Browsing by Author "Zubair, Ahmed"

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    Carbon nanotube fiber terahertz polarizer
    (AIP Publishing, 2016) Zubair, Ahmed; Tsentalovich, Dmitri E.; Young, Colin C.; Heimbeck, Martin S.; Everitt, Henry O.; Pasquali, Matteo; Kono, Junichiro
    Conventional, commercially available terahertz (THz) polarizers are made of uniformly and precisely spaced metallic wires. They are fragile and expensive, with performance characteristics highly reliant on wire diameters and spacings. Here, we report a simple and highly error-tolerant method for fabricating a freestanding THz polarizer with nearly ideal performance, reliant on the intrinsically one-dimensional character of conduction electrons in well-aligned carbon nanotubes(CNTs). The polarizer was constructed on a mechanical frame over which we manually wound acid-doped CNT fibers with ultrahigh electrical conductivity. We demonstrated that the polarizer has an extinction ratio of ∼−30 dB with a low insertion loss (<0.5 dB) throughout a frequency range of 0.2–1.1 THz. In addition, we used a THzellipsometer to measure the Müller matrix of the CNT-fiber polarizer and found comparable attenuation to a commercial metallic wire-grid polarizer. Furthermore, based on the classical theory of light transmission through an array of metallic wires, we demonstrated the most striking difference between the CNT-fiber and metallic wire-grid polarizers: the latter fails to work in the zero-spacing limit, where it acts as a simple mirror, while the former continues to work as an excellent polarizer even in that limit due to the one-dimensional conductivity of individual CNTs.
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    Carbon nanotube woven textile photodetector
    (American Physical Society, 2018) Zubair, Ahmed; Wang, Xuan; Mirri, Francesca; Tsentalovich, Dmitri E.; Fujimura, Naoki; Suzuki, Daichi; Soundarapandian, Karuppasamy P.; Kawano, Yukio; Pasquali, Matteo; Kono, Junichiro
    The increasing interest in mobile and wearable technology demands the enhancement of functionality of clothing through incorporation of sophisticated architectures of multifunctional materials. Flexible electronic and photonic devices based on organic materials have made impressive progress over the past decade, but higher performance, simpler fabrication, and most importantly, compatibility with woven technology are desired. Here we report on the development of a weaved, substrateless, and polarization-sensitive photodetector based on doping-engineered fibers of highly aligned carbon nanotubes. This room-temperature-operating, self-powered detector responds to radiation in an ultrabroad spectral range, from the ultraviolet to the terahertz, through the photothermoelectric effect, with a low noise-equivalent power (a few nW/Hz1/2) throughout the range and with a ZT-factor value that is twice as large as that of previously reported carbon nanotube-based photothermoelectric photodetectors. Particularly, we fabricated a ∼1-m-long device consisting of tens of p+−p− junctions and weaved it into a shirt. This device demonstrated a collective photoresponse of the series-connected junctions under global illumination. The performance of the device did not show any sign of deterioration through 200 bending tests with a bending radius smaller than 100 μm as well as standard washing and ironing cycles. This unconventional photodetector will find applications in wearable technology that require detection of electromagnetic radiation.
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    Charged iodide in chains behind the highly efficient iodine doping in carbon nanotubes
    (American Physical Society, 2017) Zubair, Ahmed; Tristant, Damien; Nie, Chunyang; Tsentalovich, Dmitri E.; Headrick, Robert J.; Pasquali, Matteo; Kono, Junichiro; Meunier, Vincent; Flahaut, Emmanuel; Monthioux, Marc; Gerber, Iann C.; Puech, Pascal
    The origin of highly efficient iodine doping of carbon nanotubes is not well understood. Relying on first-principles calculations, we found that iodine molecules (I2) in contact with a carbon nanotube interact to form monoiodide or/and polyiodide from two and three I2 as a result of removing electrons from the carbon nanotube (p-type doping). Charge per iodine atom for monoiodide ion or iodine atom at end of iodine chain is significantly higher than that for I2. This atomic analysis extends previous studies showing that polyiodide ions are the dominant dopants. Moreover, we observed isolated I atoms in atomically resolved transmission electron microscopy, which proves the production of monoiodide. Finally, using Raman spectroscopy, we quantitatively determined the doping level and estimated the number of conducting channels in high electrical conductivity fibers composed of iodine-doped double-wall carbon nanotubes.
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    Generation, Detection, and Manipulation of Light with Ultrahigh-Conductivity Carbon-Nanotube Fibers
    (2017-09-26) Zubair, Ahmed; Kono, Junichiro
    The ever-increasing importance in mobile and wearable technology for monitoring, sensing, and processing information demands the development of sophisticated architectures of multifunctional materials. Highly aligned multifunctional carbon nanotube (CNT) fibers combine the specific strength, lightness, and thermal conductivity of carbon fibers with the electrical conductivity of metals and ultrabroadband (ultraviolet to far-infrared) absorption. They are thus promising for flexible optoelectronics, astronomy, sensing, spectroscopy, imaging, defense, and communications applications. We fabricated unique optoelectronic devices based on these fibers for generating, detecting, and polarizing broadband electromagnetic waves. We explored the optoelectronic properties of highly aligned CNT fibers to fabricate photothermoelectric effect-based, polarization-sensitive, flexible, substrate-free, and room-temperature-operating photodetectors that work from the ultraviolet to the terahertz with low noise-equivalent power in the entire range using a novel fabrication technique. We incorporated this CNT-fiber photodetector into textiles by simply stitching it into cloth, crafting smart shirts that can collect sunlight as well as detect light on a mobile person. We will also demonstrate a simple and highly error-tolerant method for fabricating a freestanding terahertz polarizer with nearly ideal performance, reliant on the intrinsically one-dimensional character of conduction electrons in well-aligned CNTs. Finally, CNT fibers have the unique advantage of a high emissivity, nearly close to unity all over the electromagnetic spectrum, which makes them ideal as a source. We will describe a current-driven CNT-fiber-based ultrabroadband thermal light source that emits intense electromagnetic radiation from the visible to the far-infrared wavelength range. Compared to traditional thermal emitters, this emitter is more efficient, faster, more flexible, and more robust, making it a promising source for a variety of mid-infrared applications.