Determination of the stoichiometry and trace impurities in thin barium strontium titanate perovskite layers by inductively coupled plasma-mass spectrometry

The determination of the stoichiometry in semiconducting and non-conducting thin layers is of importance for the study of growth mechanisms and for th e control of defects during development and production. An analytical proce dure using inductively coupled plasma-mass spectrometry (ICP-MS) was develo ped, employing different ICP-MS instruments [one double-focusing sector fie ld ICP-MS (DF-ICP-MS) and two quadrupole ICP-MS without and with a hexapole collision cell (ICP-QMS and HEX-ICP-QMS, respectively)] for the determinat ion of the stoichiometry and trace impurities in thin BaxSrxTiO3 perovskite films (BST) on silicon substrates after the dissolution of layers. The max imum sensitivity (Ba-138(+), 1720 MHz ppm(-1): Sr-88(+) 1330 MHz ppm(-1): T i-48(+), 560 MHz ppm(-1)) lowest detection limit (Ba, 0.004 ng l(-1): Sr, 0 .007 ng l(-1): Ti, 0.08 ng l(-1)) and best precision down to 0.11% relative standard deviation (RSD, at an analyte concentration of 1 mug l(-1)) were achieved in DF-ICP-MS, HEX-ICP-QMS yielded a better sensitivity (HEX-ICP-QM S. 100-240 MHz ppm(-1); ICP-QMS, 23-50 MHz ppm(-1)) and lower detection lim it (HEX-ICP-QMS, 0.09-3.4 ng l(-1) ICP-QMS_ 0.8-19 ng l(-1)) in comparison with conventional ICP-QMS. Precision values of 0.3 and 0.2% RSD were observ ed For Ba/Sr and (Ba+Sr)/Ti ratios, respectively, by ICP-QMS and HEX-ICP-QM S at an analyte concentration of 10 mug l(1). Besides ICP-MS, inductively c oupled plasma-optical emission spectroscopy (ICP-OES) and X-ray fluorescenc e (XRF) analysis were used for the validation of the experimental results. The stoichiometric compositions measured by different methods are in good a greement taking into account the local inhomogeneity of element distributio n in thin layers and the diffusion of elements in the substrate. Due to the high sensitivity of ICP-MS, the determination of 38 trace elements was per formed in thin BaxSryTiO3 films (with a thickness less than 60 nm) with det ection limits in the low ng g(-1) range.