Effect of Geometric Nanostructures on the Absorption Edges of 1-D and 2-D TiO<sub>2</sub> Fabricated by Atomic Layer Deposition

Chang, Yung; Liu, Chien Min; Cheng, Hsin‐Ming; Chen, Chih

doi:10.1021/am302219n

Cited by 17 publications

(17 citation statements)

References 43 publications

(85 reference statements)

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“…Therefore, it is expected that the TiO 2 nanotubes grown for 3 h had the minimum band gap energy, but the tubes grown for 1 h have the minimum band gap energy (about 2.9 eV). The redshift in the peak of TiO 2 nanotubes grown for 1 h as compared with the 3 h may be due to the tube wall thickness decrease of the nanotubes grown for 3 h compare to the 1 h, which is in good agreement with the previous work [41].…”

Section: Resultssupporting

confidence: 92%

Enhanced physical properties of the anodic TiO2 nanotubes via proper anodization time

2018

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Vertically aligned titanium dioxide (TiO 2 ) nanotubes were synthesized by electrochemical anodic oxidation in an electrolyte solution containing 0.45 wt% ammonium fluoride (NH 4 F) and 2 vol% deionized water at constant potential (70 V) for various anodization time at the room temperature. The influence of the anodization time on the morphology and optical properties of the anodic TiO 2 nanotubes have been studied. Field emission scanning electron microscopy results revealed that the anodic TiO 2 nanotube morphology extremely depends on the anodization time. It was observed that by increasing anodization time, length of the anodic TiO 2 nanotubes increased and nanotubes destroyed at the top of the tubes. After a long time of anodization process (9 h), nanotubes completely destroyed. Photoluminescence measurements showed that the anodic TiO 2 nanotube band gap energy depends on the anodic TiO 2 nanotube morphology. The anodic TiO 2 nanotubes without any damage had a minimum band gap energy (2.9 eV).

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Section: Resultssupporting

confidence: 92%

Enhanced physical properties of the anodic TiO2 nanotubes via proper anodization time

2018

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“…Such weakened coupling could be responsible for the corresponding band gap shift of TiO 2 nanotube arrays. The Journal of Physical Chemistry C Article As to the band gap shift of TiO 2 nanotube arrays, Chang et al 2 claim that such band gap shift could be realized by adjusting the wall thicknesses of TiO 2 nanotubes in the range of 2.7−37.8 nm, which is based on the conventional quantum confinement effect. However, our results indicate that the band gap shift can also be acquired only by adjusting the diameters and the distances between nanotubes; even these parameters are larger than the Bohr radius of TiO 2 , and quantum effects are not responsible for this observation, since the thicknesses of these nanotubes are in the same value.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Dimensional Dependence of the Optical Absorption Band Edge of TiO₂ Nanotube Arrays beyond the Quantum Effect

Al‐Haddad

Wang

et al. 2015

J. Phys. Chem. C

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Instead of investigating the quantum effect that influences the absorption band edge of TiO 2 nanostructures, herein we report that geometrical parameters can also be utilized to manipulate the optical band gap of the TiO 2 nanotube arrays. Hexagonal arrays of TiO 2 nanotubes with an excellent crystalline quality were fabricated by techniques combining anodic aluminum oxide templates and atomic layer deposition. Through absorption spectroscopic analysis we observed that the optical absorption band edge of the TiO 2 nanotube arrays exhibited a red shift as the diameter of the nanotube was tuned to be larger and the distance between two nanotubes became smaller accordingly, while the wall thickness of the nanotube was kept constant. Subsequent finite-difference time-domain simulations supported the observation from theoretical aspect and revealed a large near-field enhancement around the outer space of the nanotubes for the arrays with densely distributed nanotubes when the corresponding arrays were exposed to the illuminations. Thus, this paper provides a new perspective for the shift of the optical band gap, which is of great significance to the research in photoelectronics. ■ INTRODUCTIONThe unique optical properties of semiconductor nanostructures have been extensively studied in the aspect of quantum confinement effects: when the dimensions of semiconductors are put at or below the characteristic size like exciton Bohr radius, the band gap becomes larger in comparison with the relevant bulk material, followed by a blue shift of the optical absorption onset. Such phenomenon is caused by localization of electrons and holes in a confined space that results in observable quantization of the energy levels of the electrons. 1−3 In this case, the optical properties of nanomaterials present a series of features that the bulk materials do not possess and have been widely applied in biomedicine, 4−6 sensors, 7 photonics, 8,9 and photovoltaics. 8,10 However, other geometrical factors excluding the quantum effects that influence the optical band gap of semiconductors are rarely reported. 11,12 These days, the development of technologies for precisely controlling morphological parameters of nanostructures and the corresponding arrays enables us with sufficient approaches to turn back to reexamine the renowned optical band gap shift of semiconductors. Specifically, the technique based on anodic aluminum oxide (AAO) template has been proven to be one of the most popular methodologies to fabricate nanostructure arrays with perfectly manipulatable morphologies, owing to the advantages in low cost, easy fabrication, and high manipulation. 13−16 Accordingly, a large diversity of nanostructure arrays, including nanopores, nanodots, nanorods, nanotubes, and even the nanocones, has been realized. 13−22 In consideration of the attractive property of TiO 2 that has been broadly utilized in dye-sensitized solar cells, 23,24 photocatalysts, 25 and photonics, 26,27 in this paper, we focus on the optical band gap modulation of TiO 2 na...

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“…demonstrated that the photocatalytic activity first increases and then decreases as the diameter and wall thickness of the nanotubes increase, because of changes in light absorption, surface area and reactant transport. Yung‐Huang Chang showed that the intensities of the absorption spectra were enhanced by an increase in the thickness of the TiO 2 thin film and tube walls.…”

Section: Resultsmentioning

confidence: 99%

Effect of the anodization voltage on the dimensions and photoactivity of titania nanotubes arrays

Atyaoui

Cachet

Sutter

et al. 2013

Surface & Interface Analysis

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This work compares the behaviors of TiO2 nanotube (TNTs) array obtained by anodization of Ti foils in an ethylene glycol/NH4F/water electrolyte with different applied voltages during a constant anodization time, and for the same electrolyte composition. The crystal structure and surface morphology of the annealed anodic films are investigated by X‐Ray diffraction system, Raman spectroscopy and scanning electron microscopy, respectively. The TiO2 nanotubes obtained at potentials of 20–40–60 V show different inner diameters (42–89–124 nm), tube length (1.2–3.3–12.7 µm) and wall thicknesses (12–15–18 nm). The influence of these geometric parameters on the photoelectrochemical properties and the photocatalytic activity were investigated in detail. The results showed that the photocatalytic performances of TNT films are improved when the specific surface, the tube length and the solid fraction are increased, but the increase is slowed down when a limiting thickness of the layer is reached. The surface states which usually show high density in nanostructured layers do not seem to influence significantly the photocatalytic activity of the layers. Copyright © 2013 John Wiley & Sons, Ltd.

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Effect of Geometric Nanostructures on the Absorption Edges of 1-D and 2-D TiO₂ Fabricated by Atomic Layer Deposition

Cited by 17 publications

References 43 publications

Enhanced physical properties of the anodic TiO2 nanotubes via proper anodization time

Enhanced physical properties of the anodic TiO2 nanotubes via proper anodization time

Dimensional Dependence of the Optical Absorption Band Edge of TiO₂ Nanotube Arrays beyond the Quantum Effect

Effect of the anodization voltage on the dimensions and photoactivity of titania nanotubes arrays

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Effect of Geometric Nanostructures on the Absorption Edges of 1-D and 2-D TiO2 Fabricated by Atomic Layer Deposition

Cited by 17 publications

References 43 publications

Enhanced physical properties of the anodic TiO2 nanotubes via proper anodization time

Enhanced physical properties of the anodic TiO2 nanotubes via proper anodization time

Dimensional Dependence of the Optical Absorption Band Edge of TiO2 Nanotube Arrays beyond the Quantum Effect

Effect of the anodization voltage on the dimensions and photoactivity of titania nanotubes arrays

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Effect of Geometric Nanostructures on the Absorption Edges of 1-D and 2-D TiO₂ Fabricated by Atomic Layer Deposition

Dimensional Dependence of the Optical Absorption Band Edge of TiO₂ Nanotube Arrays beyond the Quantum Effect