Preparing metallic bulk samples for transmission electron microscopy analysis via laser ablation in an acidic liquid

The laser ablation process has been presented as a state-of-the-art and robust method for eliminating surface layers of metallic bulk materials on the micro/nanoscale with considerable accuracy and speed. These capabilities make it an ideal instrument for the primary step of metallic bulk sample preparation for transmission electron microscopy (TEM) analysis with minimal damage to the crystal structure of the sample. This work prepared a pure aluminum plate by fiber laser scanning immersed in a 5 % perchloric acid and 95 % ethanol (by volume) solution. The laser ablation in an acidic liquid condition was used in the chemical etching process, to prevent oxidation, minimize the heat-affected region, and induce crystalline defects. For this purpose, a continuous wave fiber laser with a power of 100 W, a wavelength of 1064 nm, and a focusing distance of 305 mm was applied. The TEM analysis for the as-prepared sample by the laser ablation process was compared to the standard jet electro-polishing method in the same solution. The results showed that crystal structure variations such as grain size and lattice defects did not occur in the aluminum sample due to the thermal effects of the laser ablation process. The average size of the grains and zone axis were about 600-800 nm and z = [011], respectively, in as-prepared samples by both methods; In addition, very few dislocations were observed in the grain boundaries and inside the grains. Therefore, based on the obtained results, laser ablation could be considered an eco-friendly, comfortable, fast, and cost-effective method with a small volume of chemicals used, compared to the standard jet electro-polishing method for the TEM preparation of the metallic bulk samples.