Microwave Oxygen Plasma Research Articles

Evaluation of Low‐Pressure Microwave Oxygen Plasma as an Ecofriendly Way to Control Three of the Most Important Pests of Stored Date Fruits Infesting Egyptian Cultivar Siwi

ABSTRACTInsect pests in stored date fruits lead to significant economic losses, traditionally managed by chemical insecticides that harm the environment. This study explores low‐pressure microwave oxygen plasma treatments as an alternative pest control method against pests like Polda interpunctelia, Ephestia cautella, and Oryzaephilus surinamensis. A 20 s treatment achieved 100% mortality for all species without any adult emergence. Sensory evaluations showed no significant differences in taste, color, texture, odor, or overall acceptability between treated and untreated date fruits, indicating that the plasma treatment preserves fruit quality. Scanning electron microscopy revealed structural damage to the pests, whereas the Siwi cultivar date fruits remained unaffected. The findings suggest that this plasma treatment is an effective and environmentally friendly alternative to chemicals.

Assessment of the effect of surface functionalization of oxygen and argon microwave plasma on PVA films for optoelectronic devices

Abstract This study explores the enhancement of optical properties in polyvinyl alcohol (PVA) polymer using a low-pressure microwave plasma reactor, adapted from a microwave oven. The research focuses on the effects of oxygen and argon plasma treatments at a consistent power of 1000 W, a flow rate of 6 L min−1, and a pressure of 16 mbar on PVA films. The optimal treatment times of 10 s and 15 s were identified as particularly effective in improving the optical characteristics of the PVA films, which were created using a solution casting method. The optical properties were analyzed using a UV-vis spectrophotometer across a wavelength range of 200–900 nm. The absorption spectrum revealed a significant absorption peak at around 210 nm (photon energy = 5.8 eV) for all plasma-treated PVA films, with a subsequent decrease in absorbance. Notably, the transmittance for the PVA-oxygen treated film at 10 s reached a maximum of 90.36% beyond 360 nm, attributed to increased hydrophilicity from the oxygen content. Similar trends were observed in the extinction coefficient (k) and optical conductivity (σ opt). The optical energy band gap, calculated using the Tauc relation for both direct and indirect allowed transitions, decreased from 5.32 eV and 4.80 eV to 4.82 eV and 4.35 eV with longer exposure times. The study also noted that skin depth diminishes as the incident energy photon value increases, indicating that penetration becomes more challenging at higher frequencies. The PVA-oxygen plasma treated film, after a 10 s exposure, has improved optical properties, making it suitable for various electronic industries.

Effect of Microwave Plasma Pre-Treatment on Cotton Cellulose Dissolution.

The utilization of cellulose to its full potential is constrained by its recalcitrance to dissolution resulting from the rigidity of polymeric chains, high crystallinity, high molecular weight, and extensive intra- and intermolecular hydrogen bonding network. Therefore, pretreatment of cellulose is usually considered as a step that can help facilitate its dissolution. We investigated the use of microwave oxygen plasma as a pre-treatment strategy to enhance the dissolution of cotton fibers in aqueous NaOH/Urea solution, which is considered to be a greener solvent system compared to others. Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy, Scanning Electron Microscopy, and Powder X-ray Diffraction analyses revealed that plasma pretreatment of cotton cellulose leads to physicochemical changes of cotton fibers. Pretreatment of cotton cellulose with oxygen plasma for 20 and 40 min resulted in the reduction of the molecular weight of cellulose by 36% and 60% and crystallinity by 16% and 25%, respectively. This reduction in molecular weight and crystallinity led to a 34% and 68% increase in the dissolution of 1% (w/v) cotton cellulose in NaOH/Urea solvent system. Thus, treating cotton cellulose with microwave oxygen plasma alters its physicochemical properties and enhanced its dissolution.

Experimental investigation of the methane combustion assisted by atmospheric pressure oxygen microwave plasma torch

The atmospheric-pressure oxygen microwave plasma is employed to enhance the methane combustion in the jet-diffusion combustor. The plasma-assisted combustion (PAC) is compared with natural combustion without plasma application in terms of the flame morphology, flame temperature, and combustion efficiency. It is found experimentally that the oxygen plasma assistance in combustion is prominent in lean oxygen condition, and the active species generated in the microwave plasma torch contribute to the combustion process more dominantly than the flame temperature change caused by heating of oxygen microwave plasma. The combustion degree of CH4 in PAC is much more enhanced in lean oxygen combustion, and the exhaust gas in combustion is effectively controlled with the use of the oxygen microwave plasma torch.

An Assessment of Surface Treatments for Adhesion of Polyimide Thin Films.

Polyimide films are currently of great interest for the development of flexible electronics and sensors. In order to ensure a proper integration with other materials and PI itself, some sort of surface modification is required. In this work, microwave oxygen plasma, reactive ion etching oxygen plasma, combination of KOH and HCl solutions, and polyethylenimine solution were used as surface treatments of PI films. Treatments were compared to find the best method to promote the adhesion between two polyimide films. The first selection of the treatment conditions for each method was based on changes in the contact angle with deionized water. Afterward, further qualitative (scratch test) and a quantitative adhesion assessment (peel test) were performed. Both scratch test and peel strength indicated that oxygen plasma treatment using reactive ion etching equipment is the most promising approach for promoting the adhesion between polyimide films.

The adhesion of epoxy treated by microwave oxygen plasma

Strong adhesion between epoxy and silicone is essential for optoelectronic packaging. The adhesion of epoxy can be enhanced by microwave plasma treatment in oxygen flow. However, the plasma effect is time dependent. The shear strength of un-aged and aged epoxy for up to two months was systematically investigated as a function of plasma power (200–600 W) with different surface analysis tools. The shear strength between epoxy and silicone assembly was correlated with surface wettability, chemical, and structural properties. 300-W plasma-treated epoxy revealed the highest shear strength and the factors contributing to the improved strength were identified. The phenomenon of hydrophobic recovery was recorded after ageing, which had minimal effect on the reduction of shear strength. By keeping the plasma-treated surface for up to two months, a significant increment of shear strength was demonstrated below one week of ageing. Beyond that, a slight deterioration of the strength was observed but the reduction was still higher than the un-aged surface. The reasons behind of these observations have been elucidated and justified.

Oxidation kinetics of SiC in microwave oxygen plasma

A kinetic insight into microwave plasma oxidation on 4H-SiC is of great importance to improve the quality of SiO2 dielectric and SiO2/SiC interface in SiC MOSFETs. In this work, quantitative study on SiC plasma oxidation has been performed for a wide range of oxidation conditions by using Massoud’s empirical relation. In this relation, an additional exponential term related to the diffusion coefficient, the oxidation coefficient and the emission ratio of Si and C is introduced to describe the deviation of oxidation behavior relative to the Deal-Grove model. In plasma oxidation, the exponential term is dominant, especially in the growth-rate enhancement stage. Moreover, the contribution of the exponent increases with increasing temperature. Finally, a plausible kinetic model is proposed by considering exchange in the surface region, diffusion in oxide and reaction at the SiO2/SiC interface.

Improvement of the flowability of fine yttrium oxide powders by microwave oxygen plasma and evaluation of the dense coating layer

Ceramic powders such as yttrium oxide and aluminum oxide have been extensively used to coat the inner walls and components of chambers used in semiconductor fabrication processes. Fine powders are used to form a dense coating layer by techniques such as thermal spray coating. However, fine powders exhibit strong cohesive forces due to surface roughness and interparticle van der Waals forces. This results in low flowability, a nonuniform powder feed, and nonuniform coatings. Microwave O2 plasma is proposed to improve the flowability of fine Y2O3 powder for a uniform powder supply in the spray coating process. Microwave O2 plasma flames produce a high temperature with active oxygen species at atmospheric pressure. The active oxygen species of plasma are incorporated into the lattice of powder particles, electrically stabilizing the powder, decreasing the static electricity, and reducing interparticle van der Waals forces. In addition, the surface of the fine powder is melted and smoothed by the high temperature of the microwave plasma, so that the powder acts as a dry lubricant. The processed powder was employed to coat a surface using atmospheric thermal spray coating, and the coating was characterized in comparison to a coating produced using commercial powder. The plasma-treated powder produced a coating with higher density and strength and lower porosity and surface roughness. The plasma-treated powder has a high flowability of 2.38 g s−1 and an apparent density of 2.07 g cm−1. Accordingly, the coating layer has a higher adhesion strength of 8.75 MPa and hardness of 651 HV0.3. In addition, its surface roughness of 0.9 μm and porosity of 0.2% are lower than those of a commercial sample.

Improvement of gas sensing property for two-dimensional Ti3C2Tx treated with oxygen plasma by microwave energy excitation

Two-dimensional layered Ti3C2Tx MXene was prepared through hydrothermal etching method with LiF and hydrochloric (HCl) acid. Ti3C2Tx was further treated with oxygen plasma activated by microwave energy to obtain the activated Ti3C2Tx at different temperatures ranging from 350 °C to 550 °C. The gas-sensing properties of raw Ti3C2Tx and Ti3C2Tx activated with oxygen microwave plasma were tested toward different volatile organic compounds gases. The results indicated that Ti3C2Tx activated at 500 °C exhibited excellent gas-sensing properties at room temperature (25 °C) to 100 ppm ethanol with a value of 22.47, which is attributed to the enhancement of the amount of oxygen functional groups and defects on the MXene Ti3C2Tx film, and in turn to lead to more oxygen molecules adsorption and desorption reaction in the active defect sites. The enhancement of ethanol-sensing performance demonstrated that the activated Ti3C2Tx possess great potential in gas sensing.

Defect Engineering for Quantum Grade Rare-Earth Nanocrystals.

Nanostructured systems that combine optical and spin transitions offer new functionalities for quantum technologies by providing efficient quantum light-matter interfaces. Rare-earth (RE) ion-doped nanoparticles are promising in this field as they show long-lived optical and spin quantum states. However, further development of their use in highly demanding applications, such as scalable single-ion-based quantum processors, requires controlling defects that currently limit coherence lifetimes. In this work, we show that a post-treatment process that includes multistep high-temperature annealing followed by high-power microwave oxygen plasma processing advantageously improves key properties for quantum technologies. We obtain single crystalline Eu3+:Y2O3 nanoparticles (NPs) of 100 nm diameter, presenting bulk-like inhomogeneous line widths (Γinh) and population lifetimes (T1). Furthermore, a significant coherence lifetime (T2) extension, up to a factor of 5, is successfully achieved by modifying the oxygen-related point defects in the NPs by the oxygen plasma treatment. These promising results confirm the potential of engineered RE NPs to integrate devices such as cavity-based single-photon sources, quantum memories, and processors. In addition, our strategy could be applied to a large variety of oxides to obtain outstanding crystalline quality NPs for a broad range of applications.

Experimental study of abatement of SF6 gas using an atmospheric-pressure oxygen microwave plasma torch

An atmospheric-pressure microwave oxygen plasma torch (APMPT) is used for abating SF6 gas. The gas composition is analyzed with a Fourier transformation infrared spectrometer, and the abating effect is evaluated in terms of the destruction removal efficiency (DRE). The variation of SF6 DRE is investigated with respect to the microwave power, the gas flow rate, SF6 concentration, and the material and length of discharge tube. It is found that the existence of free-discharge regions in the vicinity of the inner wall of the discharge tube, influenced by the flow rate and microwave power, plays an important role in maintaining a stable discharge and determining the DRE value. The energy efficiency can be improved significantly by using quartz discharge tubes of a suitable length. Meanwhile, the explanations about the variation of DRE and energy efficiency for decomposing SF6 by APMPT are provided reasonably.

Effects of microwave oxygen plasma treatments on microstructure and Ge-V photoluminescent properties of diamond particles**Project supported by the Key Project of the National Natural Science Foundation of China (Grant No. U1809210), the National Key Research and Development Program of China (Grant No. 2016YFE0133200), the Belt and Road Initiative International Cooperation Project from Key Research and Development Program of Zhejiang Province,

The microstructure and Ge-V photoluminescent properties of diamond particles treated by microwave oxygen plasma are investigated. The results show that in the first 5 min of microwave plasma treatment, graphite and disordered carbon on the surface of the particles are etched away, so that diamond with regular crystal plane, smaller lattice stress, and better crystal quality is exposed, producing a Ge-V photoluminescence (PL) intensity 4 times stronger and PL peak FWHM (full width at half maximum) value of 6.6 nm smaller than the as-deposited sample. It is observed that the cycles of ‘diamond is converted into graphite and disordered carbon, then the graphite and disordered carbon are etched’ can occur with the treatment time further increasing. During these cycles, the particle surface alternately appears smooth and rough, corresponding to the strengthening and weakening of Ge-V PL intensity, respectively, while the PL intensity is always stronger than that of the as-deposited sample. The results suggest that not only graphite but also disordered carbon weakens the Ge-V PL intensity. Our study provides a feasible way of enhancing the Ge-V PL properties and effectively controlling the surface morphology of diamond particle.

Characterisation of titanium oxide layers using Raman spectroscopy and optical profilometry: Influence of oxide properties

Abstract This study evaluates the use of a combination of Raman spectroscopy and optical profilometry as a surface characterisation technique for the examination of oxide layers grown on titanium metal substrates. The titanium oxide layers with thickness of up to 8 µm, were obtained using a low-pressure oxygen microwave plasma treatment of the titanium metal substrate. The effect of the microwave plasma processing conditions (input power, pressure and treatment time) on the Raman bandwidth, intensity and peak position was evaluated. Also, the effect of these processing conditions on the surface roughness parameters (Sa, Sdq, Ssk and Sku) of the oxide layers was investigated. Analysis of the peak positions of Eg and A1g modes indicated that the effects of input power and chamber pressure was to induce a shift towards the lower frequency with increasing input power and pressure (1–2 kPa). The intensity of the Raman bands was found to be dependent on the morphology and surface chemistry of the oxide layer. The intensity of Raman band (A1g), was found to be particularly influenced by the average surface roughness (Sa) and the crystallite size. Exponential and polynomial relations were found to correlate with these properties. A two-latent variable Partial Least Squares Regression model developed on Raman spectral data could predict surface roughness with a coefficient of determination (R2) of approx. 0.87 when applied to the testing of an independent set of titanium oxide test coatings.

Aspect ratio dependence of silicon trench oxidation in downstream of microwave oxygen plasma

Silicon trench oxidation is studied in microwave oxygen plasma downstream under the conditions of radio frequency bias as well as DC bias applications. Particularly, an aspect ratio dependence of trench oxidation is precisely examined within its range from 1 to 5. It is shown that the oxidation film obtained at the trench bottom is drastically reduced at higher aspect ratios even in the bias condition in which the oxidation at the trench top shows a maximum. It is also demonstrated that the ratio of film thickness at the bottom to the top of the trench is consistent with oxygen radical fluxes coming onto the silicon dioxide film surface, indicating that the oxidation is ion-assisted but is radical flux-limited. This is because the oxidant species responsible for oxidation is O− which is formed on the surface by attachment with radicals or molecules and diffused in the silicon dioxide film. It is emphasized that the negative ions O− in plasma are also important in enhancing the oxidation by bombardment with their kinetic energy, while the positive ions are for neutralization of the charge, particularly at the bottom of trench.

Spectroscopic diagnosis of gas temperature in blown-out plasma of atmospheric-pressure microwave oxygen plasma torch

The gas temperature of atmospheric-pressure microwave oxygen plasma torch in a blown-out plasma is diagnosed by optical emission spectroscopy (OES) via the atmospheric band O2(b1Σg+ →X3Σg−). The variations of gas temperature with respect to input power and gas flow rate are investigated, as well as the spatial distribution of gas temperature along the blown-out plasma. And the limitation of OES diagnosis in the experiment is discussed extensively. Moreover, the morphology of plasma torch is also inspected at various gas flow rates and values of microwave power.

Experimental study on difference in molecular rotation temperatures between neutral molecules and molecular ions in nitrogen plasma and oxygen plasma by optical emission spectroscopy measurement

The differences in the rotational temperatures between neutral molecules and molecular ions are examined for low-pressure microwave discharge nitrogen plasma and oxygen plasma. For N2 plasma, the rotational temperatures of the second positive system (2PS) and first negative system (1NS) are measured, whereas for O2 plasma, those of the atmospheric absorption band (A-band) and 1NS are measured for neutrals and ions, respectively. The experimentally measured spectra are compared with the theoretically calculated ones to determine the vibrational and rotational temperatures as best fitting parameters. It is found that the ions have a higher rotational temperature than neutrals for the N2 plasma, while both have almost the same temperature for the O2 plasma, for which a discussion is made on the basis of atomic and molecular processes. The difference in the rotational temperature between the neutrals and the ions is also discussed from the viewpoint of the atomic and molecular processes in the plasmas.

Optical Diagnostics of Iron Oxide Nanoparticle Synthesis in Microwave Oxygen Plasma

Iron oxide nanoparticle synthesis in microwave plasma is studied by optical diagnostics. The arrangement of the plasma reactor results in well-defined reactant mixing, which makes different parts of the reaction zone clearly observable. Besides the reaction zone, digital imaging also reveals the presence of heated nanoparticles. The optical emission spectroscopy is used to determine important plasma parameters.

Erosion of amorphous carbon layers in the afterglow of oxygen microwave plasma

We present a study of the interaction of amorphous hydrogenated carbon deposits (a-C:H) with neutral oxygen atoms. Samples of a-C:H were exposed to an atomic oxygen rich atmosphere at surface temperatures from 473 K to 623 K. The source of atomic oxygen was microwave plasma, created in oxygen at pressures between 50 Pa and 200 Pa by means of a surfatron. The density of neutral oxygen atoms reached up to 4 ∙ 1021/m3. The densities of neutral atoms were measured by means of a catalytic probe. The erosion process was monitored by means of an infrared pyrometer. At each sample surface temperature, the erosion rates were found to linearly increase with the atomic oxygen density. This allowed us to calculate the reaction rate coefficient at corresponding surface temperatures. The reaction rate coefficient was found to increase exponentially with the sample surface temperature.

Mechanism of enhanced wettability of nanocrystalline diamond films by plasma treatment

The mechanism of wetting behavior of nanocrystalline diamond films is examined in terms of surface free energy, morphology, and bonding characteristics. The films are prepared by microwave plasma-enhanced chemical vapor deposition using Ar-rich/N2/CH4 and Ar-rich/H2/CH4 mixtures, followed by microwave hydrogen and oxygen plasma exposures separately. Contact angle measurement with water, ethylene glycol, and formamide reveals that both the as-deposited and hydrogen plasma treated films are hydrophobic, while the oxygen plasma treated film is extremely hydrophilic such that the contact angle is reduced down to almost zero degree. Fourier transform infrared spectroscopy reveals that the hydrogen atoms are dominantly bonded to diamond and amorphous sp3-bonded carbon, and they are removed by the oxygen plasma treatment. For the oxygen plasma treated film, the mean value of oxygen concentration for the top surface to bulk (~1μm) measured by energy-dispersive X-ray spectroscopy is ~10at.%, while that for the top several monolayers surface measured by X-ray photoelectron spectroscopy is much higher at ~37at.%, indicating a higher degree of oxidation toward the surface. The carbon bonding state in the oxidized layer is disordered by incorporation of a large amount of oxygen in form of polar CO bonds, which is accountable for a greater polar component of the apparent surface free energy and stronger dipole–dipole interactions.

Enhanced Wettability of Nanocrystalline Diamond Films for Biocoating Applications

ABSTRACTNanocrystalline diamond (NCD) films are prepared from Ar-rich/N2/CH4 and Ar-rich/H2/CH4 mixtures by microwave plasma-enhanced chemical vapor deposition, and further treated by microwave hydrogen and oxygen plasma exposures separately to enhance the wetting property. The hydrogen plasma treatment has small effect on the surface roughness, while the oxygen plasma treatment forms fine protrusions on the film surface. Results show that the wettability of the hydrogen plasma treated NCD film is nearly constant or little improvement as the polar component of the apparent surface free energy is close to the as-deposit NCD film. In contrast, the wettability of the oxygen plasma treated NCD film is improved dramatically such that the contact angle is reduced from 92º and 4.7º to almost 0º for water and 1-bromonaphthalene, respectively, and the polar component increases significantly to 34 mJ/m2. The low contact angle suggests that the film is considerably a cell adhesive friendly surface, which is essential in maintaining multicellular structure, and thus making it a favorable wetting surface for biological and biomedical applications.