Effects of Deposition Temperature and Working Pressure on the Thermal and Nanomechanical Performances of Stoichiometric Cu3N: An Adaptable Material for Photovoltaic Applications

The pursuit of efficient, profitable, and ecofriendly materials has defined solar cell research from its inception to today. Some materials, such as copper nitride (Cu3N), show great promise for promoting sustainable solar technologies. This study employed reactive radio-frequency magnetron sputtering using a pure nitrogen environment to fabricate quality Cu3N thin films to evaluate how both temperature and gas working pressure affect their solar absorption capabilities. Several characterization techniques, including X-ray diffraction (XRD), Rutherford backscattering spectrometry (RBS), Raman spectroscopy, scanning electron microscopy (SEM), nanoindentation, and photothermal deflection spectroscopy (PDS), were used to determine the main properties of the thin films. The results indicated that, at room temperature, it is possible to obtain a material that is close to stoichiometric Cu3N material (Cu/N ratio ≈ 3) with (100) preferred orientation, which was lost as the substrate temperature increases, demonstrating a clear influence of this parameter on the film structure attributed to nitrogen re-emission at higher temperatures. Raman microscopy confirmed the formation of Cu-N bonds within the 628-637 cm-1 range. In addition, the temperature and the working pressure significantly also influence the film hardness and the grain size, affecting the elastic modulus. Finally, the optical properties revealed suitable properties at lower temperatures, including bandgap values, refractive index, and Urbach energy. These findings underscore the potential of Cu3N thin films in solar energy due to their advantageous properties and resilience against defects. This research paves the way for future advancements in efficient and sustainable solar technologies.

Spectrally broad plasmonic absorption in Ga and In nanoparticle hybrids

In this work, we use Joule-effect thermal evaporation to produce hybrid structures made of Ga and In nanoparticles (NPs) on Si (100) substrates. Taking advantage of the protective oxide shell, In NPs can be used as a template for a second deposition step without structural changes, enabling the hybridization of NPs of materials. These complex structures of mixed NPs present a spectrally broad plasmonic absorption that can be optically tuned with a wide range of photon energies from UV to IR regions with a full width at half maximum range of ∼400 to 800 nm. The results suggest that the localized surface plasmon resonance (LSPR) of the hybrid NPs is mainly due to the plasmonic coupling of the in-plane modes. Furthermore, different scenarios studied by discrete dipole approximation simulations show that the interconnection between NPs is extremely sensitive to the size and the local arrangement of the nanostructures. This kind of broadening and tunable LSPR may have interest for energy transfer applications, biosensing platforms and solar cells.

Size-selective breaking of the core-shell structure of gallium nanoparticles

Core-shell gallium nanoparticles (Ga NPs) have recently been proposed as an ultraviolet plasmonic material for different applications but only at room temperature. Here, the thermal stability as a function of the size of the NPs is reported over a wide range of temperatures. We analyze the chemical and structural properties of the oxide shell by x-ray photoelectron spectroscopy and atomic force microscopy. We demonstrate the inverse dependence of the shell breaking temperature with the size of the NPs. Spectroscopic ellipsometry is used for tracking the rupture and its mechanism is systematically investigated by scanning electron microscopy, grazing incidence x-ray diffraction and cathodoluminescence. Taking advantage of the thermal stability of the NPs, we perform complete oxidations that lead to homogenous gallium oxide NPs. Thus, this study set the physical limits of Ga NPs to last at high temperatures, and opens up the possibility to achieve totally oxidized NPs while keeping their sphericity.