G. Bussetti | Politecnico di Milano (original) (raw)
Papers by G. Bussetti
Applied Surface Science, 2020
We present a multitechnique investigation of the structural and electronic properties of the prot... more We present a multitechnique investigation of the structural and electronic properties of the prototypical system composed by ultra-thin films of magnetic molecules [Co-tetraphenyl-porphyrins (Co-TPP)] grown on a ferromagnetic substrate [oxygen passivated Fe(0 0 1), namely the Fe(0 0 1)-p(1 × 1)O surface]. Low Energy electron diffraction (LEED) and scanning tunneling microscopy (STM), coupled with first-principles calculations, reveal the formation of a commensurate superstructure at monolayer coverage, made by a square array of flat-lying TPP molecules. UV–photoemission and inverse photoemission spectroscopies (UPS and IPES) are used to investigate their electronic structure. Similar to our previous results on the Zn–TPP growth on Fe(0 0 1)–p(1 × 1)O, the passivation of the metallic surface is able to preserve the photoemission features characteristic of quasi-free molecules, opening the route towards an exploitation of single oxide layers as protective films in organic/inorganic junctions. X-ray photoemission (XPS) and near edge X-ray adsorption fine structure spectroscopies (NEXAFS), are used to reveal the details of the Co–TPP interaction with the substrate.
Appl. Phys. Lett., 2019
We propose a method to grow metal tetraphenyl porphyrin (MTPP) molecular layers where a long-rang... more We propose a method to grow metal tetraphenyl porphyrin (MTPP) molecular layers where a long-range structural and magnetic order can be achieved simultaneously and at room temperature by a proper treatment of the ferromagnetic substrate. We focus in particular on the oxygen-passivated Fe(001)-p(1 × 1)O surface, where MTPP molecules (with M=Co and Ni) arrange by forming square commensurate overlayers. Spin-resolved photoemission detects a clear spin-splitting of CoTPP electronic states, while no magnetic response is obtained from NiTPP, as expected from the electronic configuration of the respective free molecules. We link these observations to the decoupling action of oxygen at the interface, whose effect is to enhance the molecular diffusivity and tune the electronic interaction with the substrate electronic structure.
ChemNanoMat, 2020
The development of novel protocols and techniques for waste treatment represents the state of the... more The development of novel protocols and techniques for waste treatment represents the state of the art in the so‐called “green conversion”. Chemical wastes deriving from industrial and power‐station processes, which involve organic crystals, can be very hazardous for the environment. Studying their dissolution mechanism, both theoretically and experimentally, represents a mandatory step in the critical task of their disposal. Surprisingly, most of the studies are focused on millimeter scale length, from which one could estimate the crystal dissolution rate. In these studies, where no information about the dissolution mechanism on a molecular scale is provided, etch‐pit formation is recognized as the ultimate mechanism of crystal dissolution.
In this work, we show the morphological evolution of organic nanocrystals on the sub‐micrometer scale range in a reactive dissolution process controlled by pH. This approach allows us to explore ranges of high undersaturation, whereby crystal dissolution occurs even though etch‐pit formation is suppressed. Adopting different surface and bulk‐sensitive techniques (atomic force microscopy, time‐of‐flight secondary ion mass spectroscopy and X‐ray/electron diffraction, Raman spectroscopy, respectively), we investigate the dissolution process of porphyrin thin films deposited on the basal plane of highly oriented pyrolytic graphite, proving that such films constitute a model system to unveil the dissolution mechanism of organic nanocrystals.
Sensors and Microsystems - Proceedings of the 10th Italian Conference, 2008
Nanoscience and Nanotechnology Letters, 2012
ABSTRACT Nickel-iron interfacial intermixing, resulting from annealing ultrathin Ni films grown o... more ABSTRACT Nickel-iron interfacial intermixing, resulting from annealing ultrathin Ni films grown on Fe(001), has been investigated by low-energy electron diffraction, Auger electron spectroscopy and scanning tunnelling microscopy. The Ni/Fe interface has been found to be highly unstable at relatively low annealing temperatures, with dramatic thermal effects on the surface morphology of the Ni/Fe(001) epitaxial films.
Physical Review Letters, 2014
A remarkable enhancement of atomic diffusion is highlighted by scanning tunneling microscopy perf... more A remarkable enhancement of atomic diffusion is highlighted by scanning tunneling microscopy performed on ultrathin metastable body-centered tetragonal Co films grown on Fe(001). The films follow a nearly perfect layer-by-layer growth mode with a saturation island density strongly dependent on the layer on which the nucleation occurs, indicating a lowering of the diffusion barrier. Density functional theory calculations reveal that this phenomenon is driven by the increasing capability of the film to accommodate large deformations as the thickness approaches the limit at which a structural transition occurs. These results disclose the possibility of tuning surface diffusion dynamics and controlling cluster nucleation and self-organization.
The Journal of Physical …
Surface Science, 2007
The ordering properties of tetraphenylporphyrin molecules sublimated on a highly oriented pyrolit... more The ordering properties of tetraphenylporphyrin molecules sublimated on a highly oriented pyrolitic graphite surface have been investigated. The morphological information obtained by scanning tunneling microscopy has been linked with the optical spectra by reflectance anisotropy spectroscopy. Measurements were performed in situ as a function of the nominal coverage.
Surface Science, 2007
The growth process of thin films and multilayers of quaterthiophene and sexithiophene onto molecu... more The growth process of thin films and multilayers of quaterthiophene and sexithiophene onto molecular single crystals has been monitored in situ and in real time during deposition by organic molecular beam epitaxy, measuring the anisotropy of the optical reflectivity. The evolution of the spectra with thickness provides the signature of an epitaxial growth of the films.
Superlattices and Microstructures, 2008
Organic molecular beam epitaxy (OMBE) is the growth technique assuring high quality films and pro... more Organic molecular beam epitaxy (OMBE) is the growth technique assuring high quality films and properly designed multilayers of organic molecular materials in view of both their fundamental studies and applications. To monitor in-situ the OMBE growth, we have applied reflectance anisotropy spectroscopy (RAS), which is particularly effective and sensitive, being non destructive for organic materials. In this work, RAS is used to monitor, in-situ, the growth of organic heterostructures. The experiment is carried out using organic single crystals as substrates and oligothiophenes as molecular materials to build a stack of layers. A layer-by-layer growth of the films is demonstrated, together with the formation of interfaces with peculiar optical behavior and structure.
Superlattices and Microstructures, 2009
ABSTRACT We have recently measured for the first time–by using Reflectance Anisotropy spectroscop... more ABSTRACT We have recently measured for the first time–by using Reflectance Anisotropy spectroscopy- the optical gap between dangling-bond states on a single-domain diamond C(111)-2 × 1 surface. The experimental result we have obtained (1.47±0.02 eV ) represents the conclusion of the long-standing effort to determine if this surface is metallic or semiconducting. The large surface gap (even larger for possible excitonic effects) opens a new scientific question: at the moment neither state-of-the-art band calculations have succeeded in obtaining it, nor has its physical origin been explained.
Physical Review Letters, 2011
A long-standing puzzle regarding the Sið111Þ À 2 Â 1 surface has been solved. The surface energy ... more A long-standing puzzle regarding the Sið111Þ À 2 Â 1 surface has been solved. The surface energy gap previously determined by photoemission on heavily n-doped crystals was not compatible with a strongly bound exciton known from other considerations to exist. New low-temperature angle-resolved photoemission and scanning tunneling microscopy data, together with theory, unambiguously reveal that isomers with opposite bucklings and different energy gaps coexist on such surfaces. The subtle energetics between the isomers, dependent on doping, leads to a reconciliation of all previous results. 8 pdos (a.u.) negative isomers positive isomers J J FIG. 3. Left panel: simulated STS of the isomers, calculated as the GW density of states projected on the upper and lower chains. Right panel: surface-state GW energies along " J " K for the two isomers, aligned to a common vacuum level. Solid (dashed) line refers to the positive (negative) isomer.
Physical Review B, 2005
The growth process of molecular thin films deposited on an interacting crystalline substrate by o... more The growth process of molecular thin films deposited on an interacting crystalline substrate by organic molecular-beam epitaxy is monitored in situ by reflectance anisotropy spectroscopy (RAS). From the RAS signal evolution measured during the early stages of deposition, evidence is found of two opposite growth modes, namely layer-by-layer and island modes, obtained when changing the supersaturation of the vapor phase on the substrate.
physica status solidi (b), 2005
Ordered films of porphyrins are routinely obtained by Langmuir-Blodgett technique, with a thickne... more Ordered films of porphyrins are routinely obtained by Langmuir-Blodgett technique, with a thickness control at the level of a single monolayer. The study of their optical anisotropy by reflectance anisotropy spectroscopy (RAS) has evidenced an interesting modification of the spectral line shape around the Soret band of the porphyrin layer after a certain critical thickness has been deposited onto the
physica status solidi (b), 2014
ABSTRACT
physica status solidi (a), 2001
Until now, with a few exceptions, Reflectance Anisotropy Spectroscopy (RAS) has been applied most... more Until now, with a few exceptions, Reflectance Anisotropy Spectroscopy (RAS) has been applied mostly to inorganic semiconductors and metals, proving to be a powerful tool to investigate their optical properties, via anisotropies introduced by the surface in otherwise isotropic bulk materials. Recently, we have shown that RAS can be successfully used to study the optical anisotropies of organic Langmuir-Blodgett films. In this paper we have extended our study to thick Langmuir-Blodgett films of porphyrins, a class of molecules widely studied for the importance of their physico-chemical properties.
New Journal of Physics, 2012
We report evidence that the body-centered cubic (bcc)-face-centered cubic (fcc) transition that o... more We report evidence that the body-centered cubic (bcc)-face-centered cubic (fcc) transition that occurs during Ni film growth on a Fe(001) substrate is preceded by a pre-martensitic phase, as demonstrated by low-energy electron diffraction. The corresponding film superstructure is characterized by a displacement of Ni atoms along the main 100 crystallographic axes of iron, without any rotation of the unit cell with respect to the (001) plane, in contrast with the martensitic transition that shows four fcc Ni domains with the Ni 211 crystallographic directions aligned with the Fe 110 axes. In addition, the martensitic transition is detected not at 6 ML, as previously believed, but above 20 ML if the Ni sample is rigorously kept at room temperature. The surface morphology of the bcc-fcc transition is characterized by the development of Ni mounds oriented along the 110 directions, as shown by scanning tunneling microscopy.
New Journal of Chemistry, 2004
Spontaneous deposition of aggregates of a tetraphenylporphyrin derivative, possessing a cationic ... more Spontaneous deposition of aggregates of a tetraphenylporphyrin derivative, possessing a cationic appended functionality, straightforwardly occurs from aqueous solutions. Combined spectroscopic studies and AFM morphological characterisation reveal that these layered films feature a ...
Langmuir, 2002
We have studied the optical anisotropy of porphyrin layers with different thicknesses deposited o... more We have studied the optical anisotropy of porphyrin layers with different thicknesses deposited onto gold substrates by the Langmuir-Schaefer technique. In coincidence with the Soret band of the molecule, the optical spectral line shape as determined by reflectance anisotropy spectroscopy exhibits a characteristic, large structure, which changes from a "peaklike" to a "derivative-like" shape at a well-defined thickness (8-10 monolayers). We interpret this result in the framework of electronic effects due to structural changes in the layers, yielding solid-state effects originating from the coupling of the π orbitals of the porphyrin macrocycles.
Applied Surface Science, 2020
We present a multitechnique investigation of the structural and electronic properties of the prot... more We present a multitechnique investigation of the structural and electronic properties of the prototypical system composed by ultra-thin films of magnetic molecules [Co-tetraphenyl-porphyrins (Co-TPP)] grown on a ferromagnetic substrate [oxygen passivated Fe(0 0 1), namely the Fe(0 0 1)-p(1 × 1)O surface]. Low Energy electron diffraction (LEED) and scanning tunneling microscopy (STM), coupled with first-principles calculations, reveal the formation of a commensurate superstructure at monolayer coverage, made by a square array of flat-lying TPP molecules. UV–photoemission and inverse photoemission spectroscopies (UPS and IPES) are used to investigate their electronic structure. Similar to our previous results on the Zn–TPP growth on Fe(0 0 1)–p(1 × 1)O, the passivation of the metallic surface is able to preserve the photoemission features characteristic of quasi-free molecules, opening the route towards an exploitation of single oxide layers as protective films in organic/inorganic junctions. X-ray photoemission (XPS) and near edge X-ray adsorption fine structure spectroscopies (NEXAFS), are used to reveal the details of the Co–TPP interaction with the substrate.
Appl. Phys. Lett., 2019
We propose a method to grow metal tetraphenyl porphyrin (MTPP) molecular layers where a long-rang... more We propose a method to grow metal tetraphenyl porphyrin (MTPP) molecular layers where a long-range structural and magnetic order can be achieved simultaneously and at room temperature by a proper treatment of the ferromagnetic substrate. We focus in particular on the oxygen-passivated Fe(001)-p(1 × 1)O surface, where MTPP molecules (with M=Co and Ni) arrange by forming square commensurate overlayers. Spin-resolved photoemission detects a clear spin-splitting of CoTPP electronic states, while no magnetic response is obtained from NiTPP, as expected from the electronic configuration of the respective free molecules. We link these observations to the decoupling action of oxygen at the interface, whose effect is to enhance the molecular diffusivity and tune the electronic interaction with the substrate electronic structure.
ChemNanoMat, 2020
The development of novel protocols and techniques for waste treatment represents the state of the... more The development of novel protocols and techniques for waste treatment represents the state of the art in the so‐called “green conversion”. Chemical wastes deriving from industrial and power‐station processes, which involve organic crystals, can be very hazardous for the environment. Studying their dissolution mechanism, both theoretically and experimentally, represents a mandatory step in the critical task of their disposal. Surprisingly, most of the studies are focused on millimeter scale length, from which one could estimate the crystal dissolution rate. In these studies, where no information about the dissolution mechanism on a molecular scale is provided, etch‐pit formation is recognized as the ultimate mechanism of crystal dissolution.
In this work, we show the morphological evolution of organic nanocrystals on the sub‐micrometer scale range in a reactive dissolution process controlled by pH. This approach allows us to explore ranges of high undersaturation, whereby crystal dissolution occurs even though etch‐pit formation is suppressed. Adopting different surface and bulk‐sensitive techniques (atomic force microscopy, time‐of‐flight secondary ion mass spectroscopy and X‐ray/electron diffraction, Raman spectroscopy, respectively), we investigate the dissolution process of porphyrin thin films deposited on the basal plane of highly oriented pyrolytic graphite, proving that such films constitute a model system to unveil the dissolution mechanism of organic nanocrystals.
Sensors and Microsystems - Proceedings of the 10th Italian Conference, 2008
Nanoscience and Nanotechnology Letters, 2012
ABSTRACT Nickel-iron interfacial intermixing, resulting from annealing ultrathin Ni films grown o... more ABSTRACT Nickel-iron interfacial intermixing, resulting from annealing ultrathin Ni films grown on Fe(001), has been investigated by low-energy electron diffraction, Auger electron spectroscopy and scanning tunnelling microscopy. The Ni/Fe interface has been found to be highly unstable at relatively low annealing temperatures, with dramatic thermal effects on the surface morphology of the Ni/Fe(001) epitaxial films.
Physical Review Letters, 2014
A remarkable enhancement of atomic diffusion is highlighted by scanning tunneling microscopy perf... more A remarkable enhancement of atomic diffusion is highlighted by scanning tunneling microscopy performed on ultrathin metastable body-centered tetragonal Co films grown on Fe(001). The films follow a nearly perfect layer-by-layer growth mode with a saturation island density strongly dependent on the layer on which the nucleation occurs, indicating a lowering of the diffusion barrier. Density functional theory calculations reveal that this phenomenon is driven by the increasing capability of the film to accommodate large deformations as the thickness approaches the limit at which a structural transition occurs. These results disclose the possibility of tuning surface diffusion dynamics and controlling cluster nucleation and self-organization.
The Journal of Physical …
Surface Science, 2007
The ordering properties of tetraphenylporphyrin molecules sublimated on a highly oriented pyrolit... more The ordering properties of tetraphenylporphyrin molecules sublimated on a highly oriented pyrolitic graphite surface have been investigated. The morphological information obtained by scanning tunneling microscopy has been linked with the optical spectra by reflectance anisotropy spectroscopy. Measurements were performed in situ as a function of the nominal coverage.
Surface Science, 2007
The growth process of thin films and multilayers of quaterthiophene and sexithiophene onto molecu... more The growth process of thin films and multilayers of quaterthiophene and sexithiophene onto molecular single crystals has been monitored in situ and in real time during deposition by organic molecular beam epitaxy, measuring the anisotropy of the optical reflectivity. The evolution of the spectra with thickness provides the signature of an epitaxial growth of the films.
Superlattices and Microstructures, 2008
Organic molecular beam epitaxy (OMBE) is the growth technique assuring high quality films and pro... more Organic molecular beam epitaxy (OMBE) is the growth technique assuring high quality films and properly designed multilayers of organic molecular materials in view of both their fundamental studies and applications. To monitor in-situ the OMBE growth, we have applied reflectance anisotropy spectroscopy (RAS), which is particularly effective and sensitive, being non destructive for organic materials. In this work, RAS is used to monitor, in-situ, the growth of organic heterostructures. The experiment is carried out using organic single crystals as substrates and oligothiophenes as molecular materials to build a stack of layers. A layer-by-layer growth of the films is demonstrated, together with the formation of interfaces with peculiar optical behavior and structure.
Superlattices and Microstructures, 2009
ABSTRACT We have recently measured for the first time–by using Reflectance Anisotropy spectroscop... more ABSTRACT We have recently measured for the first time–by using Reflectance Anisotropy spectroscopy- the optical gap between dangling-bond states on a single-domain diamond C(111)-2 × 1 surface. The experimental result we have obtained (1.47±0.02 eV ) represents the conclusion of the long-standing effort to determine if this surface is metallic or semiconducting. The large surface gap (even larger for possible excitonic effects) opens a new scientific question: at the moment neither state-of-the-art band calculations have succeeded in obtaining it, nor has its physical origin been explained.
Physical Review Letters, 2011
A long-standing puzzle regarding the Sið111Þ À 2 Â 1 surface has been solved. The surface energy ... more A long-standing puzzle regarding the Sið111Þ À 2 Â 1 surface has been solved. The surface energy gap previously determined by photoemission on heavily n-doped crystals was not compatible with a strongly bound exciton known from other considerations to exist. New low-temperature angle-resolved photoemission and scanning tunneling microscopy data, together with theory, unambiguously reveal that isomers with opposite bucklings and different energy gaps coexist on such surfaces. The subtle energetics between the isomers, dependent on doping, leads to a reconciliation of all previous results. 8 pdos (a.u.) negative isomers positive isomers J J FIG. 3. Left panel: simulated STS of the isomers, calculated as the GW density of states projected on the upper and lower chains. Right panel: surface-state GW energies along " J " K for the two isomers, aligned to a common vacuum level. Solid (dashed) line refers to the positive (negative) isomer.
Physical Review B, 2005
The growth process of molecular thin films deposited on an interacting crystalline substrate by o... more The growth process of molecular thin films deposited on an interacting crystalline substrate by organic molecular-beam epitaxy is monitored in situ by reflectance anisotropy spectroscopy (RAS). From the RAS signal evolution measured during the early stages of deposition, evidence is found of two opposite growth modes, namely layer-by-layer and island modes, obtained when changing the supersaturation of the vapor phase on the substrate.
physica status solidi (b), 2005
Ordered films of porphyrins are routinely obtained by Langmuir-Blodgett technique, with a thickne... more Ordered films of porphyrins are routinely obtained by Langmuir-Blodgett technique, with a thickness control at the level of a single monolayer. The study of their optical anisotropy by reflectance anisotropy spectroscopy (RAS) has evidenced an interesting modification of the spectral line shape around the Soret band of the porphyrin layer after a certain critical thickness has been deposited onto the
physica status solidi (b), 2014
ABSTRACT
physica status solidi (a), 2001
Until now, with a few exceptions, Reflectance Anisotropy Spectroscopy (RAS) has been applied most... more Until now, with a few exceptions, Reflectance Anisotropy Spectroscopy (RAS) has been applied mostly to inorganic semiconductors and metals, proving to be a powerful tool to investigate their optical properties, via anisotropies introduced by the surface in otherwise isotropic bulk materials. Recently, we have shown that RAS can be successfully used to study the optical anisotropies of organic Langmuir-Blodgett films. In this paper we have extended our study to thick Langmuir-Blodgett films of porphyrins, a class of molecules widely studied for the importance of their physico-chemical properties.
New Journal of Physics, 2012
We report evidence that the body-centered cubic (bcc)-face-centered cubic (fcc) transition that o... more We report evidence that the body-centered cubic (bcc)-face-centered cubic (fcc) transition that occurs during Ni film growth on a Fe(001) substrate is preceded by a pre-martensitic phase, as demonstrated by low-energy electron diffraction. The corresponding film superstructure is characterized by a displacement of Ni atoms along the main 100 crystallographic axes of iron, without any rotation of the unit cell with respect to the (001) plane, in contrast with the martensitic transition that shows four fcc Ni domains with the Ni 211 crystallographic directions aligned with the Fe 110 axes. In addition, the martensitic transition is detected not at 6 ML, as previously believed, but above 20 ML if the Ni sample is rigorously kept at room temperature. The surface morphology of the bcc-fcc transition is characterized by the development of Ni mounds oriented along the 110 directions, as shown by scanning tunneling microscopy.
New Journal of Chemistry, 2004
Spontaneous deposition of aggregates of a tetraphenylporphyrin derivative, possessing a cationic ... more Spontaneous deposition of aggregates of a tetraphenylporphyrin derivative, possessing a cationic appended functionality, straightforwardly occurs from aqueous solutions. Combined spectroscopic studies and AFM morphological characterisation reveal that these layered films feature a ...
Langmuir, 2002
We have studied the optical anisotropy of porphyrin layers with different thicknesses deposited o... more We have studied the optical anisotropy of porphyrin layers with different thicknesses deposited onto gold substrates by the Langmuir-Schaefer technique. In coincidence with the Soret band of the molecule, the optical spectral line shape as determined by reflectance anisotropy spectroscopy exhibits a characteristic, large structure, which changes from a "peaklike" to a "derivative-like" shape at a well-defined thickness (8-10 monolayers). We interpret this result in the framework of electronic effects due to structural changes in the layers, yielding solid-state effects originating from the coupling of the π orbitals of the porphyrin macrocycles.