Research About Properties Change Of Patterned Single-layer Graphene In Focused Ion Beam

Graphene, basic component of carbon allotropes, has unique two-dimensional structure. For excellent electrical, optical and mechanical properties, it has become a research hotspot in new materials field. Graphene-based devices are commonly prepared by electron beam lithography combined with plasma etching. However, the photoresist used in electron beam lithography processing will contaminate graphene surface and degrade its transport property. Focused ion beam(FIB) has been already employed in semiconductor industry with high spatial resolution, and it can avoid damaging graphene with omitting photoresist processing. In this work, FIB equipped with the gallium ion beam is used to pattern single-layer graphene. Graphene before and after ion irradiation is characterized using Raman spectroscopy(RS) and atom force microscope(AFM). The effect of different doses of gallium ion on properties of graphene is studied through varying dwell time of ion beam.The graphene samples used in this work are preparated by chemical vapor deposition(CVD) and then transported on SiO2/Si substrate. RS is used to characterize the graphene samples after ion irradiation. Pristine graphene presents a typical Raman spectrum of single-layer graphene. As the ion dose is increasing, the ratio of intensity between D peak and G peak increases first and then decreases. The full width at half maximum(FWHM) of G peak and 2D peak broaden. The intensity of G peak and 2D peak weaken. The ion irradiation induces the increase of defect density in graphene, leading to the increase of the intensity of D peak. The ion irradiation causes the lattice disorder in graphene, resulting in the decrease of the intensity and the increase of the FWHM for G peak and 2D peak. Amorphization areas increase with the defects gathering, leading to degeneration of the characteristic peaks of graphene.The peak force tapping mode of AFM is used to characterize the surface morphology of graphene. The surface roughness of graphene decreases first and then increases. At small dose of gallium ion, the ions sputter carbon atoms and bombard surface impurities, which decreases the number of large size of impurities. At the same time, the thermal annealing caused by ion irradiation decreased surface adsorbates. The surface roughness of graphene decreases. As the ion dose is increasing, the number of the dangling bonds increases, leading to accumulation of hydrocarbons. Meanwhile, the ion irradiation induces wrinkles at graphene surface. The surface roughness of graphene increases.The scanning capacitance module and kelvin probe module of AFM are used to characterize the changes of electronic property and work function, respectively. The capacitance signal of graphene sample decreases, and the work function of graphene increases first and then decreases. The ion irradiation induces the increase of the defect density and a metal-insulator transition occurs in graphene, leading to the decrease of the capacitance signal. the change in the intrinsic structure leads to the change in work function of graphene. The C-C bonds are broken by the gallium ions and become the dangling bonds. The dangling bonds are easy to absorb the dopants in atmospheric environment. The electrons transfer from the dangling bonds to the dopants, leading to p-type doping of graphene. The work function of graphene increases. Graphene changes into a completely amorphous carbon. Hence, the work function of graphene decreases.