Preparation and Physical Characterization of Carbon Nanotubes-SU8 Composites

This thesis firstly describes the synthesis and characterisation of carbon nanotubes (CNTs). We focused our research on the growth conditions of CNTs synthesized by chemical vapour deposition (CVD). In particular, the effect of the support surface structure, composition and size of the catalyst precursor, relation of catalyst size with the size of its precursor and the diameter of synthesized CNTs, as well as CNTs diameter distribution were investigated. It was found that the support surface structure strongly influenced the size, shape and chemical composition of the catalyst precursor. Moreover, the size of the catalyst was found to be not always dependent on the size of the catalyst precursor. The best graphitized CVD CNTs were produced from the completely amorphous catalyst precursor in the form of micrometer-sized lumps. Thus, it was found that the growth of CVD CNTs proceeds from the in-situ formed catalyst grains, which were often found unrelated with the support due to the precursor large size and lack of available support's surface sites favourable for the precursor binding. We optimized the CVD CNTs synthesis method towards CNTs diameter controlled growth. Furthermore, well-structured CNTs comparable with arc-discharge CNTs were synthesized for the first time by the CVD method. In particular, catalyst particles were not found in such CNTs which were closed on both ends. CNTs, few-layered graphene and graphene were successfully synthesized by the CVD method without the presence of the transitional metal catalyst. We developed the method of controlled cutting of CNTs to the prescribed length by the planetary ball milling. The second part describes preparation and physical characterisation of the composite made of the SU8 polymer and CVD CNTs previously optimized for this purpose. At first, we have optimized the preparation conditions (including the appropriate solvents, surfactants and all steps of the preparation process). CNTs dispersion in the SU8 matrix was characterized by the transmission electron microscopy (TEM) of the microtome composite and by the impedance measurements. The homogeneous CNTs-SU8 composites have been obtained and the results of the mechanical (hardness and Young's modulus), electrical (four-point measurement and resistivity as a function of temperature) and thermal characterization (thermal conductivity and thermo power) of the prepared composites were measured. The increase in hardness of 122% and in the Young's modulus of 56% (for 0.8 wt% of CNTs in SU8) and thermal conductivity of 3.7 times (for 10wt% of CNTs in SU8) was achieved for composites containing randomly oriented CNTs. Moreover, all prepared composite samples were electrically conductive. In the third part, processing of the obtained composites was successfully optimized for the ink jet printing process, photolithography and screen printing. Especially, photo-patterning was optimized at each processing step in order to minimize their drawbacks

Preparation and characterization of SU8-carbon nanotube composites

SU8-carbon nanotube composites have been produced to enhance the mechanical, electrical, and thermal properties of SU8 photoresists. Homogeneous composites materials have been obtained when multiwalled carbon nanotubes (MWCNTs) functionalized with COOH groups were used. Indeed, COOH groups can react with the epoxy ring of the SU8 molecule yielding an improved interaction between carbon nanotubes (CNTs) and the polymer matrix. Impedance spectroscopy was used to study the conducting percolation path in the composites, that is the quality of the nanotube dispersion in the epoxy matrix. It turns out that propylene glycol methyl ether acetate (PGMEA) as well as gamma-butyrolacton (GBL) are very suitable solvent to prepare SU8-MWCNTs composites of good homogeneity. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinhei

Catalytic CVD synthesis of carbon nanotubes: Towards high yield and low temperature growth

The catalytic chemical vapor deposition (CCVD) is currently the most flexible and economically attractive method for the growth of carbon nanotubes. Although its principle is simple, the precisely controlled growth of carbon nanotubes remains very complex because many different parameters influence the growth process. In this article, we review our recent results obtained on the synthesis of carbon nanotubes via CCVD. We discuss the role of the catalyst and the catalyst support. Our recent results obtained from the water assisted growth and the equimolar C₂H₂-CO₂ reaction are also discussed. Both procedures lead to significantly enhanced carbon nanotube growth. In particular, the latter allows growing carbon nanotubes on diverse substrate materials at low temperatures.status: publishe

Influence of the catalyst drying process and catalyst support particle size on the carbon nanotubes produced by CCVD

Catalytic Chemical Vapour Deposition (CCVD) is considered as the most suitable technique for the large scale and low-cost production of multiwalled carbon nanotubes. We have studied the effect of the preparation process, and of the support particle size on the catalyst efficiency, conversion yield of the carbon source and diameter of the nanotubes produced. When 50 nm calcite CaCO3 particles support the Fe2Co nanoparticles and when the catalyst is freeze dried to avoid the particles agglomeration, 85% of acetylene is converted into MWCNTs; and by using our rotary tube furnace, 1200 g of MWCNTs can be produced per day

Towards electron spin resonance of mechanically exfoliated graphene

We have attempted to prepare graphene samples by mechanical exfoliation of HOPG (highly oriented pyrolytic graphite) using scotch tape. Random testing of the flakes by AFM has shown in majority single layer graphene. Nevertheless, the presence of ultrathine graphite cannot be excluded in the large assembly of flakes needed for electron spin resonance (ESR) measurements. Graphene flakes sitting on ESR-silent scotch tapes were stacked parallel to form a multilayer sandwich. The ESR measurements performed in the 4-300 K range yielded narrow Lorentzian line. The spin susceptibility was decreasing linearly with decreasing temperature as expected for the conical band dispersion of graphene. Below 70 K the spin susceptibility started to deviate from the linear temperature dependence and a Curie-like behavior was observed. This contribution to the susceptibility is due to the existence of defects or impurities, which are in strong exchange coupling limit with conduction electrons. The temperature dependence of the linewidth suggests Elliott's mechanism for spin relaxation in graphene flakes. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinhei

Carbon nanotubes nanocomposites for microfabrication applications

A composite epoxy resin consisting in a SU-8 epoxy resin, a solvent, with or without photoinitiator and carbon nanotubes in powder. When the resin is combined with the carbon nanotubes, the mechanical, thermal and electrical properties of the nanocomposite are enhanced. That offers a wide range of composites which can be used with different microfabrication techniques, such as: lamination, spin-coating, spraying and screening for assembly, interconnect and packaging applications

Study of the mechanical response of carbon nanotubes-SU8 composites by nanoindentation

Multiwalled carbon nanotubes (MWCNTs)/SU8 composites have been produced to enhance the mechanical properties of SU8 photoresist. We have studied the influence of SU8 solvent on the structural homogeneity of composites through nano-indentation testing. It is found that acetone and propylene glycol methyl ether acetate (PGMEA) are very suitable solvents to prepare MWCNTs/SU8 composites with significant increase of the Young's modulus (E-Y). The highest increase of E-Y in respect to the parent material of 104% was obtained with acetone as solvent. It was noticed that the remaining solvent in the composite influences strongly E-Y, as well. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinhei

Catalytic CVD Synthesis of Carbon Nanotubes: Towards High Yield and Low Temperature Growth

The catalytic chemical vapor deposition (CCVD) is currently the most flexible and economically attractive method for the growth of carbon nanotubes. Although its principle is simple, the precisely controlled growth of carbon nanotubes remains very complex because many different parameters influence the growth process. In this article, we review our recent results obtained on the synthesis of carbon nanotubes via CCVD. We discuss the role of the catalyst and the catalyst support. Our recent results obtained from the water assisted growth and the equimolar C2H2-CO2 reaction are also discussed. Both procedures lead to significantly enhanced carbon nanotube growth. In particular, the latter allows growing carbon nanotubes on diverse substrate materials at low temperatures

Analysis of Quantized Electrical Characteristics of Microscale TiO2 Ink-Jet Printed Memristor

We demonstrate the ink-jet printed fabrication technique for TiO2-based memristor, followed by detailed analysis of electrical characteristics and development of a new model that considers observed phenomena of quantized conductance steps. The existence of pinched hysteretic current-voltage characteristics is evidence of memristive behavior, provided by the reversible atomic rearrangement taking place in the functional layer. For the first time, performed electrical measurement on the micrometer thickness devices based on TiO2 active layer has captured the plateaux steps of the conductance at integer multiples of elementary quantum conductance. This behavior is consistent with the assumption that transport from electrode to electrode emerges through confined paths of conductive filaments with radius in the nanometer size range. Moreover, we introduce a novel model, based on the diffusion equation for ballistic transport in memristive devices, which considers the conductance plateaux steps