Alessandra Paladini | Consiglio Nazionale delle Ricerche (CNR) (original) (raw)
Papers by Alessandra Paladini
Laser & Photonics Reviews, 2021
The study of nonthermal electrons, generated upon photoexcitation of plasmonic nanostructures, pl... more The study of nonthermal electrons, generated upon photoexcitation of plasmonic nanostructures, plays a key role in a variety of contexts, from photocatalysis and energy conversion to photodetection and nonlinear optics. Their ultrafast relaxation and subsequent release of energy to a low energy distribution of thermalized hot electrons has been the subject of a myriad of papers, mostly based on femtosecond transient absorption spectroscopy (FTAS). However, the FTAS signal stems from a complex interplay of di↵erent contributions arising from both nonthermal and thermal electrons, making the disentanglement of the two a very challenging task, so far accomplished only in terms of numerical simulations. Here a combined approach is introduced, based on a post-processing of the FTAS measurements guided by a reduced semiclassical model, the so-called Extended Two-Temperature Model, which has allowed the purely nonthermal contribution to the pump-probe experimental map recorded for 2D arrays of gold nanoellipsoids to be isolated. This approach displays the intimate correlation between electron energy and probe photon energy on the ultrafast timescale of electron thermalization. It also sheds new light on the ultrafast transient optical response of gold nanostructures, and will help the development of optimized plasmonic configurations for nonthermal electrons generation and harvesting.
Nanoscale, 2019
LSPRs in Ag nanoparticles decay through a highly efficient charge injection into the 4f levels of... more LSPRs in Ag nanoparticles decay through a highly efficient charge injection into the 4f levels of the cerium oxide matrix.
Advanced Functional Materials, 2018
The insertion of a DNA nano-layer into polymer based solar cells, between the Electron Transport ... more The insertion of a DNA nano-layer into polymer based solar cells, between the Electron Transport Layer (ETL) and the active material, is proposed to improve the charge separation eciency. Complete bulk heterojunction donor-acceptor solar cells of the layered type Glass/Electrode (ITO)/ETL/ P3HT:PC 70 BM /hole transport layer/Electrode (Ag) are investigated using femtosecond transient absorption spectroscopy both in the NIR and the UV-Vis regions of the spectrum. By varying the composition of the ETL we observe a change in the spectral and temporal response of the transient absorption
Journal of Archaeological Science: Reports, 2016
A multidisciplinary approach has been used to investigate painted plasters coming from a Roman vi... more A multidisciplinary approach has been used to investigate painted plasters coming from a Roman villa in Ponti Novi (Sabina area, Rieti, Lazio, Italy): both the plasters and the pigments have been analyzed by different techniques. In particular, optical microscopy, colorimetry, X-ray diffraction, chemical and granulometric analysis, have been performed on the opus arenatum layers of the plasters, while X-ray diffraction and μ-Raman spectroscopy have provided information on the pigments. Paleopalynological and opal analysis have also performed on the silt component of the mortar. The presence of clear imprints of incannucciata on the first preparatory layer of the plaster has been also observed on the larger part of the investigated samples. The experimental results have allowed to obtain interesting information on the materials and techniques used for the realization of the plasters and paints.
The excitation of plasmonic nanoparticles by ultrashort laser pulses sets in motion a complex ult... more The excitation of plasmonic nanoparticles by ultrashort laser pulses sets in motion a complex ultrafast relaxation process involving the gradual re-equilibration of the system's electron gas, lattice and environment. One of the major hurdles in studying these processes is the lack of direct measurements of the dynamic temperature evolution
Faraday Discussions, 2012
By exploiting the potentialities of a recently implemented grid empowered molecular simulator bas... more By exploiting the potentialities of a recently implemented grid empowered molecular simulator based on the combination of collaborative interoperable service oriented computing and the usage of high performance - high throughput technologies, the results of crossed molecular beam experiments have been virtually simulated and compared with the real (measured) laboratory data for the reactive system OH + CO. The direct comparison of theoretically predicted laboratory angular distributions with experimental raw data avoids possible uncertainties associated with the analysis of crossed beam experiments, in which trial centre-of-mass functions are tested until the best-fit of the experimental data is achieved. To make such a comparison as accurate as possible, the rotational distributions of the OH radicals employed in previous crossed beam experiments have been characterized by laser-induced-fluorescence. The capability of performing massive calculations using grid-distributed technologies has allowed the running of quasiclassical trajectory calculations for all the initial rotational states of the OH radicals present in the beam (from the ground rotational state N(OH) = 1 up to N(OH) = 10) on three different potential energy surfaces and the comparison of related outcomes.
Photochemical & Photobiological Sciences
Zn–salophen complexes are a promising class of fluorescent chemosensors for nucleotides and nucle... more Zn–salophen complexes are a promising class of fluorescent chemosensors for nucleotides and nucleic acids. We have investigated, by means of steady state UV–Vis, ultrafast transient absorption, fluorescence emission and time dependent density functional theory (TD-DFT) the behavior of the excited states of a salicylidene tetradentate Schiff base (Sal), its Zn(II) coordination compound (Zn–Sal) and the effect of the interaction between Zn–Sal and adenosine diphosphate (ADP). TD-DFT shows that the deactivation of the excited state of Sal occurs through torsional motion, due to its rotatable bonds and twistable angles. Complexation with Zn(II) causes rigidity so that the geometry changes in the excited states with respect to the ground state structure are minimal. By addition of ADP to a freshly prepared Zn–Sal ethanol solution, a longer relaxation constant, in comparison to Zn–Sal, was measured, indicative of the interaction between Zn–Sal and ADP. After a few days, the Zn–Sal–ADP sol...
Energies, 2021
Ultrafast pump-probe spectroscopies have proved to be an important tool for the investigation of ... more Ultrafast pump-probe spectroscopies have proved to be an important tool for the investigation of charge carriers dynamics in perovskite materials providing crucial information on the dynamics of the excited carriers, and fundamental in the development of new devices with tailored photovoltaic properties. Fast transient absorbance spectroscopy on mixed-cation hybrid lead halide perovskite samples was used to investigate how the dimensions and the morphology of the perovskite crystals embedded in the capping (large crystals) and mesoporous (small crystals) layers affect the hot-carrier dynamics in the first hundreds of femtoseconds as a function of the excitation energy. The comparative study between samples with perovskite deposited on substrates with and without the mesoporous layer has shown how the small crystals preserve the temperature of the carriers for a longer period after the excitation than the large crystals. This study showed how the high sensitivity of the time-resolved...
Physical chemistry chemical physics : PCCP, 2021
It is important, but challenging, to measure the (photo)induced switching of molecules in differe... more It is important, but challenging, to measure the (photo)induced switching of molecules in different chemical environments, from solution through thin layers to solid bulk crystals. We compare the cis-trans conformational switching of commercial azobenzene molecules in different liquid and solid environments: polar solutions, liquid polymers, 2D nanostructures and 3D crystals. We achieve this goal by using complementary techniques: optical absorption spectroscopy, femtosecond transient absorption spectroscopy, Kelvin probe force microscopy and reflectance spectroscopy, supported by density functional theory calculations. We could observe the same molecule showing fast switching in a few picoseconds, when studied as an isolated molecule in water, or slow switching in tens of minutes, when assembled in 3D crystals. It is worth noting that we could also observe switching for small ensembles of molecules (a few attomoles), representing an intermediate case between single molecules and bu...
Advanced Optical Materials, 2021
Noble metal nanoparticles exhibit localized plasmon resonance modes that span the visible and nea... more Noble metal nanoparticles exhibit localized plasmon resonance modes that span the visible and near‐infrared spectral ranges and have many applications. Modifying the size, shape, and composition of the nanoparticles changes the number of modes and their properties. The characteristics of these modes are transiently affected when illuminating the nano‐objects with ultrashort laser pulses. Here, core–shell gold–silver nanocuboids are synthesized and their spectral signature in the stationary and ultrafast transient regimes are measured. Their dipolar transverse mode vanishes with increasing Ag‐shell thickness, while higher‐order modes grow in the near‐ultraviolet range where no plasmon resonance can be generated with single noble metal nanoparticles. These higher‐energy modes are associated with sharp spectral variations of the ultrafast transient light extinction by the bimetallic nanocuboids. By carrying out a theoretical investigation, the different contributions to this response a...
Plasmonics, 2017
Time-resolved polarization dependent transient absorption has been used to study the plasmonicity... more Time-resolved polarization dependent transient absorption has been used to study the plasmonicity of the optical transitions of Ag nanoparticles and nanoclusters. The lack of a measureable polarization anisotropy in the nanoparticles is indicative of the ultrafast electron-electron scattering while the anisotropy with a depolarization timescale of 500 fs observed in the nanoclusters indicates the excitation of a non-plasmonic state. The short lifetime of the anisotropy is a measure of electronic coupling between nearly degenerate states and is thus proposed as a sensitive measurement of the plasmonic content of the optical transitions of nanoclusters.
Applied Sciences, 2021
This paper presents the synthesis of silver nanoparticles (AgNPs) functionalized with fluorescent... more This paper presents the synthesis of silver nanoparticles (AgNPs) functionalized with fluorescent molecules, in particular with xanthene-based dyes, i.e., fluorescein isothiocyanate (FITC, λmax = 485 nm) and rhodamine B isothiocyanate (RITC, λmax = 555 nm). An in-depth characterization of the particle–dye systems, i.e., AgNPs–RITC and AgNPs–FITC, is presented to evaluate their chemical structure and optical properties due to the interaction between their plasmonic and absorption properties. UV–Vis spectroscopy and the dynamic light scattering (DLS) measurements confirmed the nanosize of the AgNPs–RITC and AgNPs–FITC. Synchrotron radiation X-ray photoelectron spectroscopy (SR-XPS) was used to study the chemical surface functionalization by structural characterization, confirming/examining the isothiocyanate–metal interaction. For AgNPs–RITC, in which the plasmonic and fluorescence peak are not superimposed, the transient dynamics of the dye fluorescence were also studied. Transient a...
Nanotechnology, 2020
The knowledge of the carrier dynamics in nanostructures is of fundamental importance for the deve... more The knowledge of the carrier dynamics in nanostructures is of fundamental importance for the development of (opto)electronic devices. This is true for semiconducting nanostructures as well as for plasmonic nanoparticles (NPs). Indeed, improvement of photocatalytic efficiencies by combining semiconductor and plasmonic nanostructures is one of the reasons why their ultrafast dynamics are intensively studied. In this work, we will review our activity on ultrafast spectroscopy in nanostructures carried out in the recently established EuroFEL Support Laboratory. We have investigated the dynamical plasmonic responses of metal NPs both in solution and in 2D and 3D arrays on surfaces, with particular attention being paid to the effects of the NP shape and to the conversion of absorbed light into heat on a nano-localized scale. We will summarize the results obtained on the carrier dynamics in nanostructured perovskites with emphasis on the hot-carrier dynamics and in semiconductor nanosystem...
Journal of Nanoscience and Nanotechnology, 2020
Upon photoexcitation with a femtosecond laser pulse, the plasmonic resonance of a nanorod can cou... more Upon photoexcitation with a femtosecond laser pulse, the plasmonic resonance of a nanorod can couple with coherent vibrational modes generating a regular oscillating pattern in the transient absorbance of the nanostructure. The dynamics of the plasmon resonances of these materials are probed through femtosecond transient absorption spectroscopy in the spectral region between 400 nm and 1600 nm. Whereas in the visible range the spectra are comparable with the findings reported in the literature, the analysis of the transient NIR spectra revealed that their oscillation frequencies vary with wavelength, resulting in a strong distortion of the transient features that can be related to the specific lengths distribution of the nanorods contained in the sample. These findings suggest that in the design of efficient and highly sensitive gold-nanorod based plasmonic sensors a narrow size distribution of nanostructures is required.
Nanotechnology, 2019
We present femtosecond transient transmission (or absorbance) measurements in silicon nanowires i... more We present femtosecond transient transmission (or absorbance) measurements in silicon nanowires in the energy range 1.1-3.5 eV, from below the indirect band-gap to above the direct band-gap. Our pumpprobe measurements allow us to give a complete picture of the carrier dynamics in silicon. In this way we perform an experimental study with a spectral completeness that lacks in the whole literature on carrier dynamics in silicon. A particular emphasis is given to the dynamics of the transient absorbance at the energies relative to the direct band gap at 3.3 eV. Indeed, the use of pump energies below and above 3.3 eV allowed us to disentangle the dynamics of electrons and holes in their respective bands. The band gap renormalization of the direct band gap is also investigated for different pump energies. A critical discussion is given on the results below 3.3 eV where phonon-assisted processes are required in the optical transitions.
The Journal of Physical Chemistry Letters, 2018
In this work we show how to control the morphology of femtosecond laser melted gold nanosphere ag... more In this work we show how to control the morphology of femtosecond laser melted gold nanosphere aggregates. A careful choice of both laser uence and wavelength makes it possible to selectively excite dierent aggregate substructures to produce larger spherical nanoparticles, nanorods and nanoprisms or necklace-like 1D nanostructures in which the nanoparticles are interlinked by bridges. Finite integral technique calculations have been performed on the near-eld concentration of light in the nanostructures which conrm the wavelength dependence of the light concentration and suggest that the resulting localized high intensities lead to non-thermal melting. We show that by tuning the wavelength of the melting light it is possible to choose the spatial extension of the ensembles of NPs heated thus allowing us to exhibit control over the morphology of the nanostructures formed by the melting process. By a proper combination of this method with self assembly of chemically synthesized nanoparticles, one can envisage the development of an innovative high-throughput high-resolution nanofabrication technique.
Advanced Functional Materials, 2018
Journal of colloid and interface science, Jan 4, 2017
Gold nanoparticles with an average diameter of 10 nm, functionalized by the dye molecule rhodamin... more Gold nanoparticles with an average diameter of 10 nm, functionalized by the dye molecule rhodamine B isothiocyanate, have been synthesized. The resulting material has been extensively characterized both chemically, to investigate the bonding between the dye molecules and the nanoparticles, and physically, to understand the details of the aggregation induced by interaction between dye molecules on different nanoparticles. The plasmonic response of the system has been further characterized by measurement and theoretical simulation of the static UV-Vis extinction spectra of the aggregates produced following different synthesis procedures. The model parameters used in the simulation gave further useful information on the aggregation and its relationship to the plasmonic response. Finally, we investigated the time dependence of the plasmonic effects of the nanoparticles and fluorescence of the dye molecule using an ultrafast pump-probe optical method. By modulating the quantity of dye mo...
Laser & Photonics Reviews, 2021
The study of nonthermal electrons, generated upon photoexcitation of plasmonic nanostructures, pl... more The study of nonthermal electrons, generated upon photoexcitation of plasmonic nanostructures, plays a key role in a variety of contexts, from photocatalysis and energy conversion to photodetection and nonlinear optics. Their ultrafast relaxation and subsequent release of energy to a low energy distribution of thermalized hot electrons has been the subject of a myriad of papers, mostly based on femtosecond transient absorption spectroscopy (FTAS). However, the FTAS signal stems from a complex interplay of di↵erent contributions arising from both nonthermal and thermal electrons, making the disentanglement of the two a very challenging task, so far accomplished only in terms of numerical simulations. Here a combined approach is introduced, based on a post-processing of the FTAS measurements guided by a reduced semiclassical model, the so-called Extended Two-Temperature Model, which has allowed the purely nonthermal contribution to the pump-probe experimental map recorded for 2D arrays of gold nanoellipsoids to be isolated. This approach displays the intimate correlation between electron energy and probe photon energy on the ultrafast timescale of electron thermalization. It also sheds new light on the ultrafast transient optical response of gold nanostructures, and will help the development of optimized plasmonic configurations for nonthermal electrons generation and harvesting.
Nanoscale, 2019
LSPRs in Ag nanoparticles decay through a highly efficient charge injection into the 4f levels of... more LSPRs in Ag nanoparticles decay through a highly efficient charge injection into the 4f levels of the cerium oxide matrix.
Advanced Functional Materials, 2018
The insertion of a DNA nano-layer into polymer based solar cells, between the Electron Transport ... more The insertion of a DNA nano-layer into polymer based solar cells, between the Electron Transport Layer (ETL) and the active material, is proposed to improve the charge separation eciency. Complete bulk heterojunction donor-acceptor solar cells of the layered type Glass/Electrode (ITO)/ETL/ P3HT:PC 70 BM /hole transport layer/Electrode (Ag) are investigated using femtosecond transient absorption spectroscopy both in the NIR and the UV-Vis regions of the spectrum. By varying the composition of the ETL we observe a change in the spectral and temporal response of the transient absorption
Journal of Archaeological Science: Reports, 2016
A multidisciplinary approach has been used to investigate painted plasters coming from a Roman vi... more A multidisciplinary approach has been used to investigate painted plasters coming from a Roman villa in Ponti Novi (Sabina area, Rieti, Lazio, Italy): both the plasters and the pigments have been analyzed by different techniques. In particular, optical microscopy, colorimetry, X-ray diffraction, chemical and granulometric analysis, have been performed on the opus arenatum layers of the plasters, while X-ray diffraction and μ-Raman spectroscopy have provided information on the pigments. Paleopalynological and opal analysis have also performed on the silt component of the mortar. The presence of clear imprints of incannucciata on the first preparatory layer of the plaster has been also observed on the larger part of the investigated samples. The experimental results have allowed to obtain interesting information on the materials and techniques used for the realization of the plasters and paints.
The excitation of plasmonic nanoparticles by ultrashort laser pulses sets in motion a complex ult... more The excitation of plasmonic nanoparticles by ultrashort laser pulses sets in motion a complex ultrafast relaxation process involving the gradual re-equilibration of the system's electron gas, lattice and environment. One of the major hurdles in studying these processes is the lack of direct measurements of the dynamic temperature evolution
Faraday Discussions, 2012
By exploiting the potentialities of a recently implemented grid empowered molecular simulator bas... more By exploiting the potentialities of a recently implemented grid empowered molecular simulator based on the combination of collaborative interoperable service oriented computing and the usage of high performance - high throughput technologies, the results of crossed molecular beam experiments have been virtually simulated and compared with the real (measured) laboratory data for the reactive system OH + CO. The direct comparison of theoretically predicted laboratory angular distributions with experimental raw data avoids possible uncertainties associated with the analysis of crossed beam experiments, in which trial centre-of-mass functions are tested until the best-fit of the experimental data is achieved. To make such a comparison as accurate as possible, the rotational distributions of the OH radicals employed in previous crossed beam experiments have been characterized by laser-induced-fluorescence. The capability of performing massive calculations using grid-distributed technologies has allowed the running of quasiclassical trajectory calculations for all the initial rotational states of the OH radicals present in the beam (from the ground rotational state N(OH) = 1 up to N(OH) = 10) on three different potential energy surfaces and the comparison of related outcomes.
Photochemical & Photobiological Sciences
Zn–salophen complexes are a promising class of fluorescent chemosensors for nucleotides and nucle... more Zn–salophen complexes are a promising class of fluorescent chemosensors for nucleotides and nucleic acids. We have investigated, by means of steady state UV–Vis, ultrafast transient absorption, fluorescence emission and time dependent density functional theory (TD-DFT) the behavior of the excited states of a salicylidene tetradentate Schiff base (Sal), its Zn(II) coordination compound (Zn–Sal) and the effect of the interaction between Zn–Sal and adenosine diphosphate (ADP). TD-DFT shows that the deactivation of the excited state of Sal occurs through torsional motion, due to its rotatable bonds and twistable angles. Complexation with Zn(II) causes rigidity so that the geometry changes in the excited states with respect to the ground state structure are minimal. By addition of ADP to a freshly prepared Zn–Sal ethanol solution, a longer relaxation constant, in comparison to Zn–Sal, was measured, indicative of the interaction between Zn–Sal and ADP. After a few days, the Zn–Sal–ADP sol...
Energies, 2021
Ultrafast pump-probe spectroscopies have proved to be an important tool for the investigation of ... more Ultrafast pump-probe spectroscopies have proved to be an important tool for the investigation of charge carriers dynamics in perovskite materials providing crucial information on the dynamics of the excited carriers, and fundamental in the development of new devices with tailored photovoltaic properties. Fast transient absorbance spectroscopy on mixed-cation hybrid lead halide perovskite samples was used to investigate how the dimensions and the morphology of the perovskite crystals embedded in the capping (large crystals) and mesoporous (small crystals) layers affect the hot-carrier dynamics in the first hundreds of femtoseconds as a function of the excitation energy. The comparative study between samples with perovskite deposited on substrates with and without the mesoporous layer has shown how the small crystals preserve the temperature of the carriers for a longer period after the excitation than the large crystals. This study showed how the high sensitivity of the time-resolved...
Physical chemistry chemical physics : PCCP, 2021
It is important, but challenging, to measure the (photo)induced switching of molecules in differe... more It is important, but challenging, to measure the (photo)induced switching of molecules in different chemical environments, from solution through thin layers to solid bulk crystals. We compare the cis-trans conformational switching of commercial azobenzene molecules in different liquid and solid environments: polar solutions, liquid polymers, 2D nanostructures and 3D crystals. We achieve this goal by using complementary techniques: optical absorption spectroscopy, femtosecond transient absorption spectroscopy, Kelvin probe force microscopy and reflectance spectroscopy, supported by density functional theory calculations. We could observe the same molecule showing fast switching in a few picoseconds, when studied as an isolated molecule in water, or slow switching in tens of minutes, when assembled in 3D crystals. It is worth noting that we could also observe switching for small ensembles of molecules (a few attomoles), representing an intermediate case between single molecules and bu...
Advanced Optical Materials, 2021
Noble metal nanoparticles exhibit localized plasmon resonance modes that span the visible and nea... more Noble metal nanoparticles exhibit localized plasmon resonance modes that span the visible and near‐infrared spectral ranges and have many applications. Modifying the size, shape, and composition of the nanoparticles changes the number of modes and their properties. The characteristics of these modes are transiently affected when illuminating the nano‐objects with ultrashort laser pulses. Here, core–shell gold–silver nanocuboids are synthesized and their spectral signature in the stationary and ultrafast transient regimes are measured. Their dipolar transverse mode vanishes with increasing Ag‐shell thickness, while higher‐order modes grow in the near‐ultraviolet range where no plasmon resonance can be generated with single noble metal nanoparticles. These higher‐energy modes are associated with sharp spectral variations of the ultrafast transient light extinction by the bimetallic nanocuboids. By carrying out a theoretical investigation, the different contributions to this response a...
Plasmonics, 2017
Time-resolved polarization dependent transient absorption has been used to study the plasmonicity... more Time-resolved polarization dependent transient absorption has been used to study the plasmonicity of the optical transitions of Ag nanoparticles and nanoclusters. The lack of a measureable polarization anisotropy in the nanoparticles is indicative of the ultrafast electron-electron scattering while the anisotropy with a depolarization timescale of 500 fs observed in the nanoclusters indicates the excitation of a non-plasmonic state. The short lifetime of the anisotropy is a measure of electronic coupling between nearly degenerate states and is thus proposed as a sensitive measurement of the plasmonic content of the optical transitions of nanoclusters.
Applied Sciences, 2021
This paper presents the synthesis of silver nanoparticles (AgNPs) functionalized with fluorescent... more This paper presents the synthesis of silver nanoparticles (AgNPs) functionalized with fluorescent molecules, in particular with xanthene-based dyes, i.e., fluorescein isothiocyanate (FITC, λmax = 485 nm) and rhodamine B isothiocyanate (RITC, λmax = 555 nm). An in-depth characterization of the particle–dye systems, i.e., AgNPs–RITC and AgNPs–FITC, is presented to evaluate their chemical structure and optical properties due to the interaction between their plasmonic and absorption properties. UV–Vis spectroscopy and the dynamic light scattering (DLS) measurements confirmed the nanosize of the AgNPs–RITC and AgNPs–FITC. Synchrotron radiation X-ray photoelectron spectroscopy (SR-XPS) was used to study the chemical surface functionalization by structural characterization, confirming/examining the isothiocyanate–metal interaction. For AgNPs–RITC, in which the plasmonic and fluorescence peak are not superimposed, the transient dynamics of the dye fluorescence were also studied. Transient a...
Nanotechnology, 2020
The knowledge of the carrier dynamics in nanostructures is of fundamental importance for the deve... more The knowledge of the carrier dynamics in nanostructures is of fundamental importance for the development of (opto)electronic devices. This is true for semiconducting nanostructures as well as for plasmonic nanoparticles (NPs). Indeed, improvement of photocatalytic efficiencies by combining semiconductor and plasmonic nanostructures is one of the reasons why their ultrafast dynamics are intensively studied. In this work, we will review our activity on ultrafast spectroscopy in nanostructures carried out in the recently established EuroFEL Support Laboratory. We have investigated the dynamical plasmonic responses of metal NPs both in solution and in 2D and 3D arrays on surfaces, with particular attention being paid to the effects of the NP shape and to the conversion of absorbed light into heat on a nano-localized scale. We will summarize the results obtained on the carrier dynamics in nanostructured perovskites with emphasis on the hot-carrier dynamics and in semiconductor nanosystem...
Journal of Nanoscience and Nanotechnology, 2020
Upon photoexcitation with a femtosecond laser pulse, the plasmonic resonance of a nanorod can cou... more Upon photoexcitation with a femtosecond laser pulse, the plasmonic resonance of a nanorod can couple with coherent vibrational modes generating a regular oscillating pattern in the transient absorbance of the nanostructure. The dynamics of the plasmon resonances of these materials are probed through femtosecond transient absorption spectroscopy in the spectral region between 400 nm and 1600 nm. Whereas in the visible range the spectra are comparable with the findings reported in the literature, the analysis of the transient NIR spectra revealed that their oscillation frequencies vary with wavelength, resulting in a strong distortion of the transient features that can be related to the specific lengths distribution of the nanorods contained in the sample. These findings suggest that in the design of efficient and highly sensitive gold-nanorod based plasmonic sensors a narrow size distribution of nanostructures is required.
Nanotechnology, 2019
We present femtosecond transient transmission (or absorbance) measurements in silicon nanowires i... more We present femtosecond transient transmission (or absorbance) measurements in silicon nanowires in the energy range 1.1-3.5 eV, from below the indirect band-gap to above the direct band-gap. Our pumpprobe measurements allow us to give a complete picture of the carrier dynamics in silicon. In this way we perform an experimental study with a spectral completeness that lacks in the whole literature on carrier dynamics in silicon. A particular emphasis is given to the dynamics of the transient absorbance at the energies relative to the direct band gap at 3.3 eV. Indeed, the use of pump energies below and above 3.3 eV allowed us to disentangle the dynamics of electrons and holes in their respective bands. The band gap renormalization of the direct band gap is also investigated for different pump energies. A critical discussion is given on the results below 3.3 eV where phonon-assisted processes are required in the optical transitions.
The Journal of Physical Chemistry Letters, 2018
In this work we show how to control the morphology of femtosecond laser melted gold nanosphere ag... more In this work we show how to control the morphology of femtosecond laser melted gold nanosphere aggregates. A careful choice of both laser uence and wavelength makes it possible to selectively excite dierent aggregate substructures to produce larger spherical nanoparticles, nanorods and nanoprisms or necklace-like 1D nanostructures in which the nanoparticles are interlinked by bridges. Finite integral technique calculations have been performed on the near-eld concentration of light in the nanostructures which conrm the wavelength dependence of the light concentration and suggest that the resulting localized high intensities lead to non-thermal melting. We show that by tuning the wavelength of the melting light it is possible to choose the spatial extension of the ensembles of NPs heated thus allowing us to exhibit control over the morphology of the nanostructures formed by the melting process. By a proper combination of this method with self assembly of chemically synthesized nanoparticles, one can envisage the development of an innovative high-throughput high-resolution nanofabrication technique.
Advanced Functional Materials, 2018
Journal of colloid and interface science, Jan 4, 2017
Gold nanoparticles with an average diameter of 10 nm, functionalized by the dye molecule rhodamin... more Gold nanoparticles with an average diameter of 10 nm, functionalized by the dye molecule rhodamine B isothiocyanate, have been synthesized. The resulting material has been extensively characterized both chemically, to investigate the bonding between the dye molecules and the nanoparticles, and physically, to understand the details of the aggregation induced by interaction between dye molecules on different nanoparticles. The plasmonic response of the system has been further characterized by measurement and theoretical simulation of the static UV-Vis extinction spectra of the aggregates produced following different synthesis procedures. The model parameters used in the simulation gave further useful information on the aggregation and its relationship to the plasmonic response. Finally, we investigated the time dependence of the plasmonic effects of the nanoparticles and fluorescence of the dye molecule using an ultrafast pump-probe optical method. By modulating the quantity of dye mo...