Riccardo Riccitelli

Flip-Cathode Design for Carbon Nanotube-Based Vacuum Triodes

In this letter, we report on the realization of a carbon nanotube-based field emission triode with a new flip-chip design of the cathode. Our fabrication method is highly versatile and allows the use of various emitting materials, overcoming at the same time the severe limitations of material choices for the nanotriode fabrication. The obtained device shows a good modulation behavior and low losses. This technology opens a new way for the realization of highly efficient and scaled vacuum field emission devices.

Field emission from silicon nanowires: Conditioning and stability

We report the low-pressure chemical vapor deposition growth and field emission characterization of silicon nanowires (SiNWs). Our field emission results show the importance of the so called conditioning process on the reproducibility of the emission performance itself; this effect has proven to be reversible for the investigated current regime. We explained this behavior by invoking a current-driven desorption of residual adsorbed gases. A highly reproducible turn-on electric field of 27 V∕μm is found for a diode-connected SiNW planar sample. Furthermore, stability analysis is performed showing the technologically promising field emission behavior of the samples.

Fabrication of Spacer and Catalytic Layers in Monolithic Dye-Sensitized Solar Cells

Over the past few years, dye-sensitized solar cell (DSC) research has been focused on the material and process cost reduction, and on the electronics integration of the devices. Monolithic design is one of the most promising DSC architectures for mass production, because it allows the elimination of one conductive substrate and offers the possibility of printing layer-by-layer the materials that compose the structure. In this study, the formulation, the realization, and the processing of the spacer and the catalyst layers are proposed, and the relative performance in terms of J-V characteristics, incident photon to current conversion efficiency, and impedance analysis of the device with the optimized material thickness is reported. The optimized profile of the overall structure permits us to obtain masked cells with a conversion efficiency of about 5% with no chemical treatment.

Dye Solar Cells: Basic and Photon Management Strategies

After the introduction in 1991 by B. O’Regan and M. Gratzel, Dye Solar Cells (DSCs) have reached power conversion efficiency values over small area device as high as 11%. Being manufactured with relatively easy fabrication processes often borrowed from the printing industry and utilizing low cost materials, DSC technology can be considered nowadays a proper candidate for a large scale production in industrial environment for commercial purposes. This scenario passes through some challenging issues which need to be addressed such as the set-up of a reliable, highly automated and cost-effective production line and the increase of large area panels performances, in terms of efficiency, stability and life-time of the devices. In this work, an overview of the most utilized DSCs materials and fabrication techniques are highlighted, and some of the most significant characterization methods are described. In this direction, different approaches used to improves devices performances are presented. In particular, several methods and techniques known as Light Management (LM) have been reported, based to the ability of the light to be confined most of the time in the cell structure. This behavior contributes to stimulate higher levels of charge generation by exploiting scattering and reflection effects. The use of diffusive scattering layers (SLs), nanovoids, photonic crystals (PCs), or photoanodes co-sensitization approaches consisting in the use of two Dyes absorbing in two different parts of the visible range, have been demonstrated to be effective strategies to carry out the highest values of device electrical parameters. Finally, to increase the light path inside the DSCs active layer, the use of refractive element on the topside (a complementary approach to SL) has been shown a promising possibility to further improve the generated photocurrent.

Realization of a carbon nanotube-based triode

We report the design and realization of a carbon nanotube-based integrated triode. Patterned Si/SiO2/Nb/Nb2O5multilayer was successfully realized by means of a photolithographic process. Such structure constitutes the patterned substrate of the successive Hot Filament Chemical Vapour Deposition (HFCVD) process. Selective growth of highly oriented SWCNT arrays was obtained in the predefined locations while survival of the entire structure was achieved. Field emission measurements of such materials were carried out both on a diode and in a triode configuration. Good and reproducible field emission behaviour has been observed in several realized structures. In order to validate the experimental data a first simulation of the behaviour of the integrated vacuum triode with a single field emission CNT was also simulated.

Field emission vacuum triode: THz waveguide solutions for the transmission lines

A complete microwave characterization of the small-signal properties in terms of S-parameters behaviors of a flip-chip triode geometry device has been studied with CST simulator. The simulation results of a single triode and 10times10 triode array have been proposed.

Innovative design of nano-vacuum triode

An innovative procedure for the realization and the assembly of vacuum triode based on carbon nanotube cold cathode is proposed. The aim of the proposed technique is to avoid the typical problem due to the growth of carbon nanotube in the triode structure. The obtained electrical properties of the realized triode fully confirm the validity of the technique.

Towards the realization of a multielectrode field emission device: controlled growth of single wall carbon nanotube arrays

We reported the design and realization of a carbon nanotube-based integrated multielectrode device. Patterned Si/SiO2/Nb/Nb2O5 multilayer was successfully realized by means of a few, common photolithographic processes with the minimum number of mask alignment steps. Such structure constitutes the patterned substrate of successive Hot Filament Chemical Vapour Deposition (HFCVD) process. Selective growth of highly oriented SWCNT arrays was obtained in the predefined locations while survival of the entire structure was achieved. Field emission measurements of such materials were carried out. Good and reproducible field emission behaviour has been observed in several realized structures.