Measurement of ionizing radiation using carbon nanotube field effect transistor

Department of Chemistry, Stanford University, Stanford, CA 94305, USA.
Physics in Medicine and Biology (Impact Factor: 2.76). 03/2005; 50(3):N23-31. DOI: 10.1088/0031-9155/50/3/N02
Source: PubMed


Single-walled carbon nanotubes (SWNTs) are a new class of highly promising nanomaterials for future nano-electronics. Here, we present an initial investigation of the feasibility of using SWNT field effect transistors (SWNT-FETs) formed on silicon-oxide substrates and suspended FETs for radiation dosimetry applications. Electrical measurements and atomic force microscopy (AFM) revealed the intactness of SWNT-FET devices after exposure to over 1 Gy of 6 MV therapeutic x-rays. The sensitivity of SWNT-FET devices to x-ray irradiation is elucidated by real-time dose monitoring experiments and accumulated dose reading based on threshold voltage shift. SWNT-FET devices exhibit sensitivities to x-rays that are at least comparable to or orders of magnitude higher than commercial MOSFET (metal-oxide semiconductor field effect transistor) dosimeters and could find applications as miniature dosimeters for microbeam profiling and implantation.

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    • "However, very high 1.3-MeV gamma-particle doses (in excess of 16 Mrad) have led to changes in the reported SWCNT structural properties, probed via Raman spectroscopy [16]. Until additional research is conducted, TID effects will continue to be a concern for SWCNT-based devices due to radiation induced changes in the surround materials of the device, resulting from trapped charges or Schottky barrier height modification at the source and drain contacts [12]. This extrinsically induced radiation response can be convoluted with environmental factors [17], [18] making it challenging to elucidate the radiation-induced effects. "
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    ABSTRACT: The fabrication, characterization, and radiation response of single-walled carbon nanotube (SWCNT) thin-film field effect transistors (SWCNT-TFTs) has been performed. SWCNT-TFTs were fabricated on SiO<sub>2</sub>-Si substrates from 98% pure semiconducting SWCNTs separated by density gradient ultracentrifugation. Optical and Raman characterization, in concert with measured drain current I<sub>on</sub>/I<sub>off</sub> ratios, up to 10<sup>4</sup>, confirmed the high enrichment of semiconducting-SWCNTs. Total ionizing dose (TID) effects, up to 10 MRads, were measured in situ for a SWCNT-TFT under static vacuum. The results revealed a lateral translation of the SWCNT-TFT transfer characteristics to negative gate bias resulting from hole trapping within the SiO<sub>2</sub> and SiO<sub>2</sub>-SWCNT interface. Additional TID exposure conducted in air on the same device had the opposite effect, shifting the transfer characteristics to higher gate voltage, and increasing the channel conductance. No significant change was observed in the device mobility or the SWCNT Raman spectra following a TID exposure of 10 Mrad(Si), indicating extrinsic factors dominate the transfer characteristics in the SWCNT-TFT devices during irradiation. The extrinsic effects of charge trapping and the role that gas adsorption plays in the radiation response are discussed.
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    ABSTRACT: There is currently great interest in the potential use of carbon nanotubes as delivery vessels for nanotherapeutics and other medical applications. However, no data are available on the effects of sterilization methods on the properties of nanotube dispersions, the form in which most medical applications will be processed. Here we show the effects of gamma irradiation from a 60Co source on the dispersion and optical properties of single-wall carbon nanotubes in aqueous dispersion. Samples of different length-refined populations were sealed in ampoules and exposed to a dose of approximately 28 kGy, a level sufficient to ensure sterility of the dispersions. In contrast to literature results for solid-phase nanotube samples, the effects of gamma irradiation on the dispersion and optical properties of the nanotube samples were found to be minimal. Based on these results, gamma irradiation appears sufficiently non-destructive to be industrially useful for the sterilization of nanotube dispersions. KeywordsNanotube–single-wall nanotube (SWNT)–single-wall carbon nanotube (SWCNT)–gamma irradiation–sterilization–dispersion
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    ABSTRACT: This paper reports the results of two separate heavy ion irradiation experiments. In the first set, nanomaterial samples including single and multi wall carbon nanotubes and electrospun carbon nanofibers, with well-graphitized vapor grown carbon fibers as controls, were irradiated using a primary beam of Krypton-86 ions at 142 Amp MeV. The single and multi wall carbon nanotube samples sustained little damage from the highest radiation dose. In the second set, a gallium nitride nanowire-based field effect transistor was irradiated using a primary beam of Krypton-78 ions at 140 Amp MeV. The nanocircuit maintained normal function under high active bias and high radiation dose. Krypton-86 and Krypton-78 are representative of high-Z heavy ions encountered in a space radiation environment. Results from the pre-irradiation structure and optoelectronic characterization of the gallium nitride nanowires are also reported.
    No preview · Article · Jan 2005 · Proceedings of SPIE - The International Society for Optical Engineering
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