Femtosecond laser-induced breakdown spectroscopy: Elemental imaging of thin films with high spatial resolution

• Published in: Spectrochimica acta. Part B: Atomic spectroscopy 2017-10, Vol.136, p.56-65
• Main Authors: Ahamer, Christoph M., Riepl, Kevin M., Huber, Norbert, Pedarnig, Johannes D.
• Format: Article
• Language: English
• Subjects: Ablation; Analytical methods; Atomic structure; Barium; Chemical compounds; Copper; Copper oxides; Diffraction; Emission measurements; Emissions; Femtosecond laser ablation; Femtosecond pulsed lasers; Film thickness; Glass; Imaging; Imaging techniques; Laser induced breakdown spectroscopy; Laser induced breakdown spectroscopy (LIBS); Lasers; Lines; Molecular structure; Penetration depth; Raster scanning; Resolution; Spatial discrimination; Spatial resolution; Spectrochemical imaging; Spectroscopy; Spectrum analysis; Stability; Thin film; Thin films; YBa2Cu3O7 (YBCO); Yttrium; Yttrium barium copper oxide; Yttrium oxide
• ISSN: 0584-8547; 1873-3565
• DOI: 10.1016/j.sab.2017.08.005

We investigate femtosecond laser-induced breakdown spectroscopy (fs-LIBS) for the spectrochemical imaging of thin films with high spatial resolution. Chemical images are obtained by recording LIBS spectra at each site of 2D raster-scans across the samples employing one fs-laser pulse per site. The diffraction images of the Echelle spectrometer are binned to reduce the read-out time of the intensified CCD detector and to increase the stability of the emission signals against peak drifts in the echellograms. For copper thin films on glass the intensities of Cu I emission lines and the size of ablation craters vary non-monotonously with the film thickness hCu=5–500nm. The emission efficiency, defined as the Cu I line intensity per ablated volume, strongly decreases for films thicker than the optical penetration depth. The Na I line intensity from glass increases exponentially with decreasing Cu film thickness. For yttrium barium copper oxide (YBCO) thin films on MgO various atomic and molecular emission lines of the laser-induced plasma are measured (film thickness hYBCO=200–1000nm). The obtained element (Y, Ba, Cu, Mg) and molecular (Y-O) fs-LIBS images match the structure of the micro-patterned YBCO films very well. The achieved lateral resolution δr=6μm is among the best values reported for spectrochemical LIBS imaging. [Display omitted] •Chemical imaging by femtosecond laser-induced breakdown spectroscopy (fs-LIBS)•High lateral resolution in atomic and molecular fs-LIBS images of oxide thin films•On metal thin films large ablation craters impede high resolution LIBS imaging.•Ablation threshold fluence of metal films depends non-monotonously on film thickness.