amore, Alippi, Paola, Lanzilotto, Valeria, Paoletti, Anna Maria, Mattioli, Giuseppe, Zanotti, Gloria, Pennesi, Giovanna, Filippone, Francesco, Cossaro, Albano, Verdini, Alberto, Morgante, Alberto, and Bonapasta, Aldo Amore

Abstract

A number of studies have investigated the properties of monomeric and double-decker phthalocyanines (Pcs) adsorbed on metal surfaces, in view of applications in spintronics devices. In a combined experimental and theoretical study, we consider here a different member of the Pcs family, the (RuPc)(2) dimer, whose structure is characterized by two paired up magnetic centers embedded in a double-decker architecture. For (RuPc)(2) on Ag(111), we show that this architecture works as a preserving cage by shielding the Ru-Ru pair from a direct interaction with the surface atoms. In fact, while noticeable surface-to-molecule charge transfer occurs with the ensuing quenching of the molecular magnetic moment, such phenomena occur here in the absence of a direct Ru-Ag coupling or structural rearrangement, at variance with other Pcs and thanks to the above shielding effect. These unique properties of the (RuPc)(2) architecture are expected to permit an easy control of the surface-to-molecule charge-transfer process as well as of the molecular magnetic properties, thus making the (RuPc)(2) dimer a significant paradigm for innovative "cage" structures as well as a promising candidate for applications in spintronics nano or single-molecule devices.

Published
2017
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40. Defect states at the TiO2(110) surface probed by resonant photoelectron diffraction

Author

Krueger, P., Bourgeois, S., Domenichini, B., Magnan, H., Chandesris, D., LE FEVRE, P., Flank, A. M., Jupille, J., Floreano, L., Cossaro, A., Verdini, A., Morgante, Alberto, Krueger, P., Bourgeois, S., Domenichini, B., Magnan, H., Chandesris, D., LE FEVRE, P., Flank, A. M., Jupille, J., Floreano, L., Cossaro, A., Verdini, A., and Morgante, Alberto

Subjects
DEFECT STATE, ELECTRONIC-STRUCTURE, TITANIUM-DIOXIDE, Photoelectron Diffraction, PHOTOELECTRON DIFFRACTION, Resonant Photoemission, charge distribution
Abstract

The charge distribution of the defect states at the reduced TiO2(110) surface is studied via a new method, the resonant photoelectron diffraction. The diffraction pattern from the defect state, excited at the Ti-2p-3d resonance, is analyzed in the forward scattering approach and on the basis of multiple scattering calculations. The defect charge is found to be shared by several surface and subsurface Ti sites with the dominant contribution on a specific subsurface site in agreement with density functional theory calculations.

Published
2008
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41. Defects at the TiO2 surface probed by resonant photoelectron diffraction

Author

P. KRUEGER, S. BOURGEOIS, B. DOMENICHINI, H. MAGNAN, D. CHANDESRIS, P. LE FEVRE, L. FLOREANO, A. COSSARO, A. VERDINI, MORGANTE, ALBERTO, Krueger, P., Bourgeois, S., Domenichini, B., Magnan, H., Chandesris, D., LE FEVRE, P., Floreano, L., Cossaro, A., Verdini, A., and Morgante, Alberto

Subjects
Titanium dioxide, Photoelectron diffraction, Surface defects, Resonant photoemission, Surface defect
Abstract

We report photoelectron diffraction (PED) experiments of weakly sub-stoichiometric TiO2(100) rutile surfaces. Apart from standardcore-level PED from the Ti-2p3/2 line, we have studied valence band PED from the defect induced Ti-3d states in the insulating band gap. For maximum yield, the latter were resonantly excited at the Ti-2p absorption edge. The PED patterns have been analyzed within the forward scattering approximation as well as by comparison with simulated PED patterns obtained in multiple scattering calculations. The analysis shows that the defect induced Ti-3d charge is mainly located on the second layer Ti atoms.

Published
2007

42. Lead-phtalocyanine films studied by NearEdge X-ray Absorption Fine Spectroscopy

Author

E. SALOMON, N. PAPAGEORGIOU, T. ANGOT, A. VERDINI, A. COSSARO, L. FLOREANO, L. GIOVANELLI, AND G. LE LAY, MORGANTE, ALBERTO, Salomon, E., Papageorgiou, N., Angot, T., Verdini, A., Cossaro, A., Floreano, L., Morgante, Alberto, Giovanelli, L., and LE LAY, AND G.

Subjects
THIN-FILMS, PHOTOELECTRON-SPECTROSCOPY, core exciton, Near edge X-ray Absorption fine structure
Abstract

We measured NEXAFS spectra on both C and N K-edges of an ordered monolayer of lead phthalocyanine adsorbed onto an InSb(001) 4 x 2/c(8 x 2) substrate. We compared the spectra with the calculated density of unoccupied states of an isolated molecule. We demonstrate that molecules lay flat on the surface, determine the energy position of the lowest excited state, and show that it is site dependent. Finally, we compare the core exciton structure with the valence exciton structure previously measured by two different valence spectroscopic techniques and discuss their differences in terms of electron-nuclear and electron-hole Coulomb interactions.

Published
2007

43. A Ru–Ru pair housed in ruthenium phthalocyanine: the role of a “cage” architecture in the molecule coupling with the Ag(111) surface

Author

Alippi, Paola, primary, Lanzilotto, Valeria, additional, Paoletti, Anna Maria, additional, Mattioli, Giuseppe, additional, Zanotti, Gloria, additional, Pennesi, Giovanna, additional, Filippone, Francesco, additional, Cossaro, Albano, additional, Verdini, Alberto, additional, Morgante, Alberto, additional, and Amore Bonapasta, Aldo, additional

Published
2017
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44. Unexpected length dependence of excited-state charge transfer dynamics for surface-confined perylenediimide ensembles

Author

Mazaheripour, Amir, primary, Kladnik, Gregor, additional, Jocson, Jonah-Micah, additional, Wardrip, Austin G., additional, Markegard, Cade B., additional, Frey, Nathan, additional, Cossaro, Albano, additional, Floreano, Luca, additional, Verdini, Alberto, additional, Bartlett, Andrew, additional, Burke, Anthony M., additional, Hüsken, Nina, additional, Miller, Kelsey, additional, Van Wonterghem, Katarina, additional, Lopez, Robert, additional, Lu, Michelle, additional, Masurkar, Amrita, additional, Dickson, Mary N., additional, Sharifzadeh, Sahar, additional, Nguyen, Hung D., additional, Kymissis, Ioannis, additional, Cvetko, Dean, additional, Morgante, Alberto, additional, and Gorodetsky, Alon A., additional

Published
2017
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45. Electronic properties of the boroxine–gold interface: evidence of ultra-fast charge delocalization

Author

Toffoli, Daniele, primary, Stredansky, Matus, additional, Feng, Zhijing, additional, Balducci, Gabriele, additional, Furlan, Sara, additional, Stener, Mauro, additional, Ustunel, Hande, additional, Cvetko, Dean, additional, Kladnik, Gregor, additional, Morgante, Alberto, additional, Verdini, Alberto, additional, Dri, Carlo, additional, Comelli, Giovanni, additional, Fronzoni, Giovanna, additional, and Cossaro, Albano, additional

Published
2017
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46. Length‐Independent Charge Transport in Chimeric Molecular Wires

Author

Wardrip, Austin G., primary, Mazaheripour, Amir, additional, Hüsken, Nina, additional, Jocson, Jonah‐Micah, additional, Bartlett, Andrew, additional, Lopez, Robert C., additional, Frey, Nathan, additional, Markegard, Cade B., additional, Kladnik, Gregor, additional, Cossaro, Albano, additional, Floreano, Luca, additional, Verdini, Alberto, additional, Burke, Anthony M., additional, Dickson, Mary N., additional, Kymissis, Ioannis, additional, Cvetko, Dean, additional, Morgante, Alberto, additional, Sharifzadeh, Sahar, additional, Nguyen, Hung D., additional, and Gorodetsky, Alon A., additional

Published
2016
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47. Temperature driven reversible breakdown of pseudomorphism in ultrathin Fe/Cu3Au films

Author

F. BISIO, S. TERRENI, G. GONELLA, L. FLOREANO, M. CANEPA, L. MATTERA, MORGANTE, ALBERTO, F., Bisio, S., Terreni, G., Gonella, L., Floreano, Morgante, Alberto, M., Canepa, and L., Mattera

Subjects
structural phase transition, He atom scattering, pseudomorphism
Abstract

We observe that ultrathin Fe/Cu3Au(001) films in the 6-13 Angstrom thickness range, beyond the thickness of pseudomorphism breakdown at room temperature, exhibit a temperature dependent structural phase transition in the range T(c)approximate to345-380 K. In the high temperature state the Fe film becomes pseudomorphic, while breakdown of pseudomorphism reversibly occurs as the system is cooled below the transition temperature. The difference between substrate and overlayer thermal expansion coefficient is highlighted as the driving force for the observed transition.

Published
2004

48. Pseudomorphic to orthomorphic growth of Fe films on Cu3Au(001)

Author

F. BRUNO, S. TERRENI, L. FLOREANO, A. COSSARO, D. CVETKO, P. LUCHES, L. MATTERA, R. MORONI, M. REPETTO, A. VERDINI, M. CANEPA, MORGANTE, ALBERTO, Bruno, F., Terreni, S., Floreano, L., Cossaro, A., Cvetko, D., Luches, P., Mattera, L., Morgante, Alberto, Moroni, R., Repetto, M., Verdini, A., and Canepa, M.

Subjects
PHOTOELECTRON DIFFRACTION, pseudomorphic phase, epitaxial growth, GRAZING INCIDENCE X-RAY DIFFRACTION
Abstract

he structure of Fe films grown on the (001) surface of a Cu3Au single crystal at room temperature has been investigated by means of grazing incidence x-ray diffraction (GIXRD) and photo/Auger-electron diffraction (ED) as a function of thickness in the (3-36)-Angstrom range. The combination of GIXRD and ED allows one to obtain quantitative information on the in-plane spacing a from the former technique, and the ratio between the vertical spacing c and a, from the latter one. At low coverage the film grows pseudomorphic to the face-centered-cubic substrate. The experimental results obtained on a film of 8 Angstrom thickness clearly indicate the overcoming of the limit for pseudomorphic growth. Above this limit the film is characterized by the coexistence of the pseudomorphic phase with another tetragonally strained phase gamma, which falls on the epitaxial line of ferromagnetic face-centered cubic Fe. Finally, the development of a body-centered phase alpha, whose unit cell is rotated by 45degrees with respect to the substrate one, has been clearly observed at similar to17 Angstrom. alpha is the dominating phase for film thickness above similar to25 Angstrom and its lattice constant evolves towards the orthomorphic phase in strict quantitative agreement with epitaxial curves calculated for body-centered tetragonal iron phases.

Published
2002

49. Order-disorder character of the (3x3) to (sqrt3xsqrt3)R30 phase transition of Sn onGe(111)

Author

L. Petaccia, L. Floreano, A. Goldoni, D. Cvetko, L. Grill, A. Verdini, G. Paolucci, MORGANTE, ALBERTO, COMELLI, GIOVANNI, MODESTI, SILVIO, L., Petaccia, L., Floreano, A., Goldoni, D., Cvetko, Morgante, Alberto, L., Grill, A., Verdini, Comelli, Giovanni, G., Paolucci, and Modesti, Silvio

Subjects
displacive transition, surface phase transition, CHARGE-DENSITY-WAVE, PHOTOEMISSION SPECTROSCOPY
Abstract

The α phase of Sn/Ge(111) has been investigated from 120 K up to 500 K, using synchrotron radiation core-level photoemission. By means of photoelectron diffraction experiments, we verified that the rippled structure of the low-temperature (3×3) phase is preserved in the (√3×√3)R30° phase at room temperature, thus confirming the order-disorder character of the phase transition. We also found that at least two components are present in the Sn 4d core-level spectra up to 500 K, i.e., about 300 K above the onset of the transition from the low-temperature (3×3) phase to the (√3×√3)R30° phase, thus excluding the occurrence of any displacive transition.

Published
2001

50. Additive Driven Increase in Donor–Acceptor Copolymer Coupling Studied by X-ray Resonant Photoemission

Author

Garcia-Basabe, Yunier, Kladnik, Gregor, Marchiori, Cleber F. N., de Moura, Carlos E. V., Floreano, Luca, Rocha, Alexandre B., Roman, Lucimara S., Morgante, Alberto, Cvetko, Dean, and Rocco, Maria Luiza M.

Abstract

The role of additives and thermal treatment in the formation of donor–acceptor copolymer organic films of PFO–DBT (poly[2,7-(9,9-dioctylfluorene)-alt-4,7-bis(thiophen-2-yl)benzo-2,1,3-thiadiazole]) with increased transport properties is addressed by resonant Auger photoemission and core-hole clock spectroscopy, which allows an analysis of the competition between the inner shell core-hole lifetime and the motion of photoexcited electrons on a femtosecond time scale. From the branching of the competing core-hole decay channels, we study the delocalization dynamics of excited electrons over empty molecular orbitals. We find evidence of ultrafast charge-carrier transfer from specific orbitals (LUMO+1) and increased coupling in copolymer assemblies when a solvent additive (1,8 diiodooctane) is added and samples are post-treated with thermal annealing. Relative conformational energies and core-hole spectra were calculated by time-dependent density functional theory.

Published
2024
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