Development of a Custom-Built Atomic Layer Deposition Reactor for In Situ Synchrotron GISAXS and XAS Characterization

Abstract This work presents the design, implementation, and validation of a custom-built in situ atomic layer deposition (ALD) reactor developed at the ALBA Synchrotron Light Source (Cerdanyola del Vallès, Spain), enabling direct integration with synchrotron X-ray beamlines. A modular configuration allows the ALD reactor to be deployed at two ALBA Synchrotron beamlines: NCD-SWEET beamline (BL11) for Grazing Incidence Small Angle X-ray Scattering (GISAXS) and NOTOS beamline (BL16) for X-ray Absorption Spectroscopy (XAS), requiring only minimal reconfiguration. The reactor performance was validated by in situ deposition of TiO2 thin films using titanium tetraisopropoxide (TTIP) and H2O as the precursor and co-reactant, respectively, with a growth per cycle (GPC) of 0.17 Å·cycle–1 at 150 °C. This system was chosen for its low growth rate, as a demanding test of detection sensitivity. In situ GISAXS revealed the continuous evolution of film morphology and near-surface electron density over 1000 ALD cycles, while in situ X-ray absorption near-edge structure (XANES) quantitatively resolved three kinetically distinct growth regimes: prenucleation, nucleation development, and steady-state growth. The complementarity of the two techniques provides a comprehensive picture of ALD growth dynamics that neither technique could deliver independently, demonstrating the potential of the ALD system presented here for in situ multi-technique characterization of a broad range of ALD processes.