Heat-initiated Chemical Functionalization Of Graphene And Fermi Level Dependence

Graphene is a zero-band gap nanomaterial, where the valence band and the conduction band touch at the Fermi level at K(K’) point of Brillouin zone, making graphene not be able to be switched off. It needs to open a band gap the applications as a semiconducting devices. Previous studies theoretically and experimentally proposed that chemical functionalization is a simple and versatile method to open a band gap in graphene. In this thesis, a heat-initiated solid-phase chemical reaction was developed to functionalize graphene at wafer scale and functionalized graphene pattern was fabricated by combining with photolithography. Besides, the dependence of chemical functionalization on Fermi level was investigated based on the solid phase reaction.Firstly, graphene was chemically functionalized by benzoyl peroxide(BPO) by a heatinitiated chemical reaction. Single-layer graphene was grown on copper foil by lowpressure chemical vapor deposition(CVD), and was subsequently transferred onto SiO2 substrate. Raman spectroscopy was used to evaluate the graphene quality and the functionalization results. Raman spectroscopy used to evaluate the functionalization results after the reaction. For compatibility with traditional lithography, we tried various solvents, including acetone, ethanol and water. Due to the different solubility of BPO in the above solvents, graphene with different functionalization degrees was obtained when other parameters were kept the same.Secondly, functionalized graphene pattern was fabricated by combining photolithography and the heat-initiated chemical reaction. Briefly, photolithography was performed on graphene surface, obtaining photoresist stripes-covered graphene. Then, uncovered graphene was functionalized, leaving the photoresist stripes-covered graphene pristine. By this method, functionalized graphene pattern could be fabricated simply, quickly and precisely.Lastly, the dependence of chemical functionalization of graphene on Fermi level was investigated based on the heat-initiated solid-phase chemical reaction. Gate voltage was applied onto graphene to change Fermi level, which was determined by Raman spectroscopy. In our study, the functionalization was initiated on three graphene samples with different Fermi level. It is found that graphene at three different Fermi levels.The solid phase and the neutral radical eliminated the gate voltage-induced variation of the ion concentration on graphene surface in previous study. It is found that when graphene is positively gated, a faster reaction and hence a higher percentage of reacted carbon atoms was observed, while a negatively gated graphene led to a lower percentage of reacted carbon atoms.