Quantitative imaging of structured complex metal oxide thin films using online-LASIL-ICP-MS

Abstract

Complex metal oxide (CMO) thin films are used as coatings for tools (enhance abrasive resistance), for optical elements (antireflection) or as novel materials for renewable energy resources (e.g. solid oxide fuel cells, solid-state Li ion batteries). The exceptional characteristics of these thin films can be carefully tailored by adjusting the stoichiometry of the material or the use of dopants. Usually rather small amounts of dopants (in the low at% range) were used. Since most of these CMOs were applied as thin films (nm range), an analytical technique for a precise and accurate element determination of this kind of samples is required. For the analysis of solid materials, laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) is an established method, especially if laterally resolved data and depth profiles are of interest. Due to matrix effects in the ablation, transportation and ionization steps matrix matched standards are obligatory for signal quantification. Unfortunately, matrix matched standards for such novel materials are not commercially available. To overcome this drawback of classical LA-ICP-MS technique, we recently presented a new method called online laser ablation of solids in liquid (online-LASIL). In this approach, the solid sample is submerged into a liquid (e.g. H2O or diluted acid) and a laser beam is focused onto the sample surface. In the ablation process, nanoparticles are formed. These particles are immediately suspended in the liquid carrier stream and directly transported to the introduction system of the ICP-MS detection system without any manual handling step. For signal quantification, aqueous standard solutions can be used, because the yielded nanoparticle suspensions can practically be treated like liquid solutions. With this procedure the benefits of the conventional liquid measurement (use of liquid certified reference materials, high flexibility to fit sample composition and concentration) and solid sampling approaches (imaging and depth profiles) can be combined. In this contribution, we present our continuous improvements of the online-LASIL setup, such as cell design and flow injection components, data treatment and online-quantification strategies. Reduction of washout time and flow rate of carrier solution are important to obtain laterally resolved data with sufficient resolution in a reasonable time. To demonstrate the imaging capability of the current online-LASIL-ICP-MS system, geometrically structured CMO thin films prepared by pulsed laser deposition (PLD) are analysed. With this set-up areas up to some square millimetres can be analysed and accurately quantified by the use of liquid standard solutions.