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The interlaminar region is a contributing factor to the limited electrical conductivity of carbon fiber/epoxy composites. Consisting of electrically insulating epoxy matrix between conductive layers of carbon fiber, the interlaminar region prevents electrical interaction between the carbon fiber layers and electrical conduction in the through thickness direction.The interlaminar region in thin [0,0] carbon fiber/epoxy composites has been reinforced by carbon nanotubes (CNT) by two methods. First by aligned CNT forests from N12 Technologies and secondly by self-produced Buckypapers, porous CNT films, of different areal densitites. Two batches of laminates modified by aligned CNTs, having different curing conditions, and laminates modified with Buckypapers were manufactured. The laminates were evaluated by their electrical conductivity and electromagnetic interference shielding efficiency (EMI SE). The addition of external pressure to the laminates during curing brought an increase in longitudinal conductivity, a consequence of higher fiber packing. Also, both reinforcement methods increased the longitudinal conductivity through improved electrical interaction between the carbon fiber layers. However, only the Buckypaper reinforcement augmented the transversal conductivity significantly, acting as a highly conductive route in the interlaminar region. Both batches of aligned CNT modified laminates exhibited equal EMI SE, questioning the influence of the conductivity of the laminate on its EMI SE. Also, the increase in EMI SE brought by the aligned CNT forests were negligible compared to the reference. However, the reinforcement by Buckypapers proved successful, reaching -45/-50 dB at 1000 MHz, improving from 30 dB of the unmodified reference at the same frequency.

Abstract Carbon nanotubes (CNTs) are known for their excellent mechanical, electrical and thermal properties, that have fostered a vast number of applications during the last two decades, from composites, electrodes and nanoelectonics components, to sensors and biological scaffolds. Direct integration of CNTs into devices is not straightforward, as high growth temperatures (above 600 °C) challenge the chemical and thermal stability of substrates, catalysts and other nearby materials or components. However, by decreasing growth temperature and/or working out protocols that take into account the thermal stability of the materials involved, it is possible to create several new types of architectures and devices with functionalities not shown before. In this work, we show that, with selection of the appropriate substrate, diffusion barrier and catalyst materials, direct growth of functional CNT films and their micropatterns may be achieved, not only on Si chips, but also on other atypical surfaces, using chemical vapor deposition. This thesis explores low-temperature CNT synthesis over bi- and trimetallic catalysts, and investigates the effect of diffusion barrier layers on the electrical properties of substrate-to-CNT contacts. On one hand, the lowest achieved CNT synthesis temperature (400 °C) is compatible with most silicon technologies, thus enabling direct integration of CNTs with materials and devices with low thermal budgets. On the other hand, the results of diffusion barrier studies helped us in designing and demonstrating on-chip micropatterned CNT structures for super and pseudocapacitor electrodes. In addition, we also show a method for maskless growth of CNT micropatterns using laser-treated steel and superalloy surfaces, whose surface diffusion properties change as a result of barrier-type metal oxide formation. Furthermore, we present CNT growth on carbon materials and demonstrate entirely carbon-based hierarchical composites for electromagnetic interference shielding applications, exhibiting outstanding absorption-based shielding performance. The results presented in this thesis are expected to contribute to a further expansion of CNT-based technologies, in particular with potential for future advances in high-frequency devices (arrays, amplifiers and shielding materials), energy materials (electrodes and scaffolds), as well as in nanoelectromechanical systems (sensors and actuators). / Tiivistelmä Hiilinanoputket tunnetaan niiden erinomaisista mekaanisista, sähköisistä ja termisistä ominaisuuksista, joita on hyödynnetty lukuisissa sovelluksissa viimeisen kahden vuosikymmenen aikana alkaen komposiiteista, elektrodeista, nanoelektroniikkakomponenteista ja sensoreista aina biologisiin tukirakenteisiin. Nanoputkien synteesi suoraan laitteessa ei ole suoraviivaista, sillä korkeat, yli 600 °C synteesilämpötilat asettavat haasteita substraatin, katalyytin sekä muiden lähellä olevien materiaalien ja komponenttien kemialliselle ja termiselle vakaudelle. Alentamalla synteesilämpötilaa ja/tai kehittämällä termisen vakauden huomioivia menetelmiä on mahdollista luoda uudenlaisia arkkitehtuureja ja sovelluksia ennennäkemättömillä ominaisuuksilla. Tässä työssä osoitetaan, että sopivan substraatin, diffuusiosuojan ja katalyyttimateriaalin valitsemalla funktionaalisten hiilinanoputkien synteesi on mahdollista piin lisäksi myös muille, epätavallisille pinnoille käyttäen kemiallista kaasufaasipinnoitusta. Väitöstyössä käsitellään hiilinanoputkien matalan lämpötilan synteesiä hyödyntäen kaksi- ja kolmimetallisia katalyyttejä sekä tutkitaan diffuusiosuojakerroksen sähköistä vaikutusta substraatin ja hiilinanoputkien väliseen kontaktiin. Alin saavutettu synteesilämpötila (400 °C) on yhteensopiva useimpien piiteknologioiden kanssa, mikä mahdollistaa nanoputkien suoran integroinnin matalaa lämpötilaa edellyttäville materiaaleille. Työssä tutkitun diffuusiosuojakerroksen kehitys mahdollisti myös piisirun päälle toteutettujen hiilinanoputkipohjaisten super- ja pseudokondensaattorielektrodien demonstroinnin. Lisäksi työssä esitetään menetelmä, jossa laserkäsittelemällä teräs- ja supermetalliseospinta, jonka avulla mikrokuvioitu hiilinanoputkien kasvu ilman litografiaprosessia on mahdollista. Viimeisenä työssä esitetään hiilinanoputkien synteesi suoraan toiselle hiilimateriaalille ja demonstroidaan täysin hiilipohjainen, hierarkkinen komposiittimateriaali erinomaisella absorptioon perustuvalla suojauskyvyllä sähkömagneettisiin häiriösuojaussovelluksiin. Väitöstyössä esitettyjen tulosten odotetaan osaltaan edistävän hiilinanoputkipohjaisten teknologioiden kehitystä erityisesti korkean taajuuden laitteissa, energiamateriaaleissa sekä nanosähkömekaanisissa järjestelmissä.

Self-activation is a process that takes advantage of the gases emitted from the pyrolysis process of biomass to activate the converted carbon. The pyrolytic gases from the biomass contain CO2 and H2O, which can be used as activating agents. As two common methods, both of physical activation using CO2 and chemical activation using ZnCl2 introduce additional gas (CO2) or chemical (ZnCl2), in which the CO2 emission from the activation process or the zinc compound removal by acid from the follow-up process will cause environmental concerns. In comparison with these conventional activation processes, the self-activation process could avoid the cost of activating agents and is more environmentally friendly, since the exhaust gases (CO and H2) can be used as fuel or feedstock for the further synthesis in methanol production. In this research, many types of biomass were successfully converted into activated carbon through the self-activation process. An activation model was developed to describe the changes of specific surface area and pore volume during the activation. The relationships between the activating temperature, dwelling time, yield, specific surface area, and specific pore volume were detailed investigated. The highest specific surface area and pore volume of the biomass-derived activated carbon through the self-activation process were up to 2738 m2 g-1 and 2.209 cm3 g-1, respectively. Moreover, the applications of the activated carbons from the self-activation process have been studied, including lithium-ion battery (LIB) manufacturing, water cleaning, oil absorption, and electromagnetic interference (EMI) shielding.

In recent years, increased use of electronic devices and wireless operations resulted in unavoidable electromagnetic (EM) pollution which has a significant impact on civil and military sectors. Considering the foremost requirement, huge efforts were invested in the development of electromagnetic interference (EMI) shielding materials. In this context, metals are usually preferred but design complexities like high density and susceptibility towards corrosion are limiting factors; additionally, the reflection of microwaves from the surface fails to serve as EM absorbers. The concern here is to minimize the reflection of the high frequency electromagnetic wave from the surface and to enhance the microwave absorption in GHz frequencies. In this thesis, we have made an attempt to design EMI shielding materials with exceptional absorption ability derived from Polycarbonate (PC)/ Poly styrene-co-acrylonitrile (SAN) based polymer blends. Herein, unique co-continuous micro-phase separated blend structures with selective localization of microwave active nanoparticles in one of the phases were realized to be most effective for microwave attenuation over just dispersing it in one polymer matrix (i.e. PC and SAN composites). The synergistic attenuation of electric and magnetic field associated with EM radiation was achieved through incorporation of various magnetic nanoparticles, however, dispersion of magnetic nanoparticles was a challenging task. Therefore, in order to localize magnetic nanoparticles in PC phase of the blends and to enhance the dispersion state, various modification strategies have been designed. In summary, we have developed a library of engineered nanoparticles to achieve synergistic attenuation of EM radiation mostly through absorption. For instance, the PC/SAN blends containing MWNTs and rGO-Fe3O4 nanoparticles manifested in exceptional EMI shielding, well above required shielding effectiveness value for most of the commercial applications, essentially through absorption. Taken together, the finding suggests that immiscible blends containing MWNTs and the decoration of magnetic nanoparticles (rGO-Fe3O4) on the surface of reduced graphene oxide sheets can be utilized to engineer high-performance EMI shielding materials with exceptional absorption ability.