Search Results (11)

The W/Cu binary system is characterized by its mutual insolubility and excellent wettability, making W/Cu composite materials ideal for managing thermal and electrical properties in electronic components. To optimize material properties, control over the microstructure is crucial, and nanocomposites with uniform dispersion offer significant advantages. In this study, W/Cu composite nanoparticles were synthesized by feeding a blended feedstock of tungsten trioxide (WO₃) micro-powder and cupric oxide (CuO) micro-powder into a reactive radio frequency (RF) argon–hydrogen thermal plasma system. Cu-coated W nanocomposite particles were obtained through the vaporization, reduction, and condensation processes. The resulting nanocomposite particles were composed of body-centered cubic (BCC) α-W, A15 β-W, and face-centered cubic (FCC) Cu phases, with a chemical composition closely matching theoretical calculations. The phase evolution and morphological changes of the synthesized particles were analyzed as a function of heat treatment temperatures up to 1000 °C in a reducing atmosphere. Up to 600 °C, the phase composition and morphology remained stable. At 800 °C, localized diffusion and coalescence of Cu led to the formation of particulate Cu, and a significant phase transformation from metastable β-W to α-W was observed. Additionally, extensive Cu segregation due to long-range diffusion resulted in distinct Cu-rich and Cu-depleted regions. In these regions, notable sintering of W particles and the complete disappearance of β-W occurred. The results showed that the temperature-dependent redistribution of Cu plays a crucial role in the phase transformation of W and the morphology of W/Cu composite particles. Full article

We have developed surface acoustic wave (SAW) sensors with high sensitivity and a reversible response at room temperature (RT). The sensitive area of the sensor was prepared from vertically aligned graphene sheets, like carbon nanowalls (CNWs), which were deposited onto the quartz SAW sensor substrate. The CNWs were obtained by RF plasma-enhanced chemical vapor deposition (PECVD) at 600 °C, and their sensitivity was subsequently enhanced through hydrogen plasma treatment. The SAW sensors were tested at H₂ and CH₄ at RT, and they exhibited a reversible response for both gases at concentrations between 0.02% and 0.1%, with a detection limit of a few ppm. The additional hydrogen plasma treatment preserved the lamellar structure, with slight modifications to the morphology of CNW edges, as observed by scanning electron microscopy (SEM). X-ray photoelectron spectroscopy (XPS) investigations revealed the presence of new functional groups, a significant number of defects and electron transitions after the treatment. Changes in the chemical state on the CNW surface are most probably responsible for the improved gas adsorption after plasma treatment. These results identify CNWs as a promising material for designing new SAW sensors, with the possibility of using plasma treatments to enhance the detection limit below the ppm level. Full article

In this study, we report the use of a radiofrequency plasma-assisted chemical vapor deposition (RF-CVD) system with a hollow cathode geometry to hydrogenate anatase TiO₂ thin films. The goal was to create black TiO₂ films with improved light absorption capabilities. The initial TiO₂ was developed through magnetron sputtering, and this study specifically investigated the impact of hollow cathode hydrogen plasma (HCHP) treatment duration on the crucial characteristics of the resulting black TiO₂ films. The HCHP treatment effectively created in-bandgap states in the TiO₂ structure, leading to enhanced light absorption and improved conductivity. Morphological analysis showed a 24% surface area increase after 15 min of treatment. Wettability and surface energy results displayed nonlinear behavior, highlighting the influence of morphology on hydrophilicity improvement. The anatase TiO₂ phase remained consistent, as confirmed by diffractograms. Raman analysis revealed structural alterations and induced lattice defects. Treated samples exhibited outstanding photodegradation performance, removing over 45% of methylene blue dye compared to ~25% by the pristine TiO₂ film. The study emphasized the significant impact of 15-min hydrogenation on the HCHP treatment. The research provided valuable insights into the role of hydrogenation time using the HCHP treatment route on anatase TiO₂ thin films and demonstrated the potential of the produced black TiO₂ thin films for photocatalytic applications. Full article

Spherical molybdenum nano-powders were in-situ ultrafast synthesized from ammonium paramolybdate (APM) raw materials in a one-step reduction method by radio frequency (RF) hydrogen plasma. Due to the extreme conditions of the RF plasma torch such as its high temperature and large temperature gradient, the injected raw APM powder was quickly gasified and then reduced into nano-sized metal molybdenum (Mo) powder. The influences of APM powder delivery rate and H₂ concentration on the properties of the obtained powders were investigated. Field-emission scanning electron microscope (FESEM), transmission electron microscope (TEM), X-ray diffraction (XRD), nanolaser particle analyzer, and specific surface area method were used to characterize the morphology, phase, and particle size distribution of the powders. The results showed that the nano-sized Mo powder obtained by hydrogen plasma treatment had a quasi-spherical morphology and an average particle size of about 30 nm. The particle size could be successfully adjusted by varying H₂ concentrations. In addition, spherical nano-sized MoO₃ powder could be obtained when no H₂ was added into the RF plasma. Full article

Titanium for additive manufacturing presents a challenge in the control of costs in the fabrication of products with expanding applications compared with cast titanium. In this study, hydrogenated–dehydrogenated (HDH) titanium powder with a low cost was employed to produce spherical Ti powder using the radiofrequency plasma (RF) technique. The spherical Ti powder was used as the raw material for laser directed energy deposition (LDED) to produce commercially pure titanium (CP-Ti). Microstructural analyses of the powder revealed that RF treatment, not only optimized the shape of the titanium powder, but also benefited in the removal of the residual hydride phase of the powder. Furthermore, the LDED-HDH-RF-produced samples showed an excellent combination of tensile strength and tensile ductility compared to the cast and the LDED-HDH-produced samples. Such an enhancement in the mechanical properties was attributed to the refinement of the α grain size and the dense microstructure. The present work provides an approach for LDED-produced CP-Ti to address the economic and mechanical properties of the materials, while also providing insights into the expanding application of HDH titanium powder. Full article

Prions are highly resistant to physical or chemical damage, although previous studies have shown that STERRAD^®, a hydrogen gas plasma sterilizer using radiofrequency (RF) discharge, has an inactivation effect. Here, the effect of hydrogen peroxide gas combined with dielectric barrier discharge (DBD) plasma and corona discharge plasma using a RENO-S130 sterilizer on scrapie prions was examined. Scrapie prion-infected mouse brain homogenate was air-dried on a cover glass, sealed in a Tyvek pouch, and subjected to RENO-S130 treatment using either non-lumen mode (28 min) or Eco mode (45 min) with hydrogen peroxide gas derived from 50% hydrogen peroxide. Control (untreated) samples were prepared on a cover glass using the same procedure but without exposure to RENO-S130. PrPres (proteinase K (PK)-resistant prion protein), an index of the conformational variant of prion protein (PrP^Sc), was decreased by treatment with RENO-S130 under both modes of operation. Specifically, PrPres was identified after the 1st and 2nd cycles of protein misfolding cyclic amplification (PMCA) in control samples but was below the detection limit in RENO-S130-treated samples. A bioassay showed that treatment of prions with RENO-S130 (non-lumen or Eco mode) significantly prolonged mouse survival time. Taken together, these findings show hydrogen peroxide gas combined with DBD/corona discharge plasma can inactivate prions by reducing prion propagation and prion infectivity. This treatment is potentially applicable to the sterilization of prion-contaminated heat-sensitive medical devices. Full article

Atmospheric pressure plasma jets (APPJ) are widely used in industry for surface cleaning and chemical modification. In the recent past, they have gained more scientific attention especially in the processing of carbon nanomaterials. In this work, a novel power generation technique was applied to realize the stable discharge in N₂ (10 vol.% H₂) forming gas in ambient conditions. This APPJ was used to reduce solution-processed graphene oxide (GO) thin films and the result was compared with an established and optimized reduction process in a low–pressure capacitively coupled (CCP) radiofrequency (RF) hydrogen (H₂) plasma. The reduced GO (rGO) films were investigated by Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). Effective deoxygenation of GO was observed after a quick 2 s treatment by AAPJ. Further deoxygenation at longer exposure times was found to proceed with the expense of GO–structure integrity. By adding acetylene gas into the same APPJ, carbon nanomaterials on various substrates were synthesized. The carbon materials were characterized by Raman spectroscopy, scanning electron microscopy (SEM), and energy-dispersive X-ray (EDX) analyses. Fullerene-like particles and graphitic carbon with short carbon nanotubes were detected on Si and Ag surfaces, respectively. We demonstrate that the APPJ tool has obvious potential for the versatile processing of carbon nanomaterials. Full article

In this work we report on a rapid, easy-to-operate, lossless, room temperature heterogeneous H₂O plasma treatment process for the bonding of poly(methyl methacrylate) (PMMA) and double-sided polished (DSP) silicon substrates by for utilization in sandwich structured microfluidic devices. The heterogeneous bonding of the sandwich structure produced by the H₂O plasma is analyzed, and the effect of heterogeneous bonding of free radicals and high charge electrons (e⁻) in the formed plasma which causes a passivation phenomenon during the bonding process investigated. The PMMA and silicon surface treatments were performed at a constant radio frequency (RF) power and H₂O flow rate. Changing plasma treatment time and powers for both processes were investigated during the experiments. The gas flow rate was controlled to cause ionization of plasma and the dissociation of water vapor from hydrogen (H) atoms and hydroxyl (OH) bonds, as confirmed by optical emission spectroscopy (OES). The OES results show the relative intensity peaks emitted by the OH radicals, H and oxygen (O). The free energy is proportional to the plasma treatment power and gas flow rate with H bonds forming between the adsorbed H₂O and OH groups. The gas density generated saturated bonds at the interface, and the discharge energy that strengthened the OH-e⁻ bonds. This method provides an ideal heterogeneous bonding technique which can be used to manufacture new types of microfluidic devices. Full article

Oriented carbon nanostructures (OCNs) with dominant graphitic characteristics have attracted research interest for various applications due to the excellent electrical and optical properties owing to their vertical orientation, interconnected structures, electronic properties, and large surface area. Plasma enhanced chemical vapor deposition (PECVD) is considered as a promising method for the large-scale synthesis of OCNs. Alternatively, structural reformation of natural carbon precursor or phenol-based polymers using plasma-assisted surface treatment is also considered for the fabrication of OCNs. In this work, we have demonstrated a fast technique for the synthesis of OCNs by plasma-assisted structure reformation of resorcinol-formaldehyde (RF) polymer gels using radio-frequency inductively coupled plasma (rf-ICP). A thin layer of RF polymer gel cast on a glass substrate was used as the carbon source and treated with rf plasma under different plasma discharge conditions. Argon and hydrogen gases were used in surface treatment, and the growth of carbon nanostructures at different discharge parameters was systematically examined. This study explored the influence of the gas flow rate, the plasma power, and the treatment time on the structural reformation of polymer gel to produce OCNs. Moreover, the gas-sensing properties of as-prepared OCNs towards ethanol at atmospheric conditions were also investigated. Full article

A reactive high-power impulse magnetron sputtering (r-HiPIMS) and a reactive high-power impulse magnetron sputtering combined with electron cyclotron wave resonance plasma source (r-HiPIMS + ECWR) were used for the deposition of p-type CuFe_xO_y thin films on glass with SnO₂F conductive layer (FTO). The aim of this work was to deposit CuFe_xO_y films with different atomic ratio of Cu and Fe atoms contained in the films by these two reactive sputtering methods and find deposition conditions that lead to growth of films with maximum amount of delafossite phase CuFeO₂. Deposited copper iron oxide films were subjected to photoelectrochemical measurement in cathodic region in order to test the possibility of application of these films as photocathodes in solar hydrogen production. The time stability of the deposited films during photoelectrochemical measurement was evaluated. In the system r-HiPIMS + ECWR, an additional plasma source based on special modification of inductively coupled plasma, which works with an electron cyclotron wave resonance ECWR, was used for further enhancement of plasma density n_e and electron temperature T_e at the substrate during the reactive sputtering deposition process. A radio frequency (RF) planar probe was used for the determination of time evolution of ion flux density i_ionflux at the position of the substrate during the discharge pulses. Special modification of this probe to fast sweep the probe system made it possible to determine the time evolution of the tail electron temperature T_e at energies around floating potential V_fl and the time evolution of ion concentration n_i. This plasma diagnostics was done at particular deposition conditions in pure r-HiPIMS plasma and in r-HiPIMS with additional ECWR plasma. Generally, it was found that the obtained ion flux density i_ionflux and the tail electron temperature T_e were systematically higher in case of r-HiPIMS + ECWR plasma than in pure r-HiPIMS during the active part of discharge pulses. Furthermore, in case of hybrid discharge plasma excitation, r-HiPIMS + ECWR plasma has also constant plasma density all the time between active discharge pulses n_i ≈ 7 × 10¹⁶ m⁻³ and electron temperature T_e ≈ 4 eV, on the contrary in pure r-HiPIMS n_i and T_e were negligible during the “OFF” time between active discharge pulses. CuFe_xO_y thin films with different atomic ration of Cu/Fe were deposited at different conditions and various crystal structures were achieved after annealing in air, in argon and in vacuum. Photocurrents in cathodic region for different achieved crystal structures were observed by chopped light linear voltammetry and material stability by chronoamperometry under simulated solar light and X-ray diffraction (XRD). Optimization of depositions conditions results in the desired Cu/Fe ratio in deposited films. Optimized r-HiPIMS and r-HiPIMS + ECWR plasma deposition at 500 °C together with post deposition heat treatment at 650 °C in vacuum is essential for the formation of stable and photoactive CuFeO₂ phase. Full article

We employ H₂/Ar low-damage plasma treatment (H₂/Ar-LDPT) to reduce graphene oxide (GO) coating on a polymer substrate—polyethylene terephthalate (PET)—with the assistance of atomic hydrogen (H_α) at low temperature of 70 °C. Four-point probing and ultraviolet-visible (UV-Vis) spectroscopy demonstrate that the conductivity and transmittance can be controlled by varying the H₂/Ar flow rate, treatment time, and radio-frequency (RF) power. Optical emission spectroscopy reveals that the H_α intensity depends on these processing parameters, which influence the removal of oxidative functional groups (confirmed via X-ray photoelectron spectroscopy) to yield reduced GO (rGO). To further improve the conductivity while maintaining high transmittance, we introduce silver nanowires (AgNWs) between rGO and a PET substrate to obtain a hybrid rGO/AgNWs/PET with a sheet resistance of ~100 Ω/sq and 81% transmittance. In addition, the hybrid rGO/AgNWs thin film also shows high flexibility and durability and is suitable for flexible and wearable electronics applications. Full article