The adsorption and diffusion properties of scandium atom on the surfaces of tungsten and noble metals

There has been significant development in high-performance thermionic cathodes. For instance, scandate cathodes have attracted the significant interest of researchers owing to their efficient properties such as low operating temperature and high electron emission density, suitable for high power devices. Unfortunately, it has been difficult to achieve the high-density emission scandate cathodes due to numerous challenges including the nonuniformity of electron emission, poor surface contamination resistance among others.

Generally, several methods like chemical vapor deposition and plasma sintering have been developed to fabricate high-density emission scandate cathodes. However, understanding the ion bombarding insensitivity, which is the greatest challenge, will be a remarkable step towards realizing scandate cathodes. On the other hand, preventing surface contamination and depletion of the scandate are also key considerations. Contamination results from the adsorption of water, oxygen, and other organic compounds, especially when exposed to air while depletion of the scandate is caused by the destruction of the Bs-Sc-O layers due to evaporation and ion bombarding. To this end, this compromises the application of scandate cathodes and thus researchers have been looking for an alternative to supplement the depleted scandate to allow efficient electron emission recovery. Therefore, the use of the first principle calculations in predicting the scandate cathode properties have been recently identified as a promising solution.

A group of researchers at Beijing University of Technology: Dr. Chen Lai, Professor Jinshu Wang, Fan Zhou, Wenyuan Zhou, Yazhou Hua, and Feifei Wang investigated the adsorbability and diffusivity properties of the scandate atom on the surface of different noble metals. They purposed to use the research results in fabricating high-density emission scandate cathodes. The authors used the first principle calculation methods and the density functional theory method. Eventually, the obtained properties for the different metals were compared to each other. Their research work is currently published in the research journal, Applied Surface Science.

From the experimental results, the research team observed that the ion bombarding insensitivity was influenced by the adsorption energies. For instance, the scandate cathodes fabricated using the Ir, Os, Ru and Re metals exhibited significantly high adsorption energies and ion bombarding insensitivity. On the other hand, the adsorption energies of the scandate atom on metals surfaces decreased as a result of the W-doping. Furthermore, adsorbabilities and diffusivities properties of the Sc atom on the Ru and Re surfaces are far much higher than that of the W surfaces.

The study by Beijing University of Technology scientists successfully investigated the vital properties of the scandate cathodes as opposed to the initial works. According to the authors, the results indicate the potential of the Re and Ru materials to be used as the coating in the scandate cathodes to enhance the cathode electron emission recovery and the ion bombarding insensitivity. Therefore, it provides a path towards the realization of a high ion bombarding insensitivity and electron emission recovery which will further advance future thermionic cathodes used for various applications.