Gate-dependent magnetoresistance phenomena in carbon nanotubes

We report on the first experimental study of the magnetoresistance of double-walled carbon nanotubes under magnetic field as large as 50 Tesla. By varying the field orientation with respect to the tube axis, or by gate-mediated shifting the Fermi level position, evidences for unconventional magnetoresistance are presented and interpreted by means of theoretical calculations

Nanodevices for correlated electrical transport and structural investigation of individual carbon nanotubes

We report a new approach to the correlation of the structural properties and the transport properties of carbon nanotubes. Through an original combination of UV lithography, custom-made photosensitive sol–gel resist and deep reactive ion etching (RIE), we have successfully integrated membrane technology and nanodevice fabrication for the electrical connection of individual carbon nanotubes. After single wall nanotube (SWNT) deposition by molecular combing and contacting using high resolution electron beam lithography, we obtain a device that allows both the investigation of the nanotubes and the contact regions by transmission electron microscopy (TEM) and the measurement of the electronic transport properties of the same individual nano-object. The whole fabrication process is detailed and the demonstration that the micro membranes are suitable for both TEM inspection and nanoelectrode fabrication is given

Alignment and nano-connections of isolated carbon nanotubes

We report a new approach for the alignment and the electrical nano-connection of isolated carbon nanotubes (CNTs). Through a novel combination of proven technics, we have been able to align isolated carbon nanotubes and selectively contact those CNTs by high resolution electron beam lithography (HREBL). Resistance versus temperature (R(T)) experiments have been carried out to determine the reliability of the metal–CNTs interface and to probe the electronic conductance of the CNT

Single-Frequency High-Power Continuous-Wave Oscillation at 1003 nm of an Optically Pumped Semiconductor Laser

This work reports single-frequency laser oscillation at 1003.4 nm of an optically pumped external cavity semiconductor laser. By using a gain structure bonded onto a high conductivity substrate, we demonstrate both theoretically and experimentally the strong reduction of the thermal resistance of the active semiconductor medium, resulting in a high power laser emission. The spectro-temporal dynamics of the laser is also explained. Furthermore, an intracavity frequency-doubling crystal was used to obtain a stable single-mode generation of blue (501.5 nm) with an output power around 60 mW.Comment: 11 page

Probing the electronic properties of individual carbon nanotube in 35 T pulsed magnetic field

After optimization of the alignment and the nano-contact processes of isolated single wall and double-walls carbon nanotube, we investigate the high magnetic field effects on the electronic transport properties of an individual metallic CNT. We develop pioneer multi-probes magneto-transport experiments under a 35 T pulsed field which reveal an unexpected oscillatory behavior of RðHÞ inconsistent with existing theories

Nanotechnologies associées à la caractérisation et à la mesure d'un nanotube de carbone

Les travaux présentés dans cette thèse traitent des étapes nécessaires à la connexion et à l'analyse structurale de nano-objets : les nanotubes de carbone. Dans un premier temps, nous nous sommes intéressés aux contraintes et impératifs qui ont dus être pris en compte lors du développement et de la réalisation des échantillons. Ces échantillons représentent la base sur laquelle nous allons réaliser le dépôt et la connexion de nanotubes de carbone. Ces échantillons sont réalisés en faisant appel aux méthodes de fabrication parallélisée issues de la technologie silicium. Le peignage moléculaire nous permet de contrôler l'orientation et la densité d'objets déposés. Les paramètres critiques associés à ces dépôts ont été déterminés et leurs influences discutées. Après dépôt et repérage par AFM, les objets sont connectés aux échantillons par le biais d'électrodes nanométriques réalisées par lithographie électronique à haute résolution. Enfin, nous avons développé une technologie pour la réalisation de membranes d'épaisseur nanométrique, alignables et compatibles avec l'étape de connexion par lithographie électronique. L'utilisation de telles membranes permet de caractériser les nanotubes de carbone structurellement et morphologiquement tout en ayant la possibilité d'évaluer leurs propriétés de transport électronique. Plusieurs types de grilles électrostatiques ont été adaptés pour permettre une investigation approfondie de la structure de bande des nanotubes par mesure de conductivité. Enfin, plusieurs investigations croisées entre structure et propriétés de transport électronique sous 60T ont permis de valider ces technologies.We studied the different steps involved in the connexion and structural analysis of carbon nanotubes. In a first step, we developed the process required for the production of our substrates. Those substrates are the cornerstone on which deposition and connexion of the carbon nanotubes will happen. Those samples are produced thanks to the parallelized production means of the silicon technology. Molecular combing allowed us to control orientation and density of the nanotubes. The critical parameters associated with this kind of deposition and their influence have been determined. After deposition and registration through AFM observation, the nanotubes are connected thanks to nanometer sized electrodes patterned by high resolution electron beam lithography. We also developed a process for the realisation of nanometer thick membranes. Those membranes are to be aligned on the electrodes patterns and compatible with the nanoconnexion process. Such membranes allow us to structurally characterize the very nanotube that is to be measured by transport measurements. Different kind of electrostatic gates have also been developed to enable a more in-depth probing of the band structure through conductivity measurements. At last, some cross investigations between transport measurement under 60T pulsed magnetic field and structural characterisation have been performed to validate the technologies developed during this thesis.TOULOUSE-INSA (315552106) / SudocSudocFranceF

Single-Frequency High-Power Continuous-Wave Oscillation at 1003 nm of an Optically Pumped Semiconductor Laser

11 pagesInternational audienceThis work reports single-frequency laser oscillation at 1003.4 nm of an optically pumped external cavity semiconductor laser. By using a gain structure bonded onto a high conductivity substrate, we demonstrate both theoretically and experimentally the strong reduction of the thermal resistance of the active semiconductor medium, resulting in a high power laser emission. The spectro-temporal dynamics of the laser is also explained. Furthermore, an intracavity frequency-doubling crystal was used to obtain a stable single-mode generation of blue (501.5 nm) with an output power around 60 mW

Continuous-wave versus time-resolved measurements of Purcell-factors for quantum dots in semiconductor microcavities

International audienceThe light emission rate of a single quantum dot can be drastically enhanced by embedding it in a resonant semiconductor microcavity. This phenomenon is known as the Purcell effect, and the coupling strength between emitter and cavity can be quantified by the Purcell factor. The most natural way for probing the Purcell effect is a time-resolved measurement. However, this approach is not always the most convenient one, and alternative approaches based on a continuous-wave measurement are often more appropriate. Various signatures of the Purcell effect can indeed be observed using continuous-wave measurements (increase of the pump rate needed to saturate the quantum dot emission, enhancement of its emission rate at saturation, change of its radiation pattern), signatures which are encountered when a quantum dot is put on-resonance with the cavity mode. All these observations potentially allow one to estimate the Purcell factor. In this paper, we carry out these different types of measurements for a single quantum dot in a pillar microcavity and we compare their reliability. We include in the data analysis the presence of independent, non-resonant emitters in the microcavity environment, which are responsible for a part of the observed fluorescence

Reduced Lasing Thresholds in GeSn Microdisk Cavities with Defect Management of the Optically Active Region

International audienceGeSn alloys are nowadays considered as the most promising materials to build Group IV laser sources on silicon (Si) in a full complementary metal oxide semiconductor-1 arXiv:submit/3525756 [physics.app-ph] 21 Dec 2020 compatible approach. Recent GeSn laser developments rely on increasing the band structure directness, by increasing the Sn content in thick GeSn layers grown on germanium (Ge) virtual substrates (VS) on Si. These lasers nonetheless suffer from a lack of defect management and from high threshold densities. In this work we examine the lasing characteristics of GeSn alloys with Sn contents ranging from 7 % to 10.5 %. The GeSn layers were patterned into suspended microdisk cavities with different diameters in the 4-8 µm range. We evidence direct band gap in GeSn with 7 % of Sn and lasing at 2-2.3 µm wavelength under optical injection with reproducible lasing thresholds around 10 kW cm −2 , lower by one order of magnitude as compared to the literature. These results were obtained after the removal of the dense array of misfit dislocations in the active region of the GeSn microdisk cavities. The results offer new perspectives for future designs of GeSn-based laser sources

Efficacy of Caffeine in ADCY5 ‐Related Dyskinesia: A Retrospective Study

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