Research On Thinning And Patterning Of Graphene By Laser Processing

Graphene, a one-atom thick layer of graphite with densely packed sp2-bonded carbon atoms, has been extensively investigated since its first production/generation in the lab by Geim, et al. in 2004. The unique properties such as electron mobility of 2.5 × 105 cm2/v·s at room temperature, high thermal conductivity(> 3000 Wm K-1) and optical absorption of exactly πα=2.3% have been reported. Depending on these properties, graphene is considered to be the next-generation materials of transistors, transparent conductive electrodes and in other applications. The properties of graphene, such as electronic structure and optical transparency are functions of its number of layers(NOL). Therefore, it is significantly important to accurately control the number of graphene layers. Although many groups have reported the synthesizing of monol ayer or bilayer graphene, to control the NOL in graphene synthesis is still challenging. On the other hand, graphene is difficult to be used in electronic devices because of its zero-bandgap characteristic. So it is the significant purpose to control the electronic properties of graphene. Depending on these hotspot in graphene research, we propose a new method for precise control of graphene layer number and electronic properties by laser irradiation. Because this process/method has many advantages, such as one-step process, non-contact operation, substrate and environmental-friendly, and patternable thinning, it will be potentially used in the fabrication of graphene-based electronic devices.The pristine graphene with 5 layers was thinned to 2 layers by CO2 laser in vacuum by vary the laser power density and irradiation time. The conclusion was confirmed by raman spectra, TEM and transmittance. Based on the properties of CVD graphene, a new mechanism of thinning graphene by continuous laser irradiation was proposed.The thinning process was also achieved by picosecond laser in atmosphere. The graphene layer number was precisely controlled by vary the laser energy density, which means that the graphene can be thinned to specific layer number by one-step laser processing. The mechanism of picosecond laser thinning was proposed, depending on the interaction between ultrafast laser and graphene. The patternable thinning was achieved by programing the laser scanning path. Besides, the femtosecond laser was also used in patterning graphene. The thresholds of cutting monolayer graphene and multilayer graphene were obtained. Finally, the monolayer graphene was doped by picosecond laser with lower energy density. The doping result and the mechanism of doping were analyzed by Raman spectra and XPS. The doped graphene was used in graphene-silicon solar cell, by which the conversion efficiency was improved to 6.4%.