Institute of Materials Research

Geesthacht, Germany

Institute of Materials Research

Geesthacht, Germany

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Abstract: An international research team at Tohoku University's Advanced Institute of Materials Research (AIMR) succeeded in chemically interconnecting chiral-edge graphene nanoribbons (GNRs) with zigzag-edge features by molecular assembly, and demonstrated electronic connection between GNRs. The GNRs were interconnected exclusively end to end, forming elbow structures, identified as interconnection points (Fig. 1a). This configuration enabled researchers to demonstrate that the electronic architecture at the interconnection points between two GNRs (Fig. 1b) is the same as that along single GNRs; evidence that GNR electronic properties, such as electron and thermal conductivities, are directly extended through the elbow structures upon chemical GNR interconnection. This work shows that future development of high-performance, low-power-consumption electronics based on GNRs is possible. Graphene has long been expected to revolutionize electronics, provided that it can be cut into atomically precise shapes that are connected to desired electrodes. However, while current bottom-up fabrication methods can control graphene's electronic properties, such as high electron mobility, tailored band gaps and s pin-aligned zigzag edges, the connection aspect of graphene structures has never been directly explored. For example, whether electrons traveling across the interconnection points of two GNRs would encounter higher electric resistance remains an open question. As the answers to this type of questions are crucial towards the realization of future high-speed, low-power-consumption electronics, we use molecular assembly to address this issue here. "Current molecular assemblies either produce straight GNRs (i.e., without identifiable interconnection points), or randomly interconnected GNRs," says Dr. Patrick Han, the project leader. "These growth modes have too many intrinsic unknowns for determining whether electrons travel across graphene interconnection points smoothly. The key is to design a molecular assembly that produces GNRs that are systematically interconnected with clearly distinguishable interconnection points." To reach this goal, the AIMR team used a Cu substrate, whose reactivity confines the GNR growth to six directions, and used scanning tunneling microscopy (STM) to visualize the GNR electronic structures. By controlling the precursor molecular coverage, this molecular assembly connects GNRs from different growth directions systematically end to end, producing elbow structures--identified as interconnection points (Fig. 1a). Using STM, the AIMR team revealed that the delocalization of the interconnected GNR π*-states extends the same way both across a single straight GNR, and across the interconnection point of two GNRs (periodic features in Fig. 1b, bottom panel). This result indicates that GNR electronic properties, such as electron and thermal conductivities, should be the same at the termini of single GNRs and that of two connected GNRs. "The major finding of this work is that interconnected GNRs do not show electronic disruption (e.g., electron localization that increases resistance at the interconnection points)," says Han. "The electronically smooth interconnection demonstrates that GNR properties (including tailored band gaps, or even spin-aligned zigzag edges) can be connected to other graphene structures. These results show that finding a way to connect defect-free GNRs to desired electrodes may be the key strategy toward achieving high-performance, low-power-consumption electronics." About Tohoku University The Advanced Institute for Materials Research (AIMR) at Tohoku University is one of nine World Premier International Research Center Initiative (WPI) Programs established with the support of the Japanese Ministry of Education, Culture, Sports, Science and Technology (MEXT). The program aims to develop world-class research bases in Japan. After its establishment in 2007, AIMR has been active in conducting research activities and creating new systems in order to become a global center for materials science. Since 2012, AIMR has also been conducting fundamental research by finding connections between materials science and mathematics. Learn more at www.wpi-aimr.tohoku.ac.jp For more information, please click Contacts: Patrick Han 81-222-176-170 For information on AIMR and all other enquiries: Marie Minagawa Public Relations & Outreach office Advanced Institute for Materials Research, Tohoku University aimr-outreachgrp.tohoku.ac.jp Fax: +81-22-217-6146 If you have a comment, please us. Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.


Ma Y.E.,Northwestern Polytechnical University | Ma Y.E.,Cranfield University | Staron P.,Institute of Materials Research | Fischer T.,Institute of Materials Research | Irving P.E.,Cranfield University
International Journal of Fatigue | Year: 2011

The use of residual K (Kres) approaches for prediction of fatigue crack growth rates in residual stress fields was studied. Finite element models of the samples were built and the measured residual stress data put into the model. The virtual crack closure technique (VCCT) was used to calculate Kres (stress intensity factor from residual stress) together with its changes with crack length using data from the part I paper. Local K res values were used to calculate effective R values. Kop and ΔKeff values throughout the crack path in the weld. The master curve approach was used to relate these to corresponding values for crack growth rates. Predicted crack growth rates were compared with experimental results. Changes in crack growth rate found as the crack grows through the weld can successfully be predicted via application of this closure based model. Agreement between predictions and experimental data was best for tensile residual stress fields and was not as exact in compression. Possible reasons for this discrepancy are discussed. © 2011 Elsevier Ltd. All rights reserved.


Ma Y.E.,Northwestern Polytechnical University | Ma Y.E.,Cranfield University | Staron P.,Institute of Materials Research | Fischer T.,Institute of Materials Research | Irving P.E.,Cranfield University
International Journal of Fatigue | Year: 2011

Residual stress fields were measured in three different sizes of Compact-Tension (C(T)) and eccentrically loaded single edge notch (ESE(T)) specimens containing transverse or longitudinal welds. The effect of size on residual stress profiles was studied. Fatigue crack growth tests were carried out with cracks growing into or away from the weld line, as well as growing along the weld centre line. Effects of weld residual stresses on fatigue crack growth rates parallel and perpendicular to the friction stir welds were studied. It was found that compressive residual stresses around the sample notch had significant retarding effects on both crack initiation and crack growth rates for cracks growing towards the weld line. Effects of residual stress on crack growth rates declined with increasing crack length. When cracks grew parallel to the weld line in C(T) samples the crack growth rate was around 20% lower than in parent material. © 2011 Elsevier Ltd. All rights reserved.


Arrachart G.,Australian Nuclear Science and Technology Organization | Karatchevtseva I.,Australian Nuclear Science and Technology Organization | Karatchevtseva I.,CNRS Marcoule Institute for Separative Chemistry | Heinemann A.,Australian Nuclear Science and Technology Organization | And 3 more authors.
Journal of Materials Chemistry | Year: 2011

Composite powders and thin films composed of poly(methyl methacrylate) (PMMA) and functionalised titania nanoparticles are successfully prepared by in situ bulk co-polymerisation using benzoyl peroxide (BPO) as the initiator. The functionalised titania nanoparticles are synthesised by an arrested hydrolysis of Ti(OiPr) 4 with either undecylenic (UA) or undecenylphosphonic (UPA) acids used as the organic templates with the long hydrocarbon chains and functional (terminal double bond) groups. Surface-modified TiO 2 nanoparticles could be easily dispersed in organic solvent due to the long hydrocarbon chain surrounding the titanium core, and engaged as a co-monomer in polymerisation with the MMA due to the presence of a terminal double bond. TEM and small angle X-ray scattering (SAXS) data presented support the homogeneous and consistent distribution of inorganic phase within the PMMA matrix, with the larger titania nanoparticles detected when the UPA was employed to modify a TiO 2 nanoparticle. This is attributed to the UPA greater binding affinity towards the TiO 2 surfaces and therefore particles aggregation to some extent. © 2011 The Royal Society of Chemistry.


Ma S.,Institute of Materials Research | Yuan H.,Tsinghua University
Engineering Fracture Mechanics | Year: 2015

The experimental investigation shows that the damage process in sintered metals starts in almost zero loading and can be divided into three stages: the elastic stage, the secondary stage and finally the tertiary stage. A phenomenological continuum damage model is introduced to predict the inelastic behavior of the sintered material and the damage process. The numerical implicit integration algorithm is developed and implemented into ABAQUS. The proposed damaged model is computationally and experimentally verified under multi-axial loading conditions. It is confirmed that the proposed damage model is able to properly describe the mechanical behavior and the damage evolution under most different loading configurations. © 2015 Elsevier Ltd.


Hutsch L.L.,Institute of Materials Research | Hutsch J.,Institute of Materials Research | Herzberg K.,Institute of Materials Research | dos Santos J.F.,Institute of Materials Research | Huber N.,Institute of Materials Research
Materials and Design | Year: 2014

The aim of this work is to investigate the formability at room temperature of the Mg alloy AZ31 by Friction Stir Processing. Defect-free process zones were created using process speeds of up to 10. m/min, the resulting microstructure and grain size were analyzed. Microstructural zones with varying texture were identified by electron backscatter diffraction. Tensile tests supported by digital image correlation analysis revealed different deformation behavior and enhanced ductility in the thermo mechanically affected zone which was associated with the variation in grain size and texture. Finally, the sheet forming behavior of the processed material was investigated, using the Nakajima test method with Hasek specimen geometries. Forming limit diagrams for several process conditions reveal a continuous increase in formability with increasing processing speed. Additionally, the local anisotropy was analyzed by comparison of the R values at the point of highest strain, to quantify the impact of processing on formability. © 2013 Elsevier Ltd.


Todorova V.,Max Planck Institute for Solid State Research | Leineweber A.,Max Planck Institute for Intelligent Systems (Stuttgart) | Kienle L.,Institute of Materials Research | Duppel V.,Max Planck Institute for Solid State Research | Jansen M.,Max Planck Institute for Solid State Research
Journal of Solid State Chemistry | Year: 2011

Two new quaternary delafossite type oxides with the general formula Ag(Li1/3M2/3)O2, M=Rh, Ir, have been synthesized, and their structures characterized. Based on X-ray and electron diffraction analyses the structural similarity with AgRhO2 delafossite, has been evidenced. The real structures of the quaternary delafossites have been revealed, which has allowed to fully explain the diffuse scattering as observed in X-ray powder diffraction. AgRhO2 is thermally stable up to 1173 K, the behavior of the two quaternary compounds AgLi1/3Rh2/3O2 and AgLi1/3Ir 2/3O2 is comparable, and they decompose above 950 and 800 K, respectively. AgRhO2 shows temperature independent paramagnetism, while for the other two an effective magnetic moment of 1.77μB for Ir, and 1.70μB for Rh were determined, applying the CurieWeiss law. All compounds are semiconducting with activation energies of 4.97 kJ mol-1 (AgLi1/3Rh2/3O2), 11.42 kJ mol-1 (AgLi1/3Ir2/3O2) and 17.58 kJ mol-1 (AgRhO2). © 2011 Elsevier Inc. All rights reserved.


Arnold A.,Ruhr University Bochum | Bruhns O.T.,Ruhr University Bochum | Mosler J.,Institute of Materials Research
Physics in Medicine and Biology | Year: 2011

A novel finite element formulation suitable for computing efficiently the stiffness distribution in soft biological tissue is presented in this paper. For that purpose, the inverse problem of finite strain hyperelasticity is considered and solved iteratively. In line with Arnold et al (2010 Phys. Med. Biol. 55 2035), the computing time is effectively reduced by using adaptive finite element methods. In sharp contrast to previous approaches, the novel mesh adaption relies on an r-adaption (re-allocation of the nodes within the finite element triangulation). This method allows the detection of material interfaces between healthy and diseased tissue in a very effective manner. The evolution of the nodal positions is canonically driven by the same minimization principle characterizing the inverse problem of hyperelasticity. Consequently, the proposed mesh adaption is variationally consistent. Furthermore, it guarantees that the quality of the numerical solution is improved. Since the proposed r-adaption requires only a relatively coarse triangulation for detecting material interfaces, the underlying finite element spaces are usually not rich enough for predicting the deformation field sufficiently accurately (the forward problem). For this reason, the novel variational r-refinement is combined with the variational h-adaption (Arnold et al 2010) to obtain a variational hr-refinement algorithm. The resulting approach captures material interfaces well (by using r-adaption) and predicts a deformation field in good agreement with that observed experimentally (by using h-adaption). © 2011 Institute of Physics and Engineering in Medicine.


Suhuddin U.,Institute of Materials Research | Mironov S.,Tohoku University | Krohn H.,Institute of Materials Research | Beyer M.,Institute of Materials Research | Dos Santos J.F.,Institute of Materials Research
Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science | Year: 2012

The microstructural evolution during friction surfacing of an aluminum alloy 6082-T6 rod on an aluminum alloy 2024-T351 substrate was characterized using the electron backscatter diffraction technique. Crystallographic data were obtained from several regions in the consumable material and in the deposited material. From the results, it can be deduced that the grain structure formation was a complex process governed by the geometrical effect of strain and the superposition of continuous and discontinuous dynamic recrystallizations. © 2012 The Minerals, Metals & Materials Society and ASM International.


News Article | January 11, 2016
Site: www.cemag.us

An international research team at Tohoku University's Advanced Institute of Materials Research (AIMR) succeeded in chemically interconnecting chiral-edge graphene nanoribbons (GNRs) with zigzag-edge features by molecular assembly, and demonstrated electronic connection between GNRs. The GNRs were interconnected exclusively end to end, forming elbow structures, identified as interconnection points. This configuration enabled researchers to demonstrate that the electronic architecture at the interconnection points between two GNRs is the same as that along single GNRs; evidence that GNR electronic properties, such as electron and thermal conductivities, are directly extended through the elbow structures upon chemical GNR interconnection. This work shows that future development of high-performance, low-power-consumption electronics based on GNRs is possible. Graphene has long been expected to revolutionize electronics, provided that it can be cut into atomically precise shapes that are connected to desired electrodes. However, while current bottom-up fabrication methods can control graphene's electronic properties, such as high electron mobility, tailored band gaps and s pin-aligned zigzag edges, the connection aspect of graphene structures has never been directly explored. For example, whether electrons traveling across the interconnection points of two GNRs would encounter higher electric resistance remains an open question. As the answers to this type of questions are crucial towards the realization of future high-speed, low-power-consumption electronics, we use molecular assembly to address this issue here. "Current molecular assemblies either produce straight GNRs (i.e., without identifiable interconnection points), or randomly interconnected GNRs," says Dr. Patrick Han, the project leader. "These growth modes have too many intrinsic unknowns for determining whether electrons travel across graphene interconnection points smoothly. The key is to design a molecular assembly that produces GNRs that are systematically interconnected with clearly distinguishable interconnection points." To reach this goal, the AIMR team used a Cu substrate, whose reactivity confines the GNR growth to six directions, and used scanning tunneling microscopy (STM) to visualize the GNR electronic structures. By controlling the precursor molecular coverage, this molecular assembly connects GNRs from different growth directions systematically end to end, producing elbow structures — identified as interconnection points. Using STM, the AIMR team revealed that the delocalization of the interconnected GNR π*-states extends the same way both across a single straight GNR, and across the interconnection point of two GNRs. This result indicates that GNR electronic properties, such as electron and thermal conductivities, should be the same at the termini of single GNRs and that of two connected GNRs. "The major finding of this work is that interconnected GNRs do not show electronic disruption (e.g., electron localization that increases resistance at the interconnection points)," says Han. "The electronically smooth interconnection demonstrates that GNR properties (including tailored band gaps, or even spin-aligned zigzag edges) can be connected to other graphene structures. These results show that finding a way to connect defect-free GNRs to desired electrodes may be the key strategy toward achieving high-performance, low-power-consumption electronics." Release Date: January 8, 2016 Source: Tohoku University

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