Direct chemical in-depth profile analysis and thickness quantification of nanometer multilayers using pulsed-rf-GD-TOFMS
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- Valledor, R., Pisonero, J., Bordel, N. et al. Anal Bioanal Chem (2010) 396: 2881. doi:10.1007/s00216-009-3382-8
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Nanometer depth resolution is investigated using an innovative pulsed-radiofrequency glow discharge time-of-flight mass spectrometer (pulsed-rf-GD-TOFMS). A series of ultra-thin (in nanometers approximately) Al/Nb bilayers, deposited on Si wafers by dc-magnetron sputtering, is analyzed. An Al layer is first deposited on the Si substrate with controlled and different values of the layer thickness, tAl. Samples with tAl = 50, 20, 5, 2, and 1 nm have been prepared. Then, a Nb layer is deposited on top of the Al one, with a thickness tNb = 50 nm that is kept constant along the whole series. Qualitative depth profiles of those layered sandwich-type samples are determined using our pulsed-rf-GD-TOFMS set-up, which demonstrated to be able to detect and measure ultra-thin layers (even of 1 nm). Moreover, Gaussian fitting of the internal Al layer depth profile is used here to obtain a calibration curve, allowing thickness estimation of such nanometer layers. In addition, the useful yield (estimation of the number of detected ions per sputtered atom) of the employed pulsed-rf-GD-TOFMS system is evaluated for Al at the selected operating conditions, which are optimized for the in-depth profile analysis with high depth resolution.