Fabrication of hydrogen sensors with transparent titanium oxide nanotube-array thin films as sensing elements

Abstract Transparent thin films comprised of highly ordered titania nanotube-arrays were grown from titanium thin films using an anodization technique, from which highly sensitive and selective hydrogen sensors that can operate at room temperature were fabricated. Titanium films sputter deposited on glass at 500 °C were anodized in a fluorine-containing electrolyte to obtain nanotube-array films. Precise monitoring of current during the anodization enabled removal of the samples from the anodization bath at a point where the remaining metal layer became discontinuous, without destroying the nanotube architecture. The samples were then annealed in oxygen at 420 °C to crystallize the nanotube-arrays as well as oxidize any un-anodized metallic regions, yielding transparent films comprised of titanium oxide nanotube-arrays. Herein, we discuss the morphology, structure and optical characterization of these films. When coated with a 10-nm discontinuous palladium layer, the optically transparent nanotube-array films serve as excellent hydrogen sensors, exhibiting a four-order magnitude drop in resistance with exposure to 1000 ppm hydrogen at room temperature.

[1]  Craig A. Grimes,et al.  Extreme Changes in the Electrical Resistance of Titania Nanotubes with Hydrogen Exposure , 2003 .

[2]  Craig A Grimes,et al.  Enhanced photocleavage of water using titania nanotube arrays. , 2005, Nano letters.

[3]  U. Roland,et al.  On the nature of spilt-over hydrogen , 1997 .

[4]  M. Kiuchi,et al.  Structural and optical properties of titanium dioxide films deposited by reactive magnetron sputtering in pure oxygen plasma , 2004 .

[5]  Fa-min Liu,et al.  Surface and optical properties of nanocrystalline anatase titania films grown by radio frequency reactive magnetron sputtering , 2002 .

[6]  Jackie Y. Ying,et al.  Role of Particle Size in Nanocrystalline TiO2-Based Photocatalysts , 1998 .

[7]  E. Kim,et al.  Comparison of optical and photocatalytic properties of TiO2 thin films prepared by electron-beam evaporation and sol–gel dip-coating , 2003 .

[8]  Craig A. Grimes,et al.  Titanium oxide nanotube arrays prepared by anodic oxidation , 2001 .

[9]  M. Kawamura,et al.  Anodization of Al3Zr intermetallic compound film and its application to the preparation of thin‐film capacitors with high reliability , 2000 .

[10]  Patrik Schmuki,et al.  Self-Organized Porous Titanium Oxide Prepared in H 2 SO 4 / HF Electrolytes , 2003 .

[11]  H. Rubinsztein-Dunlop,et al.  Mesostructured dye-doped titanium dioxide for micro-optoelectronic applications. , 2003, Chemphyschem : a European journal of chemical physics and physical chemistry.

[12]  I. Shih,et al.  Thin film transistors with anodic gate dielectrics and chemical bath deposited active layers , 2002 .

[13]  Craig A. Grimes,et al.  Hydrogen sensing using titania nanotubes , 2003 .

[14]  D. Partlow,et al.  Formation of broad band antireflective coatings on fused silica for high power laser applications , 1985 .

[15]  Craig A. Grimes,et al.  A room-temperature TiO2-nanotube hydrogen sensor able to self-clean photoactively from environmental contamination , 2004 .

[16]  Craig A. Grimes,et al.  Fabrication of tapered, conical-shaped titania nanotubes , 2003 .

[17]  Woo-Seong Kim,et al.  Intercalation/deintercalation characteristics of electrodeposited and anodized nickel thin film on ITO electrode in aqueous and nonaqueous electrolytes , 2001 .

[18]  J. Gasiot,et al.  A simple method for the determination of the optical constants n, k and the thickness of a weakly absorbing thin film , 1976 .

[19]  Sudipta Seal,et al.  Synthesis and characterization of sol-gel derived nanocrystalline tin oxide thin film as hydrogen sensor , 2003 .

[20]  C. Grimes,et al.  Water-photolysis properties of micron-length highly-ordered titania nanotube-arrays. , 2005, Journal of nanoscience and nanotechnology.

[21]  N. Serpone,et al.  Photocatalysis: Fundamentals and Applications , 1989 .

[22]  Craig A. Grimes,et al.  Crystallization and high-temperature structural stability of titanium oxide nanotube arrays , 2003 .

[23]  Cheng-Tzu Kuo,et al.  Preparation and phase transformation of highly ordered TiO2 nanodot arrays on sapphire substrates , 2004 .

[24]  Craig A. Grimes,et al.  The effect of electrolyte composition on the fabrication of self-organized titanium oxide nanotube arrays by anodic oxidation , 2005 .

[25]  Jackie Y. Ying,et al.  Photocatalytic decomposition of halogenated organics over nanocrystalline titania , 1997 .

[26]  Zhibo Zhang,et al.  Direct formation of self-assembled nanoporous aluminium oxide on SiO2 and Si substrates , 2002 .

[27]  J. Tauc,et al.  Absorption edge and internal electric fields in amorphous semiconductors , 1970 .