Study the effect of Fe nanoparticles doped on graphene nanosheets

In this work, pulsed laser ablation has been used to produce graphene nanosheets and Fe nanoparticles using graphite and Fe plate targets in deionized water solution separately. Nanosecond pulsed Nd:YAG laser with a wavelength of 532 nm was used to ablate the targets. The dimensions of nanomaterials can be changed and controlled by changing the parameters of the laser ablation, including the ablation time and the repetition rate, and also by choosing the appropriate solvent in which the ablation process takes place. After testing different ablation times, the enhanced one was obtained 20 min for Fe target and 30 min for graphit target. Also, different repetition rates of laser have been tested and the enhanced repetition rates of 15 Hz and 20 Hz for Fe and graphene were achieved, respectively. For Fe doped graphene nanosheets, the concentration ratio of the mixed samples has been chosen 1.8 ml graphene and 0.2 ml Fe. The mixed solution was stirred for 15 minutes using ultrasonic bath at room temperature. TEM image was used to study the structural properties of the Fe doped graphene nanosheet. Fe nanoparticles have spherical structures with various dimensions. These results are in good agreement with DLS evidences. To investigate the optical properties of the samples, first of all the prepared solutions were deposited on a glass substrate by a spin coater with the coating speed of 1800 rpm. Ellipsometric method is one of the chosen techniques for studying the properties of thin layers. Spectroscopic ellipsometry method measures the change in polarized light when it is reflected on a film or transmitted through the sample. Among different methods to obtain the optical properties of thin films, spectroscopic ellipsometry method was used in the wavelength range of 250 – 950 nm and at the radiation with the angle of 60 degrees. After obtaining spectroscopic parameters (ψ,Δ) which represent the amplitude ratio and phase difference between p and s polarized light waves, respectively, spectra ray software was used to calculate the optical properties of the samples. In spectroscopic ellipsometry method, instruction of an optical model is essential. A model consists of a glass substrate, an interface layer, sample thin film, surface roughness layer and air was designed. The optical properties such as refractive index and extinction coefficient of the samples have been studied. The effect of wavelength on refractive index and extinction coefficient was clear. Both refractive index and extinction coefficient had the most values in the visible wavelength region. In refractive index results, for all samples there was a peak, which was at about 360 nm, 260 nm and 270 nm wavelength for graphene, Fe and the composition of 1.8 ml graphene with 0.2 ml Fe, respectively. By increasing wavelength, for graphene sample the extinction coefficient has been decreased to almost zero, but for the two other samples this parameter was decreased to about one. Also the band gap energy of the samples has been calculated using Tauc relation. The band gap energy of graphene, Fe and the composition of 1.8 ml graphene with 0.2 ml Fe were obtained 3.34 eV, 4.73 eV and 4.55 eV, respectively. The most and the least band gap energy belonged to Fe nanoparticles and graphene nanosheets, respectively. The results indicate that, Fe nanoparticles have been placed on graphene nanosheet properly with a homogeneous distribution. Also the effect of Fe placement on Graphene nanosheet is obvious.