Kohlenstoffnanoröhren besitzen eine Reihe von einzigartigen strukturellen, mechanischen und elektronischen Eigenschaften. Sie können in Abhängigkeit von der Chiralität metallisches oder halbleitendes Verhalten zeigen, hohe mechanische, thermische und chemische Stabilität aufweisen, können chemisch funktionalisiert werden und sind hervorragende Elektronenemitter. Vor dem Hintergrund dieser vielversprechenden Eigenschaften wurde schnell die Frage von möglichen technischen Anwendungen von Kohlenstoffnanoröhren gestellt. Vor einer umfassenden kommerziellen Umsetzung sind allerdings noch grundlegende Untersuchungen, sowohl zu den Eigenschaften als auch zu einer gezielten Herstellung und Manipulation, erforderlich. Der Mechanismus des gerichteten Wachstums der Kohlenstoffnanoröhren ist äußerst komplex, weshalb er bis heute nicht völlig aufgeklärt werden konnte. Der Grund liegt in der Vielfalt der möglichen Reaktionen zwischen den Molekülen in der Gasphase, der Wechselwirkung zwischen Gasphase und verwendeten Unterlagen und den Reaktionsmechanismen auf diesen Substratoberflächen. Bislang fehlt es an einem einheitlichen Verständnis des Entstehungsprozesses von Kohlenstoffnanoröhren bzw. –nanostrukturen. Der Schwerpunkt dieser Arbeit liegt in der Abscheidung von Kohlenstoffnanostrukturen mittels plasmaaktivierter und hitzdrahtgestützter chemischen Gasphasenabscheidung -„Plasma enhanced hot filament chemical vapor deposition“ (PE-HF-CVD). Es sollen Abscheidungsbedingungen für die Synthese von unterschiedlichen Kohlenstoffnanostrukturen gefunden und optimiert werden. Die Darstellung und Charakterisierung von „phasenreinen“, mehrwandigen, tubularen Röhren auf unterschiedlichen metallbeschichteten Substraten steht im Vordergrund der Arbeit. Das Interesse besteht in einer Abscheidung bei niedrigen Substrattemperaturen, damit temperaturempfindliche Werkstoffe wie z.B. Glas, als Substratmaterialien eingesetzt werden können. Mittels der PE-HF-CVD Methode, die als vielversprechende Technologie zur Darstellung gerichteter Kohlenstoffnanoröhren gilt, sollen Erkenntnisse zum Einfluss einzelner Abscheidungsparameter auf den Wachstumsprozess von Nanoröhren gewonnen werden, wozu auch die plasmadiagnostische Langmuirsondentechnik und die optische Emissionsspektroskopie (OES) eingesetzt werden. Dadurch soll der Zusammenhang zwischen inneren Plasmaparametern und Wachstumsprozessen der Kohlenstoffnanoröhren oder –fasern definiert werden, um eine Prozesskontrolle während der Abscheidungsphase zu ermöglichen.

Die Modifizierung von Carbon Black Partikeln und multi-walled Carbon Nanotubes mit Poly(vinylformamid-co-vinylamin) wurde in Abhängigkeit vom pH-Wert untersucht, um primäre Aminogruppen auf die Oberfläche der Kohlenstoffspezies einzuführen. Mit einer anschließenden Pfropfreaktion der Aminogruppen tragenden Nanotubes mit Maleinsäureanhydrid-Copolymeren sind eine Vereinzelung und ein Stabilisieren der der Carbon Nanotubes möglich. Durch eine Auswahl an Maleinsäureanhydrid-Copolymeren war nach einer Funktionalisierung der mit PVFA-co-PVAm beschichteten Carbon Nanotubes die Änderung der Oberflächeneigenschatften von hydrophil bis hin zu ultrahydrophob möglich. Die Charakterisierung der Partikel und Nanotubes erfolgte mit Hilfe der Elementaranalyse, BET-Untersuchungen, XPS, Kontaktwinkelmessungen, TGA-Untersuchungen, elektrokinetischer Messungen und REM-Aufnahmen.

In this thesis, bulk and local scale spectroscopic and microscopic tools have been applied to investigate the purified raw material of SWCNT and synthesized MWBNNT, BN-nanocapsules, B-doped SWCNT and SiC nanostructures. Using bulk scale sensitive techniques, including optical absorption spectroscopy, Raman spectroscopy, high-resolution electron energy-loss spectroscopy, the average response of the whole sample is obtained. On the other hand, on a local scale transmission and scanning electron microscopy as well as TEM-electron energy-loss spectroscopy provide information on single tubes or other nanostructures. First, diverse chemical and oxidation methods for the purification of as-produced SWCNT were presented. Purified samples were investigated using TEM and OAS. The analysis of the optical absorption spectra in the UV-Vis energy range revealed that some of the chemical treatments are harmful to nanotubes. In contrast to the chemical treatments an oxygen burning procedure was used on the raw material in high vacuum and a temperature range 450?650oC. The purification processes of SWCNT by HNO3 and oxygen burning procedures resulted in SWCNT comprised of selected diameters and a reduced diameter distribution. Both HNO3 and oxygen burning treatments can be used to selectively remove SWCNT with smaller diameters from the samples. In addition, an adapted substitution reaction was used for the synthesis of multiwall boron nitride nanotubes. It was shown that the IR-response of MWBNNT can be used as a fingerprint to analyse MWBNNT. As in h-BN for the analysis one has to be aware of the sample texture and the LO-TO splitting of the IR-active modes. TEM images and B1s and N 1s excitation edges of the grown material reveal the presence of multiwall BN nanotubes with an inner diameter of 3.1 nm and with a larger interplanar distance than in h-BN. The electronic properties of the multiwall BN nanotubes as derived from the q-dependent dielectric function e(w,q) are dominated by the band structure of the hexagonal-like BN sheets, as revealed by the large degree of momentum dispersion observed for the p and s+p plasmons, in agreement with that previously reported for different graphitic allotropic forms. Moreover, a fast and highly efficient synthesis route to produce BN nanocapsules with a narrow size distribution was developed. This was achieved by an adapted substitution process using SWCNT as templates followed by a rapid cooling treatment. The IR responses reveal the strong dipole active fingerprint lines of h-BN with distinct differences, which are due to texturing effects and which highlight the BN nanocapsules potential application as a reference source when deriving the sp2 to sp3 ratio in BN species due to their random orientation Furthermore, the idea of substitution was used for the systematic studies of B-doped SWCNT. The experiments carried out have resulted in 1, 5, 10, and 15 % boron incorporated into the single wall carbon nanotubes. Core level excitation spectroscopy of the B1s and C1s edges revealed that the boron atoms substitute carbon atoms in the tube lattice keeping an sp2-like bond with their nearest C neighbour atoms. Our results show that a simple rigid band model as has been applied previously to intercalated SWCNT is not sufficient to explain the changes in the electronic properties of highly doped B-SWCNT and a new type of a highly defective BC3 SWNT with new electronic properties is obtained. Finally, different silicon carbide nanostructures were produced. The spectroscopic and microscopic data led to a good understanding of the formation process. NH3 acts as a source of hydrogen that plays a key role in the formation of the structures through its ability to decompose SiC at high temperature such that along with the stacking faults that arise from the many polytypes of SiC the produced SiC nanorods become porous then hollow and eventually are completely decomposed.

The main problem addressed by this dissertation is the accurate and automated determination of electron microscope imaging conditions. This enables the restoration of the object wave, which confers direct structural information about the specimen, from sets of differently aberrated images. An important member in the imaging chain is the image recording device, in many cases now a charge-coupled device (CCD) camera. Previous characterisations of these cameras often relied on the unjustified assumption that the Modulation Transfer Function (MTF) also correctly describes the spatial frequency dependent attenuation of the electron shot noise. A new theory is therefore presented that distinguishes between signal and noise transfer. This facilitates the evaluation of both properties using a detailed Monte-Carlo simulation model for the electron and photon scattering in the scintillator of the camera. Furthermore, methods for the accurate experimental determination of the signal and noise transfer functions are presented. In agreement with the Monte-Carlo simulations, experimental results for commercially available CCD cameras show that the signal transfer is significantly poorer than the noise transfer. The centrepiece of this dissertation is the development of new methods for determining the relative aberrations in a set of images and the absolute symmetric aberrations in the restored wave. Both are based on the analysis of the phase information in the Fourier domain and give each Fourier component a weight independent of its strength. This makes the method suitable even for largely crystalline samples with little amorphous contamination, where conventional methods, such as automated diffractogram fitting, usually fail. The method is then extended to also cover the antisymmetric aberrations, using combined beam tilt and focal series. The applicability of the new method is demonstrated with object wave restorations from tilt and focal series of complex inorganic block oxides and of carbon nanotubes filled with one-dimensional inorganic crystals. The latter specimens allowed for the first time a direct comparison between the phase shift in the restored object wave of a specimen with precisely known thickness and the value predicted by simulations.

Iron filled carbon nanotubes (FeCNT) can be described as carbon nanotubes which contain an iron nanowire of several micrometers length and a diameter of approximately 10-100 nm. The carbon shells protect the iron core from oxidation and mechanical damage thus enabling a wide range of applications that require a long-term stability. The magnetic properties of the enclosed nanowire are in part determined by its small size and elongated shape. Magnetic force microscopy (MFM) measurements show that the iron wire exhibits a single domain behavior. Due to the large shape anisotropy it is magnetized along the long wire axis in the remanent state. Two magnetic monopoles of opposing polarity are located at the wire extremities. Depending on the structure and geometry of the individual nanowire, switching fields in the range of 100-400 mT can be found when the external field is applied along the FeCNT’s easy axis. Cantilever magnetometry shows that the switching can be attributed to a thermally assisted magnetization reversal mechanism with the nucleation and propagation of a domain wall. The defined magnetic properties of individual FeCNT combined with their mechanical strength make them ideal candidates for an application as high resolution high stability MFM probes. The fabrication of such probes can be achieved with the help of a micromanipulation setup in a scanning electron microscope. FeCNT MFM probes achieve a sub 25 nm lateral magnetic resolution. MFM measurements with FeCNT MFM probes in external fields show that the magnetization of these probes is exceptionally stable compared to conventional coated MFM probes. This greatly simplifies the data evaluation of such applied field MFM measurements. The emphasis of this work was put on the calibration of FeCNT probes to enable straightforward quantitative MFM measurements. The defined shape of the magnetically active iron nanowire allows an application of a point monopole description. Microscale parallel current carrying lines that produce a defined magnetic field are used as calibration structures to determine the effective magnetic moment of different MFM probes. The line geometry is varied in order to produce multiple magnetic field decay lengths and investigate the influence on the effective probe moment. The results show that while the effective magnetic monopole moment of a conventional MFM probe increases with an increasing sample stray field decay length, the effective moment of a FeCNT MFM probe remains constant. This enables a MFM probe calibration that stays valid for a large variety of magnetic samples. Furthermore, the fitted monopole moment of a FeCNT probe (in the order of 10E-9 Am) is consistent with the moment calculated from the nanowire geometry and the saturation magnetization of iron.

We theoretically investigate the influence of defect-induced long-range deformations in carbon nanotubes on their electronic transport properties. To this end we perform numerical ab-initio calculations using a density-functional-based tight-binding model for various tubes with vacancies. The geometry optimization leads to a change of the atomic positions. There is a strong reconstruction of the atoms near the defect (called 'distortion') and there is an additional long-range deformation. The impact of both structural features on the conductance is systematically investigated. We compare short and long CNTs of different kinds with and without long-range deformation. We find for the very thin (9, 0)-CNT that the long-range deformation additionally affects the transmission spectrum and the conductance compared to the short-range lattice distortion. The conductance of the larger (11, 0)-or the (14, 0)-CNT is overall less affected implying that the influence of the long-range deformation decreases with increasing tube diameter. Furthermore, the effect can be either positive or negative depending on the CNT type and the defect type. Our results indicate that the long-range deformation must be included in order to reliably describe the electronic structure of defective, small-diameter zigzag tubes.

We investigate the electronic transport properties of semiconducting (m, n) carbon nanotubes (CNTs) on the mesoscopic length scale with arbitrarily distributed realistic defects. The study is done by performing quantum transport calculations based on recursive Green's function techniques and an underlying density-functional-based tight-binding model for the description of the electronic structure. Zigzag CNTs as well as chiral CNTs of different diameter are considered. Different defects are exemplarily represented by monovacancies and divacancies. We show the energy-dependent transmission and the temperature-dependent conductance as a function of the number of defects. In the limit of many defetcs, the transport is described by strong localization. Corresponding localization lengths are calculated (energy dependent and temperature dependent) and systematically compared for a large number of CNTs. It is shown, that a distinction by (m − n)mod 3 has to be drawn in order to classify CNTs with different bandgaps. Besides this, the localization length for a given defect probability per unit cell depends linearly on the CNT diameter, but not on the CNT chirality. Finally, elastic mean free paths in the diffusive regime are computed for the limit of few defects, yielding qualitatively same statements.

In this paper, we propose strain-sensitive thin films based on chemically reduced graphene oxide (GO) and multi-walled carbon nanotubes (MWCNTs) without adding any further surfactants. In spite of the insulating properties of the thin-film-based GO due to the presence functional groups such as hydroxyl, epoxy, and carbonyl groups in its atomic structure, a significant enhancement of the film conductivity was reached by chemical reduction with hydro-iodic acid. By optimizing the MWCNT content, a significant improvement of electrical and mechanical thin film sensitivity is realized. The optical properties and the morphology of the prepared thin films were studied using ultraviolet-visible spectroscopy (UV-Vis) and scanning electron microscope (SEM). The UV-Vis spectra showed the ability to tune the band gap of the GO by changing the MWCNT content, whereas the SEM indicated that the MWCNTs were well dissolved and coated by the GO. Investigations of the piezoresistive properties of the hybrid nanocomposite material under mechanical load show a linear trend between the electrical resistance and the applied strain. A relatively high gauge factor of 8.5 is reached compared to the commercial metallic strain gauges. The self-assembled hybrid films exhibit outstanding properties in electric conductivity, mechanical strength, and strain sensitivity, which provide a high potential for use in strain-sensing applications.

The main problem addressed by this dissertation is the accurate and automated determination of electron microscope imaging conditions. This enables the restoration of the object wave, which confers direct structural information about the specimen, from sets of differently aberrated images. An important member in the imaging chain is the image recording device, in many cases now a charge-coupled device (CCD) camera. Previous characterisations of these cameras often relied on the unjustified assumption that the Modulation Transfer Function (MTF) also correctly describes the spatial frequency dependent attenuation of the electron shot noise. A new theory is therefore presented that distinguishes between signal and noise transfer. This facilitates the evaluation of both properties using a detailed Monte-Carlo simulation model for the electron and photon scattering in the scintillator of the camera. Furthermore, methods for the accurate experimental determination of the signal and noise transfer functions are presented. In agreement with the Monte-Carlo simulations, experimental results for commercially available CCD cameras show that the signal transfer is significantly poorer than the noise transfer. The centrepiece of this dissertation is the development of new methods for determining the relative aberrations in a set of images and the absolute symmetric aberrations in the restored wave. Both are based on the analysis of the phase information in the Fourier domain and give each Fourier component a weight independent of its strength. This makes the method suitable even for largely crystalline samples with little amorphous contamination, where conventional methods, such as automated diffractogram fitting, usually fail. The method is then extended to also cover the antisymmetric aberrations, using combined beam tilt and focal series. The applicability of the new method is demonstrated with object wave restorations from tilt and focal series of complex inorganic block oxides and of carbon nanotubes filled with one-dimensional inorganic crystals. The latter specimens allowed for the first time a direct comparison between the phase shift in the restored object wave of a specimen with precisely known thickness and the value predicted by simulations.

Vor dem Hintergrund zukünftiger Sensoren, basierend auf dem piezoresistiven Effekt von einwandigen Kohlenstoffnanoröhren (SWCNT), werden in dieser Arbeit umfangreiche Ergebnisse zum mechanischen Verhalten von Grenzflächen zwischen SWCNTs und edlen Metallen am Beispiel von Pd und Au präsentiert. Im Fokus steht dabei die Synergie von rechnerischen und experimentellen Methoden Molekulardynamik (MD), nanoskalige Tests und Analytik , um (1) mit guter Genauigkeit maximale Kräfte von gezogenen SWCNTs, welche in Metall eingebettet sind, vorauszuberechnen und (2) einen wertvollen Beitrag zum Verständnis der zu Grunde liegenden Fehlermechanismen zu liefern. Es wurde ein MDModell eines in eine einkristalline Matrix eingebetteten SWCNTs mit Randbedingen eines Auszugsversuchs entwickelt. Mit diesem Modell können Kraft-Weg-Beziehungen und Energieverläufe für einen quasistatischen verschiebungsgesteuerten Auszugsversuch errechnet werden. Das Modell liefert kritische Kräfte bei Versagen des Systems. Des Weiteren können mit diesem Modell der Einfluss des SWCNT-Typus, der Einbettungslänge, der Temperatur, von intrinsischen Defekten und Oberflächengruppen (SFGs) auf das Grenzflächenverhalten untersucht werden. Zum Vergleich wurden kritische Kräfte experimentell durch in situ Auszugsversuche in einem Rasterelektronenmikroskop bestimmt. Es wurde eine sehr gute Übereinstimmung von rechnerischen und experimentellen Daten festgestellt. Der vorherrschende Fehler im Experiment ist der SWCNT-Bruch, jedoch wurden auch einige SWCNT-Auszüge beobachtet. Mit Hilfe der MD-Simulationen wurde gefunden, dass die SFGs als kleine Anker in der umgebenden metallischen Matrix wirken und somit die maximalen Kräfte signifikant erhöhen. Diese Grenzflächenverstärkung kann Zugspannungen verursachen, die genügend hoch sind, so dass SWCNT-Bruch initiert wird. Im Gegensatz dazu zeigten Simulationen von Auszugstests mit idealen SWCNTs nur kleine Auszugskräfte, welche meistens unabhängig von der Einbettungslänge des SWCNTs sind. Dieses Verhalten wird mit einer inkommensurablen Konfiguration der Kristallstrukturen an der Grenzfläche von SWCNTs und der einbettenden Edelmetalle interpretiert. Zur Qualifizierung der Existenz von carboxylatischen Oberflächengruppen auf dem genutzten SWCNT-Material wurden analytische Untersuchungen mittels Fluoreszenzmarkierung von Oberflächengruppen durchgeführt. In Übereinstimmung mit Literaturstellen zum gesicherten Nachweis von SFGs, bedingt durch technologische Behandlungen, weisen diese Experimente stark auf das Vorhandensein von carboxylatischen Oberflächengruppen auf dem genutzten SWCNT-Material hin. Demnach kann der dominante SWCNT-Bruch Fehler durch die Grenzflächenverstärkung auf Grund von SFGs erklärt werden. / In the light of future sensors, that are based upon the piezoresistive effect of singlewalled carbon nanotubes (SWCNTs), this work presents comprehensive results of studies on the mechanical behavior of interfaces between SWCNTs and noble metals using the examples of Pd and Au. With this contribution, the focus is on a synergy between computational and experimental approaches involving molecular dynamics (MD) simulations, nanoscale testing, and analytics (1) to predict to a good degree of accuracy maximum forces of pulled SWCNTs embedded in a noble metal matrix and (2) to provide valuable input to understand the underlying mechanisms of failure. A MD model of a SWCNT embedded in a single crystalline matrix with pull-out test boundary conditions was developed. With this model, force-displacement relations and energy evolutions for a quasi-static displacement controlled test can be computed. The model provides critical forces for failure of the system. Furthermore, the influence of SWCNT type, embedding length, temperature, intrinsic defects and surface functional groups (SFGs) on the interface behavior can be studied using this model. For comparison, critical forces were experimentally determined by conducting pull-out tests in situ, inside a scanning electron microscope. A very good agreement of computational and experimental values was discovered. The dominant failure mode in the experiment was a SWCNT rupture, although several pull-out failures were also observed. From MD simulations, it was found that SFGs act as small anchors in the metal matrix and significantly enhance the maximum forces. This interface reinforcement can lead to tensile stresses sufficiently high to initiate SWCNT rupture. In contrast, pull-out test simulations of ideal SWCNTs show only small pull-out forces, which are mostly independent on SWCNT embedding length. This behavior is interpreted with an incommensurate configuration of crystal structures at the interface between SWCNTs and embedding noble metals. To qualify the existence of carboxylic SFGs on the used SWCNT material, an analytical investigation by means of fluorescence labeling of surface species was performed. In agreement with literature reports on the secured verification of SFGs due to necessary technological treatments, these experiments strongly indicate the presence of carboxylic SFGs on the used SWCNT material. Thus, the dominant SWCNT rupture failure is explained with an interface reinforcement by SFGs.