Nb- Doped Colloidal TiO 2 Nanocrystals with Tunable Infrared Absorption

Transcription

1 Nb- Doped Colloidal TiO 2 Nanocrystals with Tunable Infrared Absorption Luca De Trizio 1, Raffaella Buonsanti 2, Alina M. Schimpf 3, Anna Llordes 2, Daniel R. Gamelin 3, Roberto Simonutti 1, and Delia J. Milliron 2 * 1 Department of Materials Science, University of Milano Bicocca, Via Cozzi 53, Milano, Italy 2 The Molecular Foundry, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California 94720, USA 3 Department of Chemistry, University of Washington, Seattle, Washington 98195, USA Figure S1. Low (A) and high resolution (B) TEM images of NTO NCs obtained using a relative amount of NbCl 5 precursor of 5%. The scalebar is 20nm in the image A and 5 nm in B. B) HRTEM image of a rounded shaped crystal and its fast Fourier transformation (FFT) exhibiting the (101) and (004) lattice planes of the body- centered tetragonal structure of TiO 2 anatase and showing measured d- spacing of 3.49 Å and 2.35 Å, respectively. Thermal Annealing XRD measurements were performed on a Rigaku SmartLab X- ray diffractometer operating at 40 kv and 150 ma. The diffractometer was equipped with Cu source and a Gobel mirror in order to have a parallel beam and it was used in 2- theta/omega scan geometry for the acquisition of the data. In thermal annealing experiments, the silicon substrate with the NTO NCs obtained using 10% of NbCl 5 deposited on top was annealed from room temperature (RT) to 900 C under vacuum ( 10-8 torr) recording XRD patterns at 450 C and 900 C.

2 Figure S2. XRD patterns collected during the thermal annealing from RT to 900 C of NTO NCs synthesized using 10% of NbCl 5. It is possible to see that the NTO NCs are stable at 450 C and no differences can be noticed in the corresponding XRD reflections. Annealing the sample at 900 C leads to the sintering of TiO2 crystals (sharper anatase XRD peaks) and to the concomitant formation of a TiNb 2 O 7 crystal phase (evidenced by the appearance of very small XRD peaks) that is thermodynamically favorable, as predicted by the Nb 2 O 5 - TiO 2 phase diagram.

3 Figure S3. A) TEM micrograph of TiO 2 NCs obtained without using Oleic Acid and B) the corresponding XRD pattern. The reference bulk reflections of TiO 2 anatase are shown in the bottom (JCPDS card ). C- D) TEM pictures of the TiO 2 anatase NCs obtained using 13mmol of OAc and 1mmol C) or 2mmol D) of ODAL.

4 Figure S4 XPS characterization of Nb- doped TiO2 nanocrystals. A) XPS survey spectra for the NTO NCs synthesized at different NbCl5 loading. Corresponding High- Resolution XPS spectra for B) Nb 3d and (C) Ti 2p in the Nb- doped TiO2 NCs. S4

5 Figure S5. A) UV- VIS- NIR absorption curves of solutions of NTO NCs, equimolar in titanium, dispersed in tetrachloroethylene (TCE). The weak peaks appearing above 1600nm are due to the Oleic Acid necessary to stabilize the colloidal solutions. B) FTIR- ATR spectra of the corresponding dropcasted NTO solutions. It should be noted that the optical properties of the samples obtained using 20% and 30% of NbCl5 are extremely similar. C) XRD patterns of the as- prepared NTO NCs with different Nb precursor loadings: 0%, 20% and 30% NbCl5. % NbCl5 precursor %Nb in NTO NCs (ICP)a %Nb in NTO NCs (XPS)b S5

6 Table S1. The relative amount of precursor used and the composition of the NTO samples are reported. a The amount of Nb in the products was measured by ICP- AES. b The amount of Nb and Ti was calculated from XPS hi- res measurements considering the Ti 2p 3/2 and the Nb 3d 5/2 peaks. Figure S6. (A, B) HAADF- STEM images of NTO NCs synthesized using 10% and 20% of NbCl 5, respectively. In (A) no presence of external NbO x inorganic network was detected around the NCs. (C, D) Statistical analysis of the concentration of niobium inside the NTO nanocrystals as derived by EDS mapping on 50 single NCs. An extremely large variation in the doping level of individual NCs is clearly shown. However, a bigger population should be considered for extracting more reliable statistical data.

7 Figure S7. A) UV- Vis- NIR absorption curves of NTO samples obtained varying the reaction temperature from 290 C to 260 C and using TIP instead of TEO. B) Picture of the vials containing the corresponding NTO colloidal solutions. The coloration of the colloidal dispersions is indicative of the effective TiO 2 doping with Nb n k 1.4 n or k Wavelength (nm) Figure S8. Complex refractive index extracted from the ellipsometry measuraments for a 10% doped NTO NC film.