Self-oscillations in field emission nanowire mechanical resonators: a nanometric DC-AC conversion

We report the observation of self-oscillations in a bottom-up nanoelectromechanical system (NEMS) during field emission driven by a constant applied voltage. An electromechanical model is explored that explains the phenomenon and that can be directly used to develop integrated devices. In this first study we have already achieved ~50% DC/AC (direct to alternative current) conversion. Electrical self-oscillations in NEMS open up a new path for the development of high speed, autonomous nanoresonators, and signal generators and show that field emission (FE) is a powerful tool for building new nano-components

Current Saturation in Field Emission from H-Passivated Si Nanowires

International audienceThis paper explores the field emission (FE) properties of highly crystalline Si nanowires (NWs) with controlled surface passivation. The NWs were batch-grown by the vapor_liquid_solid process using Au catalysts with no intentional doping. The FE current_voltage characteristics showed quasi-ideal current saturation that resembles those predicted by the basic theory for emission from semiconductors, even at room temperature. In the saturation region, the currents were extremely sensitive to temperature and also increased linearly with voltage drop along the nanowire. The latter permits the estimation of the doping concentration and the carrier lifetime, which is limited by surface recombination. The conductivity could be tuned over 2 orders of magnitude by in situ hydrogen passivation/desorption cycles. This work highlights the role of dangling bonds in surface leakage currents and demonstrates the use of hydrogen passivation for optimizing the FE characteristics of Si NWs

Field emission measure of the time response of individual semiconducting nanowires to laser excitation

International audienceA simple technique is explored to determine the temporal photo-response, s, of individual semiconducting SiC and Si nanowires (NWs), with a high time resolution. Laser-assisted field emission (LAFE) from the NWs is first shown to be highly sensitive to continuous laser illumination. Pulsed illumination is then combined with measurements of the total energy distributions to determine s which were rather large, 4-200 ls. The time response scaled roughly with the square of the NWs length and could be attributed to laser-induced heating. LAFE is thus a new tool for quantifying rapid thermo-optical effects in such nano-objects

Direct growth of carbon nanotubes on new high-density 3D pyramid-shaped microelectrode arrays for brain-machine interfaces

Silicon micromachined, high-density, pyramid-shaped neural microelectrode arrays (MEAs) have been designed and fabricated for intracortical 3D recording and stimulation. The novel architecture of this MEA has made it unique among the currently available micromachined electrode arrays, as it has provided higher density contacts between the electrodes and targeted neural tissue facilitating recording from different depths of the brain. Our novel masking technique enhances uniform tip-exposure for variable-height electrodes and improves process time and cost significantly. The tips of the electrodes have been coated with platinum (Pt). We have reported for the first time a selective direct growth of carbon nanotubes (CNTs) on the tips of 3D MEAs using the Pt coating as a catalyzer. The average impedance of the CNT-coated electrodes at 1 kHz is 14 k. The CNT coating led to a 5-fold decrease of the impedance and a 600-fold increase in charge transfer compared with the Pt electrode

Studies of the physical properties of individual silicon carbide nanowires by field emission

Ce travail s’inscrit dans le cadre de la caractérisation physique de nanofils (NF) semiconducteurs (SC) qui est un domaine en plein essor ces dernières années. Plus précisément, nous explorons l’émission de champ (EC) de NFs individuels de Carbure de Silicium (SiC) pour leur potentialité comme source d'électrons, mais surtout pour étudier leurs propriétés de transport électrique, optiques et mécaniques.Le rôle important joué par la surface dans ces NFs a été prouvé par des traitements in situ qui ont eu des conséquences radicales sur l’EC dévoilant ainsi des propriétés d’émission propres aux SCs. En particulier, un régime de saturation, en accord avec la théorie d’EC des SCs, associé à une forte dépendance de l'émission à la température et à l’illumination laser a été révélé pour la première fois pour un NF. Ces mesures ouvrent des perspectives importantes tant pour la recherche fondamentale que pour les applications telles que la réalisation de photocathodes et de sources d’électrons pilotées optiquement ou par la température. Les caractéristiques courant-tension-température associées à l’analyse en énergie des électrons émis nous ont permis de déterminer le mécanisme de transport dans ces NFs, qui est limité par le nombre de porteurs dans le volume et contrôlé par les pièges présents dans la bande interdite par l’effet Poole-Frenkel. Finalement, la caractérisation mécanique a révélé des valeurs du facteur de qualité élevé (160000) et du module de Young allant jusqu’à 700GPa. Ces valeurs sont très prometteuses pour l’utilisation de ces NFs dans les systèmes nano-électro-mécaniques et dans les composites.We use field emission (FE) from individual silicon carbide nanowires (NWs) to explore their potential as electron sources, and especially as a versatile tool for studying transport, optical and mechanical properties of NWs. These studies fall within the larger framework of the physics of semiconducting (SC) nanowires, which is presently a large and rapidly expanding domain. The important role played by the surface in the transport and optical properties of NWs was clearly demonstrated by the radical consequences induced by in situ treatments on the FE properties. This permitted the observation of the specific behavior expected for SCs, particularly, a current saturation regime in agreement with the theory of FE for SCs. We found that the saturation was concomitant with a strong dependence of the emission on temperature and laser illumination, revealed for the first time for a NF. These measurements open important perspectives for both fundamental research and applications such as the realization of optically or thermally controlled FE electron sources. The current-voltage-temperature characteristics were carried out in parallel with measurement of the energy distributions of the emitted electrons, thus permitting the determination of the transport mechanism in the NWs. We found that the transport was limited by the carrier density in the volume and by the traps in the gap that generate current through the Poole-Frenkel effect. Finally, the mechanical characterization revealed high quality factors, as high as 160,000, and a Young’s modulus up to 700 GPa. These values are very promising for the use of these NWs in nano-electro-mechanical systems (NEMS) and composites

Étude des propriétés physiques de nanofils individuels de carbure de silicium par émission de champ

We use field emission (FE) from individual silicon carbide nanowires (NWs) to explore their potential as electron sources, and especially as a versatile tool for studying transport, optical and mechanical properties of NWs. These studies fall within the larger framework of the physics of semiconducting (SC) nanowires, which is presently a large and rapidly expanding domain. The important role played by the surface in the transport and optical properties of NWs was clearly demonstrated by the radical consequences induced by in situ treatments on the FE properties. This permitted the observation of the specific behavior expected for SCs, particularly, a current saturation regime in agreement with the theory of FE for SCs. We found that the saturation was concomitant with a strong dependence of the emission on temperature and laser illumination, revealed for the first time for a NF. These measurements open important perspectives for both fundamental research and applications such as the realization of optically or thermally controlled FE electron sources. The current-voltage-temperature characteristics were carried out in parallel with measurement of the energy distributions of the emitted electrons, thus permitting the determination of the transport mechanism in the NWs. We found that the transport was limited by the carrier density in the volume and by the traps in the gap that generate current through the Poole-Frenkel effect. Finally, the mechanical characterization revealed high quality factors, as high as 160,000, and a Young’s modulus up to 700 GPa. These values are very promising for the use of these NWs in nano-electro-mechanical systems (NEMS) and composites.Ce travail s’inscrit dans le cadre de la caractérisation physique de nanofils (NF) semiconducteurs (SC) qui est un domaine en plein essor ces dernières années. Plus précisément, nous explorons l’émission de champ (EC) de NFs individuels de Carbure de Silicium (SiC) pour leur potentialité comme source d'électrons, mais surtout pour étudier leurs propriétés de transport électrique, optiques et mécaniques.Le rôle important joué par la surface dans ces NFs a été prouvé par des traitements in situ qui ont eu des conséquences radicales sur l’EC dévoilant ainsi des propriétés d’émission propres aux SCs. En particulier, un régime de saturation, en accord avec la théorie d’EC des SCs, associé à une forte dépendance de l'émission à la température et à l’illumination laser a été révélé pour la première fois pour un NF. Ces mesures ouvrent des perspectives importantes tant pour la recherche fondamentale que pour les applications telles que la réalisation de photocathodes et de sources d’électrons pilotées optiquement ou par la température. Les caractéristiques courant-tension-température associées à l’analyse en énergie des électrons émis nous ont permis de déterminer le mécanisme de transport dans ces NFs, qui est limité par le nombre de porteurs dans le volume et contrôlé par les pièges présents dans la bande interdite par l’effet Poole-Frenkel. Finalement, la caractérisation mécanique a révélé des valeurs du facteur de qualité élevé (160000) et du module de Young allant jusqu’à 700GPa. Ces valeurs sont très prometteuses pour l’utilisation de ces NFs dans les systèmes nano-électro-mécaniques et dans les composites

Direct Growth of Carbon Nanotubes on New High-Density 3D Pyramid-Shaped Microelectrode Arrays for Brain-Machine Interfaces

Silicon micromachined, high-density, pyramid-shaped neural microelectrode arrays (MEAs) have been designed and fabricated for intracortical 3D recording and stimulation. The novel architecture of this MEA has made it unique among the currently available micromachined electrode arrays, as it has provided higher density contacts between the electrodes and targeted neural tissue facilitating recording from different depths of the brain. Our novel masking technique enhances uniform tip-exposure for variable-height electrodes and improves process time and cost significantly. The tips of the electrodes have been coated with platinum (Pt). We have reported for the first time a selective direct growth of carbon nanotubes (CNTs) on the tips of 3D MEAs using the Pt coating as a catalyzer. The average impedance of the CNT-coated electrodes at 1 kHz is 14 kΩ. The CNT coating led to a 5-fold decrease of the impedance and a 600-fold increase in charge transfer compared with the Pt electrode

Recent advances in the synthesis of Silicon and Boron-based nanowires

International audienc