Diagnostics of Electron Temperature in Laser produced Plasma and Determination of its Effect on Some Deposited Films Properties

Abstract

The aim of this study is to produce plasma by laser, (LPP) from different targets; iron, copper, gold and tin, with different thicknesses, and to correlate effect of the temperature on the thin film properties. In this work, two different techniques have been used to determine the plasma temperature. The first technique uses the X-ray emitted from plasma which helps to calculate the temperature from the X-ray line intensity ratio in a chamber evacuated to 10-2 mbar. The second technique; Laser Induced Forward Transfer of metals, (LIFT) was done under normal atmosphere to achieve thin films. For the purpose of achieving the objectives of the study, the same laser system has been applied in both techniques, the frequency doubled Nd:YAG laser 532 nm, 40 picoseconds pulse duration. The energy on target is about 30 mJ and the repetition rate is (1to 10) Hz and power density of 1013 Wcm2. X-ray spectra in the range of 12 to 17 Å for the iron target and 9 to 12 Å for the copper target. To detect the X-ray signal, PIN diode has been used with 1 GHz LeCroy oscilloscope. According to Boltzmann law, a plot of the logarithmic term versus ΔE yields, a straight line whose slope, S, is equal to – 1/T. The plasma electron temperature was ~ 13.18 eV for Fe. Difficulties due to mismatches between the theoretical IV parameters and experimental spectral lines have affected the accuracy of the used method and prevented the data of Cu from being completed because of the absence of the Einstein coefficient for the recorded copper lines in the wavelength rage from 9 to 12 Å. In the second technique, the pressures, velocities and temperatures of the ejected particles were calculated, showing a slight dependence on the laser intensity. It was clear that the higher the laser power density, the faster the shock wave and higher electron temperature can be achieved. For the used elements, and at laser intensity from 2 to 6× 1013 W/cm2 rang, the plasma temperature values were found to be in the range between (4.8 and 10.15 eV), (5.13 to 10.92 eV), (5.28 to 11.1 eV) and (3.45 to 6.42 eV) for Al, Au, Sn and Fe, respectively. The ejected material was deposited on two different substrates; the first one is copper and second one is lattice of agate. There was a link between the characteristics of the deposited film and both the laser intensity and plasma temperature. From the plasma temperature calculations and from both SEM and EDAX images taken for the deposited film parameters, the power density threshold values needed for achieving the deposition without having any crater on the substrate was found to be between 1 and 1.5×1013W/cm 2. At laser intensity higher than the ablation threshold, the achieved plasma temperature was high and V takes values greater than 5 eV depending on the laser intensity and the target material. Thus the particles were moved at velocity up to 11 Km/s causes a deep crater on the substrate and the deposited film was re-ablated again; therefore no deposition was achieved. Using intermediate laser intensity, slightly above the threshold, the plasma temperature average value was equal to 3.45 eV, and the film transition from the rough phase to a much smoother phase. It was found in this work, that the optimum parameters to achieve the best homogeneous film were 2 μm target thickness, 2×1013 W/cm2 laser intensity, target-substrate are in-contact and targets were put out of focal point of the lens about 2 cm.