Depth profile analysis nanometric layers by Laser Induced Breakdown Spectroscopy

Depth profile analysis and coating thickness measurement of nanometric layers of copper sample coated on steel substrates by Laser Induced Breakdown Spectroscopy (LIBS) are carried out. In this technique several laser pulses are fired successively at the same position of the layer surface. The laser pulses ablate the layer and penetrate gradually inside the sample to reach to the substrate. Accompanied with ablation, a hot plasma is created in the front of sample which its emission contains information about the ablated material. By spectroscopy of plasma emission, it is determined that laser is fired on the layer or substrate. Average ablation rate (AAR) are determined by dividing a known layer thickness to the number of laser pulses needed for removing the layer (NL). After determination AAR, an unknown thickness is determined by NL times AAR. The less ablation rate means the better resolution for depth profiling. AAR depends on different experimental parameters. To determine the minimum ablation rate, different laser pulse energy and focusing distances are examined. Results show that a minimum ablation rate is achieved at laser pulse energy 7 mJ and focusing distance 33 mm.

Keywords:

Nanometric Layers , Depth profiling , Thickness Measurement , Laser Induced Breakdown Spectroscopy