Scandium thin films of 5-30 nm thickness deposited on clean W(100) surfaces de-wet from the tungsten surface when heated to temperatures < 0.5 T_melt. The dewetting temperature and the resulting droplet size are a function of the initial scandium film thickness.

Several operating modes of cathode lens emission microscopy are used to observe scandium on W(100), including mirror microscopy, thermionic emission microscopy, and low energy electron diffraction. Scandium thin films are deposited by thermal evaporation from a metal source onto W(100). The scandium films on W(100) are observed to dewet from the W(100) surface and to form droplets when the surface is heated: the dewetting temperature is thickness dependent and spans a range from 500 to 900 °C, which is far below the melting temperature (1541 °C). Thinner films produce smaller droplets; a range of film thicknesses from 5 to 30 nm was tested. X-ray photoelectron spectroscopy of the scandium films exposed to oxygen was also measured in order to understand the function of scandium in thermionic cathodes. The shift of the W 4f peaks upon oxygen absorption, scandium adsorption, and subsequent heating indicates that oxygen preferentially bonds to scandium. The shift in the scandium 3p level indicates formation of Sc2O3.

We report the electronic characterization of n-ScN in heterojunctions, including deep level transient spectroscopy of electrically active deep levels. ScN material has been grown by plasma assisted physical vapor deposition on commercial p+ Si substrates. Current–voltage and capacitance–voltage measurements indicate that the built-in voltages for the heterojunctions used in this study are approximately 1.74 and 0.40 eV, as seen by electrons and holes. Deep level transient spectroscopy results show the presence of an electronic trap with activation energy EC−ET=0.51 eV. The trap has a higher concentration (1.2–1.6×1013 cm−3) closer to the ScN/Si interface.

Perovskite SrVO3 has recently been proposed as a novel electron emission cathode material. Density functional theory (DFT) calculations suggest multiple low work function surfaces, and recent experimental efforts have consistently demonstrated effective work functions of ∼2.7 eV for polycrystalline samples, both results suggesting, but not directly confirming, that some fraction of even lower work function surface is present. In this work, thermionic electron emission microscopy (ThEEM) and high-field ultraviolet photoemission spectroscopy (UPS) are used to study the local work function distribution and measure the work function of a partially oriented- (110)-SrVO3 perovskite oxide cathode surface. Our results show direct evidence of low work function patches of about 2.0 eV on the cathode surface, with a corresponding onset of observable thermionic emission at 750 °C. We hypothesize that, in our ThEEM and UPS experiments, the high applied electric field suppresses the patch field effect, enabling the direct measurement of local work functions. This measured work function of 2.0 eV is comparable to the previous DFT-calculated work function values of the SrVO-terminated (110) SrVO3 surface (2.3 eV) and SrO-terminated (100) surface (1.9 eV). The measured 2.0 eV value is also much lower than the work function for the (001) LaB6 single crystal cathode (∼2.7 eV) and comparable to the effective work function of B-type dispenser cathodes (∼2.1 eV). If SrVO3 thermionic emitters can be engineered to access domains of this low 2.0 eV work function, they have the potential to significantly improve thermionic emitter-based technologies.