Mina Farahani | Searcharxiv

arXiv2026

Enhanced hydrogen response of copper-doped TiO$_2$ synthesised by helium-assisted magnetron sputtering

Cu-doped TiO$_2$ thin films for hydrogen sensing were synthesised by reactive DC magnetron sputtering in Ar/O$_2$/He mixtures, with the He fraction used as a control parameter for film growth. By combining normal-angle deposition (NAD) and glancing-angle deposition (GLAD) with post-deposition annealing, the effects of He on microstructure formation and sensor performance were examined. X-ray diffraction and electron microscopy revealed that He promotes nanostructuring, lattice expansion in as-deposited NAD films, increased porosity after annealing, and a stronger anatase character in the final oxide layers. These structural changes, which enhance the reactive surface area, lead to improved hydrogen sensing at 300\,$^\circ$C in 1~vol.\,\% H$_2$. The response of NAD films increased from 1.4 to 6.0 simply by replacing part of the argon with helium, whereas GLAD films showed only a modest increase. The observed nanostructuring is discussed in terms of a simulation-supported growth scenario involving energetic backscattered He, a reduced hammering effect, and cooling-related suppression of adatom mobility, which together favour the formation of a more open sensing layer. Helium-assisted sputtering represents a useful physical route for tailoring oxide thin films for gas-sensing applications.

cond-mat.mtrl-sci↗

arXiv2025

Deposition rate and energy to substrate in chopped and standard HiPIMS: identifying optimal pulse parameters

High-Power Impulse Magnetron Sputtering (HiPIMS) offers higher ionized flux fractions at the cost of lower deposition rates compared to conventional DCMS. A fine optimization of the deposition conditions is crucial for specific applications. Chopped or multi-pulse HiPIMS (segmenting pulses into shorter micropulses) has been proposed to mitigate ion back-attraction and promote working gas recovery. This study investigates how micropulse length, delay time between segments, and magnetic field strength influence energy flux, deposition rate, and ionized flux fraction in chopped and standard HiPIMS. These quantities are evaluated by passive thermal probe, biasable QCM and mass spectrometer measurements at the substrate position. Deposition-averaged and pulse-averaged power is kept constant for all conditions to facilitate meaningful comparison. Results indicate that chopping the HiPIMS pulse consistently leads to higher energy flux and total deposition rate compared to standard HiPIMS at the same total pulse length, primarily due to increased ion flux. A weaker unbalanced magnetic field configuration enhances deposition rates and ion transport. In chopped HiPIMS, increasing micropulse length decreased energy flux and deposition rates, whereas increasing the delay time between micropulses substantially improved these parameters. Importantly, standard HiPIMS, which operated at higher frequencies and short pulse lengths, demonstrated superior performance (with higher total energy and particle fluxes) than chopped HiPIMS when compared at similar short pulse durations. This suggests that consistent short pulse durations and sufficient off-times for complete gas refill are paramount for maximizing ion fluxes and deposition rates.

physics.plasm-ph↗