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We have undertaken low-temperature conduction measurements on arc-discharge synthesized, semiconducting multiwalled carbon nanotubes (MWNT). The diameters of these are in the range 2.5–10 nm, corresponding to the sizes just above single-walled carbon nanotubes (SWNT), up to middle-sized MWNTs. The energy gap, inversely related to the diameter, varies strongly in this range, and consequently there is a strong dependence of the transport on tube diameter. Certain transport characteristics are much alike those found in SWNTs, such as the ON-state resistance and Coulomb blockade. However, the transport gap has a more complex behavior than the corresponding one in semiconducting SWNTs, and a number of features, such as negative differential resistance are commonly observed. Different models for the small bias transport behavior are briefly discussed, and we consider especially the possibility of conduction via the second layer. Graphical abstract

Carbon nanotubes can be utilized in several ways to enhance the performance of silicon-based anodes. In the present work, thermally carbonized mesoporous silicon (TCPSi) microparticles and single-walled carbon nanotubes (CNTs) are conjugated to create a hybrid material that performs as the Li-ion battery anode better than the physical mixture of TCPSi and CNTs. It is found out that the way the conjugation is done has an essential role in the performance of the anode. The conjugation should be made between negatively charged TCPSi and positively charged CNTs. Based on the electrochemical experiments it is concluded that the positive charges, i.e., excess amine groups of the hybrid material interfere with the diffusion of the lithium cations and thus they should be removed from the anode. Through the saturation of the excess positive amine groups on the CNTs with succinic anhydride, the performance of the hybrid material is even further enhanced.

Arc-discharge synthesized multiwalled carbon nanotubes (AD-MWNT), or related MWNTs, exhibit a good quality compared to the more common type of MWNT synthesized by catalytic chemical vapor deposition methods. Yet experimental measurements on these are rather few and typically have not correlated data from different measurement techniques. Here, the authors report Raman spectroscopy, scanning probe microscopy, conductivity measurements, and force microscopy on single AD-MWNTs. The results demonstrate the high quality of AD-MWNTs and are compatible with the view of them as the best approximation of MWNTs as an assembly of defect-free concentric individual single-walled carbon nanotubes. The authors also demonstrate conductance measurements over a step on the surface of an AD-MWNT, which is due to an abruptly broken outer layer(s), whereby the interlayer resistance is measured. peerReviewed

International audience; Retention and detachment of colloidal particles from surfaces is often considered only in terms of spontaneous chemical dispersion when the surface is already fully submerged. Nevertheless, interfacial processes, where the particles are caught on a mobile liquid contact line by capillary effects are ubiquitous. Theoretical description of such interfacial processes exist for spherical microcolloids, while for anisotropic shapes the literature is limited. Arc-discharge synthesized multiwalled carbon nanotube (MWNT) material contains besides the very anisotropic tubes also irregular amorphous carbon particles (ACP) that both are strongly hydrophobic. As a water–air–solid contact line is swept over a deposition of MWNT material on a hydrophilic substrate, it causes selective detachment of the spherical ACPs over the one dimensional MWNTs. In this work we investigate the detachment process and the balance between the surface tension force and adhesive forces. Our results show that on hydrophilic substrates the surface tension force of the liquid interface dominates over adhesion, sweeping away most of the material. However, clean MWNTs oriented perpendicular to the contact line are able to resist detachment. On the other hand, on hydrophobic surfaces adhesive forces dominate, possibly via the hydrophobic interaction. We discuss these results with conventional models of capillarity and adhesion, including the van der Waals force and the electrostatic double layer interaction. However, a fully satisfactory analysis will require e.g. computational modelling of the problem.

This thesis reports a novel approach for purification of carbon nanotube (CNT) samples deposited on smooth silicon substrates through a mobile liquid interface interacting with carbonaceous debris particles that contaminate the deposition. The method is based on physical interaction of the particles and the three-phase contact line via capillary interface forces, i.e. the surface tension, which results in the detachment of chemically indispersible colloids from the sample surface. In the experiments reported in this work, we focus primarily on arc-discharge grown multi-walled carbon nanotubes, whose synthesis is particularly plagued by carbonaceous debris that is difficult to remove without harsh chemical treatments. The irregular debris particles are preferentially captured by the mobile contact line, while tubular CNTs are retained in large numbers due to their appreciably stronger adhesion. Our cleaning method has the added benefit that the intrinsic chemical properties of the CNTs are fully preserved, since no chemical treatments are needed; only prerequisite is the hydrophilic treatment of the underlying substrate, which on silicon wafers can be accomplished through oxygen plasma. Various aspects of the cleaning process, including the effects of contact line velocity, chemical composition of the immersion liquid, and the CNT orientation relative to the liquid front are investigated in this thesis. Furthermore, atomic force microscopy (AFM) imaging and the image analysis methodology is discussed. Ad- ditionally, we demonstrate some research applications that directly benefit from our technique, e.g. microraman spectroscopy of individual carbon nanotubes, and nanomechanical investigation of suspended tubes via AFM-deflection measurements. Theoretical treatment of the detachment process is presented in the framework developed for spherical microcolloids in existing works. In this model, the particle detachment is primarily attributed to the surface tension force. Other forces affecting the process include adhesion, which in liquid electrolyte medium can be estimated via the DLVO adhesion theory, and hydrophobic interactions. We conclude that the particle detachment is qualitatively well-explained by the physical interactions at the contact line, while the selectivity of the process for the irregular debris particles in favor of the tubular CNTs probably stems from differences in the magnitude of the adhesion force. Chemical factors associated with the composition of the immersion liquid on the other hand seem to only have very limited effect on the quantitative cleaning result. Regarding to detachment of CNTs, orientation-dependent behavior is implied, with species oriented perpendicular to the advancing contact line reflecting the greatest probability to be retained. Overall, the detachment of all particles is found to increase with decreasing velocity of the liquid interface. These results are generally in qualitative agreement with existing works dealing with spherical microcolloids

Tässä pro gradu -tutkielmassa pyrittiin valmistamaan hiilinanoputkilla vahvistettuja itsekantavia Al2O3-ohutkalvoja. Ohutkalvot kasvatettiin märkäetsauksella ja atomikerroskasvatuksella ja niitä vahvistettiin levittämällä hiilinanoputkia Al2O3-kerrosten väliin. Hiilinanoputkia linkitettiin verkostomaiseksi rakenteeksi ionisäteilytyksellä. Kalvoja karakterisoitiin valmistuksen aikana ja sen jälkeen elektronimikroskopialla, atomivoimamikroskopialla, profilometrialla ja ramanspektroskopialla. Käytettyjen karakterisointimenetelmien perusteella hiilinanoputkien linkittymistä saattoi olla havaittavissa. Hiilinanoputkilla vahvistettujen itsekantavien Al2O3-kalvojen Youngin moduulin arvoksi saatiin 300 GPa:a ja vahvistamattomille kalvoille saatiin Youngin moduulin arvoksi 790 GPa:a. Tulosten perusteella Al2O3-kalvojen mekaaninen kestävyys heikkeni. Tuloksista ei voida tehdä varmoja johtopäätöksiä lukuisten optimoimattomien vaiheiden takia, mutta niitä voidaan pitää suuntaa antavina. On the market of free-standing thin films there is demand for new innovative products. The goal of this master's thesis was to find out if the mechanical properties of free-standing Al2O3 thin films can be enhanced with carbon nanotubes because in earlier studies it has been possible to reinforce Al2O3 films by utilising graphene. The motivation was the easy growth process of Al2O3 by atomic layer deposition and earlier results that show that carbon nanotubes can be linked with ion irradiation. In this study experimental methods from University of Jyväskylä's Nanoscience center and Accelerator laboratory are combined. The main focus of the study was in the creation of a manifacturing process for the Al2O3 thin films, but characterisation was also performed in several steps of the process. The free-standing Al2O3 thin films were manifactured by wet etching silicon from SiN-coated substrate and growing Al2O3 by atomic layer deposition on top. The Al2O3 films were attempted to reinforce by spreading ion irradiated carbon nanotube networks in between of two Al2O3 layers. On the characterisation of the thin films atomic force microscopy, electronmicroscopy, profilometry, and ramanspectroscopy were used. Based on the characterisation methods used, carbon nanotube linking might have been observed. The value of Young's modulus for carbon naotube reinforced Al2O3 films was found to be 300 GPa, which is in the same order of magnitude as other studies utilising graphene have found. For the non-reinforced films the value of Young's modulus was found to be 790 GPa. According to the results the carbon nanotube layer works to actually weaken the Al2O3 thin films. But due to many unknown parameters in the manufacturing process and low amount of repetitions these results can't be considered too trustworthy but directional instead.

Carbon nanotubes (CNTs) and graphene have shown promising potential as next-generation transparent conducting materials due to their high electrical and thermal conductance, flexibility and transparency in both visible and infrared spectral regions. In this study transparent and conductive thin films with a novel hemicellulose and double-walled carbon nanotube (HC-DWCNT) hybrid material were produced with spray-coating, droplet casting and vacuum filtration deposition methods. HC-DWCNT material is easily dispersed in water and usable for mass-production. These films showed good conductivity, stability at ambient air, very good transparency in the visible and excellent transparency in the infrared spectral regions while having few percent haze. The best sample had sheet resistance of 115 ± 9 ohm/sq and direct transmittance of 81.6 % at 550 nm wavelength. The properties of the prepared films were compared to CNT, graphene and their hybrid films reported by research groups by reviewing their fabrication methods and film performances. While many of these other films have shown higher shortterm quality, it was found that the performances of HC-DWCNT films were quite promising for future development considering the stability of the films and the fact that dopants or post-treatments were not used for enhancing the performance of the best samples.

Työssä mitattiin hiilinanoputkista ja hemiselluloosasta koostuvan läpinäkyvän ohutkalvon sähkönjohtavuutta. Materiaali on Nemcel Oy:n kehittämä. Valmistimme useita näytteitä erilaisia mittauksia varten ja testataksemme eri valmistusmenetelmiä. Valmistetun ohutkalvon merkittävimmät ominaisuudet ovat läpinäkyvyys ja hyvä sähkönjohtavuus. Valmistetut kalvot olivat pääasiassa läpinäkyviä, mikä edellytti kalvon ohuutta. Itse materiaali toimitettiin vesiliuoksena, jossa oli 1:1 hiilinanoputkia ja hemiselluloosaa. Kalvot valmistettiin joko spinnaamalla tai kuivattamalla yksittäisiä pisaroita pinnalle. Näytteet valmistettiin pintaoksidioidulle piille, johon oli tehty kultaelektrodit. Kalvoa kuvattiin optisella-, atomivoima- ja elektronitransmissio mikroskoopeilla. Optinen kuvantaminen osoitti kalvon epätasaisuuden. Atomivoimamikroskoopilla saatiin kuva kalvon kuitumaisesta hienorakenteesta, sekä pystyttiin määrittämään kalvon paksuus. Rakenteessa havaittiin hiilinanoputkista muodostuvia renkaita, joita päätettiin kuvata tarkemmin elektronitransmissiomikroskoopilla. Näissä kuvissa nähtiin renkaiden käämiä muistuttava rakenne. Sähkönjohtavuusmittauksia tehtiin useita ja niissä käytettiin nelipistemittausta. Ensimmäisenä mitattiin luonnollisesti johtavuus huoneilmassa, mistä siirryttiin matalan lämpötilan mittauksiin. Näytteet jäähdytettiin noin 4,2~K:iin, minkä aikana niiden johtavuuden havaittiin heikkenevän ensin hyvin hitaasti ja lopuksi, kymmenien kelvinien lämpötilassa, nopeammin. Matalassa lämpötilassa virran ja jännitteen suhteen havaittiin muuttuvan epälineaariseksi. Transistoriominaisuuksia testattiin myös 4,2 K:ssa, mutta niitä ei havaittu. Jäähdytyksen aikana kerätyn datan havaittiin noudattavan pääasiassa VRH-mallia (variable range hopping), joka on eräs tapa kuvata sähkönjohtavuuden lämpötilariippuvuutta epäsäännöllisen hilan materiaaleissa. Kalvon sähkönjohtokykyä testattiin myös muissa olosuhteissa. Ilman kosteuden huomattiin heikentävän kalvon johtavuutta selkeästi noin 50 % :n suhteellisen kosteuden yläpuolella ja johtavuus palautui ennalleen erittäin hitaasti. Johtavuutta yritettiin mitata myös kalvoa lämmitettäessä huoneilmaa korkeampiin lämpötiloihin, mutta karkeasti toteutetulla laitteistolla ei onnistuttu saamaan luotettavia tuloksia lämmityksen vaikutuksesta.

We have successfully finalized the process of creating small microfluidic channels on glass chips, having 4 inlet/outlet holes for liquid flow. The fabricated channel structures can be as complex as electron beam lithography can make them. Working channels have the minimum width and depth of 4 µm x 4 µm. The microfluidics is controlled with Fluigent MFCS, enabling pressures up to 345 mbar. Liquid flow rates range from 40 pl/s up to 1.2 nl/s. Objects in such small channels still run with channel speeds of tens of micrometers or even millimeters per second. With a T-junction structure, droplets of water/oil can be formed and controlled. The system is coupled with a Raman microscope, enabling at least the detection of carbon nanotubes inside the droplets. However, due to high channel speeds, the droplets need to be stationary to get good measurements. Carbon nanotubes also tend to form bundles and finally block the channels. Raman spectrum of multiple nanotubes was observed. The stage is now set for further and more complex measurements. Due to its limitations, this system will so far stay only in small-scale research. Olemme onnistuneet viimeistelemään valmistusprosessin, jossa lasilla oleviin mikrofluidistisiin kanaviin saadaan neljä sisään-/ulostuloaukkoa nesteille. Kanavat voivat olla muodoltaan niin monimutkaisia kuin elektronisuihkulitografialla on mahdollista tehdä. Toimivissa kanavissa syvyys ja leveys ovat pienimmillään 4 µm x 4 µm. Mikrofluidiikkaa hallitaan Fluigent MFCS – laitteistolla, joka mahdollistaa tasaisen paineen aina 345 mbar:iin asti. Nestevirtauksen nopeutta voidaan säätää välillä 40 pl/s – 1,2 nl/s. Objektit hyvin pienissä kanavissa liikkuvat kuitenkin kymmeniä mikrometrejä tai jopa millimetrejä sekunnissa. T-liitoksen avulla voidaan tehdä öljy-vesi pisaroita ja niiden liikettä hallita. Järjestelmä on yhdistetty Raman-spektroskopiaan, jolloin hiilinanoputket kanavissa voidaan ainakin havaita. Suurten kanavanopeuksien vuoksi mitattavien pisaroiden tulee olla pysähdyksissä mittausten ajan. Hiilinanoputket myös pyrkivät kasaantumaan keskenään ja tukkivat kanavan helposti. Useiden hiilinanoputkien yhtäaikainen Raman-spektri pystyttiin havaitsemaan laitteistolla. Järjestelmä on nyt valmis uusille ja monimutkaisemmille mittauksille. Rajoitustensa vuoksi järjestelmä pysyy toistaiseksi vain pienen mittakaavan tutkimuskäytössä.

Hiilinanoputket ovat todella herkkiä niiden lähiympäristössä tapahtuville muutoksille, joten niiden virrankuljetusominaisuuksia pystytään suhteellisen helposti muokkaamaan. Aromaattiset molekyylit esimerkiksi vuorovaikuttavat hiilinanoputken kanssa pii-pii -vuorovaikutusten välityksellä, jolloin molekyylien ja hiilinanoputken välillä voi tapahtua varausten siirtoa. Varausten siirtyminen taas muuttaa hiilinanoputken Fermi-tasoa ja vaikuttaa putken virrankuljetusominaisuuksiin. Myös atomeja voidaan kiinnittää hiilinanoputken seinämiin esimerkiksi sähköstaattisten vuorovaikutusten avulla, jolloin varausten siirron ja Fermi-tason muutoksen myötä putken virrankuljetusominaisuudet muuttuvat. Näiden esimerkkien kaltaista hiilinanoputkien sähköisten ominaisuuksien kemiallista muuttamista kutsutaan tavallisesti ”douppaukseksi”. Hiilinanoputkitransistorit, joiden elektrodit on tehty tavanomaisista metalleista, kuten kullasta tai palladiumista, ovat yleensä p-tyyppiä. Douppaus on yksi keino saada myös n-tyypin hiilinanoputkitransistoreja, joita tarvitaan loogisissa piireissä. Höyrystettyjä alkalimetalleja on yleisesti käytetty hiilinanoputkitransistoreiden n-tyypin douppaukseen, ja muutos p-tyypistä n-tyyppiin on vahvistettu hiilinanoputken virrankuljetusominaisuuksia mittaamalla. Samankaltaisia suoria sähköisiä mittauksia ei ole ennen tehty yksittäisille hiilinanoputkille, jotka on altistettu liuosfaasissa olevalle alkalimetallille. Tästä johtuen tämän gradun päätarkoitus oli tutkia liuosfaasissa olevan alkalimetallin douppausvaikutuksia yksittäisten hiilinanoputkien virrankuljetusominaisuuksiin. Alunperin puhtaasti p-tyypin hiilinanoputkitransistorit havaittiin muuttuvan puhtaasti n-tyypin transistoreiksi, jotka myös säilyttivät melko hyvin alkuperäiset ominaisuutensa, kuten esimerkiksi ON/OFF -suhteensa ja hilariippuvaisen virran kulmakertoimensa transitioalueella. Hiilinanoputkitransistorit ovat erittäin lupaavia pohjarakenteita nanosensorisovelluksille johtuen hiilinanoputkien herkkyydestä lähiympäristön muutoksille. Tutkimuksen toisena tavoitteena oli löytää douppausprosessin aikariippuvuus ja näin ollen testata hiilinanoputkitransistorin toimintaa nanosensorina. Sopivalla alkaliliuoksen laimennoksella hiilinanoputkitransistori saatiin doupattua kokonaan muutamassa tunnissa ja alkalikationien tarrautuminen hiilinanoputken pinnalle havaittiin yli kolmen kertaluvun virran muutoksena.

Current thesis presents computational studies of the torsional twist in single walled carbon nanotubes (SWCNTs). Since SWCNTs can be viewed as rolled up graphene sheets, our aim is to explain their torsion constants via shear mod- ulus of graphene in pristine, and single- and double vacancy cases. In addition, fundamental energy gap response to torsion is investigated. Calculations of defected structures is computationally expensive as it requires larger simula- tion cell with large number of atoms. To reduce the cost of computations we take the advantage of chiral symmetry of nanotubes instead of translational one, and faster performance of density-functional tight-binding method compared to other computational methods. Shear modulus calculations show that its value approaches that of graphene for large diameter tubes and is most sensitive to size in case of armchair tubes. Vacancies diminish shear modulus for most of the nanotubes and concentration-induced decrease has linear character regardless of chirality. Studies on direction-dependent shearing of graphene reveals that in the presence of double vacancy shear modulus has the biggest fluctuations from its average value compared to pristine and single vacancy instances. Torsion significantly modifies electronic structure as well - metallic tubes undergo tran- sition to semiconducting state, during which band gap change is linear, peaking and decreasing to zero again for most of the tubes. Results give the ground for assumption that for large diameter tubes the peak values, reached during torsion, converge.

The experiments described in this Master's thesis aim to assess the practicality of using dielectrophoresis (DEP) for assembling memory elements from carbon nanotubes (CNTs). These elements were field-effect transistors (FETs) with a wide hysteresis window. The devices assessed were made on a silicon substrate with a HfO2 - TiO2 - HfO2 gate dielectric layer to ensure a predictable hysteresis for memory operation. The FETs were used for further research in regard to environmental effects in their operation. An average yield of 12.5 % over 26 different trapping attempts, a total of 650 gaps, was achieved for single trapped CNTs in a two-electrode configuration with a 1 µm gap between electrodes with a width of 300 nm. The electrical parameters for DEP (f = 300 kHz, VPP = 5 V, t = 2 min) were consistent in the batch, but the CNT mass concentration of the 1,2-dichloroethane suspension varied between 1/98000 and 1/270000. 47 successful FETs with hysteresis were produced in the 350 devices evaluated by electrical measurements. Trapping the nanotubes exclusively on electrode tips was not possible with the configuration used in the experiments. Additionally, controlling the concentration of CNTs in the suspension was difficult. This resulted in unpredictable amounts of material between different samples as well as separate gaps between electrodes in the same sample. Because surfactants weren't used, the widespread attachment of the CNTs to each other also posed a problem. The FET operation testing was hampered by current leaks through the gate dielectric. The devices that were produced also had a relatively high current in the off-state, which resulted in low on/off ratios for the CNTFETs.

The interaction of light with carbon nanomaterials is the main focus of this thesis. I explore several nanostructured systems involving different allotropes of carbon, and characterize them both electrically, if applicable, and optically. Special attention is paid to search for plasmon-like excitations on the systems, or utilizing surface plasmons on characterization. The first objective is to achieve control of carbon nanotube (CNT) conductivity with surface plasmon polaritons (SPPs), which resulted in the first CNT field-effect transistor (FET) that can be gated definitively with SPPs. The second objective is the investigation of optical properties of various thin carbon-based molecular networks. Recently developed methods allow separation of different types of CNTs. Inspired by that, films consisting of only metallic-type single-walled (SW)CNTs were studied, which led to the discovery of a dispersive collective optical resonance in these thin films.With similar methods, conductive polymer films were also measured. To pursue the first goal, a FET was fabricated using a semiconducting-type SWCNT and a thin silver film as a backgate, on which SPPs were excited close to the CNT via the Kretschmann total internal reflection (TIR) configuration. As a result, the CNT FET could be gated at a low optical excitation power using SPPs, which most likely trigger desorption on the device, alter the Schottky barriers on CNT contacts and modulate the current. A scanning near-field optical microscope was also used to measure the local photosensitivity of the CNT FETs. Thin films of chirality-selected SWCNTs were measured with optical spectroscopy in TIR conditions, and a new collective excitation was discovered in metallictype SWCNTs. This dispersive phenomenon appeared only with a polarization not able to excite regular SPPs, and was linked to the excitonic transitions of the tubes. It shared features with SPPs such as the dependence on both the film thickness and the properties of the surrounding medium. Transparent conductive polymer films, some with graphene flakes, were also characterized, and their optical properties evaluated with TIR spectroscopy. No plasmonic or other peculiar resonances were detected, but the study led to a method to evaluate the optical anisotropy in thin polymer films. Using this method, it was possible to measure thick and uneven films, that are unsuitable for ellipsometry.