To fulfill the potential of carbon nanotube (CNT) as thermal interface material (TIM), the packing density of CNT array needs improvement. In this work, two potential ways to increase the packing density of CNT array are tested. They are liquid precursor(LP)CVD and cycled catalyst deposition method. Although LP-CVD turned out to be no help for packing density increase, it is proved to enhance the CNT growth rate. The packing density of CNT array indeed increases with the cycle number. The thermal conductivity of the CNT array increases with the packing density. This work is believed to be a step closer to the real life application of CNT in electronic packaging industry.

This study elucidates the effect of various processing parameters on polyacrylonitrile (PAN) /carbon nanotube (CNT) composite fiber structure and properties. Interaction between PAN and MWNT enabled the gel-spun PAN/MWNT composite fiber to be drawn to a higher draw ratio, than the control PAN fiber, resulting in the composite fiber tensile strength value as high as 1.3 GPa. PAN/MWNT composite fibers were stabilized and carbonized, and the resulting fibers have been characterized for their structure and properties. The effect of precursor fiber shelf-time on the mechanical properties of the gel-spun PAN/MWNT composite fibers is also reported. A rheological study of PAN-co-MAA/few wall nanotube (FWNT) composite solution has been conducted. At low shear rates, the network of FWNTs contributes to elastic response, resulting in higher viscosity and storage modulus for the composite solution as compared to the control solution. On the other hand, at high shear rates, the network of FWNTs can be broken, resulting in lower viscosity for the composite solution than that for the control solution. Larger PAN crystal size (~16.2 nm) and enhanced mechanical properties are observed when the fiber was drawn at room temperature (cold-drawing) prior to being drawn at elevated temperature (~ 165 °C; hot-drawing). Azimuthal scan of wide angle X-ray diffraction (WAXD) and Raman G-band intensities were used for the evaluation of Herman's orientation factor for PAN crystal (fPAN) and FWNT (fFWNT), respectively. Significantly higher nanotube orientation was observed than PAN orientation at an early stage of fiber processing (i.e during spinning, cold-drawing). Differential scanning calorimetry (DSC) revealed that PAN-co-MAA fiber can be converted into cyclic structure at milder conditions than those for PAN. Continuous in-line stabilization, carbonization, and characterization of the resulting carbon fibers were carried out. Rheological and fiber spinning studies have also been carried out on PAN-co-MAA/VGCNF (vapor grown carbon nano fiber). The diameter of PAN-co-MAA/VGCNF composite fiber is smaller than that of the PAN-co-MAA control fiber with same draw ratio due to the suppressed die-swell in the presence of VGCNF. The mechanical properties of PAN-co-MAA control and PAN-co-MAA/VGCNF composite fibers were characterized. Crystalline structure and morphology of the solution-spun PAN-co-MAA/VGCNF fibers are characterized using WAXD and scanning electron microscopy (SEM), respectively. The volume fraction of PAN-CNT interphase in PAN matrix has been calculated to illustrate the impact of CNTs on structural change in PAN matrix, when ordered PAN molecules are developed in the vicinity of CNTs during fiber processing. The effect of PAN-CNT interphase thickness, CNT diameter, and mass density of CNT on volume fraction of PAN-CNT interphase has been explored.

Synthetic single-walled metal oxide (aluminosilicate) nanotubes (SWNTs) are emerging materials for a number of applications involving molecular transport and adsorption due to their unique pore structure, high surface reactivity, and controllable dimensions. In this thesis, I discuss the potential for employing SWNTs in next generation separation platforms based upon recent progress on synthesis, interior modification, molecular diffusion properties, transport modeling and composite membrane preparation of metal oxide SWNTs. First, I describe the structure, synthesis, and characterization of the SWNTs. Thereafter, chemical modification of the nanotube interior is described as a means for tuning the nanotube properties for molecular separations. Interior functionalization of SWNTs (e.g. carbon nanotubes and metal oxide nanotubes) is a long-standing challenge in nanomaterials science. After controlled dehydration and dehydroxylation of the SWNTs, I then demonstrate that the SWNT inner surface can be functionalized with various organic groups of practical interest via solid-liquid heterogeneous reactions. Finally, I describe a mass transport modeling and measurements for composite membranes composed of SWNTs as fillers. This work demonstrates the use of SWNTs for novel scalable separation units from both a nanoscale and a macroscale point of view.

Cette thèse est consacrée à l'étude expérimentale des propriétés électroniques des nanotubes de carbone par des techniques de spectroscopie de photoluminescence.<br /> Le travail a d'abord consisté en la préparation et la caractérisation d'échantillons de nanotubes de carbone isolés les uns des autres dans une suspension de surfactant. Ils présentent alors de la luminescence. Intégrés ensuite dans un gel, ils sont adaptés aux températures entre 10 et 300 K. <br /> Le premier volet d'expériences a concerné la spectroscopie de luminescence en régime stationnaire. Les mesures sur des ensembles macroscopiques permettent d'identifier les classes de chiralité présentes et mettent en évidence divers phénomènes de couplage des nanotubes entre eux et à leur environnement. Grâce à un montage de microscopie confocale, on a en outre étudié la luminescence d'un nanotube unique. On s'affranchit ainsi de l'inhomogénéité de l'échantillon, comme le montrent les faibles largeurs de raies (moins de 1 meV à 10 K) et les phénomènes de diffusion spectrale et de clignotement observés à l'échelle de la seconde.<br /> Le second volet d'expériences est consacré à la spectroscopie de photoluminescence résolue en temps à l'échelle picoseconde, sur des ensembles de nanotubes. On mesure la dynamique de recombinaison des excitations élémentaires (excitons), sur 3 ordres de grandeur de variation, dans les chiralités (9,4) et (10,2). L'évolution du temps de vie (300 ps à 10 K, 50 ps à 300 K) et de l'intensité de la luminescence (présentant un maximum à 50 K) donne des informations sur la structure des états excitoniques. On estime en particulier qu'il existe un niveau noir 4 meV en dessous de l'état luminescent.

Polymer nanocomposite foams have attracted tremendous interests due to their multifunctional properties in addition to the inherited lightweight benefit of being foamed materials. Polymer nanocomposite foams using high performance polymer and bio-degradable polymer with carbon nanotubes were fabricated, and the effects of foam density and pore size on properties were characterized. Electrical conductivity modeling of polymer nanocomposite foams was conducted to investigate the effects of density and pore size. High performance polymer Polyetherimide (PEI) and multi-walled carbon nanotube (MWCNT) nanocomposites and their foams were fabricated using solvent-casting and solid-state foaming under different foaming conditions. Addition of MWCNTs has little effect on the storage modulus of the nanocomposites. High glass transition temperature of PEI matrix was maintained in the PEI/MWCNT nanocomposites and foams. Volume electrical conductivities of the nanocomposite foams beyond the percolation threshold were within the range of electro-dissipative materials according to the ANSI/ESD standard, which indicates that these lightweight materials could be suitable for electro-static dissipation applications with high temperature requirements. Biodegradable Polylactic acid (PLA) and MWCNT nanocomposites and their foams were fabricated using melt-blending and solid-state foaming under different foaming conditions. Addition of MWCNTs increased the storage modulus of PLA/MWCNT composites. By foaming, the glass transition temperature increased. Volume electrical conductivities of foams with MWCNT contents beyond the percolation threshold were again within the range of electro-dissipative materials according to the ANSI/ESD standard. The foams with a saturation pressure of 2 MPa and foaming temperature of 100 °C showed a weight reduction of 90% without the sacrifice of electrical conductivity. This result is promising in terms of multi-functionality and material saving. At a given CNT loading expressed as volume percent, the electrical conductivity increased significantly as porosity increased. A Monte-Carlo simulation model was developed to understand and predict the electrical conductivity of polymer/MWCNT nanocomposite foams. Two different foam morphologies were considered, designated as Case 1: volume expansion without nanotube rearrangement, and Case 2: nanotube aggregation in cell walls. Simulation results from unfoamed nanocomposites and the Case 1 model were validated with experimental data. The results were in good agreement with those from PEI/MWCNT nanocomposites and their foams, which had a similar microstructure as modeled in Case 1. Porosity effects on electrical conductivity were investigated for both Case 1 and Case 2 models. There was no porosity effect on electrical conductivity at a given volume percent CNT loading for Case 1. However, for Case 2 the electrical conductivity increased as porosity increased. Pore size effect was investigated using the Case 2 model. As pore size increased, the electrical conductivity also increased. Electrical conductivity prediction of foamed polymer nanocomposites using FEM was performed. The results obtained from FEM were compared with those from the Monte-Carlo simulation method. Feasibility of using FEM to predict the electrical conductivity of foamed polymer nanocomposites was discussed. FEM was able to predict the electrical conductivity of polymer nanocomposite foams represented by the Case 2 model with various porosities. However, it could not capture the pore size effect in the electrical conductivity prediction. The FEM simulation can be utilized to predict the electrical conductivity of Case 2 foams when the percolation threshold is determined by Monte-Carlo simulation to save the computational time. This has only been verified when the pore size is small in the range of a few micrometers. / text

The use of nanotechnology to develop methods for fabrication and characterization of organized hybrid nanostructures that include integrated polymeric, biological and inorganic compounds has increased exponentially during the last decade. Such bio-nano-composite materials could be used in solving current biomedical problems spanning from nanomedicine to tissue engineering and biosensing. In this dissertation, a systematic study has been carried out on the synthesis, characterization, of two interfaces between naturally derived and synthetic nanostructures. Carbon nanotubes and porous silicon represent the synthetic nanostructures that were developed for the purpose of interfacing with the naturally derived bovine type I collagen and respiratory syncytial virus DNA respectively. Firstly, the synthesis of collagen-carbon nanotubes by two different techniques: fibrillogenesis through slow wet fiber drawing (gelation process) and electrospinning has been highlighted. Characterization of the novel nanocomposite was conducted using electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, nanoindentation, and Raman spectroscopy. The collagen-carbon nanotube gelation process was found to have superior nanoscale surface mechanical properties that were more conducive to higher osteoblast specific protein expression such as osteocalcin. Applications of the developed nanofibers are detailed in the fields of orthopaedics and tissue engineering. Secondly, an overview of porous silicon synthesized by hydrofluoric acid is presented. A parametric study was performed to determine the optimal pore size was carried out. The use of porous silicon as a biosensor to detect RSV virus by DNA hybridization was then provided and the importance of the interface chemistry was highlighted.

Hydrogen sensor technology is a crucial component for safety and many other practical concerns in the hydrogen economy. To achieve a desired sensor performance, proper choice of sensing material is critical, because it directly affects the main features of a sensor, such as response time, sensitivity, and selectivity. Palladium is well-known for its ability to sorb a large amount of hydrogen. Most hydrogen sensors use Pd-based sensing materials. Since hydrogen sensing is based on surface and interfacial interactions between the sensing material and hydrogen molecules, nanomaterials, a group of low dimensional systems with large surface to volume ratio, have become the focus of extensive studies in the potential application of hydrogen sensors. Pd nanowires and Pd-coated carbon nanotubes have been successfully used in hydrogen sensors and excellent results have been achieved. Motivated by this fact, in this dissertation, we perform theoretical modeling to achieve a complete and rigorous description of molecular interactions, which leads to the understanding of molecular behavior and sensing mechanisms.To demonstrate the properties of Pd-based sensing materials, two separate modeling techniques, but with the same underlying aim, are presented in this dissertation. Molecular dynamic simulations are applied for the thermodynamic, structural and dynamic properties of Pd nanomaterials. Ab initio calculations are utilized for the study of sensing mechanism of Pd functionalized single wall carbon nanotubes. The studies reported in this dissertation show the applications of computational simulations in the area of hydrogen sensors. It is expected that this work will lead to better understanding and design of molecular sensor devices.

Device fabrication on multi walled carbon nanotubes (MWCNTs) using electrical beam lithography (EBL), electron beam induced deposition (EBID), ion beam induced deposition (IBID) methods was carried out, followed by device electrical characterization using a conventional probe station. A four-probe configuration was utilized to measure accurately the electrical resistivity of MWCNTs with similar results obtained from devices fabricated by different methods. In order to reduce the contact resistance of the beam deposited platinum electrodes, single step vacuum thermal annealing was performed. Microscopy and spectroscopy were carried out on the beam deposited electrodes to follow the structural and chemical changes occurring during the vacuum thermal annealing. For the first time, a core-shell type structure was identified on EBID Pt and IBID Pt annealed electrodes and analogous free standing nanorods previously exposed to high temperature. We believe this observation has important implications for transport properties studies of carbon materials. Apart from that, contamination of carbon nanostructure, originating from the device fabrication methods, was also studied. Finally, based on the observations of faster processing time together with higher yield and flexibility for device preparation, we investigated EBID to fabricate devices for other discrete carbon nanostructures.

Σκοπός της παρούσας διπλωματικής εργασίας είναι η μελέτη της ροής υγρών μέσω νανοπορώδων μεμβρανών που φέρουν προσροφημένα συσταδικά συμπολυμερή διαφόρων μοριακών βαρών υπό συνθήκες ροής με καλό διαλύτη (τολουένιο) καθώς και με μίξη διαλυτών καλού και κακού όπως είναι το τολουένιο και το κυκλοεξάνιο αντιστοίχως. Μελετήθηκαν δύο κατηγορίες συμπολυμερών δισυσταδικά και τα τρισυσταδικά συμπολυμερή. Η πρώτη κατηγορία αναφέρεται στα polystyrene-b-polyethylene oxide (PS-PEO) δισυσταδικά συμπολυμερή διαφόρων μοριακών βαρών. Τα μοριακά βάρη που μελετήσαμε ήταν το 32.000, 70.500, 80.000, 147.000, 182.700, 184.000 , 239.000 και 322.000 g/mol. Το πρωτόκολλο που ακολουθήθηκε περιλαμβάνει τα παρακάτω βήματα: αρχικά μέτρηση της γυμνής μεμβράνης στο φασματοφωτόμετρο FTIR και μετά έλεγχος σε ροή με διαλύτη τολουένιο. Στη συνέχεια έγινε η τοποθέτηση της μεμβράνης σε διάλυμα του εκάστοτε πολυμερούς στο τολουένιο, Το τουλουένιο επιλέχτηκε διότι είναι καλός διαλύτης προς την συστάδα PS. Η μεμβράνη παρέμεινε στο διάλυμα για κάποιο χρονικό διάστημα της τάξεως ημερών έτσι ώστε να επιτευχθεί η διαδικασία της φυσιοπροσρόφησης. Λόγω του ότι το τουλουένιο αποτελεί κακό διαλύτη για το PEO έχουμε αγκύστρωση των πολυμερικών βουρτσών PEO στα κυλινδρικά τοιχώματα της νανοπορώδους μεμβράνης. Αφού πραγματοποιηθεί μέτρηση του υπέρυθρου φάσματος της μεμβράνης για να τεκμηριωθεί η προσρόφηση του πολυμερούς, ακολούθως γινόταν προσαρμογή της προσροφημένης μεμβράνης στην διάταξη και ροή με διαλύτη τολουένιο. Με χρήση του νόμου του Poiseuille βρίσκεται το πάχος των πολυμερικών βουρτσών, υπολογίζοντας έτσι κατά πόσο οι πολυμερικές βούρτσες με την εισχώρηση του διαλύτη από τους πόρους εκτείνονται κάθετα της επιφάνειας που έχουν προσροφηθεί. Τέλος με χρήση του φασματοφωτόμετρου FTIR και πάλι γινόταν έλεγχος εάν έχει γίνει αποκόλληση των πολυμερικών βουρτσών από τα τοιχώματα της μεμβράνης λόγω της ροής. Επίσης πραγματοποιήθηκε η μελέτη της συμπεριφοράς κάποιων από αυτά τα συμπολυμερή σε μίγμα διαλυτών τολουολίου και κυκλοεξανίου. Ακολουθώντας την ίδια διαδικασία όπως προηγουμένως αλλάζοντας μόνο το στάδιο της ροής, ο έλεγχος σε αυτή την περίπτωση ξεκινούσε από 100% τολουένιο, 70% τολουένιο-30% κυκλοεξάνιο, 50%τολουένιο – 50%κυκλοεξάνιο ,30% τολουένιο – 70 % κυκλοεξάνιο και καταλήγαμε με 100% κυκλοεξάνιο. Ελεγχόταν έτσι η απόκριση των πολυμερικών βουρτσών κατά την εναλλαγή του διαλύτη. Με χρήση του νόμου του Poiseuille μπορούσε να υπολογισθεί το πάχος των πολυμερικών βουρτσών και να προσδιορισθεί κατά πόσο μετά το τέντωμα τους από την επαφή τους με τον καλό διαλύτη το τολουένιο, συρρικνώνονται όταν έρχονται σε επαφή με τον κακό διαλύτη το κυκλοεξάνιο. Στην δεύτερη κατηγορία ανήκουν τα τρισυσταδικά συμπολυμερή . Τα τρισυσταδικά πολυμερή που μελετήσαμε ήταν το polyvinyl-2-pyridine-b-polystyrene-b- polyvinyl-2-pyridine (PV2P-PS-PV2P) 30K-180K-30K, το PEO-PS-PEO 18.6K-45.2K-18.6K και το PEO-PS-PEO 2.3K-16.7K-2.3K. Ακολουθώντας το ίδιο πρωτόκολλο πειραματικής διαδικασίας όπως στα δισυσταδικά συμπολυμερή, έγινε η μελέτη της συμπεριφοράς των τρισυσταδικών συμπολυμερών σε ροή με τουλουένιο, το οποίο αποτελεί καλό διαλύτη προς την μια συστάδα (PS) του συμπολυμερούς. Τα τρισυσταδικά συμπολυμερή κατά την διαδικασία της φυσιοπροσρόφησης, δηλαδή της αγκίστρωσης των πολυμερικών βουρτσών μέσω των συστάδων PEO και PV2P στα κυλινδρικά τοιχώματα της νανοπορώδους μεμβράνης παρουσιάζουν τον σχηματισμό βρόχου (loop) . Στην συνέχεια γινόταν τοποθέτηση της μεμβράνης στην διάταξη και ο έλεγχος σε ροή με διαλύτη τολουένιο όπως και στην περίπτωση των δισυσταδικών συμπολυμερών. Τέλος με την χρήση του φασματοφωτόμετρου FTIR γινόταν έλεγχος εάν έχει γίνει αποκόλληση των πολυμερικών βουρτσών από τα τοιχώματα της μεμβράνης. Το πάχος της προσροφημένης βούρτσας υπολογιζόταν με χρήση του νόμου του Poiseuille όπως και με τα δισυσταδικά συμπολυμερή. / -

Information anytime and anywhere has ushered in a new technological age where massive amounts of ‘big data’ combined with self-aware and ubiquitous interactive computing systems is shaping our daily lives. As society gravitates towards a smart living environment and a sustainable future, the demand for faster and more computationally efficient electronics will continue to rise. Keeping up with this demand requires extensive innovation at the transistor level, which is at the core of all electronics. Up until recently, classical silicon transistor technology has traditionally been weary of disruptive innovation. But with the aggressive scaling trend, there has been two dramatic changes to the transistor landscape. The first was the re-introduction of metal/high-K gate stacks with strain engineering in the 45 nm technology node, which enabled further scaling on silicon to smaller nodes by alleviating the problem of gate leakage and improving the channel mobility. The second innovation was the use of non-planar 3D silicon fins as opposed to classical planar architectures for stronger electrostatic control leading to significantly lower off-state leakage and other short-channel effects. Both these innovations have prolonged the life of silicon based electronics by at least another 1-2 decades. The next generation 14 nm technology node will utilize silicon fin channels that have gate lengths of 14 nm and fin thicknesses of 7 nm. These dimensions are almost at the extreme end of current lithographic capabilities. Moreover, as fins become smaller, the parasitic capacitances and resistances increase significantly resulting in degraded performance. It is of popular consensus that the next evolutionary step in transistor technology is in the form of gate-all-around silicon nanowires (GAA NWFETs), which offer the tightest electrostatic configuration leading to the lowest possible leakage and short channel characteristics in over-the-barrier type devices. However, to keep scaling on silicon, the amount of current generated per device has to be increased while keeping short channel effects and off-state leakage at bay. The objective of this doctoral thesis is the investigation of an innovative vertical silicon based architecture called the silicon nanotube field effect transistor (Si NTFET). This topology incorporates a dual inner/outer core/shell gate stack strategy to control the volume inversion properties in a hollow silicon 1D quasi-nanotube under a tight electrostatic configuration. Together with vertically aligned source and drain, the Si NTFET is capable of very high on-state performance (drive current) in an area-efficient configuration as opposed to arrays of gate-all-around nanowires, while maintaining leakage characteristics similar to a single nanowire. Such a device architecture offsets the need of device arraying that is needed with fin and nanowire architectures. Extensive simulations are used to validate the potential benefits of Si NTFETs over GAA NWFETs on a variety of platforms such as conventional MOSFETs, tunnel FETs, junction-less FETs. This thesis demonstrates a novel CMOS compatible process flow to fabricate vertical nanotube transistors that offer a variety of advantages such as lithography-independent gate length definition, integration of epitaxially grown silicon nanotubes with spacer based gate dielectrics and abrupt in-situ doped source/drain junctions. Experimental measurement data will showcase the various materials and processing challenges in fabricating these devices. Finally, an extension of this work to topologically transformed wavy channel FinFETs is also demonstrated keeping in line with the theme of area efficient high-performance electronics.