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Habilitation à diriger des recherches

Contribution à l'électronique moléculaire : de la jonction au composant

Stéphane Lenfant 1
1 NCM
IEMN - Institut d’Électronique, de Microélectronique et de Nanotechnologie (IEMN) - UMR 8520
Abstract : The growing number of studies in molecular electronics since several decades is based on the fascinating perspective to use molecular "bricks" for nanoscale electronics. The work presented here take place in this perspective with the particularity to form the molecular system with self-assembled monolayers (SAMs). The summary of this research in molecular electronic over the last 10 years at the IEMN will be presented. During this presentation we will focused specifically on four aspects of these activities. First, we will discuss the problem of the molecular junction formation (metal or semiconductor/ molecule/ metal junctions). Then, we will detailed the experimental realization of various molecular junctions: coplanar electrodes (spaced from 50 µm to 16 nm), shadow mask, micro-nanopore, contact with liquid electrode (eGain and Hg drop) and Conducting AFM. Secondly, we will talk about mechanisms of electron transport through the junction. To do this, we will used the Transition Voltage Spectroscopy (or TVS) to measure the energy offset (i.e. the position of one of the molecular orbitals with respect to the electrode Fermi energy) at the electrode/ molecule interface in a molecular junction. Our approach in this part is based on the analysis by TVS of various molecular junctions formed by different techniques and different molecules. The results will be compared with those obtained by UPS and IPES to estimate the relevance of the TVS. We will see that this work highlights the importance of the interface on the interpretation of the results obtained by TVS. The third aspect will focus on the realization of a molecular component: a field effect transistor with a conductive channel based on a SAM. The fabrication of this component, named Self Assembled Monolayer Field Effect Transistor or SAMFET, will be described. We will see that the mobility obtained with this transistor is close to those obtained on organic transistors with a conductive channel thicker. The device operates at very low bias (less than 2V), which may open the way to low consumption device. The final part will center on the achievement of stimulable molecular junctions, i.e. the conductance of the molecular junction changes under the influence of external excitation. Three aspects will be detailed: first of all, we will compare the conditions of grafting on gold substrate for SAMs consisting of quaterthiophene derived molecules with one or two thiol group(s); then we will examine a SAM based on molecules able to react with Pb2+ and modify its electronic properties; and finally, we will present electro-optical switches. For this last example, the junction consists of a molecule with an azobenzene group. This group can switch optically between two isomers reversibly. These two isomers have different conductance, the average ratio of conductance was measured at about 1.5 103 with a maximum value of 7 103. This conductance ratio between the two isomers remains the highest measured for molecular junctions with derived azobenzene molecule.
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Submitted on : Thursday, December 19, 2013 - 9:22:55 AM
Last modification on : Friday, December 4, 2020 - 2:29:58 PM
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  • HAL Id : tel-00918954, version 2

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Stéphane Lenfant. Contribution à l'électronique moléculaire : de la jonction au composant. Science des matériaux [cond-mat.mtrl-sci]. Université des Sciences et Technologie de Lille - Lille I, 2013. ⟨tel-00918954v2⟩

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