Structure, Morphology, and Dielectric Properties of Nanocomposite Oxide Films Formed by Anodizing of Sputter-Deposited Ta-Al Bilayers

Mozalev, Alexander; Sakairi, Masatoshi; Takahashi, Hiroki

doi:10.1149/1.1796445

Cited by 46 publications

(73 citation statements)

References 28 publications

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“…This may be possible because it is reported that the AAO walls are porous. 25 Once part of the AAO wall is dissolved, the diameter of the AAO pore become bigger. On …”

Section: Resultsmentioning

confidence: 99%

Ultrafast Initial Growth Rate of Self-Assembled TiO[sub 2] Nanorod Arrays Fabricated by Ti Anodization

Chang¹,

Lin²,

Chen³

2011

Electrochem. Solid-State Lett.

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The growth mechanism of TiO 2 nanorods fabricated by the anodization of Ti films using a mask of anodic aluminum oxide is investigated by examining the growth rate and morphology of the fabricated nanorods. It is found that the growth rate is 250 nm/s within the first 0.1 s at 117 V and decreases abruptly to 0.79 nm/s after 3 s. In addition, the diameter of the nanorods is larger near the top than near the root of the nanorods. A growth mechanism is proposed to explain these interesting phenomena.Zero-dimensional ͑0D͒ and one-dimensional ͑1D͒ metal oxide nanostructures have attracted considerable attention in recent years due to their unique physical properties and many potential applications in areas such as electronics, optoelectronics, and sensing devices. 1 A thin film of anodic aluminum oxide ͑AAO͒ is employed as a template to grow 0D and 1D metal oxide nanostructures. 2,3 With the aid of the AAO template, large-scale arrays of nanostructures can be fabricated on either semiconductor or glass substrates.In recent years, TiO 2 has drawn much attention due to its promising photoconductive properties that can be tailored for the development of photovoltaic devices. [4][5][6][7][8][9][10][11] The anodization process is adopted to form 0D and 1D nanostructures. 12-20 Because anodization is a cost-effective process, it has the potential to grow large-scale arrays of nanostructures for device applications. It is reported that arrays of TiO 2 nanotubes can be fabricated in bulk Ti and in Ti films. 13 Arrays of TiO 2 nanostructures such as nanodots and nanorods can be fabricated from the same materials using an AAO mask. 2,12 With an AAO mask, TiO 2 nanostructures can be fabricated on semiconductor or glass substrates for device applications. In addition, TiO 2 nanostructures grown on semiconductors, such as Si, are able to form heterojunctions and have interesting photoconductive properties. 21 The growth mechanism is well studied for the TiO 2 nanostructures grown from bulk Ti. However, the growth rate and growth mechanism are not clear for TiO 2 nanostructures grown in AAO pores by anodization.In this study, we investigated the growth mechanism of TiO 2 nanorods in AAO nanopores using anodic oxidation under various conditions. The growth rate and morphology are examined at different stages. It was found that the TiO 2 nanorods grow very quickly in the beginning and reach saturation in growth within 3 s. A possible growth mechanism is proposed to explain this interesting observation. ExperimentalTo fabricate anodic TiO 2 nanostructures, first, a Ti film with a thickness of 130 nm was deposited on a P-type ͑100͒ silicon substrate by an e-gun evaporator. Subsequently, a 700-nm Al film was deposited by a thermal evaporator. To control the morphology of the anodic TiO 2 nanostructures, a two-step anodization process was carried out on the Al/Ti films. 17,22 The first anodization was carried out in a 0.3 M oxalic acid ͑H 2 C 2 O 4 ͒ electrolyte by a 40-V bias at room temperature until the current dropped down to 1 mA. A...

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“…This may be possible because it is reported that the AAO walls are porous. 25 Once part of the AAO wall is dissolved, the diameter of the AAO pore become bigger. On …”

Section: Resultsmentioning

confidence: 99%

Ultrafast Initial Growth Rate of Self-Assembled TiO[sub 2] Nanorod Arrays Fabricated by Ti Anodization

Chang¹,

Lin²,

Chen³

2011

Electrochem. Solid-State Lett.

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“…The first anodization was conducted in the aqueous electrolytes of 0.3 M oxalic acid under a potentiostatic mode of 40 V at 1 ºC with platinum counter electrode. The formation of tungsten oxide through the penetration into the AAO barrier layer was ascribed to the dissolution of Al-O bonds at the AAO barrier layer [6]. During the formation of AAO, the current increased with the anodization time (region i) and decreased abruptly (region ii).…”

Section: Methodsmentioning

confidence: 99%

“…Among them, tungsten oxides with amorphous or crystalline structures have been widely studied for the applications to electrochromic devices, electrochemical capacitors, and gas sensing devices [2][3][4]. Many researchers have investigated the nanostructured materials with high specific surface area for the applications to the anodic and cathodic electrodes of batteries and capacitors [5][6][7]. Many researchers have investigated the nanostructured materials with high specific surface area for the applications to the anodic and cathodic electrodes of batteries and capacitors [5][6][7].…”

Section: Introductionmentioning

confidence: 99%

Template-Assisted Growth of Tungsten Oxide Nanorods on Substrates and Their Electrochemical Properties

et al. 2010

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Tungsten oxide nanorods (TONs) with the diameters of 40 nm and the length of 130 nm have been synthesized on substrates using two step electrochemical anodizing processes. The TONs were vertically well-ordered on the substrates with the average interdistance of 100 nm. The TONs had amorphous structure and was mainly composed of W, Al, and O elements, of which the contents varied gradually along the nanorod length from the top surface to the bottom. The cyclic voltammograms (CVs) and galvanostatic charge-discharge analyses showed that TONs had the typical electrochemical pseudocapacitive features of rectangular CV hysteresis and symmetric charge-discharge behaviors, respectively. When the TONs were heat-treated at 600℃ in vacuum, they showed the maximum specific capacitance of 660 ㎌/cm 2 , which was higher, by an order of magnitude, than that (68 ㎌/cm 2 ) of the TONs annealed at 300 ℃ in ambient atmosphere.

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“…The O 2 evolution has been associated with an amorphousto-crystalline transition of the bottom oxide (hereafter the 'field crystallization'), [16] the phenomenon being generally known for barrier-type anodic film growth on Ti surface at relatively low potentials of less than~15-20 V. [19][20][21] However, anodic oxides on other valve metals like Ta, Nb, or W grow generally amorphous during the barrier-type anodizing up to substantially higher potentials, [22][23][24][25] and their PAA-assisted anodizing results in long-aspect-ratio amorphous and stable nanocolumns or rods, [26][27][28][29] without obvious O 2 evolution. It is anticipated that alloying of titanium with one of these metals could suppress the field crystallization and void formation in the anodic oxide, as well as minimize the incorporation of alumina in the root composition and, therefore, improve the stability of the column arrays.…”

Section: Introductionmentioning

confidence: 99%

Porous‐Alumina‐Assisted Growth of Nanostructured Anodic Films on Ti−Nb Alloys

et al. 2018

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Porous-anodic-alumina (PAA)-assisted anodizing is employed, for the first time, for growing arrays of oxide nanocolumns on TiÀNb alloy films with up to 58 at% Nb. Beyond about 24 at% Nb in the alloy, the system allows for high formation potentials of 250-420 V, giving columns that are 500-700 nm long, which are 100 % stable during the PAA etch. The stability worsens when lowering the Nb content in the alloy, owing to contamination of the column roots by alumina, which arises from the amorphous-to-crystalline transition of the anodic oxide, oxygen evolution, formation of O 2 -filled nanobubbles within the roots, and development of bigger voids. The voids force the roots to regrow and spread laterally along with anodizing the surrounding Al residues, which increases alumina content in the titania-based nanoroots. The incorporation of sufficient amounts of Nb 2 O 5 in the anodic TiO 2 hinders oxide crystallization and lowers alumina content in the roots, which stabilizes the columns. The two oxides are distributed uniformly along the columns, indicating comparable migration rates of Ti 4 + and Nb 5 + ions in the mixed anodic oxide. This uniform distribution, combined with possibly mixing the oxides at atomic level, is expected to narrow the band gap of the material, which is of vast importance for solar energy conversion applications.[a] Dr.

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Structure, Morphology, and Dielectric Properties of Nanocomposite Oxide Films Formed by Anodizing of Sputter-Deposited Ta-Al Bilayers

Cited by 46 publications

References 28 publications

Ultrafast Initial Growth Rate of Self-Assembled TiO[sub 2] Nanorod Arrays Fabricated by Ti Anodization

Ultrafast Initial Growth Rate of Self-Assembled TiO[sub 2] Nanorod Arrays Fabricated by Ti Anodization

Template-Assisted Growth of Tungsten Oxide Nanorods on Substrates and Their Electrochemical Properties

Porous‐Alumina‐Assisted Growth of Nanostructured Anodic Films on Ti−Nb Alloys

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