Dans ce travail, nous décrivons la méthode de synthèse, la structure, les propriétés et quelques applications en catalyse de différentes formes du carbone, en particulier les nanostructures carbonées (Chapitre I). La technique de dépôt chimique en phase vapeur en réacteur à lit fluidisé a été utilisée pour le dépôt de métaux ou d’oxydes de métaux sur des supports comme l’alumine ou la silice. Le matériau résultant est utilisé comme catalyseur pour la synthèse de diverses nanostructures carbones par dépôt chimique en phase vapeur catalytique : nanotubes de carbone mono- et multi-feuillets (SWCNTs, MWCNTs), nanofibres de carbone (CNFs), et des nanotubes de carbone (N-MWCNTs) ou nanofibres (N-CNFs) dopés en azote (Chapitre II). Après dissolution du catalyseur par un traitement a l'acide sulfurique ou par la soude, suivit dans le cas des MWCNTs et CNFs, par un traitement à l'acide nitrique pour générer des fonctions carboxyliques de surface, les nanostructures carbonées ont été utilisées comme supports de catalyseurs. L’hydrogénation du cinnamaldehyde a été choisit comme réaction modèle pour comparer les performances de différents catalyseurs bimétalliques de Pt-Ru en fonction de la nature du support. Une étude paramétrique détaillée ainsi que l'étude de l'effet d'un traitement thermique sur l'amélioration des performances du catalyseur de Pt-Ru/MWCNT sont présentes. Une explication de l'augmentation des performances catalytiques sera proposée après analyses du catalyseur par HREM, EDX, EXAFS et WAXS (Chapitre III). Les nanostructures carbonées préparées seront également testées comme supports conducteurs d'électrocatalyseurs pour l'élaboration d'électrodes de "polyelectrolyte membrane fuel cells" (PEMFC). / In this work, we describe the synthesis, structure, physical properties and some applications in catalysis of previously known carbon allotropes, and recently discovered carbon nanostructure (Chapter I). First, FB-OM-CVD deposition was used for metal or metal oxide deposition on metal oxide supports like alumina or silica, leading to the production of supported catalysts. The resulting material was used as catalyst for catalytic chemical vapor deposition of carbonaceous nanostructures i.e single- and multi-walled carbon nanotubes (SWCNTs, MWCNTs), carbon nanofibers (CNFs), and nitrogen doped carbon nanotubes (N-MWCNTs) and nanofibers (N-CNFs) (Chapter II). After catalyst removal by a H2SO4 or NaOH treatments and carboxylic surface group generation by a HNO3 treatment in the case of MWCNTs and CNFs, the carbon nanostructures were used as supports for heterogeneous catalysis. The hydrogenation of cinnamaldehyde was used as a model reaction to compare the performance of different bimetallic Pt-Ru catalysts as a function of the nature of the support. Detailed parametric studies as well as the effect of a heat treatment on the performance improvement of the Pt-Ru/MWCNT catalyst are presented. An explanation for the increase of performances upon heat treatment will be proposed after HREM, EDX, EXAFS and WAXS characterization of the catalyst (Chapter III). The prepared carbon nanostructures were also tested as supports for Pd based electrocatalysts for direct alkaline fuel cells applications in both cathodes for the ORR reaction and anodes for alcohols oxidation.

No description available.

Les réactions pallado-catalysées permettant la formation de liaisons carbone-carbone trouvent de nombreuses applications en synthèse organique et constituent l’étape clé de la synthèse d’un grand nombre de molécules. La première partie de cette thèse décrit la préparation et l’étude de catalyseurs hétérogènes et réutilisables comportant du palladium supporté sur un polymère portant des groupements phosphinés, polymère dérivé soit d'une résine de Merrifield soit d’une résine Rasta. De très bons résultats ont été obtenus pour leur utilisation dans les couplages croisés de Hiyama, Heck et Suzuki et dans chaque cas la possibilité de réutilisation jusqu’à 4 fois du catalyseur a été vérifiée. Notre travail constitue une des premières utilisations d’un catalyseur réutilisable dans le couplage de Hiyama. Nous avons aussi mis au point des conditions permettant d’effectuer le couplage de Heck en présence d’une quantité infime de palladium. Notre étude sur les résines Rasta constitue la première application de ces supports en pallado-catalyse. La deuxième partie de la thèse décrit l’étude de la préparation de catalyseurs où le palladium serait supporté sur des nanoparticules superparamagnétiques et qui pourraient donc être récupérés de tout milieu réactionnel grâce à un champ magnétique externe. Des nanoparticules de cobalt ont été préparées puis recouvertes de pyrocarbone par dépôt chimique en phase vapeur. Des groupements organiques ont été fixés sur la coque de carbone, ce qui permet l’introduction de ligands phosphinés. La structure de ces particules a été étudiée par microscopie électronique en transmission et leur préparation optimisée en fonction des résultats structuraux. / Palladium-catalyzed reactions forming carbon-carbon bonds have found widespread applications in organic synthesis as they represent the key step of many important syntheses in various domains. The first part of this work describes the preparation and study of heterogeneous, reusable, catalysts containing palladium supported on a polymer bearing phosphino groups derived from either a Merrifield resin or a Rasta resin. Very good results have been obtained for the use of these catalysts in Hiyama, Heck and Suzuki cross-couplings and, in each case, the possibility of reuse of the catalyst at least 4 times has been verified. Our work constitutes one of the first use of a reusable catalyst in a Hiyama coupling. We have also found experimental conditions allowing to run the Heck coupling in the presence of only a minimal amount of palladium. Our work constitutes the first use of Rasta resins to prepare heterogeneous palladium catalysts. The second part of the thesis describes the study of the preparation of catalysts where palladium would be supported on superparamagnetic nanoparticles and which could therefore be recovered from any reaction medium by using a magnetic field. Cobalt nanoparticles were prepared and then covered by pyrocarbon by Chemical Vapor Deposition. Organic groups, allowing the subsequent introduction of phosphino ligands, were then grafted on the carbon shells. The structure of the particles was determined by Transmission Electron Microscopy and their preparation optimized according to these structural results.

Recent developments in the field of nano-structured materials for technological as well as scientific prospective are quite interesting. In this context carbon plays a dominant role. Few examples such as carbon nanotubes (CNTs), fullerene, nanostructured diamond, as well as, amorphous carbon film, particularly, diamond-like carbon (DLC) coating are the areas of today’s research. This thesis deals with ECR plasma deposition of carbon in two different forms, i.e., Diamond-like carbon (DLC) and carbon nanotubes (CNTs) In the case of DLC coatings the chemical vapor deposition (CVD) and sputtering CVD configuration has been used. The carbon nanotubes have been grown using CVD configuration. DLC films were deposited by ECR-rf CVD mode, as well as, ECR sputtering mode. In case of CVD films, about 0 — 100 Watts rf bias was employed in steps of 20 Watts, corresponding to effective negative self bias voltage of 15 — 440 V. CH4 and C2H2 have been used as source gas for CVD films. Microwave power was optimized at 300 Watts. In case of sputtering, a cylindrical graphite target (diameter 9 cm and length 6 cm) kept at the exit of the Ar plasma was biased with -200 V. Films were deposited on floating substrate (temperature ~100 oC). Films were deposited on Si, quartz, and steel substrates and characterized by FT-IR, Raman, UV-Visible, Photoluminescence spectroscopy (PL), spectroscopic ellipsometry. Nanoindentation was used to evaluate the film’s elastic property. Pin-on-disk measurement was used to study the tribological property of the films. Electrical properties of the films deposited on Si [p-(100), 10 Ω cm] were studied using picoammeter / source measuring instrument by two probe method. FT-IR analysis showed sp3C-H absorption peak at 2930 cm-1 for the CVD films, while sputtered films did not show any C-H absorption. Raman spectroscopy was used to evaluate bonding aspects as well as hydrogen content of the films. Comparison of sp3C : sp2C among the films was done based on I(D) / I(G) of the Raman peaks, while hydrogen content was estimated based on background slope of the Raman spectra. It was observed that increase in rf bias induces more sp2C while hydrogen content decreases. An optimum substrate bias of 40 Watts was predicted from the Raman spectra. For sputtered films Raman spectra indicated the formation of nanocrystal diamond in a-C matrix. UV-Visible-NIR optical transmission spectroscopy was used to determine the band gap (Tauc), E0, of the films. It showed that increase in rf bias increases the absorption coefficient α. The films deposited from CH4 with a substrate bias of 0 and 20 Watts (i.e., high hydrogen content in the film) followed (hνα)1/2 = const. (hν –E0), while other films hνα = const. (hν –E0) ( h is Plank constant ν is frequency of light). E0 varied from 1.1 — 2.5 eV. It was assumed that for π--π* transition follows root relation while π--σ * transition follows linear relation. Spectroscopic ellipsometry was used to determine optical constants, film thickness, and interface thickness. Deposition rate found out to be ~100 nm / mints for C2H2, ~10 nm / mints for CH4, and ~2.5 nm /mints for sputtered films. Formation of interface layer of thickness about 5 —30 nm due to high energy ion bombardment takes place for the films deposited at 40 Watts rf bias or higher. Band gap and related phenomena was revisited from the data that was obtained from this instrument which reasonably matches with the earlier results. PL experiments were carried out at room temperature using lamp excitation source as well as laser excitation source (457.9 nm wavelength). In case of lamp excitation source any wavelength from 200 —900 nm region can be selected. PL spectra showed that there are two sources of PL signal, one from nanocrystal diamond and other from sp2C phase. To obtain PL signal from diamond UV excitation wavelength was required. This diamond phase is highly efficient emitter as compared to sp2C phase. Based on the closeness of diamond’s optical centre labeling of the peaks was done. For CVD films N3 ( 457 nm), H4 (495 nm), H3 (520 nm), [N-V]0 (~590 nm) optical centers of diamond was observed. For sputtered films [N-V]0 (2.08 eV), H3 (2.38 eV), H4 (2.50 eV), N3 (2.81eV), N3 (2.96 eV), 3.3 eV ( undocumented peak), 5RL ( 4.14 eV) optical centers of diamond as well as band-edge emission (5.01 eV ) was observed. Nanoindentation technique was used to estimate the elastic property and related phenomena of the films. It shows that the films are having hardness of 5—17 GPa and reduced modulus of 20 —120 GPa depending on the deposition parameters. All the films show highly elastic response at lower load, i.e., at low indentation depth where elastic recovery is 85—95 %. At higher load substrate effect comes into the picture. Further morphology in and around the region was evaluated using scanning probe microscopy (SPM). It was shown that substrate effect comes into picture that is based on film’s thickness as well as its elastic property. Films were further characterized by pin-on-disk experiments. C2H2 based films were used because of high deposition rate. Since 40 Watts, 60 Watts, and 100 Watts films adhere well with steel only on these films tribological test was possible. A hardened bearing-steel was used as substrate and a 2 mm diameter cylindrical pin made of tool steel was use as pin. Studies were carried out with three different loads of 20, 40, and 60 N. Friction coefficient varied from 0.02 — 0.04 and wear rate was found to be 10-6 — 10-9 mm3 / N m. A sputtered film of 0.1 μ m on the top of the CVD film, in many respects, enhances the tribological properties. It was shown that certain amount of wear is required for low friction of DLC. Electrical characterization of the films deposited from CH4 showed that they are highly insulating with resistivity of 1013 —1011 Ω-cm, and current conduction mechanism has been found to be predominantly space charge limited conduction (SCLC). Similar to the observations of Tauc’s relation, the film deposited with 0 and 20 Watts bias behave differently and followed the relation , where as, all other films exhibited the relation ( α, n are constants). It signifies that for 0 and 20 Watts rf biased films traps are uniformly distributed across the band gap while for others it decreases from the conduction band. For 0 and 20 Watts rf biased films no Ohmic current was observed at a detection level of 10-11 A. 40 Watts and higher rf biased films showed that three distinct regions in the I-V curves; initially Ohmic region, next to it SPLC region, and finally breakdown region. Increase in rf bias causes increase in Ohmic current. Film deposited from C2H2 showed diode-like behavior with higher conduction current limited by resistive control, and the resistivity of the films was ~ 109 — 105 Ω-cm. Difference in resistivity between the films deposited from CH4 and C2H2 was explained by considering the impurities in the source gas resulting in nitrogen doping concentration. Increase in Ohmic current for the CH4 films was explained by assuming the widening of the σ--σ * gap. Similar diode-like behavior was observed with the sputtered film. The last part of the work deals with the growth mechanism of aligned CNTs and their field emission (FE) properties. Nanotubes were grown at 700 0C on Ni coated (thickness 40 nm, 70 nm, and 150 nm) Si substrate using a mixture of CH4 and H2 gas. Microwave power of 500 Watts was optimized for nanotube growth. Nickel nanoparticle formation mechanism from a continuous Ni film was explained by considering the stress that is generated due to the difference in thermal expansion coefficients of Si and Ni at 700 oC. Though the thicker film such as 150 nm does not form nanoparticle due to stress, hydrogen induced fragmentation of the film due the brittleness of the film even causes formation of finer nanoparticles. A substrate bias in the range 0— 250 V was used to align the nanotubes. Perfectly aligned CNTs were obtained at -250 V substrate bias. The density of the tubes varied from 108 —109 / cm2 while its length was 0.5 — 2 μ m. Due to hydrogen induced fragmentation of the films, 150 nm Ni thick film showed smallest diameter 2 — 5 nm CNTs. 40 nm films showed nanotube diameter of 10 — 30 nm and 150 — 300 nm while 70 nm showed 10 — 30 nm diameter nanotubes. Diameter of the nanotubes was estimated using transmission electron microscopy (TEM). Field emission analysis of these CNTs was done using Fowler-Nordheim (F-N) plot and the investigation revealed that the field emission properties strongly depend on density and aspect ratios. The non-linearity in the F-N plot or current saturation phenomena was explained in terms of change in work function due to heating effect during FE which was pronounced in case of longer nanotube. Suitable efficient cold-cathode emitters for a particular usage (assuming that the variables are applied field and emission current) could be designed from the obtained results. An ammonia gas sensor using thick nonaligned CNTs was realized. For this purpose a thick film of CNTs (~ 0.5 μm) was deposited. This sensor can detect 100 ppm level of ammonia. About 1.5 — 4.5 % change of resistance depending on ammonia concentration (100 —1000 ppm) was observed.

High quality ammonium oxofluorotitanate discoid crystal is successfully grown on glass with an aqueous solution of ammonium hexafluorotitanate and boric acid at the molar ratio of 0.6. The concentration of hydrofluoric acid is less on the glass substrate surface and enhances the ammonium oxofluorotitanate nucleation growth. The growth rate is much higher than that grown on dioctadecyldimethylammonium. From the examinations of X-ray diffraction and high-resolution transmission electron microscopy, the crystal shows high crystalline quality and uniformity. Each titanium oxide octahedral is linked with fluorine and nitrogen atoms. Therefore, ammonium oxofluorotitanate has high potential to be thermally decomposed into high crystalline fluorine and nitrogen co-doped titanium oxide. A simple process for the preparation of nanocrystalline anatase phase titanium oxide converted from ammonium oxofluorotitanate by thermal treatment was developed. The nanocrystalline anatase phase titanium oxide shows a large bandgap reduction due to the co-doping of high concentrations of fluorine and nitrogen. Due to the excellent nanocrystalline quality and the co-doping of higher concentrations of fluorine and nitrogen at the thermal treatment temperature of 800 OC, it is 1.3 times the photocatalytic activities of P-25 due to the visble region usage of Hg lamp light source. The 11.2 times the visible photocatalytic activities of P-25 using blue light-emitting diode as the light source is obtained from thermal treatment temperature of 600 OC. There is one to one correspondence between carrier lifetime and photocatalytic activity. As a result, a highly reactive and visible-light-driven photocatalysis is achieved. The heterostructure of zinc selenide/titanium oxide and zinc sulfide/titanium oxide were prepared by metal-organic chemical vapor deposition on the above-prepared titanium oxide. The energy bandgap of zinc sulfide is much larger than that of titanium oxide and can act as a window for titanium oxide. It would not hinder titanium oxide absorption and preserve the role of fluorine and nitrogen co-doping. The energy bandgap of zinc selenide is near the maximum intensity of solar spectrum and acts as a sensitizer of titanium oxide. The lifetime of electron and hole pairs of heterostructure are about 240 and 207 nsec, which are longer than 65 nsec of titanium oxide prepared at 800 oC thermal treatment. Their photocatalytic activities are further improved to 2.0 and 1.5 times higher than that of commercial P-25. The photocatalysis of titanium oxide is very sensitive to the surface states. Titanium oxide surface defects can act as trapping sites for photo-induced holes and facilitate the separation of photo-induced carriers. Zinc selenide and zinc sulfide can passivate the surface well. It may say that titanium oxide surface defects removal has a negative impact. The density, height, diameter, PL wavelength and intensity of zinc selenide self-assembled quantum dots grown on zinc sulfide/gallium arsenide with the zinc sulfide thickness from 15 to 160 nm are studied. For a fixed 30 sec zinc selenide self-assembled quantum dots growth, it cannot be formed with the zinc sulfide thickness below 15 nm due to the close lattice match between zinc sulfide and gallium arsenide. The zinc sulfide/gallium arsenide is fully lattice relaxed with the zinc sulfide thickness higher than 130 nm examined by X-ray diffraction. The higher quality and density of zinc selenide self-assembled quantum dots can be obtained on zinc sulfide/gallium arsenide with the zinc sulfide thickness far beyond its critical thickness. The maximum zinc selenide self-assembled quantum dots density of 4.9 x 109 cm-2 with the strongest photoluminescence intensity is obtained at the zinc sulfide/gallium arsenide thickness of 130 nm. Clusters are formed on the surface of zinc selenide/gallium arsenide. The selenium segregation is the main mechanism for the formation of clusters. The dislocations will enhance the selenium segregation. Higher zinc selenide cluster corresponds to higher density of dislocations. The non-spherical cluster is formed from the mergence of the two clusters. High quality zinc oxide rods and zinc hydroxide slices are successfully grown on gallium arsenide with the aqueous solution of zinc nitrate and hexamethylenetetramine. The growth can be controlled by the appropriate nitric acid concentration incorporation in the solution. After thermal annealing, the zinc oxide slices transformed from zinc hydroxide slices can contribute much higher photocatalytic activity to 1.2 times to P-25.

Today there is a great deal of interest in the development of gas sensors for applications like air pollution monitoring, indoor environment control, detection of harmful gases in mines etc. Based on different sensing principles, a large variety of sensors such as semiconductor gas sensors, thermoelectric gas sensors, optical sensors and thermal conductivity sensors have been developed. The present thesis reports a detailed account of a novel method followed for the design and development of a thermoelectric gas sensor for sensing of Volatile Organic Compounds. Thermoelectric effect is one of the highly reliable and important working principles that is widely being put into practical applications. The thermoelectric property of semiconducting tin oxide film has been utilized in the sensor that has been developed. The thermoelectric property of semiconducting tin oxide film has been utilized in the sensor. The deposition parameters for sputtering of tin oxide film have been optimized to obtain a high seebeck coefficient. A test set-up to characterize the deposited films for their thermoelectric property has been designed and developed. A novel method of increasing the seebeck coefficient of tin oxide films has been successfully implemented. Thin films of chromium, copper and silver were used for this purpose. Deposition of the semiconducting oxide on strips of metal films has led to a noticeable increase in the seebeck coefficient of the oxide film without significantly affecting its thermal conductivity. The next part of our work involved development of a gas sensor using this thermoelectric film. These sensors were further tested for their response to volatile organic compounds. The sensor showed significant sensitivity to the test gases at relatively low temperatures. In addition to this, the developed sensor is also selective to acetone gas.

Στόχος της διδακτορικής αυτής διατριβής ήταν η ανάπτυξη μιας μεθόδου παραγωγής νανοσωλήνων άνθρακα η οποία στηρίζεται στη χημική απόθεση ατμών, χρησιμοποιώντας ως πηγή του άνθρακα ενώσεις σε υγρή μορφή, όπως οι αλκοόλες. Επιπρόσθετα μελετήθηκαν διάφορες παράμετροι της πειραματικής διαδικασίας (πηγή άνθρακα, θερμοκρασία απόθεσης, είδος και συγκέντρωση μετάλλου και υποστρώματος, παρουσία υδρογόνου κ.ά), τόσο ως προς την επίδρασή τους στο ρυθμό εξέλιξης της διεργασίας, όσο και ως προς το είδος των παραγόμενων προϊόντων, με σκοπό τη στοχευμένη παραγωγή νανοσωλήνων άνθρακα με συγκεκριμένες ιδιότητες. Η κύρια πειραματική διάταξη αποτελούνταν από έναν θερμοβαρομετρικό αντιδραστήρα, ο οποίος επέτρεπε τη συνεχή μέτρηση των μεταβολών του βάρους του δείγματος σε συνάρτηση με το χρόνο, ενώ και φασματογράφος μάζας ήταν συνδεδεμένος στην έξοδο του αντιδραστήρα για να μελετηθεί η αέρια φάση των αντιδράσεων. Τα προϊόντα προκειμένου να πιστοποιηθούν ως προς το είδος των νανοσωλήνων που παρήχθησαν, χαρακτηρίστηκαν με τη βοήθεια ηλεκτρονικής μικροσκοπίας σάρωσης (SEM) και διερχόμενης δέσμης (TEM), καθώς και με φασματοσκοπία Raman και θερμοσταθμική ανάλυση (TGA). Τα αποτελέσματα των πειραμάτων οδήγησαν στο συμπεράσμα πως οι ατμοί της αιθανόλης είναι καλύτερη πηγή άνθρακα σε σύγκριση με της μεθανόλης, οδηγώντας μάλιστα στη παραγωγή μίγματος πολυφλοιϊκών και μονοφλοιϊκών νανοσωλήνων άνθρακα, με καθαρότητες που ξεπερνούσαν το 90%. Επιτακτική αποδείχθηκε η παρουσία του μετάλλου, το οποίο και αποτελεί το κέντρο πυρημοποιήσης για την ανάπτυξη των νανοσωλήνων, ενώ καθοριστική είναι και η χρήση υποστρώματος προκειμένου ο άνθρακας να αποτεθεί με τη μορφή αυτή. Επιπρόσθετα, η παρουσία του υδρογόνου αύξησε σημαντικά το ποσοστό του άνθρακα που αποτέθηκε οδηγώντας μάλιστα στο σχηματισμό μεταλλικών μονοφλοικών νανοσωλήνων άνθρακα πολύ μικρής διαμέτρου, η οποία υπολογίστηκε ίση με 0.45nm. / The main goal of this research was the development of a new method for the production of carbon nanotubes, based on chemical vapor deposition (CVD), which employs a liquid carbon source. In addition, a detailed investigation of the effect of several parameters (carbon source, deposition temperature, kind and metal concentration and support, hydrogen addition e.t.c.) on both the process and the final carbon product was carried out. For this purpose, a CVD experimental apparatus was developed, which uses vapors of liquid precursors and allows the continuously recording of sample weight changes in correlation with time. In some cases, a mass spectrometer was used as a way to determine the kind of processes that take place in the gas phase during carbon deposition. The solid product was characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy and thermogravimetric analysis (TGA). The experimental results led to the conclusion that ethanol vapors are preferable because they lead to higher yield of both multi-wall and single-wall carbon nanotubes. Also, it was proved that the presence of a metal catalyst and support is necessary, because the first one is the active site of carbon nanotubes formation, and the second leads to the deposition of carbon in this form. Additionally, it was proved that the use of hydrogen in the gas mixture of the process is very important, as a way to reduce catalyst, leading to the formation of metalic single-wall carbon nanotubes of very small diameter (0.45nm).

Gegenstand dieser Arbeit ist die Modifizierung von Oberflächen durch die Abscheidung alternierender Schichtsysteme auf Kohlenstofffasern und die Abscheidung von Aluminiumoxid auf organischen Membranen. Im ersten Kapitel wird das Vorgehen zur Abscheidung von organischen und anorganischen Schichten auf Kohlenstofffasern mittels der Atomlagenabscheidung und der oberflächeninitiierten Gasphasenabscheidung betrachtet. Dabei wird als Erstes auf die Abscheidung von Einzellagen und deren Optimierung eingegangen sowie im Anschluss auf die Übertragung dieser Parameter auf die Abscheidung von alternierenden Multilagensystemen. Mittels elektronenmikroskopischen-Untersuchungen, Rasterelektronenmikroskopie und energiedispersiver Röntgenspektroskopie, wird die Abscheidung der Materialien untersucht. Weiterhin können mit Hilfe von thermogravimetrischen Analysen die Oxidationsbeständigkeit der beschichteten Kohlenstofffasern sowie die einzelnen Schichtdicken bestimmt werden. Im zweiten Kapitel wird auf die Beschichtung von organischen Membranen eingegangen. Das Hauptaugenmerk liegt dabei auf der Beschichtung von nicht-hierarchisch und hierarchisch strukturierten Membranen mit Aluminiumoxid. Dafür werden die Atomlagenabscheidung und die Grenzflächenreaktion der Gasphase mit der im Feststoff gebundenen Flüssigphase angewendet. Unter Anwendung dieser beiden Verfahren ist es gelungen, dünne und gleichmäßige Schichten auf den Membranen abzuscheiden. Die Charakterisierung erfolgte mittels Rasterelektronenmikroskopie und energiedispersiver Röntgenspektroskopie. Zum Schluss wurden Filtrationsexperimente zum Vergleich der Stabilität und Durchflussraten der beschichteten mit den unbeschichteten Membranen durchgeführt.

Carbon nanotubes (CNT) and graphene have been one of the noticeable research areas in science and technology. In recent years, the assembly of these carbon nanostructures is one of the most interesting topic to the scientific world due to its variety of applications from nano to macroscale. These bulk nanostructures to be applicable in shock absorbers, batteries, sensors, photodetectors, actuators, solar cells, fuel cells etc. The present work is motivated to study the detailed compressive behavior of three dimensional cellular assemblies of CNT and graphene. The CNT foams are synthesized by chemical vapor deposition method. It is interesting to study the compressive behavior of CNT foam in the presence external magnetic field applied perpendicular to CNT axis. The peak stress and energy absorption capability of CNT foam enhances by four and nearly two times in the presence of magnetic field as compared to the absence of the magnetic field. In the absence of magnetic field the deformation of CNT foam is obtained elastic, plateau and densification regions. Further CNT foam is loaded with iron oxide nanoparticles of diameter is ~ 40nm on the surface and detailed study of the compressive behavior of the foam by varying iron nanoparticles concentration. The peak stress and energy absorption capability of CNT foam initially decreases with increasing the intensity of the magnetic field, further increases the intensity of the magnetic field the maximum stress and energy absorption capability increases which is due to magnetic CNT and particles align in the direction of the magnetic field. CNT surfaces were further modified by fluid of different viscosities. The mechanical behavior of CNT foam filled with fluids of varying viscosities like 100%, 95% and 90% glycerol and silicone oil are 612, 237, 109 and 279 mPa-s respectively. The mechanical behavior of CNT foam depends on both the intensity of magnetic field and fluid viscosity. The non linear relation between peak stress of CNT and magnetic field intensity is σp(B, η) = σ0 ± α(B-B0) where σ0 is the peak stress at B = B0 , η is the fluid viscosity, parameter α depends on properties of the MR fluid and B0 is an optimum magnetic field for which peak stress is maximum or minimum depending on the fluid viscosity. Graphene is assembled into a three dimensional structure called graphene foam. The graphene foam is infiltrated with polymer and study the detailed compressive behavior of graphene foam and graphene foam/PDMS at different strains of 20, 40, 60 and 70%. The maximum stress and energy absorption capability of graphene foam/PDMS is six times higher than the graphene foam. Also the graphene foam/PDMS is highly stable and reversible for 100 cycles at strains of 30 and 50%. The mechanical behavior of CNT, graphene foam, CNT/PDMS and graphene foam/PDMS is compared. Among all the foams, graphene foam/PDMS has shown the highest elastic modulus as compared to other foams. This behavior can be attributed to the wrinkles formation during the growth of graphene and a coupling between PDMS and interfacial interactions of graphene foam. Therefore it suggests potential applications for dampers, cushions and electronic packaging. Furthermore, the interaction between nanoparticles and polymer in a novel architecture composed of PDMS and iron oxide nanoparticles is studied. The load bearing capacity of uniform composites enhanced by addition of nanoparticles, reaching to a maximum to 1.5 times of the PDMS upon addition of 5wt.% of nanoparticles, and then gradually decreased to 1/6th of PDMS upon addition of 20wt.% of nanoparticles. On the other hand, the load bearing capacity of architectured composites at high strains (≥40%) monotonically increased with addition of nanoparticles in the pillars.

L'étape clé pour intégrer des nanotubes de carbone à une échelle industrielle demeure un meilleur contrôle de leur croissance et notamment le contrôle sélectif de leurs chiralités en lien avec leurs propriétés électroniques. Ce travail a pour but de s'intéresser à la synthèse in-situ et à la caractérisation de nanotubes de carbone individuels par émission de champ pour mieux comprendre les mécanismes de nucléation et de croissance qui conditionnent sa chiralité. Nous avons développé un microscope à émission de champ couplé à un réacteur CVD (Chemical Vapor Deposition) pour observer directement la croissance catalytique de nanotubes de carbone individuels sur des pointes émettrices. Nous avons ainsi découvert que les nanotubes tournent souvent axialement pendant leur croissance, soutenant ainsi un modèle de « dislocation de vis ». L’analyse détaillée des résultats obtenus montre que nous observons directement la croissance atome par atome d'un nanotube monofeuillet individuel avec ajout d’un dimère de carbone à la fois à sa base. Parallèlement, des échantillons ont été caractérisés en détail sous émission de champ. Nous avons établi un protocole de collage de nanotubes individuels à l’apex d’une pointe métallique sous microscopies optique et électronique à balayage à l’aide d’un nanomanipulateur. Leur dépendance en température à très bas courant a été mise en évidence avec un compteur d’électrons afin d'identifier les différents domaines d'émission électronique. L'analyse des distributions énergétiques a fait apparaître un phénomène de chauffage induit qui peut mener à des températures de l’ordre de 2000 K à l’extrémité du nanotube lorsqu’il est soumis à un fort champ. / The key issue for realizing the potential of carbon nanotubes has always been, and still remains, a better control of their growth and in particular the selective control of their chirality related to their electronic properties. This work aims to address the in-situ synthesis and characterization of individual carbon nanotubes by field emission to better understand the mechanisms of nucleation and growth that determine their chirality. We have developed a field emission microscope coupled to a CVD reactor (Chemical Vapor Deposition) to observe directly the catalytic growth of individual carbon nanotubes on metallic tips. We found that nanotubes often turn axially during growth, thereby supporting a model of "screw dislocation". Detailed analysis of results shows that we directly observe the atom by atom growth of one individual single wall nanotube with addition of a carbon dimer to the base. In parallel, certain samples were characterized by in-depth field emission studies. For this we established a protocol of bonding individual nanotubes at the apexes of metal tips under optical and scanning electron microscopies using a nanomanipulator. Their temperature dependence at very low current has been demonstrated with an electron counter to identify the various fields of electron emission. Analysis of energy distributions revealed an induced heating phenomenon that can lead to temperatures of about 2000 K at the end of the nanotube subjected to strong fields that create high current emission.