Search

An anodic porous alumina mold with tapered pores, which can be used to form moth-eye structures, was formed by repetitions of anodization and etching. It was shown that the controllability of the pore shape of the anodic porous alumina mold improved with the number of repetitions of anodization and etching. However, it was found that even when the total anodization time or anodic charge (electrical current × time) was kept constant, the thickness of anodic films was not constant because the total etching time varied. This is because the etching of the anodic porous alumina mold not only increases the pore size but also reduces the thickness of the barrier layer so that pore growth proceeds after the barrier layer is re-formed during re-anodization. Therefore, it was found that if anodization is performed with the additional anodic charge required to re-form the barrier layer, anodic porous alumina mold with tapered pores and uniform film thickness can be produced even if the etching time is varied. Nanoimprinting using the resulting anodic porous alumina mold was shown to form a moth-eye structure with a reflectance of less than 0.1% over the entire visible light range

Establishing a process to fabricate anodic porous alumina with an ordered array of uniform-sized pores on a substrate is an important challenge of fabricating various functional devices. In this study, ordered anodic porous alumina was fabricated on glass substrates by a stamping process using a flexible stamp. This process enables the formation of a resist mask at a low pressure on the sample surface to pattern the starting point for pore generation during anodization. Therefore, it is possible to pattern samples without breaking the glass substrate, and subsequent anodization can generate ordered anodic porous alumina on the substrate. The stamping process using flexible stamps can be applied regardless of the roughness of the Al film on a substrate because the stamp deforms according to the Al surface shape, even when there is a protruding structure on the Al surface. In addition, it was shown that this process could be used to form ordered anodic porous alumina even on Al surfaces with three-dimensional curvatures, such as convex lenses.

A surface with a simple nanopillar array and hierarchical micro-/nano structures consisting of microconvexes and a surface with a nanopillar array were fabricated by nanoimprinting using two types of anodic porous alumina mold. On both surfaces, the height of polymer nanopillars could be controlled by adjusting the anodization time for the preparation of the anodic porous alumina mold. Regarding water-repellent properties, a higher contact angle was observed on the surface with a hierarchical structure than on the surface with a simple nanopillar array. In the measurement of the water droplet sliding angle, the surface with a hierarchical structure showed higher performance characteristics than the surface with a simple nanopillar array. This is because the surface with a hierarchical structure can more easily trap air between the substrate surface and the water droplet than the surface with a simple nanopillar array. The hierarchical micro-/nano structures could be prepared repeatedly by nanoimprinting using a single mold. The method developed here for preparing a superhydrophobic surface is used for various applications, such as those requiring superhydrophobic surfaces with sliding angles.

Electrodeposition and electrodissolution of Li metal in an anodic porous alumina that has an ideal hole array structure were demonstrated. Electrodeposition and electrodissolution of Li metal in the hole array structures could be repeatedly carried out without any formation of dendritic Li. Although the hole diameter of the anodic porous alumina was reduced from the micrometer to nanometer scale, deposition and dissolution of Li metal could be stably conducted. The present process is expected to be applicable to the fabrication of a safe rechargeable Li-metal battery.

Ordered anodic porous WO3 was prepared by the anodization of a W substrate with a depression pattern under a constant voltage of 18 V in concentrated phosphoric acid at 120 °C. However, the behavior of hole formation induced in depressions was found to be strongly affected by the depth and diameter of the depressions. Multiple holes were formed in a shallow depression during the initial stage of anodization, whereas only one hole was formed in a deep depression. In addition, when the depression diameter was small, the growth of fine holes around the induced holes was observed. Since the fine holes formed on the surface of anodic porous WO3 prevented the induced holes from growing in the depth direction, the formation of large-diameter depressions allowed the induced holes to grow deeper. The obtained ordered anodic porous WO3 can be used for various applications such as in photocatalysis and electrochromic devices.

A nanohole array structure with a regular array of cylindrical holes of a high aspect ratio with a period of 63 nm can be obtained by anodizing 304 stainless steel with a concave pattern. It was shown that matching the concave period to the anodization voltage is important to achieving the fabrication of nanohole arrays with a high aspect ratio. This is because the interhole distance of anodic porous oxide obtained by the anodization of 304 stainless steel in ethylene glycol containing 0.1 M ammonium fluoride depends on the anodization voltage. By optimizing the fabrication conditions, it was possible to fabricate highly ordered nanohole arrays with aspect ratios exceeding 100. The nanohole arrays obtained in this study are promising as key materials for fabricating various functional devices.

Ideally ordered anodic porous alumina with controlled interpore distances was formed by fabricating a resist mask using a flexible mold and subsequent anodization. Prior to forming the resist pattern on the surface of an Al substrate, Al was pre-anodized at 10 V to prepare the fine porous structure, which acts as a resist adhesive layer. After the formation of the resist mask using a flexible mold, an arranged array of cavities with Al exposed at the bottom was formed by the selective dissolution of the oxide layer at resist openings. The subsequent anodization of the sample with the cavity array generated ideally ordered anodic porous alumina because alumina holes were formed at the bottom of cavities during anodization. This process allows the preparation of ideally ordered anodic porous alumina even on a curved Al surface owing to the flexibility of the mold. In addition, this process can also be applied to the preparation of an ideally ordered anodic porous alumina with a large sample area because the Al substrate can be patterned without high pressure. The obtained sample can be used for various applications requiring an ideally ordered hole array structure.

Geometrically controlled Li nanohole arrays with high aspect features were fabricated by a two-step replication process using ordered anodic porous alumina as a template. The use of an appropriate electrolyte for Li electrodeposition and organic solvent for the removal of the polymer (PMMA) template allowed the preparation of Li nanohole arrays with precisely replicated nanostructures. The application of a template with the structures for the electrodeposition of Li contributed to the suppression of the formation of Li dendrites, contributing to the precise replication.

Anodic porous alumina, which is a typical self-ordered nanohole array material formed by anodization of Al in an appropriate acid solution, has recently attracted increasing interest as a key material for the fabrication of functional devices1,2). For the various applications of ordered anodic porous alumina, the preparation of through-hole membranes is important. The fabrication process for porous alumina through-hole membranes has been investigated for a long time3). However, a facile and reliable process that does not require special techniques has not yet been established. To overcome this problem, we have been developing a new high-throughput process for fabricating through-hole alumina membranes4). This process is based on the new finding that through-hole membranes can be easily obtained by dissolving a two-layered sample in an appropriate etchant, which was formed by a first anodization under standard anodizing conditions and a subsequent anodization in concentrated H2SO4. This is because the oxide layer formed in the concentrated H2SO4 can be easily dissolved in an appropriate etchant. After the detachment of the membrane, the residual Al substrate could be repeatedly used for the preparation of ordered through-hole membranes. In this report, recent results of the preparation of ordered anodic porous alumina through-hole membranes and its applications will be presented. References 1) T. Yanagishita and T. Hidaka, M. Suzuki, and H. Masuda, J. Vac. Sci. Technol. B, 34, 021804 (2016). 2) H. Masuda and K. Fukuda, Science, 268, 1466 (1995). 3) H. Masuda and M. Satoh, Hpn. J. Appl/ Phys., 35, L126 (1996). 4) T. Yanagishita and H. Masuda, Electrochim. Acta, 184, 80 (2015).

We investigated the dependence of the solubility of the oxide layer formed by anodization of Al on the concentration of sulfuric acid. As a result, it was found that the solubility of anodic porous alumina formed in sulfuric acid electrolyte could be controlled by adjusting the concentration of sulfuric acid. On the basis of these results, highly ordered alumina through-hole membranes with reduced hole intervals, 30–50 nm, were formed by two-layer anodization, where one of the oxide layers was selectively dissolved in accordance with the concentration of sulfuric acid used for anodization in the postetching treatment. The obtained ordered alumina through-hole membranes with reduced hole intervals are expected to be applied to various functional devices requiring a highly ordered through-hole array of reduced size.

Ordered anodic porous alumina through-hole membranes with a hole period larger than 500 nm were fabricated by two-layer anodization. Formation of the ordered anodic porous alumina with a hole period larger than 500 nm was carried out by anodization of Al in phosphoric acid or mixture of malic acid and phosphoric acid. Two-layered structures comprising porous alumina layers with different solubilities were formed by anodization using two electrolytes, one of which was 17.6 M sulfuric acid. The membranes were prepared by selectively etching the lower part of the alumina layer formed in 17.6 M sulfuric acid. The thickness of the membranes was controlled by adjusting the anodization time. The obtained membranes are expected to be used in various applications such as filtration membranes.

High-aspect nanostructure, such as a nanohole and a coaxial nanocable, are considered as a powerful candidate for a light waveguide. Especially, a coaxial nanocable can efficiently propagate the incident light because the coaxial nanocable does not have cut-off wavelength as seen in a nanohole. In addition, by reducing the opening size of the coaxial nanocable, the coaxial nanocable can propagate the light to an area less than a wavelength of the incident light beyond the diffraction limit. Therefore, the coaxial nanocable is expected to be applied to fabricate various types of functional optical devices, such as nanoimaging device and high-density optical recording device. However, it is still difficult to fabricate the high-aspect nanostructure with complicated geometrical features such as the coaxial nanocable because of fabrication difficulties. Until now, our group had been reported fabrication process of the high-aspect metal nanostructures using an anodic porous alumina and its optical property [1-3]. Anodic porous alumina has an ordered array of straight nanoholes having high aspect ratio. Due to this unique geometrical character, anodic porous alumina is commonly used as a starting material to fabricate nanostructures having high aspect feature. In our previous work, we reported fabrication of the coaxial nanocables having high aspect ratio using anodic porous alumna [3]. In addition, it was observed that the coaxial nanocable could efficiently propagate the visible light. In the present work, with the aim of improving the performance of the functional devices based on the coaxial nanocable, reduction of opening size of the coaxial nanocable and evaluation of the optical property were demonstrated. This fabrication process is expected to be applied to fabricate various types of functional optical devices requiring the fine coaxial nanocable. K. Nishio, M. Nakao, A. Yokoo, H. Masuda, Jpn. J. Appl. Phys., 42, L83 (2003). T. Kondo, N. Kitagishi, T. Yanagishita, H. Masuda, Appl. Phys. Express, 8, 06200 (2015). T. Kondo, R. Ichinose, M. Kurosawa, T. Yanagishita, H. Masuda, The 87th ECSJ Spring Meeting, 1C06 (2020).

Ordered through-hole membranes, which have a unique geometrical structure composed of hexagonally arranged array of straight holes with uniform diameters, have attracted growing interest owing to its various applications such as filtration membranes, sensors, and templates. Anodization process of metals is an effective method for the preparation of ordered hole array structures of metal oxides. One advantageous point of this process is controllability of the geometrical structures of the obtained porous oxides based on the anodization conditions [1]. In addition, the naturally occurring self-ordered ordered nanoporous structures can be obtained under the appropriate anodization conditions. In our previous work, we reported a high-throughput process for the preparation of ordered alumina through-hole membranes by two-layer anodization using concentrated sulfuric acid [2-4]. In this process, the second highly soluble alumina layer is formed under the first porous alumina layer by the anodization of samples in concentrated sulfuric acid. The porous alumina through-hole membrane can be obtained by selective dissolution of the second alumina layer formed in concentrated sulfuric acid. This process allows repeated preparation of ordered through-hole membranes from a single metal substrate by repetition of the process. Based on this process, ordered TiO2 through-hole membranes were also obtained using an electrolyte containing fluoride ions[5]. The hole period of the obtained TiO2 membranes could be controlled by changing the anodizing voltage. In the present report, preparation of various types of metal oxide through-hole membranes will be presented. For example, the preparation of ideally ordered TiO2 through-hole membranes by the combination process of two-layer anodization and pretexturing of Ti was described. H. Masuda and K. Fukuda, Science, 268, 1466 (1995). T. Yanagishita and H. Masuda, Electrochim. Acta, 184, 80 (2015). T. Yanagishita, A. Kato, T. Kondo, and H. Masuda, Jpn. J. Appl. Phys., 56, 035202 (2017). T. Yanagihsita, A. Kato, T. Kondo, and H. Masuda, Jpn. J. Appl. Phys., 59, 038002 (2020). T. Yanagishita, H. Inada, T. Kondo, N. T. Nguyen, P. Schmuki, and H. Masuda, J. Electrochem. Soc., 165, E763 (2018).

Moth-eye structures composed of an ordered array of tapered pillars have attracted increasing interest owing to their application such as displays, lenses and solar cells. A large number of methods have been reported for the preparation of moth-eye structures. Among them, nanoimprinting is a promising method for the high-throughput preparation of moth-eye structures with large sample areas. In our previous works, we have reported that an ordered anodic porous alumina can be used for a nanoimprinting mold to prepare seamless moth-eye surfaces with large sample areas [1,2]. In this process, the moth-eye structures with optimized antireflection properties was obtained by adjusting the preparation conditions of porous alumina molds. One problem currently limiting the practical use of moth-eye structures is their low durability. This problem originates from the fine, high-aspect geometrical features of moth-eye structures. Improved durability is essential for practical application of moth-eye structures as antireflection surfaces. In the present report, we describe the preparation of renewable antireflection surfaces by nanoimprinting using an anodic porous alumina mold. Renewable antireflection surfaces were formed by the lamination of polymer thin films with moth-eye structured surfaces [3]. Thin-film lamination was performed using a photocurable monomer as an adhesive. A renewed low-reflectance moth-eye structured surface could be exposed by peeling the uppermost film from the sample. Each exposed surface with moth-eye structure successfully lowered the reflection of incident light. The obtained renewable antireflection surfaces are expected to be applicable to several types of optical devices requiring high durability, such as the surface panels of displays. T. Yanagishita, K. Nishio, and H. Masuda, Appl. Phys. Express, 2, 022001 (2009). T. Yanagishita, T. Hidaka, M. Suzuki, and Hideki Masuda, J. Vac. Sci. Technol. B, 34, 021804 (2016). T. Yanagishita, T. Kondo, and H. Masuda, J. Vac. Sci. Technol. B, 36, 031802 (2018).

The semiconductor materials with naturally occurring self-ordered nanostructures have attracted growing interest for the preparation of functional nanodevices for energy conversion.1 To obtain the nanodevices with optimized performance, control of the geometrical structure of semiconductors is essential. For example, the fabrication of highly ordered structures of semiconductors contributes to the efficient absorption of the incident light and also enhance the charge separation in the interfaces. Anodization process of metals is an effective method for the preparation of ordered hole array structures of metal oxides. One advantageous point of this process is controllability of the geometrical structures of the obtained porous structures based on the anodization conditions.2 In addition, the naturally occurring self-ordered ordered nanoporous structures can be obtained under the appropriate anodization conditions. In our previous reports, we described that ordered nanothrough-hole membranes can also be obtained effectively by two-layer anodization process.3,4 This process allows repeated preparation of ordered through-hole membranes from a single metal substrate by repetition of the process. As an application to semiconductor through-hole membranes, ordered TiO2 through-hole membranes were obtained by two-layer anodization using an electrolyte containing fluoride ions.5 The hole period of the obtained TiO2 membranes could be controlled by changing the anodizing voltage. In the present report, preparation of various types of semiconductor through-hole membranes will be presented. For example, the preparation of ideally ordered TiO2 through-hole membranes by the combination process of two-layer anodization and pretexturing of Ti was described. The obtained TiO2 through-hole membranes with controlled geometrical structures will be applied to various types of energy conversion devices. 1. P. Roy, S. Berger, P. Schmuki, Angew. Chem. Int. Ed., 50, 2904 (2011). 2. H. Masuda and K. Fukuda, Science, 268, 1466 (1995). 3. T. Yanagishita and H. Masuda, Electrochim. Acta, 184, 80 (2015). 4. T. Yanagishita, A. Kato, T. Kondo, and H. Masuda, Jpn. J. Appl. Phys., 56, 035202 (2017). 5. T. Yanagishita, H. Inada, T. Kondo, N. T. Nguyen, P. Schmuki, and H. Masuda, J. Electrochem. Soc., 165, E763 (2018).

For the preparation of functional nanodevices for efficient energy conversion, the use of the naturally occurring self-ordered structures is considered an effective process due to its capability of formation of precisely controlled fine nanostructures. To optimize the performance of the obtained devices, fabrication of precisely controlled geometrical structures of metals and semiconductors is essential. For example, the fabrication of highly ordered structures of metal and semiconductors contributes to the efficient absorption of the incident light and also enhance the charge separation in the interfaces. The anodization processes of metals have been widely applied to the fabrication of nanostructures of metal oxides. One advantageous point of this process is controllability of the geometrical structures of the obtained porous structures based on the anodization conditions. In addition, the ordered nanoporous structures can be obtained under the appropriate anodization conditions. In the present report, recent results concerning the preparation of nanoporous semiconductors with controlled geometrical structures and its applications are described. As a typical example, naturally ordered processes1 or pretexturing process2were applied to the preparation of nanoporous TiO2 with controlled geometrical structures. In addition, a high through-put process for the preparation of the through-hole membrane of TiO2 was also described. This process is based on the two-layer anodization used for the preparation of porous alumina through hole membranes3. The tow-layer anodization, which generates TiO2 layers with different solubility, and subsequent selective dissolution generate the through hole membrane of TiO2 4. Repetition of the process allows the high-throughput preparation of the ordered TiO2 through hole membranes. In addition to the self-ordered TiO2, preparation of the ideally ordered TiO2 through hole membranes is demonstrated. The obtained TiO2 through-hole membranes with controlled geometrical structures will be applied to various types of energy conversion devices. P. Roy, S. Berger, P. Schmuki, Angew. Chem. Int. Ed., 50, 2904 (2011). T. Kondo, S. Nagao, T. Yanagishita, N. T. Nguyen, K. Lee, P. Schmuki, H. Masuda, Electrochem. Commun., 50, 73 (2014). T. Yanagishita and H. Masuda, Electrochim. Acta, 184, 80 (2015). T. Yanagishita, H. Inada, T. Kondo, N. T. Nguyen, P. Schmuki, and H. Masuda, J. Electrochem. Soc., 165, E763 (2018).

An anodic porous alumina with precisely controlled size and depth of holes was prepared and used for nanoimprinting of a polymer. As a typical application of nanoimprinting, antireflection (AR) structures of polymer were prepared. The obtained AR structure with optimized geometrical structures exhibited a low reflectance of less than 0.2 %. The present process allows the high throughput production of polymer AR structures with large sizes.

Nanoporous Si particles were fabricated by the electrochemical etching of closely packed Si particles in an electrolyte containing HF. The geometrical structures of the obtained porous layers on the surface of the particles could be controlled by adjusting the preparation conditions. The process reported here is effective for the high-throughput preparation of nanoporous Si particles with controlled geometrical structures.

Efficient synthesis of the ordered nanostructures of semiconductors is important issue to be solved for the preparation of the photo-energy conversion systems with high efficiency [1]. For the effective preparation of the ordered nanostructures of semiconductors, the use of the naturally occurring ordered nanomaterials is promising for the synthesis due to its capability of the preparation of ordered nanostructures with high efficiency. Among them, anodic porous alumina, which is formed by anodization of Al in acidic electrolyte, is one of promising material due to ist precisely controllable geometrical nanostructures [2]. In the present report, the synthesis of the ordered nanostructures of semiconductors using anodic porous alumina templates will be described. The template synthesis using highly ordered anodic porous alumina allows the preparation of ordered nanostructures of the semiconductors. In addition, the application of the highly ordered anodic porous alumina with reduced hole intervals (~25 nm) and hole sizes (~10 nm) prepared under the low voltage anodization [3] generated the ordered structures of semiconductors with small dimensions. In the experiment, semiconductor (ZnO [4,5], CdS) nanorod arrays were prepared by electrochemical or hydrothermal synthesis of semiconductors using anodic porous alumina templates. The geometrical structure of the obtained nanorod arrays of semiconductors could be precisely controlled based on the ordered structures of anodic porous alumna. The synthesis of the nanorod arrays on the conducting substrates (ITO etc.) could provide the current collection electrodes with large surface area. The present process will be used for the preparation of nanostructures of semiconductors, which are required for the preparation of various kinds of photoenergy conversion systems with high efficiency, such as organic photovoltaic solar cells [6]. 1. T. Shinagawa, S. Watase, M. Izaki, Cryst. Growth Des., 11, 5533 (2011). 2. H. Masuda and K. Fukuda, Science, 268, 1466 (1995). 3. H. Masuda, K. Takenaka, T. Ishii, K. Nishio, Jpn. J. Appl. Phys., 45, L1165 (2006). 4. M. Izaki, T. Omi, Appl. Phys. Lett., 98, 2439 (1996). 5. T. Özdal, R. Taktakoğlu, H. Özdamar, M. Esen, D. K. Takҫi, H. Kavak, Thin Solid Films, 592, 143 (2015). 6. B. Kippelen, J.-L. Brédas, Energy Environ. Sci., 2, 251 (2009).

The anodic porous alumina, which is formed by anodization of Al in an acidic electrolyte, has attracted much interest as the starting materials for various types of functional nanodevices due to its unique geometrical structures.1) It has been reported that long-range-ordered anodic porous alumina with an ideally ordered hole arrangement can be obtained under appropriate anodization conditions.2-4) Such ordered structures are useful for the preparation of the functional nanodevices, which require the ordered nano- structures. The control of hole intervals and hole sizes of anodic porous alumina while retaining the long-range ordered hole arrangement is very important for expanding the application fields of the anodic porous alumina. As an example of the expansion of the range of the hole intervals and hole sizes with long-range ordered hole arrangement, we have shown the formation of long-range-ordered anodic porous alumina with reduced hole intervals and hole sizes. In this process, highly ordered anodic porous alumina with reduced hole interval of ~25 nm can be obtained by the appropriate anodizing condition5,6). In the present report, the formation of the highly ordered anodic porous alumina with various hole intervals and hole sizes will be presented. In addition, the template synthesis of the ordered nanostructures with reduced dimensions will be also reported. 1. T. Yanagishita, T. Hidaka, M. Suzuki, and H. Masuda, J. Vac. Sci. Technol. B, 34, 021804 (2016). 2. H. Masuda and K. Fukuda, Science, 268, 1466 (1995). 3. H. Masuda, F. Hasegawa, and S. Ono, J. Electrochem. Soc., 144,L127 (1997). 4. H. Masuda, K. Yada, and A. Osaka, Jpn. J. Appl. Phys., 37, L1340 (1998). 5. H. Masuda, M. Nagae, T. Morikawa, and K. Nishio, Jpn. J. Appl. Phys., 45, L406 (2006). 6. H. Masuda, K. Takenaka, T. Ishi, and K. Nishio, Jpn. J. Appl. Phys., 43, L1165 (2006).

The fabrication of ordered semiconductor nanostructures has attracted increasing interest due to its applicability to various functional devices. Among them, the semiconductor nanorods array is one of typical nanostructures available for the functional optical devices including solar cells, and display devices due to its unique physical properties originated from the geometrical structures. Although various fabrication processes for the nanorod arrays have been reported, the efficient fabrication process of the ordered semiconductor nanorods array has not been established so far [1]. In the present report, the formation of the highly ordered semiconductor (ZnO) nanorods array based on anodic porous alumina templates will be presented. The anodic porous alumina, which is formed by anodization of Al in acidic electrolyte, is one of typical self-ordered material with highly ordered hole arrangement [2]. The advantage of this material is its high controllability of the geometrical structures based on the anodizing conditions. Especially, under the appropriate low voltage anodization condition, the highly ordered hole array structures with small hole interval and hole size can be obtained [3]. The hole interval and hole size in this highly ordered porous alumina were typically 25 nm and 10 nm, respectively. In the present work, ZnO nanorods arrays were fabricated through the hydrothermal reaction [4] using the anodic porous alumina as a template for the synthesis. Based on the present process, the highly ordered arrays of ZnO nanorods could be fabricated on the substrates. The geometrical structures of the ZnO nanorods arrays were controlled by changing the structures of the porous alumina templates. The obtained nanostructures will be applied to the fabrication of various kinds of energy conversion devices, which require the highly ordered nanostructures of semiconductors. 1. W. I. Park, D. H. Kim, S.-W. Jung, G.-C. Yi, Appl. Phys. Lett., 80, 4232 (2002). 2. H. Masuda and K. Fukuda, Science, 268, 1466 (1995). 3. H. Masuda, K. Takenaka, T. Ishii, K. Nishio, Jpn. J. Appl. Phys., 45, L1165 (2006). 4. T. Shinagawa, S. Watase, M. Izaki, Cryst. Growth Des., 11, 5533 (2011).

There has been increasing interests in the fabrication process of ordered metal nanostructures due to its applicability to the enhancement of the electric field of the incident light based on the localized surface plasmon resonance (LSPR). Various functional optical devices based on LSPR have been proposed, such as sensing devices, nonlinear optics, photovoltaic cells, and so on. The performance of the optical devices is dependent on the shapes and arrangement of metals because the efficiency of the enhancement of the electric field by LSPR is determined by the geometrical structures of metals. However, the fabrication process of geometrically controlled metal nanostructures with large sample area has not been established so far because of the difficulties in the precise fabrication of nanostructures. We have reported the fabrication of highly ordered metal nanostructures using anodic porous alumina and its application to the functional optical devices based on LSPR [1,2]. Anodic porous alumina, which is formed by anodization of Al in acidic solutions, is a typical self-ordered mesoporous material. The ordered metal nanostructures could be obtained using the anodic porous alumina as a template for the fabrication. One of advantageous points of the process using the anodic porous alumina is the precise controllability of the geometrical structures. In the report, the fabrication of various types of the metal nanostructures and its application to the substrate for the measurements of surface-enhanced Raman scattering (SERS) will be presented. The highly ordered metal nanostructures (dots or wires) were fabricated using anodic porous alumina templates. The obtained structures were applied to the substrates for the SERS measurements. The SERS activity was optimized by controlling the shape and arrangement of the metal nanostructures. The present process can be used not only for the fabrication of the SERS substrates but also for the fabrication of functional optical devices requiring the highly ordered metal nanostructures. [1] T. Kondo, K. Nishio, H. Masuda, Appl. Phys. Express, 6, 102401 (2013). [2] T. Kondo, H. Masuda, K. Nishio, J. Phys. Chem. C, 117, 2531 (2013).

The fabrication of micro - and nanostructured materials with controlled geometrical structures has attracted increasing interest for the preparation of various types of energy conversion devices with high efficiencies. The use of the material, which has naturally occurring ordered structures, is effective for the fabrication of the micro- and nanostructures of various kinds of materials. Anodic porous alumina, which is formed by anodization of Al in acidic solution, is a promising candidate for the fabrication of micro- and nanostructured materials with controlled geometrical structures1,2. One of commonly used process for the fabrication of micro- and nanostructures using anodic porous alumina is a template synthesis3,4. This process can generate the micro- and nanostructures with controlled geometrical structures, which are useful for the fabrication of high efficient energy conversion devices. However, the problem of the usual template synthesis is the low throughput due to the difficulty of the repeated use of the template. To solve this problem, we have been studying the new types of processes, which allow the high throughput formation of micro- and nanostructures. In the present report, recent results concerning the high throughput fabrication process for the micro- and nanostructures of metals and metal oxides, which can be applied to the energy conversion devices. The processes include the molding fabrication process for metal nanowires, and the membrane emulsification for uniform sized nanoparticles of metal oxides5,6 by using anodic porous alumina. These processes allow the high throughput fabrication of micro- and nanostructures because the starting structures of anodic porous alumina can be used many times. The obtained micro- and nanostructures will be useful for the fabrication of energy conversion devices with high efficiency due to their precisely controlled geometrical fine structures. 1. T. Yanagishita, K. Nishio, and H. Masuda, Appl. Phys. Express, 1, 067004 (2008). 2. H. Masuda and K. Fukuda, Science, 268, 1466 (1995). 3. K. Yasui, T. Morikawa, K. Nishio, and H. Masuda, Jpn. J. Appl. Phys., 15, L469 (2005). 4. T. Kondo, T. Fukushima, K. Nishio, and H. Masuda, Appl. Phys. Express, 2, 125001 (2009). 5. T. Yanagishita, R. Fujimura, K. Nishio, and H. Masuda, Langmuir, 26, 1516 (2009). 6. T. Yanagishita, Y. Maejima, K. Nishio, and H. Masuda, RSC Adv., 4, 1538 (2014).

Organic thin film solar cells have attracted much attention as a next generation energy conversion devices due to their unique properties [1-3]. Control of the nanostructures of organic heterojunctions is essential to improve the conversion efficiency of the organic solar cells. In the present report, we describe the fabrication of the organic solar cells with controlled nanostructures and their photovoltaic properties. Fabrication of organic heterojunctions with controlled geometrical nanostructures was carried out by using the substrates with ordered textured patterns of nanometer scale, which were prepared by nanoimprinting using anodic porous alumina molds. Anodic porous alumina, which is formed by anodization of Al in acidic electrolyte, is a typical self-ordered material and is promising candidate for the starting material for making nanostructures [4]. Use of anodic porous alumina as a mold for nanoimprinting allows the high throughput formation of the substrates with ordered nanostructures of polymers [5,6]. The heterojunctions of organic thin layers were formed on the substrates with ITO layer using a vacuum deposition apparatus. The ordered nanostructure of the substrates could be maintained even at the organic layer of heterojunctions. Optical properties of the obtained samples and the photovoltaic properties were examined. In the samples with controlled geometrical structures prepared by the present processes, improvement of conversion efficiencies was confirmed compared to the samples without controlled geometrical structures. This improvement was thought to be caused by the increase of absorption of light at the heterojunctions due to the antireflection effect caused by the periodic nanostructures. The controlled nanostructure of the heterojunction also contributed to the improvement of the conversion efficiency due to the effective charge separation at the junction. The present process, which allows high throughput formation of the organic heterojunctions with controlled geometrical structures, will be used for the formation of organic solar cells with high conversion efficiencies. 1. A. W. Hins, Z. Liang, M. A. Woodhouse, and B. A. Gregg, Chem. Rev., 110, 6689 (2010). 2. C. J. Brabec, S. Gowrisanker, J. J. M. Halls, D. Laird, S. Jia, and S. P. Williams, Adv. Mater., 22, 3839 (2010). 3. T. M. Clark and J. R. Durrant, Chem. Rev., 110, 6736 (2010). 4. H. Masuda and K. Fukuda, Science, 268, 1466 (1995). 5. T. Yanagishita, K. Yasui, T. Kondo, K. Nishio, and H. Masuda, Chem. Lett., 36, 530 (2007). 6. T. Yanagishita, T. Kondo, K. Nishio, and H. Masuda, J. Vac. Sci. Technol. B, 26, 1856 (2008).

not Available.

not Available.

not Available.

not Available.

not Available.

not Available.

not Available.