Francesco Mercuri

Redox-switchable devices based on functionalized graphene nanoribbons

The possibility of tuning the electronic properties of graphene by tailoring the morphology at the nanoscale or by chemical functionalization opens interesting perspectives towards the realization of devices for nanoelectronics. Indeed, the integration of the intrinsic high carrier mobilities of graphene with functionalities that are able to react to external stimuli allows in principle the realization of highly efficient nanostructured switches. In this paper, we report a novel approach to the design of reversible switches based on functionalized graphene nanoribbons, operating upon application of an external redox potential, which exhibit unprecedented ON/OFF ratios. The properties of the proposed systems are investigated by electronic structure and transport calculations based on density functional theory and rationalized in terms of valence-bond theory and Clars sextet theory.

The interaction of Cr(CO)3 on the (n, 0) nanotube side-walls: a density functional study through a cluster model approach

Density functional calculations have been performed to investigate the functionalization of single-wall carbon nanotubes (SWNTs) with the Cr(CO)3 metal fragment, employing extended molecular models. A circumcoronene molecule (C54H18), made by the fusion of 19 hexagonal carbon rings, can be regarded as a fragment of a graphene sheet. To reproduce the curvature of the SWNT surface, suitable geometric constraints have been imposed on the C54H18 model, freezing the positions of the outer hydrogens along the directions of the nanotube C-C bonds. Geometry optimizations have then been performed under this constraint on the Cr(CO)3-C54H18 complexes, pointing out the most favourable coordination sites on the hexagonal rings of the carbon atom surface and the electronic properties of the resulting system. The effect of the curvature on the metal coordination to nanotubes has been analysed by investigating the interaction of the Cr(CO)3 metal complex with the C54H18 molecules, modelling (n, 0) nanotubes with different degrees of curvature, i.e. with various values of the chiral vector (n, 0).

Influence of substituents and length of silanylene units on the electronic structure of π-conjugated polymeric organosilicon systems

Abstract The electronic structure of several silicon- and germanium-containing π -conjugated linear chain polymers was studied using extended Huckel tight-binding calculations. Emphasis has been put on the effects of the electronic structure of model compounds –[(ER 2 ) x –CHR] n - varying: (1) the π system CHR (chromophore); (2) substituents on silicon and germanium atoms; (3) the inorganic atom E (Si and Ge); (4) the number x of silanylene units. The results indicate in all cases a σ HOCO because of the delocalized interaction along the polymer skeleton and a π * LUCO caused by an antibonding interaction localized on the chromophore.

Semiempirical calculations on the electronic properties of finite-length models of carbon nanotubes based on Clar sextet theory

Electronic structure calculations on carbon nanotubes (CNTs) and related materials constitute an active and challenging field of research. Computational approaches to the problem require (i) the definition of consistent models of CNTs and (ii) calculation of the properties of such models with accurate electronic structure methods. In this work, we perform semiempirical AM1 calculations on finite-length models of CNTs based on Clar sextet theory. In particular, the use of the Accelrys Materials Studio® package allows us to perform both the model building and computing steps through a simple and user-friendly interface. The consistency of such an approach is demonstrated by the smooth and monotonic decrease of the highest-occupied molecular orbital (HOMO)–lowest-unoccupied molecular orbital (LUMO) energy gap with length of models for metallic nanotubes and fast convergence to a finite value for models of semiconducting CNTs. As a further example of the applicability of the method outlined in this paper, the dependence of the HOMO–LUMO gap with the diameter for a series of analogous CNTs was also analysed.

Chapter 8:Theoretical Strategies for Functionalisation and Encapsulation of Nanotubes

Nanotubular materials like carbon nanotubes (CNTs) and inorganic nanotubes (INNTs) were proposed as promising materials for a large variety of nanotechnological applications. Due to intrinsic experimental limitations, the theoretical modeling plays a crucial role in the understanding of the properties of these materials. The present chapter is intended to provide a comprehensive overview of some theoretical concepts for modeling of CNTs functionalization and the encapsulation of inorganic material into CNTs and INNTs. The work is divided into two main parts. In the first, a methodological background is given along with some basic structural features of the “nano-objects” taken into account. In particular the application of the Clar sextet theory to the case of CNTs is analyzed in detail. Several applications of this concept are reported in the second part. Some basic electronic properties of the CNTs are analyzed from the Clar sextet theory point of view. DFT calculations on Clar-consistent CNTs models provide a suitable route for the understanding of the chemical reactivity of semiconducting chiral CNTs. Another possible field of application of NTs concerns the development of novel materials by making use of NTs as nano-sized templates of nanostructured materials. A detailed overview of theoretical understanding of capillary properties of carbon and inorganic BN and MoS2 nanotubes is given. Therein, results from classical MD simulations on the imbibition process for a molten salt into a nanotube and on the crystallization of the melt within the nanotubular cavity are shown.