Muhammad Zakaullah

Optical emission of selected nitrogen bands is analyzed for different nitrogen fill pressure and input electrical power to find the changes in spectral intensities with changing discharge conditions....

Fabrication of non-functionalized gold nanoparticles is interesting owing to their potential applications in sensing and biomedicine. We report on the synthesis of surfactant-free gold nanoparticles (AuNPs) by Plasma-Liquid Interaction (PLI) technique, using micro-atmospheric pressure D.C. plasma. The effects of discharge parameters, such as discharge current, precursor concentration and gas flow rates on the structure and morphology of AuNPs have been investigated. Optical Emission Spectroscopy (OES) was employed to estimate the UV radiation intensity and OH radical density. Scanning electron microscopy (SEM) and ultraviolet-visible (UV-Vis) optical spectroscopy were employed to study the morphology and structure of AuNPs. The normalized intensities of UV radiation and OH radical density found to increase with increase in discharge current. We observed that the particle size can be tuned by controlling any of the following parameters: intensity of the UV radiation, OH radical density, and concentration of the Au precursor. Interestingly, we found that addition of 1% Ar in the feedstock gas results in formation of relatively uniform size distribution of nanoparticles. The surfactant-free AuNPs, due to their bare-surface, exhibit excellent surface-enhanced Raman scattering (SERS) properties. The SERS study of Rhodamine 6G using AuNPs as substrates, shows significant Raman enhancement and fluorescence quenching, which makes our technique a potentially powerful route to detection of trace amounts of dangerous explosives and other materials.

Low-pressure H2-N2 mixture pulsed DC plasmas with a cathodic cage (active screen) are widely used for plasma nitriding applications. In this study, the low-pressure H2-N2 mixture plasma with a cathodic cage generated by 50 Hz pulsed DC source is investigated with triple Langmuir probe and optical emission spectroscopy. The electron temperature (T e LP) and electron number density (n e ) are measured using a triple Langmuir probe (TLP). The excitation temperature (T exc OES) is calculated spectroscopically using Boltzmann plot method whereas nitrogen dissociation fraction is estimated using actinometry as well as the intensity ratio method (I N (746.83 nm)/I N2(337.1 nm)). The results show that the electron and excitation temperatures, electron density and nitrogen atomic species density [N] all increase with the argon admixture, however, the important molecular ionized species density [N2 +] significantly decreases beyond 30% addition. This study provides useful information about the influence of the argon addition on plasma parameters and active species generation. As a result it helps to optimize the plasma nitriding system as a function of argon admixture to avoid random trials in the processing.

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 Boltzmann's 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 Boltzmann's 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.

Active screen cage-pulsed dc plasmas are widely used in the material processing applications such as plasma nitriding, carburizing and nitrocarburizing. Specifically for plasma nitriding applications, a H₂–N₂ mixture is used. In this article, a study of the electron number density (n_e), atomic nitrogen density ([N]), electron temperature and the excitation temperature is reported in the presence of an active screen cage-pulsed dc plasma. The n_e and are determined here by a triple Langmuir probe, while [N] and are estimated by optical emission spectroscopy (OES). The two temperatures and their ratio are compared for different input parameters (such as applied power, gas pressure and H₂ percentage). This study is useful in active screen cage plasma nitriding applications where only few plasma diagnostic measurements have been reported.