We used XPS to compare the composition of the films grown at 85 ºC and 150 ºC (Figure ). Spectra were measured on each film both as prepared and after a 30 s exposure to an in situ Ar plasma. The sputtering step was used to differentiate the air- exposed surface from the internal composition of the film. The Ti 2p (Figure ) and O 1s (Figure ) features for the as prepared films were indistinguishable from one another. The positions of these peaks (459.0 eV in the Ti 2p, 530.4 eV for O 1s) are consistent with the expected binding energies for rutile TiO2. Both samples showed an increase in the intensity for each peak after Ar sputtering, likely corresponding to the removal of adventitious carbon and other adsorbates, such as atmospheric oxygenates (E = 532.6 eV in the O 1s spectra). Additionally, the plasma induced a slight reduction of Ti to Ti 3+ in both films as indicated by the appearance of a slight peak at E = 457.3 eV in both TiO2 samples. The Ar + -induced reduction of metal oxide surfaces in XPS depth profiling has been observed in previous work. The main difference in composition of films grown at 85 ºC is the presence of a slight amount of N (Figure ), which is likely due to the incomplete decomposition of the ligand at the lower temperature. N was observed in the film grown at 85 ºC after sputtering, which indicates that it is part of the bulk composition rather than just remaining on the surface after deposition. Nitrogen doping in TiO2 can potentially cause light absorption in the visible spectrum which can have a negative impact on the concentrating effects targeted here. Confirming the ALD of TiO2 at 85 ºC enables the use of a PS template for the fabrication of a light trapping surface texture with high refractive index contrast. The general structure we studied is comprised of a PS core (self-assembled, close-packed monolayer of PS nanospheres) and a TiO2 shell deposited by ALD. We studied this growth on ALD TiO2-coated Si wafers. Figure shows the core-shell surface structure of 500 cycles of TiO2 grown at 85 ºC on a templating monolayer of 350 nm PS nanospheres. The monolayer of nanospheres was deposited by evaporative selfassembly at 50 ºC from a 0.0025% (w/w) solution on a TiO2-coated Si wafer. Large areas of the close-packed monolayer (Figure ) were observed near the middle of the 1 cm x 1 cm wafer. The substrate also had large areas of disordered multilayers and sparser single-layer deposition. The same core-shell structure and large-area deposition was observed for a similar 500 cycle deposition of TiO2 grown on a close-packed monolayer of 500 nm PS nanospheres self-assembled from a 0.003% (w/w) solution at The significant deposition of TiO2 on PS nanospheres is somewhat unexpected due to the hydrophobic organic surface of the nanospheres and the lack of surface hydroxyls for seeding the reactions with TDMAT. The thickness of the coatings observed on PS nanospheres was much thicker than expected from the planar deposition on Si. A potential explanation may be that the TDMAT precursor has a favorable non-covalent interaction with the polymer itself that retains the molecule through the purge cycle of the deposition sequence. When exposed to water, small TiO2 particles seed the PS surface to facilitate true ALD on the surface. This is not observed for ALD precursors in general, as PS surfaces have been used to prevent ALD of ZnO from diethylzinc or Al2O3 from trimethylaluminum, for example. Further studies are needed to improve the understanding of the relevant TDMAT-PS molecular interactions.