A simple KPFM-based approach for electrostatic-free topographic measurements: the case of MoS2_2 on SiO2_2

A simple implementation of Kelvin probe force microscopy is reported that enables recording topographic images in the absence of any component of the electrostatic force. Our approach is based on a close loop z-spectroscopy operated in data cube mode. Curves of the tip-sample distance as a function of time are recorded onto a 2D grid. A dedicated circuit holds the KPFM compensation bias and subsequently cut off the modulation voltage during well-defined time-windows within the spectroscopic acquisition. Topographic images are recalculated from the matrix of spectroscopic curves. This approach is applied to the case of transition metal dichalcogenides (TMD) monolayers grown by chemical vapour deposition on silicon oxide substrates. In addition, we check to what extent a proper stacking height estimation can also be performed by recording series of images for decreasing values of the bias modulation amplitude. The outputs of both approaches are shown to be fully consistent. The results exemplify how in the operating conditions of non-contact AFM under ultra-high vacuum, the stacking height values can dramatically be overestimated due to variations in the tip-surface capacitive gradient, even though the KPFM controller nullifies the potential difference. We show that the number of atomic layers of a TMD can be safely assessed, only if the KPFM measurement is performed with a modulated bias amplitude reduced at its strict minimum or, even better, without any modulated bias. Last, the spectroscopic data reveal that defects at the TMD/oxide interface can have a counterintuitive impact on the electrostatic landscape, resulting in an apparent decrease of the measured stacking height by conventional nc-AFM/KPFM compared to non-defective sample areas. Hence, electrostatic free z-imaging proves to be a promising tool to assess the existence of defects in atomically thin TMD layers grown on oxide

Recent Advances in Molecular Electronics Based on Carbon Nanotubes

Carbon nanotubes (CNTs) have exceptional physical properties that make them one of the most promising building blocks for future nanotechnologies. They may in particular play an important role in the development of innovative electronic devices in the fields of flexible electronics, ultra-high sensitivity sensors, high frequency electronics, opto-electronics, energy sources and nano-electromechanical systems (NEMS). Proofs of concept of several high performance devices already exist, usually at the single device level, but there remain many serious scientific issues to be solved before the viability of such routes can be evaluated. In particular, the main concern regards the controlled synthesis and positioning of nanotubes. In our opinion, truly innovative use of these nano-objects will come from: i) the combination of some of their complementary physical properties, such as combining their electrical and mechanical properties, ii) the combination of their properties with additional benefits coming from other molecules grafted on the nanotubes, and iii) the use of chemically- or bio-directed self-assembly processes to allow the efficient combination of several devices into functional arrays or circuits. In this article, we outline the main issues concerning the development of carbon nanotubes based electronics applications and review our recent results in the field

Influence of Molecular Organization on the Electrical Characteristics of {\pi}-conjugated Self-assembled Monolayers

Two new thiol compounds with {\sigma}-{\pi}-{\sigma} structure were synthesized and self-assembled on gold substrates. The morphology and the structural characterization of SAMs assessed by infrared spectroscopy, contact angle, XPS, electrochemistry and scanning tunneling microscopy (STM) show the formation of monolayers. SAMs with a terthiophene (3TSH) core as conjugated system are much better organized compared to those with a naphthalene carbodiimide (NaphSH) core as demonstrated by the cyclic voltammetry and STM studies. The surface concentration of 3TSH and NaphSH is respectively three and six times lower than ordered SAMs of pure alkyl chains. A large number of I/V characteristics have been studied either by STS measurements on gold substrates or by C-AFM on gold nanodots. Transition Voltage Spectroscopy (TVS) was used to clearly identify the transport in these partially organized monolayers. The chemical nature of the conjugated system, donor for 3TSH and acceptor for NaphSH, involves an opposite rectification associated to the asymmetrical coupling of the molecular orbitals and the electrodes. The conductance histograms show that the 3TSH junctions are less dispersed than those of NaphSH junctions. This is explained by a better control of the molecular organization in the molecular junctions.Comment: Full paper with supporting informatio

Physical Realization of a Supervised Learning System Built with Organic Memristive Synapses

International audienceMultiple modern applications of electronics call for inexpensive chips that can perform complex operations on natural data with limited energy. A vision for accomplishing this is implementing hardware neural networks, which fuse computation and memory, with low cost organic electronics. A challenge, however, is the implementation of synapses (analog memories) composed of such materials. In this work, we introduce robust, fastly programmable, nonvolatile organic memristive nanodevices based on electrografted redox complexes that implement synapses thanks to a wide range of accessible intermediate conductivity states. We demonstrate experimentally an elementary neural network, capable of learning functions, which combines four pairs of organic memristors as synapses and conventional electronics as neurons. Our architecture is highly resilient to issues caused by imperfect devices. It tolerates inter-device variability and an adaptable learning rule offers immunity against asymmetries in device switching. Highly compliant with conventional fabrication processes, the system can be extended to larger computing systems capable of complex cognitive tasks, as demonstrated in complementary simulations

Carbon nano-materials for high-performance and flexible electronics : status and prospects

International audienc

Analyse architecturale et pertinence des techniques de représentation numériques: Une expérience pédagogique

Depuis une dizaine d’années, l’exploration des techniques de représentation numériques susceptibles de se substituer ou d’étendre le champ des moyens traditionnels utilisés dans le cadre de l’analyse architecturale constitue un axe important de notre approche pédagogique. L’élaboration de courts-métrages en synthèse d’image en tant que supports à l’analyse architecturale est analysée, ici, à la lumière de deux préoccupations majeures. D’une part, l’inévitable continuité historique dans laquelle s’inscrivent les technologies numériques de représentation architecturale. D’autre part, la contamination — entendue dans un sens positif — des moyens traditionnels par une culture visuelle nourrie par le cinéma, la publicité ou le jeu vidéo.info:eu-repo/semantics/publishe

Analyse architecturale et pertinence des techniques de représentation numérique

Depuis une dizaine d’années, l’exploration des techniques de représentation numériques susceptibles de se substituer ou d’étendre le champ des moyens traditionnels utilisés dans le cadre de l’analyse architecturale constitue un axe important de notre approche pédagogique. L’élaboration de courts-métrages en synthèse d’image en tant que supports à l’analyse architecturale est analysée, ici, à la lumière de deux préoccupations majeures. D’une part, l’inévitable continuité historique dans laquelle s’inscrivent les technologies numériques de représentation architecturale. D’autre part, la contamination — entendue dans un sens positif — des moyens traditionnels par une culture visuelle nourrie par le cinéma, la publicité ou le jeu vidéo.info:eu-repo/semantics/nonPublishe