The thermal and plasma-enhanced atomic layer deposition (ALD) growth of titanium oxide using an alkylamine precursor - tetrakis(dimethylamino)titanium (TDMAT) - was investigated. The surface species present during both the precursor and co-reactant pulse were studied with in situ reflection mid-IR spectroscopy (FTIR) and in vacuo X-ray photoelectron spectroscopy (XPS). The thermal process using H2O vapor proceeds through a typical ligand exchange reaction mechanism. The plasma-enhanced ALD processes using H2O-plasma or O2-plasma exhibit an additional decomposition and combustion reaction mechanism. After the plasma exposure, imine (N[double bond, length as m-dash]C) and isocyanate (N[double bond, length as m-dash]C[double bond, length as m-dash]O) surface species were observed by in situ FTIR. In addition, nitrites (NOx) were detected using in vacuo XPS during the O2-plasma process. This study presents the importance of the use of in situ FTIR and in vacuo XPS as complementary techniques to learn more about the ALD reaction mechanism. While in situ FTIR is very sensitive to changes of chemical bonds at the surface, exact identification and quantification could only be done with the aid of in vacuo XPS.