The potential of quantum wires in optoelectronics, non-linear optics, chemical sensors, and photocatalysis has motivated research on growing ETS-10 crystals with controlled morphology, size and defect concentration. Titanosilicate ETS-10, a microporous zeotype material built of corner-sharing TiO₆ octahedra and SiO₄ tetrahedra [1], shows potential as a natural occurring alignment of monatomic ...Ti-O-Ti-O-Ti... chains or wires. These titania chains are separated from one another by an insulating silicate matrix [2], and show unique quantum confinement effects and make ETS-10 a promising candidate for quantum wire applications [3].

Hydrothermal synthesis of ETS-10 was conducted at 473 K by adjusting the Na₂O/K₂O ratio and water content in synthesis mixtures. Square truncated bipyramidal ETS-10 crystals with increasing basal width and decreasing aspect ratio were grown upon decreasing Na₂O/K₂O ratio and increasing water content. Plate-like ETS-10 crystals with dimensions up to ~80x80x22 mm were obtained. These are the largest ETS-10 reported to date. Atomic force microscopy and high resolution SEM revealed the presence of stepped island-like structures on the square facets of ETS-10 crystals. Linear dimensions of these island-like structures increased concomitantly with the increasing crystal dimensions. These results suggest that the replacement of Na ions by K ions and increasing water content in synthesis mixtures suppressed both three- and two-dimensional nucleation of ETS-10. Consistent with the microtopographic analysis results, UV-vis diffuse reflectance spectroscopic analysis showed that the band attributed to the delocalized charge transfer transitions along the ...Ti-O-Ti-O-Ti... chains had smaller FWHM for the larger ETS-10 crystals that are expected to have less crystal defects. X-ray photoelectron spectroscopic analysis showed that the area ratio of the Ti 2P_3/2 peak assigned to the five coordinated Ti species to the Ti 2P_3/2 peak assigned to the octahedral Ti species decreased for the larger ETS-10 crystals. Since the five coordinated Ti species were assigned to Ti appearing in the defects of ...Ti-O-Ti-O-Ti... chains or on the external crystal surfaces where these chains end [4], the lower five coordinated Ti to octahedral Ti peak area ratio indicated the lower defect concentration in the larger ETS-10 crystals. Currently, further confocal Raman spectroscopic analysis is being performed on these ETS-10 crystals with various morphologies, sizes, and defect concentrations. The spectroscopic analyses of these crystals will improve understanding of nucleation and crystal growth of ETS-10 and thus help growing ETS-10 crystals with desired properties for potential quantum wire applications.

[1] S.M. Kuznicki, US Patent 4,853,202 1989. [2] M.W Anderson, O. Terasaki, T. Ohsuna, P.J.O. Malley, A. Philippou, S.P. MacKay, A. Ferreira, J. Rocha, S. Lidin, Philosophical Magazine B 71 (1995) 813. [3] C. Lamberti, Micropor. Mesopor. Mater. 30 (1999) 155. [4] L. Lv, F.Y. Lee, J. Zhou, F. Su, X.S. Zhao, Micropor. Mesopor. Mater. 96 (2006) 270.