Fundamental Strategy for Creating VLS Grown TiO2 Single Crystalline Nanowires

A single crystalline TiO 2 nanowire grown by a size and position controllable vapor–liquid–solid (VLS) method is a promising candidate to control and design the physical and chemical properties for various TiO 2 -based applications. However, creating TiO 2 nanowires by VLS has been a challenging issue due to a difficulty on controlling and understanding the complex material transport events across three phases. Here we propose a fundamental strategy to create a TiO 2 single crystalline nanowire by the VLS mechanism. We show that a VLS growth of TiO 2 nanowires can emerge intrinsically only within a quite narrow range of material flux, which is a sharp contrast to typical VLS oxides including MgO, SnO 2, In 2 O 3, and ZnO, whose nanowires are easily grown by VLS with much wider ranges of material flux. We reveal that a condensation of Ti atoms at a vapor–solid interface, which is detrimental for VLS, is responsible to limit a window of material flux for TiO 2 nanowires. In addition, we found that our rutile-TiO 2 nanowires preferentially grow along ⟨001⟩ direction, which interestingly differs from a typical ⟨110⟩ oriented growth of TiO 2 nanowires formed by the vapor-phase method. The present approach based on a control of material flux provides a foundation to tailor VLS grown TiO 2 nanowires based on a scientific strategy rather than a rule of thumb.