Oxygen bubble mould effect: serrated nanopore formation and porous alumina growth

Zhu, Xufei; Liu, Lin; Song, Ye; Jia, Hongbing; Yu, Huadong; Xiao, Xuemei; Yang, Xiuli

doi:10.1007/s00706-008-0893-5

Cited by 105 publications

(132 citation statements)

References 28 publications

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“…29,30 Two methods were successfully used to verify the oxygen gas within the nanopores, one way was to add the reductive agent to the electrolytes, 31,32 the other way was to perform anodization under the vacuum circumstance. 31,33 In our recent works, the theoretical expressions for time dependent ionic current and electronic current were successfully derived from the anodizing process of aluminum and titanium.…”

mentioning

confidence: 99%

Forming Process of Anodic TiO₂Nanotubes under a Preformed Compact Surface Layer

Zhang

et al. 2014

J. Electrochem. Soc.

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133

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Anodic TiO 2 nanotubes (NTs) have been studied extensively for many years. However, the growth kinetics still remains unclear, because it is hardly derived by direct in situ methods. Here, an interesting approach is proposed to overcome this challenge. A combinatorial anodization was exploited to monitor the pore initiation and nanotube growth under a preformed compact surface layer (CSL). The preformed CSL and the NTs under the CSL (UCSL-NTs) were formed in fluoride-free and fluoride-containing electrolytes, respectively. The forming process of UCSL-NTs was discussed as compared with that of the general NTs, mainly focusing on the differences of current-time curves and electric charge quantity (Coulomb). The results show that pore embryos of UCSL-NTs have already been achieved under the CSL before the CSL is dissolved. There are five stages in the current-time curve of UCSL-NTs, which is significantly different from three stages of the general NTs. A new growth model, based on a comprehensive review of the existing theories, is proposed to explain the current decrease and increase. And the forming process of TiO 2 NTs is considered to be dominated by the oxide plastic flow around the oxygen bubbles.Anodic TiO 2 nanotubes (NTs) and other porous anodic oxides have attracted considerable scientific interests due to their various applications (e.g., solar energy materials, magnetic semiconductors and biosensors) 1-3 and mysterious formation mechanisms. 4,5 Different mechanisms of TiO 2 NTs have been reported in many electrochemical journals in recent years. 4-8 It is well known that field-assisted dissolution (FAD) (TiO 2 + 6F − + 4H + → [TiF 6 ] 2− + 2H 2 O) of the oxide leads to pore formation in anodic titania films, 8-10 similar to that in porous anodic alumina (PAA) films (Al 2 O 3 + 6H + → 2Al 3 + + 3H 2 O), 11-14 despite a lack of direct experimental evidence that confirms this expectation. 14 As the formation mechanism is impossible to be derived by direct in situ experimental methods, much remains to be done along these directions. 15 Garcia-Vergara et al. 16,17 proposed the field-assisted 'plastic flow' model, the constant thickness of the barrier layer is maintained by flow of oxide from the pore bottom toward the pore wall, driven by compressive stresses from electrostriction and possibly through volume expansion. 16 In fact, the plastic flow is contrary to expectations of the FAD. 16 The behavior of incorporated species in PAA is always incompatible with the FAD model. 16 The flow model has been recognized and exploited for explaining the formation of TiO 2 NTs and serrated nanochannels. 18,19 However, Zhou et al. 12 indicated that both the FAD and the flow models cannot explain the formation of gaps among nanotubes. In recent tracer studies on Ti thin films, the expansion factors increase from 1.5 to 3.0, 20,21 these findings cannot be clarified. Furthermore, anodized TiO 2 NTs have been achieved in an aqueous H 2 SO 4 solution as well as other fluoride free solutions, 12,22,23 this fact puts the flu...

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confidence: 99%

Forming Process of Anodic TiO₂Nanotubes under a Preformed Compact Surface Layer

Zhang

et al. 2014

J. Electrochem. Soc.

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133

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“…This reaction leads to the growth of the barrier oxide layer. The electronic current is responsible for the oxygen evolution (2O 2-→O 2 ↑+4e or 4OH -→O 2 ↑+2H 2 O+4e) [21,32,34]. With the existence of the gas bubbles, the barrier oxide must flow upward Page 9 of 36 A c c e p t e d M a n u s c r i p t 9 around the bubble mold just like the 'plastic flow' model [16,17,34].…”

Section: <Fig 1>mentioning

confidence: 98%

“…However, we found that ATNTs with lotus-root-shaped nanostructure can also be fabricated when the same voltage is adopted in the second-step anodization as the first-step anodization. For the NH 4 F concentration of 0.2 wt%, there is too little anionic incorporation into the barrier oxide to cause enough electronic current for the release of O 2 gas, leading to the half-opening-pore feature in provide an alternative explanation according to the oxygen bubble mould [32][33][34][35][36][37].…”

Section: <Fig5>mentioning

confidence: 99%

“…Herein, the three stages of the total anodizing current density-time curves can be elucidated by the electronic current and the 'oxygen bubble mold' [32][33][34][35][36][37]. When the constant voltage (60 V) is applied on the cell, the electric field is high, and the ionic current is the predominant mode of charge transport, the total anodizing current decreases with the increase of barrier oxide [34].…”

Section: Total Anodizing Current and Concentration Of Nh 4 Fmentioning

confidence: 99%

“…And these three stages change a lot with the change of anodization parameters, including applied voltages and pulse periods [23][24][25][26], anodizing duration [25,26], temperatures [15,24], water content and other parameters [27][28][29][30]. However, as Hebert et al [5,31] Based on the 'plastic flow' model [16,17] rather than 'field-assisted dissolution', the 'oxygen bubble mold' and the electronic current model were proposed by Zhu and coworkers [21,22,32,33] to explain the formation of nanotube embryo and gaps around the nanotubes [34][35][36]. Two theoretical formulas of the ionic current and the electronic current were derived from the general definitions of ionic conductivity and electronic conductivity [37].…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Simulation of anodizing current-time curves and morphology evolution of TiO2 nanotubes anodized in electrolytes with different NH4F concentrations

Zhang

Fan

et al. 2015

Electrochimica Acta

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Understanding and morphology control of pore modulations in nanoporous anodic alumina by discontinuous anodization

Santos¹,

Vojkuvka²,

Alba³

et al. 2012

Physica Status Solidi (a)

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Here, we report on an electrochemical approach so‐called discontinuous anodization (DA) for controlling the generation of pore modulations in nanoporous anodic alumina (NAA) under self‐ordering conditions. In this method, the anodization of aluminium is performed by voltage pulses under mild anodization regime and thermal‐acidic conditions. Furthermore, we perform an exhaustive and systematic study about the relationship between the pore modulation morphology and the main anodization parameters (i.e. acid electrolyte temperature and relax time between consecutive voltage pulses). The generation mechanism of the pore modulations is associated with the formation of a gel‐like layer under these thermal‐acidic conditions and its subsequent detachment during the beginning of each voltage pulse. All this makes it possible to control the pore modulation morphology in NAA at will, what is crucial for developing new nanostructures with accurately controlled geometry for such purposes as nanofluidics, magnetic nanostructures, optical biosensors, templates, selective molecular separators and so forth. A three‐dimensional network based on NAA with controlled geometry: The DA by voltage pulses under hydrothermal conditions yields an accurate control over the pore modulation morphology. Therefore, the structure of the resulting 3D‐NAA network can be designed at will for later applications.

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Oxygen bubble mould effect: serrated nanopore formation and porous alumina growth

Cited by 105 publications

References 28 publications

Forming Process of Anodic TiO₂Nanotubes under a Preformed Compact Surface Layer

Forming Process of Anodic TiO₂Nanotubes under a Preformed Compact Surface Layer

Simulation of anodizing current-time curves and morphology evolution of TiO2 nanotubes anodized in electrolytes with different NH4F concentrations

Understanding and morphology control of pore modulations in nanoporous anodic alumina by discontinuous anodization

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Oxygen bubble mould effect: serrated nanopore formation and porous alumina growth

Cited by 105 publications

References 28 publications

Forming Process of Anodic TiO2Nanotubes under a Preformed Compact Surface Layer

Forming Process of Anodic TiO2Nanotubes under a Preformed Compact Surface Layer

Simulation of anodizing current-time curves and morphology evolution of TiO2 nanotubes anodized in electrolytes with different NH4F concentrations

Understanding and morphology control of pore modulations in nanoporous anodic alumina by discontinuous anodization

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Forming Process of Anodic TiO₂Nanotubes under a Preformed Compact Surface Layer

Forming Process of Anodic TiO₂Nanotubes under a Preformed Compact Surface Layer