You are here: Home » Research » Publications Details

Publications of the Department


Boschi, Alex, (2021)  - Studio dei meccanismi di trasporto di carica in film sottili a base di materiali correlati al grafene (GRM)  - , Tesi di dottorato - (, , Universitą degli studi di Modena e Reggio Emilia ) - pagg. -

Abstract: The development of cheap techniques to produce large sheets of monoatomic thick materials, such as graphene [1], opened new avenues to design nanostructured materials with pre-programmed chemical and physical properties. Most of the technologically relevant graphene-related materials (GRMs) systems are networks composed of randomly distributed and highly defective 2D microsheets [2]. While the charge transport has been extensively studied in single nanosheets [3], a comprehensive study that correlates the electrical properties of networks composed of purely 2D graphene-based materials with the complexity of the material structure and morphology is still missing. The aim of this work is to investigate charge transport (CT) in GRMs films, going towards structures with increasing disorder. In particular we investigated the CT mechanisms occurring at the sheet-to-sheet interface – typically the interfacial mechanisms are considered as bottlenecks – as well as the role of the geometrical complexity of the network in the overall electrical conductivity of the nanosheets assemblies. As prototypical 2D material we used single monolayer sheets of graphene oxide (GO), which consists of a conductive graphene lattice including oxygen functionalities/ defects both on the basal plane and at the edges of the sheet. Electrical insulating GO sheets are deposited on silicon oxide substrates and thermally reduced restoring partially the conductive properties of the 2D sheets. In addition to reduced GO, we employed a GRM made of multiple staked sheets of (partially oxidised) graphene bilayers: electrochemical exfoliated GO (eGO) [4].We exploited different deposition methods: i) spin-coating, ii) spray-coating and iii) vacuum-assisted filtration to fabricate macroscopic GRMs thin films with sheets partially stacked. Chemical and morphological properties of the films were characterized by X-ray Photoelectron Spectroscopy (XPS), Atomic Force Microscopy (AFM) and X-ray Diffraction (XRD) measurements. We investigated transport mechanisms measuring the temperature-dependence of the electrical resistivity (ρ) from room temperature down to 5 K. Possible ambiguities on the quantitative analysis of ρ(T) were solved by using a robust self-consistent method based on the reduced activation energy [5], i.e. the logarithmic derivative of resistivity versus temperature: W(T)=-(d ln⁡ρ)⁄(d ln⁡T ). This mathematical transformation allowed to analyse ρ(T) dataset with linear functions. We correlated the transport characteristic parameters with the degree of order of our samples and elucidate the role of the sheets vertical stacking, that is of the π-π interaction between overlapped aromatic clusters, in the CT in the film. We also highlighted the differences in CT between reduced GO based films and eGO ones. The presented work could pave the way to develop new models and protocols to access the CT mechanisms in realistic GRMs, such as inks and polymer composites. [1] Ferrari, A. C. et al. Nanoscale 7, 4598-4810, (2015). [2] Palermo V., Chem. Comm. 49, 28, 2848-2857 (2013); Kelly A. et al, Science 356, 6333 (2017). [3] Eda G. et al, J. Physics. Chem.C 113, 15768 (2009); Kaiser a. et al, Nano Letters 9, 1787 (2009); Joung D. and Khondaker S., Phys. Rev. B 86, 235423 (2012). [4] Xia Z. et al, J. Physics. Chem.C 123, 15122 (2019). [5] Zabrodskii A. G., Philos. Mag. B 81, 1131 (2001).