In nature, tiny amounts of inorganic impurities, such as metals, are incorporated in the protein structures of some biomaterials and lead to unusual mechanical properties of those materials. A desire to produce these biomimicking new materials has stimulated materials scientists, and diverse approaches have been attempted. In contrast, research to improve the mechanical properties of biomaterials themselves by direct metal incorporation into inner protein structures has rarely been tried because of the difficulty of developing a method that can infiltrate metals into biomaterials, resulting in a metal-incorporated protein matrix. We demonstrated that metals can be intentionally infiltrated into inner protein structures of biomaterials through multiple pulsed vapor-phase infiltration performed with equipment conventionally used for atomic layer deposition (ALD). We infiltrated zinc (Zn), titanium (Ti), or aluminum (Al), combined with water from corresponding ALD precursors, into spider dragline silks and observed greatly improved toughness of the resulting silks. The presence of the infiltrated metals such as Al or Ti was verified by energy-dispersive x-ray (EDX) and nuclear magnetic resonance spectra measured inside the treated silks. This result of enhanced toughness of spider silk could potentially serve as a model for a more general approach to enhance the strength and toughness of other biomaterials.

Cu nanoparticle chains encapsulated in Al2O3 nanotubes were successfully generated in a controlled manner by reduction of CuO nanowires embedded in Al2O3 at a sufficiently high temperature. The Al2O3 coating was deposited by atomic layer deposition (ALD). The particles mainly show a rodlike shape and are regularly distributed. The particle diameters and chain lengths corresponding to the inner diameters and lengths of the tubes, respectively, are controlled by the size of the CuO nanowire templates. Rayleigh instability, assisted by the uniform volume shrinkage created by the reduction of oxide to metal, is proposed to induce the formation of the nanochains. This method may potentially be extended to the synthesis of nanochains of other metals by reducing corresponding oxide nanowires embedded in ALD shells.

The present work suggests a mass-producible and large-scale fabrication method of superhydrophobic polymeric surfaces by means of material processing equipments which can maximize productivity and cost effectiveness. We fabricated two types of polymeric lotus leaf replicas using a nickel mold, i.e. R1 from intrinsically hydrophobic polydimethylsiloxane by means of polymer casting (PC) and R2 from an intrinsically hydrophilic UV-curable photopolymer by means of UV-nanoimprint lithography (UV-NIL). In the case of R1 from PC, although the nano-scaled structures were not well reproduced, the contact angle (CA) was remarkably high and the sliding angle (SA) was also close to that of the original lotus leaf, resulting in a superhydrophobic surface. In contrast to R1, in the case of R2 from UV-NIL, the nano-scaled structures as well as micro-scaled structures were also relatively well reproduced and the CA was increased noticeably by around 99° in comparison to a flat photopolymer. However, unexpectedly, the SA of R2 was much higher than that of R1. This work provides useful tips of polymeric material selection for the industrial mass production of the superhydrophobic polymer surface.

The stretchability of CVD graphene with a large area is much lower than that of mechanically exfoliated pristine graphene owing to the intrinsic and extrinsic defects induced during its synthesis, etch-out of the catalytic metal, and the transfer processes. This low stretchability is the main obstacle for commercial application of CVD graphene in the field of flexible and stretchable electronics. In this study, artificially layered CVD graphene is suggested as a promising candidate for a stretchable transparent electrode. In contrast to single-layer graphene (SLG), multi-layer graphene has excellent electromechanical stretchability owing to the strain relaxation facilitated by sliding among the graphene layers. Macroscopic and microscopic electromechanical tensile tests were performed to understand the key mechanism for the improved stretchability, and crack generation and evolution were systematically investigated for their dependence on the number of CVD graphene layers during tensile deformation using lateral force microscopy. The stretchability of double-layer graphene (DLG) is much larger than that of SLG and is similar to that of triple-layer graphene (TLG). Considering the transmittance and the cost of transfer, DLG can be regarded as a suitable candidate for stretchable transparent electrodes.

A few percent of transition metals impregnated inside some biological organisms in nature remarkably improve such organisms' mechanical stability. Although the lure to emulate them for development of new biomimetic structural materials has been great, the practical advances have been rare because of the lack of proper synthetic approaches. Multiple pulsed vapor phase infiltration proved successful for the preparation of such transition metal impregnated materials with highly improved mechanical stability. The artificially infiltrated metals (Al, Ti, or Zn) from gas phase lead to around 3 times increase of toughness (in terms of breaking energy) of natural collagen in a dried state. In addition, the infiltrated metals apparently induce considerable crystallographic changes in the natural collagen structures. This infiltration approach can be used as guide for the synthesis of bioinspired structural materials related to metal infiltration.

Carbothermic reduction in the chemistry of metal extraction (MO(s) + C(s) → M(s) + CO(g)) using carbon as a sacrificial agent has been used to smelt metals from diverse oxide ores since ancient times. Here, we paid attention to another aspect of the carbothermic reduction to prepare an activated carbon textile for high-rate-performance supercapacitors. On the basis of thermodynamic reducibility of metal oxides reported by Ellingham, we employed not carbon, but metal oxide as a sacrificial agent in order to prepare an activated carbon textile. We conformally coated ZnO on a bare cotton textile using atomic layer deposition, followed by pyrolysis at high temperature (C(s) + ZnO(s) → C'(s) + Zn(g) + CO(g)). We figured out that it leads to concurrent carbonization and activation in a chemical as well as mechanical way. Particularly, the combined effects of mechanical buckling and fracture that occurred between ZnO and cotton turned out to play an important role in carbonizing and activating the cotton textile, thereby significantly increasing surface area (nearly 10 times) compared with the cotton textile prepared without ZnO. The carbon textiles prepared by carbothermic reduction showed impressive combination properties of high power and energy densities (over 20-fold increase) together with high cyclic stability.

Many plant leaves found in nature are known to exhibit a characteristic of superhydrophobicity (‘lotus leaf effect’). The present study proposes a mass-production method of highly hydrophobic surfaces by simply replicating the highly hydrophobic plant leaf surfaces in two steps: the first step of making a nickel mould via electroforming and the second step of replication via a UV-nanoimprint lithography. Making a nickel mould, either a plant leaf or its negative polymer replica is used as a mandrel in electroforming, and final products become positive or negative polymer replicas of a plant leaf, respectively. It is found that the nickel-mould making using the plant leaf as a mandrel is quite successful and the final products in the form of a positive replica are better than those in the form of a negative replica in terms of replication quality and hydrophobicity. Contact angle values of the positive replicas are less than those of the natural leaves’ surfaces by only 2°–5°.

The concept of 3D photonic intermediate reflectors for micromorph silicon tandem solar cells has been investigated. In thin‐film silicon tandem solar cells consisting of amorphous and microcrystalline silicon with two junctions of a‐Si/μc‐Si, efficiency enhancements can be achieved by increasing the current density in the a‐Si top cell. It is one goal to provide an optimized current matching at high current densities. For an ideal photon‐management between top and bottom cell, a spectrally selective intermediate reflective layer (IRL) is necessary, which is less dependent of the angle of incidence than state‐of‐the‐art thickness dependent massive interlayers. The design, preparation and characterization of a 3D photonic thin‐film filter device for this purpose has been pursued straight forward in simulation and experimental realization. The inverted opal is capable of providing a suitable optical band stop with high reflectance and the necessary long wavelength transmittance as well and provides further options for improved light trapping. We have determined numerically the relative efficiency enhancement of an a‐Si/μc‐Si tandem solar cell using a conductive 3D‐photonic crystal. We have further fabricated such structures by ZnO‐replication of polymeric opals using chemical vapour deposition and atomic layer deposition techniques and present the results of their characterization. Thin film photonic IRL have been prepared at the rear side of a‐Si solar cells. Completed with a back contact, this is the first step to integrate this novel technology into an a‐Si/μc‐Si tandem solar cell process. The spectral response of the cell is presented and compared with reference cells. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)