The research activity I have performed during my PhD was centred on the study of several aspects of the interaction of graphene with surfaces and adsorbates including atoms and molecules. In particular, I have investigated how the latter is modified by a metal substrate supporting graphene. The unique electronic and mechanical properties of graphene make it an ideal candidate for applications in high efficiency nanoelectronic devices. However, these properties are modified when it interacts with such species, and this represents one of the major issues still preventing its wide-spread adoption. For this reason, in the first phase of my research I have investigated the factors which govern the intensity of the graphene-substrate interaction. In particular, by characterising and comparing the properties of several graphene/metal interfaces, I have shown that the interaction occurring between them is due to the coupling of the d-band of the substrate with the π band of graphene. Following this, I have investigated the interaction between small inorganic molecules (such as CO) and atoms (Ar) with metal-supported graphene. My results show that these interactions, which are based on van der Waals forces, increase when graphene is supported on a strongly interacting surface. In collaboration with computational scientists, I have shown that the main factor influencing the adsorption energy of CO on graphene is the chemical composition of the substrate’s topmost layer, while the distance between graphene and the substrate plays a negligible role. This proves that this increased adsorption energy is due to the modifications induced by the substrate on the bands of graphene by their coupling with the substrate’s d-band. A contribution due to the transparency of graphene to van der Waals interaction, which had been proposed by some works in literature, could instead be refuted. Another issue related to the wide-scale application of graphene which I have addressed here is the cost-effectiveness of its synthesis. In particular, part of my research work was dedicated to the identification of the factors which can be address to improve the existing synthesis techniques. More in detail, I have demonstrated the important role of the adsorption energy of atoms and small clusters of carbon on graphene on the dynamics of its growth, and therefore on the quality of the final product. Finally, I have studied some possible applications which exploit the modifications induced by the interaction of graphene with its substrate and with species adsorbed on it on the properties of the latter, in fields such as magnetism and catalysis. More in detail, I have studied the dynamics leading to a magnetic superexchange between graphene supported on a magnetic material and molecular adsorbates. Furthermore, I have characterised the geometric and electronic structure of titania nanoparticles supported on different graphene/substrate interfaces, which have shown a 20-fold increase in their photocatalytic activity with respect to a graphene-less control system. In parallel to these activities, I have worked on the development of a mass-selected nanocluster source, whose final aim is to allow the characterisation of the properties of nanoclusters as a function of their mass with space-averaging experimental techniques. To improve my knowledge on this kind of apparatus, I have made a 3-month traineeship (within the Erasmus + project) at the Chemistry Department of Technische Universität München, where I have worked on the commissioning of an analogous device.

L’attività di ricerca del mio dottorato è stata dedicata allo studio di diversi aspetti dell’interazione del grafene con superfici e con adsorbati quali atomi e molecole e di come quest’ultima sia modificata da un substrato metallico sotto il grafene. Le proprietà elettroniche e meccaniche uniche del grafene lo rendono un candidato ideale per lo sviluppo di dispositivi nanoelettronici ad alta efficienza. Tuttavia, le modifiche indotte alle proprietà del grafene dalla sua interazione con tali specie sono uno dei principali problemi che impediscono un suo utilizzo su scala industriale. Pertanto, la prima fase della mia ricerca ha riguardato l’identificazione dei fattori che governano l’intensità dell’interazione grafene-substrato. In particolare, studiando e confrontando le proprietà di diverse interfacce grafene/metallo, ho dimostrato che l’interazione fra di essi dipende dall’accoppiamento fra la banda d della superficie metallica e la banda π del grafene. La fase successiva della mia ricerca è stata dedicata allo studio dell’interazione di piccole molecole inorganiche (principalmente CO) ed atomi (Ar) con grafene supportato su diverse superfici metalliche. I miei risultati dimostrano che le interazioni di van der Waals tra il grafene ed i suoi adsorbati sono aumentate in presenza di un substrato fortemente interagente. Grazie ad una collaborazione con ricercatori del campo della fisica computazionale, ho dimostrato che il fattore che influenza maggiormente l’energia di adsorbimento del CO sul grafene è la composizione chimica dello strato superficiale del substrato metallico, mentre la distanza tra grafene e substrato ha un effetto molto più ridotto. Questo dimostra che l’aumento dell’energia di adsorbimento è originata dalle alterazioni indotte nelle bande del grafene dal loro accoppiamento con la banda d del substrato e non, come sostenuto da diverse fonti in letteratura, da una trasparenza del grafene alle interazioni di van der Waals. Un altro limite alla possibilità di utilizzare il grafene su scala industriale dipende dai suoi elevati costi di produzione, rispetto alla qualità ottenuta. Ho pertanto dedicato una parte del mio lavoro di tesi anche allo studio delle tecniche di crescita del grafene su superfici metalliche, con lo scopo di identificare i possibili margini di miglioramento. Nello specifico, ho dimostrato che l’energia di adsorbimento di atomi e piccoli cluster di carbonio riveste un ruolo importante già nel determinare le dinamiche di crescita del grafene, e conseguentemente la qualità e le proprietà del prodotto. Infine, ho studiato alcune possibili applicazioni delle modifiche indotte dall’interazione del grafene con il substrato e con specie adsorbite su di esso in alcuni campi quali il magnetismo e la catalisi. In particolare, ho studiato le dinamiche del superscambio magnetico che si instaura quando il grafene è supportato su un materiale magnetico fra quest’ultimo e le specie adsorbite sul grafene. Inoltre, ho caratterizzato la struttura geometrica ed elettronica di nanoparticelle di titania supportate sul grafene, per le quali il grafene porta ad un aumento dell’attività fotocatalitica di un ordine di grandezza. In parallelo a queste attività, mi sono dedicato anche allo sviluppo di una sorgente di nanocluster selezionati in massa, il cui fine è di permetterne lo studio con tecniche sperimentali mediate nello spazio. Per ampliare le mie conoscenze su questo tipo di strumenti, ho svolto un tirocinio di tre mesi (nell’ambito del programma Erasmus + Traineeship) presso il Dipartimento di Chimica della Technische Universität München, dove ho partecipato alla messa in funzione di uno strumento analogo.

Adsorption and interaction of atoms, molecules and nanoclusters on epitaxial graphene / Presel, Francesco. - (2018 Mar 08).

Adsorption and interaction of atoms, molecules and nanoclusters on epitaxial graphene.

PRESEL, FRANCESCO
2018-03-08

Abstract

The research activity I have performed during my PhD was centred on the study of several aspects of the interaction of graphene with surfaces and adsorbates including atoms and molecules. In particular, I have investigated how the latter is modified by a metal substrate supporting graphene. The unique electronic and mechanical properties of graphene make it an ideal candidate for applications in high efficiency nanoelectronic devices. However, these properties are modified when it interacts with such species, and this represents one of the major issues still preventing its wide-spread adoption. For this reason, in the first phase of my research I have investigated the factors which govern the intensity of the graphene-substrate interaction. In particular, by characterising and comparing the properties of several graphene/metal interfaces, I have shown that the interaction occurring between them is due to the coupling of the d-band of the substrate with the π band of graphene. Following this, I have investigated the interaction between small inorganic molecules (such as CO) and atoms (Ar) with metal-supported graphene. My results show that these interactions, which are based on van der Waals forces, increase when graphene is supported on a strongly interacting surface. In collaboration with computational scientists, I have shown that the main factor influencing the adsorption energy of CO on graphene is the chemical composition of the substrate’s topmost layer, while the distance between graphene and the substrate plays a negligible role. This proves that this increased adsorption energy is due to the modifications induced by the substrate on the bands of graphene by their coupling with the substrate’s d-band. A contribution due to the transparency of graphene to van der Waals interaction, which had been proposed by some works in literature, could instead be refuted. Another issue related to the wide-scale application of graphene which I have addressed here is the cost-effectiveness of its synthesis. In particular, part of my research work was dedicated to the identification of the factors which can be address to improve the existing synthesis techniques. More in detail, I have demonstrated the important role of the adsorption energy of atoms and small clusters of carbon on graphene on the dynamics of its growth, and therefore on the quality of the final product. Finally, I have studied some possible applications which exploit the modifications induced by the interaction of graphene with its substrate and with species adsorbed on it on the properties of the latter, in fields such as magnetism and catalysis. More in detail, I have studied the dynamics leading to a magnetic superexchange between graphene supported on a magnetic material and molecular adsorbates. Furthermore, I have characterised the geometric and electronic structure of titania nanoparticles supported on different graphene/substrate interfaces, which have shown a 20-fold increase in their photocatalytic activity with respect to a graphene-less control system. In parallel to these activities, I have worked on the development of a mass-selected nanocluster source, whose final aim is to allow the characterisation of the properties of nanoclusters as a function of their mass with space-averaging experimental techniques. To improve my knowledge on this kind of apparatus, I have made a 3-month traineeship (within the Erasmus + project) at the Chemistry Department of Technische Universität München, where I have worked on the commissioning of an analogous device.
8-mar-2018
BARALDI, Alessandro
30
2016/2017
Settore FIS/03 - Fisica della Materia
Università degli Studi di Trieste
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11368/2919623
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