An Investigation of Various Oxides of Tantalum Produced by Pulsed Laser Ablation and Continuous Wave Laser Heating

Ta₂O₅ exists in multiple crystalline and amorphous phases and is used in a variety of applications (e.g. microelectronics, optics). In this work, we show that different phases of Ta₂O₅ can be generated in high-temperature laser experiments by varying input laser parameters. In our experiments, we used both CW and nanosecond pulse Nd:YAG lasers (1064 nm), which were focused onto a Ta metal target to generate particulates via local ablation/vaporization. Scanning electron microscopy (SEM) and Raman spectroscopy of particulates formed by nanosecond laser ablation show the presence of two distinct oxide phases. The first phase comprised micrometer-sized particulates having a Raman spectrum consistent with a previously observed amorphous Ta₂O₅ phase. The second phase comprised particulates ~5-10 micrometers in diameter having Raman spectra similar, but not identical, to that of known crystalline β-Ta₂O₅. Transmission electron microscopy (TEM) of particulates from CW laser processing yielded good agreement with a monoclinic H-Ta₂O₅ crystalline phase. Additionally, the unique Raman signature was observed proximate to the point of laser impingement in the CW laser experiments that confirms this structure. Further from that point produced particulate with a Raman spectrum that matched β-Ta₂O₅. We discuss these results in the context of different oxide cooling histories.