Sineurop Nanotech GmbH

Stuttgart, Germany

Sineurop Nanotech GmbH

Stuttgart, Germany

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Ackermann T.,Fraunhofer Institute for Manufacturing Engineering and Automation | Sahakalkan S.,Fraunhofer Institute for Manufacturing Engineering and Automation | Kolaric I.,Fraunhofer Institute for Manufacturing Engineering and Automation | Roth S.,Sineurop Nanotech GmbH
Physica Status Solidi - Rapid Research Letters | Year: 2015

This work addresses the impact of co-percolating carbon nanotubes within a silver nanowire network with regard to the optoelectrical performance as a transparent electrode. We carried out a comprehensive measurement series and focused on ultra-transparent electrodes with optical transmission above 95%. We found an immense improvement of the optoelectrical performance for networks near the percolation threshold of the silver nanowires after carbon nanotubes have been added. We were able to decrease the sheet resistance of the silver nanowire networks by a factor of up to 70 after adding carbon nanotubes. We produced transparent electrodes with industrially acceptable sheet resistance at optical transmission of higher than 97%. This work outlines the potential of co-percolating rod-like conductors as a network for ultra-transparent electrodes. Our experimental work confirms theoretical approaches in percolation theory since we systematically evaluated films with high optical transmission. The most transparent films are beyond the descriptiveness with the percolation scaling law. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Koizhaiganova R.B.,Korea University | Hwang D.H.,Korea University | Lee C.J.,Korea University | Roth S.,Korea University | And 2 more authors.
Physica Status Solidi (B) Basic Research | Year: 2010

We investigated the chemical doping of the single-walled carbon nanotubes (SWCNTs) networks by a treatment with aromatic amines. Adsorption and intercalation of amine molecules in bundled SWCNTs leads to typical n-type doping observed already for alkali metals. The electron donation to SWCNTs is demonstrated by the X-ray-induced photoelectron spectra (XPS), where the carbon C 1s peak observed at 284.4eV for the sp2 carbon in pristine samples is shifted by up to 0.3eV to higher binding energy upon chemical treatment. The development of a Breit-Wigner-Fano component on the lower energy side of the G- mode in the Raman spectrum as well as a shift of the G+ to lower frequency provide evidence for charge accumulation in the nanotube π system, and indication for the n-type doping. The spectroscopic changes are accompanied by the modification of the electrical properties of the SWCNTs. A reduction of conductivity depends on the doping level and implies the decreasing concentration of the charge carriers in the naturally p-doped tubes. Comparing the two selected n-type dopants, the tetramethyl-p-phenylenediamine, shows more pronounced changes in the XPS and the Raman spectra than tetramethylpyrazine, indicating that the sp3 hybridization of nitrogen in the amine groups attached to phenyl ring is much more effective in interaction with the tube π system than the sp2 hybridization of nitrogen in the aromatic pyrazine ring. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Piao M.,Korea University | Na J.,Korea University | Choi J.,Korea University | Kim J.,Korea University | And 5 more authors.
Carbon | Year: 2013

We prepared and characterized flexible thermoelectric (TE) materials based on thin films of single-walled carbon nanotube (SWCNT) composites with polyvinylalcohol. While pristine SWCNTs incorporated in a polymer matrix generated a p-type TE material, chemical functionalization of SWCNTs by using polyethyleneimine produced an n-type TE material. TE modules made of both p- and n-type composite were fabricated to demonstrate TE voltage and power generation. A single p-n junction made of two composite strips containing 20 wt.% of SWCNTs generated a high TE voltage of 92 μV per 1 K temperature gradient (ΔT). By combining five electrically connected p-n junctions an output voltage of 25 mV was obtained upon the applying ΔT = 50 K. Furthermore, this module generated a power of 4.5 nW when a load resistance matched the internal module resistance of 30 kΩ. These promising results show the potential of TE energy conversion provided by the SWCNT composite films connected in scalable modules for applications that require light weight and mechanical flexibility. © 2013 Elsevier Ltd. All rights reserved.


Uddin S.M.,Sineurop Nanotech GmbH | Uddin S.M.,University of Ulm | Mahmud T.,Fraunhofer Institute for Manufacturing Engineering and Automation | Wolf C.,Fraunhofer Institute for Manufacturing Engineering and Automation | And 8 more authors.
Composites Science and Technology | Year: 2010

Utilizing the extra-ordinary properties of carbon nanotube (CNT) in metal matrix composite (MMC) for macroscopic applications is still a big challenge for science and technology. Very few successful attempts have been made for commercial applications due to the difficulties incorporating CNTs in metals with up-scalable processes. CNT reinforced copper and copper alloy (bronze) composites have been fabricated by well-established hot-press sintering method of powder metallurgy. The parameters of CNT-metal powder mixing and hot-press sintering have been optimized and the matrix materials of the mixed powders and composites have been evaluated. However, the effect of shape and size of metal particles as well as selection of carbon nanotubes has significant influence on the mechanical and electrical properties of the composites. The hardness of copper matrix composite has improved up to 47% compared to that of pure copper, while the electrical conductivity of bronze composite has improved up to 20% compared to that of the pure alloy. Thus carbon nanotube can improve the mechanical properties of highly-conductive low-strength copper metals, whereas in low-conductivity high-strength copper alloys the electrical conductivity can be improved. © Elsevier Ltd.


Dettlaff-Weglikowska U.,Korea University | Dettlaff-Weglikowska U.,Sineurop Nanotech GmbH | Yoshida J.,Toyota Motor Corporation | Sato N.,Toyota Motor Corporation | And 2 more authors.
Journal of the Electrochemical Society | Year: 2011

Single-walled carbon nanotubes (SWNTs) and carbon black (CB) were used as conductive additives in lithium-ion batteries. Composites containing nanostructured LiCo O2 and carbon additives were applied as positive electrodes in coin-type electrochemical cells with Li metal as a counter electrode. The conductive SWNTs with their wirelike shape and high aspect ratio are proved to have significant impact on the electrochemical performance of the electrode. The electrode composite containing 0.5 wt % of SWNTs has an internal resistance comparable to that of the 10 wt % of carbon black. Whereas the discharge capacity of the electrode containing 0.5 wt % of CB drops to 0 when increasing the rate to 5C, the capacity of the electrode containing the same weight fraction of SWNTs retains 67% of its initial capacity even at 18C. Cycling performance measured up to 23 cycles demonstrates that the SWNTs at a low concentration are as efficient in the capacity retention as the 10 wt % of carbon black. We interpret the SWNT-induced electrode performance by formation of a flexible, electrically wired network of conducting SWNTs in close contact with LiCo O2 nano-particles, which accelerates the exchange of the Li ions and allows a rapid transfer of electrons throughout the electrode. © 2010 The Electrochemical Society.


Piao M.,Korea University | Kim G.,Korea University | Kennedy G.P.,Korea University | Roth S.,Korea University | And 2 more authors.
Physica Status Solidi (B) Basic Research | Year: 2013

We report on single walled carbon nanotubes (SWCNTs) used as a filler material for polycarbonate (PC) composites in this paper. Thin flexible composite films were prepared by solvent casting with a viscous dispersion of SWCNTs in a polymer matrix. The interaction of SWCNTs with PC was studied by Raman spectroscopy. Our investigations focus on the electrical conductivity and thermopower of the carbon nanotube network formed within the matrix. In this paper, we demonstrate that the incorporation of carbon nanotubes in the polymer composite profoundly modifies the electrical properties of the polymer composite in proportion with the SWCNT concentration. Although, the electrical conductivity of the composite increases by 16 orders of magnitude upon adding 1wt% of SWCNTs, the Seebeck coefficient, which characterizes the thermoelectric properties, appears to be dominated by the type of polymer matrix and decreased slightly throughout the tested filler loading. A reasonable Seebeck coefficient of 65μVK-1 was determined for these SWCNT composite films and, thus, suggests that thermoelectric power generation would be a good application for them. We also demonstrated that both the electrical conductivity and the Seebeck coefficient of SWCNTs embedded in a polymer can be efficiently modified by means of chemical treatments. In this way, flexible composite films exhibiting positive and negative Seebeck coefficients were fabricated. Assembling these films into a sandwich structure with alternating p/n junctions should produce a higher potential difference when a temperature gradient is applied across a multilayer thermoelectric device. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Piao M.,Korea University | Kim G.,Korea University | Kennedy G.P.,Korea University | Roth S.,Sineurop Nanotech GmbH | Dettlaff-Weglikowska U.,Korea University
Physica Status Solidi (B) Basic Research | Year: 2013

This report demonstrates application of expanded graphite (ExG) for thermoelectric energy conversion, where it serves as a filler for both p- and n-type organic materials. Thin ExG composite films showing improved thermoelectric properties were prepared. In particular, composites with intrinsically conducting polymer poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) yielding high electrical conductivity (up to 104Sm-1) and enhanced thermopower (Seebeck coefficient) provided promising p-type material. Chemical doping experiments performed on ExG dispersed in polyvinyl alcohol (PVA) revealed that the exfoliated graphitic sheets can be efficiently n-doped with polyethyleneimine (PEI). As a result, n-type ExG/PVA/PEI composite thin films showing improved n-type characteristics with thermopower values as high as -25.3μVK-1 were prepared. With a 25wt% ratio of PEI to ExG, the electrical conductivity was measured to be ~103Sm-1, which is remarkably high for n-type polymer composites. Strips of composite films containing 50wt% of ExG in PEDOT:PSS were used as p-type components, and composite films containing 20wt% of ExG in PVA doped with PEI were used as n-type components in thermoelectric modules to demonstrate thermoelectric voltage with one, two, and three p-n couples connected in series. The testing modules produced an output voltage of ~4mV at a temperature gradient of 50K. The module generated 1.7nW power, when a load resistance matched the internal module resistance of 1kΩ. Our results show that chemical functionalization of ExG in thin composite films resulted in more effective thermoelectric properties. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Roth S.,Korea University | Roth S.,Sineurop Nanotech Gmbh | Roth S.,Max Planck Institute for Solid State Research | Park H.J.,Max Planck Institute for Solid State Research
Chemical Society Reviews | Year: 2010

This tutorial review discusses the contradictory material properties of electrical conductivity and optical transparency for the examples of graphene films and carbon nanotube networks. It is argued that for homogeneous films both properties are linked by basic laws of physics and that for perfect monoatomic layers conductivity and transparency can be calculated from the fine structure constant. To beat these limitations, inhomogeneous films are required, such as graphene with an array of holes or nanotube networks. An overview is given on literature values of transparency and conductivity, both for graphene films and for nanotube networks. © 2010 The Royal Society of Chemistry.


Kaymaksiz S.,Max Planck Institute for Solid State Research | Kaskhedikar N.,Max Planck Institute for Solid State Research | Sato N.,Toyota Motor Corporation | Roth S.,Max Planck Institute for Solid State Research | And 3 more authors.
ECS Transactions | Year: 2010

We investigated the synthesis of the nanocrystalline LiMnPO4 and its composite with single-walled carbon nanotubes (SWCNT) as me potential material for lithium ion batteries. Three synthesis routes, sol-gel, precipitation in microemulsion and hydrothermal procedure have been evaluated with regard to the morphology, particle size, porosity, phase purity and crystallinity. Even though all preparation methods produce crystalline material with expected olivine type structure, the battery performance strongly differs. We found out that me Li-ion diffusion, not the electrical conductivity, determines the battery capacity. Particles smaller than 30 nm provided by precipitation via microemulsion and incorporated into network of SWNTs significantly improve the battery performance. Our results confirm that the high capacity can only be achieved when the nanocrystalline particles provided by the synthesis are sufficiently separated and prevented from agglomeration in the working electrode. ©The Electrochemical Society.


Grant
Agency: European Commission | Branch: FP7 | Program: BSG-SME | Phase: SME-1 | Award Amount: 1.47M | Year: 2008

NANORAY aims to realize an innovative device capable to generate X-rays by means of a novel concept of cold cathode, based on carbon nanotubes selectively grown upon ad-hoc synthesized nanostructures (such as vertically oriented nanotubes on metallic tips, selected deposition of CNTs on predetermined areas, array of oriented bundles, etc..) Its performances can be wrapped up by mentioning some of the most relevant features:1)A reduced focal spot (down to 0.1 mm, well below the actual state of art for commercial X-Ray tubes;2)A very low power consumption (due to the use of a field-emission based cathode);3)A pulsed x-ray radiation with programmable width and repetition4)A long life-time.Moreover, the system will be portable, with an overall weight of less than 5 kg (including power supply), allowing the use of X-rays in places like ambulances or in field security surveys. In addition to portability and easiness to use, the system will provide higher image resolution with respect to the state of the art of X-rays devices thanks to the smaller focal spot, and it will represent a cost effective solution for everyone is facing the economic issues related to the maintenance of thermionic cathodes.

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