The laser-induced structures are results of particle aggregation. Particle aggregation takes Entospletinib chemical structure place as part of vapor

condensation by the collision of nucleus. To generate nanofibrous structures, an immense amount of nanoparticle aggregation is required. Therefore, continuous arrival of the laser pulses is needed in order to ablate the target material great enough to maintain the plume nucleus density at the www.selleckchem.com/products/R406.html critical level. Hence, critical amount of laser fluence should be transferred to the substrate in order to initiate the plume and keep it at the certain level. As a result, the formation of nanofibrous structures is not possible in lower laser pulse energies, and instead, microstructures would be generated. The evaporation rate by a single laser pulse ablation is a function of material properties and laser parameters [16]: (1) Here, P avg is the average power (in W), measured directly from incident laser pulse, R rep (in s−1) is the laser pulse repetition rate, P pulse = P avg/R rep is the laser pulse energy, and A foc (in cm2) is the irradiation focal spot area.

It can be obtained by calculating the theoretical laser minimum spot diameter (D 0) as where λ 0 is the wavelength of the laser, f is the effective focal length of the lens, and D denotes the laser beam diameter. As Equation 1 suggests, increasing the laser average power results in a rise in the total laser energy P5091 flux transferred to the irradiated spot. The higher transferred laser energy flux for the optimum evaporation regime leads to an increase in the number of evaporated

particles; then, the deposition rate of synthesized structures will be analogous to the number of evaporated particles. The experiments were carried on at different numbers of laser pulses on both rice husk and wheat straw specimens. Figures 3 and 4 illustrate the structures synthesized at different numbers of laser pulses on rice husk and wheat straw substrates, respectively. Decreasing the number selleck chemicals llc of pulses hitting the target leads to a reduction in the laser fluence transferred to a substrate. This results in a decrease in plume volume and nucleus density inside it, which will lead to the generation of microstructures rather than nanofibrous structures. Figure 3 SEM micrographs of the structures synthesized from rice husks by 1,300 consecutive laser pulses. The laser pulse energies were (a) 0.19 and (b) 0.38 mJ. Figure 4 SEM micrographs of the structures synthesized from wheat straws by 1,300 consecutive laser pulses. The laser pulse energies were (a) 0.19 and (b) 0.38 mJ. EDS analyses in Figures 5 and 6 compare the composition changes of the structures synthesized by 2,600 consecutive laser pulses at pulse energies of 0.19, 0.38, and 0.58 mJ on rice husk and at pulse energy of 0.19 mJ on wheat straw, respectively. Since the experiments have been carried out at ambient conditions, the presence of oxygen is noticeable in the EDS graphs.