Browsing by Author "Tarkiainen, Reeta"

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    Multiwalled carbon nanotubes as single electron transistors
    (Aalto University, 2001) Ahlskog, Markus; Tarkiainen, Reeta; Roschier, Leif; Paalanen, Mikko; Hakonen, Pertti J.; Teknillisen fysiikan laitos; Department of Applied Physics; Perustieteiden korkeakoulu; School of Science
    Single electron transistors (SET) are fabricated from multiwalled carbon nanotubes (MWNT) by manipulation with an atomic force microscope. The devices consist of either a single MWNT with Au contacts at the ends or of two crossing tubes. In the latter device, the lower nanotube acted as the central island of a single electron transistor while the upper one functioned as a gate electrode. Coulomb blockade oscillations were observed on the nanotube at low temperatures. The voltage noise of the nanotube-SET was gain dependent as in conventional SETs. The charge sensitivity at 10 Hz was 6x10 exp -4 e/√Hz. Furthermore, in another device where the MWNT is suspended above the substrate between the electrodes, we measure an extremely high charge sensitivity of 6x 10 exp -6 e/√Hz at 45 Hz, comparable to the best of the conventional SETs.
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    Shot noise of a multiwalled carbon nanotube field effect transistor
    (American Physical Society (APS), 2007) Wu, Fan; Tsuneta, Taku; Tarkiainen, Reeta; Gunnarsson, David; Wang, Tai-Hong; Hakonen, Pertti J.; Teknillisen fysiikan laitos; Department of Applied Physics; Perustieteiden korkeakoulu; School of Science
    We have investigated shot noise in a 6−nm-diameter, semiconducting multiwalled carbon nanotube field effect transistor at 4.2 K over the frequency range of 600–950 MHz. We find a transconductance of 3–3.5 μS for optimal positive and negative source-drain voltages V. For the gate referred input voltage noise, we obtain 0.2 and 0.3 μV/√Hz for V > 0 and V < 0, respectively. As effective charge noise, this corresponds to (2–3)×10 exp −5 e/√Hz.
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    Transport and tunneling in multiwalled carbon nanotubes
    (Helsinki University of Technology, 2005-06-03) Tarkiainen, Reeta; Department of Engineering Physics and Mathematics; Teknillisen fysiikan ja matematiikan osasto; Low Temperature Laboratory; Kylmälaboratorio
    Carbon nanotubes are promising new candidates for the construction of molecular-scale electronic circuits. However, the widely varying quality of the material, synthesized using different methods, results in large variation in electronic transport properties. In this Thesis, electronic transport in both disordered and good-quality multiwalled carbon nanotubes was studied. The transport in disordered samples, synthesized using chemical vapor deposition method, was studied to this extent for the first time. The transport in disordered samples was found to be diffusive. The mean free path is so short that the quantum corrections to conductivity, the weak localization correction and the interaction correction, are best described using the theory for a two-dimensional conductor. The samples are found to be close to the strong localization limit, and the electron dephasing cannot be fully accounted for using the standard electron-electron scattering only. An additional dephasing mechanism is required, such as magnetic impurities. As bias voltage is increased the sample resistance was observed to change in accordance with an electron heating model. The tunneling conductivity of both disordered and good-quality samples was measured, and a zero bias anomaly was discovered in both cases. However, the results differ due to the larger resistivity of the disordered samples. In the disordered case, the functional form of the anomaly was successfully compared with the non-perturbative theory of electron tunneling into a disordered 1D electrode. In the good-quality samples, the anomaly obeyed a power law, which can result from both environmental quantum fluctuation theory for ultra-small junctions and the Luttinger model. At high voltages the predictions differ, and better agreement with the environmental quantum fluctuation theory was found. Construction of single-electron transistors, with good charge sensitivity, was demonstrated. Current fluctuations were observed to originate both from background charge fluctuations and resistance fluctuations of the device itself.