Julio César Sagás

Plasma-activated water (PAW) was investigated as an oxidizing precursor in atomic layer deposition (ALD) of Al2O3 films on Si(100) in the temperature range of 100–200 °C for 250, 500, and 1000 deposition cycles. PAW was produced using a pin-to-liquid plasma system, and depositions were carried out using trimethylaluminum (TMA) with different oxidants: PAW, deionized water, aqueous solutions containing O3, H2O2, NO3−, and a composite solution combining all three species at concentrations matching those found in PAW. PAW-ALD produced thicker films than conventional ALD, demonstrating enhanced surface oxidation efficiency, particularly at low temperatures, with a growth per cycle (GPC) increase of up to 17.98% at 100 °C. While film thickness slightly increased with temperature for conventional ALD, an opposite trend was observed for PAW-ALD. Among the individual aqueous solutions, only nitrate-containing solutions led to an increase in film thickness, though not to the same extent as PAW, indicating that additional species or synergistic effects in PAW contribute to the growth enhancement. Film characterization by X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FTIR), and reflectance spectroscopy confirmed near-ideal stoichiometry and optical properties comparable to conventionally deposited films, indicating that PAW enhances growth kinetics without degrading film quality. The results suggest that nitrates may contribute to surface oxidation through direct reaction with surface methyl groups or through water-cluster-mediated transport mechanisms, though the complete elucidation of PAW-ALD chemistry requires further investigation.

Co-doping in TiO2 thin films enables modulation of optical and electronic properties, expanding their applicability in photocatalytic and optoelectronic devices. In this work, Co:TiOx films were deposited by reactive magnetron sputtering using a mosaic Ti–Co target, allowing growth of films with distinct cobalt concentrations under identical plasma conditions. Structural and chemical analyses by XRD and XPS confirmed the coexistence of Co dopped TiO2, as well as CoO and Co3O4 phases, depending on the distance between the substrates and the Co inserts in the target. AFM and SEM/EDS measurements revealed smooth, homogeneous surfaces with uniform elemental distribution. Optical transmittance and reflectance spectra showed a systematic red shift of the absorption edge, accompanied by a reduction of the indirect band gap from 2.9 eV to 1.8 eV as cobalt content increased. These results indicate that Co-induced impurity states and oxygen-vacancy–related defects play a key role in promoting band-gap narrowing. Overall, the findings demonstrate that mosaic-target sputtering is an effective single-step strategy for tuning composition, electronic structure, and optical response in Co-doped TiO2 thin films, offering a scalable approach for advanced functional materials.

The present paper investigated the deposition of oxygen-functionalized graphene (GO) on copper (Cu) substrates using a low-voltage electrophoretic deposition (EPD) compared to a bipolar high-impulse electrophoretic deposition (HI-EPD) as a function of electrode distance and deposition time. The conventional deposition was conducted with a constant voltage of +10 V. Bipolar HI-EPD used 1.0 μs period pulses, alternating pulses of +600 and −600 V. The pulses train consisted of four individual pulses, two positive and two negative (2p+ and 2p−), with a 20.0 μs off-time between the pulse sets. GO films were characterized by scanning electron microscopy, water contact angle, atomic force microscopy, relative sheet resistance, Raman, x-ray photoelectron spectroscopy, and adhesion tests. For conventional EPD, the minimal deposition time necessary to obtain homogeneous GO films was 10 min with a distance between electrodes of 1.0 cm. When bipolar HI-EPD was used, a homogeneous deposition was obtained in 5.0 min. The samples with GO films had an average reduction in the contact angle by 28% in comparison to the Cu surface, showing hydrophilic behavior, and an increase in relative sheet resistance compared to Cu by 104 times for deposition through conventional EPD and up to 105 times for deposition through bipolar HI-EPD. The presence of GO increased the surface roughness. The bipolar HI-EPD showed no apparent water electrolysis even under high-voltage pulse deposition. Thus, the bipolar HI-EPD demonstrates a promising process for producing homogeneous film depositions of GO nanoparticles in an aqueous medium with lower deposition time.

Plasma-activated water (PAW) is enriched with reactive oxygen and nitrogen species (RONS), which significantly alter its physicochemical properties and expand its applicability in fields like materials science, biomedicine, and agriculture. This study investigates the specific contributions of key long-lived RONS—hydrogen peroxide (H₂O₂), nitrate ions (NO₃ ⁻), and ozone (O₃)—to the physicochemical properties of PAW. PAW was produced using a pin-to-liquid plasma system, and its properties were characterized using UV–Vis spectroscopy, Raman spectroscopy, Fourier-transform infrared spectroscopy, and measurements of pH, electrical conductivity, total dissolved solids (TDS), and oxidation-reduction potential (ORP). To isolate the effects of individual RONS, aqueous solutions containing H₂O₂, NO₃ ⁻, O₃, and a composite solution with the three species at concentrations equivalent to those measured in PAW were prepared and analyzed using the same characterization techniques. The individual RONS solutions revealed specific influences on the physicochemical parameters: H₂O₂ led to slight acidification and increased conductivity; NO₃ ⁻; significantly increased conductivity and TDS; and O₃ had minimal effect on the measured properties. The composite solution is the only one that has a positive ORP; it is an oxidant. However, none of the individual solutions replicated the comprehensive alterations observed in PAW. The composite solution containing all three RONS showed more pronounced changes but still did not fully match PAW’s properties. This difference hints to the presence of unidentified long-lived reactive species in PAW, possibly originating from electrode degradation, as spectroscopic analyses indicate. Understanding the individual and combined effects of long-lived RONS is crucial for optimizing PAW generation and tailoring its properties for specific applications.

This study investigates the impact of vapour-phase precursor flow rates—specifically those of trimethylaluminum (TMA) and deionized water (H₂O)—on the deposition of aluminum oxide (Al₂O₃) thin films through atomic layer deposition (ALD). It explores how these flow rates influence film growth kinetics and surface reactions, which are critical components of the ALD process. The research combines experimental techniques with a zero-dimensional theoretical model, designed specifically to simulate the deposition dynamics. This model integrates factors such as surface reactions and gas partial pressures within the ALD chamber. Experimentally, Al₂O₃ films were deposited at varied TMA and H₂O flow rates, with system conductance guiding these rates across different temperature settings. Film properties were rigorously assessed using optical reflectance methods and attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy. The experimental findings revealed a pronounced correlation between precursor flow rates and film growth. Specifically, at 150 °C, film thickness reached saturation at a TMA flow rate of 60 sccm, while at 200 °C, thickness peaked and then declined with increasing TMA flow above this rate. Notably, higher temperatures generally resulted in thinner films due to increased desorption rates, whereas higher water flow rates consistently produced thicker films, emphasizing the critical role of water vapour in facilitating surface reactions. This integrative approach not only deepens the understanding of deposition mechanics, particularly highlighting how variations in precursor flow rates distinctly affect the process, but also significantly advances operational parameters for ALD. These insights are invaluable for enhancing the application of ALD technologies across diverse sectors, including microelectronics, photovoltaics, and biomedical coatings, effectively bridging the gap between theoretical predictions and empirical results.