Investigation of work function and chemical composition of thin films of borides and nitrides

Abstract

Thin films of various borides, nitrides, and barium fluorides were tentatively deposited by pulsed laser deposition and by magnetron sputtering in order to develop the components of thermionic‐photovoltaic devices for the high‐temperature thermal to electrical conversion by solid state. To improve the device performance, the materials characterized by a low work function were selected. In the present work, the chemical composition and work function of obtained films were investigated by X‐ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy techniques. The values of work function were determined from the cut‐off in the He I valence band spectra. Different films were compared and estimated on the basis of X‐ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy results.

Thermionic-enhanced near-field thermophotovoltaics

“…In this article, we examine one possible implementation of nTiPV ( Figure 1) in which the emitter is made of tungsten coated with a thin (10 nm) LaB6 layer, which is regarded as an ideal thermionic cathode due to its low workfunction (2.5-3 eV) and high electrical conductivity [7], [8], [22]. The collector consists of an extremely thin (1-3 nm) BaF2 layer, which can be directly deposited on the TPV cell front surface to provide a very low workfunction, in the range of 1-2 eV [22], and negligible absorptance.…”

“…In this article, we examine one possible implementation of nTiPV ( Figure 1) in which the emitter is made of tungsten coated with a thin (10 nm) LaB6 layer, which is regarded as an ideal thermionic cathode due to its low workfunction (2.5-3 eV) and high electrical conductivity [7], [8], [22]. The collector consists of an extremely thin (1-3 nm) BaF2 layer, which can be directly deposited on the TPV cell front surface to provide a very low workfunction, in the range of 1-2 eV [22], and negligible absorptance. The TPV cell consist of a thin InGaAs p-n junction (0.4 µm p-region on top of a 0.7 µm n-region), whose low bandgap (0.74 eV) enables photogeneration of electron-hole pairs from absorption of thermal radiation emitted at temperatures comprised between 1400 and 2000 K (see section 1 of the Supplementary Information).…”

“…The far-field counterpart of this device [19] is being experimentally implemented in ultra-high vacuum (UHV) conditions by using dielectric micro-spacers between the emitter and the PV cell, along with a combination of borides and fluorides as thermionic coatings [21], [22].…”

Thermionic-enhanced near-field thermophotovoltaics for medium-grade heat sources

“…The far-field counterpart of this device 17 is being experimentally developed 20,21 . The experimental device operates in ultra-high vacuum (UHV) conditions and uses dielectric microspacers to create a micrometer vacuum gap between the emitter and the PV cell.…”

Lanthanum (oxy)boride thin films for thermionic emission applications

“…Shirley background subtraction and mixed Lorentzian/Gaussian peak shape (30%) were used for the peak fitting. Additional details are reported elsewhere [16].…”