N. U. Rehman

Double and Triple Langmuir Probes Measurements in Inductively Coupled Nitrogen Plasma

The double and triple Langmuir probe diagnostic systems with their necessary driving circuits are developed successfully for the characterization of laboratory built low pressure inductively coupled nitrogen plasma, generated by 13.56MHz radio frequency (RF) power supply along with an automatic impedance matching network. Using the DC properties of these two probes, the discharge plasma parameters like ion saturation current (Iio), electron temperature (kTe) and electron number density (ne) are measured at the input RF power ranging from 250 to 400W and fllling gas pressures ranging from 0.3 to 0.6mbar. An increasing trend is observed in kTe and ne with the increase of input RF power at a flxed fllling gas pressure of 0.3mbar, while a decreasing trend is observed in kTe and ne with the increase of fllling gas pressure at a flxed input RF power of 250W.

Symmetric and Asymmetric Double Langmuir Probes Characterization of Radio Frequency Inductivley Coupled Nitrogen Plasma

The symmetric and asymmetric double Langmuir probe systems with their necessary driving circuits are developed for characterization of low pressure inductively coupled nitrogen plasma, generated and sustained with 13.56 MHz RF source and an automatic impedance matching network. First of all, the plasma parameters such as ion saturation current, electron temperature and electron number density are determined with symmetric double probe system at different input RF powers, filling gas pressures and radial distance Received 4 March 2011, Accepted 28 March 2011, Scheduled 30 March 2011 Corresponding author: Muhammad Yasin Naz (yasin603@yahoo.com).

Effect of Excitation and Vibrational Temperature on the Dissociation of Nitrogen Molecules in Ar-N2 Mixture RF Discharge

ABSTRACT Non-equilibrium argon-nitrogen mixture plasma generated at 13.56 MHz is characterized by optical emission spectroscopy and Langmuir probe techniques. The excitation and vibrational temperature are studied as a function of argon percentage in the mixture, at 30-Pa filling pressure and input RF powers of 200 and 300 watt, to find out their role in dissociation of N2 molecules. In this work, the excitation temperature is determined from Ar-I emission line intensities by using the simple Boltzmann plot method and is found to increase with argon mixing in nitrogen plasma. In similar fashion, the vibrational temperature of second positive system has been determined and is found to also have increasing trend with argon addition. The effect of excitation and vibrational temperature on the nitrogen molecular dissociation level is also monitored. It is observed that N/N 2 ratio increases with increase in excitation and vibrational temperature and falls slightly at the end.

Evolution of plasma parameters in a He- N2/Ar magnetic pole enhanced inductive plasma source

A magnetic pole enhanced inductively coupled He- N2/Ar plasma is studied at low pressure, to monitor the effects of helium mixing on plasma parameters like electron number density  (ne), electron temperature  (Te), plasma potential (Vp) , and electron energy probability functions (EEPFs). An RF compensated Langmuir probe is employed to measure these plasma parameters. It is noted that electron number density increases with increasing RF power and helium concentration in the mixture, while it decreases with increase in filling gas pressure. On the other hand, electron temperature shows an increasing trend with helium concentration in the mixture. At low RF powers and low helium concentration in the mixture, EEPFs show a “bi-Maxwellian” distribution with pressure. While at RF powers greater than 50 W and higher helium concentration in the mixture, EEPFs evolve into “Maxwellian” distribution. The variation of skin depth with RF power and helium concentration in the mixture, and its relation with EEPF are als...

Development of Simple Designs of Multitip Probe Diagnostic Systems for RF Plasma Characterization

Multitip probes are very useful diagnostics for analyzing and controlling the physical phenomena occurring in low temperature discharge plasmas. However, DC biased probes often fail to perform well in processing plasmas. The objective of the work was to deduce simple designs of DC biased multitip probes for parametric study of radio frequency plasmas. For this purpose, symmetric double probe, asymmetric double probe, and symmetric triple probe diagnostic systems and their driving circuits were designed and tested in an inductively coupled plasma (ICP) generated by a 13.56 MHz radio frequency (RF) source. Using I-V characteristics of these probes, electron temperature, electron number density, and ion saturation current was measured as a function of input power and filling gas pressure. An increasing trend was noticed in electron temperature and electron number density for increasing input RF power whilst a decreasing trend was evident in these parameters when measured against filling gas pressure. In addition, the electron energy probability function (EEPF) was also studied by using an asymmetric double probe. These studies confirmed the non-Maxwellian nature of the EEPF and the presence of two groups of the energetic electrons at low filling gas pressures.

Trace-Rare-Gas Optical Emission Spectroscopy of Nitrogen Plasma Generated at a Frequency of 13.56 MHz

Optical emission spectroscopic measurement of trace rare gas is carried out to determine the density of nitrogen (N) atom, in a nitrogen plasma, as a function of filling pressure and RF power applied. 2% of argon, used as an actinometer, is mixed with nitrogen. In order to normalize the changes in the excitation cross section and electron energy distribution function at different operational conditions, the Ar-I emission line at 419.83 nm is used, which is of nearly the same excitation efficiency coefficient as that of the nitrogen emission line at 493.51 nm. It is observed that the emission intensity of the selected argon and atomic nitrogen lines increases with both pressure and RF power, as does the nitrogen atomic density.

Characterization of nonthermal Ne–N2 mixture radio frequency discharge

This paper deals with optical emission spectroscopic studies of low pressure (p=0.1⇒0.5 mbar) Ne–N2 capacitively coupled radio frequency (rf) plasma that can be used for plasma nitriding, etc. It reports the methods to calculate the electron temperature (Te) in nonthermal plasmas. Since, the selected Ne I lines, used to calculate electron temperature, are found in corona balance; therefore, it allows us to use modified Boltzmann technique to calculate electron temperature. Langmuir probe is also used to calculate electron temperature and electron energy distribution functions (EEDFs). The measurements are worked out for different discharge parameters like neon percentage, filling pressure and RF power. It is found that electron temperature increases with the increase in neon percentage and decreases with the increase in pressure, whereas excitation temperature (Texc) increases with power, neon percentage, and decreases with pressure. It is also observed that electron temperature measured by Langmuir probe...

Characterization of RF He-N2/Ar mixture plasma via Langmuir probe and optical emission spectroscopy techniques

A Magnetic Pole Enhanced inductively coupled RF He-  N2/  Ar plasma is characterized using a Langmuir probe and optical emission spectroscopy (OES) techniques. The effect of helium mixing on electron density  (ne) and temperature  (Te), electron energy probability functions (EEPFs), [ N] atomic density, and N2  dissociation is investigated. A Langmuir probe and a zero slope method based on trace rare gas-optical emission spectroscopy (TRG-OES) are employed to measure the electron temperature. It is noted that the electron temperature shows an increasing trend for both methods. However, the temperature measured by a zero slope method Te(Z·S) approaches the temperature measured by a Langmuir probe; Te(L·P) at 56% and above helium concentration in the discharge. “Advance actinometry” is employed to monitor the variation in [ N] atomic density with helium concentration and gas pressure. It is noted that [ N] atomic density increases at 56% and above helium in the discharge, which is consistent with the trend ...

Optical emission spectroscopy of He–N2 mixture plasma

Nitrogen–helium mixture plasma is investigated via optical emission spectroscopy and the effect of helium mixing on the excitation temperature, vibrational temperature of the second positive system and first negative system of nitrogen plasma is monitored. The excitation temperature is calculated from He–I lines by using Boltzmanns plot method, which increases with an increase in helium percentage in the mixture. On the other hand, it is noted that the vibrational temperature of the second positive system increases with an increase in helium percentage but it decreases for the selected first negative system of nitrogen. It is also observed that vibrational temperature increases with an increase in filling gas pressure. To confirm whether the selected vibrational bands follow Boltzmanns distribution, a linearization process is employed. The vibrational temperature of the ground state of nitrogen is calculated from on the basis of inverse Franck–Condon factors.

OPTICAL CHARACTERIZATION OF 50 Hz ATMOSPHERIC PRESSURE SINGLE DIELECTRIC BARRIER DISCHARGE PLASMA

A low frequency (50Hz) dielectric barrier discharge (DBD) system with a single dielectric cover on copper coil anode is designed to generate and sustain the micro-discharge plasma which is very practical for material processing applications. The DBD system is powered by a high tension ac source consisting of a conventional step up transformer and variac. The dielectric barriers (quartz and glass) between the conducting electrodes appreciably influences the discharge plasma characterized by optical emission spectroscopy technique. Using intensity ratio method, the electron temperature and electron number density are determined from recorded spectra as function of ac input voltage, type and thickness of dielectric barrier and inter-electrode gap. It is observed that both the electron temperature and electron number density increase with the increase in ac input voltage and r/d ratio, while a decreasing trend is observed with increase in inter-electrode gap.