Low work function nanocrystalline lanthanum boride thin films by room temperature femtosecond pulsed laser deposition for novel hybrid thermionic conversion devices

Lanthanum hexaboride (LaB6) is a well-known material for electron emission applications. Many works concerning the production of LaB6 thin-films were reported in the last two decades. In particular, PLD demonstrated to be one of the most feasible deposition technique for the synthesis of LaB6 thin films, with optimal results in terms of crystallinity and values of work function lower than 2.8 eV. However, such technique is characterized by a low deposition rate at substrate temperatures higher than 500 °C, required for the proper crystallinity and structure quality. Previous works published in the literature report results obtained by the exclusive use of nanosecond laser assisted PLD. Conversely, a high growth-rate of the films may be correlates to the use of ultrashort pulse lasers as well as deposition at low temperatures. Hence, we propose for the first time PLD assisted by femtosecond pulse laser as an effective method for the development of LaB6 thin films with the desired bulk and surface physical properties to act as excellent thermionic emitters, prepared at room temperature (RT) and with extremely high deposition rates.