Michele Ortolani | Università degli Studi "La Sapienza" di Roma (original) (raw)

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Papers by Michele Ortolani

Research paper thumbnail of Infrared Nanospectroscopy of Individual Extracellular Microvesicles

Molecules

Extracellular vesicles are membrane-delimited structures, involved in several inter-cellular comm... more Extracellular vesicles are membrane-delimited structures, involved in several inter-cellular communication processes, both physiological and pathological, since they deliver complex biological cargo. Extracellular vesicles have been identified as possible biomarkers of several pathological diseases; thus, their characterization is fundamental in order to gain a deep understanding of their function and of the related processes. Traditional approaches for the characterization of the molecular content of the vesicles require a large quantity of sample, thereby providing an average molecular profile, while their heterogeneity is typically probed by non-optical microscopies that, however, lack the chemical sensitivity to provide information of the molecular cargo. Here, we perform a study of individual microvesicles, a subclass of extracellular vesicles generated by the outward budding of the plasma membrane, released by two cultures of glial cells under different stimuli, by applying a ...

Research paper thumbnail of Intersubband Transition Engineering in the Conduction Band of Asymmetric Coupled Ge/SiGe Quantum Wells

Crystals

n-type Ge/SiGe asymmetric coupled quantum wells represent the building block of a variety of nano... more n-type Ge/SiGe asymmetric coupled quantum wells represent the building block of a variety of nanoscale quantum devices, including recently proposed designs for a silicon-based THz quantum cascade laser. In this paper, we combine structural and spectroscopic experiments on 20-module superstructures, each featuring two Ge wells coupled through a Ge-rich SiGe tunnel barrier, as a function of the geometry parameters of the design and the P dopant concentration. Through a comparison of THz spectroscopic data with numerical calculations of intersubband optical absorption resonances, we demonstrated that it is possible to tune, by design, the energy and the spatial overlap of quantum confined subbands in the conduction band of the heterostructures. The high structural/interface quality of the samples and the control achieved on subband hybridization are promising starting points towards a working electrically pumped light-emitting device.

Research paper thumbnail of Cross-Correlation of THz Pulses from the Electron Storage Ring BESSY II

Condensed Matter

Coherent synchrotron radiation from an electron storage ring is observed in the THz spectral rang... more Coherent synchrotron radiation from an electron storage ring is observed in the THz spectral range when the bunch length is shortened down to the sub-mm-range. With increasing stored current, the bunch becomes longitudinally unstable and modulates the THz emission in the time domain. These micro-instabilities are investigated at the electron storage ring BESSY II by means of cross-correlation of the THz fields from successive bunches. The investigations allow deriving the longitudinal length scale of the micro bunch fluctuations and show that it grows faster than the current-dependent bunch length. Our findings will help to set the limits for the possible time resolution for pump-probe experiments achieved with coherent THz synchrotron radiation from a storage ring.

Research paper thumbnail of Electron Population Dynamics in Optically Pumped Asymmetric Coupled Ge/SiGe Quantum Wells: Experiment and Models

Photonics

n-type doped Ge quantum wells with SiGe barriers represent a promising heterostructure system for... more n-type doped Ge quantum wells with SiGe barriers represent a promising heterostructure system for the development of radiation emitters in the terahertz range such as electrically pumped quantum cascade lasers and optically pumped quantum fountain lasers. The nonpolar lattice of Ge and SiGe provides electron–phonon scattering rates that are one order of magnitude lower than polar GaAs. We have developed a self-consistent numerical energy-balance model based on a rate equation approach which includes inelastic and elastic inter- and intra-subband scattering events and takes into account a realistic two-dimensional electron gas distribution in all the subband states of the Ge/SiGe quantum wells by considering subband-dependent electronic temperatures and chemical potentials. This full-subband model is compared here to the standard discrete-energy-level model, in which the material parameters are limited to few input values (scattering rates and radiative cross sections). To provide an...

Research paper thumbnail of N-Type Heavy Doping with Ultralow Resistivity in Ge by Sb Deposition and Pulsed Laser Melting

Research paper thumbnail of Infrared Spectroscopy of the Topological Surface States of Bi2Se3 by Use of the Berreman Effect

Research paper thumbnail of n-type Ge/SiGe Multi Quantum-Wells for a THz Quantum Cascade Laser

Research paper thumbnail of Out-of-Equilibrium Collective Oscillation as Phonon Condensation in a Model Protein

Research paper thumbnail of Fractal-Like Plasmonic Metamaterial with a Tailorable Plasma Frequency in the near-Infrared

Research paper thumbnail of Nanoscale thermal gradients activated by antenna-enhanced molecular absorption in the mid-infrared

Applied Physics Letters

We investigate local heat generation by molecules at the apex of polymer-embedded vertical antenn... more We investigate local heat generation by molecules at the apex of polymer-embedded vertical antennas excited at resonant midinfrared wavelengths, exploiting the surface enhanced infrared absorption effect. The embedding of vertical nanoantennas in a non-absorbing polymer creates thermal isolation between the apical hotspot and the heat sink represented by the substrate. Vibrational mid-infrared absorption by strongly absorbing molecules located at the antenna apex then generates nanoscale temperature gradients at the surface.We imaged the thermal gradients by using a nano-photothermal expansion microscope, and we found values up to 10K/lm in conditions where the radiation wavelength resonates with both the molecule vibrations and the plasmonic mode of the antennas. Values up to 1000 K/lm can be foreseen at maximum quantum cascade laser power. The presented system provides a promising thermoplasmonic platform for antenna-assisted thermophoresis and resonant mid-infrared photocatalysis.

Research paper thumbnail of Near-Field Imaging of Free Carriers in ZnO Nanowires with a Scanning Probe Tip Made of Heavily Doped Germanium

Research paper thumbnail of Heterogeneity of the Transmembrane Protein Conformation in Purple Membranes Identified by Infrared Nanospectroscopy

Small (Weinheim an der Bergstrasse, Germany), 2017

Cell membranes are intrinsically heterogeneous, as the local protein and lipid distribution is cr... more Cell membranes are intrinsically heterogeneous, as the local protein and lipid distribution is critical to physiological processes. Even in template systems embedding a single protein type, like purple membranes, there can be a different local response to external stimuli or environmental factors, resulting in heterogeneous conformational changes. Despite the dramatic advances of microspectroscopy techniques, the identification of the conformation heterogeneity is still a challenging task. Tip-enhanced infrared nanospectroscopy is here used to identify conformational changes connected to the hydration state of the transmembrane proteins contained in a 50 nm diameter cell membrane area, without the need for fluorescent labels. In dried purple membrane monolayers, areas with fully hydrated proteins are found among large numbers of molecules with randomly distributed hydration states. Infrared nanospectroscopy results are compared to the spectra obtained with diffraction-limited infrar...

Research paper thumbnail of Development of a THz heterodyne receiver with quantum cascade laser and hot electron bolometer mixer for standoff detection of explosive material

Terahertz Physics, Devices, and Systems III: Advanced Applications in Industry and Defense

ABSTRACT The terahertz (THz) portion of the electromagnetic spectrum provides specific spectrosco... more ABSTRACT The terahertz (THz) portion of the electromagnetic spectrum provides specific spectroscopic information for substance identification. It has been shown that the spectral features of explosive materials might be used for detection and identification at stand-off distances. We report on the development of a THz spectrometer for explosive detection and identification. The system is based on THz quantum cascade lasers working at different frequencies. These are used for illumination of the object under test. The reflected and backscattered radiation from the object under test is detected with a sensitive heterodyne receiver. As a first step a single frequency, liquid-cryogen free heterodyne receiver operating at 2.5 THz has been developed. In order to realize maximum sensitivity a phonon-cooled NbN hot electron bolometric mixer with a quantum cascade laser as local oscillator were chosen. The concept of the system and first results will be presented.

Research paper thumbnail of Loading the Antenna Gap with Two-Dimensional Electron Gas Transistors: A Versatile Approach for the Rectification of Free-Space Radiation

Research paper thumbnail of Infrared study of a La0.7Sr0.3MnO3-dLa0.7Sr0.3MnO3-d micrometric transistor channel

Research paper thumbnail of Effects of Superconductivity and Charge Order on the sub-Terahertz reflectivity of La$_{1.875}$Ba$_{0.125-y}$Sr$_{y}$CuO$_4$

Research paper thumbnail of Topologically protected Dirac plasmons and their evolution across the quantum phase transition in a (Bi 1−x In x ) 2 Se 3 topological insulator

Nanoscale, 2016

We report on the plasmonic behavior across the quantum-phase transition among a Topological Insul... more We report on the plasmonic behavior across the quantum-phase transition among a Topological Insulator and a trivial insulator.

Research paper thumbnail of GaN Field Effect Transistors with integrated antennas for THz heterodyne detectors

ABSTRACT We realized GaN based Field Effect Transistors to be used both for direct and heterodyne... more ABSTRACT We realized GaN based Field Effect Transistors to be used both for direct and heterodyne detection of mm wave / THz signals. Polarization-sensitive, planar antennas were designed and integrated on chip. Device were fabricated relying on an industrial III-V platform. Spectral response in the 0.22-0.38 THz range was acquired. An efficient mixing between gate voltage and drain current was shown.

Research paper thumbnail of The ENEA activity on applications with FELs

2009 IEEE International Vacuum Electronics Conference, 2009

Two Free Electron Laser sources have been developed at ENEA-Frascati and are available for a vari... more Two Free Electron Laser sources have been developed at ENEA-Frascati and are available for a variety of applications: a Compact Free Electron Laser (C-FEL) that provides coherent radiation in the frequency range between 90 and 150 GHz, and a second source, FEL-CATS, which utilizes a peculiar radio-frequency structure to generate coherent emission in the range 0.4 to 0.7 THz without

Research paper thumbnail of Superconductivity-Induced Transparency in Terahertz Metamaterials

ACS Photonics, 2014

ABSTRACT A plasmonic analogue of electromagnetically induced transparency is activated and tuned ... more ABSTRACT A plasmonic analogue of electromagnetically induced transparency is activated and tuned in the terahertz (THz) range in asymmetric metamaterials fabricated from high critical temperature (Tc) superconductor thin films. The asymmetric design provides a near-field coupling between a superradiant and a subradiant plasmonic mode, which has been widely tuned through superconductivity and monitored by Fourier transform infrared spectroscopy. The sharp transparency window that appears in the extinction spectrum exhibits a relative modulation up to 50% activated by temperature change. The interplay between ohmic and radiative damping, which can be independently tuned and controlled, allows for engineering the electromagnetically induced transparency of the metamaterial far beyond the current state-of-the-art, which relies on standard metals or low-Tc superconductors.Keywords: superconductivity; electromagnetic-induced transparency; THz; dark mode; Fano resonance; tunable metamaterials

Research paper thumbnail of Infrared Nanospectroscopy of Individual Extracellular Microvesicles

Molecules

Extracellular vesicles are membrane-delimited structures, involved in several inter-cellular comm... more Extracellular vesicles are membrane-delimited structures, involved in several inter-cellular communication processes, both physiological and pathological, since they deliver complex biological cargo. Extracellular vesicles have been identified as possible biomarkers of several pathological diseases; thus, their characterization is fundamental in order to gain a deep understanding of their function and of the related processes. Traditional approaches for the characterization of the molecular content of the vesicles require a large quantity of sample, thereby providing an average molecular profile, while their heterogeneity is typically probed by non-optical microscopies that, however, lack the chemical sensitivity to provide information of the molecular cargo. Here, we perform a study of individual microvesicles, a subclass of extracellular vesicles generated by the outward budding of the plasma membrane, released by two cultures of glial cells under different stimuli, by applying a ...

Research paper thumbnail of Intersubband Transition Engineering in the Conduction Band of Asymmetric Coupled Ge/SiGe Quantum Wells

Crystals

n-type Ge/SiGe asymmetric coupled quantum wells represent the building block of a variety of nano... more n-type Ge/SiGe asymmetric coupled quantum wells represent the building block of a variety of nanoscale quantum devices, including recently proposed designs for a silicon-based THz quantum cascade laser. In this paper, we combine structural and spectroscopic experiments on 20-module superstructures, each featuring two Ge wells coupled through a Ge-rich SiGe tunnel barrier, as a function of the geometry parameters of the design and the P dopant concentration. Through a comparison of THz spectroscopic data with numerical calculations of intersubband optical absorption resonances, we demonstrated that it is possible to tune, by design, the energy and the spatial overlap of quantum confined subbands in the conduction band of the heterostructures. The high structural/interface quality of the samples and the control achieved on subband hybridization are promising starting points towards a working electrically pumped light-emitting device.

Research paper thumbnail of Cross-Correlation of THz Pulses from the Electron Storage Ring BESSY II

Condensed Matter

Coherent synchrotron radiation from an electron storage ring is observed in the THz spectral rang... more Coherent synchrotron radiation from an electron storage ring is observed in the THz spectral range when the bunch length is shortened down to the sub-mm-range. With increasing stored current, the bunch becomes longitudinally unstable and modulates the THz emission in the time domain. These micro-instabilities are investigated at the electron storage ring BESSY II by means of cross-correlation of the THz fields from successive bunches. The investigations allow deriving the longitudinal length scale of the micro bunch fluctuations and show that it grows faster than the current-dependent bunch length. Our findings will help to set the limits for the possible time resolution for pump-probe experiments achieved with coherent THz synchrotron radiation from a storage ring.

Research paper thumbnail of Electron Population Dynamics in Optically Pumped Asymmetric Coupled Ge/SiGe Quantum Wells: Experiment and Models

Photonics

n-type doped Ge quantum wells with SiGe barriers represent a promising heterostructure system for... more n-type doped Ge quantum wells with SiGe barriers represent a promising heterostructure system for the development of radiation emitters in the terahertz range such as electrically pumped quantum cascade lasers and optically pumped quantum fountain lasers. The nonpolar lattice of Ge and SiGe provides electron–phonon scattering rates that are one order of magnitude lower than polar GaAs. We have developed a self-consistent numerical energy-balance model based on a rate equation approach which includes inelastic and elastic inter- and intra-subband scattering events and takes into account a realistic two-dimensional electron gas distribution in all the subband states of the Ge/SiGe quantum wells by considering subband-dependent electronic temperatures and chemical potentials. This full-subband model is compared here to the standard discrete-energy-level model, in which the material parameters are limited to few input values (scattering rates and radiative cross sections). To provide an...

Research paper thumbnail of N-Type Heavy Doping with Ultralow Resistivity in Ge by Sb Deposition and Pulsed Laser Melting

Research paper thumbnail of Infrared Spectroscopy of the Topological Surface States of Bi2Se3 by Use of the Berreman Effect

Research paper thumbnail of n-type Ge/SiGe Multi Quantum-Wells for a THz Quantum Cascade Laser

Research paper thumbnail of Out-of-Equilibrium Collective Oscillation as Phonon Condensation in a Model Protein

Research paper thumbnail of Fractal-Like Plasmonic Metamaterial with a Tailorable Plasma Frequency in the near-Infrared

Research paper thumbnail of Nanoscale thermal gradients activated by antenna-enhanced molecular absorption in the mid-infrared

Applied Physics Letters

We investigate local heat generation by molecules at the apex of polymer-embedded vertical antenn... more We investigate local heat generation by molecules at the apex of polymer-embedded vertical antennas excited at resonant midinfrared wavelengths, exploiting the surface enhanced infrared absorption effect. The embedding of vertical nanoantennas in a non-absorbing polymer creates thermal isolation between the apical hotspot and the heat sink represented by the substrate. Vibrational mid-infrared absorption by strongly absorbing molecules located at the antenna apex then generates nanoscale temperature gradients at the surface.We imaged the thermal gradients by using a nano-photothermal expansion microscope, and we found values up to 10K/lm in conditions where the radiation wavelength resonates with both the molecule vibrations and the plasmonic mode of the antennas. Values up to 1000 K/lm can be foreseen at maximum quantum cascade laser power. The presented system provides a promising thermoplasmonic platform for antenna-assisted thermophoresis and resonant mid-infrared photocatalysis.

Research paper thumbnail of Near-Field Imaging of Free Carriers in ZnO Nanowires with a Scanning Probe Tip Made of Heavily Doped Germanium

Research paper thumbnail of Heterogeneity of the Transmembrane Protein Conformation in Purple Membranes Identified by Infrared Nanospectroscopy

Small (Weinheim an der Bergstrasse, Germany), 2017

Cell membranes are intrinsically heterogeneous, as the local protein and lipid distribution is cr... more Cell membranes are intrinsically heterogeneous, as the local protein and lipid distribution is critical to physiological processes. Even in template systems embedding a single protein type, like purple membranes, there can be a different local response to external stimuli or environmental factors, resulting in heterogeneous conformational changes. Despite the dramatic advances of microspectroscopy techniques, the identification of the conformation heterogeneity is still a challenging task. Tip-enhanced infrared nanospectroscopy is here used to identify conformational changes connected to the hydration state of the transmembrane proteins contained in a 50 nm diameter cell membrane area, without the need for fluorescent labels. In dried purple membrane monolayers, areas with fully hydrated proteins are found among large numbers of molecules with randomly distributed hydration states. Infrared nanospectroscopy results are compared to the spectra obtained with diffraction-limited infrar...

Research paper thumbnail of Development of a THz heterodyne receiver with quantum cascade laser and hot electron bolometer mixer for standoff detection of explosive material

Terahertz Physics, Devices, and Systems III: Advanced Applications in Industry and Defense

ABSTRACT The terahertz (THz) portion of the electromagnetic spectrum provides specific spectrosco... more ABSTRACT The terahertz (THz) portion of the electromagnetic spectrum provides specific spectroscopic information for substance identification. It has been shown that the spectral features of explosive materials might be used for detection and identification at stand-off distances. We report on the development of a THz spectrometer for explosive detection and identification. The system is based on THz quantum cascade lasers working at different frequencies. These are used for illumination of the object under test. The reflected and backscattered radiation from the object under test is detected with a sensitive heterodyne receiver. As a first step a single frequency, liquid-cryogen free heterodyne receiver operating at 2.5 THz has been developed. In order to realize maximum sensitivity a phonon-cooled NbN hot electron bolometric mixer with a quantum cascade laser as local oscillator were chosen. The concept of the system and first results will be presented.

Research paper thumbnail of Loading the Antenna Gap with Two-Dimensional Electron Gas Transistors: A Versatile Approach for the Rectification of Free-Space Radiation

Research paper thumbnail of Infrared study of a La0.7Sr0.3MnO3-dLa0.7Sr0.3MnO3-d micrometric transistor channel

Research paper thumbnail of Effects of Superconductivity and Charge Order on the sub-Terahertz reflectivity of La$_{1.875}$Ba$_{0.125-y}$Sr$_{y}$CuO$_4$

Research paper thumbnail of Topologically protected Dirac plasmons and their evolution across the quantum phase transition in a (Bi 1−x In x ) 2 Se 3 topological insulator

Nanoscale, 2016

We report on the plasmonic behavior across the quantum-phase transition among a Topological Insul... more We report on the plasmonic behavior across the quantum-phase transition among a Topological Insulator and a trivial insulator.

Research paper thumbnail of GaN Field Effect Transistors with integrated antennas for THz heterodyne detectors

ABSTRACT We realized GaN based Field Effect Transistors to be used both for direct and heterodyne... more ABSTRACT We realized GaN based Field Effect Transistors to be used both for direct and heterodyne detection of mm wave / THz signals. Polarization-sensitive, planar antennas were designed and integrated on chip. Device were fabricated relying on an industrial III-V platform. Spectral response in the 0.22-0.38 THz range was acquired. An efficient mixing between gate voltage and drain current was shown.

Research paper thumbnail of The ENEA activity on applications with FELs

2009 IEEE International Vacuum Electronics Conference, 2009

Two Free Electron Laser sources have been developed at ENEA-Frascati and are available for a vari... more Two Free Electron Laser sources have been developed at ENEA-Frascati and are available for a variety of applications: a Compact Free Electron Laser (C-FEL) that provides coherent radiation in the frequency range between 90 and 150 GHz, and a second source, FEL-CATS, which utilizes a peculiar radio-frequency structure to generate coherent emission in the range 0.4 to 0.7 THz without

Research paper thumbnail of Superconductivity-Induced Transparency in Terahertz Metamaterials

ACS Photonics, 2014

ABSTRACT A plasmonic analogue of electromagnetically induced transparency is activated and tuned ... more ABSTRACT A plasmonic analogue of electromagnetically induced transparency is activated and tuned in the terahertz (THz) range in asymmetric metamaterials fabricated from high critical temperature (Tc) superconductor thin films. The asymmetric design provides a near-field coupling between a superradiant and a subradiant plasmonic mode, which has been widely tuned through superconductivity and monitored by Fourier transform infrared spectroscopy. The sharp transparency window that appears in the extinction spectrum exhibits a relative modulation up to 50% activated by temperature change. The interplay between ohmic and radiative damping, which can be independently tuned and controlled, allows for engineering the electromagnetically induced transparency of the metamaterial far beyond the current state-of-the-art, which relies on standard metals or low-Tc superconductors.Keywords: superconductivity; electromagnetic-induced transparency; THz; dark mode; Fano resonance; tunable metamaterials