Le transport d’ions et de molécules à l’intérieur de canaux nanométriques diffère du transport à l’échelle micro- ou macroscopique du fait de rapports surface/volume bien plus élevés conduisant à de nouveaux phénomènes de transport. Les nanotubes de carbone avec leurs propriétés uniques apparaissent comme des canaux exceptionnellement intéressants pour mieux comprendre le transport ionique et fluidique à l’échelle nanométrique et pour d’éventuelles applications nanofluidiques. Ce travail est dédié à l’étude et la compréhension des mécanismes de transport des ions en phase aqueuse à l’intérieur de nanotubes de carbone, un sujet particulièrement important pour le développement d’applications dans le domaine du séquençage de l’ADN ou de l’analyse biochimique de petites molécules.Durant ce travail, un protocole a été développé pour la fabrication de dispositifs microfluidiques intégrant des nanotubes de carbone et permettant des mesures à la fois électriques et optiques. Les propriétés de transport à l’intérieur de nanotubes de carbone mono-feuillets ont été étudiées en combinant mesures de courant ionique sous application d’un champ électrique, spectroscopie Raman et modélisation théorique. Les résultats obtenus par cette étude démontrent la forte influence de l’environnement du nanotube sur la densité et la distribution des charges de surface et donc sur les propriétés de transport à l’intérieur de ces nano-canaux dont les parois sont d’épaisseur atomique. Les ordres de grandeur des courants ioniques mesurés expérimentalement sont en bon accord avec les modèles standards de transport ionique dans un nanocanal en considérant des densités de charge de surface et des longueurs de glissement physiquement raisonnables. De manière importante, ce travail a permis de mettre en évidence un transport ionique activé par champ électrique à l’intérieur de nanotubes de carbone, qui peut être expliqué en considérant un modèle de transport plus élaboré intégrant une ou plusieurs barrières d’énergie le long du nanotube. Les résultats de la caractérisation Raman suggèrent que ces barrières d’énergie résultent d’un dopage hétérogène le long du nanotube induit par la matrice polymère. / Ionic and molecular transport inside nanometer scale geometries is distinct from micro- and macroscale transport due to the large surface-to-volume ratios which lead to unique transport phenomena. Carbon nanotubes with their peerless properties appear as exceptional channels for understanding fluidic and ionic transport at the nanoscale and for developing nanofluidics-based applications. This work is devoted at studying and understanding the transport mechanisms of ions in aqueous phase through carbon nanotubes, which is especially important for various applications such as DNA sequencing or biochemical analysis of small molecules.During this work, a protocol was developed for the fabrication of carbon nanotubes-based microfluidic devices which are suitable for both electrical and optical measurements. The transport properties through single-walled carbon nanotubes were investigated by combining ion current measurements under an applied voltage, Raman spectroscopy and theoretical modelling. The results obtained from this study highlight the strong influence of the nanotube environment on their surface charge density and distribution and hence on the ionic transport properties through these nanochannels having walls of atomic thickness. The orders of magnitude of the ionic currents experimentally measured are in good agreement with the standard models of ion transport through nanochannels when considering physically reasonable values of surface charge densities and slip lengths. Importantly, this work allowed us to evidence a novel voltage-activated transport of ions through carbon nanotubes which can be accounted for by considering a more elaborate transport model including the presence of one or more energy barriers along the nanotube. Raman characterization results support that these energy barriers result from a heterogeneous doping along the nanotubes induced by the polymer matrix.

Carbon nanotubes (CNTs) and graphene nanoplatelets (GNPs) are attractive reinforcements for lightweight and high strength metal matrix composites due to their excellent mechanical and physical properties. The present work is an attempt towards investigating the effect of CNT and GNP reinforcements on the mechanical properties of nickel matrix composites. The CNT/Ni (dry milled) nanocomposites exhibiting a tensile yield strength of 350 MPa (about two times that of SPS processed monolithic nickel ~ 160 MPa) and an elongation to failure ~ 30%. In contrast, CNT/Ni (molecular level mixed) exhibited substantially higher tensile yield strength (~ 690 MPa) but limited ductility with an elongation to failure ~ 8%. The Ni-1vol%GNP (dry milled) nanocomposite exhibited the best balance of properties in terms of strength and ductility. The enhancement in the tensile strength (i.e. 370 MPa) and substantial ductility (~40%) of Ni-1vol%GNP nanocomposites was achieved due to the combined effects of grain refinement, homogeneous dispersion of GNPs in the nickel matrix, and well-bonded Ni-GNP interface, which effectively transfers stress across metal-GNP interface during tensile deformation. A second emphasis of this work was on the detailed 3D microstructural characterization of a new class of Ni-Ti-C based metal matrix composites, developed using the laser engineered net shaping (LENSTM) process. These composites consist of an in situ formed and homogeneously distributed titanium carbide (TiC) as well as graphite phase reinforcing the nickel matrix. 3D microstructure helps in determining true morphology and spatial distribution of TiC and graphite phase as well as the phase evolution sequence. These Ni-TiC-C composites exhibit excellent tribological properties (low COF), while maintaining a relatively high hardness.

As part of the EU SmartVista project to develop a multi-modal wearable sensor for health diagnostics, field-effect transistor (FET) based biosensors were explored, with glucose as the analyte, and carbon nanotubes (CNTs) or monolayer MoS2 as the semiconducting sensing layer.  Numerous arrays of CNT-FETs and MoS2-FETs were fabricated by photolithographic methods and packaged as integrated circuits.  Functionalization of the sensing layer using linkers and enzymes was performed, and the samples were characterized by atomic force microscopy, scanning electron microscopy, optical microscopy, and electrical measurements. ON/OFF ratios of 102 p-type and < 102 n-type were acheived, respectively, and the work helped survey the viability of realizing such sensors in a wearable device. / EU Horizon 2020 - SmartVista (825114)

Eine Reihe wichtiger Wachstums- und Integrationsaspekte von Kohlenstoff-Nanoröhren wurde im Rahmen dieser Arbeit untersucht. Der Schwerpunkt der experimentellen Arbeit lag dabei hauptsächlich bei einschaligen Kohlenstoffnanoröhren (SWCNT). Das große Potential dieser Nanoröhren für Transistor-Anwendungen wurde durch die Herstellung einer Vielzahl funktionierender Bauelemente aus diesen Kohlenstoffnanoröhren mittels relativ einfacher Herstellungsprozesse demonstriert. Ein fundiertes Verständnis für die Abhängigkeiten des Nanoröhrenwachstums von einer Vielzahl an Parametern wurde mit Hilfe mehrerer tausend Wachstumsexperimente gesammelt. Verschiedene Katalysatormetalle, Kohlenstoffquellen und Katalysatorunterlagen wurden detailliert untersucht. Ein Hauptaugenmerk wurde dabei auf eine Reduzierung der Wachstumstemperatur gerichtet. Die niedrige Wachstumstemperatur spielt eine große Rolle für eine möglichst hohe Kompatibilität mit konventionellen Herstellungsverfahren der Silizium-Halbleitertechnik. Ein einfaches phänomenologisches Wachstumsmodell wurde für die Synthese von Nanoröhren mittels katalytisch-chemischer Gasphasen-Abscheidung (CCVD) formuliert. Dieses Modell basiert hauptsächlich auf der Oberflächendiffusion von adsorbierten Kohlenstoffverbindungen entlang der Seitenwände der Nanoröhren sowie auf der Oberfläche der Katalysatorunterlage. Das Modell ist eine wichtige Ergänzung zu dem VLS-Mechanismus. Ein Wachstumsverfahren zur Herstellung von Nanoröhren für niedrigere Temperaturen bis zu 600 °C wurde entwickelt. Experimentell wurde nachgewiesen, dass der Durchmesser des Katalysatorteilchens fast ausschließlich bestimmt, wie viele Schalen eine wachsende Nanoröhre bei geeigneten Wachstumsbedingungen hat. Es wurde zum ersten Mal gezeigt, dass einschalige Kohlenstoffnanoröhren auf Metallelektroden wachsen werden können, insofern eine dünne Aluminiumschicht als Trennschicht verwendet wird. Dadurch können in-situ kontaktierte Nanoröhren einfach hergestellt werden, was deren elektrische Charakterisierung weitaus erleichtert. Mittels stromloser Abscheidung von Nickel oder Palladium aus einer Lösung konnte eine deutliche Verbesserung der Kontaktwiderstände der in-situ-kontaktierten Nanoröhren erreicht werden. Durch Einbettung von Nanoröhren in eine Tantaloxidschicht konnten Transistoren mit einem Dielektrikum mit hoher relativer Dielektrizitätskonstante hergestellt werden. Die Tantaloxidschicht wurde mit einem neu entwickelten Tauchprozess abgeschieden. Erstmalig wurden Transistoren basierend auf Kohlenstoffnanoröhren hergestellt, die relativ hohe Ströme (Milliampere) mit einer Modulation bis zu einem Faktor 500 schalten können. Diese Transistoren beruhen auf einer Parallelschaltung einer großen Anzahl an Nanoröhren. Mit Hilfe der hergestellten Transistoren konnten die Eigenschaften einer großen Zahl von Nanoröhren untersucht werden, wobei große Unterschiede in den elektronischen Eigenschaften von metallischen Nanoröhren, halbleitenden Nanoröhren und Nanoröhren mit einer kleinen Bandlücke beobachtet wurden. / A number of very important growth and integration aspects of carbon nanotubes have been investigated during the course of this thesis. The focus was mainly on single-walled carbon nanotubes. Their potential for transistor applications was demonstrated by the successful fabrication of a variety of devices using rather simple processes. A detailed understanding of the dependence of SWCNT growth on a variety of parameters was obtained as the result of several thousand growth experiments. Various catalyst materials, gaseous carbon sources, and catalyst supports have been investigated. Special attention was paid to a considerable reduction of the growth temperature. A simple phenomenological growth model could be derived for CCVD of SWCNTs taking into account a number of effects observed during the various growth experiments. The model presented is mainly based on the surface diffusion of carbon species along the sidewalls of the carbon nanotubes or on the catalyst support and is an addition to the vapor-liquid-solid (VLS) mechanism. Growth methods for the CCVD synthesis of SWCNTs were developed for temperatures as low as 600 °C. It has been found that the size of the catalyst particle alone determines whether a SWCNT, DWCNT, or MWCNT will nucleate from a specific particle under suitable growth conditions. It could be demonstrated for the first time that SWCNTs can be grown on a variety of conducting materials if the catalyst is separated from the electrode by a thin Al layer. In-situ contacted SWCNTs can be easily obtained that way, largely facilitating the electronic characterization of as-grown SWCNTs. A tremendous improvement of the contacts of in-situ contacted SWCNTs could be achieved by electroless deposition. SWCNT growth on appropriate electrodes allowed the encapsulation of the nanotubes by electroless deposition of Ni and Pd, yielding good and reliable contacts. SWCNT transistors with a high-k dielectric could be fabricated by encapsulation of the nanotube with a tantalum oxide layer. The tantalum oxide was deposited by a newly developed dip-coat process. High-current SWCNT transistors consisting of a large number of SWCNTs in parallel were demonstrated for the first time during this work. Finally, the properties of a large number of CCVD grown SWCNTs have been investigated by electronic transport measurement. Large differences in the electronic transport have been observed for metallic, small band gap semiconducting (SGS), and semiconducting SWCNTs with small diameters.

<p>U ovom radu, izvr&scaron;ena je sinteza i karakterizacija bionanokompozitnih materijala na osnovu poli(laktida) i vi&scaron;eslojnih ugljeničnih nanocevi. Ispitivan je uticaj različitih tehnika funkcionalizacije nanocevi, kao i izbor uslova sinteze i odnosa polaznih komponenti sistema, na svojstva dobijenih kompozitnih materijala na osnovu poli(L-laktida). Radi postizanja uniformne raspodele nanopunila u kompozitima, vi&scaron;eslojne ugljenične nanocevi su modifikovane hemijskom i radijacionom funkcionalizacijom. Izvr&scaron;ena je karakterizacija ugljeničnih nanocevi, sa ciljem utvrđivanja uspe&scaron;nosti primenjenih tehnika modifikacije na njihova svojstva i stepen funkcionalizacije. Metodom in situ polimerizacije L-laktida sa povr&scaron;ina modifikovanih nanocevi, pripremljene su serije uzoraka kompozitnih materijala sa različitim sadrţajem funkcionalizovanih nanocevi. Detaljno je ispitan uticaj funkcionalizovanih nanocevi na toplotna, kristalna, morfolo&scaron;ka, mehanička i električna svojstva sintetisanih kompozitnih materijala. Postignuta homogena disperzija nanocevi unutar biorazgradive, biokompatibilne matrice polimera koji se dobija iz obnovljivih sirovina, uticala je na pobolj&scaron;anje svojstava, kao i na uspostavljanje novih funkcionalnosti dobijenih materijala. Značajno pobolj&scaron;anje toplotnih i mehaničkih svojstva sintetisanih materijala, zajedno sa postignutom električnom provodljivo&scaron;ću, omogućava pro&scaron;irenje oblasti primene kompozita na osnovu poli(laktida) i ugljeničnih nanocevi.</p> / <p>In this thesis, bionanocomposites based on poly(lactide) and multi-walled carbon nanotubes were synthesized and characterised. Poly(L-lactide) was used as a matrix for the composite synthesis; the influence of nanofillers content, the methods of their functionalization, as well as the synthesis parameters, on the properties of obtained materials were investigated. In order to achieve a uniform dispersion of nanofillers in composite materials, multi-walled carbon nanotubes were modified using chemical and radiation functionalization. Characterization of carbon nanotubes was performed in order to determine the influence of applied modification techniques on their properties and degree of functionalization. A series of composite materials with different content of modified nanotubes were prepared by in situ polymerization of L-lactide from the surface of functionalized nanotubes. The influence of functionalized nanotubes on the thermal, crystal, morphological, mechanical and electrical properties of synthesized composites was investigated in detail. The homogeneous dispersion of carbon nanotubes within the biodegradable, biocompatible, biobased polymer matrix, has influenced the improvement of the properties, as well as the acquiring of new functionalities of synthesized materials. The significant improvement of thermal and mechanical properties of composites, and the achievement of its electrical conductivity, allow the field of application of composites based on poly(lactide) and carbon nanotubes to be expanded.</p>

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In this dissertation, we use finite element method together with other numerical techniques to study advanced electron devices. We study the radiation properties in electron waveguide structure with multi-step discontinuities and soft wall lateral confinement. Radiation mechanism and conditions are examined by numerical simulation of dispersion relations and transport properties. The study of geometry variations shows its significant impact on the radiation intensity and direction. In particular, the periodic corrugation structure exhibits strong directional radiation. This interesting feature may be useful to design a nano-scale transmitter, a communication device for future nano-scale system. Non-quasi-static effects in AC characteristics of carbon nanotube field-effect transistors are examined by solving a full time-dependent, open-boundary Schrödinger equation. The non-quasi-static characteristics, such as the finite channel charging time, and the dependence of small signal transconductance and gate capacitance on the frequency, are explored. The validity of the widely used quasi-static approximation is examined. The results show that the quasi-static approximation overestimates the transconductance and gate capacitance at high frequencies, but gives a more accurate value for the intrinsic cut-off frequency over a wide range of bias conditions. The influence of metal interconnect resistance on the performance of vertical and lateral power MOSFETs is studied. Vertical MOSFETs in a D2PAK and DirectFET package, and lateral MOSFETs in power IC and flip chip are investigated as the case studies. The impact of various layout patterns and material properties on RDS(on) will provide useful guidelines for practical vertical and lateral power MOSFETs design.

No / The objective of this review is to provide an overview concerning what the authors believe to be the most important photoelectrochemical techniques for the study of semiconductor nanoparticles. After a short historical background and a brief introduction to the area of photoelectrochemistry, the working principles and experimental setups of the various static and dynamic techniques are presented. Experimental details which are of crucial importance for their correct execution are emphasized, and applications of the techniques as found in the recent research literature as applied to semiconductor nanoparticles are illustrated.

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