Using a scanning tunnel microscope or mechanically controllable break junctions atomic contacts for Au, Pt, and Ir are pulled to form chains of atoms. We have recorded traces of conductance during the pulling process and averaged these for a large number of contacts. An oscillatory evolution of conductance is observed during the formation of the monoatomic chain suggesting a dependence on the numbers of atoms forming the chain being even or odd. This behavior is not only observed for the monovalent metal Au, as was predicted, but is also found for the other chain-forming metals, suggesting it to be a universal feature of atomic wires. ; This work is part of the research program of the "Stichting FOM." G. R. acknowledges support of the Spanish DGI by the Project No. MAT 2001-1281. C.U. has been supported by the European Union under Contract No. HPMF-CT-2000-00724.
This is the Accepted Manuscript version of an article accepted for publication in Nanotechnology. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at https://doi.org/10.1088/1361-6528/ab0bc1 ; Few-layer GaSe is one of the latest additions to the family of two-dimensional semiconducting crystals whose properties under strain are still relatively unexplored. Here, we study rippled nanosheets that exhibit a periodic compressive and tensile strain of up to 5%. The strain profile modifies the local optoelectronic properties of the alternating compressive and tensile regions, which translates into a remarkable shift of the optical absorption band-edge of up to 1.2 eV between crests and valleys. Our experimental observations are supported by theoretical results from density functional theory calculations performed for monolayers and multilayers (up to seven layers) under tensile and compressive strain. This large band gap tunability can be explained through a combined analysis of the elastic response of Ga atoms to strain and the symmetry of the wave functions ; Research supported by the Spanish MINECO through Grants MAT2017–88693-R, MAT2014-57915-R, FIS2016-80434- P (AEI/FEDER, EU), BES-2015-071316, the Ramón y Cajal programme RYC-2011-09345, the Fundación Ramón Areces and the María de Maeztu Programme for Units of Excellence in R&D (MDM-2014-0377), as well as from the Comunidad Autónoma de Madrid (CAM) MAD2D-CM Program (S2013/MIT-3007) and the European Union Seventh Framework Programme under grant agreement No. 604391 Graphene Flagship. JJP acknowledges Fulbright Fellowship for Sabbatical leave at University of Texas at Austin, EEUU. We acknowledge the computer resources and assistance provided by the Centro de Computación Científica of the Universidad Autónoma de Madrid
The electronic version of this article is the complete one and can be found online at: http://link.springer.com/article/10.1186/1556-276X-7-233 ; We fabricate freely suspended nanosheets of molybdenum disulphide (MoS2) which are characterized by quantitative optical microscopy and high-resolution friction force microscopy. We study the elastic deformation of freely suspended nanosheets of MoS2 using an atomic force microscope. The Young's modulus and the initial pre-tension of the nanosheets are determined by performing a nanoscopic version of a bending test experiment. MoS2 sheets show high elasticity and an extremely high Young's modulus (0.30 TPa, 50% larger than steel). These results make them a potential alternative to graphene in applications requiring flexible semiconductor materials ; This work was supported by MICINN (Spain) through the programs MAT2008-01735, MAT2011-25046 and CONSOLIDER-INGENIO-2010 'Nanociencia Molecular' CSD-2007-00010, Comunidad de Madrid through program Nanobiomagnet S2009/MAT-1726, and the European Union (FP7) through the program RODIN
We fabricate and characterize carbon-fiber tips for their use in combined scanning tunneling and force microscopy based on piezoelectric quartz tuning fork force sensors. An electrochemical fabrication procedure to etch the tips is used to yield reproducible sub-100-nm apex. We also study electron transport through single-molecule junctions formed by a single octanethiol molecule bonded by the thiol anchoring group to a gold electrode and linked to a carbon tip by the methyl group. We observe the presence of conductance plateaus during the stretching of the molecular bridge, which is the signature of the formation of a molecular junction ; This work was supported by MICINN (Spain) through the programs MAT2008-01735, MAT2011-25046 and CONSOLIDER-INGENIO-2010 'Nanociencia Molecular' CSD-2007-00010; Comunidad de Madrid through program Nanobiomagnet S2009/MAT-1726; and European Union through programs BIMORE (MRTN-CT-2006-035859) and ELFOS (FP7)
The fabrication of van der Waals heterostructures, artificial materials assembled by individual stacking of 2D layers, is among the most promising directions in 2D materials research. Until now, the most widespread approach to stack 2D layers relies on deterministic placement methods, which are cumbersome and tend to suffer from poor control over the lattice orientations and the presence of unwanted interlayer adsorbates. Here, we present a different approach to fabricate ultrathin heterostructures by exfoliation of bulk franckeite which is a naturally occurring and air stable van der Waals heterostructure (composed of alternating SnS 2-like and PbS-like layers stacked on top of each other). Presenting both an attractive narrow bandgap (<0.7 eV) and p-type doping, we find that the material can be exfoliated both mechanically and chemically down to few-layer thicknesses. We present extensive theoretical and experimental characterizations of the material's electronic properties and crystal structure, and explore applications for near-infrared photodetectors ; A.C.-G. acknowledges financial support from the BBVA Foundation through the fellowship 'I Convocatoria de Ayudas Fundacion BBVA a Investigadores, Innovadores y Creadores Culturales' ('Semiconductores ultradelgados: hacia la optpelectronica flexible'), from the MINECO (Ramón y Cajal 2014 program, RYC-2014-01406), from the MICINN (MAT2014-58399-JIN) and from European Commission under the Graphene Flagship, contract CNECTICT-604391. E.M.P. acknowledges financial support from the European Research Council (MINT, ERC-StG-307609) and from the MINECO of Spain (CTQ2014-60541-P). E.G. gratefully acknowledges the AMAROUT II fellowship program for receiving a grant for transnational mobility (Marie Curie Action, FP7-PEOPLE- 2011-COFUND (291803)). A.J.M.-M., G.R.-B. and N.A. acknowledge the support of the MICCINN/MINECO (Spain) through the programmes MAT2014-57915-R, BES-2012-057346 and FIS2011-23488 and Comunidad de Madrid (Spain) through the programme S2013/MIT-3007 (MAD2D). J.O.I. and H.S.J.v.d.Z. acknowledge the support of the Dutch organization for Fundamental Research on Matter (FOM) and by the Ministry of Education, Culture, and Science (OCW). M.A.N. acknowledeges the support of the MICCINN/MINECO (Spain) through the programmes MAT2013-49893-EXP and MAT2014-59315-R. Authors M.A.N., A.J.M.-M. and A.C.-G. acknowledge the support from ALBA Synchrotron for the experiments performed at Circe beamline (BL24-CIRCE) at ALBA Synchrotron with the collaboration of ALBA staff (proposal ID 2015091399). W.S.P. acknowledges CAPES Foundation, Ministry of Education of Brazil, under grant BEX 9476/13-0. W.S.P. and J.J.P. acknowledge MICCINN/MINECO (Spain) for financial support under grant FIS2013-47328-C02-1; the European Union structural funds and the Comunidad de Madrid MAD2D-CM programme under grant nos. P2013/MIT-3007 and P2013/MIT-2850; the Generalitat Valenciana under grant no. PROMETEO/2012/011
A key goal in molecular electronics has been to find molecules that facilitate efficient charge transport over long distances. Normally, molecular wires become less conductive with increasing length. Here, we report a series of fused porphyrin oligomers for which the conductance increases substantially with length by > 10-fold at a bias of 0.7 V. This exceptional behavior can be attributed to the rapid decrease of the HOMO-LUMO gap with the length of fused porphyrins. In contrast, for butadiyne-linked porphyrin oligomers with moderate inter-ring coupling, a normal conductance decrease with length is found for all bias voltages explored (±1 V), although the attenuation factor (β) decreases from ca. 2 nm-1 at low bias to <1 nm-1 at 0.9 V, highlighting that β is not an intrinsic molecular property. Further theoretical analysis using density functional theory underlines the role of intersite coupling and indicates that this large increase in conductance with length at increasing voltages can be generalized to other molecular oligomers. ; R.J.N., S.H., E.L. and A.H. acknowledge the UK Engineering and Physical Sciences Research Council (EPSRC) for the funding of this research under grant numbers EP/M014169/1, P/M029522/1 and EP/M005046/1. N.A., C.L., S.S. and I.G. acknowledge the European Commission (EC) FP7 ITN "MOLESCO" (project no. 606728) and the EPSRC (grant nos. EP/M014452/1 and EP/N017188/1). H.L.A. thanks the EPSRC (grants EP/N017188/1, EP/D076552/1 and EP/ M016110/1), UK National Mass Spectrometry Facility at Swansea University, for recording mass spectra. H.S. acknowledges the Leverhulme Trust for Leverhulme Early Career Fellowship no. ECF-2017-186. S.S. acknowledges the Leverhulme Trust for Leverhulme Early Career Fellowship no. ECF-2018-375. N.A. and G.R.B. acknowledge the Spanish MINECO (Grant MAT2014-57915-R, MAT2017-88693-R and MDM-2014-0377) and Comunidad de Madrid (Grant NANOFRONTMAG-CM, S2013/MIT-2850). N.A. and C.L. have received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement no. 767187. IMDEA Nanociencia acknowledges support from the 'Severo Ochoa' Programme for Centres of Excellence in R&D (MINECO, Grant SEV-2016-0686)
