Synthesis of large monodisperse ETS-10 crystals and observation of quantum confinement effects from very long titanate quantum wires

摘要

Synthetic conditions to produce highly crystalline monodisperse ETS-10 crystals with the length along the [11 0] direction (L_([110])) between 17 and 55 μm and the length along the [001] direction between 15 and 80 μm were developed. This was achieved by varying the amounts of KF in the gel consisting of Na2SiO3, titanium isopropoxide, HC1, NaCI, KF, and H2O. The UV-vis spectra of the ETS-10 crystals revealed that the absorption band red-shifts with increasing L_([110]. The plot of band gap energies (E_g values) with respect to L_([110] values revealed a progressively decaying relationship. The mixing of the newly observed data set with that reported previously from the ETS-10 crystals with L_([110] between 0.3 and 20 μm gave a smooth exponential decay relationship, E_g=0.2578 exp)(-L_([110]/13.751)+3.7667, as if they came from a single data set Analysis shows that the quantum confinement effect still operates in TiO3~(2-) quantum wires with the estimated length of 368 nm. The μ_(xy) and μ_z values are 15.2 and 0.0006 m_e, respectively. A monotonous quadratic relationship exists between L_([110] and /. Thus the length of the titanate quantum wire increases more than the degree the crystal size increases, indicating that the degree of defect per unit volume decreases as the crystal size increases.