In Situ X-ray Fluorescence Measurements During Atomic Layer Deposition: Nucleation and Growth of TiO2 on Planar Substrates and in Nanoporous Films

Synchrotron-based X-ray fluorescence (XRF) is introduced as a promising in situ technique to monitor atomic layer deposition cycle-per-cycle. It is shown that the technique is greatly suitable to study initial nucleation on planar substrates. The initial growth of TiO 2 from tetrakis(dimethylamino)titanium (TDMAT) and H 2 O is found to be linear on thermally grown SiO 2, substrate-inhibited on H-terminated Si and substrateenhanced on atomic layer deposited Al 2 O 3 . Furthermore, in situ XRF is employed to monitor the Ti uptake during deposition of TiO 2 in nanoporous silica films. In mesoporous films, the Ti content varied quadratically with the number of cycles, a behavior that is attributed to a decreasing surface area with progressing deposition. In microporous films, the XRF data suggest that 1−3 ALD cycles shrunk the pore diameters below the kinetic diameter of the TDMAT molecule.