Electron Irradiation-Induced Degradation of TiN Thin Films on Quartz and Sapphire Substrates

In this contribution, we investigated the properties of magnetron-sputtered TiN thin films on sapphire and quartz substrates before and after 5 MeV electron irradiation with a fluence of 7 × 1013 e/cm2. Structural, morphological, optical, and electrical properties were analyzed to observe the impact of electron irradiation on the TiN thin films. The results showed improved electrical properties of the TiN thin films due to high-energy electron irradiation, resulting in increased specific conductivity compared to the as-deposited thin films on both sapphire and quartz substrates. The structural features of the TiN thin films on the sapphire substrate transformed from polycrystalline to amorphous, while the TiN thin films deposited on the quartz substrate remained unchanged. Chemical state analysis indicated changes in the metallic bonding between Ti and N in the deposited TiN on the sapphire substrate, while TiN deposited on the quartz substrate retained its Ti-N bonding. This study provides insights into the effects of electron irradiation on TiN thin films, emphasizing the importance of investigating radiation resistance for the reliable operation of optoelectronic devices and photovoltaic systems in extreme ionizing radiation environments.

Interstellar photovoltaics

The term 'Solar Cell' is commonly used for Photovoltaics that convert light into electrical energy. However, light can be harvested from various sources not limited to the Sun. This work considers the possibility of harvesting photons from different star types, including our closest neighbor star Proxima Centauri. The theoretical efficiency limits of single junction photovoltaic devices are calculated for different star types at a normalized light intensity corresponding to the AM0 spectrum intensity with AM0 = 1361 W/m2. An optimal bandgap of > 12 eV for the hottest O5V star type leads to 47% Shockley-Queisser photoconversion efficiency (SQ PCE), whereas a narrower optimal bandgap of 0.7 eV leads to 23% SQ PCE for the coldest red dwarf M0, M5.5Ve, and M8V type stars. Organic Photovoltaics (OPVs) are the most lightweight solar technology and have the potential to be employed in weight-restricted space applications, including foreseeable interstellar missions. With that in mind, the Sun's G2V spectrum and Proxima Centauri's M5.5Ve spectrum are considered in further detail in combination with two extreme bandgap OPV systems: one narrow bandgap system (PM2:COTIC-4F, Eg = 1.14 eV) and one wide bandgap system (PM6:o-IDTBR, Eg = 1.62 eV). Semi-empirically modeled JV-curves reveal that the absorption characteristics of the PM2:COTIC-4F blend match well with both the G2V and the M5.5Ve spectrum, yielding theoretical PCEs of 22.6% and 12.6%, respectively. In contrast, the PM6:o-IDTBR device shows a theoretical PCE of 18.2% under G2V illumination that drops sharply to 0.9% under M5.5Ve illumination.

Coupling between structural properties and charge transport in nano-crystalline and amorphous graphitic carbon films, deposited by electron-beam evaporation

Nano-crystalline and amorphous films of graphitized carbon were deposited by electron-beam evaporation of bulk graphite. Structural properties and the size of graphite nanoclusters (L ≈ 1.2-5 nm) in the films were determined from the analysis of their Raman spectra. Electrical properties of the bulk nano-crystalline graphite reference sample and the deposited graphitic carbon films were measured by means of the Hall effect technique within the temperature range from 290 to 420 K. The electrical conductivity σ and Hall mobility μ_H of all samples exhibited exponential temperature dependences, indicating on the non-metallic behavior. Electrical properties of the amorphous graphitic carbon thin films, deposited at low substrate temperatures (620 and 750 K) were analyzed in the scope of the hopping charge transport mechanism via localized states. We have shown that the charge transport in the bulk and thin film (920 K) nano-crystalline graphite samples is carried out via the tunneling and thermionic emission over potential barriers at the grain boundaries.This paper contributes towards better understanding of coupling between structural and electrical properties of graphitic carbon thin films.