Hybrid Van der Waals heterostructures

Layered heterostructures integrating two-dimensional materials such as graphene or transition metal dichalcogenides and nanometer-scale layers of inorganic materials are attracting considerable attention since a few years. Organic materials remain however poorly explored in this context, in particular for ultra-thin layers down to the single molecule level. Mixed-dimensional, hybrid heterostructures have a lot to offer in terms of interface physics in fields such as, for instance, polaritonics, excitonics or topological phases and provide new emergent behavior for electronics and optoelectronics

We recently started works to provide a better fundamental understanding of the interface in hybrid, mixed-dimensional Van der Waals heterostructures with high electronic bandwidth. We will design, fabricate and study vertical heterostructures in the form of organic/graphene/organic stacks and the quality of the organic/graphene interface will be investigated to optimize charge injection through the graphene base, with potential applications in vertical, permeable-base organic transistors.

Work in progress, more to come.

Main coll.: M. Calame (EMPA, Dübendorf, Switzerland)

Other results in molecular electronics (before 2015)

Self-assembled molecular nanodielectrics and molecular transistors

– Demonstration of the suppression of tunneling charge transfer through self-assembled monolayers (SAMs) of organic molecules (alkylsilane). [1, 2].
– First nanofabrication of an organic nanotransistor (OFET) with a 30 nm channel length (world record until 2004), using such an organic monolayer self-assembly as a gate insulator film. [3, 4, 5].
– Demonstration of a fully functioning organic transistor where both the gate dielectric and the semiconductor are embedded into a single self-assembled monolayer. [6].

Dynamic properties of molecular junctions.

– First measurements of low frequency noise (1/f and RTS) in molecular junctions. Correlation with defects in the junctions as measured by admittance spectroscopy in the range 1Hz to 1MHz. [7, 8] and with dipolar relaxation in molecular junctions. [9]
– Detailed study of the conductance statistics in Au nano-dot(<10 nm)/molecule/C-AFM molecular junctions [10] and coupled study (exp. and DFT) of the mechanical strain effect induced by the C-AFM tip on the transport properties (dipole reorientation at the molecule/metal interface) [11].
– Determination of the intermolecular interaction (π-π energy coupling) from conductance histograms [25].

Molecular diodes, switches and memories

– Experimental demonstration of the current rectification in a molecular junction with a structure metal/donor-bridge-acceptor molecule/metal as theoretically proposed by Aviram and Ratner in 1976. [12, 13].
– Design and synthesis a new type of molecular diodes by sequential chemisorption of molecules on silicon [14, 15].
– Demonstration of a “record” “on/off” conductance ratio up to 7,000  for a new azobenzene-thiophene molecular switch [16].
– Nanoparticule/molecule self-assembled networks with light-induced reconfiguration [26], negative differential resistance, memory and reconfigurable logic functions [27].
– First molecular diode working at high frequency (18 GHz) with a cut-off frequency of 550 GHz [24].

Neuro-inspired organic nano-devices

– New concept of a nanoparticle organic memory and field effect transistor (NOMFET) [17, 18] which exhibits the main behavior of a biological spiking synapse. [19], and working at low voltage (1V) [20].
– Demonstration that organic synapstors (synapse-transistor) behave as memristors, and demonstration of STDP, spike-timing dependent plasticity) [21].
– Compact model of organic synapstors developed, validated and implemented in a device/circuit simulator [22]
– Demonstration of neuro-inspired circuits (associative memory showing a pavlovian learning) with organic synapstors [23].

  1. C. Boulas et al. Phys. Rev. Lett. 76(25), 4797 (1996).
  2. D. Vuillaume et al. Phys. Rev. B 58(24), 16491-16498 (1998).
  3. J. Collet et al. Appl. Phys. Lett. 76(14), 1941-1943 (2000).
  4. D.K. Aswal et al. Small 1(7), 725-729 (2005).
  5. D.K. Aswal et al., Ana. Chem. Acta 568(1-2), 84-108 (2006).
  6. M. Mottaghi et al. Adv. Func. Mater. 17, 597-604 (2007).
  7. N. Clément et al. Phys. Rev. B 76, 205407 (2007).
  8. N. Clément et al. Phys. Rev. B 82, 035404 (2010).
  9. S. Pleutin et al. Phys. Rev. B 82(12) 125436 (2010).
  10. K. Smaali et al. ACS Nano 6, 4639-4647 (2012).
  11. K. Smaali et al. Nanoscale 7, 1809-1819 (2015).
  12. R.M. Metzger et al. J. Am. Chem. Soc. 119(43), 10455 (1997).
  13. C. Krzeminski et al. Phys. Rev. B. 64, 085405 (2001).
  14. S. Lenfant et al. Nano Letters 3(6), 741-746 (2003).
  15. S. Lenfant et al. J. Phys. Chem. B 110(28), 13947-13958 (2006).
  16. K. Smaali et al. ACS Nano, 4(4), 2411-2421 (2010).
  17. D. Tondelier et al. Appl. Phys. Lett. 85(23), 5763-5765 (2004).
  18. C. Novembre et al. Appl. Phys. Lett. 92(10), 103314 (2008).
  19. F. Alibart et al. Adv. Func. Mater. 20(2), 330-337 (2010),
  20. S. Desbief et al. Org. Electron. 21, 47-53 (2015).
  21. F. Alibart et al. Adv. Func. Mater. 22, 609-616 (2012).
  22. O. Bichler et al. IEEE Trans. Electron. Dev. 57(11), 3115-3122 (2010).
  23. O. Bichler et al. Neural Computation 25(2), 549-566 (2013).
  24. J. Trasabares et al., Nature Communications 7, 12850 (2016).
  25. J. Trasobares et al., Nano Lett., 17, 3215-3224 (2017).
  26. Y. Viero et al., J. Phys. Chem. C 119, 21173-21183 (2015).
  27. T. Zhang et al., J. Phys. Chem. C , 121, 10131-10139 (2017).

Molecular nanostructures

 

  • Electron transport through tripeptides self-assembled monolayers

Capture d’écran 2019-03-23 à 10.52.36We report how the electron transport (C-AFM measurements and first-principle calculations) through a solid-state metal/Gly-Gly-His tripeptide (GGH) monolayer/metal junction are modified by the GGH complexation with Cu2+ ions. Complexed copper to low density GGH-monolayer induces a new gap state slightly above the Au Fermi energy that is absent in the high density monolayer. [E. Mervinetsky et al., J. Phys. Chem. C (2019)]

Main Coll. : S. Yitzchaik (Institute of Chemistry, The Hebrew University of Jerusalem, Israel); R. Gutierrez (Institute for Materials Science and Max Bergmann Center of Biomaterials, TU Dresden, Germany).

  • Polyoxometalates

POM-diazo

Polyoxometalates (POMs) are nano-sized early-transition metal oxide clusters obeying to the general formula [Xx MpOy]n- (X= P, Si …; M = Mo, W, V…), encompassing a wide variety of compositions,
sizes and shapes, and exhibiting a range of properties that are unique in their combination.

We have studied how the electron transport in POM-based molecular junctions (POMs on various substrates: Si-H, Si/SiO2, Au) depends on:
– the chemical nature of the metal atoms [PM11O39{Sn(C6H4)C[triple bond, length as m-dash]C(C6H4)N2}]3− (M = Mo, W) [M. Laurans et al., Nanoscale (2018)].
– the type of POM immobilization on the electrodes (covalent vs. electrostatic) [K. Dalla Francesca et al., Nanoscale (2019)].
– the chemical nature of the linkers between the POMs and the electrodes [M. Laurans et al., in preparation].

POM-JACSWe have explored a novel surface anchoring mode (organo- amino group−Au surface) in an approach to render magnetically functionalized POMs accessible to charge transport experiments in distinct environments, , and we have determined the electronic structure of these metal/magnetic POMs/metal junctions [X. Yi et al., J. Am. Chem. Soc. (2017)].

Main Coll. : P. Kögerler (Inst. Inorg. Chem., Aachen univ. & Peter Grünberg Institute, Jülich, Germany), A. Proust (IPCM, CNRS, Sorbonne University).

  • Electron transport in molecular nanostructures

nanolett-tocWe studied electron transport through tiny Au nanodot (sub-10nm)-molecules-CAFM junctions (NMJ) (see a mini-review : D. Vuillaume, ChemPlusChem (2019)) and we have obtained several advances.

(i) Relation between several conductance peaks and the molecular organization in the junctions [K. Smaali et al., Nanoscale (2015)].
(ii) role and determination of the π-π intermolecular interaction energies [J. Trasobares et al., Nano Letters (2017)].
(iii) First demonstration of a molecular diode operating at 17 GHz (using interferometric scanning microwave microscope), and estimation of a cut-off frequency at 500 GHz [J. Trasobares et al. Nature Comm. (2016)].

Main coll. : P. Leclere, J. Cornil (LCNM, U. Mons, Belgium); T. Martin (CPT, U. Marseille); T. Frederiksen, D. Sanchez-Portal (Donostia International Physics Center, San Sebastián, Spain); E. Levillain (CNRS, Moltech-Anjou, U. Angers), D. Théron (IEMN/NAM6).

Molecular nanostructures & computing

 

  • Organic synapstor (synapse-transistor)

org synapstorIn 2010, we demonstrated the concept of synapstor (synapse transistor) that the main functionalities of a biological synapse are achievable with an organic hybrid transistor (organic semiconductor and gold nanoparticles) [F. Alibart et al. Adv. Func. Mater.  (2010), F. Alibart et al., Adv. Func. Mater. (2012)]. Recently, we extended these results with the demonstration of the operation of these synapstors at very low voltages (50 mV), in an electrolyte-gated configuration [S. Desbief et al. Org. Electron. (2015); M. di Lauro et al., Adv. Electron. Mater. (2017)], and we demonstrated that they can be interfaced with living biological neurons [S. Desbief et al. Org. Electron. (2016)], which made these devices prone for a possible brain/neurocomputer interface.

Main coll.: C. Gamrat (CEA-LIST), F. Biscarini (Dipartimento di Scienze della Vita,
Università di Modena e Reggio Emilia, Modena, Italy); Y. Geerts (Lab. Chimie des Polymères,
Université Libre de Bruxelles, Belgium).

  • Organic electrochemical transistors for reservoir computing.

OECT-RCWe investigated iono-electronic materials and devices, in which electronic conduction is controlled by ion dynamics [S. Pecqueur et al., Org. Electron. (2018), S.Pecqueur et al. Org. Electron. (2019)]. We have demonstrated pattern recognitions in a network of OECTs (organic electrochemical transistor) interacting in a common electrolyte [S. Pecqueur et al., Adv. Electron. Mater. (2018)]. based on the concept of  “reservoir computing” (i.e. a spatio-temporal data processing in a network with complex dynamics and strong non-linearities).

Main coll.: P. Blanchard, J. Roncali (CNRS, Moltech-Anjou, U. Angers); C. Gamrat (CEA-LIST, Saclay), Z. Crljen (RBI, Zagreb, Croatia).

Thermoelectric properties of molecular nanostructures

We recently started using the SThM (scanning thermal microscope) technique to measure the thermal conductivity of various molecular nanosctructures, self-assembled monolayers and organic thin films. We aim to provide a better fundamental understanding of these thermoelectronic properties at the nanoscale, e.g. the role of molecular structures, quantum interference in molecules, molecule/electrode interfaces,…

Work in progress, more to come.

Main coll. : A. Carella, R. Demadrille (CEA, Grenoble), Y. Geerts (Univ. Libre de Bruxelles, Belgium), J. Cornil (LCMN, U. Mons, Belgium), K. Costuas, S. Rigaut (ISCR, CNRS, U. Rennes), E. Scheer (U. Konstanz, Germany).

Magnetic molecules & molecular spintronics

  • Molecular spintronics with functional molecules

This project aims at tailoring spintronics devices by molecular engineering using self-assembled monolayers (SAMs) of functional molecules. Our aim is to go beyond the state-of-the-art of fundamental knowledge to develop and evaluate the potential of multifunctional molecular spintronics devices. We use functional molecules controlled by external stimuli (light or electric field) to modify the molecule/electrode spin hybridization in-situ.

Capture d’écran 2020-03-25 à 22.22.43 We report on the phosphonic acid route for the grafting of functional molecules, optical switch (dithienylethene diphosphonic acid, DDA), on La0.7Sr0.3MnO3 (LSMO). A partial light-induced conductance switching between the open and closed forms of the DDA is observed for the LSMO/DDA/C-AFM tip molecular junctions (closed/open conductance ratio of about 8). [L. Thomas et al., Nanoscale (2020)]

A second system is azobenzene derivatives on cobalt electrodes [L. Thomas et al., in preparation].

Main coll.: R. Mattana, P. Seneor (Unité Mixte de Physique CNRS/Thales, France); J. Cornil (LCNM, U. Mons, Belgium); Y. Pei, T. Mallah (ICMMO, CNRS, U. Paris-Saclay, France).

  • Molecular junctions with magnetic molecules

We study electron transport through molecular junctions made of magnetic molecules.

POM-JACSWe have explored a novel surface anchoring mode (organo- amino group−Au surface) in an approach to render magnetically functionalized polyoxometalates (POMs) accessible to charge transport experiments in distinct environments, and we have determined the electronic structure of these metal/magnetic POMs/metal junctions. [X. Yi et al., J. Am. Chem. Soc. (2017)].

 

Capture d’écran 2020-05-02 à 12.47.16We are currently studying the electronic properties of nano-devices made of magnetic nanoparticles of Prussian blue analogs (PBA). We report electron transport measurements through nano-scale devices consisting of 1 to 3 (PBA) nanoparticles connected between two electrodes. We compare two types of cubic nanoparticles, CsCoIIIFeII (15 nm) and CsNiIICrIII (6 nm), with low decay factors β, in the range 0.05 – 0.1 nm-1 and 0.15 – 0.18 nm-1 for the CsCoFe and the CsNiCr nanoparticles, respectively. Conductance values measured for multi-nanoparticle nano-scale devices (2 and 3 nanoparticles between the electrodes) are consistent with a multi-step coherent tunneling in the off-resonance case between adjacent PBAs, a simple model gives a strong coupling (around 0.3 eV) between the adjacent PBA nanoparticles, mediated by electrostatic interactions. [R. Bonnet et al., submitted].

Main Coll. : P. Kögerler (Inst. Inorg. Chem., Aachen univ. & Peter Grünberg Institute, Jülich, Germany), T. Mallah (ICMMO, CNRS, U. Paris-Saclay, France).

 

2D molecular networks

 

  • Optically and redox switching molecular networks

npsan-JPCCNDR-npsan-JPPCIn the continuation of our work on the design and synthesis of photo-addressable switch molecules (azobenzene derivatives)  [K. Smaali et al., ACS Nano (2010)], we have integrated these molecules, and also redox molecules (thiophene derivatives), in organized gold nanoparticle networks and demonstrated a non-volatile optoelectronic memory effect [Y. Viero et al., J. Phys. Chem. C (2015)], a negative differential resistance effect [T. Zhang et al., J. Phys. Chem. C (2017), T. Zhang et al., Nanoscale Advances (2019)].

ToCWe use a network of molecularly linked gold nanoparticles to demonstrate the electrical detection (conductance variation) of a plasmon-induced isomerization (PII) of azobenzene derivatives (azobenzene bithiophene : AzBT). Possible PII mechanisms are discussed: electric field-induced isomerization, two-phonon process, plasmon-induced resonant energy transfer (PIRET), the latter being the most likely [D. Stievenard et al., Nanoscale (2018)].

Main coll. : P. Blanchard, J. Roncali (CNRS, Moltech-Anjou, U. Angers); M. Calame (EMPA & Univ. Basel, Switzerland), F. Cleri, C. Krzeminski (IEMN/Physique/NAMASTE), C.A. Nijhuis (Chem. Dept., NUS, Singapore).

  • Molecular networks for neuromorphic computing

ToCWe demonstrate optically-driven switchable logical operations in nanoparticles self-assembled networks of molecular switches (azobenzene derivatives) interconnected by Au nanoparticles.  The complex non-linearity of electron transport and dynamics in these highly connected and recurrent networks of molecular junctions exhibit rich high harmonics generation (HHG) required for reservoir computing (RC) approaches. These results, without direct analogs in semiconductor devices, open new perspectives to molecular electronics in unconventional computing  [Y. Viero et al., Adv. Func. Mater. (2018)].

Main coll. : M. Calame (EMPA & Univ. Basel, Switzerland).

 

Molecular switches

  • Optical  molecular switches

new switchWe have reported the electron-transport properties of a new photoaddressable molecular switch. The switching process relies on a new concept based on linear π-conjugated dynamic systems, in which the geometry and, hence, the electronic properties of an oligothiophene chain can be reversibly modified by the photochemical trans−cis isomerization of an azobenzene unit fixed in a lateral loop.  [S. Lenfant et al., J. Phys. Chem. C (2017)].

AzBT-ACS Nano

We have also designed and synthesized a new azobenzene-thiophene molecular switch exhibiting a high “on/off” conductance ratio up to 7,000 (C-AFM on SAMs).  [K. Smaali et al., ACS Nano (2010)].

Main coll. : P. Blanchard, J. Roncali (CNRS, Moltech-Anjou, U. Angers); J. Cornil (LCNM, U. Mons, Belgium); C. van Dyck (Dept. Chem., Northwestern Univ., Evanston, USA); A. Rochefort (Ecole Polytechnique Montréal, Quebec, Canada).

  • Chemical molecular switches

Capture d’écran 2020-03-27 à 11.52.42We demonstrate that the conductance switching of benzo-bis(imidazole) molecules upon protonation depends on the lateral functional groups. The protonated H-substituted molecule shows a higher conductance than the neutral one, explained by a reduction of the LUMO-HOMO gap. The opposite is observed for a molecule laterally functionalized by amino-phenyl groups, consistent with a shift of HOMO, which reduces the density of states at the Fermi energy [H. Audi et al., Nanoscale (2020)].

Main coll. : O. Siri, H. Klein (CINAM, CNRS, Marseille, France), I.M. Grace, C.J. Lambert (Physics Dept., Lancaster Univ. UK).