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Completely Printed, Flexible, Stable, and Hysteresis-Free Carbon Nanotube Thin-Film Transistors via Aerosol Jet Printing

Application: Transistors

Citation: Changyong Cao, Joseph B. Andrews, Aaron D. Franklin,Adv. Electron. Mat.. (2015), 10 April 2017.

Summary: Nanomaterials offer an attractive solution to the challenges faced for low-cost printed electronics, with applications ranging from additively manufactured sensors to wearables. This study reports hysteresis-free carbon nanotube thin-film transistor (CNT-TFTs) fabricated entirely using an aerosol jet printing technique; this includes the printing of all layers: semiconducting CNTs, metallic electrodes, and insulating gate dielectrics. It is shown that, under appropriate printing conditions, the gate dielectric ink can be reliably printed and yield negligible hysteresis and low threshold voltage in CNT-TFTs. Flexible CNT-TFTs on Kapton film demonstrate minimal variations in performance for over 1000 cycles of aggressive bending tests. New insights are also gained concerning the role of charge trapping in Si substrate-supported devices, where exposure to high substrate fields results in irreversible degradation. This work is a critical step forward as it enables a completely additive, maskless method to fully print CNT-TFTs of direct relevance for the burgeoning areas of flexible/foldable, wearable, and biointegrated electronics.

Improving contact interfaces in fully printed carbon nanotube thin-film transistors

Application: Transistors

Citation: C Cao, JB Andrews, A Kumar, AD Franklin,ACS nano (2015), 10.5 (2016): 5221-5229.

Summary: Single-walled carbon nanotubes (CNTs) printed into thin films have been shown to yield high mobility, thermal conductivity, mechanical flexibility, and chemical stability as semiconducting channels in field-effect, thin-film transistors (TFTs). Printed CNT-TFTs of many varieties have been studied; however, there has been limited effort toward improving overall CNT-TFT performance. In particular, contact resistance plays a dominant role in determining the performance and degree of variability in the TFTs, especially in fully printed devices where the contacts and channel are both printed. In this work, we have systematically investigated the contact resistance and overall performance of fully printed CNT-TFTs employing three different printed contact materials. Ag nanoparticles, Au nanoparticles, and metallic CNTseach in the following distinct contact geometries: top, bottom, and double. The active channel for each device was printed from the dispersion of highpurity (>99%) semiconducting CNTs, and all printing was carried out using an aerosol jet printer. Hundreds of devices with different channel lengths (from 20 to 500 μm) were fabricated for extracting contact resistance and determining related contact effects. Printed bottom contacts are shown to be advantageous compared to the more common top contacts, regardless of contact material. Further, compared to single (top or bottom) contacts, double contacts offer a significant decrease (>35%) in contact resistance for all types of contact materials, with the metallic CNTs yielding the best overall performance. These findings underscore the impact of printed contact materials and structures when interfacing with CNT thin films, providing key guidance for the further development of printed nanomaterial electronics.

A hybrid enrichment process combining conjugated polymer extraction and silica gel adsorption for high purity semiconducting single-walled carbon nanotubes (SWCNT)

Application: Other Research

Citation: Jianfu Ding, Zhao Li, Jacques Lefebvre, Fuyong Cheng, Jeffrey L. Dunford, Patrick R. L. Malenfant, Jefford Humes, Jens Kroeger, Nanoscale (2015), 10.1039/C5NR04851F.

Summary: A novel purification process for the enrichment of sc-SWCNTs that combines selective conjugated polymer extraction (CPE) with selective adsorption using silica gel, termed hybrid-CPE (h-CPE), has been developed, providing a high purity sc-SWCNT material with a significant improvement in process efficiency and yield. Using the h-CPE protocol, a greater than 5 fold improvement in yield can be obtained compared to traditional CPE while obtaining sc-SWCNT with a purity >99.9% as assessed by absorption spectroscopy and Raman mapping. Thin film transistor devices using the h-CPE derived sc-SWCNTs as the semiconductor possess mobility values ranging from 10–30 cm2 V−1 s−1 and current ON/OFF ratio of 104–105 for channel lengths between 2.5 and 20 μm.

Fully Printed Foldable Integrated Logic Gates with Tunable Performance Using Semiconducting Carbon Nanotubes

Application: Transistors

Citation: Le Cai, Suoming Zhang, Jinshui Miao, Zhibin YuChuan Wang,Adv. Functi. Mat.. (2015), Volume 25, Issue 35, pages 5698–5705.

Summary: The realization of large-area and low-cost flexible macroelectronics relies on both the advancements in materials science and the innovations in manufacturing techniques. In this study, extremely bendable and foldable carbon nanotube thin film transistors and integrated logic gates are fabricated on a piece of ultrathin polyimide substrate through an ink-jet-like printing process. The adoption of a hybrid gate dielectric layer consisting of barium titanate nanoparticles and poly(methyl methacrylate) has led to not only excellent gating effect but also superior mechanical compliance. The device characteristics show negligible amount of change after up to 1000 cycles of bending tests with curvature radii down to 1 mm, as well as very aggressive folding tests. Additionally, the electrical characteristics of each integrated logic gate can be tuned and optimized individually by using different numbers of carbon nanotube printing passes for different devices, manifesting the unique adaptability of ink-jet printing as a digital, additive, and maskless method. This report on fully printed and foldable integrated logic gates represents an inspiring advancement toward the practical applications of carbon nanotubes for high-performance and low-cost ubiquitous flexible electronics.

Polymer/metal oxide hybrid dielectrics for low voltage field-effect transistors with solution-processed, high-mobility semiconductors

Application: Transistors

Citation: Martin Held, Stefan P. Schieß, Dominik Miehler, Florentina Gannott, Jana Zaumseil,Appl. Phys. Lett.. (2015), 107, 083301.

Summary: Transistors for future flexible organic light-emitting diode (OLED) display backplanes should operate at low voltages and be able to sustain high currents over long times without degradation. Hence, high capacitance dielectrics with low surface trap densities are required that are compatible with solution-processable high-mobility semiconductors. Here, we combine poly(methyl methacrylate) (PMMA) and atomic layer deposition hafnium oxide (HfOx) into a bilayer hybrid dielectric for field-effect transistors with a donor-acceptor polymer (DPPT-TT) or single-walled carbon nanotubes (SWNTs) as the semiconductor and demonstrate substantially improved device performances for both. The ultra-thin PMMA layer ensures a low density of trap states at the semiconductor-dielectric interface while the metal oxide layer provides high capacitance, low gate leakage and superior barrier properties. Transistors with these thin (≤70 nm), high capacitance (100–300 nF/cm2) hybrid dielectrics enable low operating voltages (<5 V), balanced charge carrier mobilities and low threshold voltages. Moreover, the hybrid layers substantially improve the bias stress stability of the transistors compared to those with pure PMMA and HfOx dielectrics.

Label-Free Electrical Immunosensor for Highly Sensitive and Specific Detection of Microcystin-LR in Water Samples

Application: Biomedical

Citation: Feng Tan, Nuvia Maria Saucedo, Pankaj Ramnani, Ashok Mulchandani,Environ. Sci. Technol. (2015), 49 (15), pp 9256–9263.

Summary: Microcystin-LR (MCLR) is one of the most commonly detected and toxic cyclic heptapeptide cyanotoxins released by cyanobacterial blooms in surface waters, for which sensitive and specific detection methods are necessary to carry out its recognition and quantification. Here, we present a single-walled carbon nanotube (SWCNTs)-based label-free chemiresistive immunosensor for highly sensitive and specific detection of MCLR in different source waters. MCLR was initially immobilized on SWCNTs modified interdigitated electrode, followed by incubation with monoclonal anti-MCLR antibody. The competitive binding of MCLR in sample solutions induced departure of the antibody from the antibody–antigen complexes formed on SWCNTs, resulting in change in the conductivity between source and drain of the sensor. The displacement assay greatly improved the sensitivity of the sensor compared with direct immunoassay on the same device. The immunosensor exhibited a wide linear response to log value of MCLR concentration ranging from 1 to 1000 ng/L, with a detection limit of 0.6 ng/L. This method showed good reproducibility, stability and recovery. The proposed method provides a powerful tool for rapid and sensitive monitoring of MCLR in environmental samples.

Photochemical processes developed in composite based on highly separated metallic and semiconducting SWCNTs functionalized with polydiphenylamine

Application: Optoelectronic Devices

Citation: Mihaela Baibarac, Ioan Baltog, Ion Smaranda, Arnaud Magrez,Carbon (2015), 81, pp 426-438.

Summary: The electrochemical polymerization of diphenylamine (DPA) onto electrodes of Pt coated with highly separated metallic (98%) or semiconducting (99%) single-walled carbon nanotubes (SWCNTs) in the presence of H3PW12O40 was performed by cyclic voltammetry in order to obtain composite materials based on polydiphenylamine (PDPA) doped with heteropolyanions of H3PW12O40 and carbon nanotubes. Our data demonstrate that the photoluminescence quenching effect of the PDPA doped with H3PW12O40 heteropolyanions in the presence of SWCNTs is due to the metallic component. Under UV irradiation of SWCNTs highly separated in metallic and semiconducting tubes functionalized with PDPA doped with heteropolyanions of H3PW12O40 new photochemical reactions are evidenced by photoluminescence studies. These reactions lead to a shortening of the macromolecular chain of PDPA. The photochemical process is more intense in the case semiconducting SWCNTs functionalized with PDPA doped with heteropolyanions in comparison to metallic SWCNTs functionalized with PDPA in doped state, it being a consequence of an additional chemical interaction between the DPA dimer doped with H3PW12O40 heteropolyanions and semiconducting SWCNTs.

Diameter Refinement of Semiconducting Arc Discharge Single-Walled Carbon Nanotubes via Density Gradient Ultracentrifugation

Application: Optoelectronic Devices

Citation: Jung-Woo T. Seo, Nathan L. Yoder, Tejas A. Shastry, Jefford J. Humes, James E. Johns, Alexander A. Green, and Mark C. HersamJ. Phys. Chem. Lett. (2013), 4(17), pp 2805-2810.

Summary: Arc discharge single-walled carbon nanotubes (SWCNTs) possess superlative optical and electronic properties that are of high interest for technologically important applications including fiber optic communications, biomedical imaging, and field-effect transistors. However, as-grown arc discharge SWCNTs possess a mixture of metallic and semiconducting species in addition to a wide diameter distribution (1.2 to 1.7 nm) that limit their performance in devices. While previous postsynthetic sorting efforts have achieved separation by electronic type and diameter refinement for metallic arc discharge SWCNTs, tight diameter distributions of semiconducting arc discharge SWCNTs have not yet been realized. Herein, we present two advances in density gradient ultracentrifugation that enable the isolation of high purity (>99%) semiconducting arc discharge SWCNTs with narrow diameter distributions centered at 1.6 and 1.4 nm. The resulting diameter-refined populations of semiconducting arc discharge SWCNTs possess monodisperse characteristics that are well-suited for high-performance optical and electronic technologies.

High-frequency performance of scaled carbon nanotube array field-effect transistors

Application: Transistors

Citation: Ralph Krupke , Mathias Steiner , Michael Engel , Yu-Ming Lin , Yanging Wu , Keith Jenkins , Damon Farmer , Jefford Humes , Nathan Yoder , Jung-Woo Seo , Alexander Green , Mark Hersam , Phaedon Avouris, Nature Nanotechnology (2013), 101, 053123 (2012).

Summary: We report the radio-frequency performance of carbon nanotube array transistors that have been realized through the aligned assembly of highly separated, semiconducting carbon nanotubes on a fully scalable device platform. At a gate length of 100 nm, we observe output current saturation and obtain as-measured, extrinsic current gain and power gain cut-off frequencies, respectively, of 7 GHz and 15GHz. While the extrinsic current gain is comparable to the state-of-the-art, the extrinsic power gain is improved. The de-embedded, intrinsic current gain and power gain cut-off frequencies of 153 GHz and 30 GHz are the highest values experimentally achieved to date. We analyze the consistency of DC and AC performance parameters and discuss the requirements for future applications of carbon nanotube array transistors in high-frequency electronics.

Vacuum filtration based formation of liquid crystal films of semiconducting carbon nanotubes and high performance transistor devices

Application: Other Research

Citation: Benjamin King and Balaji Panchapakesan, Nanotechnology 25 175201, 2014.

Summary: In this paper, we report ultra-thin liquid crystal films of semiconducting carbon nanotubes using a simple vacuum filtration process. Vacuum filtration of nanotubes in aqueous surfactant solution formed nematic domains on the filter membrane surface and exhibited local ordering. A 2D fast Fourier transform was used to calculate the order parameters from scanning electron microscopy images. The order parameter was observed to be sensitive to the filtration time demonstrating different regions of transformation namely nucleation of nematic domains, nanotube accumulation and large domain growth.Transmittance versus sheet resistance measurements of such films resulted in optical to dc conductivity of σ opt/σdc = 9.01 indicative of purely semiconducting nanotube liquid crystal network.Thin films of nanotube liquid crystals with order parameters ranging from S = 0.1–0.5 were patterned into conducting channels of transistor devices which showed high I on/Ioff ratios from 10–19 800 and electron mobility values μ e = 0.3–78.8 cm2 (V-s)−1, hole mobility values μ h = 0.4–287 cm2 (V-s)−1. High I on/I off ratios were observed at low order parameters and film mass. A Schottky barrier transistor model is consistent with the observed transistor characteristics. Electron and hole mobilities were seen to increase with order parameters and carbon nanotube mass fractions. A fundamental tradeoff between decreasing on/off ratio and increasing mobility with increasing nanotube film mass and order parameter is therefore concluded. Increase in order parameters of nanotubes liquid crystals improved the electronic transport properties as witnessed by the increase in σ dc/σ opt values on macroscopic films and high mobilities in microscopic transistors. Liquid crystal networks of semiconducting nanotubes as demonstrated here are simple to fabricate, transparent, scalable and could find wide ranging device applications.

Enrichment of large-diameter semiconducting SWCNTs by polyfluorene extraction for high network density thin film transistors

Application: Transistors

Citation: Jianfu Ding, Zhao Li, Jacques Lefebvre, Fuyong Cheng, Girjesh Dubey, Shan Zou, Paul Finnie, Amy Hrdina, Ludmila Scoles, Gregory P. Lopinski, Christopher T. Kingston, Benoit Simard, and Patrick R. L. MalenfantNanoscale Issue 4, 14 Jan 2014.

Summary: A systematic study on the use of 9,9-dialkylfluorene homopolymers (PFs) for large-diameter semiconducting (sc-) single-walled carbon nanotube (SWCNT) enrichment is the focus of this report. The enrichment is based on a simple three-step extraction process: (1) dispersion of as-produced SWCNTs in a PF solution; (2) centrifugation at a low speed to separate the enriched sc-tubes; (3) filtration to collect the enriched sc-SWCNTs and remove excess polymer. The effect of the extraction conditions on the purity and yield including molecular weight and alkyl side-chain length of the polymers, SWCNT concentration, and polymer/SWCNT ratio have been examined. It was observed that PFs with alkyl chain lengths of C10, C12, C14, and C18, all have an excellent capability to enrich laser-ablation sc-SWCNTs when their molecular weight is larger than 10 000 Da. More detailed studies were therefore carried out with the C12 polymer, poly(9,9-di-n-dodecylfluorene), PFDD. It was found that a high polymer/SWCNT ratio leads to an enhanced yield but a reduced sc-purity. A ratio of 0.5–1.0 gives an excellent sc-purity and a yield of 5–10% in a single extraction as assessed by UV-vis-NIR absorption spectra. The yield can also be promoted by multiple extractions while maintaining high sc-purity. Mechanistic experiments involving time-lapse dispersion studies reveal that m-SWCNTs have a lower propensity to be dispersed, yielding a sc-SWCNT enriched material in the supernatant. Dispersion stability studies with partially enriched sc-SWCNT material further reveal that m-SWCNTs : PFDD complexes will re-aggregate faster than sc-SWCNTs : PFDD complexes, providing further sc-SWCNT enrichment. This result confirms that the enrichment was due to the much tighter bundles in raw materials and the more rapid bundling in dispersion of the m-SWCNTs. The sc-purity is also confirmed by Raman spectroscopy and photoluminescence excitation (PLE) mapping. The latter shows that the enriched sc-SWCNT sample has a narrow chirality and diameter distribution dominated by the (10,9) species with d= 1.29 nm. The enriched sc-SWCNTs allow a simple drop-casting method to form a dense nanotube network on SiO2/Si substrates, leading to thin film transistors (TFTs) with an average mobility of 27 cm2 V−1 s−1 and an average on/off current ratio of 1.8 × 106 when considering all 25 devices having 25 μm channel length prepared on a single chip. The results presented herein demonstrate how an easily scalable technique provides large-diameter sc-SWCNTs with high purity, further enabling the best TFT performance reported to date for conjugated polymer enriched sc-SWCNTs.

25th Anniversary Article: Label-Free Electrical Biodetection Using Carbon Nanostructures

Application: Chemical and Biological Sensors

Citation: Kannan Balasubramanian, Klaus KernAdvanced Materials Vol. 26, Issue 8, pp. 1154-1175, 26 Feb. 2014.

Summary: Nanostructures are promising candidates for use as active materials for the detection of chemical and biological species, mainly due to the high surface-to-volume ratio and the unique physical properties arising at the nanoscale. Among the various nanostructures, materials comprised of sp2-carbon enjoy a unique position due to the possibility to readily prepare them in various dimensions ranging from 0D, through 1D to 2D. This review focuses on the use of 1D (carbon nanotubes) and 2D (graphene) carbon nanostructures for the detection of biologically relevant molecules. A key advantage is the possibility to perform the sensing operation without the use of any labels or complex reaction schemes. Along this spirit, various strategies reported for the label-free electrical detection of biomolecules using carbon nanostructures are discussed. With their promise for ultimate sensitivity and the capability to attain high selectivity through controlled chemical functionalization, carbon-based nanobiosensors are expected to open avenues to novel diagnostic tools as well as to obtain new fundamental insight into biomolecular interactions down to the single molecule level.

Electrical conductivity enhancement of metallic single-walled carbon nanotube networks by CoO decoration

Application: Electrochemical

Citation: Do-Hyun Kim, Sang Yun Lee, Jun Eon Jin, Gyu Tae Kima, and Dong-Jin Lee, Phys. Chem. Chem. Phys. Jan 2014.

Summary We report that the decoration of metallic single-walled carbon nanotube (m-SWCNT) networks with cobalt(II) oxide (CoO) can improve the electrical conductivity of the networks. To measure the electrical conductivity, we prepared m-SWCNT networks between the source and drain electrodes of field-effect transistors (FETs). Then, the amount of CoO nanoparticles (NPs) used for decoration was controlled by treating the FETs with different volumes of a solution containing Co(NO3)2•6H2O. Atomic force microscopy imaging showed that CoO NPs were intensively deposited on the intertubular junction of the m-SWCNT networks. X-ray photoelectron spectroscopy confirmed that the oxidation state of the Co element on m-SWCNT was CoO. Raman spectra revealed that heavy decoration of CoO increased the D-band intensity of the m-SWCNT, indicating that the CoO NPs disordered the sp2 hybridized carbon atoms of the m-SWCNT via decoration. The electrical conductivity of the m-SWCNT networks was enhanced up to 28 times after decoration, and this was attributed to the CoO NPs connecting the m-SWCNTs at junctions of the networks.

Band Gap Expansion, Shear Inversion Phase Change Behaviour and Low-Voltage Induced Crystal Oscillation in Low-Dimensional Tin Selenide Crystals

Application: Electromechanical

Citation: Robin Carter, Mikhail Suyetin, Samantha Lister, M. Adam Dyson, Harrison Trewhitt, Sanam Goel, Zheng Liu, Kazu Suenaga, Cristina Giusca, Reza Jalilikashtiban, John L Hutchison, J C Dore, Gavin Bell, Elena Bichoutskaia, and Jeremy Sloan 07 Mar 2014.

Summary: In common with rocksalt-type alkali halide phases and also semiconductors such as GeTe and SnTe, SnSe forms all-surface two atom-thick low dimensional crystals when encapsulated within single walled nanotubes (SWNTs) with diameters below ~1.4 nm. Whereas previous Density Functional Theory (DFT) studies indicate that optimised low-dimensional trigonal HgTe changes from a semi-metal to a semi-conductor, low-dimensional SnSe crystals typically undergo band-gap expansion. In slightly wider diameter SWNTs (~1.4-1.6 nm), we observe that three atom thick low dimensional SnSe crystals undergo a previously unobserved form of a shear inversion phase change resulting in two discrete strain states in a section of curved nanotube. Under low-voltage (i.e. 80-100 kV) imaging conditions in a transmission electron microscope, encapsulated SnSe crystals undergo longitudinal and rotational oscillations, possibly as a result of the increase in the inelastic scattering cross-section of the sample at those voltages.

Improving the Energy Storage Performance of Graphene through Insertion of Pristine CNTs and Ordered Mesoporous Carbon Coating

Application: Electrochemical

Citation: Dr. Bo You1, Lili Wang, Prof. Na Li, Chaolun ZhengChemElectroChem 30 Jan 2014.

Summary: Graphene-based energy storage devices, such as supercapacitors and lithium ion batteries have triggered substantial research interests due to the remarkable physical and chemical properties. However, the restacking due to intensive π–π interactions dramatically decreases the specific surface area, leading to the poor energy storage performance. In addition, the electrical conductivity of commonly reduced graphene oxide (G) is several orders of magnitude lower than pristine graphene due to the incomplete reduction and the presence of numerous defects. Here, we report a doubl enhanced strategy to improve the energy storage performance of G through pristine CNTs directly dispersed by GO and subsequent multicomponent surface self-assembly coating of ordered mesoporous carbon. The resulted graphene–CNT ordered mesoporous carbon ternary hybrids (GCMCs) possess an ordered, interconnected mesostructure, a high specific surface area of 1411 m2 g−1, large mesopores of 4.3 nm, and good conductivity. With their tailored architecture, the GCMCs-based supercapacitor shows high specific capacitance (2.4–16.5 times higher than G) and excellent cycle along with 100 % capacitance after 1000 cycles. Additionally, lithium ion battery anodes made of these GCMCs have exhibited a high reversible capacity of 903 mAh g−1 at 0.1 A g−1 after 100 cycles, which is 3.9 times higher than that of G.

l-Lactic acid biosensor based on multi-layered graphene

Application: Biosensors

Citation: Antonio Radoi, Alexandru Cosmin Obreja, Sandra A. V. Eremia, Adina Bragaru, Adrian Dinescu, Gabriel-Lucian Radu,Journal of Applied Electrochemistry October 2013, Volume 43, Issue 10, pp 985-994.

Summary: Pristine graphene platelets and graphene oxide were used as electrode modifiers, aiming the investigation of their electrochemical efficacy towards β-nicotinamide adenine dinucleotide (NADH). The electrochemical detection of NADH is one of the most studied areas of bioelectroanalysis because of the ubiquity of NAD(P)H-based enzymatic reactions in nature. Commercially available graphene and laboratory prepared graphene oxide were used to modify glassy carbon electrodes and the behaviour of such modified electrodes against potassium ferricyanide (III) and NADH was reported. Relying on the graphene-modified transducer, l-lactic dehydrogenase (l-LDH) was successfully immobilised in a 1 % Nafion® membrane. The developed biosensor, working at +250 mV versus Ag/AgCl reference electrode, was used to assess l-lactic acid in four different types of yogurts, revealing an l-lactic acid concentration ranging between 0.3 and 0.6 %.p>

All-printed and transparent single walled carbon nanotube thin film transistor devices

Application: Transistors

Citation: Sajed, Farzam ;Rutherglen, Christopher;Applied Physics Letters Sep 2013, 103, 14,143303 - 143303-4.

Summary: We present fully transparent single-walled all-carbon nanotube thin film transistors (SWCNT TFT) fabricated using low-cost inkjet printing methods. Such a demonstration provides a platform towards low cost fully printed transparent electronics. The SWCNT TFTs were printed with metallic and semiconducting SWCNT using a room temperature printing process, without the requirement of expensive cleanroom facilities. The unoptimized SWCNT TFTs fabricated exhibited an Ion/off ratio of 92 and mobility of 2.27 cm2V-1s-1 and transmissivity of 82%. The combination of both high electrical performance and high transparency make all-SWCNT TFTs desirable for next generation transparent display backplanes and products such as Google Glass.

Carbon Nanotube Active-Matrix Backplanes for Mechanically Flexible Visible Light and X-ray Imagers

Application: Optoelcetronic Devices

Citation: Toshitake Takahashi, Zhibin Yu, Kevin Chen, Daisuke Kiriya, Chuan Wang, Kuniharu Takei, Hiroshi Shiraki, Teresa Chen , Biwu Ma, and Ali Javey;Nano Lett. 2013, 13 (11), pp 5425–5430.

Summary: We report visible light and X-ray imagers on lightweight and mechanically flexible plastic substrates. The process involves solution processing of organic photodetectors on top of an active-matrix backplane consisting of carbon nanotube thin-film transistors. The system takes advantage of the high mobility of nanotube transistors for low operating voltages and efficient light absorption of organic bulk-heterojunctions for high imaging sensitivity. With this highly scalable process scheme, 18 × 18 pixel-array flexible imagers (physical size of 2 cm × 1.5 cm) with high performance are successfully demonstrated. In addition, as the absorption peak of the adopted organic photodiodes covers the green band of the light spectrum, X-ray imaging is readily demonstrated by placing a scintillator film on top of the flexible imagers.

Tuning the redox activity of encapsulated metal clusters via the metallic and semiconducting character of carbon nanotubes

Application: Other Research

Citation: Fan Zhanga, Xiulian Pana, Yongfeng Hub, Liang Yua, Xiaoqi Chena, Peng Jianga, Hongbo Zhanga, Shibin Dengc, Jin Zhangc, Trudy B. Bolind, Shuo Zhange, Yuying Huange, and Xinhe Baoa,1,Proceedings of the National Academy of Sciences of the United States of America Vol. 110, No. 37, pp 14861-148866.

SummaryWe demonstrate that reactions confined within single-walled carbon nanotube (SWCNT) channels are modulated by the metallic and semiconducting character of the hosts. In situ Raman and X-ray absorption near-edge structure spectroscopies provide complementary information about the electronic state of carbon nanotubes and the encapsulated rhenium species, which reveal electronic interactions between encapsulated species and nanotubes. More electrons are transferred from metallic tubes (m-SWCNTs) to oxidic rhenium clusters, leading to a lower valence state rhenium oxide than that in semiconducting tubes (s-SWCNTs). Reduction in 3.5% (vol/vol) H2/Ar leads to weakened host–guest electronic interaction. The high valence state Re within s-SWCNTs is more readily reduced when raising the temperature, whereas only a sluggish change is observed for Re within m-SWCNTs. Only at 400 °C does Re reach a similar electronic state (mixture of Re0 and Re4+) in both types of tubes. Subsequent oxidation in 1% O2/Ar does not show changes for Re in s-SWCNTs up to 200 °C. In comparison, m-SWCNTs facilitate the oxidation of reduced rhenium (160 °C). This can be exploited for rational design of active catalysts with stable species as a desired valence state can be obtained by selecting specific-type SWCNTs and a controlled thermal treatment. These results also provide a chemical approach to modulate reversibly the electronic structure of SWCNTs without damaging the sidewalls of SWCNTs.

High-performance H2S detection by redox reactions in semiconducting carbon nanotube-based devices

Application: Chemical Sensors

Citation: Hyun Young Jung, Young Lae Kim, Sora Park, Aniket Datara, Hyung–June Lee, Jun Huanga, Sivasubramanian Somua, Ahmed Busnainaa, Yung Joon Junga, and Young–Kyun KwonRoyal Society of Chemistry, Analyst 2013, 138, 7206-7211.

Summary: Here we report the highly effective detection of hydrogen sulfide (H2S) gas by redox reactions based on single-walled carbon nanotubes (SWCNTs) functionalized with 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) as a catalyst and we also discuss the important role of water vapor in the electrical conductivity of SWCNTs during the sensing of H2S molecules. To explore the H2S sensing mechanism, we investigate the adsorption properties of H2S on carbon nanotubes (CNTs) and the effects of the TEMPO functionalization using first-principles density functional theory (DFT) and we summarize current changes of devices resulting from the redox reactions in the presence of H2S. The semiconducting-SWCNT (s-SWCNT) device functionalized with TEMPO shows a very high sensitivity of 420% at 60% humidity, which is 17 times higher than a bare s-SWCNT device under dry conditions. Our results offer promising prospects for personal safety and real-time monitoring of H2S gases with the highest sensitivity and low power consumption and potentially at a low cost.

Fully Printed, High Performance Carbon Nanotube Thin-Film Transistors on Flexible Substrates

Application: Transistors

Citation: Pak Heng Lau, Kuniharu Takei, Chuan Wang, Yeonkyeong Ju , Junseok Kim , Zhibin Yu, Toshitake Takahashi, Gyoujin Cho, and Ali Javey;Nano Lett. 2013, 13 (8), pp 3864–3869.

Summary: Fully printed transistors are a key component of ubiquitous flexible electronics. In this work, the advantages of an inverse gravure printing technique and the solution processing of semiconductor-enriched single-walled carbon nanotubes (SWNTs) are combined to fabricate fully printed thin-film transistors on mechanically flexible substrates. The fully printed transistors are configured in a top-gate device geometry and utilize silver metal electrodes and an inorganic/organic high-κ (17) gate dielectric. The devices exhibit excellent performance for a fully printed process, with mobility and on/off current ratio of up to 9 cm2/(V s) and 105, respectively. Extreme bendability is observed, without measurable change in the electrical performance down to a small radius of curvature of 1 mm. Given the high performance of the transistors, our high-throughput printing process serves as an enabling nanomanufacturing scheme for a wide range of large-area electronic applications based on carbon nanotube networks.


Short-Channel Transistors Constructed with Solution-Processed Carbon Nanotubes

Application: Transistors

Citation: Sung-Jin Choi, Patrick Bennett, Kuniharu Takei, Chuan Wang, Cheuk Chi Lo, Ali Javey, and Jeffrey Bokor, ACSNano 2013, 7 (1), pp. 798-803.

Summary: We develop short-channel transistors using solution-processed single-walled carbon nanotubes (SWNTs) to evaluate the feasibility of those SWNTs for high-performance applications. Our results show that even though the intrinsic field-effect mobility is lower than the mobility of CVD nanotubes, the electrical contact between the nanotube and metal electrodes is not significantly affected. It is this contact resistance which often limits the performance of ultrascaled transistors. Moreover, we found that the contact resistance is lowered by the introduction of oxygen treatment. Therefore, high-performance solution-processed nanotube transistors with a 15 nm channel length were obtained by combining a top-gate structure and gate insulators made of a high-dielectric-constant ZrO2 film. The combination of these elements yields a performance comparable to that obtained with CVD nanotube transistors, which indicates the potential for using solution-processed SWNTs for future aggressively scaled transistor technology.

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