The interdependence of ‘size’ and ‘volume-fraction’ hinders the identification of their individual role in the interface properties of metal nanoparticles (NPs) embedded in a matrix. Here, the case of Cu NPs embedded in a C matrix is presented for their profound antibacterial activity. Cu:C nanocomposite thin films with fixed Cu content (≈12 atomic%) are prepared using a plasma process where plasma energy controls the size of Cu NPs (from 9 nm to 16 nm). An inverse relationship between the size-effect on antibacterial activity against Escherichia coli and Staphylococcus aureus bacteria is established through the real time monitoring of an aliquot by inductively coupled plasma mass spectrometry, which confirmed the inverse relationship of Cu ion release from the nanocomposite with varied Cu NP sizes. It was found that enhancing the total power density increases the plasma density as well as effective kinetic energy of the plasma species, which in turn creates a large number of nucleation sites and restricts the island kind of growth of Cu NPs. The mechanism of NP size-control is illustrated on the basis of ion density and nucleation and the growth regime of plasma species. This physical approach to NP size reduction anticipates a contamination-free competitive recipe of size-control to capping based chemical methods.

Atmospheric pressure plasma (APP) jets or plasma plumes have recently shown the potential for applications such as plasma surface modification and plasma medicine. These applications need insight into their plasma chemistry and discharge behavior, which are strongly influenced by the plasma parameters. In contrast to conventional APP jet devices, the present study utilizes a combination of six electrodes, and the outer ground electrodes are separated by Teflon to form a moderate-sized plasma column of nearly 10 mm. This atmospheric pressure plasma jet can be used to generate non-thermal plasma bullets away from the plasma generation region. The characteristics of the plasma plume were extensively diagnosed using current–voltage measurements, ICCD camera, and optical emission spectroscopy (OES). The APP plasmas, excited by a relatively low-pulsed dc voltage, were characterized in terms of discharge power, gas temperature, electron excitation temperature, electron temperature, and electron density. With simplified assumptions, these discharge parameters were determined from the OES measurements. Electron densities of the orders of magnitude of 10¹⁴ and 10¹⁵ cm⁻³ relevant to the electron temperature from ∼1.5 to 1.8 eV were obtained for the center regions in the jet discharge when the discharge power was varied from ∼10 to 55 W. Moreover, the effect of various operating parameters on the APP jet propagation was studied, and it was observed that the applied voltage plays a crucial role in the propagation of the plasma jet. Additionally, experiments involving APP plasma treatment on deionized water demonstrate noticeable effects of the He gas flow rate on the discharge behavior near the liquid surface. With the increase in the gas flow rate, the plasma column diameter on the liquid surface increases. Further, the deionized water treated with the APP jet shows the signatures of various active species such as oxygen and nitrogen, which are attributed to the transfer of the charged particles to the liquid. Moreover, due to a relatively low gas temperature (∼310–330 K) along with a high plasma plume, the possibility for the plasma application of this device was realized.

An advanced plasma process using plasma chemistry and energy control for engineering Si thin film growth and microstructure is demonstrated.

This study investigates low-temperature plasma nitriding of hydrogenated silicon (SiN _x :H) film in radio frequency (RF) and RF–ultra-high frequency (UHF) hybrid plasmas. To study the optimized conditions for the deposition of SiN _x :H film, this work adopts a systematic plasma diagnostic approach in the nitrogen–silane and nitrogen–silane–ammonia plasmas. This work also evaluates the capability of plasma and radical formation by utilizing different plasma sources in the PECVD process. For the plasma diagnostics, we have purposefully used the combination of optical emission spectroscopy (OES), intensified CCD (ICCD) camera, vacuum ultraviolet absorption spectroscopy (VUVAS), and RF compensated Langmuir probe (LP). Data reveal that there is significant enhancement in the atomic nitrogen radicals, plasma densities, and film properties using the hybrid plasmas. Measurements show that addition of a small amount of NH ₃ can significantly reduce the electron temperature, plasma, and radical density. Also, optical and chemical properties of the deposited films are investigated on the basis of plasma diagnostics. Good quality SiN _x :H films, with atomic nitrogen to hydrogen ratio of 4:1, are fabricated. The plasma chemistry of the hybrid plasmas is also discussed for its utility for plasma applications.