| 1. |
- Devid, E. J., et al.
(author)
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Spin Transition in Arrays of Gold Nanoparticles and Spin Crossover Molecules
- 2015
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In: ACS Nano. - : American Chemical Society (ACS). - 1936-086X .- 1936-0851. ; 9:4, s. 4496-4507
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Journal article (peer-reviewed)abstract
- We investigate if the functionality of spin crossover molecules is preserved when they are assembled into an interfacial device structure. Specifically, we prepare and investigate gold nanoparticle arrays, into which room-temperature spin crossover molecules are introduced, more precisely, [Fe(AcS-BPP)(2)](ClO4)(2), where AcS-BPP = (S)-(4-{[2,6-(dipyrazol-1-yl)pyrid-4-yl]ethynyl}phenyl)ethanethioate (in short, Fe(S-BPP)(2)). We combine three complementary experiments to characterize the molecule-nanoparticle structure in detail. Temperature-dependent Raman measurements provide direct evidence for a (partial) spin transition in the Fe(S-BPP)(2)-based arrays. This transition is qualitatively confirmed by magnetization measurements. Finally, charge transport measurements on the Fe(S-BPP)(2)-gold nanoparticle devices reveal a minimum in device resistance versus temperature, R(T), curves around 260-290 K. This is in contrast to similar networks containing passive molecules only that show monotonically decreasing R(T) characteristics. Backed by density functional theory calculations on single molecular conductance values for both spin states, we propose to relate the resistance minimum in R(T) to a spin transition under the hypothesis that (1) the molecular resistance of the high spin state is larger than that of the low spin state and (2) transport in the array is governed by a percolation model.
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| 2. |
- Devid, E. J., et al.
(author)
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The influence of molecular mobility on the properties of networks of gold nanoparticles and organic ligands
- 2014
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In: Beilstein Journal of Nanotechnology. - : Beilstein Institut. - 2190-4286. ; 5:1, s. 1664-1674
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Journal article (peer-reviewed)abstract
- We prepare and investigate two-dimensional (2D) single-layer arrays and multilayered networks of gold nanoparticles derivatized with conjugated hetero-aromatic molecules, i.e., S-(4-{[2,6-bipyrazol-1-yl)pyrid-4-yl]ethynyl}phenyl) thiolate (herein S-BPP), as capping ligands. These structures are fabricated by a combination of self-assembly and microcontact printing techniques, and are characterized by electron microscopy, UV-visible spectroscopy and Raman spectroscopy. Selective binding of the S-BPP molecules to the gold nanoparticles through Au-S bonds is found, with no evidence for the formation of N-Au bonds between the pyridine or pyrazole groups of BPP and the gold surface. Subtle, but significant shifts with temperature of specific Raman S-BPP modes are also observed. We attribute these to dynamic changes in the orientation and/or increased mobility of the molecules on the gold nanoparticle facets. As for their conductance, the temperature-dependence for S-BPP networks differs significantly from standard alkanethiol-capped networks, especially above 220 K. Relating the latter two observations, we propose that dynamic changes in the molecular layers effectively lower the molecular tunnel barrier for BPP-based arrays at higher temperatures.
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| 3. |
- Godel, F., et al.
(author)
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Voltage-controlled inversion of tunnel magnetoresistance in epitaxial nickel/graphene/MgO/cobalt junctions
- 2014
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In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 105:15, s. Art. no. 152407-
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Journal article (peer-reviewed)abstract
- We report on the fabrication and characterization of vertical spin-valve structures using a thick epitaxial MgO barrier as spacer layer and a graphene-passivated Ni film as bottom ferromagnetic electrode. The devices show robust and scalable tunnel magnetoresistance, with several changes of sign upon varying the applied bias voltage. These findings are explained by a model of phonon-assisted transport mechanisms that relies on the peculiarity of the band structure and spin density of states at the hybrid graphene vertical bar Ni interface.
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| 4. |
- Lunca Popa, P, et al.
(author)
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Heteronanojunctions with atomic size control using a lab-on-chip electrochemical approach with integrated microfluidics
- 2011
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In: NANOTECHNOLOGY. - : IOP PUBLISHING LTD, DIRAC HOUSE, TEMPLE BACK, BRISTOL BS1 6BE, ENGLAND. - 0957-4484 .- 1361-6528. ; 22:21, s. 215302-
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Journal article (peer-reviewed)abstract
- A versatile tool for electrochemical fabrication of heteronanojunctions with nanocontacts made of a few atoms and nanogaps of molecular spacing is presented. By integrating microfluidic circuitry in a lab-on-chip approach, we keep control of the electrochemical environment in the vicinity of the nanojunction and add new versatility for exchanging and controlling the junctions medium. Nanocontacts made of various materials by successive local controlled depositions are demonstrated, with electrical properties revealing sizes reaching a few atoms only. Investigations on benchmark molecular electronics material, trapped between electrodes, reveal the possibility to create nanogaps of size matching those of molecules. We illustrate the interest of a microfluidic approach by showing that exposure of a fabricated molecular junction to controlled high solvent flows can be used as a reliability criterion for the presence of molecular entities in a gap.
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| 5. |
- Mahmood, A., et al.
(author)
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Room temperature dry processing of patterned CVD graphene devices
- 2015
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In: Carbon. - : Elsevier BV. - 0008-6223. ; 86, s. 256-263
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Journal article (peer-reviewed)abstract
- We present a strategy for avoiding polymeric residues, excessive heating and solvent exposure when transforming large area transferred CVD graphene single layer films into series of planar devices. Such dry process is a key prerequisite for chemical functionalization applications or for organic electronics compatibility, and opens the possibility to integrate graphene electrodes with thermally or chemically sensitive materials, as well as substrates incompatible with lithography processing. Patterning and metal evaporation are performed through a multi-step mechanical stencils methodology, and low temperatures magneto transport measurements are used to validate devices with preserved electrical fingerprints of graphene. This is particularly critical for the argon beam milling process step. Remarkably, the Quantum Hall signature of our devices remains robust, even though defective sample edges result from the beam exposure. Shubnikov-de Hass (SdH) oscillations and weak (anti-) localization signatures of monolayer graphene confirm the excellent intrinsic properties of such processed samples, rarely observed on CVD-processed devices.
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| 6. |
- Mouafo, L. D. N., et al.
(author)
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Tuning contact transport mechanisms in bilayer MoSe2 transistors up to Fowler-Nordheim regime
- 2017
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In: 2D Materials. - : IOP Publishing. - 2053-1583. ; 4:1
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Journal article (peer-reviewed)abstract
- Atomically thin molybdenum diselenide (MoSe2) is an emerging two-dimensional (2D) semiconductor with significant potential for electronic, optoelectronic, spintronic applications and a common platform for their possible integration. Tuning interface charge transport between such new 2D materials and metallic electrodes is a key issue in 2D device physics and engineering. Here, we report tunable interface charge transport in bilayer MoSe2 field effect transistors with Ti/Au contacts showing high on/off ratio up to 107 at room temperature. Our experiments reveal a detailed map of transport mechanisms obtained by controlling the interface band bending profile via temperature, gate and source-drain bias voltages. This comprehensive investigation leads to demarcating regimes and tuning in transport mechanisms while controlling the interface barrier profile. The careful analysis allows us to identify thermally activated regime at low carrier density, and Schottky barrier driven mechanisms at higher carrier density demonstrating the transition from low-field direct tunneling/ thermionic emission to high-field Fowler–Nordheim tunneling. Furthermore, we show that the transition voltage Vtrans to Fowler–Nordheim correlates directly to the difference between the chemical potential of the metal electrode and the conduction band minimum in the 2D semiconductor, which opens up opportunities for new theoretical and experimental investigations. Our approach being generic can be extended to other 2D materials, and the possibility of tuning contact transport regimes is promising for designing MoSe2 device applications.
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| 7. |
- Zanettini, S., et al.
(author)
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Magnetoconductance anisotropy of a polymer thin film at the onset of metallicity
- 2015
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In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 106:6, s. Art. no. 063303-
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Journal article (peer-reviewed)abstract
- Thin films of poly(2,5-bis(3-dodecyl-2-yl)-thieno[3,2-b] thiophene) (C12-PBTTT) polymer under electrolyte gating and doping are investigated as model systems for organic thin films devices approaching the metallic side of a metal-insulator (M-I) transition. For the most doped samples, with an estimated density reaching 8 x 10(20) cm(-3) holes and a conductivity exceeding 1000 S cm(-1), a positive high-field magnetoconductance is found in a limited temperature range window and only when the field is perpendicular to the sample plane. This signature of weak localization, combined with indications of finite zero-temperature conductivity, allows us to identify delocalized metallic-like transport in these thin films, even though the conductivity decreases when cooling down the samples.
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