Guillaume Zoppi

Machining titanium alloys is challenged by high friction and temperature at the tool–workpiece interface, leading to rapid tool wear and poor surface integrity. While cutting fluids during machining have been used to avert this, they have been observed to induce irreversible chemical reactions with the machined surfaces, while also presenting manufacturers with additional cutting fluid purchase, use, and disposal costs, in addition to environmental and health concerns. This has motivated a shift towards dry machining. This study investigates the performance of MoS ₂ -alloyed TiAlSiN thin film coatings (referred to as n :MoS ₂ ) deposited by magnetron sputtering on tungsten carbide cutting tools for dry rough turning of Ti-6Al-4V alloy. After deposition, the MoS ₂ -alloyed coatings maintained mechanical properties comparable to the TiAlSiN thin films (H ∼ 10 GPa and H/E ∼ 0.06), while significantly improving the tribological behaviour of the coated tools (coefficient of friction: TiAlSiN ∼ 0.16 and n :MoS ₂ ∼ 0.13). Moreover, the n : MoS ₂ -coated tools exhibited reduced and steady cutting temperatures, smoother chip flow, and the lowest flank wear, VB _B (∼0.191 mm), corresponding to wear reductions of approximately 71% compared to the as-manufactured (VB _B = 0.651 mm) and 20% relative to TiAlSiN-only coated tools (VB _B = 0.239 mm). The enhanced performance was attributed to the effective self-lubrication and improved heat dissipation at the cutting interface. These results demonstrate the strong potential of MoS ₂ -alloyed TiAlSiN coatings for enabling high-performance, environmentally sustainable dry machining of titanium alloys.

Achieving high performance efficiency of copper zinc tin sulphide (CZTS) thin film solar cells is a challenging issue, mainly hindered by a large open circuit-voltage deficit ( V _OC ) owing in large part to the presence of various Cu–Zn related defects and associated non-radiative recombination. Cation substitution at the Zn site offers a promising route to suppress these defects and engineer the optoelectronic properties of the absorber layer. In this work, we present the first systematic study of partial Zn-site substitution by Al across a wide compositional range (0 < x < 0.75) in Cu ₂ (Zn, Al)SnS ₄ (CZATS) thin films deposited by the low-cost and scalable ultrasonic spray pyrolysis. X-ray diffraction and Raman spectroscopy confirmed the formation of the kesterite phase across all compositions, with structural degradation emerging at x = 0.75. The optical band gap decreases progressively from 1.51 eV to 1.25 eV with increasing Al content, a trend mechanistically linked to growing lattice microstrain and enhanced band tailing. Electrically, hole mobility improves substantially as x increases from 0 to 0.5, consistent with grain growth and suppression of donor-type intrinsic defects, before deteriorating sharply at x = 0.75 due to increased dislocation density. Furthermore, the numerical analysis of the photovoltaic performance of CZATS solar cells using one-dimensional solar cell capacitance simulator with experimentally measured data revealed that the highest simulated power conversion efficiency is achieved at the composition x = 0.25, demonstrating the benefit of moderate Al substitution for photovoltaic performance. These results establish an optimal substitution window ( x = 0.25−0.5) and provide a physically coherent framework linking Al content, kesterite defect chemistry, and solar cell performance, offering a practical and scalable pathway toward higher-efficiency CZTS devices.

Cu₂ZnSn(SxSe₁₋ₓ)₄ (CZTSSe) has emerged as a promising non-toxic absorber material. However, a major challenge with thin-film PV fabrication is the high energy consumption and extended processing cycles, typically associated with conventional furnace annealing methods. Interactions between lasers and materials are valued for enabling precise, efficient, and high-speed material processing. This research underscores the effectiveness of annealing via diode laser irradiation as a fast and resource-efficient technique for crystallising CZTS semiconductor layers. A continuous 808 nm diode laser was employed to anneal CZTS films on flexible molybdenum substrate. By optimising laser parameters in an argon atmosphere, enhanced crystallinity and grain growth were achieved. X-ray diffraction confirmed mixed-phase CZTS formation, while particle size, stoichiometry, and photoluminescence analyses verified improved material quality and composition. Energy assessments show laser annealing is ~30 times more efficient than furnace processing with with significantly faster rates. These findings support scalable, cost-effective, and low-carbon manufacturing to photovoltaic technology.

Efficient light management is crucial for enhancing the performance of thin film solar cells. This study investigates the use of solution-processed zinc oxide (ZnO) nanorod (NR) arrays with novel hemispherical nanostructures as light scatterers for thin film solar cell applications. The morphology of the ZnO NR arrays is controlled by varying the seed layer deposition method [slot-die coating versus physical vapour deposition (PVD)] and thickness. A thin slot-die coated seed layer (i.e. ∼100 nm) promotes the formation of hemispherical nanostructures, which exhibit enhanced light-scattering properties compared with vertically aligned NRs grown on PVD seed layers. This study reveals that in-plane stress induced by lattice mismatches along the c -axis of NRs causes the thin seed layer to arch upwards, developing these hemispherical light scatterers. COMSOL simulations further reveal that the enhanced scattering is due to a combination of total internal reflection and refraction within the NR arrays. The deposition of a CdS buffer layer on the hemispherical arrays further improves light scattering, achieving a high average haze value of 0.72 in the wavelength range from 400 nm to 1000 nm. Bringing together the light-scattering features of these structures, SCAPS simulations demonstrate that incorporation of ZnO NR hemispherical light scatterers into cadmium telluride solar cells can significantly enhance photogenerated carrier collection, potentially enabling thinner absorber layers and reduced material consumption. This work offers a promising pathway towards cost-effective and high-efficiency thin film solar cells through innovative nanostructure design and solution-based fabrication techniques.

A CZTS– Sporomusa ovata photobiohybrid couples solar CO ₂ reduction to acetate and ethanol with microbial chain elongation, enabling sustainable production of C ₄ –C ₆ fatty acids.

Degenerate boron-doped silicon is prone to interstitial clustering, which adversely impacts key electrical properties, such as carrier concentration and mobility. Clustering becomes increasingly important with device miniaturisation, due to the high boron concentrations involved. Here we use vibrational and Compton electron energy-loss spectroscopy (EELS) in a (scanning) transmission electron microscope to measure changes in the vibrational and electronic properties of the silicon host lattice due to degenerate boron doping ( 10 20 cm − 3 hole concentration). A broad phonon defect band centred at 1064 cm ⁻¹ wavenumber was detected. Subtle changes in bonding anisotropy due to boron doping along [110] and [100] directions were also observed. Density-functional-theory modelling showed that boron acceptors had very little effect on the phonon and bonding properties. Instead boron interstitial clusters two to three atoms in size produce changes that agree more closely with experiment. However, the limited vibrational EELS energy resolution and background thermal diffuse scattering artefacts in Compton profiles do not allow a precise identification of the numerous cluster configurations that could potentially form. The results nevertheless suggest the potential of using high-spatial-resolution EELS for the detection of clustering phenomena at the device level.