Influence of the voltage waveform during nanocomposite layer deposition by aerosol-assisted atmospheric pressure Townsend discharge

Abstract

This work examines the growth dynamics of TiO2-SiO2 nanocomposite coatings in plane-to-plane Dielectric Barrier Discharges (DBDs) at atmospheric pressure operated in a Townsend regime using nebulized TiO2 colloidal suspension in hexamethyldisiloxane as the growth precursors. For low-frequency (LF) sinusoidal voltages applied to the DBD cell, with voltage amplitudes lower than the one required for discharge breakdown, Scanning Electron Microscopy of silicon substrates placed on the bottom DBD electrode reveals significant deposition of TiO2 nanoparticles (NPs) close to the discharge entrance. On the other hand, at higher frequencies (HF), the number of TiO2 NPs deposited strongly decreases due to their “trapping” in the oscillating voltage and their transport along the gas flow lines. Based on these findings, a combined LF-HF voltage waveform is proposed and used to achieve significant and spatially uniform deposition of TiO2 NPs across the whole substrate surface. For higher voltage amplitudes, in the presence of hexamethyldisiloxane and nitrous oxide for plasma-enhanced chemical vapor deposition of inorganic layers, it is found that TiO2 NPs become fully embedded into a silica-like matrix. Similar Raman spectra are obtained for as-prepared TiO2 NPs and for nanocomposite TiO2-SiO2 coating, suggesting that plasma exposure does not significantly alter the crystalline structure of the TiO2 NPs injected into the discharge.

Modification of the optical properties and nano-crystallinity of anatase TiO2nanoparticles thin film using low pressure O2 plasma treatment

“…In this context, the results presented in Figure 7 confirm that spin-coated TiO2 NPs are anatase crystallites and small in size. Moreover, after the plasma treatment, the Eg band peak maintains a similar asymmetrical shape but shifts to 150 cm -1 ; such feature can be related to an increase in the mean crystallite size of TiO2 NPs [42,45], in very good agreement with the conclusions of in situ spectroscopic ellipsometry (Section 3.1) and TEM (middle of Figure 5) in Section 3.3.…”

Control of composite thin film made in an Ar/isopropanol/TiO2 nanoparticles dielectric barrier discharge by the excitation frequency

“…This can be understood by comparing coating without (Figure a) and with modulation (Figure b) for a frequency of 10 kHz. Even if the discharge works in filamentary regime, the results show the same effects as the investigation conducted by Profili et al in Townsend regime.…”

“…Moreover it seems that in their configuration, most of the NPs are deposited before the edge of the DBD electrode due to the shape of the electric field in this area. In order to improve the substrate coverage, that is, the spatial homogeneity of the deposited NPs all along the substrate, Profili et al used a new complex excitation waveform where two frequencies are alternatively employed. It was shown that a homogenous Townsend discharge regime can be maintained even by injecting precursors and that a more uniform concentration of NPs can be obtained all along the substrate.…”

Recent Advancements in the Use of Aerosol-Assisted Atmospheric Pressure Plasma Deposition

“…The versatility of these methods is straightforward: by changing the monomer and the additive dispersed in the atomizer mixture in Ia, or changing the monomer in the auxiliary line and the additive in the aerosol, it is possible to deposit a wide range of multicomponent coatings. In particular, for Ib, the dispersion of nanoparticles (NPs) in monomers has been reported: TiO 2 /organosilicon [50,60], AlCeO 3 /HMDSO/ethanol [45], ZnO octane [57], polyhedral oligomeric silsesquioxane (POSS)/HMDSO [76]. In case II, a gaseous monomer is often inlet, as ethylene, with an aerosol in an aqueous solution of vancomycin [63,73,74], gentamicin [72] or lysozyme [59]; on the other hand, the monomer can be inlet by means of a bubbling system, as reported for the deposition of Ag NPs containing films [62], or silica layers entrapping TiO 2 NPs [61].…”