Browsing by Author "Mudimela, Prasantha R."

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Single-Walled Carbon Nanotube Network Field Effect Transistor as a Humidity Sensor
(2012) Mudimela, Prasantha R.; Grigoras, Kestutis; Anoshkin, Ilya V.; Varpula, Aapo; Ermolov, Vladimir; Anisimov, Anton S.; Nasibulin, Albert G.; Novikov, Sergey; Kauppinen, Esko I.
School of Science | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Single-walled carbon nanotube network field effect transistors were fabricated and studied as humidity sensors. Sensing responses were altered by changing the gate voltage. At the open channel state (negative gate voltage), humidity pulse resulted in the decrease of the source-drain current, and, vice versa, the increase in the source-drain current was observed at the positive gate voltage. This effect was explained by the electron-donating nature of water molecules. The operation speed and signal intensity was found to be dependent on the gate voltage polarity. The positive or negative change in current with humidity pulse at zero-gate voltage was found to depend on the previous state of the gate electrode (positive or negative voltage, respectively). Those characteristics were explained by the charge traps in the gate dielectric altering the effective gate voltage, which influenced the operation of field effect transistor.
Synthesis of Carbon Nanotubes and Nanofibers on Silica and Cement Matrix Materials
(2009) Mudimela, Prasantha R.; Nasibulina, Larisa I.; Nasibulin, Albert G.; Cwirzen, Andrzej; Valkeapää, Markus; Habermehl-Cwirzen, Karin; Malm, Jari E. M.; Karppinen, Maarit; Penttala, Vesa; Koltsova, Tatiana S.; Tolochko, Oleg V.; Kauppinen, Esko I.
School of Chemical Technology | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
In order to create strong composite materials, a good dispersion of carbon nanotubes (CNTs) and nanofibers (CNFs) in a matrix material must be obtained. We proposed a simple method of growing the desirable carbon nanomaterial directly on the surface of matrix particles. CNTs and CNFs were synthesised on the surface of model object, silica fume particles impregnated by iron salt, and directly on pristine cement particles, naturally containing iron oxide. Acetylene was successfully utilised as a carbon source in the temperature range from 550 to 750 C. 5–10 walled CNTs with diameters of 10–15 nm at 600 C and 12–20 nm at 750 C were synthesised on silica particles. In case of cement particles, mainly CNFs with a diameter of around 30 nm were grown. It was shown that high temperatures caused chemical and physical transformation of cement particles.