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Low-pressure inductively coupled oxygen plasma was loaded by ethanol (C2H5OH), methanol (CH3OH) or acetone (C3H5OH) vapours and characterized by means of optical emission spectroscopy. Plasma was generated by inductively coupled RF generator (RIZ SW-amp.) with the frequency of 13.56 MHz and adjustable output power up to 300 W. The plasma was maintained in a glass discharge tube with the inner diameter of 3.6 cm. The discharge tube was pumped with a rotary pump. Vapors were introduced into plasma region through glass capillary tube connected to temperature stabilized liquid container through precise Teflon valve. Partial pressures in the tube were measured by a Baratron gauge. Plasma radiation was measured with CCD Ocean Optics spectrometers (UV- VIS-CGI or LIBS2000+). Emission from highly excited species was found in the ultraviolet, visible and infrared part of the spectra from 200 to 1000 nm. The rich emission spectra were dominated by molecular spectra of CO (3rd positive band and Angstrom band) and OH (A-X band) radicals. Atomic transition lines from hydrogen (H , H ) and oxygen O(3p5P  3s5S), and O(4p3P  3s3S) were observed as well. By observing spectral line intensity ratios, relative abundance of OH, CO, H and O radicals was studied versus oxygen/vapor pressure ratio and discharge power. Optimum conditions for production of various radicals are discussed in terms of vapors characteristics and possible dissociation and recombination mechanisms.

Optical emission spectroscopy was applied for plasma characterization during sterilization of substrates contaminated with bacteria. The amount of 10cfi Escherichia coli was carefully applied to glass substrates and exposed to oxygen plasma at different pressure between 30 and 100 Pa. Plasma was created in a glass discharge tube by an inductively coupled RF generator at the frequency of 27.12MHz and output power of about 250W. The electron temperature and plasma density were estimated with a double Langmuir probe and were between 3 and 5 eV, and between 2 and 20x1016 m-3. Density of neutral oxygen atoms was measured with a catalytic probe and was between 2 and 6x1021m-3. Optical emission spectroscopy was performed with a low resolution spectrometer. The integration time of 300ms was enough to obtain measurable intensities of major spectral features. The predominant features were atomic oxygen lines, but other features including hydrogen, nitrogen, carbon monoxide and hydrogen oxide also appeared. The emission from carbon monoxide and OH molecules was used to monitor the evolution of bacteria degradation. Both signals expressed a well defined maximum corresponding to the peak erosion of bacteria by plasma radicals. As the sterilization was accomplished, both CO and OH bands fell below the detection limit of the spectrometer. The bacteria degradation was also monitored by scanning electron microscopy (SEM). The SEM images corresponded well with the evolution of CO and OH bands so the optical emission spectroscopy was found a reliable tool for monitoring the sterilization process.

Optical emission spectroscopy (OES) was applied for real-time measuring of the reaction products during plasma treatment of a polyethyleneteraftalate (PET) foil. Plasma was created in pure oxygen by inductively coupled radiofrequency (RF) discharge. The discharge chamber was a glass tube with the length of 50 cm and the inner diameter of 3.6 cm. It was pumped with a two stage rotary pump with the ultimate pressure of about 0.1Pa and the pumping speed of 4.4 dm3s-1. Oxygen was leaked continuously into the discharge tube so the pressure during experiments was 75Pa. Plasma parameters were measured in the discharge tube prior to experiments with the PET foil with a double Langmuir probe and a catalytic probe. The electron temperature was about 6eV, plasma density about 1x1016m-3 and the neutral atom density about 1x1022m-3. Polymer foil with the thickness of 0.023 mm was cut to rectangular samples with the dimension of 2x4 cm2. Optical emission spectra were measured in the range from 200 to 950 nm with the Ocean Optics spectrometer. For the first 10s of plasma treatment the OES showed the presence of oxygen radicals only, the predominant lines were at 777 and 844 nm, corresponding to neutral oxygen atom transition 3p6P – 3s6S0 and 3p3P – 3s3S0, respectively. As the plasma treatment was continued, the OES spectra became richer with significant emission from CO (both Angstrom and 3rd positive band) and OH (A-X band). The appearance of these bands was attributed to extensive PET oxidation. The lines corresponding to relaxation of hydrogen atoms (Balmer series) appeared, too. Simultaneously, the O peaks decreased significantly. While the intensity of the O atom line at 777 decreased to about a tenth of its original value, the line at 844 virtually disappeared at all. After prolonged plasma treatment, the O peaks recovered, the CO band vanished while the OH and H peaks still persisted. In the final period of the treatment, only atomic oxygen lines remained. The appearance of the oxygen-containing functional groups on the sample surface was measured simultaneously during the plasma treatment by XPS. The concentration of these functional groups was the highest after about 10s of plasma treatment, i.e. just when the CO and OH became measurable. The results showed that OES analysis was a powerful method for studying the evolution of PET oxidation by plasma treatment.