Salvatore Bagiante - Academia.edu (original) (raw)

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Papers by Salvatore Bagiante

2023 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)

Nano Letters, 2022

Judiciously designed two-dimensional THz metamaterials consisting of resonant metallic structures... more Judiciously designed two-dimensional THz metamaterials consisting of resonant metallic structures embedded in a dielectric environment locally enhance the electromagnetic field of an incident THz pulse to values sufficiently high to cause nonlinear responses of the environment. In semiconductors, the response is attributed to nonlinear transport phenomena via intervalley scattering, impact ionization, or interband tunneling and can affect the resonant behavior of the metallic structure, which results, for instance, in mode switching. However, details of mode switching, especially time scales, are still debated. By using metallic split-ring resonators with nm-size gaps on intrinsic semiconductors with different bandgaps, we identify the most relevant carrier generation processes. In addition, by combining nonlinear THz time-domain spectroscopy with simulations, we establish the fastest time constant for mode switching to around hundred femtoseconds. Our results not only elucidate dominant carrier generation mechanisms and dynamics but also pave the route toward optically driven modulators with THz bandwidth.

Journal of Applied Physics, 2011

The stacking of Fresnel zone plates is a known method for the production of highly efficient zone... more The stacking of Fresnel zone plates is a known method for the production of highly efficient zone plate optics [1]. However, positioning of the zone plates requires a mechanical setup or permanent gluing to keep their alignment within a fraction of the smallest zone width. We present a novel approach for the production of double sided zone plates by patterning both the front and the back side of the same support membrane to significantly increase the efficiency. The two zone plates on the same membrane provide the same benefits as stacked zone plates, but in an easy to use monolithic form. Patterning two identical high resolution zone plates on the same membrane allows us to double the effective structure height to produce better diffraction efficiency at high photon energies. We combined this with the zone doubling technique [2], by patterning two HSQ resist templates on the membrane and coating it with Iridium to produce double sided zone plates with 30 nm smallest zone width and ...

2021 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)

Optics Express, 2016

Generation of high intensity terahertz radiation in the low frequency region (f < 5 THz) is still... more Generation of high intensity terahertz radiation in the low frequency region (f < 5 THz) is still a challenging task and only few experimental demonstrations exceeding 1 MV/cm have been reported so far. One viable option is the use of resonant metallic structures which act as amplifiers for the impinging radiation. Here with the aid of finite difference time domain simulations, we design and realize a set of isolated resonant elements which allow us to reach a 28-fold enhancement of freely propagating THz radiation at f ≈ 1 THz. These elements are deposited on a GaP sample allowing the direct measurement of the field enhancement using electro-optical sampling. Interestingly, we experimentally show strong modifications of the antennas resonance which is interpreted in terms of interference effects. These are particularly important in samples thinner than half the spatial pulse length.

Http Dx Doi Org 10 1080 10420151003723014, Jun 1, 2010

ABSTRACT We have produced silver colloids by ablating metal targets in water and using two differ... more ABSTRACT We have produced silver colloids by ablating metal targets in water and using two different laser wavelengths. The obtained sols have been characterized by optical spectroscopy and electron microscopy, revealing a definite double size distribution centered at a few tens and a few hundreds of nanometers with a mild difference between the two wavelengths employed. On the contrary, a marked difference in shape has been found for the biggest aggregates, revealing sharp cubic or octahedral structures when visible or infrared radiations are used, respectively. This fact is explained by the re-irradiation processes induced on the already formed colloid and taking place during the ablation.

Nature Communications, 2015

The remarkable electrical and optical properties of single-walled carbon nanotubes have allowed f... more The remarkable electrical and optical properties of single-walled carbon nanotubes have allowed for engineering device prototypes showing great potential for applications such as photodectors and solar cells. However, any path towards industrial maturity requires a detailed understanding of the fundamental mechanisms governing the process of photocurrent generation. Here we present scanning photocurrent microscopy measurements on a double-gated suspended semiconducting single-walled carbon nanotube and show that both photovoltaic and photothermal mechanisms are relevant for the interpretation of the photocurrent. We find that the dominant or non-dominant character of one or the other processes depends on the doping profile, and that the magnitude of each contribution is strongly influenced by the series resistance from the band alignment with the metal contacts. These results provide new insight into the interpretation of features in scanning photocurrent microscopy and lay the foundation for the understanding of optoelectronic devices made from single-walled carbon nanotubes.

Scientific Reports, 2015

Today's pulsed THz sources enable us to excite, probe, and coherently control the vibrational or ... more Today's pulsed THz sources enable us to excite, probe, and coherently control the vibrational or rotational dynamics of organic and inorganic materials on ultrafast time scales. Driven by standard laser sources THz electric field strengths of up to several MVm 21 have been reported and in order to reach even higher electric field strengths the use of dedicated electric field enhancement structures has been proposed. Here, we demonstrate resonant electric field enhancement structures, which concentrate the incident electric field in sub-diffraction size volumes and show an electric field enhancement as high as ,14,000 at 50 GHz. These values have been confirmed through a combination of near-field imaging experiments and electromagnetic simulations.

2007 15th International Conference on Advanced Thermal Processing of Semiconductors, 2007

In this paper we discuss the laser annealing crystallization of hydrogenated a-Si film deposited ... more In this paper we discuss the laser annealing crystallization of hydrogenated a-Si film deposited at 250degC by means of PECVD technique. Abrupt out-diffusion of hydrogen damages the deposited layers during single shot high energy density laser annealing. On the contrary, a multisteps laser annealing approach, from low to high energy density, allows us to achieve good poly-Si film, without any

Physica E-Low-Dimensional Systems & Nanostructures, 2012

Arc discharge is commonly used for the synthesis of carbon nanotubes (CNTs), even though not much... more Arc discharge is commonly used for the synthesis of carbon nanotubes (CNTs), even though not much is known concerning the process itself and the role of the discharge parameters on the formation of different kinds of nanostructures. We have investigated the formation and the morphology of the C deposit on the cathode, after arc discharge between two graphite electrodes immersed in liquid nitrogen. The deposit consists of disordered carbon structures at the bottom and on the external part of the deposit, forming like a bowl that contains randomly oriented CNTs, aggregated in several pillars in the internal part and on top. We have found that the applied voltage not only influences the macroscopic structure of the C deposit, but also the structural properties of the individual CNTs.

Radiation Effects and Defects in Solids, 2010

We have produced silver colloids by ablating metal targets in water and using two different laser... more We have produced silver colloids by ablating metal targets in water and using two different laser wavelengths. The obtained sols have been characterized by optical spectroscopy and electron microscopy, revealing a definite double size distribution centered at a few tens and a few hundreds of nanometers with a mild difference between the two wavelengths employed. On the contrary, a marked difference in shape has been found for the biggest aggregates, revealing sharp cubic or octahedral structures when visible or infrared radiations are used, respectively. This fact is explained by the re-irradiation processes induced on the already formed colloid and taking place during the ablation.

physica status solidi (b), 2010

Journal of Raman Spectroscopy, 2012

Multi-wall carbon nanotubes (MWCNTs) produced by the arc discharge between two graphite rods in l... more Multi-wall carbon nanotubes (MWCNTs) produced by the arc discharge between two graphite rods in liquid nitrogen have been investigated with the use of Raman spectroscopy and transmission electron microscopy (TEM). The effects of the applied voltage on the structural properties of the produced MWCNTs have been observed, in particular, as it concerns the size of the innermost and outermost diameters. The apparent discrepancies observed between the Raman and TEM results are explained through the observation of a selective response of the MWCNTs to the excitation laser energy in Raman spectroscopy, similar to the case of single-wall CNTs. Electronic structure calculations correlate such behavior with optical transitions, in the presence of strong electronic localizations, spatially confined in a few neighboring walls.