Two-dimensional photonic crystals based on anodic porous TiO<sub>2</sub> with ideally ordered hole arrangement

Kondo, Toshiaki; Hirano, Shota; Yanagishita, Takashi; Nguyen, Nhat Truong; Schmuki, P.; Masuda, Hideki

doi:10.7567/apex.9.102001

Cited by 8 publications

(3 citation statements)

References 23 publications

(23 reference statements)

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“…While aluminum oxide is an insulator, both the anatase and rutile forms of titanium dioxide are wide bandgap n-type semiconductors, due to which TNTAs (and TNRAs) are used as the active layer in photocatalysts [8][9][10], photoelectrodes [11,12] and biosensors [13,14], and as an electron transport layer in halide perovskite-, quantum dot-and dyesensitized solar cells [15][16][17][18][19][20][21], organic bulk heterojunction solar cells [22,23], batteries and super-capacitors [24][25][26], and memristors [27,28]. Furthermore, self-organized TiO 2 nanotubes have been used to form 1D, 2D and 3D photonic crystals without recourse to lithographic patterning [29][30][31][32][33][34][35][36]. Therefore TiO 2 nanotube arrays offer a potentially superior platform for both fundamental studies and practical applications of metamaterials.…”

Section: Introductionmentioning

confidence: 99%

Optical anisotropy in vertically oriented TiO₂nanotube arrays

et al. 2017

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Nanofabricated optically anisotropic uniaxial thin films with deep submicron feature sizes are emerging as potential platforms for low-loss all-dielectric metamaterials, and for Dyakonov surface wave-based subwavelength optical confinement and guiding at interfaces with isotropic media. In this context, we investigate the optical properties of one such uniaxial platform, namely self-organized titania nanotube arrays (TNTAs) grown by the bottom-up nanofabrication process of electrochemical anodization on silicon wafer substrates, and subsequently annealed at different temperatures, i.e. 500 °C and 750 °C. We performed detailed quantitative analysis of the structure of the TNTAs using x-ray diffraction and Raman spectroscopy, which revealed a measurable phonon confinement in TNTAs annealed at 500 °C. Variable angle spectroscopic ellipsometry was used to investigate the optical anisotropy in two kinds of TNTAs-those constituted by anatase-phase and those containing a mixture of anatase and rutile phases. Both kinds of TNTAs were found to have positive birefringence (Δn) exceeding 0.06 in the spectral region of interest while mixed phase TNTAs exhibited Δn as high as 0.15. The experimentally measured anisotropy in the refractive index of the TNTAs was compared with the predictions of two different effective medium approximations incorporating the uniaxial geometry. The measured value of Δn for TNTAs exceeded that of bulk anatase single crystals, indicating the potential of nanostructured dielectrics to outperform dielectric crystals of the same material with respect to the magnitude of the achievable directional refractive index contrast.

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Section: Introductionmentioning

confidence: 99%

Optical anisotropy in vertically oriented TiO₂nanotube arrays

et al. 2017

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“…9 Some top-down nanofabrication methods such as electrochemical anodisation are considered good alternative approaches to overcome the inherent drawbacks of traditional microfabrication by enabling the in-depth engineering of a broad range of photonic crystal structures, including optical mirrors, Fabry-Perót interferometers, resonators, bandpass filters, microcavities, distributed Bragg reflectors, rugate filters and so on. [10][11][12][13][14][15][16][17][18][19][20][21][22][23] Among the different materials produced by electrochemical anodisation, nanoporous anodic alumina (NAA) produced by anodisation of aluminium foils has recently gained reinvigorated attention as a platform to develop photonic crystal structures due to its advantageous properties: industrial scalability, cost competitiveness, well established fabrication processes, controllable and versatile nanoporous structure, thermal stability, chemical resistance, mechanical robustness, and optical properties. [24][25][26][27] The effective medium of NAA can be engineered in depth with precision during anodisation in order to produce photonic crystal structures of high aspect ratio with features of precise regularity and optimal resolution to diffract electromagnetic waves within the UV-visible-NIR spectrum.…”

Section: Introductionmentioning

confidence: 99%

Fine tuning of optical signals in nanoporous anodic alumina photonic crystals by apodized sinusoidal pulse anodisation

et al. 2016

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In this study, we present an advanced nanofabrication approach to produce gradient-index photonic crystal structures based on nanoporous anodic alumina. An apodization strategy is for the first time applied to a sinusoidal pulse anodisation process in order to engineer the photonic stop band of nanoporous anodic alumina (NAA) in depth. Four apodization functions are explored, including linear positive, linear negative, logarithmic positive and logarithmic negative, with the aim of finely tuning the characteristic photonic stop band of these photonic crystal structures. We systematically analyse the effect of the amplitude difference (from 0.105 to 0.840 mA cm), the pore widening time (from 0 to 6 min), the anodisation period (from 650 to 950 s) and the anodisation time (from 15 to 30 h) on the quality and the position of the characteristic photonic stop band and the interferometric colour of these photonic crystal structures using the aforementioned apodization functions. Our results reveal that a logarithmic negative apodisation function is the most optimal approach to obtain unprecedented well-resolved and narrow photonic stop bands across the UV-visible-NIR spectrum of NAA-based gradient-index photonic crystals. Our study establishes a fully comprehensive rationale towards the development of unique NAA-based photonic crystal structures with finely engineered optical properties for advanced photonic devices such as ultra-sensitive optical sensors, selective optical filters and all-optical platforms for quantum computing.

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“…The exact morphology, structure, and organization degree of such TiO 2 “scaffolds” as well as their processing methodologiesthat may involve soft (block-polymer templating) and hard (solid spheres assembly) lithographic approaches, nanoimprinting processes, ,, anodization treatments, etc.have been further discussed as these crucially influence both optical and electronic properties of the PSCs. ,, In comparison with unstructured mesoporous layers consisting of randomly packed spherical TiO 2 nanoparticles, one- (1D), two- (2D), and three-dimensional (3D) photonically structured layers specifically allow not only for increased and more organized porosity, achieving more controlled perovskite infiltration, but also for improved carrier transportation and recombination behavior.…”

Section: Introductionmentioning

confidence: 99%

Photonic Structuration of Hybrid Inverse-Opal TiO₂—Perovskite Layers for Enhanced Light Absorption in Solar Cells

Maho

Lobet

Daem

et al. 2021

ACS Appl. Energy Mater.

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Photonic structuration is an efficient way to improve light harvesting in multiple optoelectronic applications. In this study, photonically structured TiO2 is considered as a photoanode layer for perovskite solar cells to enhance light absorption through the excitation of quasi-guided modes within the photoactive perovskite material, while optimizing the charge collection in the photovoltaic assembly and therefore its global efficiency. Practically, polystyrene beads of various diameters are used as hard templating sacrificial agents for the design of inverse-opal TiO2 through spin-coating protocols. The positive impact of the porous photonic structuration in comparison with compact, unstructured photoactive layers is demonstrated. An optimum of light absorption is shown for hybrid TiO2–perovskite structures composed of ∼400 nm diameter TiO2 hollow spheres filled with CH3NH3PbI3, confirming recent numerical predictions. However, electronic-related countereffects are observed in consecutively assembled solar cells when pore dimensions exceed the estimated diffusion length of electrons in the infiltrated perovskite material. Upper conversion efficiency is obtained with solar cells composed of ∼220 nm diameter large TiO2 pores filled with CH3NH3PbI3.

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Two-dimensional photonic crystals based on anodic porous TiO₂ with ideally ordered hole arrangement

Cited by 8 publications

References 23 publications

Optical anisotropy in vertically oriented TiO₂nanotube arrays

Optical anisotropy in vertically oriented TiO₂nanotube arrays

Fine tuning of optical signals in nanoporous anodic alumina photonic crystals by apodized sinusoidal pulse anodisation

Photonic Structuration of Hybrid Inverse-Opal TiO₂—Perovskite Layers for Enhanced Light Absorption in Solar Cells

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Two-dimensional photonic crystals based on anodic porous TiO2 with ideally ordered hole arrangement

Cited by 8 publications

References 23 publications

Optical anisotropy in vertically oriented TiO2nanotube arrays

Optical anisotropy in vertically oriented TiO2nanotube arrays

Fine tuning of optical signals in nanoporous anodic alumina photonic crystals by apodized sinusoidal pulse anodisation

Photonic Structuration of Hybrid Inverse-Opal TiO2—Perovskite Layers for Enhanced Light Absorption in Solar Cells

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Two-dimensional photonic crystals based on anodic porous TiO₂ with ideally ordered hole arrangement

Optical anisotropy in vertically oriented TiO₂nanotube arrays

Optical anisotropy in vertically oriented TiO₂nanotube arrays

Photonic Structuration of Hybrid Inverse-Opal TiO₂—Perovskite Layers for Enhanced Light Absorption in Solar Cells