Growth Mechanism of Highly Branched Titanium Dioxide Nanowires via Oriented Attachment (original) (raw)
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Journal of Materials Science & Technology, 2015
TiO 2 nanowire arrays were successfully fabricated by liquid-phase deposition method using porous alumina templates. The obtained TiO 2 nanowires were characterized using Raman spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and selected area electron diffraction (SAED) analysis. Results of electron microscopic observations indicated that the nanowires were smooth and uniform with a diameter of about 50-80 nm and several micrometers in length. SAED, Raman, and XRD measurements showed that TiO 2 nanowires were single-crystalline with a pure rutile structure after heating at 800 °C for 10 h. In this situation, the nanowire constituents grew preferentially along the <001> direction. Furthermore, the formation process and mechanistic study of the TiO 2 nanowire arrays were proposed and discussed in detail. The nanowires are clearly produced by the deposition of TiO 2 particles on the inner wall of the template nanochannels.
CrystEngComm, 2014
A new approach has been employed to grow large size and high number density rutile TiO 2 nanorods (NRs) by low cost chemical methods. Nuclei layers of low (~30 nm) and high (~150 nm) thickness have been optimized on glass substrates for growing NRs using spin coating and chemical spray pyrolysis methods respectively. The scanning electron and atomic force microscopic images clearly show that randomly aligned, large size, exotic NRs have grown on low thickness seed layers at a high temperature (180°C), and that interconnected, NRs with good number density have grown on high thickness seed layers at a low temperature (120°C) via hydrothermal synthesis. The structural studies clearly reveal that the as-grown
Patterned Growth of TiO 2 Nanowires on Titanium Substrates
Applied Physics Express, 2011
Single-crystalline rutile TiO 2 nanowires (NWs) were synthesized by the vapor-liquid-solid (VLS) method on Ti foil substrates patterned with catalytic Sn nano-islands. NWs of 3 to 8 m in length and 50 to 500 nm in diameter were grown along the [1 10] axis exhibiting a rectangular cross section with the and side facets. This facile approach to TiO 2 NW fabrication with fast induction heating and short processing time utilizes the Ti foil both as a substrate and as a metal supply, thus eliminating the need for a separate titanium source.
Anisotropic growth of oxide nanocrystals: insights into the rutile TiO2 phase
The Journal of …, 2007
In this work, we report the synthesis of titanium oxide nanocrystals, especially the rutile TiO 2 phase with nanorod morphology, by a method based on peroxotitanium complex decomposition. The results indicate that the anisotropic morphology reported for rutile TiO 2 nanocrystals is related to the oriented attachment process. Despite the predominance of rutile nanocrystals at longer treatment times, the nanocrystals were obtained also in the anatase type, according to the degradation time adopted. XANES results evidenced the absence of structural correlation between the peroxytitanium complex and phase evolution, and the coexistence of the two phases strongly suggests a correlation of the oriented attachment mechanism and the rutile phase stabilization.
Microscopic origin of lattice contraction and expansion in undoped rutile TiO 2 nanostructures
Journal of Physics D: Applied Physics, 2014
We have investigated the microscopic origin of lattice expansion and contraction in undoped rutile TiO 2 nanostructures by employing several structural and optical spectroscopic tools. Rutile TiO 2 nanostructures with morphologies such as nanorods, nanopillars and nanoflowers, depending upon the growth conditions, are synthesized by an acid-hydrothermal process. Depending on the growth conditions and post-growth annealing, lattice contraction and expansion are observed in the nanostructures and it is found to correlate with the nature and density of intrinsic defects in rutile TiO 2 . The change in lattice volume correlates well with the optical bandgap energy. Irrespective of growth conditions, theTiO 2 nanostructures exhibit strong near infrared (NIR) photoluminescence (PL) at 1.43 eV and a weak visible PL, which are attributed to the Ti interstitials and O vacancies, respectively, in rutile TiO 2 nanostructures. Further, ESR study reveals the presence of singly ionized oxygen vacancy defects. It is observed that lattice distortion depends systematically on the relative concentration and type of defects such as oxygen vacancies and Ti interstitials. XPS analyses revealed a downshift in energy for both Ti 2p and O 1s core level spectra for various growth conditions, which is believed to arise from the lattice distortions. It is proposed that the Ti 4+ interstitial and F + oxygen vacancy defects are primarily responsible for lattice expansion, whereas the electrostatic attraction between Ti 4+ interstitial and O 2− interstitial defects causes the lattice contraction in the undoped TiO 2 nanostructures. The control of lattice parameters through the intrinsic defects may provide new routes to achieving novel functionalities in advanced materials that can be tailored for future technological applications.
Synthetic precursor to vertical TiO 2 nanowires
Materials Research Express, 2014
An easy protocol for improvement in formation of the photoanode in a dye sensitized solar cell is addressed. Specifically, a novel synthesis for the formation of a TiO 2 precursor: titanium butanediolate, is detailed. This precursor is found to have higher thermal and temporal stability than commercially available TiO 2 precursors and it has successfully been employed in the one-pot synthesis of rutile nanowires grown directly on a conducting substrate: fluorine doped tin oxide (FTO). This synthesis has been further extended to directly form a mixed phase TiO 2 film consisting of rutile nanowires along with anatase spherical particles on FTO and this assembly has been used as the photoanode in a dye-sensitized solar cell. The synergistic effect of the two phases has provided a net DSSC efficiency of 4.61% with FF = 61%.
Fundamental Strategy for Creating VLS Grown TiO 2 Single Crystalline Nanowires
The Journal of Physical Chemistry C, 2012
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.