Giuseppe Faraci

Quantum size effects in Raman spectra of Si nanocrystals

First order Raman spectra of Si nanocrystals exhibit large shift and width, strongly exceeding the theoretical calculated values. The disagreement between theory and experiment is dramatically increasing for the smallest nanocrystal sizes. Here, we present a novel theoretical approach showing one-, two-, or three-dimensional quantum effects, due to the limited size of the corresponding coordinate of the quantum structure. The method can be applied to nanosized layers, quantum wires and/or quantum dots. The agreement of the present theory with experimental data is dramatically improved.

An open framework to enable NetFATE (Network Functions at the edge)

In the last few years, Software Defined Networks (SDN) and Network Functions Virtualization (NFV) have been introduced in the Internet as a new way to design, deploy and manage networking services. Working together, they are able to consolidate and deliver the networking components using standard IT virtualization technologies not only on high-volume servers, but even in the end user premises. In this context, this paper presents the NetFATE architecture, a platform aimed at putting virtual network functions (VNF) at the edge of the network. This platform is based on free and open source software on Provider Equipment (PE) and Customer Premise Equipment (CPE) nodes, so allowing function deployment simplification and management cost reduction. Finally, the paper proposes a case study, consisting in the implementation of two virtual personal firewalls used by two clients moving between two access points located at the edge of the core network.

An Analytical Model to Design and Manage a Green SDN/NFV CPE Node

In the last few years, SDN and NFV have been introduced with the potential to change the ossified Internet paradigm, with the final goal of creating a more agile and flexible network, at the same time reducing both CAPEX and OPEX costs. For this reason, a lot of research efforts have been devoted to optimize the implementation of these technologies, also inheriting experience from data center management. However, orchestration and management of SDN/NFV nodes present new challenges with respect to data center management, mainly due to the telecommunications context where NFV resides. With this in mind, the target of this paper is to define a management model for NFV customers and service providers, a green policy of the customer premises equipment (CPE) nodes, and an analytical model to support their design. The model is then applied to a case study to demonstrate how it can be used to optimize system performance and choose the most important parameters characterizing the design of a CPE node.

Al Intermediate Oxidation-States Observed by Core-Level Photoemission Spectroscopy

Aluminum oxidation states in stoichiometric or substoichiometric configuration are studied by core level photoemission spectroscopy on different substrates (SiO2, graphite). They are compared with recent results reported for the interface Si–Aln+O. Three Al oxidation states have been identified and their space distribution (binding energy, intensity, and width) is determined in the region from the interface with the substrate up to the surface of a thick overlayer. The Al2+–O intermediate oxidation state is shown to be confined at the interface; on the contrary, the Al1+–O oxidation state and the stoichiometric oxide (alumina) are present beyond the interface region. From the attenuation of the substrate core level peak, the deposition morphology and the attenuation length of the photoelectrons have been deduced.

Order and disorder of carbon deposit produced by arc discharge in liquid nitrogen

We have investigated the formation and the morphology of carbon deposit on the cathode, after arc discharge between two graphite electrodes immersed in liquid nitrogen. We show that the deposit is mainly composed of disordered carbon structures at the bottom and at the external part of the deposit, forming like a bowl, whereas randomly oriented carbon nanotubes (CNTs) aggregated as pillars are found at the center of the deposit. The spatial distribution of the two kinds of structures in the deposit, the size and the sharpness of the CNT pillars are found to depend both on the applied voltage and the current values used for the arc discharge. A correlation between the plasma temperature field and the morphology of the deposit is reported.

Superconducting tunnel junctions with a non conventional insulator.

Abstract A method in performing tunnel junctions is discussed, employing a thin film of plastic material as insulator. Lead energy gap measurements exhibit good agreement with B.C.S. theory prevision.

Giant photoluminescence emission in crystalline faceted Si grains

Empowering an indirect band-gap material like Si with optical functionalities, firstly light emission, represents a huge advancement constantly pursued in the realization of any integrated photonic device. We report the demonstration of giant photoluminescence (PL) emission by a newly synthesized material consisting of crystalline faceted Si grains (fg-Si), a hundred nanometer in size, assembled in a porous and columnar configuration, without any post processing. A laser beam with wavelength 632.8 nm locally produce such a high temperature, determined on layers of a given thickness by Raman spectra, to induce giant PL radiation emission. The optical gain reaches the highest value ever, 0.14 cm/W, representing an increase of 3 orders of magnitude with respect to comparable data recently obtained in nanocrystals. Giant emission has been obtained from fg-Si deposited either on glass or on flexible, low cost, polymeric substrate opening the possibility to fabricate new devices.

Logarithmic-derivative curves of A1-Formvar-Pb junctions and trap-assisted current transport

Abstract Two types of structures in (d/d V >)[ln ( J / V )] are observed for A1-Formvar-Pb sandwiches. One occurs at high voltages and is expected for tunneling through trapezoidal barriers. The other occurs around zero bias and is interpreted as being due to localized traps in the insulator.

Raman and photoluminescence spectroscopy of Si nanocrystals: Evidence of a form factor

We investigated the quantum confinement in Si nanocrystals embedded in a SiO2 matrix. The size was accurately controlled in the range 3–8 nm by annealing at high temperature Si/SiO2 multilayers fabricated by chemical vapour deposition. Raman shift and line width were compared with existing theoretical models for each cluster size. We found evidence of uni-dimensional confinement in 3 nm crystals, whereas for 4.5 nm crystals the confinement appears three-dimensional. This conclusion is supported by the luminescence spectra shifting towards higher wavelengths for the smaller size, in opposite direction for larger sizes.

Binding-Energies and Cluster Formation at Low Metal-Deposition - Ag on Si and Sio2

A comparison of photoemission spectra from Ag clusters deposited on silicon oxide and on cleaved silicon substrate has allowed us to discriminate initial and final state effects in the binding energies of the valence band and of the 3d core level of the metal.