Generating a Sustained Oxygen-Stable Atomic Concentration in a High-Temperature Gas Effect Investigation

Modulated laser absorption spectroscopy is an ideal technique for evaluating flow-field parameters and determining flow-field quality by measuring the atoms dissociated in high-temperature environments. However, to obtain the absolute number density of atoms in the flow field, it is necessary to compare the measured modulated absorption spectroscopy signal with a known atomic concentration and establish a quantitative relationship through concentration calibration. Nevertheless, it remains a challenging task to prepare transient atomic samples with known concentrations that meet the calibration requirements. This study utilized the alternating-current glow discharge technique to dissociate oxygen in the air flow, resulting in the continuous generation of oxygen atoms. The absolute number densities of the generated oxygen atoms were determined by measuring the direct absorption spectra of centered on 777 nm for oxygen atoms. The number densities of the generated atoms were finely tuned by adjusting the discharge parameters. Throughout the 120-min continuous operation of the discharge system, the concentration of excited-state oxygen atoms remained stable within the range of (2.51 ± 0.02) × 108 cm-3, demonstrating the remarkable stability of the transient atomic concentration generated by the glow discharge plasma. This observation suggests that the generated atoms can be utilized as a standardized atomic sample of known concentration for absolute concentration calibration purposes.

GD-OES Investigations of Lithium-Ion Battery Graphite Anodes: Impact of Plasma Parameters and Electrode Properties

Due to the demand of lithium-ion battery investigations with glow discharge optical emission spectroscopy (GD-OES), a fundamental study of the influence of essential GD-OES parameters toward graphite anodes in an argon plasma was conducted and compared to previous investigations of massive materials. It is shown that increased applied voltage (500-700 V) enhances the sputtering rate by up to 100%/100 V while keeping the crater shape unaffected. In contrast to this, gas pressure variation seems to be the main tool for crater shape adjustment. Enhancement of the gas pressure (160-300 Pa) pushes the crater profile from a concave to flat shape and to concave again. Known plasma effects are discussed and correlated with the observations. A set of measuring parameters providing a good balance between the crater shape and the sputtering rate is proposed. Additionally, an increase of the duty cycle in the pulsed glow discharge mode leads to a linear increase of the sputtering rate, while a pulse duration rise enhances the sputtering rate in a nonlinear fashion. Thus, different pulsing conditions represent instruments for enhancement of the sputtering rate without affecting the crater shape significantly. Our investigation of different electrode densities shows that lower densities lead to a larger sputtered volume as well as a larger concavity of the released crater.

The Effect of Preconditioning Strategies on the Adsorption of Model Proteins onto Screen-Printed Carbon Electrodes

The preconditioning and modification of the supporting electrode surface is an essential step in every biosensor architecture. In particular, when using screen-printed carbon electrodes (SPEs) as inexpensive and convenient disposable sensor substrates, their somewhat lower electrochemical (surface) reproducibility might represent a complex hurdle. Herein, we investigated the effect of selected preconditioning strategies, such as cyclic voltammetric pretreatment, in H₂SO₄ and H₂O₂ and plasma pretreatment with a positive and negative glow discharge, which all improved the electrochemical stability of the unmodified SPEs. Furthermore, we studied the influence of preconditioning strategies on the adsorption kinetics of the two most commonly used building blocks for biosensor preparation, i.e., bovine serum albumin (BSA) and protein A. We observed an advantageous effect of all the examined preconditioning strategies for the modification of SPEs with protein A, being the most effective the negative glow discharge. On the other hand, BSA exhibited a more complex adsorption behavior, with the negative glow discharge as the only generally beneficial preconditioning strategy providing the highest electrochemical stability. Protein A revealed a more substantial impact on the electrochemical signal attenuation than BSA considering their same concentrations in the modification solutions. For both BSA and protein A, we showed that the concentrations of 5 and 10 μg mL⁻¹ already suffice for an electrochemically satisfactorily stable electrode surface after 60 min of incubation time, except for BSA at the positive-plasma-treated electrode.

Dusty Plasma in Inhomogeneous Magnetic Fields in a Stratified Glow Discharge

We study the dynamics of dust particles in a stratified glow discharge in inhomogeneous magnetic fields. Dust structures are formed in standing striations, in which traps for dust particles arise. When a magnetic field is applied, these structures begin to rotate. The observations were carried out in striations near the end of the solenoid, where the region of an inhomogeneous magnetic field begins. With an increase in the magnetic field, the dusty structure can be deformed. The rotation of a dusty structure in an inhomogeneous magnetic field has been studied in detail; it has its own peculiarities in comparison with rotation in a uniform field. We have considered the mechanisms of such rotation and estimated its velocity.

Effect of radio frequency glow-discharge treatment of titanium on human gingival fibroblasts as a function of distance

The mechanical stability and long-term success of an implant depends on the early healing phase and osseointegration of the bone around it. In addition, a healthy gingival tissue around the implant acts as a barrier that prevents bacteria and pathological byproducts from reaching the implant site. This study investigated the in-vitro attachment and spreading of human gingival fibroblasts (HGF) on bacterial grade polystyrene (PS) at different distances from radio-frequency glow-discharge (RFGD)-treated commercially pure titanium (cpTi) specimens. Controls included sterile cpTi specimens without RFGD treatment. A second set of experiments utilized media transferred to new bacterial grade polystyrene dishes (no cpTi) after the medium was conditioned by exposure to cpTi, either with or without RFGD treatment, for 24 hr. Surface characterization of the dishes was conducted through contact angle measurements and infrared spectroscopy. Cell numbers and surface areas were determined from Image J analysis of multiple microscopic images of fixed, stained cells. The results showed significantly greater numbers and surface areas on bacterial grade PS dishes at distances up to 15 mm from the RFGD-treated cpTi groups than for the controls. Moreover, a significant effect of the conditioned medium from RFGD-treated cpTi versus control cultures was shown on the numbers of fibroblasts attached to bacterial grade polystyrene dishes after 24 hr (p < 0.005) and 48 hr (p = 0.002) incubation. Surface areas of cells exposed to conditioned medium were not significantly different (p ≥ 0.05). Surface characterization of the PS dishes showed a higher value of the critical surface tensions of the treated group when compared to the control group.

High Quality Graphene Thin Films Synthesized by Glow Discharge Method in A Chemical Vapor Deposition System Using Solid Carbon Source

Arc discharge is traditionally used to synthesize randomly arranged graphene flakes. In this paper, we substantially modify it into a glow discharge method so that the discharge current is much more reduced. The H₂ and/or Ar plasma etching of the graphitic electrode (used to ignite the plasma) is hence much gentler, rendering it possible to grow graphene in thin film format. During the growth at a few mbar, there is no external carbon gas precursor introduced. The carbon atoms and/or carbon containing particles as a result of the plasma etching are emitted in the chamber, some of which undergo gas phase scattering and deposit onto the metallic catalyst substrates (Cu-Ni alloy thin films or Cu foils) as graphene sheets. It is found that high quality monolayer graphene can be synthesized on Cu foil at 900 °C. On Cu-Ni, under the same growth condition, somewhat more bilayer regions are observed. It is observed that the material quality is almost indifferent to the gas ratios, which makes the optimization of the deposition process relatively easy. Detailed study on the deposition procedure and the material characterization have been carried out. This work reveals the possibility of producing thin film graphene by a gas discharge based process, not only from fundamental point of view, but it also provides an alternative technique other than standard chemical vapor deposition to synthesize graphene that is compatible with the semiconductor planar process. As the process uses solid graphite as a source material that is rich in the crust, it is a facile and relatively cheap method to obtain high quality graphene thin films in this respect.

Glow Discharge in a High-Velocity Air Flow: The Role of the Associative Ionization Reactions Involving Excited Atoms

A kinetic scheme for non-equilibrium regimes of atmospheric pressure air discharges is developed. A distinctive feature of this model is that it includes associative ionization with the participation of N(2D, 2P) atoms. The thermal dissociation of vibrationally excited nitrogen molecules and the electronic excitation from all the vibrational levels of the nitrogen molecules are also accounted for. The model is used to simulate the parameters of a glow discharge ignited in a fast longitudinal flow of preheated (T0 = 1800-2900 K) air. The results adequately describe the dependence of the electric field in the glow discharge on the initial gas temperature. For T0 = 1800 K, a substantial acceleration in the ionization kinetics of the discharge is found at current densities larger than 3 A/cm2, mainly due to the N(2P) + O(3P) → NO+ + e process; being the N(2P) atoms produced via quenching of N2(A3∑u+) molecules by N(4S) atoms. Correspondingly, the reduced electric field noticeably falls because the electron energy (6.2 eV) required for the excitation of the N2(A3∑u+) state is considerably lower than the ionization energy (9.27 eV) of the NO molecules. For higher values of T0, the associative ionization N(2D) + O(3P) → NO+ + e process (with a low-activation barrier of 0.38 eV) becomes also important in the production of charged particles. The N(2D) atoms being mainly produced via quenching of N2(A3∑u+) molecules by O(3P) atoms.

Enhancement of Laser-Induced Breakdown Spectroscopic Signals in a Liquid Jet with Glow Discharge

In this work, emission signals of laser-induced breakdown (LIBS) plasma of a flowing liquid jet in the absence and presence of an air-supported glow discharge have been investigated. In combination with a needle-to-needle glow discharge, a Q-switched neodymium-doped yttrium aluminum garnet (Nd:YAG) laser (1064 nm, 5 ns) with power density ∼10¹⁰W/cm² was used to generate a plasma from a liquid jet. Emission lines of Mg, Ca, Al, Li, Na, and K all showed significant enhancements in the presence of the glow discharge. Lower continuum background was also observed. Mechanisms of the line emission enhancement and continuum radiation reduction were discussed.

Plasma-based ambient mass spectrometry techniques: The current status and future prospective

Plasma-based ambient mass spectrometry is emerging as a frontier technology for direct analysis of sample that employs low-energy plasma as the ionization reagent. The versatile sources of ambient mass spectrometry (MS) can be classified according to the plasma formation approaches; namely, corona discharge, glow discharge, dielectric barrier discharge, and microwave-induced discharge. These techniques allow pretreatment-free detection of samples, ranging from biological materials (e.g., flies, bacteria, plants, tissues, peptides, metabolites, and lipids) to pharmaceuticals, food-stuffs, polymers, chemical warfare reagents, and daily-use chemicals. In most cases, plasma-based ambient MS performs well as a qualitative tool and as an analyzer for semi-quantitation. Herein, we provide an overview of the key concepts, mechanisms, and applications of plasma-based ambient MS techniques, and discuss the challenges and outlook.

Plasma deactivation of oral bacteria seeded on hydroxyapatite disks as tooth enamel analogue

PURPOSE

To study the plasma treatment effects on deactivation of oral bacteria seeded on a tooth enamel analogue.

METHODS

A non-thermal atmospheric pressure argon plasma brush was used to treat two different Gram-positive oral bacteria including Lactobacillus acidophilus (L. acidophilus) and Streptococcus mutans (S. mutans). The bacteria were seeded on hydroxyapatite (HA) disks used as tooth enamel analogue with three initial bacterial seeding concentrations: a low inoculum concentration between 2.1 x 10(8) and 2.4 x 10(8) cfu/mL, a medium inoculum concentration between 9.8x10(8) and 2.4 x 10(9) cfu/mL, and a high inoculum concentration between 1.7 x 10(10) and 3.5 x 10(10) cfu/mL. The bacterial survivability upon plasma exposure was examined in terms of plasma exposure time and oxygen addition into the plasmas. SEM was performed to examine bacterial morphological changes after plasma exposure.

RESULTS

The experimental data indicated that a 13-second plasma exposure time completely killed all the bacteria when initial bacterial seeding density on HA surfaces was less than 6.9 x 10(6) cfu/cm2 for L. acidophilus and 1.7 x 10(7) cfu/cm2 for S. mutans, which resulted from low initial seeding inoculum concentration between 2.1 x 10(8) and 2.4 x 10(8) cfu/mL. Plasma exposure of the bacteria at higher initial bacterial seeding density obtained with high initial seeding inoculum concentration, however, only resulted in approximately 1.5 to 2 log reduction and approximately 2 to 2.5 log reduction for L. acidophilus and S. mutans, respectively. It was also noted that oxygen addition into the argon plasma brush did not affect the plasma deactivation effectiveness. SEM images showed that plasma deactivation mainly occurred with the top layer bacteria, while shadowing effects from the resulting bacterial debris reduced the plasma deactivation of the underlying bacteria.

Surface analysis of titanium biological modification with glow discharge

BACKGROUND

Glow discharge plasma (GDP) technology has been used to graft various proteins to the titanium surface, including albumin, type I collagen, but without fibronectin.

PURPOSE

The aim of this study was to evaluate and analyze the physical properties of fibronectin-grafted titanium surfaces after GDP treatment.

MATERIALS AND METHODS

Grade II titanium discs after cleaning and autoclaving were considered as original specimens, thus divided into four groups. The groups were different upon two treatments (GDP only and fibronectin grafting after GDP) and two storage temperature (4°C and 25°C). The implant surface morphology was characterized by scanning electron microscopy (SEM), roughness measurement, and wettability evaluation. The concentration relationship of fibronectin was by fluorescein isothiocyanate (FITC) labeling.

RESULTS

SEM images showed that regular planar texture revealed on the surface of GDP-treated group, and irregular-folding protein was found on the fibronectin-grafted discs. Fibronectin-grafted groups had higher hydrophilicity and greater surface roughness than GDP-treated specimens. The storage temperature did not make obvious difference on the surface topography, wettability, and roughness. The number of fibronectin dots on the titanium surface labeling by FITC had positive relationship with the concentration of fibronectin solution used.

CONCLUSIONS

Biologically modified titanium surface is more hydrophilic and rougher than GDP-treated ones. GDP treatment combined with fibronectin grafting increased the surface hydrophilicity and surface roughness of titanium discs, which may attribute to the affinity of cell adhesion, migration, proliferation, and differentiation.

Fabrication of palladium/graphene oxide composite by plasma reduction at room temperature

Pd nanoparticles were fabricated on graphene oxide (GO) using a deposition-precipitation method with a glow discharge plasma reduction at room temperature. Argon was employed as the plasma-generating gas. The novel plasma method selectively reduces the metal ions. The graphene oxide has no change with this plasma reduction according to the Fourier transform infrared analysis. The Pd nanoparticles on the GO were uniformly distributed with an average diameter of 1.6 nm. The functional groups on the GO not only prevent Pd nanoparticles from further aggregation but also provide a strong hydrophilic property to the Pd/GO composite, which can form stable colloidal dispersions in water.

Oral bacterial deactivation using a low-temperature atmospheric argon plasma brush

OBJECTIVE

To study the plasma treatment effects on deactivation effectiveness of oral bacteria.

METHODS

A low temperature atmospheric argon plasma brush were used to study the oral bacterial deactivation effects in terms of plasma conditions, plasma exposure time, and bacterial supporting media. Oral bacteria of Streptococcus mutans and Lactobacillus acidophilus with an initial bacterial population density between 1.0×10(8) and 5.0×10(8)cfu/ml were seeded on various media and their survivability with plasma exposure was examined. Scanning electron microscopy was used to examine the morphological changes of the plasma treated bacteria. Optical absorption was used to determine the leakage of intracellular proteins and DNAs of the plasma treated bacteria.

RESULTS

The experimental data indicated that the argon atmospheric plasma brush was very effective in deactivating oral bacteria. The plasma exposure time for a 99.9999% cell reduction was less than 15s for S. mutans and within 5 min for L. acidophilus. It was found that the plasma deactivation efficiency was also dependent on the bacterial supporting media. With plasma exposure, significant damages to bacterial cell structures were observed with both bacterium species. Leakage of intracellular proteins and DNAs after plasma exposure was observed through monitoring the absorbance peaks at wavelengths of 280 nm and 260 nm, respectively.

CONCLUSION

The experimental results from this study indicated that low temperature atmospheric plasma treatment was very effective in deactivation of oral bacteria and could be a promising technique in various dental clinical applications such as bacterial disinfection and caries early prevention.