D. Cvetko - Academia.edu (original) (raw)
Papers by D. Cvetko
The Journal of Physical Chemistry B, 2005
We report on a high-resolution X-ray photoemission spectroscopy study on molecular-thick layers o... more We report on a high-resolution X-ray photoemission spectroscopy study on molecular-thick layers of L-cysteine deposited under ultrahigh vacuum conditions on Au(110). The analysis of core level shifts allowed us to distinguish unambiguously the states of the first-layer molecules from those of molecules belonging to the second layer. The first-layer molecules strongly interact with the metal through their sulfur headgroup. The multipeaked structure of the N 1s, O 1s, and C 1s core levels is interpreted in terms of different molecular moieties. The neutral acidic fraction (HSCH2CH(NH2)COOH) is abundant at low coverage likely associated with isolated molecules or dimers. The zwitterionic phase (HSCH2CH(NH3+)COO-) is largely dominant as the coverage approaches the monolayer limit and is related to the formation of ordered self-assembled molecular structures indicated by electron diffraction patterns. The occurrence of a small amount of cationic molecules (HSCH2CH(NH3+)COOH) is also discussed. The second-layer molecules mainly display zwitterionic character and are weakly adsorbed. Mild annealing up to 100 degrees C leads to the desorption of the second-layer molecules leaving electronic states of the first layer unaltered.
Progress in Surface Science, 2003
The electronic properties of thin metallic films deviate from the corresponding bulk ones when th... more The electronic properties of thin metallic films deviate from the corresponding bulk ones when the film thickness is comparable with the wavelength of the electrons at the Fermi level. This phenomenon, referred to as quantum size effect (QSE), is also expected to affect the film morphology and structure leading to the "electronic growth" of metals on semiconductors. Shuch effect may be observed when metals are grownon substrates held at low temperature and are manifested through the occurrence of "magical" thickness islands or critical thickness for layer-by-layer growth. In particular, layer-by-layer growth of Pb(111) films has been reported for deposition on Ge(001) below ∼ 130 K. An extremely flat morphology is preserved throughout deposition from four up to a dozen of monolayers. These flat films are shown to be metastable and to reorganize into large clusters uncovering the first Pb layer pseudomorphic to the underlying Ge(001) substrate already at room temperature. Indications of QSE induced structural variations of the growing films have been reported for Pb growth on both Si(111) and Ge(001). In the latter case, the apparent height of the Pb(111) monatomic step was shown to change in an oscillatory fashion by He atom scattering (HAS) during layer-by-layer growth at low temperature. The extent of the structural QSE has been obtained by a comparison of the HAS data with X-ray diffraction (XRD) and reflectivity experiments. Whereas step height variations as large as 20% have been measured by HAS reflectivity, the displacement of the atomic planes from their bulk position, as measured by XRD, has been found to mainly affect the topmost Pb layer, but with a lower extent, i.e. the QSE observed by HAS are mainly due to a perpendicular displacement of the topmost layer charge density. The effect of the variable surface relaxation on the surface vibration has been studied from the acoustic dispersion of the low energy phonons, as measured by inelastic HAS.
Surface Science, 1993
ABSTRACT
Physical Review B, 2010
We present a combined multimethod experimental and theoretical study of the geometric and electro... more We present a combined multimethod experimental and theoretical study of the geometric and electronic properties of Co-tetraphenyl-porphyrin (Co-TPP) molecules adsorbed on a Ag(111) surface. Scanning tunneling microscopy (STM) topographs reveal that Co-TPP ...
Physical Review B, 2001
The bonding geometry of Sn on Ge(111) has been quantitatively determined for the (3×3) phase at 1... more The bonding geometry of Sn on Ge(111) has been quantitatively determined for the (3×3) phase at 150 K. Energy scan photoelectron diffraction of the Sn 4d core levels has been used to independently measure the bond length between Sn and its nearest neighbour Ge atoms and the vertical distance between Sn and the Ge atom beneath. This latter distance is found to be ∼ 0.3Å larger for one Sn atom out of the three contained in the lattice unit cell. The bond lengths and the bond directions, obtained by the angular scans, are found to be practically the same for the three Sn atoms within ± 0.03Å and ± 3 • , respectively. The three nearest neighbour Ge atoms thus partially follow the Sn atom in its vertical ripple.
Physical Review B, 1993
ABSTRACT The (1×2)-Au(110) surface has been studied using He-beam scattering with time-of-flight ... more ABSTRACT The (1×2)-Au(110) surface has been studied using He-beam scattering with time-of-flight detection. The experiments included measurement of the diffraction pattern and the specular intensity as a function of azimuthal angle of incidence; the latter curve is found to be highly structured. The data have been modeled using the local-density approximation to calculate the charge distribution in atoms, and treating the He-surface potential as a superposition of pseudopairwise terms. The diffraction pattern and azimuthal data can be well fitted using close-coupled channel calculations and varying only three parameters, giving confidence that the calculated electron density is accurate. It is found that the peak-to-peak corrugation of the 10-3 A&#778-3 isoelectron density surface is ~=1.2 Å, showing a substantial smoothing with respect to the corrugation of 1.55 Å found when superposing the calculated free atomic densities. In addition we have examined the sensitivity of the model calculations to geometric structure. They are consistent only with the expected missing row structure, and yield the separation between the first and second layers with an accuracy of 6%.
Surface Science, 2002
We report on the structural and magnetic properties of thin Fe films grown on the Cu(1 1 0) surfa... more We report on the structural and magnetic properties of thin Fe films grown on the Cu(1 1 0) surface. In-plane grazing-incidence X-ray diffraction has been used to measure the lateral lattice spacing of the Fe films. Complementary information about the structure of the topmost layers has been obtained by means of Auger and photoelectron diffraction. The Fe film grows pseudomorphic with the substrate up to a thickness of about 0.8 nm. The diffraction feature of a new phase is observed at 1.6 nm, with a corresponding interplanar distance close to the bulk body centered cubic (bcc) Fe one, which is eventually recovered at higher thickness (6.4 nm). From comparison between X-ray diffraction and photoelectron diffraction, it is suggested that the bcc-like Fe grows on the (1 0 0) surface with its [1 1 0] axis oriented along the [0 0 1] substrate direction. The photoelectron diffraction data also indicate a strong faceting in the [1 1 0] substrate direction. This morphology is believed to contribute to the in-plane uniaxial magnetic anisotropy observed by Kerr effect and Brillouin light scattering from spin waves. Ó
Solid State Communications, 1994
ABSTRACT
Physica Status Solidi (a), 1999
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2001
Coincidence measurements have been extensively performed in atomic and molecular physics since ea... more Coincidence measurements have been extensively performed in atomic and molecular physics since early 1970s. To apply this methodology to solids and surfaces has been a major target since early days, but the long average time needed to complete a coincidence experiment has hampered its attainment. In particular the coincidence technique has not been yet applied in an angle resolved way such for studying the momentum correlation in the ejection of electron pairs from solid surfaces. The experimental chamber at the ALOISA beamline at Elettra, by means of a set of seven homemade electron analyzers, is the first apparatus able to perform Angle Resolved -Auger Photoelectron Coincidence Spectroscopy (AR-APECS) from solid surfaces. In the typical setup ten different pairs of coincident electrons can be measured simultaneously, so reducing the acquisition time by one order of magnitude. # 2001 Elsevier Science B.V. All rights reserved. PACS: 72.90.F Keywords: Auger photoelectron coincidence spectroscopy 0168-9002/01/$ -see front matter # 2001 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 -9 0 0 2 ( 0 1 ) 0 0 7 2 1 -5
Journal of Applied Physics, 2014
Physical Review B, 1997
... D. Cvetko, V. De Renzi, L. Floreano, R. Gotter, A. Morgante, M. Peloi, and F. Tommasini Labor... more ... D. Cvetko, V. De Renzi, L. Floreano, R. Gotter, A. Morgante, M. Peloi, and F. Tommasini Laboratorio Tecnologie Avanzate Superfici e Catalisi ... The temperature-dependent behavior of the Rh(111)-(22)-1O phase was investigated by He-atom scatter-ing (HAS) and low-energy ...
Physical Review B, 1996
... M. Buongiorno Nardelli,* D. Cvetko,† V. De Renzi,‡ L. Floreano,§ R. Gotter,§ A. Morgante, M. ... more ... M. Buongiorno Nardelli,* D. Cvetko,† V. De Renzi,‡ L. Floreano,§ R. Gotter,§ A. Morgante, M. Peloi, and F. Tommasini§ Laboratorio TASC dell ... The surface temperature during deposition was selected at 375 K.29 At this temperature the mobility of T6 molecules is high enough to ...
Surface Science, 1994
ABSTRACT The evolution of surface defects created by low energy ion bombardment on InSb(110) is s... more ABSTRACT The evolution of surface defects created by low energy ion bombardment on InSb(110) is studied by He beam scattering experiments. At surface temperatures above 500 K the ion erosion is found to proceed layer-by-layer without changing the stoichiometric composition of the surface. This indicates that the nucleation of surface islands driven by vacancy diffusion is faster than the ion erosion. After different doses of Ar+ ion bombardment, the surface is left in a non-equilibrium state whose time evolution is monitored by measuring the profiles of the He diffraction peaks. It is seen that the coalescence of islands proceeds with anisotropic island size distributions.
Surface Science, 2014
ABSTRACT Early stages of thin Pb film growth on Ge(001) substrate, exhibiting quantum size effect... more ABSTRACT Early stages of thin Pb film growth on Ge(001) substrate, exhibiting quantum size effects (QSE), are characterized by means of Photoelectron Diffraction and Helium Atom Scattering. Pb is found to form a commensurate first monolayer, while an ordered layer-by-layer growth only sets in after deposition of 4 monolayers. In the intermediate coverage range no long range order of the overlayer is established and we find that uncorrelated islands of preferred four-layer thickness are formed. Continuous Pb film with long range order emerges through islands coalescence close to a coverage of 4 monolayers, upon which a more regular layer-by-layer growth mode sets in.
Physical Review B, 2001
We have measured the long range order of the α-phase of Sn on the Ge(111) surface throughout
Monolayer-thick crystals, such as graphene, are an area of intense interest in condensed matter r... more Monolayer-thick crystals, such as graphene, are an area of intense interest in condensed matter research. However, crystal deformations in these 2D systems are known to adversely affect conductivity and increase local chemical reactivity. Additionally, surface roughness in graphene complicates band-mapping and limits resolution in techniques such as angle resolved photoemission spectroscopy (ARPES), the theory of which was developed for atomically
Physical Review B, 1995
He beam scattering measurements of the erosion of the InSb(110) surface by low-energy Ar+ bombard... more He beam scattering measurements of the erosion of the InSb(110) surface by low-energy Ar+ bombardment are reported. Layer-by-layer erosion is observed for surface temperatures above 510 K and is found to proceed by nucleation of vacancy islands, island growth, and coalescence. The average island distance is measured at different stages of the erosion process and it is found to evolve
Physical Review B, 1995
We present a study of low-energy vibrations at the InSb(110) surface along the GammaY¯ direction.... more We present a study of low-energy vibrations at the InSb(110) surface along the GammaY¯ direction. Surface phonons have been measured by He inelastic scattering and a theoretical analysis has been performed by means of first-principles calculations. We have been able to distinguish the surface acoustic mode above the Rayleigh wave and to identify a surface resonance and an optical surface
The Journal of Physical Chemistry B, 2005
We report on a high-resolution X-ray photoemission spectroscopy study on molecular-thick layers o... more We report on a high-resolution X-ray photoemission spectroscopy study on molecular-thick layers of L-cysteine deposited under ultrahigh vacuum conditions on Au(110). The analysis of core level shifts allowed us to distinguish unambiguously the states of the first-layer molecules from those of molecules belonging to the second layer. The first-layer molecules strongly interact with the metal through their sulfur headgroup. The multipeaked structure of the N 1s, O 1s, and C 1s core levels is interpreted in terms of different molecular moieties. The neutral acidic fraction (HSCH2CH(NH2)COOH) is abundant at low coverage likely associated with isolated molecules or dimers. The zwitterionic phase (HSCH2CH(NH3+)COO-) is largely dominant as the coverage approaches the monolayer limit and is related to the formation of ordered self-assembled molecular structures indicated by electron diffraction patterns. The occurrence of a small amount of cationic molecules (HSCH2CH(NH3+)COOH) is also discussed. The second-layer molecules mainly display zwitterionic character and are weakly adsorbed. Mild annealing up to 100 degrees C leads to the desorption of the second-layer molecules leaving electronic states of the first layer unaltered.
Progress in Surface Science, 2003
The electronic properties of thin metallic films deviate from the corresponding bulk ones when th... more The electronic properties of thin metallic films deviate from the corresponding bulk ones when the film thickness is comparable with the wavelength of the electrons at the Fermi level. This phenomenon, referred to as quantum size effect (QSE), is also expected to affect the film morphology and structure leading to the "electronic growth" of metals on semiconductors. Shuch effect may be observed when metals are grownon substrates held at low temperature and are manifested through the occurrence of "magical" thickness islands or critical thickness for layer-by-layer growth. In particular, layer-by-layer growth of Pb(111) films has been reported for deposition on Ge(001) below ∼ 130 K. An extremely flat morphology is preserved throughout deposition from four up to a dozen of monolayers. These flat films are shown to be metastable and to reorganize into large clusters uncovering the first Pb layer pseudomorphic to the underlying Ge(001) substrate already at room temperature. Indications of QSE induced structural variations of the growing films have been reported for Pb growth on both Si(111) and Ge(001). In the latter case, the apparent height of the Pb(111) monatomic step was shown to change in an oscillatory fashion by He atom scattering (HAS) during layer-by-layer growth at low temperature. The extent of the structural QSE has been obtained by a comparison of the HAS data with X-ray diffraction (XRD) and reflectivity experiments. Whereas step height variations as large as 20% have been measured by HAS reflectivity, the displacement of the atomic planes from their bulk position, as measured by XRD, has been found to mainly affect the topmost Pb layer, but with a lower extent, i.e. the QSE observed by HAS are mainly due to a perpendicular displacement of the topmost layer charge density. The effect of the variable surface relaxation on the surface vibration has been studied from the acoustic dispersion of the low energy phonons, as measured by inelastic HAS.
Surface Science, 1993
ABSTRACT
Physical Review B, 2010
We present a combined multimethod experimental and theoretical study of the geometric and electro... more We present a combined multimethod experimental and theoretical study of the geometric and electronic properties of Co-tetraphenyl-porphyrin (Co-TPP) molecules adsorbed on a Ag(111) surface. Scanning tunneling microscopy (STM) topographs reveal that Co-TPP ...
Physical Review B, 2001
The bonding geometry of Sn on Ge(111) has been quantitatively determined for the (3×3) phase at 1... more The bonding geometry of Sn on Ge(111) has been quantitatively determined for the (3×3) phase at 150 K. Energy scan photoelectron diffraction of the Sn 4d core levels has been used to independently measure the bond length between Sn and its nearest neighbour Ge atoms and the vertical distance between Sn and the Ge atom beneath. This latter distance is found to be ∼ 0.3Å larger for one Sn atom out of the three contained in the lattice unit cell. The bond lengths and the bond directions, obtained by the angular scans, are found to be practically the same for the three Sn atoms within ± 0.03Å and ± 3 • , respectively. The three nearest neighbour Ge atoms thus partially follow the Sn atom in its vertical ripple.
Physical Review B, 1993
ABSTRACT The (1×2)-Au(110) surface has been studied using He-beam scattering with time-of-flight ... more ABSTRACT The (1×2)-Au(110) surface has been studied using He-beam scattering with time-of-flight detection. The experiments included measurement of the diffraction pattern and the specular intensity as a function of azimuthal angle of incidence; the latter curve is found to be highly structured. The data have been modeled using the local-density approximation to calculate the charge distribution in atoms, and treating the He-surface potential as a superposition of pseudopairwise terms. The diffraction pattern and azimuthal data can be well fitted using close-coupled channel calculations and varying only three parameters, giving confidence that the calculated electron density is accurate. It is found that the peak-to-peak corrugation of the 10-3 A&#778-3 isoelectron density surface is ~=1.2 Å, showing a substantial smoothing with respect to the corrugation of 1.55 Å found when superposing the calculated free atomic densities. In addition we have examined the sensitivity of the model calculations to geometric structure. They are consistent only with the expected missing row structure, and yield the separation between the first and second layers with an accuracy of 6%.
Surface Science, 2002
We report on the structural and magnetic properties of thin Fe films grown on the Cu(1 1 0) surfa... more We report on the structural and magnetic properties of thin Fe films grown on the Cu(1 1 0) surface. In-plane grazing-incidence X-ray diffraction has been used to measure the lateral lattice spacing of the Fe films. Complementary information about the structure of the topmost layers has been obtained by means of Auger and photoelectron diffraction. The Fe film grows pseudomorphic with the substrate up to a thickness of about 0.8 nm. The diffraction feature of a new phase is observed at 1.6 nm, with a corresponding interplanar distance close to the bulk body centered cubic (bcc) Fe one, which is eventually recovered at higher thickness (6.4 nm). From comparison between X-ray diffraction and photoelectron diffraction, it is suggested that the bcc-like Fe grows on the (1 0 0) surface with its [1 1 0] axis oriented along the [0 0 1] substrate direction. The photoelectron diffraction data also indicate a strong faceting in the [1 1 0] substrate direction. This morphology is believed to contribute to the in-plane uniaxial magnetic anisotropy observed by Kerr effect and Brillouin light scattering from spin waves. Ó
Solid State Communications, 1994
ABSTRACT
Physica Status Solidi (a), 1999
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2001
Coincidence measurements have been extensively performed in atomic and molecular physics since ea... more Coincidence measurements have been extensively performed in atomic and molecular physics since early 1970s. To apply this methodology to solids and surfaces has been a major target since early days, but the long average time needed to complete a coincidence experiment has hampered its attainment. In particular the coincidence technique has not been yet applied in an angle resolved way such for studying the momentum correlation in the ejection of electron pairs from solid surfaces. The experimental chamber at the ALOISA beamline at Elettra, by means of a set of seven homemade electron analyzers, is the first apparatus able to perform Angle Resolved -Auger Photoelectron Coincidence Spectroscopy (AR-APECS) from solid surfaces. In the typical setup ten different pairs of coincident electrons can be measured simultaneously, so reducing the acquisition time by one order of magnitude. # 2001 Elsevier Science B.V. All rights reserved. PACS: 72.90.F Keywords: Auger photoelectron coincidence spectroscopy 0168-9002/01/$ -see front matter # 2001 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 -9 0 0 2 ( 0 1 ) 0 0 7 2 1 -5
Journal of Applied Physics, 2014
Physical Review B, 1997
... D. Cvetko, V. De Renzi, L. Floreano, R. Gotter, A. Morgante, M. Peloi, and F. Tommasini Labor... more ... D. Cvetko, V. De Renzi, L. Floreano, R. Gotter, A. Morgante, M. Peloi, and F. Tommasini Laboratorio Tecnologie Avanzate Superfici e Catalisi ... The temperature-dependent behavior of the Rh(111)-(22)-1O phase was investigated by He-atom scatter-ing (HAS) and low-energy ...
Physical Review B, 1996
... M. Buongiorno Nardelli,* D. Cvetko,† V. De Renzi,‡ L. Floreano,§ R. Gotter,§ A. Morgante, M. ... more ... M. Buongiorno Nardelli,* D. Cvetko,† V. De Renzi,‡ L. Floreano,§ R. Gotter,§ A. Morgante, M. Peloi, and F. Tommasini§ Laboratorio TASC dell ... The surface temperature during deposition was selected at 375 K.29 At this temperature the mobility of T6 molecules is high enough to ...
Surface Science, 1994
ABSTRACT The evolution of surface defects created by low energy ion bombardment on InSb(110) is s... more ABSTRACT The evolution of surface defects created by low energy ion bombardment on InSb(110) is studied by He beam scattering experiments. At surface temperatures above 500 K the ion erosion is found to proceed layer-by-layer without changing the stoichiometric composition of the surface. This indicates that the nucleation of surface islands driven by vacancy diffusion is faster than the ion erosion. After different doses of Ar+ ion bombardment, the surface is left in a non-equilibrium state whose time evolution is monitored by measuring the profiles of the He diffraction peaks. It is seen that the coalescence of islands proceeds with anisotropic island size distributions.
Surface Science, 2014
ABSTRACT Early stages of thin Pb film growth on Ge(001) substrate, exhibiting quantum size effect... more ABSTRACT Early stages of thin Pb film growth on Ge(001) substrate, exhibiting quantum size effects (QSE), are characterized by means of Photoelectron Diffraction and Helium Atom Scattering. Pb is found to form a commensurate first monolayer, while an ordered layer-by-layer growth only sets in after deposition of 4 monolayers. In the intermediate coverage range no long range order of the overlayer is established and we find that uncorrelated islands of preferred four-layer thickness are formed. Continuous Pb film with long range order emerges through islands coalescence close to a coverage of 4 monolayers, upon which a more regular layer-by-layer growth mode sets in.
Physical Review B, 2001
We have measured the long range order of the α-phase of Sn on the Ge(111) surface throughout
Monolayer-thick crystals, such as graphene, are an area of intense interest in condensed matter r... more Monolayer-thick crystals, such as graphene, are an area of intense interest in condensed matter research. However, crystal deformations in these 2D systems are known to adversely affect conductivity and increase local chemical reactivity. Additionally, surface roughness in graphene complicates band-mapping and limits resolution in techniques such as angle resolved photoemission spectroscopy (ARPES), the theory of which was developed for atomically
Physical Review B, 1995
He beam scattering measurements of the erosion of the InSb(110) surface by low-energy Ar+ bombard... more He beam scattering measurements of the erosion of the InSb(110) surface by low-energy Ar+ bombardment are reported. Layer-by-layer erosion is observed for surface temperatures above 510 K and is found to proceed by nucleation of vacancy islands, island growth, and coalescence. The average island distance is measured at different stages of the erosion process and it is found to evolve
Physical Review B, 1995
We present a study of low-energy vibrations at the InSb(110) surface along the GammaY¯ direction.... more We present a study of low-energy vibrations at the InSb(110) surface along the GammaY¯ direction. Surface phonons have been measured by He inelastic scattering and a theoretical analysis has been performed by means of first-principles calculations. We have been able to distinguish the surface acoustic mode above the Rayleigh wave and to identify a surface resonance and an optical surface