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Fabrication of complete titania nanoporous structures via electrochemical anodization of Ti.

Ali G, Chen C, Yoo SH, Kum JM, Cho SO - Nanoscale Res Lett (2011)

Bottom Line: However, a complete titania nano-porous (TNP) structures are obtained when the second anodization is conducted in a viscous electrolyte when compared to the first one.The average pore diameter is approximately 70 nm, while the average inter-pore distance is approximately 130 nm.These TNP structures are useful to fabricate other nanostructure materials and nanodevices.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Nuclear and Quantum Engineering, Korea Advanced Institute of Science and Technology (KAIST), 373-1 Guseong, Yuseong, Daejeon 305-701, Republic of Korea. socho@kaist.ac.kr.

ABSTRACT
We present a novel method to fabricate complete and highly oriented anodic titanium oxide (ATO) nano-porous structures with uniform and parallel nanochannels. ATO nano-porous structures are fabricated by anodizing a Ti-foil in two different organic viscous electrolytes at room temperature using a two-step anodizing method. TiO2 nanotubes covered with a few nanometer thin nano-porous layer is produced when the first and the second anodization are carried out in the same electrolyte. However, a complete titania nano-porous (TNP) structures are obtained when the second anodization is conducted in a viscous electrolyte when compared to the first one. TNP structure was attributed to the suppression of F-rich layer dissolution between the cell boundaries in the viscous electrolyte. The structural morphologies were examined by field emission scanning electron microscope. The average pore diameter is approximately 70 nm, while the average inter-pore distance is approximately 130 nm. These TNP structures are useful to fabricate other nanostructure materials and nanodevices.

No MeSH data available.


Related in: MedlinePlus

FESEM images of TiO2 nanotubes fabricated in glycerol containing 0.5 wt% NH4F and 0.2 wt% H2O via second-step anodization: (a) top surface view at low magnification, (b) top surface view at high magnification, (c) top surface view of patterned Ti-substrate anodized for 10 min, (d) cross-sectional view at low magnification, (e) cross-sectional view of the marked area at high magnification.
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Figure 5: FESEM images of TiO2 nanotubes fabricated in glycerol containing 0.5 wt% NH4F and 0.2 wt% H2O via second-step anodization: (a) top surface view at low magnification, (b) top surface view at high magnification, (c) top surface view of patterned Ti-substrate anodized for 10 min, (d) cross-sectional view at low magnification, (e) cross-sectional view of the marked area at high magnification.

Mentions: A complete TNP structure was obtained when a pre-patterned Ti-substrate, obtained in EG-based electrolyte via first-step anodization, is secondly anodized in glycerol-based electrolyte. Figure 5a,b shows the top surface view of the TNP structure at a low- and a high-magnification, respectively, without post-anodizing treatment. It is evident from these images that the nanopores are very clear, regular, uniform, and highly-oriented. The average pore diameter is approximately 70 nm, while the inter-pore distance (distance between centers of the pores) is about 130 nm. It is important to note that the hexagonal shape of original pre-patterns dimples of honeycomb-like morphology (Figure 2d) is converted in to a circular-like shape during the second-step anodization in glycerol. This kind of morphology has been reported for pre-patterned Al and Ti during anodization [28] and ascribed to a long anodization time. However, we assume that this kind of circular shape morphology is also due to the viscosity of the electrolyte. It has been reported that pore diameters of nanotubes also depend upon the nature of electrolyte [23] as well as the anodization potential and the anodizing time [21]. An electrolyte with a high viscosity will produce nanopores/nanotubes with small diameters and vice versa. This is clearly evident from Figure 5c, which shows the top surface morphology of the pre-patterned Ti-substrate after 5-10 min of the second-step anodization in glycerol-based electrolyte. Since the viscosity of glycerol is 945 cP at 25°C while that of EG is 16 cP at 25°C [33], therefore, the pore diameter will be smaller in glycerol as compared to that in EG. It is because of this fact that growth of nanopores start within the honeycomb-like hexagonal pre-patterned ring during the second-step anodization in glycerol-based electrolyte and resulted in a smaller pore diameter with circular shape morphology. The thickness of honeycomb-like patterned hexagonal rings is also greater after the second-step anodization in glycerol compared to the thickness of original honeycomb-like hexagonal pre-pattern before the second-step anodization (Figure 2d). This result further supports our assumption about the growth of nanopores within the original honeycomb-like hexagonal pattern ring morphology during the second-step anodization in glycerol-based electrolyte. The cross-sectional morphology at a low- and a high-magnification is shown in Figure 5d,e, respectively. Uniform and parallel nano-channels can be clearly seen in these micrographs. The width of the nano-channel is approximately 70 nm, while the inter channel distance is approximately 130 nm which is matched well with the top surface morphology of the TNP. This kind of parallel channel morphology has been reported in the literature for TNP structure [34]. Very recently Schmuki and co-workers [31] also reported a TNP structure. According to their findings, the formation of TNP structure is due to the optimized content of water in the electrolyte which suppresses the dissolution of F-rich layer in the cell boundaries. F-rich layer is always present at the bottom of TiO2 nanotubes as well as at the cell boundaries. Energy dispersive X-ray spectroscopy (EDX) analysis (Figure 6; Table 1) of the top and the bottom surface of TNP structure is in line with the literature [35]. Significant amount of C and F is also found besides Ti and O. The presence of F-rich layer in the boundaries between the cells is essential for the formation of nano-porous structure. According to Stokes-Einstein relation, the diffusion coefficient is inversely proportional to the viscosity of the electrolyte. Since the viscosity of glycerol is approximately 60 times higher than EG at 25°C, the diffusion of H+ is expected to be reduced in glycerol during anodization and thus H+ cannot diffuse easily in the cell boundaries. This will protect F-rich layer between the cell boundaries from dissolution and hence resulted in the formation of nano-porous structure. As a consequence, F-rich layer in the cell boundaries can be protected from dissolution which led to the formation of nano-porous structure. This is evident from the content of F in the top and bottom surface of TNP in the EDX analysis (Table 1). However, dissolution of the F-rich layer between the cells boundaries results in the formation of the nanotubular structure [31].


Fabrication of complete titania nanoporous structures via electrochemical anodization of Ti.

Ali G, Chen C, Yoo SH, Kum JM, Cho SO - Nanoscale Res Lett (2011)

FESEM images of TiO2 nanotubes fabricated in glycerol containing 0.5 wt% NH4F and 0.2 wt% H2O via second-step anodization: (a) top surface view at low magnification, (b) top surface view at high magnification, (c) top surface view of patterned Ti-substrate anodized for 10 min, (d) cross-sectional view at low magnification, (e) cross-sectional view of the marked area at high magnification.
© Copyright Policy - open-access
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3211420&req=5

Figure 5: FESEM images of TiO2 nanotubes fabricated in glycerol containing 0.5 wt% NH4F and 0.2 wt% H2O via second-step anodization: (a) top surface view at low magnification, (b) top surface view at high magnification, (c) top surface view of patterned Ti-substrate anodized for 10 min, (d) cross-sectional view at low magnification, (e) cross-sectional view of the marked area at high magnification.
Mentions: A complete TNP structure was obtained when a pre-patterned Ti-substrate, obtained in EG-based electrolyte via first-step anodization, is secondly anodized in glycerol-based electrolyte. Figure 5a,b shows the top surface view of the TNP structure at a low- and a high-magnification, respectively, without post-anodizing treatment. It is evident from these images that the nanopores are very clear, regular, uniform, and highly-oriented. The average pore diameter is approximately 70 nm, while the inter-pore distance (distance between centers of the pores) is about 130 nm. It is important to note that the hexagonal shape of original pre-patterns dimples of honeycomb-like morphology (Figure 2d) is converted in to a circular-like shape during the second-step anodization in glycerol. This kind of morphology has been reported for pre-patterned Al and Ti during anodization [28] and ascribed to a long anodization time. However, we assume that this kind of circular shape morphology is also due to the viscosity of the electrolyte. It has been reported that pore diameters of nanotubes also depend upon the nature of electrolyte [23] as well as the anodization potential and the anodizing time [21]. An electrolyte with a high viscosity will produce nanopores/nanotubes with small diameters and vice versa. This is clearly evident from Figure 5c, which shows the top surface morphology of the pre-patterned Ti-substrate after 5-10 min of the second-step anodization in glycerol-based electrolyte. Since the viscosity of glycerol is 945 cP at 25°C while that of EG is 16 cP at 25°C [33], therefore, the pore diameter will be smaller in glycerol as compared to that in EG. It is because of this fact that growth of nanopores start within the honeycomb-like hexagonal pre-patterned ring during the second-step anodization in glycerol-based electrolyte and resulted in a smaller pore diameter with circular shape morphology. The thickness of honeycomb-like patterned hexagonal rings is also greater after the second-step anodization in glycerol compared to the thickness of original honeycomb-like hexagonal pre-pattern before the second-step anodization (Figure 2d). This result further supports our assumption about the growth of nanopores within the original honeycomb-like hexagonal pattern ring morphology during the second-step anodization in glycerol-based electrolyte. The cross-sectional morphology at a low- and a high-magnification is shown in Figure 5d,e, respectively. Uniform and parallel nano-channels can be clearly seen in these micrographs. The width of the nano-channel is approximately 70 nm, while the inter channel distance is approximately 130 nm which is matched well with the top surface morphology of the TNP. This kind of parallel channel morphology has been reported in the literature for TNP structure [34]. Very recently Schmuki and co-workers [31] also reported a TNP structure. According to their findings, the formation of TNP structure is due to the optimized content of water in the electrolyte which suppresses the dissolution of F-rich layer in the cell boundaries. F-rich layer is always present at the bottom of TiO2 nanotubes as well as at the cell boundaries. Energy dispersive X-ray spectroscopy (EDX) analysis (Figure 6; Table 1) of the top and the bottom surface of TNP structure is in line with the literature [35]. Significant amount of C and F is also found besides Ti and O. The presence of F-rich layer in the boundaries between the cells is essential for the formation of nano-porous structure. According to Stokes-Einstein relation, the diffusion coefficient is inversely proportional to the viscosity of the electrolyte. Since the viscosity of glycerol is approximately 60 times higher than EG at 25°C, the diffusion of H+ is expected to be reduced in glycerol during anodization and thus H+ cannot diffuse easily in the cell boundaries. This will protect F-rich layer between the cell boundaries from dissolution and hence resulted in the formation of nano-porous structure. As a consequence, F-rich layer in the cell boundaries can be protected from dissolution which led to the formation of nano-porous structure. This is evident from the content of F in the top and bottom surface of TNP in the EDX analysis (Table 1). However, dissolution of the F-rich layer between the cells boundaries results in the formation of the nanotubular structure [31].

Bottom Line: However, a complete titania nano-porous (TNP) structures are obtained when the second anodization is conducted in a viscous electrolyte when compared to the first one.The average pore diameter is approximately 70 nm, while the average inter-pore distance is approximately 130 nm.These TNP structures are useful to fabricate other nanostructure materials and nanodevices.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Nuclear and Quantum Engineering, Korea Advanced Institute of Science and Technology (KAIST), 373-1 Guseong, Yuseong, Daejeon 305-701, Republic of Korea. socho@kaist.ac.kr.

ABSTRACT
We present a novel method to fabricate complete and highly oriented anodic titanium oxide (ATO) nano-porous structures with uniform and parallel nanochannels. ATO nano-porous structures are fabricated by anodizing a Ti-foil in two different organic viscous electrolytes at room temperature using a two-step anodizing method. TiO2 nanotubes covered with a few nanometer thin nano-porous layer is produced when the first and the second anodization are carried out in the same electrolyte. However, a complete titania nano-porous (TNP) structures are obtained when the second anodization is conducted in a viscous electrolyte when compared to the first one. TNP structure was attributed to the suppression of F-rich layer dissolution between the cell boundaries in the viscous electrolyte. The structural morphologies were examined by field emission scanning electron microscope. The average pore diameter is approximately 70 nm, while the average inter-pore distance is approximately 130 nm. These TNP structures are useful to fabricate other nanostructure materials and nanodevices.

No MeSH data available.


Related in: MedlinePlus