Temporally resolved laser induced plasma diagnostics of single crystal silicon - effects of ambient pressure

Laser-Induced Breakdown Spectroscopy of silicon was performed using a nanosecond pulsed frequency doubled Nd:YAG (532 nm) laser. The temporal evolution of the laser ablation plumes in air at atmospheric pressure and at an ambient pressure of ∼10−5 mbar is presented. Electron densities were determined from the Stark broadening of the Si (I) 288.16 nm emission line. Electron densities in the range of 6.91×1017 to 1.29×1019 cm−3 at atmospheric pressure and 1.68×1017 to 3.02×1019 cm−3 under vacuum were observed. Electron excitation temperatures were obtained from the line to continuum ratios and yielded temperatures in the range 7600–18,200 K at atmospheric pressure, and 8020–18,200 K under vacuum. The plasma morphology is also characterized with respect to time in both pressure regimes

Optical Emission and Mass Spectrometric Diagnostics of Laser-Induced Silicon Plasmas

Optical Emission Spectroscopy (OES) and Mass Spectrometry (MS) were employed in tandem for diagnostic studies of Nd:YAG (532 nm) laser induced plasma plumes. OES measurements of laser-induced silicon plasmas were performed through a range of ambient pressure regimes from atmospheric pressure down to ~10-4 mbar. The temporal evolution of the plasmas was characterised in terms of electron excitation temperature Te, ionisation temperature Ti, and electron density Ne. Electron densities were determined in the range 2.86 × 1016 to 5.53 × 1019 cm-3, electron temperatures were calculated in the range 8794 to 21229 K, and ionic species temperatures calculated in the range 13658 to 22551K. The requirements for OES analysis based on the assumption of Local Thermal Equilibrium (LTE) conditions existing within the plasmas are discussed. The plasma morphology and expansion dynamics with respect to pressure are described. Response Surface Methodology (RSM) was employed to optimise Laser-Induced Breakdown Spectroscopy (LIBS) analyses of silicon at atmospheric pressure and under vacuum conditions. Multivariate analysis software was used to design and analyse several multi-level, full factorial RSM experiments. A Quality Factor (QF) was conceived as the response parameter for the experiments, representing the quality of the LIBS spectrum captured for a given hardware configuration. A full parametric study of the LIBS hardware configuration was performed to determine the true response of the system; the outcome of which compares favourably with the results yielded from the RSM investigation.MS analyses of silicon and copper laser-induced plasma plumes were performed using a commercially available Residual Gas Analyser (RGA). The RGA sampling configuration was investigated in order to maximise neutral and ionic species detection from the laser-induced plasmas

Swagelok Ultra-Torr based feed-through design for coupling optical fibre bundles into vacuum systems

We report the design of an inexpensive and flexible fibre-optic bundle high vacuum feed-through that can be constructed from easily available Swagelok Ultra-TorrTM stock parts. The fibre bundle extends through the vacuum envelope and thus does not suffer the transmission losses encountered when using face-to-face couplings. The flexibility of construction allows the fitting to be customised to suit all flange designs such as CF, KF or custom mountings. The use of VitonTM o-rings allows modest baking (max 200 C) for high vacuum applications and fibre bundles can be easily repositioned, removed or replaced

The influence of operating parameters on pulsed D.C. magnetron sputtering plasma

This paper describes the breakdown voltage characteristics in a pulsed D.C. magnetron sputtering system under varying conditions of frequency, current and pulse-off time. The behaviour of the breakdown voltage with pulsing frequency at different pressures and constant pulse-off time was recorded and revealed that the breakdown voltage decreased consistently as the frequency increased up to 70 kHz. Above this frequency, perturbation in the breakdown voltage was noted, possibly due to the rise in pre-breakdown current during the few microseconds of pulse-on time. This perturbation effect was no longer observed when the operating current was increased. The breakdown voltage was seen to decrease when the pulse-off time was increased while keeping the total period of the pulse constant