Combining oxygen and ethanol (C2H5OH) could be important for extending plasma chemistry applications [3]. The discharge vessel was a linear tube with outer ...
Optical emission spectroscopy characterization of ethanol vapor inductively coupled RF plasma S. Milošević1, N. Glavan-Vukelić1,2, Z. Kregar1, N. Krstulović1 1
2
Institute of Physics, Bijenička 46, HR-10000 Zagreb Croatia Faculty of Engineering, University of Rijeka, Vukovarska 58, 51000 Rijeka, Croatia
Ethanol vapor plasma has a high potential in various applications such as hydrogen productions [1], materials surface modifications or for nanostructures growth [2]. RF inductively coupled plasma allows achievement of various plasma conditions by change of plasma device design characteristics. In the present work we have applied OES technique for characterisation of pure ethanol and oxygen-ethanol vapour mixture plasma emission. Combining oxygen and ethanol (C2H5OH) could be important for extending plasma chemistry applications [3]. The discharge vessel was a linear tube with outer diameter of 4 cm made of a borosilicate glass. The tube was connected to the vacuum system, which provides the pumping speed of 35 m3/h and the base pressure of 1 Pa. The total pressure in the system was measured with a Baratron gauge. Plasma was created within 8 turn coil connected through a matching network to a RF amplifier. The amplifier was fed by oscillation from a frequency generator at a frequency of 13.56 MHz. The discharge power was adjustable up to 300 W. Forward and reflected power components were monitored at the amplifier. The position of the coil could be varied along the glass tube. Ethanol vapor was loaded into the discharge vessel through a capillary glass tube (outer diameter 0.6 cm, inner 0.1 cm, opening about 0.03 cm). Ethanol vapor pressure was regulated by a precise Teflon valve. Glass vessel that contains pure ethanol was kept at the room temperature. Oxygen gas was added into the plasma through separate needle valve, and the flow measured by a mechanical flow meter.
Figure 1: Typical emission spectrum of oxygen-ethanol vapor plasma
The emission was observed both perpendicularly to the plasma tube and along the whole plasma column. Perpendicular measurements were performed by means of a LIBS2000+ spectrometer system from Ocean Optics. The nominal spectral resolution was 0.1 nm in the spectral range from 200-980 nm. Longitudinal observation was made simultaneously by means of broad band spectrometer having spectral resolution of 1 nm. The spectral response of spectrometers was determined by means of a combined deuterium tungsten reference light source. Figure 1 shows typical optical emission spectrum of oxygen-ethanol vapor plasma in longitudinal direction. The applied plasma power was 120 W, total pressure 0.3 torr and partial ethanol vapor pressure 0.15 torr. Main spectral features identified were: two prominent CO molecular bands - the Angstrom band (450-700 nm region) and the 3rd positive band (260- 400 nm region). They correspond to the B1 Σ+−A1 Π and b3 Σ+−a3 Π electronic transitions of the CO molecule, respectively. In addition, region of the Angstrom band is spectrally overlapped with structured continuum which extends from 300 nm to 800 nm. The most probably it originates from the chemiluminiscence resulting from the radiative combination of atomic oxygen and carbon monoxide which form the CO2 molecule. Other spectral features include OH band at 309 nm and hydrogen and oxygen atomic lines. Spatial and temporal spectral profiles were measured for different oxygen and ethanol vapor partial pressures. Hysteresis effect was observed depending on the change of the ethanol vapor partial pressure. It is probably due to deposition of carbon compounds on the walls of the discharge vessel and subsequent cleaning. This could be of importance for the OES real time monitoring of processes involving ethanol plasma applications. Spectral simulations and modeling of the plasma was performed to support interpretation of measured spectra. References [1] A. Yanguas-Gil, J.L. Hueso, J. Cotrino, A. Caballero, A. R. Gonzales-Elipe, Appl. Phys. Lett. 85, 4004, 2004. [2] K. Ostrikov and S. Xu, Plasma-Aided Nanofabrication, Wiley-VCH, 2007. [3] Z. Kregar, N. Krstulović, S. Milošević, K.Kenda, U. Cvelbar and M. Mozetič, IEEE Transactions on Plasma Science, 36 (2008) 1368-1369.
