G. Ulisse

Influence of TiO2 electronic structure and strong metal–support interaction on plasmonic Au photocatalytic oxidations

Aiming at understanding how plasmonic reactions depend on important parameters such as metal loading and strong metal–support interaction (SMSI), we report the plasmonic photodegradation of formic acid (FA) under green LED irradiation employing three TiO2 supports (stoichiometric TiO2, N-doped TiO2, black TiO2) modified with Au nanoparticles (NPs) 3–6 nm in size. The rate of FA photooxidation follows different trends depending on Au loading for stoichiometric and doped Au/TiO2 materials. In the first case, the only contribution of hot electron transfer produces a volcano-shaped curve of photoreaction rates with increasing Au loading. When TiO2 contains intra-bandgap states the photoactivity increases linearly with the amount of Au NPs due to the concomitant enhancement produced by hot electron transfer and plasmon resonant energy transfer (PRET). The role of PRET is supported by finite element method simulations, which show that the increase in both Au NP inter-distance and SMSI enhances the probability of charge carrier generation at the Au/TiO2 interface.

Study of the Influence of Transverse Velocity on the Design of Cold Cathode-Based Electron Guns for Terahertz Devices

This paper presents the design of an electron gun for terahertz vacuum tubes realized with a nanowire or nanotube cold cathode. This technology is particularly interesting in this field since it allows the reduction of gun dimensions and of power consumption with respect to the thermionic guns. We found that focusing is a rather critical aspect since cold cathodes show a relevant transverse velocity, which increases the divergence of the beam and typically induces high current losses on the anode. An analysis of the parameters that influence the transverse velocity has been performed together with the identification of a proper design procedure that reduces the transverse velocity effects. Different electron guns have been designed that deliver a circular beam in the range of 1-4 mA with a radius in the range of 30 μm.

3-D Simulation and Optimization of Organic Solar Cell With Periodic Back Contact Grating Electrode

In this paper, we report an investigation of the optical and electrical properties of an organic solar cell (OSC) with a back contact grating architecture through 3-D numerical simulations. By using finite-element methods for both optical and transport properties, we have modeled the behavior of OSC with a grating architecture and compared with a conventional planar structure. Based on these optoelectrical simulations, we optimized the back contact grating, obtaining an increment of up to 17.5% in power conversion efficiency with respect to a planar structured OSC. This enhancement is the result of an increase of both short-circuit current and fill factor.

Hybrid thermal-field emission of ZnO nanowires

The electron emission properties of an array of ZnO nanowires were studied in the temperature range of 300-473 K. An almost doubling of the current density at 473 K under an electric field of 8 V/μm (j(T=473 K) = 190 μA/cm2, j(T=300 K) = 114 μA/cm2) was observed together with a reduction of the turn-on field from 552 V/μm to 482 V/μm. Theoretical model that combines the thermal-field emission for high electric field and the Schottky emission for the low field can satisfactorily account for temperature dependence of current at low as well as at high applied bias. The obtained effect is particularly appealing for the application in micro-gun for THz vacuum tubes.

Cross-Bar Design of Nano-Vacuum Triode for High-Frequency Applications

In this letter, a new nano-vacuum triode based on carbon nanotubes (CNTs) has been designed. The use of CNTs as emitters with their extremely high aspect ratio and their characteristics to be patterned in specific emitting areas allowed the realization of a cross-bar geometry for which the transconductance is maximized and the grid-cathode capacitance is reduced. This allowed us to achieve a device cutoff frequency of 156 GHz, which is well beyond the state of the art.

A multifinger microtriode with carbon nanotubes field emission cathode operating at GHz frequency.

Vacuum microelectronic devices play an important role in the field of micro- and nano-electronics and they have been strongly developed in recent decades. Vacuum microelectronics are mainly based on the field emission effect and the employment of electrons in vacuum in a device with dimensions from tenths to hundredths of a micrometer. In this work, we present the development of a carbon-nanotube-based multifinger microtriode operating from 0.5 to 2 GHz. In this frequency range, a minimum RF signal gain of 5 dB is achieved. Such a device represents an optimized alternative to the standard Spindt-type microtriode. The advantage of such multifinger architecture consists in the possibility to reduce the cathode-grid capacitance by reducing the overlap between the two electrodes using a parallel patterning. This approach allows increasing the cut-off frequency of the devices with respect to the Spindt-type triode. We realized a prototype of the multifinger triode and the field emission properties have been characterized. The frequency behavior has been measured, demonstrating the possibility to amplify RF signal.

Particle tracing simulation of a vacuum electron gun for THz application

This paper presents the design of an electron gun employable in THz vacuum tubes. A Multiphysics (MP) approach has been used in the electron gun design in order to study the effect of the multiple influencing factors such as mechanical stress or thermal expansion togheter with charged particle in electrostatic and magnetostatic fields.

The OPTHER project: Progress toward the THz amplifier

This paper describes the status of the OPTHER (OPtically driven TeraHertz AmplifiERs) project and progress toward the THz amplifier realization. This project represents a considerable advancement in the field of high frequency amplification. The design and realization of a THz amplifier within this project is a consolidation of efforts at the international level from the leading scientific and industrial European organizations working with vacuum electronics.

European research on THz vacuum amplifiers

The OPTHER (OPtically Driven TeraHertz AmplifiERs) project represents a considerable advancement in the field of high frequency amplification. The design and realization of a THz amplifier within this project is a consolidation of efforts at the international level from the main players of the European research, academy and industry in vacuum electronics. This paper describes the status of the project and progress towards the THz amplifier realization.

Electrostatic Beam Focusing of Carbon Nanotubes Electron Source

In this paper, we present the realization and characterization of a carbon nanotubes (CNTs) electron gun. The gun consists of a CNT cathode with an external extracting grid, that reached a maximum current density of 0, 6 A/cm2, assembled with an electrostatic focusing grid. The realized compact electron gun achieved a maximum output current density of 0, 11 A/cm2. This represents one of the first examples of a CNTs electron gun with an electrostatic focusing grid with high-output current density. The assembly process and the relative issues are described in detail together with the field emission characteristics of the cathodes and of the electron gun.