Graphene is the thinnest known material, which gathered a lot of attention after its discovery because of unique electrical and mechanical properties such as high stiffness and electron mobility. Besides, the small size and mass of graphene make it an ideal candidate for nanoelectromechanical systems (NEMS), which offer potential for new applications such as single atom mass sensors. In addition to the mentioned features, the interplay between mechanical and electrical properties of graphene is an interesting functionality for designing NEMS. This interplay is called “piezoresistivity” and is investigated by gauge factor (GF) which is the ratio of relative changes in the electrical resistance to the applied mechanical strain. In this thesis we report for the first time the experimental study of the piezoresistivity in few layer graphene “nanodrums”, that are suspended flakes over circular holes. We measure the electrical resistance of the flake while the flake is deformed by means of the force-distance measurements by an atomic force microscopy (AFM) under ambient condition. Furthermore, the analysis of the experimental data required the writing of a program in Matlab to merge the results of the AFM and electrical measurements. By this program the measured force-distance curves and changes in the electrical resistance while the AFM tip is deforming the flake are plotted. In addition to that the spatial profile of the compliance of the flake is plotted to show the pattern of the deformability of the flake. Moreover, the spatial profile of the changes in the electrical resistance of the flake while the tip is pushing the flake and the flake is deformed is plotted. This factor gives information about the changes in the GF and the piezoresistivity of the graphene flakes. The results proved that our method to use AFM under ambient condition as a measurement tool can be used to derive information on the piezoresistive behavior of graphene. According to the results at the center of the hole the flake is more easily deflected than the edges. Moreover, the deformation of the drums through AFM affects the electrical resistance of the flake (by approximately 10%) and it shows that graphene illustrates piezoresistive behavior in practice. This is a promising prospect for applications of the graphene nanodrum as the sensor of very small mass (individual molecules) or pressure changes in NEMS.
Il grafene, l’unico materiale conosciuto in forma di singolo strato atomico, ha attratto molta attenzione fin dalla sua scoperta grazie alle proprietà elettriche e meccaniche uniche (elevato modulo e mobilità di carica). Inoltre, la ridotta massa di un flake di grafene e le sue ridotte dimensioni ne fanno un candidato ideale per sistemi nano-elettromeccanici (NEMS) che potrebbero condurre allo sviluppo di nanosensori di massa e pressione. In particolare l’accoppiamento tra le proprietà meccaniche ed elettriche del grafene (la piezoresistività) rappresenta il parametro fisico che può essere utilmente sfruttato nella costruzione di dispositivi alla scala nanometrica. In questa tesi si riporta uno studio sperimentale originale della piezoresistività di “nanotamburi” di grafene a pochi strati. Tali nanotamburi sono costituiti da flake di grafene sospesi su buchi circolari ricavati su substrati di silicio. Nel corso della tesi è stata misurata (a temperatura e pressione ambiente) la variazione della resistenza della membrana di grafene del nanotamburo sotto l’azione deformante della punta di un AFM. L’analisi dei dati sperimentali ha richiesto la scrittura di un programma Matlab per elaborare ed unire i risultati delle misure simultanee AFM ed elettrica. Tale programma permette di visualizzare sia il profilo spaziale della deformazione della membrana grafenica del nanotamburo (misurata con l’AFM) che quello della resistenza elettrica della membrana. In questo modo è possibile caratterizzare esaustivamente il comportamento piezoresistivo della membrana grafenica del nanotamburo. I risultati delle misure effettuate mostrano che il centro della membrana è più facilmente deformato dei suoi bordi, come atteso. Sotto l’azione della punta AFM si misurano variazioni dell’ordine del 10% nella resistenza elettrica della membrana. Questo rappresenta un risultato promettente nei confronti della possibile realizzazione di nanosensori di masse ridottissime (singole molecole) o di piccoli cambiamenti di pressione.
Piezoresistivity of graphene
KHATIBI, ELHAM
2010/2011
Abstract
Graphene is the thinnest known material, which gathered a lot of attention after its discovery because of unique electrical and mechanical properties such as high stiffness and electron mobility. Besides, the small size and mass of graphene make it an ideal candidate for nanoelectromechanical systems (NEMS), which offer potential for new applications such as single atom mass sensors. In addition to the mentioned features, the interplay between mechanical and electrical properties of graphene is an interesting functionality for designing NEMS. This interplay is called “piezoresistivity” and is investigated by gauge factor (GF) which is the ratio of relative changes in the electrical resistance to the applied mechanical strain. In this thesis we report for the first time the experimental study of the piezoresistivity in few layer graphene “nanodrums”, that are suspended flakes over circular holes. We measure the electrical resistance of the flake while the flake is deformed by means of the force-distance measurements by an atomic force microscopy (AFM) under ambient condition. Furthermore, the analysis of the experimental data required the writing of a program in Matlab to merge the results of the AFM and electrical measurements. By this program the measured force-distance curves and changes in the electrical resistance while the AFM tip is deforming the flake are plotted. In addition to that the spatial profile of the compliance of the flake is plotted to show the pattern of the deformability of the flake. Moreover, the spatial profile of the changes in the electrical resistance of the flake while the tip is pushing the flake and the flake is deformed is plotted. This factor gives information about the changes in the GF and the piezoresistivity of the graphene flakes. The results proved that our method to use AFM under ambient condition as a measurement tool can be used to derive information on the piezoresistive behavior of graphene. According to the results at the center of the hole the flake is more easily deflected than the edges. Moreover, the deformation of the drums through AFM affects the electrical resistance of the flake (by approximately 10%) and it shows that graphene illustrates piezoresistive behavior in practice. This is a promising prospect for applications of the graphene nanodrum as the sensor of very small mass (individual molecules) or pressure changes in NEMS.| File | Dimensione | Formato | |
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Piezoresistivity of Graphene (Elham Khatibi 737093).pdf
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https://hdl.handle.net/10589/16787