Argon Glow Discharge Plasma Research Articles

Observations of structured and long-range transport in a large volume dusty (complex) plasma experiment

DUPLEX—the DUsty PLasma EXperiment at the Naval Research Laboratory—is a large volume dc glow discharge plasma device. The DUPLEX chamber is a transparent polycarbonate cylinder that is 40 cm in radius and 80 cm in height. Argon dc glow discharge plasmas are generated between a grounded cathode and a biased anode. The anode and cathode are separated by 15 to 20 cm. Clouds of 1 μm diameter alumina microparticles are suspended in the plasma—with the highest density directly above the cathode. However, particles have been detected throughout the entire plasma volume. This article reports on previously unidentified, and possibly unknown, phenomena observed in a dusty plasma. Two specific features will be the focus of this article. First, large microparticle clouds—up to 15 cm in diameter in some locations—with highly complex internal structures are identified. Second, long range—20 to 30 cm distances—periodic transport of microparticles from one region of the plasma to another is identified. It is believed that the large size and nonconducting boundary of the DUPLEX chamber facilitates the observation of these phenomena.

Wavelength table of chromium emission lines in argon glow discharge optical emission spectrometry

A wavelength table of chromium lines emitted from an argon glow discharge plasma, which comprises 2049 atomic and ionic emission lines in the wavelength range of 200–440 nm, is presented. The relative intensities are rather different from the data of published wavelength tables based on arc-excited and spark-excited spectra. Emission lines of Ar, Ti, V, Fe, Ni, and Cu in the neighborhood of the prominent Cr emission lines are also compiled as a table. These tables could be employed for the analytical applications in glow discharge optical emission spectrometry. All of the data are presented as Supplementary Electronic Material.

A method to measure electric field strengths in an argon glow discharge plasma using laser spectroscopy

A method for electric field measurement based on laser spectroscopy of argon atoms has been developed and calibrated. Measurements were made using both laser optogalvanic spectroscopy and laser-induced fluorescence spectroscopy. Measurements using several different transitions in argon were carried out, and it was found that the 4s/spl rarr/7f and 4s/spl rarr/8f transitions were the most suitable for measurements in the sheath region of glow discharges. The lower limit for electric field measurements was estimated to be 500 V/cm. A minimal pressure of about 100 mtorr was required to detect optogalvanic signals and about 1 torr was required for the fluorescence signals to be detectable. These detection limits make this method applicable for measurement of sheath electric fields for a wide range of discharge conditions.

Macroscopic study of fine particle plasmas generated by the boat method

The aluminum fine particles generated by the boat method were made into the fine particle plasmas by the irradiation of u.v. light and mixture of gaseous plasmas. The motion of the cloud around the charged sphere indicated that the fine particle cloud irradiated by u.v. light was in mixtures of positively charged particles and negatively charged particles. When fine particle plasmas immersed in argon glow discharge plasmas, the fine particles took a negative charge and were attracted to a positively charged small sphere and wire. This fact was clearly explained by Spitzer's investigation.

Effect of oxygen addition to an argon glow-discharge plasma source in atomic emission spectrometry

Small amounts of oxygen gas greatly change the characteristics of the argon plasma light source in glow-discharge emission spectrometry. The influence of oxygen addition on the sputtering rate and the excitation of the analytes in the argon plasma was investigated by employing argon-oxygen binary mixed gases having well-defined compositions. Strong quenching by oxygen was observed from the intensity of the emission lines originating from the analyte element as well as the gas species. The negative effect caused by oxygen gas in analytical applications with the glow-discharge lamp should be noted.

Electron temperature measurements in uhv systems by spectroscopic and Langmuir probe techniques

The spectroscopic and Langmuir probe characteristics of a low pressure argon glow discharge plasma were studied and the electron temperature ( T e) was measured independently by both methods. The experiments were carried out in a SS 304 uhv chamber used for studying glow discharge cleaning techniques. Two types of excitation sources, dc and rf, were used. The Corona model was used to evaluate T e from spectral line intensities and other atomic data. The electron temperatures measured by both methods agree well, thereby indicating the usefulness of emission spectroscopy as a simple, non-invasive and reliable technique to measure the average value of T e over the line of sight of a detector. In the pressure range of 0.2–0.002 mbar used in this experiment, T e increased with an increase in dc current and rf power and also with the reduction in pressure.

Langmuir Probe Determination of Charged Particles in Ar and He Discharge Plasmas

This paper presents results of cylindrical single Langmuir probe measurements of the electron and ion densities in argon and helium glow discharge plasmas. The gas pressure veries from 5 to 150 Pa. The electron density is determined from the electron probe current at the space potential. The positive ion density is determined from the probe ion saturated current according to Bohm pre-sheath model as well as according to collisional Zakrzewski and Kopiczynski model. At basic pressures of 80 Pa and higher, good agreement is obtained, for both gases, between the electron and ion densities with both models. For basic pressures less than 80 Pa down to 5 Pa, satisfactory agreement between the electron and ion densities is achieved with Zakrzewski and Kopiczynski model where the destruction of the orbital motion of ions in the sheath is still considered.

Effects of helium addition to an argon glow discharge plasma on emission lines of sputtered particles

Effects of helium addition to an argon glow discharge plasma on emission lines of sputtered particles

Characterization of atomic emission lines from argon, neon, and nitrogen glow discharge plasmas

Characterization of atomic emission lines from argon, neon, and nitrogen glow discharge plasmas

Effect of glow discharge treatment of substrates on parylene-substrate adhesion

A detailed investigation of the effect of argon, oxygen, and methane glow discharge (plasma) treatment of substrates on the adhesion characteristics of parylene polymer to a variety of substrates is reported. It is found that methane glow discharge treatment, which results in the deposition of a glow discharge polymer of methane on the substrate surface, is most effective in improving the bonding strength of the parylene polymer, while the oxygen glow discharge treatment which produces a hydrophilic substrate surface with no or insignificant polymer deposition is detrimental to parylene adhesion. The effect of argon glow discharge treatment may vary from true cleaning of the substrate surface to deposition of a thin layer of a polymeric coating produced by the simultaneous glow discharge polymerization of the ablated organic materials existing in the reactor and may or may not improve parylene adhesion. These results are supported by the Auger electron spectroscopy and contact angle measurements of the glow discharge-treated surfaces. Model studies using substrates of different surface free energies indicate that water-resistant adhesion of parylene polymer increases with the hydrophobicity of the substrate material and is in harmony with the above findings. From the viewpoint of adhesion the most advantageous and dependable effect is obtained with the methane plasma treatment. The treatment results not only in the formation of a more compatible, hydrophobic surface but also produces radical sites for covalent bonding with the parylene.