arXiv subjects

Claudia Lazzaroni

Publications and source records attributed to Claudia Lazzaroni.

3 recordsLinked to original sources

arXiv2026

Proof of operation of a micro-hollow cathode discharge driven by a true ns-pulsed high voltage: emission properties and atomic nitrogen production

The implementation of Micro-Hollow Cathode Discharges (MHCDs) for the efficient and controlled dissociation of molecular nitrogen into reactive N-atoms remains a central challenge in the synthesis of strategic materials such as hexagonal boron nitride (h-BN). Traditional MHCDs driven with DC high voltages (HV) can generate N-atoms under low-to-moderate gas pressures. However, they are prone to intrinsic instabilities that eventually induce arcing, increase thermal load and limit significantly their lifetimes. In this work we aim to enhance N2 dissociation efficiency in an Ar/N2 MHCD driven by a true nanosecond (ns) pulsed positive HV which has not been yet considered in MHCDs. A testbed reactor is employed to investigate microplasma behavior under ns-pulsed operation, which is then compared to a conventional DC MHCD. Specifically, we combined optical emission and ns-TALIF diagnostics under suitable operating conditions of each HV regime comprising different gas mixtures, pressures, and electrical parameters. These measurements allowed for the identification of key excited species and mapping of ground-state N-atoms absolute density in the low-pressure chamber of the MHCD reactor. It is demonstrated that ns-pulsed excitation produces a more symmetric discharge expansion on the cathodic surface compared to a standard DC excitation, while generating similar nature of emissive species and consuming up to 2 orders of magnitude lower average power depending on the operating frequency and voltage. Importantly, up to 6-fold enhancement in absolute N-atoms density (maximum value measured: 1.14x10 15 cm -3 ) is achieved with the ns-pulsed MHCD making it very promising for h-BN synthesis.

physics.plasm-ph↗

arXiv2026

A Comprehensive multi-species comparison of rotational temperature probes in a DC Ar/N$_2$ micro-hollow cathode discharge

Accurate gas temperature ($T_{\rm Gas}$) determination in microplasmas is critical for optimizing their applications, yet isolated diagnostic approaches may yield misleading results, especially under strong non-equilibrium conditions. Here, high resolution rotational spectra of N$_2$(C), OH(A), NH(A) and NO(A), generated in the plasma jet of a DC Ar/N$_2$ microhollow cathode discharge (MHCD), are recorded and their associated rotational temperatures ($T_{\rm rot}$) are cross compared. A detailed experimental analysis and robust fitting of the rotational spectra are performed, achieving a reliable estimation of $T_{\rm Gas}$. The dominant formation mechanisms of these species and their corresponding impact on rotational population distributions are also interrogated. Particularly, our findings indicate that the $T_{\rm rot}$of N$_2$(C) is significantly influenced by energy transfers from argon metastables (Ar$^m$) and spectral interference from NH(A). This makes it unreliable as a thermometric probe in Ar-rich MHCD, unless complex analyses are employed. In contrast, OH(A) rotational population distribution appears to be less sensitive to Ar-induced perturbations across various discharge currents and pressures, providing more straightforward results. For all molecules considered, this study reveals the conditions under which all the measured $T_{\rm rot}$ can be reliably considered to be in equilibrium with $T_{\rm Gas}$. This highlights the importance of crossvalidating multiple thermometric probes and investigating relevant excitation kinetics when measuring $T_{\rm rot}$ in reactive microplasmas.

physics.plasm-ph↗

arXiv2025

Hexagonal boron nitride thin film synthesis with a ns-pulsed MHCD: in-situ plasma diagnostics and post-growth film characterization

Hexagonal boron nitride (h-BN) is deposited on Si <100> wafer ($\approx$20 cm2) via Plasma Enhanced Chemical Vapor Deposition (PECVD) using a ns-pulsed N2/Ar Micro Hollow Cathode Discharge (MHCD) as a microplasma source. For the first time, aluminum nitride (AIN) is employed as the dielectric material in the MHCD to mitigate film contamination by atomic oxygen, an issue previously observed with conventional Al 2O3 dielectrics. A comprehensive multi-diagnostic approach is followed to characterize the deposited h-BN, including Raman spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), and X-ray photoelectron microscopy (XPS). In parallel, in-situ diagnostics such as optical emission spectroscopy (OES) and intensified CCD (ICCD) imaging are used to monitor plasma properties, including emission profiles, gas temperature and discharge morphology. Raman spectra reveal the E2g phonon mode of h-BN around 1366 cm_____, confirming successful synthesis. SEM imaging reveals an almost complete surface coverage by the film, with localized delamination. This is probably due to an uneven resistive heating of the Si wafer, rapid post-deposition cooling ($\sim$13 K/min) and ambient exposure. AFM analysis indicates an average thickness of about 33 nm after 90 minutes of deposition ($\sim$22 nm/h deposition rate). XPS measurements reveal an average B/N atomic ratio of $\sim$1.5 along the wafer diameter. Deviations from ideal film properties (e.g., stoichiometric unity, uniform morphology) are attributed to plasma-induced inhomogeneities (such as non-uniform species flux and temperature gradients) among other factors (e.g., ambient exposure post-deposition), which affect nitrogen and boron incorporation and localized film properties. Despite these challenges, the MHCD-driven PECVD process demonstrates strong potential for scalable h-BN synthesis, with further optimization of the reactor design, plasma conditions, and gas chemistry required to grow ideal films.

physics.plasm-ph↗