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.

Carbon nano tubes (CNT’s) are promising candidates for several sensor applications such as optical sensors, strain gauges or flow sensors. For certain sensor structures liquid CNT dispersions are required. These are important not only for the realization of CNT-films for sensors like strain gauges but also for technological processes such as dielectrophoresis. CNT-films are realized by deposing the dispersion on a carrier material followed by a drying process. The dispersion properties depend on several parameters like CNT concentration, surfactant concentration, sonication time, centrifugation time, storing time and other parameters. Methods for characterization of dispersions are up to now limited to UV/VIS spectroscopy. This is generally limited to low CNT concentrations. This paper discusses the possibility to use impedance spectroscopy as characterization method for the stability of the dispersions. The impedance of the dispersion was measured using a conductivity measurement cell with platinum electrodes. The behavior of characteristic points of the impedance spectrum was investigated for three identically prepared samples during 7 days of storing time. The systematic trend observed is definitively larger than the variance between different samples. With increasing time after preparation the CNT fallout will increase and the amount of deposable CNT’s will decrease. The decreasing imaginary part indicates an easier diffusion of surfactant molecules because they are not longer attached to CNT’s.

Machine Learning interatomic potentials (ML-IAP) are currently the most promising Non-empirical IAPs for molecular dynamic (MD) simulations. They use Machine Learning (ML) methods to fit the potential energy surface (PES) with large reference datasets of the atomic configurations and their corresponding properties. Promising near quantum mechanical accuracy while being orders of magnitudes faster than first principle methods, ML-IAPs are the new “hot topic” in material science research. Unfortunately, most of the available publications require advanced knowledge about ML methods and IAPs, making them hard to understand for beginners and outsiders. This work serves as a plain introduction, providing all the required knowledge about IAPs, ML, and ML-IAPs from the beginning and giving an overview of the most relevant approaches and concepts for building those potentials. Exemplary a gaussian approximation potential (GAP) for amorphous carbon is used to simulate the defect induced deformation of carbon nanotubes. Comparing the results with published density-functional tight-binding (DFTB) results and own Empirical IAP MD-simulations shows that publicly available ML-IAP can already be used for simulation, being indeed faster than and nearly as accurate as first-principle methods. For the future two main challenges appear: First, the availability of ML-IAPs needs to be improved so that they can be easily used in the established MD codes just as the Empirical IAPs. Second, an accurate characterization of the bonds represented in the reference dataset is needed to assure that a potential is suitable for a special application, otherwise making it a 'black-box' method.:1 Introduction 2 Molecular Dynamics 2.1 Introduction to Molecular Dynamics 2.2 Interatomic Potentials 2.2.1 Development of PES 3 Machine Learning Methods 3.1 Types of Machine Learning 3.2 Building Machine Learning Models 3.2.1 Preprocessing 3.2.2 Learning 3.2.3 Evaluation 3.2.4 Prediction 4 Machine Learning for Molecular Dynamics Simulation 4.1 Definition 4.2 Machine Learning Potentials 4.2.1 Neural Network Potentials 4.2.2 Gaussian Approximation Potential 4.2.3 Spectral Neighbor Analysis Potential 4.2.4 Moment Tensor Potentials 4.3 Comparison of Machine Learning Potentials 4.4 Machine Learning Concepts 4.4.1 On the fly 4.4.2 De novo Exploration 4.4.3 PES-Learn 5 Simulation of defect induced deformation of CNTs 5.1 Methodology 5.2 Results and Discussion 6 Conclusion and Outlook 6.1 Conclusion 6.2 Outlook

Die hier vorgelegte Arbeit beschäftigt sich mit der Aufklärung von Wasserstoffsorptionsphänomenen an Kohlenstoffmodifikationen, welche in der Literatur kontrovers diskutiert werden. Ziel war, die publizierten Ergebnisse nachzuvollziehen, die Phänomene zu erklären und Struktur-Eigenschafts-Beziehungen herzustellen. Dabei wurde zum Einen die Sorption von Wasserstoff an Graphit-Nano-Fasern und zum Andern die Sorption von Wasserstoff an alkalisalzdotiertem Graphit untersucht. Es konnte mit der vorliegenden Arbeit zweifelsfrei nachgewiesen werden, dass die zunächst publizierten Ergebnisse zur Wasserstoffspeicherung in Graphit-Nano-Fasern in keiner Weise realisierbar sind. Es wurde jedoch im Rahmen dieser Arbeit eine ungewöhnliche Sorptionscharakteristik der Graphit-Nano-Fasern gefunden. Des weiteren wurde im Rahmen dieser Arbeit festgestellt, dass die von Chen et. al. publizierten Ergebnisse zur Wasserstoffspeicherung an Lithium dotiertem Graphit zum großen Teil auf eine Reaktion mit Feuchtigkeit zurückzuführen sind. Jedoch konnte weiterhin eine deutliche Massenzunahme mit gereinigtem Wasserstoff nachgewiesen werden. Es ist anzunehmen, dass dieses Verhalten mit den insitu gefundenen neuen Phasen der Proben zusammen hängt.

Single-walled carbon nanotubes (SWCNTs) were decorated with metal nanoparticles. Using a complementary analysis with spatially resolved micro-Raman spectroscopy, high resolution transmission electron microscopy, electron diffraction, and tip-enhanced Raman spectroscopy, we show that the SWCNTs form bundles in which smaller diameter SWCNTs are the ones preferentially affected by the presence of Au and Ag nanoparticles. This result is exploited to evaluate the structural organization of SWCNTs with mixed chiralities in bundles, leading us to postulate that smaller diameter SWCNTs surround larger ones. We found that this effect occurs for very distinct scenarios including SWCNTs both in nanometer thin films and in field effect transistor configurations at the wafer-level, suggesting a universal phenomenon for SWCNTs deposited from dispersions. / Einwandige Kohlenstoffnanoröhren (SWCNTs) wurden mit Metallnanopartikeln dekoriert. Nach Anwendung von ortsauflösender Raman-Mikroskopie und -Spektroskopie, Transmissionselektronenmikroskopie, Elektronenbeugung und spitzenverstärkter Ramanspektroskopie wird festgestellt, dass sich aus den SWCNTs fasrige Bündel formen, wobei die analytischen Signaturen der SWCNTs mit kleinerem Durchmesser stärker von der Präsenz der Gold- und Silbernanopartikel beeinflusst werden als die der größeren. Dieses Resultat kann damit erklärt werden, dass in der Struktur solcher Bündel SWCNTs mit kleinerem Durchmesser außen und SWCNTs mit größerem Durchmesser innen zu liegen kommen. Wir konnten diesen Effekt für verschiedene Szenarien nachweisen: i) für SWCNTs in nanometerdünnen ungeordneten Filmen und ii) für SWCNTs, ausgerichtet zwischen Elektroden in der Geometrie eines Feldeffekttransistors. Diese Feststellung legt nahe, dass es sich um ein universelles Phänomen für aus flüssigen Dispersionen abgeschiedene SWCNTs handelt. / Dieser Beitrag ist aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.

Since the rediscovery of carbon nanotubes (CNTs) due to the publication of Sumio Iijima's article Helical microtubules of graphitic carbon in the magazine Nature in 1991 the interest in carbon nanotubes has rapidly increased. This bachelor thesis also deals with this popular material with the aim to functionalize CNTs for further uses in the microelectronic industry. A promising approach is the functionalization of the CNTs with metal nanoparticles or metal films. To achieve this, one can perform an atomic layer deposition (ALD) on CNTs. In the present work the Trimethylaluminum (TMA) ALD is the chosen process for the functionalization of the CNTs, which will be studied here. Since the available knowledge on the CNT-functionalization by gas phase reactions is very limited, a theoretical study of possible reaction pathways is necessary. Those studies are carried out with two modern quantumchemical programs, Turbomole and DMol³, which are described together with an introduction into Density Functional Theory, as well as an introduction of CNTs and the ALD process. A basic model of a CNT with a Single Vacancy defect, which had been selected according to the demands of the studies, is introduced. Because the TMA ALD process requires hydroxyl groups as its starting point, not only is the performance of a TMA ALD cycle on a CNT studied, but also reactions which result in the CNTs owning of hydroxyl groups. Consequently, this bachelor thesis will focus on two di erent aspects: The performance of one TMA ALD cycle and the study of possible educts for the TMA ALD process. This study of the educts includes possible structures which can be formed when a CNT comes into contact with air.

Diese Arbeit beschäftigt sich mit der Entwicklung und Implementierung eines Algorithmus zur Berechnung des diffusiven elektronischen Transportes durch Kohlenstoffnanoröhrchen-Feldeffekttransistoren (CNTFETs) unter Verwendung des Drift-Diffusions-Modells. Als Grundlage dient ein bekannter, eindimensionaler Algorithmus für klassische Halbleiter, durch welchen das elektrostatische Potential im stationären Zustand berechnet werden kann. Dieser Algorithmus wird erweitert, um die geometrischen und physikalischen Besonderheiten von CNTFETs, insbesondere die Quasi-Eindimensionalität, zu berücksichtigen. Wichtige Kenngrößen des CNTFETs werden berechnet und deren Abhängigkeit von den Bauteilparametern wird untersucht.:1. Einleitung 2. Theoretische Betrachtungen 2.1. Kohlenstoffnanoröhrchen 2.1.1. Graphen als Baustein für CNTs 2.1.2. Eigenschaften von CNTs 2.2. Drift-Diffusions-Modell 2.2.1. Drift-Diffusions-Gleichungen 2.2.2. Kontinuitätsgleichungen 2.2.3. Poisson-Gleichung 3. Implementierung 3.1. Modell für klassische Halbleiter 3.1.1. Herleitung der dimensionslosen Bewegungsgleichungen 3.1.2. Umformung der Drift-Diffusions-Gleichungen 3.1.3. Iterative Lösung des Gleichungssystems 3.2. Anwendung des Modells auf Kohlenstoffnanoröhrchen 3.2.1. Betrachtetes Modell 3.2.2. Separationsansatz und Poisson-Gleichung 3.2.3. Anpassung der Drift-Diffusions-Gleichungen 3.2.4. Gate-Spannung 3.2.5. Intrinsische Ladungsträgerdichte und Ladungsträgerrandbedingungen 3.2.6. Dielektrizität 3.3. Numerik 3.3.1. Berechnung der Ladungsträgerdichten 3.3.2. Lösung der Poisson-Gleichung 3.3.3. Iterative Veränderung von Parameterwerten 3.3.4. Überprüfung der Konvergenz des Gitters 4. Auswertung 4.1. Literaturmodelle 4.2. Ergebnisse 4.2.1. Potentialverlauf 4.2.2. Potentialplateau 4.2.3. Abschirmlänge 4.2.4. Stromfluss 4.2.5. Rechenzeit 5. Zusammenfassung Anhang A. Herleitung der Drift-Diffusions-Gleichungen aus der Boltzmann-Transportgleichung B. Herleitung der eindimensionalen Poisson-Gleichung aus dem Separationsansatz

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 choice of suitable materials influences the sensor properties. Carbon materials such as graphene are promising for electrochemical sensors. Laser-induced graphene (LIG) offers a cost-effective alternative to conventional methods. This work investigates the potential of LIG to improve electrochemical sensors by optimizing the synthesis parameters. We develop LIG-based sensors for the measurement of nitrite and 4-aminophenol in water samples. The working electrode of the 4-aminophenol sensor was fabricated from LIG and multi-walled carbon nanotubes with polyaniline (MWCNT-PANI), which improves sensitivity and stability. For the detection of nitrite, the LIG was modified with carbon nanotubes and gold nanoparticles (f-MWCNT-AuNPs). The LIG sensors show excellent properties. The 4-aminophenol sensor on bare LIG reaches a detection limit of 9.23 nM, with MWCNT-PANI 6 nM. The nitrite sensor on LIG/f-MWCNT-AuNPs shows linear behavior from 10 to 140 μM, with a detection limit of 0.9 μM. The results show that LIG is suitable for versatile electrochemical sensors. The fabrication approach simplifies production and reduces costs. For the first time, an unmodified LIG electrode was used to detect 4-AP in contaminated water samples.:CHAPTER 1. INTRODUCTION CHAPTER 2. THEORETICAL BACKGROUND ON ELECTROCHEMICAL SENSORS CHAPTER 3. LASER-INDUCED GRAPHENE CHAPTER 4. ENHANCEMENT OF LIG ELECTROCHEMICAL SENSORS CHAPTER 5. 4-AMINOPHENOL DETECTION IN PARACETAMOL AND WATER SAMPLES USING LIG MODIFIED BY MWCNT-PANI CHAPTER 6. NITRITE DETECTION IN WATER SAMPLES USING LIG FUNCTIONALIZED BY F-MWCNT AND AUNPS CHAPTER 7. CONCLUSION APPENDIX

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.