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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.

In the last years, a hybrid thermionic-photovoltaic (TIPV) direct converter has been proposed and developed for the conversion of concentrated solar energy in the frame of European H2020 project AMADEUS. In order to improve the device performance, the active materials must be characterized by a low work function. Not only, for the thermionic anode must be selected a material with specific characteristics: 1) work function lower than that of the cathode; 2) optical transparency to the blackbody radiation emitted by the emitter. A good strategy is represented by the deposition of a functional coating on the TPV surface. For this reason, BaF2 thin films have been deposited on GaAs substrates by electron-beam thermal evaporation. The thickness of the BaF2 coating has been varied from hundreds of nm down to 1 Å, in order to select the sample with the best performance. The influence of the thickness on the chemical composition and on the work function has been investigated by XPS and UPS, respectively. In particular, the work function values have been calculated from the signal cut-off in acquired He I valence band spectra. In order to avoid the low kinetic energy cut-off caused by the spectrometer, a negative bias V has been applied to the samples. The obtained results revealed that a low work function of 2.1 eV can be reached, when the thickness of the film is of ≈ 1 nm, which is a promising value for a practical application in hybrid TIPV devices. A very interesting effect appeared in the ultra-thin layers of BaF2 with a thickness of only few Å:a new peak positioned at low kinetic energy, near the signal cut-off, appeared in the valence band spectra. This result could be interpreted by considering that conductive band maximum moves above the vacuum level, resulting in negative electron affinity.

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.&nbsp

In the last years, a hybrid thermionic-photovoltaic (TIPV) direct converter has been proposed and developed for the conversion of concentrated solar energy in the frame of European H2020 project AMADEUS. In order to improve the device performance, the active materials must be characterized by a low work function. Not only, for the thermionic anode must be selected a material with specific characteristics: 1) work function lower than that of the cathode; 2) optical transparency to the blackbody radiation emitted by the emitter. A good strategy is represented by the deposition of a functional coating on the TPV surface. For this reason, BaF2 thin films have been deposited on GaAs substrates by electron-beam thermal evaporation. The thickness of the BaF2 coating has been varied from hundreds of nm down to 1 Å, in order to select the sample with the best performance. The influence of the thickness on the chemical composition and on the work function has been investigated by XPS and UPS, respectively. In particular, the work function values have been calculated from the signal cut-off in acquired He I valence band spectra. In order to avoid the low kinetic energy cut-off caused by the spectrometer, a negative bias V has been applied to the samples. The obtained results revealed that a low work function of 2.1 eV can be reached, when the thickness of the film is of ≈ 1 nm, which is a promising value for a practical application in hybrid TIPV devices. A very interesting effect appeared in the ultra-thin layers of BaF2 with a thickness of only few Å:a new peak positioned at low kinetic energy, near the signal cut-off, appeared in the valence band spectra. This result could be interpreted by considering that conductive band maximum moves above the vacuum level, resulting in negative electron affinity.

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.

Low-cost carbon-conductive films were screen-printed on a Plexiglas&reg, substrate, and then, after a standard annealing procedure, subjected to femtosecond (fs) laser treatments at different values of total accumulated laser fluence &Phi, A. Four-point probe measurements showed that, if &Phi, A &gt, 0.3 kJ/cm2, the sheet resistance of laser-treated films can be reduced down to about 15 &Omega, /sq, which is a value more than 20% lower than that measured on as-annealed untreated films. Furthermore, as pointed out by a comprehensive Raman spectroscopy analysis, it was found that sheet resistance decreases linearly with &Phi, A, due to a progressively higher degree of crystallinity and stacking order of the graphitic phase. Results therefore highlight that fs-laser treatment can be profitably used as an additional process for improving the performance of printable carbon electrodes, which have been recently proposed as a valid alternative to metal electrodes for stable and up-scalable perovskite solar cells.