Speaker
Description
The high photon flux and energy tunability of synchrotron facilities provide a clear advantage for the characterization of Atomic Layer Deposition (ALD) processes. A mobile custom-built ALD reactor (ALD2) has been developed at the ALBA Synchrotron to enable in situ monitoring of film growth using, up to now, two X-ray-based techniques: Grazing Incidence Small Angle X-ray Scattering (GISAXS) at NCD-SWEET (BL11) and X-ray Absorption Spectroscopy (XAS) at NOTOS (BL16).
The setup consists of a high-vacuum, pump-type reactor compatible with multiple precursors and oxidants, therefore enabling the combination of different ALD coatings during the same experiment. It achieves a base pressure of 10–6 mbar (limited by the semi-transparent windows used for the X-ray measurements, i.e. Kapton and mica) and can also operate under rough vacuum (10–3-10–2 mbar). The mobile reactor is a modular system that can be accommodated for different specific geometries: for GISAXS, two CF40 flanges with 50 µm-thick mica windows allow the passage of incident, reflected and scattered X-rays along the beam direction, being recorded with the SAXS detector (Pilatus3 S 1M) placed at 6.5 m; while for XAS, the two CF40 are rearranged in a perpendicular orientation in the horizontal plane and changed by 25 µm-thick Kapton windows, enabling measurements covering all the beamline energy range (4.7 - 30 keV), with the fluorescence detector used (Silicon Drift Detector with 13 channels from Canberra Olen) which is located at 90° with respect to the X-ray beam (and the sample at around 30° with respect to the incident beam).
The reactor was validated with in situ deposition of TiO2 thin films using the TTIP/H2O at 100, 150 and 200 °C as a deliberately demanding test case given its low growth per cycle (0.17 Å·cycle⁻¹). At NCD-SWEET, real-time GISAXS monitoring over 1000 ALD cycles resolved the progressive evolution of film morphology through model-independent analysis of the diffuse scattering signal, capturing the full sequence from the first cycles to steady-state growth. At NOTOS, in situ Ti K-edge XANES analysis of the edge jump evolution quantitatively identified three kinetically distinct growth regimes, with linearity in the steady-state regime confirming the self-limiting character of the process. The combination of both techniques provides a detailed picture of TiO2 ALD growth dynamics: with XAS capturing early chemical nucleation and GISAXS tracking morphological evolution, demonstrating the potential of the ALD2 reactor for multi-technique in situ characterisation of ALD processes at ALBA Synchrotron.