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In Situ Raman Spectroscopic Study of Al-Infiltrated Spider Dragline Silk under Tensile Deformation
Lee, Seung-Mo,Pippel, Eckhard,Moutanabbir, Oussama,Kim, Jae-Hyun,Lee, Hak-Joo,Knez, Mato American Chemical Society 2014 ACS APPLIED MATERIALS & INTERFACES Vol.6 No.19
<P>Natural materials consisting of protein structures impregnated with a tiny amount of metals often exhibit impressive mechanical behavior, which represents a new design paradigm for the development of biomimetic materials. Here, we produced Al-infiltrated silks by applying a modified Al2O3 atomic layer deposition process to the dragline silk of the Nephila pilipes spider, which showed unusual mechanical properties. The deformation behavior of the molecular structure of the Al-infiltrated silk was investigated by performing in situ Raman spectroscopy, where Raman shifts were measured concurrently with macroscopic mechanical deformations. For identifying the role of the infiltrated Al atoms, the study was performed in parallel with untreated silk, and the results were compared. Our experimental results revealed that superior mechanical properties of the Al-infiltrated silk are likely to be caused by the alterations of the sizes of the beta-sheet crystals and their distribution.</P>
Tailor-Made Inorganic Nanopeapods: Structural Design of Linear Noble Metal Nanoparticle Chains
Liu, Lifeng,Lee, Woo,Scholz, Roland,Pippel, Eckhard,Gö,sele, Ulrich WILEY-VCH Verlag 2008 Angewandte Chemie Vol.47 No.37
<B>Graphic Abstract</B> <P>Pt@CoAl<SUB>2</SUB>O<SUB>4</SUB> inorganic nanopeapods (see picture) consisting of well-defined Pt nanoparticle chains embedded in CoAl<SUB>2</SUB>O<SUB>4</SUB> are synthesized by the pulsed electrodeposition of Co/Pt multilayered nanowires into an anodic aluminum oxide (AAO) membrane and a subsequent high-temperature solid-state reaction between Co/Pt nanowires and AAO. The pulse durations for Pt and Co depositions control the size and separation of Pt nanoparticles. <img src='wiley_img/14337851-2008-47-37-ANIE200801931-content.gif' alt='wiley_img/14337851-2008-47-37-ANIE200801931-content'> </P>
Dislocations as native nanostructures - electronic properties
Reiche, Manfred,Kittler, Martin,Uebensee, Hartmut,Pippel, Eckhard,Hopfe, Sigrid Techno-Press 2014 Advances in nano research Vol.2 No.1
Dislocations are basic crystal defects and represent one-dimensional native nanostructures embedded in a perfect crystalline matrix. Their structure is predefined by crystal symmetry. Two-dimensional, self-organized arrays of such nanostructures are realized reproducibly using specific preparation conditions (semiconductor wafer direct bonding). This technique allows separating dislocations up to a few hundred nanometers which enables electrical measurements of only a few, or, in the ideal case, of an individual dislocation. Electrical properties of dislocations in silicon were measured using MOSFETs as test structures. It is shown that an increase of the drain current results for nMOSFETs which is caused by a high concentration of electrons on dislocations in p-type material. The number of electrons on a dislocation is estimated from device simulations. This leads to the conclusion that metallic-like conduction exists along dislocations in this material caused by a one-dimensional carrier confinement. On the other hand, measurements of pMOSFETs prepared in n-type silicon proved the dominant transport of holes along dislocations. The experimentally measured increase of the drain current, however, is here not only caused by an higher hole concentration on these defects but also by an increasing hole mobility along dislocations. All the data proved for the first time the ambipolar behavior of dislocations in silicon. Dislocations in p-type Si form efficient one-dimensional channels for electrons, while dislocations in n-type material cause one-dimensional channels for holes.
Structural engineering of nanoporous anodic aluminium oxide by pulse anodization of aluminium.
Lee, Woo,Schwirn, Kathrin,Steinhart, Martin,Pippel, Eckhard,Scholz, Roland,Gö,sele, Ulrich Nature Pub. Group 2008 Nature nanotechnology Vol.3 No.4
<P>Nanoporous anodic aluminium oxide has traditionally been made in one of two ways: mild anodization or hard anodization. The first method produces self-ordered pore structures, but it is slow and only works for a narrow range of processing conditions; the second method, which is widely used in the aluminium industry, is faster, but it produces films with disordered pore structures. Here we report a novel approach termed 'pulse anodization' that combines the advantages of the mild and hard anodization processes. By designing the pulse sequences it is possible to control both the composition and pore structure of the anodic aluminium oxide films while maintaining high throughput. We use pulse anodization to delaminate a single as-prepared anodic film into a stack of well-defined nanoporous alumina membrane sheets, and also to fabricate novel three-dimensional nanostructures.</P>
Heon Kim, Young,Bhatnagar, Akash,Pippel, Eckhard,Alexe, Marin,Hesse, Dietrich American Institute of Physics 2014 Journal of Applied Physics Vol.115 No.4
Microstructure and electronic structure of highly strained bismuth ferrite (BiFeO3) thin films grown on lanthanum aluminate substrates are studied using high-resolution transmission and scanning transmission electron microscopies and electron energy loss spectroscopy (EELS). Monoclinic and tetragonal phases were observed in films grown at different temperatures, and a mix of both phases was detected in a film grown at intermediate temperature. In this film, a smooth transition of the microstructure was found between the monoclinic and the tetragonal phases. A considerable increase in the c-axis parameters was observed in both phases compared with the rhombohedral bulk phase. The off-center displacement of iron (Fe) ions was increased in the monoclinic phase as compared with the tetragonal phase. EEL spectra show different electronic structures in the monoclinic and the tetragonal phases. These experimental observations are well consistent with the results of theoretical first-principle calculations performed. (C) 2014 AIP Publishing LLC.
Park, Cheolmin,So, Hye-Mi,Jeong, Hyeon Jun,Jeong, Mun Seok,Pippel, Eckhard,Chang, Won Seok,Lee, Seung-Mo American Chemical Society 2014 ACS APPLIED MATERIALS & INTERFACES Vol.6 No.18
<P>Impressive biophotonic functions of flora in Mother Nature are often attributed to the optical diffraction occurring on hierarchically structured surfaces. The petals, displaying vivid colors, have diverse surface structures. The shapes of those structures alter significantly depending on the part of the petal, and they adjust the intensity of the reflected color and the light absorbance. Here, we added semi-conducting properties to those intriguing optical functions arising from the unique surface structures. By means of atomic layer deposition (ALD), we conformally deposited a ZnO layer on the yellow rose petal, which has hierarchical surface structures and exhibits peculiar light absorbance behaviors. The resulting ZnO/petal composites revealed unique optoelectronic characteristics by synergetic effects between the biophotonic structures and inherent semiconducting properties. From several control experiments, we identified that the biophotonic hierarchical structures give rise to strong modulation of the light absorbance. We found that ZnO/petal exhibits superior mechanical stability to the raw petal likely due to the Zn infiltration into the petal. The design inspired by floral creatures with photonic structures and manufactured in the form of composite with mechanical stability and distinctive optoelectronic properties is believed to offer a new paradigm for the preparation of bioinspired photonic devices.</P>
Shin, Ho Sun,Hamdou, Bacel,Reith, Heiko,Osterhage, Hermann,Gooth, Johannes,Damm, Christine,Rellinghaus, Bernd,Pippel, Eckhard,Nielsch, Kornelius The Royal Society of Chemistry 2016 Nanoscale Vol.8 No.28
<P>We systematically investigated the role of topological surface states on thermoelectric transport by varying the surface-to-volume ratio (s/v) of Bi2Se3 nanowires. The thermoelectric coefficients of Bi2Se3 nanowires were significantly influenced by the topological surface states with increasing the s/v. The Seebeck coefficient of Bi2Se3 nanowires decreased with increasing the s/v, while the electrical conductivity increased with increasing the s/v. This implies that the influence of metallic surface states become dominant in thermoelectric transport in thin nanowires, and the s/v is a key parameter which determines the total thermoelectric properties. Our measurements were corroborated by using a two-channel Boltzmann transport model.</P>