CNR IMM

We aim to exploit the properties of the quantum confinement of Silicon quantum dots (Si-QD) and to use an IR 808nm laser source for heat treatments. The use of Si-QD is expected to increase efficiency in the conversion of solar energy. Through the effects of quantum confinement, in fact, you can get adjustable bandgap materials that absorb photons in a wider and selected range of energies. The study of formation and structural properties of nano crystals of Si is carried out through X-ray diffraction and scattering using a high angular resolution diffractometer and through Electron Energy Loss Spectroscopy. The realization of Si-QD with traditional techniques, like high temperature furnace treatments, rules out the possibility of making solar cells on substrates other than Si. Instead, depositing Si and its compounds at low temperature (e.g. 70 °C) by an Inductively Coupled Plasma Chemical Vapor Deposition and subsequently treating the material with "laser annealing” allows to make QD on glass or ceramic substrates. Achieving this goal would have the double advantage of combining the increased efficiencies provided by the QD with the low cost of the substrate allowing for the integration of cells in buildings.

Contact person: Giovanni Mannino

To further reduce production costs and lighten the weight of the cells, hybrid solar cells based on polymeric materials are the best candidates. This type of cells represents a challenge for the scientific community since their conversion efficiency of solar radiation is still low, below 8%. As a possible scheme, we plan to incorporate transparent polycrystalline TiO2 layers, deposited by DC magnetron sputtering and having the structure of anatase, with a mixture of donor and acceptor polymers (e.g. Poly 3-Hexylthiophene (P3HT)) and a soluble form of conjugated polymers blended with fullerenes (PCBM). In this way we obtain a double heterojunction device, with interfaces TiO2/P3HT and P3HT/PCBM as the site of charge separation. The role of TiO2 in the hybrid cell is crucial, and is linked to its ability to accept and carry electrons from the active material. We plan to use TiO2 either as a continuous layer in multilayer structures or as mesoporous material (e.g. nanotubes) in multilayered structures organic / inorganic. The deposition of mesoporous TiO2 by sputtering is a recent and critical task that requires a systematic study on the optimization and implementation of its structural and optical properties. The structural characterization of TiO2 as a function of growth parameters is performed via X-ray techniques using a high angular resolution diffractometer. The analysis will provide detailed information on the nature of the material (polycrystalline or amorphous) and on the crystal structure, the density, thickness and roughness.

Contact person: Alessandra Alberti

The activity concerns the issue of metal contacts integration in flexible electronics and focuses on low temperature formation of thin layers of Ni-silicide as source and drain of Thin Film Transistors (TFT) on polymeric substrate. The conventional TFT architecture would require highly doped Si for the source and drain area to be realised at temperatures above 1000 °C. The idea of replacing such doped regions with Ni-silicide metallic contacts arises from the incompatibility of high temperature processes with the stability of the polymeric substrate. By using silicided source and drain area, the physical mechanisms ruling the device operation are modified, as the charge carriers are transferred from the source to the conduction channel through a Schottky barrier. In this configuration the short channel effects can be neglected and also the parasitic capacitance is lowered, even reducing the device size. Using Ni-silicides offers some other crucial advantages: the flow-chart is simplified by avoiding ion implantation and dopant activation; the contact can be realised at temperatures below 350 °C; the metallic layers can be selectively obtained on the source and drain regions, through a so called self-aligned process.

We have realised Ni-Silicide contacts via Ni deposition by DC magnetron sputtering on PECVD amorphous silicon on PEN or Polymmide (plastics), and via subsequent irradiation of the contact area by an excimer laser (ELA) with wavelength of 308 nm. ELA is a process compatible with the presence of the polymer in the structure, as this radiation is absorbed in Si within a distance of ~ 20 nm.. Heat is transferred from Si to the polymer and induces an increase of temperature up to ~ 600 °C only for a few μs, as evaluated by phase field calculations, such that no detrimental modification of the elastic characteristics of the polymer occurs. ELA promoted both the reaction between Ni and silicon in the contact area, and the crystallization of the substrate. The resulting silicide layer is continuously distributed all over the contact area offering the advantage of smoothing the surface from the roughness induced by the Si crystallization process. The Schottky barrier between silicide and silicon can be tuned from a quasi ohmic (low barrier) to a rectifiant behaviour (high barrier) b y changing the structural properties of the silicide

Contact person: Alessandra Alberti

Over the past few years, the interest for the nano-sized C-based materials has received a growing interest, due to peculiar properties that may lead to several applications in electronic devices and sensors. This class of materials ranges from carbon-based hard materials, such as diamondlike carbon and carbon nitride thin films, to carbon nanotubes (CNTs) and linear carbon chains (LCCs). The activity on C-based Nanostructures at IMM-CNR in Catania started in 2005. In particular, we have focused our attention on the synthesis of CNTs by RF magnetron sputtering, that is a technique not commonly used for this purpose, and arc discharge in liquid environments. Arc discharge in gaseous environments is much more used for the CNT production, with respect to the same technique in liquids. Nevertheless, in both cases, not so much is known as concerns the process itself and the role of the experimental parameters on the control of the produced structures.

One of the aims of our study is to find such a correlation between the discharge parameters and the nanostructures produced. In particular, we have already found the suitable parameters in order to obtain the formation of hybrid systems, formed by LCCs inserted in CNTs, by arc discharge in liquid nitrogen.
The characterization of these materials is usually done by scanning electron microscope (SEM, ZEISS SUPRA35 FE-SEM), transmission electron microscopy (TEM, JEM 2010F JEOL), and Raman spectroscopy.

Contact person: Silvia Scalese

This activity aims to the development and implementation of advanced codes for the simulation of manufacturing processes (e.g. plasma etching, ultra fast thermal annealing) and the electronic transport in nano and molecular devices. The activity has two interconnected characteristics: a) the tight collaboration with the experimental counter-part and b) the use of the multi-scale paradigm in the simulation approach. Indeed, the current research in the micro, nano and molecular electronics generally  deals with the investigation of  a complex phenomenology which can hardly addressed by a single theoretical methodology. In turn the application of a set of complementary methods (e.g. ab-initio calculations, Molecular Dynamics techniques, Kinetic Monte Carlo simulation, Continuum modeling) appears the most effective and accurate simulation approach.  The activity core is the modeling development and implementation which is “per se” relevant. However, we would like to cite some application examples of the developed codes:

1. Electronic Transport code based on the Non Equilibrium Green Function formalism => Transport mechanism in Carbon Nanotube and Grephene Based devices
2. Kinetic Monte Carlo Code => simulation of etching and deposition processes in nano-structured samples 
3. Ab-initio and MD codes => calibration of kinetics model
4. Continuum Modeling => Simulation of the Laser annealing processes in nano structured samples.  Simulation of the dielectrophoresis phenomena in trapping devices

Contact person: Antonino La Magna