Ultrafast light interaction with Graphene oxide aqueous solution

Abstract

Abstract Graphene is a 2-dimensional honeycomb structure of bonded carbon atoms. Graphene oxide has excellent characteristics such a large surface to volume ratio, high electric conductance and high transparency which make it a promising candidate for applications such as sensors and ultrafast transistors. Significant research effort is being directed at the Removal of oxygen atoms from oxidized graphene sheets without causing damage. Such oxygen removal can be done by electronic excitation with a femtosecond laser [1]. Compared with nanosecond lasers, femtosecond laser has a pulse duration that is shorter than electron cooling time, which minimizes the damage from thermal energy diffusing into the graphene network. In this work, the aqueous graphene oxide (GO) solution was exposed with a Ti:Sapphire ultrafast regenerative amplified laser operating at a wavelength of 800 nm, 1 kHz repetition rate, 100 fs pulse width, and laser powers of 150 mW and 200 mW for various durations in the range of 10 min to 45 min. The UV-visible spectra of untreated and exposed aqueous GO were compared in Fig.1. As can be seen from in the figure, the UV absorption cut-off edge of the GO solution was shifted towards longer wavelengths on increasing the laser power (Fig.1a) and exposure time at fixed laser power of 150mW (Fig.1b) and 200mW (Fig.1c). Fig. 2 compares the FTIR spectra of untreated and exposed aqueous GO solution. The broad absorption band observed at 3420 cm -1 was attributed to the stretching OH groups, The vibration band of the C≡C was observed at 2099 cm -1 ,The vibration band of noninteracting carbonyl groups(C=O), asymmetric C-O band and deformation vibration of epoxy groups were observed at 1644 cm -1 , 899cm -1 and 823 cm -1 respectively [2-3]. It is clear that on increasing the exposure time at a fixed laser power (Fig.2a and Fig.2b) the amount of absorption of hydroxyl (O-H) and carboxyl (-C=O:) groups was reduced which confirms the reduction of oxygen components in the aqueous GO solution. On comparing the Fig.2a and Fig.2b, it is also clear that on increasing the laser power, the line width of the absorption peak due reduction of OH groups which could be attributed to the reduction of C-OH and COOH bonds in the carbon honeycomb chain structure. From Fig.1 and Fig.2, it can be also concluded that on increasing the laser power and exposure time, it is possible to minimize the oxygen component groups GO solution. The Raman spectra of the aqueous GO solution before and after femtosecond laser exposure were reported in Fig. 3 for different laser power. It can be seen that, on increasing the laser power the line width of the G-band and the D-band was increased. It was also found that on increasing the laser power from 0 to 200mW, the position of the D-band and G-band were shifted towards longer wavelengths. Also observed, was the configurational change of the bilayer graphene structure (1584 cm -1 ) in untreated GO solution in to the monolayer graphene (1596 cm -1 ) form as a result of femtosecond laser exposure. The ID/IG ratio was calculated as 0.94, 1.47, and 1.12 for untreated and exposed GO solution at the exposure power of 150 mW and 200 mW, respectively. The increased ID/IG ratio could be attributed to increasing formation of new graphitic crystallites structures