Spelling suggestions: "subject:"singlewalled carbon nanotubes"" "subject:"singlewalled carbon canotubes""
51 |
A Theoretical Study: The Connection between Stability of Single-Walled Carbon Nanotubes and Observed Products / En Teoretisk Studie: Sambandet mellan Stabiliteten for Enkelväggiga Kolnanorör och Observerade ProdukterHedman, Daniel January 2017 (has links)
Over the past 20 years’ researchers have tried to utilize the remarkable properties of single-walled carbon nanotubes (SWCNTs) to create new high-tech materials and devices, such as strong light-weight composites, efficient electrical wires and super-fast transistors. But the mass production of these materials and devices are still hampered by the poor uniformity of the produced SWCNTs. These are hollow cylindrical tubes of carbon where the atomic structure of the tube wall consists of just a single atomic layer of carbon atoms arranged in a hexagonal grid. For a SWCNT the orientation of the hexagonal grid making up the tube wall is what determines its properties, this orientation is known as the chirality of a SWCNT. As an example, tubes with certain chiralities will be electrically conductive while others having different chiralities will be semiconducting. Today’s large scale methods for producing SWCNTs, commonly known as growth of SWCNTs, gives products with a large spread of different chiralities. A mixture of chiralities will give products with a mixture of different properties. This is one of the major problems holding back the use of SWCNTs in future materials and devices. The ultimate goal is to achieve growth where the resulting product is uniform, meaning that all of the SWCNTs have the same chirality, a process termed chirality-specific growth. To achieve chirality-specific growth of SWCNTs requires us to obtain a better fundamental understanding about how they grow, both from an experimental and a theoretical point of view. This work focuses on theoretical studies of SWCNT properties and how they relate to the growth process, thereby giving us vital new information about how SWCNTs grow and taking us ever closer to achieving the ultimate goal of chirality-specific growth. In this thesis, an introduction to the field is given and the current state of the art experiments focusing on chirality-specific growth of SWCNTs are presented. A brief review of the current theoretical works and computer simulations related to growth of SWCNTs is also presented. The results presented in this thesis are obtained using first principle density functional theory. The first study shows a correlation between the stability of SWCNT-fragments and the observed products from experiments. Calculations confirm that in 84% of the investigated cases the chirality of experimental products matches the chirality of the most stable SWCNT-fragments (within 0.2 eV). Further theoretical calculations also reveal a previously unknown link between the stability of SWCNT-fragments and their length. The calculations show that at specific SWCNT-fragment lengths the most stable chirality changes. Thus, introducing the concept of a switching length for SWCNT stability. How these new results link to the existing understanding of SWCNT growth is discussed at the end of the thesis.
|
52 |
Biodistribution and biological impact of nanoparticles using multimodality imaging techniques : (Magnetic resonance imaging) / Biodistribution et effet biologique des nanoparticules utilisant des techniques d’imagerie multimodale : (Imagerie de résonance magnétique)Faraj, Achraf Al 30 June 2009 (has links)
En raison de leurs propriétés uniques, des nanoparticules industriellement fabriquées comme les nanotubes de carbone (NTC) ont révolutionné le domaine de la nanotechnologie. Il apparait nécessaire de développer des techniques d’investigation in vivo basées sur les propriétés intrinsèques de ces particules et permettant un suivi longitudinal pour évaluer leur risque après inhalation accidentelle par voie respiratoire. Un protocole d’IRM pulmonaire non-invasive utilisant l’hélium-3 hyper polarisé sous respiration spontanée a été développé en complément d’un protocole d’IRM systémique proton pour permettre la détection des NTC grâce à l’effet de susceptibilité magnétique induit par les impuretés de fer, associées aux nanotubes après leur exposition intra pulmonaire. Combiné avec l’IRM pulmonaire proton et des analyses en microscopie optique et électronique à différents temps d’investigation, ce protocole d’imagerie multimodale permet d’évaluer la biodistribution et l’impact biologique des NTC bruts après exposition intra pulmonaire.Une accentuation des réactions inflammatoires (granulomes multifocaux, dépôt de fibres de collagène…) avec le temps et la dose administrée a été observée.De l’évaluation de l’impact biologique des NTC après une exposition intra pulmonaire vers leurs applications biomédicales, les nanotubes de carbone avec leurs propriétés physicochimiques fascinantes et leur forme spécifique laissent entrevoir des applications potentielles en nanomédecine. La bio distribution et le profil pharmacologique des différents types de NTC ont été évalués longitudinalement par IRM et dosage dans le sang et les organes cibles après une injection intraveineuse, et leur impact biologique sur le métabolisme du foie a été examiné ex vivo par RMN haute résolution à l’angle magique (HR-MAS). Aucun signe de toxicité aiguë (variation du métabolisme du foie) n’a été observé et les analyses statistiques conduits sur les spectres RMN (tests PCA) ne montrent aucune différence entre les échantillons analysés et donc l’absence de discrimination entre les différents groupes par rapport aux animaux contrôles. / As novel engineered nanoparticles such as single-walled carbon nanotubes (SWCNT) are extensively used in nanotechnology due to their superior properties, it becomes critical to fully understand their biodistribution and effect when accidently inhaled. There fore, development of animaging technique which allow longitudinal in vivo follow-up of SWCNT effect based on their intrinsic properties is highly desirable. Non invasive free-breathing hyperpolarized 3He lung MRI protocol was developed complementary to proton systemic MR protocol to allow monitoring SWCNT based on their intrinsic iron impurities after intrapulmonary exposition. Combined toproton lung MRI and ex vivo optical and electron microscopy at different time points, this protocol represents a powerful multimodality imaging techniques which allows a full characterization of the biodistribution and biological impacts of iron containing SWCNT. SWCNT was found to produce granulomatous and inflammatory reactions in a time and dose dependent manner with their bio persistenc eafter intrapulmonary exposition.From biological impact evaluations after intrapulmonary exposition towards biomedical applications, SWCNT hold promise for applications in nanomedicine field with their distinct architecture and their novel physicochemical properties. The biodistribution and pharmacological profile of various well-dispersed pristine and functionalized SWCNT were assessed in blood and target tissues after their intra venous administration by longitudinal in vivo susceptibility weighted MRI and their potential effect on liver metabolism by ex vivo HRMAS 1H NMR. No presence ofacute toxicological effect (variation in liver metabolism) was observed confirmed by the absence of clustering in NMR spectra using Principal Component Analysis (specific biomarkers of toxicity).
|
53 |
Investigation of multicomponent catalyst systems for type-selective growth of SWCNTs by CVDMotaragheb Jafarpour, Saeed 25 February 2020 (has links)
Excellent electronic properties of semiconducting single-walled carbon nanotubes (sc-SWCNTs) motivated the investigation for using them in different application areas such as microelectronics, sensorics, MEMS and MOEMS. However, challenges arise from the lack of selectivity with respect to electronic type and chirality as well as ensuring high quality, high purity and well-aligned SWCNTs during fabrication process. Catalytic chemical vapour deposition (CCVD) has shown great potential in direct synthesis of high quality SWCNTs with chiral or type selectivity.
This thesis addresses three important aspects for growth of sc-SWCNT covering method development for fast screening for complex catalyst systems, process development for type-selective growth of SWCNTs and transfer of processes to a specific CVD reactor capable to scale the processes up to 8-inches wafer embedded in the microtechnologic process line. Multi-wavelengths Raman spectroscopy is applied to analyze type and chiral compositions of SWCNTs. In addition, different microscopic techniques of SEM, TEM and AFM are utilized to analyze surface morphology of catalyst layers and size of the nanoparticles as well as structure-related properties of SWCNTs. Initially, systematic studies on monometallic Co and bimetallic Co-Mo systems with different bilayer thickness configurations and their influences on the properties of grown SWCNTs are conducted on chip level. It is shown by adjusting the catalyst deposition conditions of bilayer catalyst as well as optimization of gas environments in CCVD process, structure-related properties of SWCNTs are dramatically enhanced. Furthermore, by utilizing shutter-assisted sputter deposition of gradient layer catalyst, a fast and efficient method for screening different bilayer configurations of Co-Mo, Co-Ru and Ni-Ru has been developed. By utilizing gradient layer deposition with finely resolved catalyst thicknesses, random network SWCNT is grown on bimetallic Co-Mo system under certain process condition with 45% (at 633 nm) and 75% (at 785 nm) semiconducting enrichment of long and high quality SWCNT. In contrast, bimetallic Co-Ru system under certain process condition is developed to grow in-plane SWCNT with 85% (at 633 nm) and 75% (at 785 nm) semiconducting enrichment of short and low quality SWCNT. In addition, different configurations of the bimetallic Co-Ru system are prepared from salt precursors by spin-coating technique. For a mixture of cobalt (II) chloride and ruthenium (III) nitrosylacetate, random network SWCNT with 70% (at 633 nm) and 95% (at 785 nm) semiconducting enrichment of long SWCNTs with high quality is obtained on wafer level. Random network SWCNT with high degree of semiconducting enrichment is used as channel material for thin-film transistors fabrication that results in CNTFET with on/off ratio in the order of 10*3:Bibliographic description 3
Vorwort 9
List of abbreviations and symbols 11
1 Introduction 15
2 Fundamentals of carbon nanotubes 21
2.1 Chemical bonds in carbon structures 21
2.2 Different allotropes of carbon 22
2.3 History of carbon nanotubes research 23
2.4 Structure of carbon nanotubes 24
2.5 Electronic properties of carbon nanotubes 26
2.6 Synthesis of carbon nanotubes 27
2.7 Growth mechanism of carbon nanotubes by CCVD 29
2.8 Catalyst for CCVD synthesis of SWCNTs 31
2.8.1 Catalyst nanoparticle formation from thin film 32
2.8.2 Mechanism of solid state dewetting 33
2.9 CCVD synthesis of SWCNT 35
2.10 Selective synthesis of SWCNT 37
3 Experimental 39
3.1 Preparation of different catalyst/support systems 39
3.1.1 Homogenous layer of catalyst prepared by PVD 39
3.1.2 Gradient layer deposition of catalyst by IBSD 41
3.1.3 Homogenous layer of catalyst prepared by spin coating 45
3.2 CVD reactors for synthesis of SWCNT 46
3.2.1 R&D vertical flow CVD reactor with showerhead 46
3.2.2 Industrial vertical flow CVD reactor with showerhead 47
3.2.3 Horizontal flow tube CVD reactor 49
3.3 Methods for characterization 50
3.3.1 Atomic force microscopy 50
3.3.2 Raman spectroscopy 50
3.3.3 Spectroscopic ellipsometry 56
3.3.4 X-ray reflection 56
3.3.5 Scanning electron microscopy 56
3.3.6 Transmission electron microscopy 56
4 Growth of SWCNT using PVD catalyst layer in vertical CVD reactor A 57
4.1 Monometallic Co catalyst supported on SiO2 57
4.1.1 Surface and morphological analysis of SiO2/Co 57
4.1.2 Analysis of CCVD grown SWCNT on SiO2/Co 59
4.1.3 Chirality and diameter analysis of SWCNTs on SiO2/Co 61
4.2 Monometallic Co catalyst supported on Al2O3 62
4.2.1 Surface and morphological analysis of Al2O3/Co 62
4.2.2 Analysis of CCVD grown SWCNT on Al2O3/Co 63
4.2.3 Chirality and diameter analysis of SWCNTs on Al2O3/Co 67
4.3 Bimetallic Co-Mo catalyst supported on Al2O3 68
4.3.1 Surface and Morphological analysis of Al2O3/Co-Mo 68
4.3.2 Effect of IBSD deposition parameters on NP formation 71
4.3.3 Analysis of CCVD grown SWCNT on Al2O3/Co-Mo 72
4.3.4 Chirality and diameter analysis of SWCNTs on Al2O3/Co-Mo 76
4.4 Comparison of SWCNT from different catalyst configurations 77
5 Growth of SWCNT using gradient layer of catalyst 79
5.1 Analysis of grown SWCNT on Co-Mo using step gradient A 79
5.2 Analysis of grown SWCNT on Co-Mo using step gradient B 80
5.2.1 Growth of SWCNT by utilizing shutter at position I 80
5.2.2 Growth of SWCNT by utilizing shutter at position II 82
5.2.3 Effect of vacuum breaking on CCVD growth of SWCNT 83
6 Growth of SWCNT using gradient layer catalyst in vertical CVD reactor B 87
6.1 SWCNT growth on gradient layer of monometallic catalyst 87
6.1.1 Analysis of CCVD grown SWCNT on gradient layer of Co 87
6.1.2 Analysis of CCVD grown SWCNT on gradient layer of Ni 89
6.1.3 Comparison of SWCNT properties for monometallic of Ni and Co 90
6.2 SWCNT growth on gradient layer of bimetallic catalyst 92
6.2.1 Analysis of CCVD grown SWCNT on gradient layer of Co-Mo 92
6.2.2 Analysis of CCVD grown SWCNT on gradient layer of Co-Ru 95
6.2.3 Comparison of SWCNTs on Co-Mo and Co-Ru catalyst systems 98
6.2.4 Analysis of CCVD grown SWCNTs on gradient layer of Ni-Ru 100
7 Growth of SWCNT using spin-coated catalyst precursor in horizontal CVD reactor 103
7.1 Effect of CCVD growth temperature on SWCNT properties 103
7.2 Effect of catalyst calcination temperature on SWCNT properties 103
7.3 Analysis of CCVD grown SWCNT on Co and Co-Ru 105
7.3.1 Monolayer configuration of different Co precursors 105
7.3.2 Bilayer configuration of Co and Ru precursors 106
7.3.3 Trilayer configuration of Co and Ru precursors 107
7.3.4 Monolayer configuration of Mixture Co and Ru precursors 109
7.3.5 Comparison of SWCNTs on different catalyst configurations 110
8 Growth of SWCNT using spin-coated catalyst precursor in vertical CVD reactor B 113
8.1 Growth of SWCNT on Mixture of Co and Ru precursors 113
8.2 Effect of CVD reactor geometry on SWCNT properties 115
8.3 Effect of catalyst preparation technique on SWCNT properties 116
8.4 Wafer-level growth of SWCNT on bimetallic Co-Ru 117
9 SWCNT-based device fabrication 119
9.1 Different approaches for SWCNT-based device fabrication 119
9.2 Growth-based technique for SWCNT-based device fabrication 121
9.2.1 FET fabrication on in-plane random network SWCNT 121
9.2.2 FET fabrication on out-of-plane random network SWCNT 123
10 Summary and outlook 127
Appendix 131
Bibliography 171
List of tables 183
List of figures 185
Versicherung 197
Theses 199
Curriculum vitae 201
List of publications 203 / Die hervorragenden elektronischen Eigenschaften von halbleitenden, einwandigen Kohlenstoff-Nanoröhren (sc-SWCNTs haben die Untersuchung dazu veranlasst, sie in verschiedenen Anwendungsbereichen wie der Mikroelektronik, Sensorik, MEMS und MOEMS einzusetzen. Herausforderungen ergeben sich jedoch aus dem Mangel an Selektivität bezüglich elektronischer Bauart und Chiralität sowie der Sicherstellung hoher Qualität, hoher Reinheit und gut aufeinander abgestimmter SWCNTs während des Herstellungsprozesses. Die Katalytische chemische Gasphasenabscheidung (CCVD) zeigt ein großes Potenzial bei der direkten Synthese von hochqualitativen SWCNTs mit Chiraler- oder Typenselektivität.
Diese Dissertation behandelt drei wichtige Aspekte für das Wachstum von sc-SWCNT und deckt die Methodenentwicklung des schnellen Screenings für komplexe Katalysatorsysteme, die Prozessentwicklung für das typselektive Wachstum von SWCNTs und die Übertragung von Prozessen in einen spezifischen CVD-Reaktor ab. Der Reaktor, welcher eingebettet in die mikrotechnologische Prozesslinie ist, kann Wafer bis zu 8- Zoll verarbeiten. Raman-Spektroskopie mit mehreren Wellenlängen wird verwendet, um die Zusammensetzung von SWCNTs zu analysieren. Darüber hinaus werden verschiedene mikroskopische Techniken von REM, TEM und AFM verwendet, um die Oberflächenmorphologie von Katalysatorschichten und die Größe der Nanopartikel sowie die strukturbezogenen Eigenschaften von SWCNTs zu analysieren. Zunächst werden systematische Untersuchungen an monometallischen Co- und Bimetall-Co-Mo-Systemen mit unterschiedlichen Doppelschichtdickenkonfigurationen durchgeführt und deren Einfluss auf die Eigenschaften gewachsener SWCNTs auf Chipebene untersucht. Es wird gezeigt, dass durch Einstellung der Katalysatorabscheidungsbedingungen des Doppelschichtkatalysators sowie durch Optimierung der Gasumgebung im CCVD-Prozess die strukturbezogenen Eigenschaften von SWCNTs drastisch verbessert werden können. Darüber hinaus wurde durch die Verwendung eines Gradientenschichtkatalysators, welcher mittels einer Shutter-unterstützten Zerstäubungsabscheidung hergestellt wurde, ein schnelles und effizientes Verfahren zum Untersuchen verschiedener Doppelschichtkonfigurationen von Co-Mo, Co-Ru und Ni-Ru entwickelt. Unter Verwendung der Abscheidung einer Gradientenschicht mit einer fein aufgelösten Katalysatordicke wurden ungerichtete SWCNTs auf einem bimetallischen Co-Mo-System unter definierten Prozessbedingungen mit 45% (bei 633 nm) und 75% (bei 785 nm) halbleitender Anreicherung von langem und hochwertigem SWCNT gezüchtet. Im Gegensatz dazu wird das bimetallische Co-Ru-System unter definierten Prozessbedingungen entwickelt, um SWCNT in der Ebene mit 85% (bei 633 nm) und 75% (bei 785 nm) halbleitender Anreicherung von kurzer und geringer Qualität von SWCNT zu wachsen. Außerdem werden verschiedene Konfigurationen des Bimetall-Co-Ru-Systems aus Salzvorläufern durch Spin-Coating-Technik hergestellt. Es zeigt sich für die Bimetallkonfiguration, die durch Mischung von Cobalt (II) -chlorid und Ruthenium (III) -nitrosylacetat, ein zufälliges Netzwerk SWCNT zu 70% (bei 633 nm) und 95% (bei 785 nm) halbleitender Anreicherung langer SWCNTs mit hohem Anteil hergestellt wurde Qualität wird auf Waferebene gewachsen. Ein zufälliges Netzwerk-SWCNT mit einem hohen Grad an halbleitender Anreicherung wird als Kanalmaterial für die Herstellung von Dünnschichttransistoren verwendet, was zu einem CNTFET mit einem Ein / Aus-Verhältnis um 10*3 führte.:Bibliographic description 3
Vorwort 9
List of abbreviations and symbols 11
1 Introduction 15
2 Fundamentals of carbon nanotubes 21
2.1 Chemical bonds in carbon structures 21
2.2 Different allotropes of carbon 22
2.3 History of carbon nanotubes research 23
2.4 Structure of carbon nanotubes 24
2.5 Electronic properties of carbon nanotubes 26
2.6 Synthesis of carbon nanotubes 27
2.7 Growth mechanism of carbon nanotubes by CCVD 29
2.8 Catalyst for CCVD synthesis of SWCNTs 31
2.8.1 Catalyst nanoparticle formation from thin film 32
2.8.2 Mechanism of solid state dewetting 33
2.9 CCVD synthesis of SWCNT 35
2.10 Selective synthesis of SWCNT 37
3 Experimental 39
3.1 Preparation of different catalyst/support systems 39
3.1.1 Homogenous layer of catalyst prepared by PVD 39
3.1.2 Gradient layer deposition of catalyst by IBSD 41
3.1.3 Homogenous layer of catalyst prepared by spin coating 45
3.2 CVD reactors for synthesis of SWCNT 46
3.2.1 R&D vertical flow CVD reactor with showerhead 46
3.2.2 Industrial vertical flow CVD reactor with showerhead 47
3.2.3 Horizontal flow tube CVD reactor 49
3.3 Methods for characterization 50
3.3.1 Atomic force microscopy 50
3.3.2 Raman spectroscopy 50
3.3.3 Spectroscopic ellipsometry 56
3.3.4 X-ray reflection 56
3.3.5 Scanning electron microscopy 56
3.3.6 Transmission electron microscopy 56
4 Growth of SWCNT using PVD catalyst layer in vertical CVD reactor A 57
4.1 Monometallic Co catalyst supported on SiO2 57
4.1.1 Surface and morphological analysis of SiO2/Co 57
4.1.2 Analysis of CCVD grown SWCNT on SiO2/Co 59
4.1.3 Chirality and diameter analysis of SWCNTs on SiO2/Co 61
4.2 Monometallic Co catalyst supported on Al2O3 62
4.2.1 Surface and morphological analysis of Al2O3/Co 62
4.2.2 Analysis of CCVD grown SWCNT on Al2O3/Co 63
4.2.3 Chirality and diameter analysis of SWCNTs on Al2O3/Co 67
4.3 Bimetallic Co-Mo catalyst supported on Al2O3 68
4.3.1 Surface and Morphological analysis of Al2O3/Co-Mo 68
4.3.2 Effect of IBSD deposition parameters on NP formation 71
4.3.3 Analysis of CCVD grown SWCNT on Al2O3/Co-Mo 72
4.3.4 Chirality and diameter analysis of SWCNTs on Al2O3/Co-Mo 76
4.4 Comparison of SWCNT from different catalyst configurations 77
5 Growth of SWCNT using gradient layer of catalyst 79
5.1 Analysis of grown SWCNT on Co-Mo using step gradient A 79
5.2 Analysis of grown SWCNT on Co-Mo using step gradient B 80
5.2.1 Growth of SWCNT by utilizing shutter at position I 80
5.2.2 Growth of SWCNT by utilizing shutter at position II 82
5.2.3 Effect of vacuum breaking on CCVD growth of SWCNT 83
6 Growth of SWCNT using gradient layer catalyst in vertical CVD reactor B 87
6.1 SWCNT growth on gradient layer of monometallic catalyst 87
6.1.1 Analysis of CCVD grown SWCNT on gradient layer of Co 87
6.1.2 Analysis of CCVD grown SWCNT on gradient layer of Ni 89
6.1.3 Comparison of SWCNT properties for monometallic of Ni and Co 90
6.2 SWCNT growth on gradient layer of bimetallic catalyst 92
6.2.1 Analysis of CCVD grown SWCNT on gradient layer of Co-Mo 92
6.2.2 Analysis of CCVD grown SWCNT on gradient layer of Co-Ru 95
6.2.3 Comparison of SWCNTs on Co-Mo and Co-Ru catalyst systems 98
6.2.4 Analysis of CCVD grown SWCNTs on gradient layer of Ni-Ru 100
7 Growth of SWCNT using spin-coated catalyst precursor in horizontal CVD reactor 103
7.1 Effect of CCVD growth temperature on SWCNT properties 103
7.2 Effect of catalyst calcination temperature on SWCNT properties 103
7.3 Analysis of CCVD grown SWCNT on Co and Co-Ru 105
7.3.1 Monolayer configuration of different Co precursors 105
7.3.2 Bilayer configuration of Co and Ru precursors 106
7.3.3 Trilayer configuration of Co and Ru precursors 107
7.3.4 Monolayer configuration of Mixture Co and Ru precursors 109
7.3.5 Comparison of SWCNTs on different catalyst configurations 110
8 Growth of SWCNT using spin-coated catalyst precursor in vertical CVD reactor B 113
8.1 Growth of SWCNT on Mixture of Co and Ru precursors 113
8.2 Effect of CVD reactor geometry on SWCNT properties 115
8.3 Effect of catalyst preparation technique on SWCNT properties 116
8.4 Wafer-level growth of SWCNT on bimetallic Co-Ru 117
9 SWCNT-based device fabrication 119
9.1 Different approaches for SWCNT-based device fabrication 119
9.2 Growth-based technique for SWCNT-based device fabrication 121
9.2.1 FET fabrication on in-plane random network SWCNT 121
9.2.2 FET fabrication on out-of-plane random network SWCNT 123
10 Summary and outlook 127
Appendix 131
Bibliography 171
List of tables 183
List of figures 185
Versicherung 197
Theses 199
Curriculum vitae 201
List of publications 203
|
54 |
Thermo-Mechanische Charakterisierung von Grenzflächen zwischen Einwandigen Kohlenstoffnanoröhren und Metallen mittels Auszugsversuchen / Thermo-Mechanical Characterization of Interfaces between Single-WalledCarbon Nanotubes and Metals by Pull-Out TestingHartmann, Steffen 04 February 2016 (has links)
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.
|
Page generated in 0.0586 seconds