Diagnostics of assymetrical and plan parallel radiofrequency plasma systems with a goal of defining plasma chemical processes during treatments of both organic and inorganic samples

Abstract

Plazma na niskom pritisku se već duži niz godina primenjuje u industrijama poput automobilske, elektronske ili tekstilne. Zbog načina na koji plazma interaguje sa površinama, može se koristiti za precizno nagrizanje ili pripremu površine za nanošenje nekog materijala, poput boje ili polimera. Upotrebom plazme umesto hemijskih metoda je u mnogim industrijama moguće postići isti efekat ali na način koji ostavlja daleko manje ekološke posledice. Primene u tretmanima bioloških uzoraka, poput semena, poslednjih godina privlače pažnju kako naučnika tako i industrije u tolikoj meri da je razvijena nova oblast istraživanja pod imenom plazma-agrikultura. Unapređenje efikasnosti svih vrsta plazma tretmana zahteva pre svega dublje upoznavanje sa osobinama same plazme ali i interakcije plazme sa površinama. Kako bi se omogućio tretman uzoraka koji su osetljivi na visoke temperature, u Laboratoriji za neravnotežne procese i primenu plazme Instituta za fiziku je razvijen asimetrični reaktor velike zapremine i cilindrične geometrije. Disertacija sadrži rezultate detaljne karakterizacije pražnjenja u ovom reaktoru u smeši gasova koja je sačinjena od 99% kiseonika (O2) i 1 % argona (Ar). Metodom masene spektrometrije je ispitan hemijski sastav gasa i praćen je doprinos atoma i molekula kiseonika kao i atoma argona u zavisnosti od primenjene snage pražnjenja i pritiska u komori. Masenom spektrometrijom praga za jonizaciju praćena je količina pobuđenih molekula i atoma kiseonika. Derivativnim sondama su ispitane strujno naponske karakteristike sistema, frekventni sastav strujnog i naponskog signala i određen je stepen efikasnosti predaje snage pražnjenju. Snimljeni su emisioni spektri plazme a primenom metode optičke aktinometrije je izmerena apsolutna koncentracija atoma kiseonika i stepen disocijacije molekula. Kako bi se procenilo kako na osobine plazme utiče odnos površina uzemljene i napajane elektrode ali i kako blizina uzemljenog zida utiče na masene spektre i količinu pobuđenih čestica, sva merenja su rađena za dve različite dimenzije uzemljenih elektroda. Dvodimenzionalnom simulacijom je procenjeno kako će postavljanje dodatne, manje, uzemljene elektrode uticati na protok gasova kroz komoru. Derivativnim sondama su rađene identične analize u reaktoru plan paralelne geometrije tokom pražnjenja u azotu i argonu za dva različita rastojanja između napajane i uzemljene elektrode. Sa ciljem boljeg razumevanja interakcije plazme sa površinama tretiranog uzorka, u istom reaktoru su snimljeni emisioni spektri tokom pražnjenja u tim gasovima (N2 i Ar) i praćena je vremenska evolucija karakterističnih linija. Ova snimanja su rađena kako tokom tretmana tako i tokom pražnjenja bez uzorka u komori. Uniformnost pražnjenja u radijalnom smeru je ispitana Langmirovom sondom. U okviru saradnje sa dve grupe iz Ljubljane, katalitičkom sondom je merena koncentracija atomskog kiseonika na tri različite pozicije, daleko od izvora jonizacije, u reaktoru mikrotalasne pobude. Nakon karakterizacije, u sva tri reaktora je rađen tretman tekstila sa ciljem nanošenja mikrokapsula. Pored toga, u asimetričnom reaktoru je rađen i tretman semena različitih biljaka. Tretmanom semena industrijskih biljaka je pokazano kako se plazmom može uticati na klijavost i na stepen infekcije. Izlaganjem semena caričinog drveta (paulownia tomentosa) plazmi je pokazano kako tretman semena utiče na aktivnost enzima tokom perioda klijanja biljke.Low pressure plasmas have been used for a long time in industries such as car production, electronic industry or textile industry. Due to the specific way it interacts with the surfaces, plasma can be used for precise etching or surface preparation for the application of materials such are paints or polymers. By using plasma instead of the traditional chemical methods, in many industries, it is possible to achieve the same effect but in a way that is much more environmentally friendly. In recent years, applications in treatments of biological samples, such are seeds, have gathered attention of both scientists and the industry in such an extent that new area of research have been developed. It is called plasma-agriculture. In order to improve all kinds of plasma treatments it is necessary to achieve deeper understanding of both plasma itself and plasma-surface interactions as well. With an aim to facilitate treatments of thermally sensitive samples, large asymmetrical plasma reactor of cylindrical geometry has been developed in Laboratory for non-equilibrium processes and application of plasmas in Institute of physics. Results of detailed characterisation of discharges in this plasma reactor, in gas mixture of 99 % oxygen (O2) and 1 % argon (Ar), are presented in the doctoral dissertation in front of you. In order to determine chemical composition of the gasses and to track yields of O2, O and Ar versus pressure and applied power we have applied technique of mass spectrometry. Number of excited O and O2 particles was tracked by means of threshold ionisation mass spectrometry. Derivative probes were used in order to determine current-voltage characteristics of the system, current and voltage signal spectrum and power transfer efficiency. Plasma emission spectra were also recorded while optical actinometry was used to determine absolute O atom concentration and oxygen molecule dissociation degree. In order to assess how does the ratio of grounded to powered electrode surface is affecting plasma parameters and how does vicinity of the chamber wall is changing mass spectra, all of the measurements were performed with the two different sized grounded electrodes. Additionally, two-dimensional computer simulation was used to determine influence of additional, smaller, grounded electrode on the gas flow through the chamber. The derivative probes were used to perform the same characterisation but of a plan parallel system during nitrogen and argon discharges at two different distances between the powered and the grounded electrodes. Optical emission spectra were recorded and distinct emission line of, both nitrogen and argon, were tracked through the time in order to deepen the understanding of interaction between the plasma and the treated sample. These recordings were performed during plasma treatment and during discharge without the sample in the chamber. Plasma uniformity in radial directions was evaluated by the Langmuir probe measurements. Within the cooperation with two research groups from Ljubljana, oxygen atom concentration was measured by means of catalytic probe in a microwave discharge afterglow. After all the diagnostics, textile treatments were performed in all three reactors with the aim of applying microcapsules. Besides that, seeds of various plants were treated in the asymmetrical reactor. We have shown how plasma treatment of industrial plant seeds can influence their germination and infection rate. Paulownia tomentosa seeds were exposed to the plasma and we have shown what kind of influence plasma treatments have on enzyme activity during subsequent seed germination phase