Abstract
Laser ablation - spark discharge - optical emission spectroscopy (LA-SD-OES) and Laser-induced breakdown spectroscopy (LIBS) are applied for the analysis of minor elements Manganese (Mn) and Chromium (Cr) in steel and for the chemical imaging of micro-patterned photoresist layers. In LA-SD-OES a weak laser pulse (typical energy 50 μJ to 5 mJ) triggers an electric discharge between a high voltage electrode and the laser ablated spot on the sample surface. Intense emission lines of neutral and singly-ionized atoms are observed with both spectroscopic techniques. However, lines of doubly-ionized atoms are detected with LA-SD-OES only. The line intensities of C III and Al III increase with decreasing laser pulse energy, surprisingly. The appearance of intense doubly-ionized lines indicates that the mechanisms of plasma excitation are different in LA-SD-OES compared to LIBS and that the combined plasma is not in local thermodynamic equilibrium at low laser energy. The calibration curves of Mn and Cr in industrial steel reveal steeper slope (higher sensitivity) for the Mn II and Cr II lines measured with LA-SD-OES and for the Mn I and Cr I lines measured with LIBS. Chemical imaging of the photoresist layer with LA-SD-OES at the atomic lines of C I and C III and the molecular band of CN reveals all details of the sample. Similar images are obtained for C I and CN using LIBS, however, no image contrast is obtained at the C III line. The very low pulse energy in LA-SD-OES enables soft sampling and may be beneficial also for the analysis and imaging of sensitive material.
Highlights
The detection of chemical elements and the quantification of material compositions are important in many areas of materials research, chemistry, and physics and for many different applications, for example, in industrial production and for materials inspection and sorting
In laserinduced breakdown spectroscopy (LIBS) the analytical plasma is excited by pulsed-laser ablation of sample material and the optical emission of the laser-induced plasma (LIP) is measured [6,7,8]
We report on LA-SD-Optical emission spectroscopy (OES) and LIBS measurements of steel and aluminum bulk samples
Summary
The detection of chemical elements and the quantification of material compositions are important in many areas of materials research, chemistry, and physics and for many different applications, for example, in industrial production and for materials inspection and sorting. In spark-OES, a plasma is induced by an electric spark discharge to the surface of the sample material and the optical plasma emission is measured [1]. This technique has become one of the standard methods, especially for element analysis of metallurgical materials [2,3]. In laserinduced breakdown spectroscopy (LIBS) the analytical plasma is excited by pulsed-laser ablation of sample material and the optical emission of the laser-induced plasma (LIP) is measured [6,7,8]. Comparative studies on LIBS and spark-OES showed comparable analytical
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