REPOSITORY > RESULTS

Abstract

Non-equilibrium atmospheric pressure plasmas are used in many areas, such as food and agriculture, plasma medicine, plasma surface modification, material synthesis and deposition. Because of their versatility, many plasma setups have been developed. Of greater interest are those that operate at atmospheric pressure, like atmospheric pressure plasma jets (APPJs). Regarding applications, there are two main advantages of this type of plasma – simplicity and availability that comes with operation at atmospheric pressure, and low operating temperature that enables treatments of temperature-sensitive materials and substrates. Versatility and wide application of APPJs make detailed and standardized diagnostics a necessity.
This dissertation tries to prove that optical emission spectroscopy is an efficient method for observing plasma properties generated within inert gases of argon and helium, and can provide all necessary data on plasma parameters and conditions. Consequently, optical emission spectroscopy enables in situ monitoring to understand physical and chemical processes occurring on surfaces, during synthesis or deposition. Therefore, the goal of the dissertation is to follow and investigate two objectives: (i) tracking APPJ surface modifications by optical emission spectroscopy for improved functionalization of nanomaterial surfaces or nanoparticles in colloidal solutions, and (ii) monitoring treatment of biological substrates with optical emission spectroscopy for the safe APPJ treatment of skin, decontamination of surfaces and removal of bacteria, as well as mitigations of plasma damages on cells relevant to clinical practice.
In order to test the hypothesis, the research is based on three steps – setting up a plasma system, implementing plasma diagnostic tools and monitoring different changes in materials, either biological responses or chemical and morphological change. The used plasma setups are APPJs with different power sources, either operating in radio frequency or kHz regimes, with a possibility of aerosol injection. Implementation of plasma diagnostic tools means that gas-phase diagnostics are combined with electrical characterization of the power source. Optical diagnostics consist of optical emission spectroscopy, spatial and time-resolved, and fast intensified charged coupled device imaging of the plasma streamer. Electrical characterization and power measurements are performed by HV probes and current monitoring. Lastly, to uncover plasma properties indirectly, we look at different analyses and responses of substrates based on chemical (liquid chemistry), morphological (scanning electron microscopy, transmission electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, ultraviolet–visible spectroscopy, Fourier-transform infrared spectroscopy) and biological analysis (cell viability tests, determination of viable bacteria after the plasma treatment, fluorescence microscopy for evaluation of skin damage and infrared imaging of the mouse skin surface).
The results support our hypothesis – optical emission spectroscopy is a great multipurpose tool for monitoring and tracking atmospheric pressure plasma processes in jets and changes when accompanied with appropriate and detailed substrate analysis. If we want to gain even more, other diagnostic techniques should be added to the research. However, the optical emission spectroscopy will be a future cornerstone sensor for monitoring and controling the atmospheric pressure plasma processes initiated by jets in either nanofabrication or treatments of biological materials.