Facile electrochemical-assisted synthesis of TiO2 nanotubes and their role in Schottky barrier diode applications

doi:10.1016/j.spmi.2017.11.009

Superlattices and Microstructures

Volume 113, January 2018, Pages 310-318

https://doi.org/10.1016/j.spmi.2017.11.009 Get rights and content

Highlights

•
TiO₂ NTAs were synthesized by facile electrochemical assisted route.
•
Structural and morphological properties of TiO₂ NTAs were evaluated by XRD and SEM.
•
Electrical properties were analyzed by means of Schottky junction.

Abstract

Highly ordered TiO₂ nanotube arrays were fabricated by electrochemical anodization of Ti foils. XRD measurements confirmed that properties of nanotube arrays belong to mixed anatase and rutile TiO₂ phases with tetragonal crystal structure. Inter planar distance values of TiO₂ nanotubes were determined with respect to Miller indices and varied from 0.16695 to 0.35339 nm. Furthermore, a Schottky diode made by Ag/TiO₂ nano tube arrays/Ti was fabricated and current-voltage (I-V) characteristics of the device were analyzed at room temperature to investigate device performance. Ideality factor and barrier height have been determined as 2.39 and 0.92 eV, respectively. Results have been discussed in details.

Introduction

TiO₂ is one of the most widely studied semiconductors due to its favorable electrical and optical properties which make it suitable for several applications such as thin layer in DSCC, organic and perovskite solar cells, chemical sensors, photocatalyst, coating against wear, etc. These properties mainly depend on crystallite size, shape and phase of the TiO₂ material. TiO₂ has three different crystal structures: rutile, anatase and brookite, which lead to different materials' characteristics. As an example, anatase exhibit an indirect band gap which is larger (3.2 eV) than that of rutile (3.0 eV). For pure phases, it is generally accepted that catalytic activity of anatase is higher compared to rutile. Therefore, unique physical, chemical, electronic and optical properties of the different TiO₂ phases may be used and/or tailored according to the different applications [1]. Moreover, TiO₂ is also non-toxic, and has got a high dielectric constant and a high photocatalytic activity. However, the brookite phase of TiO₂ is usually unstable during the reactions and it is difficult to prepare in a pure form at low temperature, and it is therefore rarely used as a catalyst [2]. Although rutile phase is chemically more stable than anatase one, it shows less efficiency in photovoltaic applications [3], [4]. With the improve of nanotechnology, researchers have tried to develop low cost nanostructures with high surface to volume ratios and size depended properties for application in a variety of devices. Different morphologies of TiO₂ such as nanowire [5], nanosphere [6] and nanotubes [7], [8] have been investigated and showed enhanced physicochemical properties with respect to bulk materials. Among these nanostructures, TiO₂ nanotubes play an important role due to their chemical stability, electrical and optical properties and low costs fabrication. The high surface area and the large pore volume of TiO₂ nanotubes are exploited in a wide range of applications ranging from solar cells to cosmetic products [2]. However, as a result of the high surface area and the large amount of grain boundaries between nanoparticles, electron-hole recombination centers are favored [8]. Generally, electron transport for wide band gap semiconductors depends on diffusion and higher electron diffusion makes devices more efficient [9]. Therefore, synthesis of one dimensional (1-D) TiO₂ nanotubes seems to be a possible way to enhance electron diffusion rate. However, the high resistivity of TiO₂ and the aggregation of nanoparticles at high temperature and long term operation may limit the efficiency of the devices. For examples, Comini et al. [10] found that the resistance should not exceed tens of MΩ for chemical sensors application and therefore they used Nb doped TiO₂ nanotubes with higher electrical conductivity for their investigations. Also, Macak et al. [11] showed that the conductivity of TiO₂ nanotubes can be enhanced by filling the TiO₂ nanotubes with Cu. In another study, Zhou et al. [12] demonstrated that the capacitance features of TiO₂ nanotubes might be enhanced by formation of oxygen vacancies and they introduced hydroxyl group on the surface of TiO₂ nanotubes during the cathodic reaction process. Rectifying junctions based on metal-semiconductor play a very important role in electronic applications. A Schottky barrier may occur at the metal-nanotube interface and its properties depend generally on the metal used to contact the semiconductor. Thus, the Fermi level stabilization occurs via downward shifting of the Fermi level of the semiconductor [13]. Liu and Chen showed in their study that the barrier height was 1.10eV for Ag/TiO₂ nanoparticles/Ti devices [14]. In our study we aim to determine microstructural and morphological features of TiO₂ nanotubes arrays (NTAs) and to correlate them to device performances. TiO₂ nanotubes arrays were synthesized by electrochemical anodization on Ti foils and employed in a Schottky junction. Morphological and microstructural characteristic of TiO₂-NTAs and electrical performances of NTAs-based Schottky junctions were investigated.

Section snippets

Experimental

TiO₂ nanotube arrays were grown by electrochemical anodization of Ti foils, as described in Refs. [1], [7]. Pieces of 2 × 3 mm Ti foils (0.25 mm thickness, 99.7% purity from Sigma Aldrich) were cleaned by ultrasonic bath in acetone, isopropyl alcohol and deionized water for 30 min, respectively, then dried with nitrogen gas. Ti foils and Pt mesh were placed in a Teflon electrochemical cell as working and counter electrode, respectively. Electrochemical cell was filled with electrolyte

Result and discussion

Microstructural features of TiO₂ nanotubes array grown on Ti substrate, obtained by X-Ray diffraction measurements are shown in Fig. 2. Diffractogram shows 7 diffraction peaks at 2θ = 25.2°, 36.9°, 37.8°, 38.5°, 48°, 53.8° and 55° corresponding to crystal planes (101), (103), (004), (112), (200), (105), (211) of anatase TiO₂ nanotubes, a small rutile peak at 28.3° and 3 diffraction peaks at 2θ = 35.1°, 40° and 53° corresponding to the Ti substrate. According to XRD pattern of TiO₂ nanotubes,

Conclusions

Highly ordered TiO₂ nanotube arrays (NTAs) were synthesized on Ti substrate by using an electrochemical process. NTAs were investigated by XRD and SEM measurements. According to XRD analysis, NTAs yield an anatase TiO₂ phase with tetragonal crystal structure. Inter planar distance d values varied from 0.16695 to 0.35339 nm. As a following process, Ag was deposited onto TiO₂ NTAs in order to fabricate an Ag/TiO₂ NTAs Schottky diode. Analysis of Ag/TiO₂ NTAs Schottky diode was carried out by dark

Acknowledgements

This research was supported by the Ataturk University Research Fund, Project Numbers 2015/120.

References (39)

S.H. Kang et al.
Columnar rutile TiO₂ based dye-sensitized solar cells by radio-frequency magnetron sputtering
J. Power Sources
(2008)
J.M. Macak et al.
TiO₂ nanotubes: self-organized electrochemical formation, properties and applications
Curr. Opin. Solid State Mater. Sci.
(2007)
L. Giorgi et al.
Titania nanotubes self-assembled by electrochemical anodization: semiconducting and electrochemical properties
Thin Solid Films
(2016)
E. Comini et al.
Highly conductive titanium oxide nanotubes chemical sensors
Microporous Mesoporous Mater.
(2015)
J. Liu et al.
Plasmon enhanced photoelectrochemical activity of Ag-Cu nanoparticles on TiO₂/Ti substrates
Int. J. Electrochem. Sci.
(2012)
B. Liu et al.
Facile formation of mixed phase porous TiO₂ nanotubes and enhanced visible-light photocatalytic activity
J. Alloys Compd.
(2013)
S. Das et al.
Influence of annealing temperatures on the properties of low aspect-ratio TiO₂ nanotube layers
Electrochimica Acta
(2016)
A. Tighineanu et al.
Conductivity of TiO₂ nanotubes: influence of annealing time and temperature
Chem. Phys. Lett.
(2010)
B.B. Cirak et al.
Synthesis, surface properties, crystal structure and dye sensitized solar cell performance of TiO₂ nanotube arrays anodized under different voltages
Vacuum
(2017)
H. Yamashita et al.
Nanostructured Photocatalysts: Advanced Functional Materials
(2016)

N.-G. Park et al.

Comparison of dye-sensitized rutile- and anatase-based TiO₂ solar cells

J. Phys. Chem. B

(2000)

X. Zhang et al.

Electrochemical fabrication of single-crystalline anatase TiO₂ nanowire arrays

J. Electrochem. Soc.

(2001)

K. Lee et al.

One-dimensional titanium dioxide nanomaterials: nanotubes

Chem. Rev.

(2014)

A.B. Martinson et al.

Radial electron collection in dye-sensitized solar cells

Nano Lett.

(2008)

J. M. Macak et al.

Filling of TiO₂ nanotubes by self-doping and electrodeposition

Adv. Mater

(2007)

H. Zhou et al.

Enhancing the capacitance of TiO₂ nanotube arrays by a facile cathodic reduction process

J. Power Sources

(2008)

S. Rahbarpour, P. Mohsen, Silver-Rutile Schottky Diode Fabricated on Oxidized Titanium Foil, IOP Conference Series:...

R. Meng et al.

Reassessment of the roles of Ag in TiO₂ nanotubes anode material for lithium ion battery

Ceram. Int.

(2015)

M. Yilmaz et al.

The effect of Mn incorporation on the structural, morphological, optical, and electrical features of nanocrystalline ZnO thin films prepared by chemical spray pyrolysis technique

Metallurgical Mater. Trans. A

(2015)

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Facile electrochemical-assisted synthesis of TiO2 nanotubes and their role in Schottky barrier diode applications

Highlights

Abstract

Introduction

Section snippets

Experimental

Result and discussion

Conclusions

Acknowledgements

J. Power Sources

Curr. Opin. Solid State Mater. Sci.

Thin Solid Films

Microporous Mesoporous Mater.

Int. J. Electrochem. Sci.

J. Alloys Compd.

Electrochimica Acta

Chem. Phys. Lett.

Synthesis, surface properties, crystal structure and dye sensitized solar cell performance of TiO2 nanotube arrays anodized under different voltages

Vacuum

Nanostructured Photocatalysts: Advanced Functional Materials

Comparison of dye-sensitized rutile- and anatase-based TiO2 solar cells

J. Phys. Chem. B

Electrochemical fabrication of single-crystalline anatase TiO2 nanowire arrays

J. Electrochem. Soc.

One-dimensional titanium dioxide nanomaterials: nanotubes

Chem. Rev.

Radial electron collection in dye-sensitized solar cells

Nano Lett.

Filling of TiO2 nanotubes by self-doping and electrodeposition

Adv. Mater

Enhancing the capacitance of TiO2 nanotube arrays by a facile cathodic reduction process

J. Power Sources

Reassessment of the roles of Ag in TiO2 nanotubes anode material for lithium ion battery

Ceram. Int.

The effect of Mn incorporation on the structural, morphological, optical, and electrical features of nanocrystalline ZnO thin films prepared by chemical spray pyrolysis technique

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Facile electrochemical-assisted synthesis of TiO₂ nanotubes and their role in Schottky barrier diode applications

Synthesis, surface properties, crystal structure and dye sensitized solar cell performance of TiO₂ nanotube arrays anodized under different voltages

Comparison of dye-sensitized rutile- and anatase-based TiO₂ solar cells

Electrochemical fabrication of single-crystalline anatase TiO₂ nanowire arrays

Filling of TiO₂ nanotubes by self-doping and electrodeposition

Enhancing the capacitance of TiO₂ nanotube arrays by a facile cathodic reduction process

Reassessment of the roles of Ag in TiO₂ nanotubes anode material for lithium ion battery