Low-temperature Microwave Plasma Research Articles

The Effect of Low-Temperature Microwave Plasma on Wound Regeneration in Diabetic Rats

Impaired wound healing in diabetic individuals presents a significant clinical challenge, and this study explores the impact of low-temperature microwave plasma in an argon atmosphere, a type of cold atmospheric plasma (CAP), on wound regeneration in diabetic rats. The findings reveal that this CAP treatment accelerates wound regeneration in diabetic rats, promoting faster wound closure, reducing inflammation, and enhancing critical regenerative processes such as angiogenesis, collagen synthesis, and extracellular matrix remodeling. Additionally, CAP exhibits anti-inflammatory effects by modulating the immune response towards a pro-regenerative state. These results underscore the potential of CAP in diabetic wound care, offering a promising approach to address delayed wound healing in diabetic patients and potentially improving the quality of life for those with chronic diabetic wounds.

Effect of radical on defect and molecular structure of monolayer MoS2 by low temperature plasma treatment

The aim of this study is to form the sulfur defects on monolayer molybdenum disulfide (MoS2) by low temperature microwave plasma treatment suppressing disturbance of molecular structure. CVD-grown and plasma treated multilayer MoS2 surface were analyzed to investigate the effects of H2 and Ar plasma treatment on sulfur defects and molecular structure. It was found that the disturbance of molecular structure was suppressed in the H2 plasma treatment compared to the Ar plasma treatment. Varying the incident ratio of hydrogen ions H+ and radicals H*, the influences of H2 plasma treatment with high and low H*/H+ ratio on monolayer MoS2 structure were discussed. As a result of X-ray photoelectron spectroscopy, Raman spectroscopy and photoluminescence analysis, sulfur defects increased with the increase in total amount of radical incident on MoS2. In addition, it is speculated that the etching with radical contributed to form sulfur defects suppressing the disturbance of molecular structure.

Application of Low-temperature Plasma for Treatment of Barley Seeds

It has been established that treatment with lowtemperature argon microwave plasma of atmospheric pressure for 1 to 10 minutes does not statistically significantly change laboratory germination, as well as the degree of damage and prevalence of helminthosporiasis in seven-day-old barley seedlings. Processing for 10 minutes reduces the wet weight. The barley seeds germination energy decreases when exposed for 5 and 10 minutes.

Stability of the surface termination of nanocrystalline diamond and diamond-like carbon films exposed to open air conditions

Tailorable surface termination of nanocrystalline diamond (NCD) and diamond-like carbon (DLC) films significantly contribute to their wide potential applications in biomedicine which require defined and stable surface towards aging. Here, we present a comparative study on the surface termination stability of NCD and DLC films in terms of XPS and water contact angle (WCA) measurements. The samples were plasma-treated with hydrogen, oxygen or nitrogen containing functional groups employing low temperature radio frequency (RF) or high temperature microwave (MW) plasma. The samples were exposed to air up to 30 days, during which the termination stability was analyzed by XPS, WCA, AFM, Raman spectroscopy and SEM measurements. It was shown that NCD films were more efficiently hydrogenated in the high temperature MW plasma than in RF plasma, and also the surface stability was better. However, the MW plasma deteriorated the surface of the DLC film. In RF plasma treatment, a contrast between WCA and XPS data was observed. Surprisingly, while the XPS measurements showed relatively stable surface termination for all cases (H-, O- and NH2-terminated surfaces), the WCA values for O- and NH2-treated samples increased by ~200 ÷ 300%. Generally, the NCD film showed more stable surface termination than DLC. The possible reasons of the different behavior of WCA and XPS results, as well as complex characterization of the surface properties of H-, O- and NH2-terminated NCD and DLC film regarding to the aging and surface termination stability are discussed in the article.

Structural and optical properties of nanoparticulate Y2O3:Eu2O3

Nanoparticulate Y2 O3 :Eu2 O3 with a small, uniform particle size and a well-defined composition was synthesized using a low temperature microwave plasma process. The structural evolution and the luminescence properties were studied in different states of annealing and Eu2 O3 addition using X-ray diffraction, transmission electron microscopy, and UV-photoluminescence spectroscopy. As synthesized, the samples were amorphous and showed only weak luminescence. Subsequent annealing steps from 500°C to 800°C lead to the formation and growth of cubic Y2 O3 :Eu2 O3 nanocrystals (5–20 nm) and a concomitant strong increase of the luminescence yield already at small grain sizes in the range of 10 nm. No self-quenching effects were observed up to 11 mol% Eu2 O3 .

Nucleation of diamond micro-patterns with photoluminescent SiV centers controlled by amorphous silicon thin films

Selective deposition of diamond allows bottom-up growth of diamond nanostructures and nanoscale devices. However, it remains challenging to reduce the size of the patterns and to suppress parasitic spontaneous nucleation. We show here that thin layers of hydrogenated amorphous silicon (down to 40 nm) efficiently suppress spontaneous nucleation of diamond. The suppression of diamond nucleation does not depend on the substrate materials below hydrogenated amorphous silicon (Si, SiO2, Pt, Ni). We attribute the suppressed diamond nucleation to surface disorder on atomic scale. By using a structured layer of hydrogenated amorphous silicon, highly selective growth of diamond micro-patterns with optically active SiV centers by low-temperature microwave plasma chemical vapor deposition is achieved.

Study on electronic properties of diamond/SiNx-coated AlGaN/GaN high electron mobility transistors operating up to 500 °C

We report on the research related to integration and characterization of AlGaN/GaN heterostructure-based circular high electron mobility transistors (c-HEMTs) with diamond thin films. Prior to diamond deposition the transistors were coated by thin SiNx layer in order to protect AlGaN/GaN heterostructure from deposition process impact. The diamond thin film was selectively grown on the top of SiNx-coated c-HEMTs using low-pressure low-temperature microwave plasma deposition equipment with substrate table 20 × 30 cm2 from C/O/H gas mixture. We demonstrate the functionality of the diamond/SiNx-coated and the SiNx-coated AlGaN/GaN-based c-HEMTs in the temperature range from room temperature to 500 °C. The electrical measurements revealed increase of c-HEMTs' leakage currents at reversed gate voltages after diamond deposition, although the transistors remained operable in the tested temperature range. The increase of gate leakage currents and thus more negative pinch-off voltages were attributed to hydrogen penetrated towards AlGaN/GaN interface during the 60 h deposition process despite the SiNx protection. The influence of temperature rise on electronic properties of the diamond/SiNx-coated and the SiNx-coated AlGaN/GaN-based c-HEMTs is discussed.

Electrical characterization of graphene films synthesized by low-temperature microwave plasma chemical vapor deposition

In this Letter, we discuss the results of Hall effect measurements to examine the electrical properties of the graphene films synthesized by low-temperature microwave plasma chemical vapor deposition. Van der Pauw devices with sizes of 50–100 μm were fabricated, for which we observed p-type conduction and mobility from 10 to 100 cm2/V s. To investigate the mobility dispersion, we performed Raman mapping to quantify the number of defects and the disorder in graphene films. The results suggest that the D-band/G-band intensity ratio is correlated with the mobility. Moreover, we discuss the factors controlling the mobility and how to improve the quality of the graphene films by reducing the number of defects.

Low-temperature atmospheric plasma increases the expression of anti-aging genes of skin cells without causing cellular damages

Efforts to employ various types of plasma in the field of skin care have increased consistently because it can regulate many biochemical reactions that are normally unaffected by light-based therapy. One method for skin rejuvenation adopted a high-temperature plasma generator to remove skin epithelial cells. In this case, the catalyzing effects of the plasma were rarely used due to the high temperature. Hence, the benefits of the plasma were not magnified. Recently, many types of low-temperature plasma devices have been developed for medical applications but their detailed functions and working mechanisms are unclear. The present study examined the effect of low-temperature microwave plasma on skin cells. Treatment with low-temperature plasma increased the expression of anti-aging genes in skin cells, including collagen, fibronectin and vascular endothelial growth factor. Furthermore, the plasma treatment did not cause cell death, but only induced slight cell growth arrest at the G2 phase. Although the cells treated with low-temperature plasma showed moderate growth arrest, there were no signs of thermal or genetic damage of skin cells. Overall, this low-temperature microwave plasma device induces the expressions of some anti-aging-related genes in skin cells without causing damage.

Effects of gas residence time on microwave plasma enhanced CVD of ultrananocrystalline diamond in mixtures of methane and argon without hydrogen or oxygen additives

For low-power and low-temperature microwave plasma CVD of UNCD in gas mixtures of methane and argon without hydrogen and oxygen additives, excessive carbon containing species often induce gas phase synthesis of non-diamond carbon phases, which fall on diamond growing surfaces to become part of the deposited diamond films. To prevent undesirable gas phase reactions, effects of gas residence time, or equivalently, the total gas flow rate at a fixed gas pressure and compositions, on the microwave plasma and its deposition of UNCD are studied. The gas residence time is increased by by-passing an increasing amount of a pre-set mixture of methane and argon at a fixed total flow rate through a mass flow controller to a vacuum pump while allowing the rest of the gas feed to flow through the reaction chamber. The gas composition, gas pressure, microwave power, and substrate temperature are kept constant. Optimization of the UNCD growth is, thus, achieved by increasing the gas residence time to deposit UNCD of high phase purity.

Mechanisms of suppressing secondary nucleation for low-power and low-temperature microwave plasma self-bias-enhanced growth of diamond films in argon diluted methane

We report on mechanisms for suppressing diamond secondary nucleation in microwave plasma self-bias-enhanced growth (SBEG) of diamond films in methane diluted by argon. High-density plasma at a small distance from the substrate induces a floating potential which promotes high-flux, low-energy ion bombardment on diamond growing surfaces along with an equal flux of electrons. Increased atomic hydrogen generated by electron impact dissociation of methane and low-energy ion bombardment help remove hydrocarbon coatings on diamond grains in favor of continuous grain growth and, therefore, the suppression of secondary diamond nucleation. Energetic meta-stable excited argon, abundant C2 dimers, and enhanced effective surface temperature due to low-energy ion bombardment further promote the diamond grain growth resulting in the deposition of a diamond film with columnar diamond grains of much larger grain sizes and a much lower density of grain boundaries than ultrananocrystalline diamond (UNCD) films grown under similar conditions without optimized plasma-substrate interactions. SEM, XRD, PL, and Raman scattering help confirm the deposition of diamond films with columnar grains.

Structural and optical properties of nanoparticulate Y2O3:Eu2O3 made by microwave plasma synthesis

Nanoparticulate Y2O3:Eu2O3 with a small, uniform particle size and a well-defined composition was synthesized using a low temperature microwave plasma process. The structural evolution and the luminescence properties were studied in different states of annealing and Eu2O3 addition using X-ray diffraction, transmission electron microscopy, and UV-photoluminescence spectroscopy. As synthesized, the samples were amorphous and showed only weak luminescence. Subsequent annealing steps from 500°C to 800°C lead to the formation and growth of cubic Y2O3:Eu2O3 nanocrystals (5–20 nm) and a concomitant strong increase of the luminescence yield already at small grain sizes in the range of 10 nm. No self-quenching effects were observed up to 11 mol% Eu2O 3.

Mechanism of peptide modification by low-temperature microwave plasma

The possibility of changing the biological function of peptides was investigated using low pressure microwave plasma, aiming to develop a new and efficient technique to inactivate biohazardous proteinaceous molecules such as abnormal prions and figure out the insights of the interactions between non-reactive plasmas and peptide molecules. In the present research, a peptide, Arginine Vasotocin, having an inherent bio-function of controlling the water penetrability through amphibian abdominal skin was used. The interaction with low temperature plasma is investigated. The mechanisms involved in the modifications produced by argon plasma exposure are discussed, according to the obtained results of X-ray photoelectron spectroscopy, mass spectrometry, nuclear magnetic resonance, and water penetrability tests. The loss of water enhancement property of the peptide molecules after argon plasma treatment is explained.

Response of Deinococcus radiodurans to low-pressure low-temperature plasma sterilization processes

Characterize the response of Deinococcus radiodurans R1 cells to low-pressure low-temperature nitrogen-oxygen microwave plasma and identify repair processes during recovery. Cells coated onto glass slides exhibited a biphasic plasma inactivation kinetics. Treatment with various plasmas and subsequent incubation in recovery medium prolonged the lag phase in a part of the survivors, during which the ability to grow on stress medium was recovered. This recovery strongly depended on transcriptional and translational processes and cell wall synthesis, as revealed by addition of specific inhibitors to the recovery medium. Genes involved in DNA repair, oxidative stress response, and cell wall synthesis were induced during recovery, as determined by quantitative RT-PCR. Damage to chromosomal DNA caused by plasma agents and repair during recovery was directly shown by quantitative PCR. Plasmas with less UV radiation emission were also effective in killing D. radiodurans cells but resulted in less DNA damage and lower induction of the investigated genes. The response of D. radiodurans to plasma indicates that DNA, proteins, and cell wall are primary targets of plasma finally leading to the cell death. Protein oxidation is more important for killing of D. radiodurans cells than of Bacillus subtilis spores. Thus, the contaminating biological material affects the plasma composition to be used for sterilization. The results in this study provide new insight into the interaction of plasma with bacterial cells. This knowledge contributes to the definition of useful parameters for novel plasma sterilization equipment to control process safety.

Fast deposition of microcrystalline Si films from SiH 2Cl 2 using a high-density microwave plasma source for Si thin-film solar cells

Fast deposition rate of 27 Å/s for microcrystalline (μc-) Si films was investigated using a high-density and low-temperature microwave plasma source with a spoke antenna of SiH 4–H 2 and SiH 2Cl 2–H 2 mixtures. The film crystallization was promoted efficiently when film was fabricated using SiH 4 with an aid of large amount of hydrogen atom, while the volume fraction of void in the film was relatively the larger of 10–20%. On the other hand, the volume fraction of amorphous silicon phase in the μc-Si films were 20–30% with no significant void fractions in films fabricated from SiH 2Cl 2, although the volume fraction of the crystalline silicon phase was 75–85%. The role of chlorine in the growth of μc-Si films is discussed in terms of the chemistry of the H and Cl terminated growing surface. The preliminary result of p–i–n Si thin-film solar cell is demonstrated using μc-Si:H:Cl films as an intrinsic layer.

Characterization of Microwave Plasma Torch for Decontamination

AbstractAn atmospheric low‐temperature microwave plasma torch has been developed and applied to disinfection. The size of the plasma output is relatively large (35 mm in diameter). Ar gas at a flow rate of 2.2 slm and 85 W microwave power are used. Plasma discharges are produced between the tip of each electrode and the inner surface of the cylinder. When an Escherichia coli culture is placed for 2 min at 20 mm below the torch, where the gas temperature is sufficiently cool, the bacteria are almost completely killed within a 40 mm diameter circle. The UV radiation is one of the major players responsible for killing bacteria, others being the reactive species and the charged particles.magnified image

Plasma synthesis of nanopowders

There is a huge variety of plasma processes for synthesis of nanoparticulate powders. They may be grouped with respect to operating temperature, which is the essential parameter with respect to the properties of the products. In view of industrial production, the highest degree of maturity is found in high temperature processes working under ambient pressure. For products, where well-defined properties are demanded, low temperature microwave plasma processes are best suited. Additionally, these processes allow coating of the produced particles, even with organic phases. Other processes where plasmas are involved, such as laser or flame processes coupled with electric fields have, to some extent, a high potential for development.

High-density microwave plasma-enhanced chemical vapor deposition of microcrystalline silicon from dichlorosilane

Fast deposition of hydrogenated chlorinated microcrystalline (μc–) Si:H:Cl films was investigated using the high-density and low-temperature microwave plasma source utilizing a spoke antenna of a SiH 2Cl 2–H 2 mixture. The optical emission spectroscopy study revealed that the SiCl intensity and the H a/SiCl intensity ratio are the possible monitors for the film deposition rate and the degree of the film crystallinity, respectively. The μc–Si:H:Cl films fabricated from SiH 2Cl 2 possessed less volume fraction of void and defect density rather than μc–Si:H from SiH 4 while maintaining a high deposition rate of 40 Å/s. These originate from the chemical reactivity of H and Cl terminated growing surface. The fine structure of μc–Si:H:Cl film is discussed and compared with that of μc–Si:H film from SiH 4.

Emission spectroscopy diagnostics of rare gases in the PNX-U facility

Results are presented from measurements of the electron temperature and neutral atom density in a low-temperature microwave plasma by the method of emission spectroscopy. The measurements were conducted in the PNX-U facility—a magnetic confinement system with a “magnetic wall.” Multichord measurements of plasma radiation at a wavelength of 750.37 nm were performed with the help of an absolutely calibrated monochromator. The neutral atom density was calculated using the collisional-radiative model. The degree of plasma ionization near the axis of the facility was found to be close to unity. The electron temperature of the argon plasma was measured from the relative intensities of the spectral lines of neutral helium injected in small amounts into the plasma (the so-called helium thermometer method). At a low microwave heating power, the results of these measurements agree well with the results of probe measurements.

High rate growth highly crystallized microcrystalline silicon films using SiH 4/H 2 high-density microwave plasma

The plasma parameter for fast deposition of highly crystallized microcrystalline silicon (μc-Si) films with low defect density is presented using the high-density and low-temperature microwave plasma (MWP) of a SiH 4–H 2 mixture. A very high deposition rate of ∼ 65 Å/s has been achieved at SiH 4 concentration of 67% diluted in H 2 with high Raman crystallinity I c / I α > 3 and low defect density of 1–2 × 10 16 cm − 3 by adjusting the plasma condition. Contrary to the conventional rf plasma, the defect density of the μc-Si films strongly depend on substrate temperature T s and it increased with increasing T s despite T s below 300 °C, suggesting that the real surface temperature at the growing surface was higher than the monitored value. The sufficient supply of deposition precursors such as SiH 3 at the growth surface under an appropriate ion bombardment was effective for the fast deposition of highly crystallized μc-Si films as well as the suppression of the incubation and transition layers at the initial growth stage.