Abstract
Titanium oxide compounds TiO,Ti2O3, and TiO2 with a considerable extent of nonstoichiometry were fabricated by pulsed laser ablation in water and characterized by X-ray/electron diffraction, X-ray photoelectron spectroscopy and electron energy loss spectroscopy. The titanium oxides were found to occur as nanoparticle aggregates with a predominant 3+ charge and amorphous microtubes when fabricated under an average power density of ca. 1 × 108W/cm2 and 1011W/cm2, respectively followed by dwelling in water. The crystalline colloidal particles have a relatively high content of Ti2+ and hence a lower minimum band gap of 3.4 eV in comparison with 5.2 eV for the amorphous state. The protonation on both crystalline and amorphous phase caused defects, mainly titanium rather than oxygen vacancies and charge and/or volume-compensating defects. The hydrophilic nature and presumably varied extent of undercoordination at the free surface of the amorphous lamellae accounts for their rolling as tubes at water/air and water/glass interfaces. The nonstoichiometric titania thus fabricated have potential optoelectronic and catalytic applications in UV–visible range and shed light on the Ti charge and phase behavior of titania-water binary in natural shock occurrence.
Highlights
Nanobelts of semiconducting oxides of zinc, tin, indium, cadmium, and gallium were discovered by evaporating the desired commercial metal oxide powders at high temperatures [1]
The titanium oxides were found to occur as nanoparticle aggregates with a predominant 3? charge and amorphous microtubes when fabricated under an average power density of ca. 1 9 108 W/cm2 and 1011 W/cm2, respectively followed by dwelling in water
We focused on the nonstoichiometry, shape, coalescence, and dense structure, if any, of the TiOx nanocondensates and the phase behavior upon electron irradiation as of concern to the space charge, the surface/interface energetics in terms of unrelaxed or relaxed state and theoretical band gap of such metastable phases [13, 14] for potential optoelectronic applications
Summary
Nanobelts of semiconducting oxides of zinc, tin, indium, cadmium, and gallium were discovered by evaporating the desired commercial metal oxide powders at high temperatures [1]. We used an alternative route of pulsed laser ablation in liquid (PLAL) to synthesize nonstoichiometric TiOx nanoparticles and nanotubes in a subsequent waterdriven assembly process. This stabilizer-free approach is quite different from surfactant/copolymers or other template-assisted assembly of TiOx nanoparticles in a desired manner. The synthesis of such a tubular material from atom clusters and their lamellar derivative is analogous to the fabrication of carbon onions via arc discharge in water [11] and Au tubes via PLAL and subsequent dwelling in water [12]. We focused on the nonstoichiometry, shape, coalescence, and dense structure, if any, of the TiOx nanocondensates and the phase behavior upon electron irradiation as of concern to the space charge, the surface/interface energetics in terms of unrelaxed or relaxed state and theoretical band gap of such metastable phases [13, 14] for potential optoelectronic applications
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