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.
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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 CNTseach 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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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>
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.
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.
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.
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.
Summary: We demonstrate that thin films of randomly oriented metallic single-walled carbon nanotubes possess optical resonances with significant dispersion. The resonances are observed in the Kretschmann configuration as minima in reflection spectra close to 400 nm and 700 nm wavelengths. The dispersions are visible only when the material is excited with s-polarized light, and most prominent in layers with thickness near 100 nm. We conclude that magnetic plasmon polaritons arising from intertube interactions are a likely explanation. Closeness of the M11 and M22 transition energies to the observed resonances points to a possible coupling with excitons.
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.
Summary: Molecular adsorption onto carbon nanotube surfaces is one of the important topics in the science and technology of carbon nanotubes due to their specific 1D structures with very high aspect ratios. In order to reveal the effect of bundles of single-walled carbon nanotubes (SWNTs) on molecular adsorption at the molecular level, we introduce an HPLC system; namely, we fabricated HPLC columns coated with bundled-SWNTs, isolated-SWNTs or graphene as the stationary HPLC phase, and discovered that polycyclic aromatic hydrocarbons having a one-dimensional shape, such as p-terphenyl and anthracene, exhibit an unusually high affinity to the bundled SWNTs compared to that of the isolated SWNTs. In contrast, no such notable specificity was obtained on a graphene-coated HPLC column. These results indicated that grooves with one-dimensional structures formed by the SWNT-bundles provide a favorable spatial geometry for the specific molecular recognition of aromatic hydrocarbons.
Summary: We developed a scalable, label-free all-electronic sensor for D-glucose based on a carbon nanotube transistor functionalized with pyrene-1-boronic acid. This sensor responds to glucose in the range 1 μM–100 mM, which includes typical glucose concentrations in human blood and saliva. Control experiments establish that functionalization with the boronic acid provides high sensitivity and selectivity for glucose. The devices show better sensitivity than commercial blood glucose meters and could represent a general strategy to bloodless glucose monitoring by detecting low concentrations of glucose in saliva.
Citation: Ashok Kumar Sundramoorthy †, Sara Mesgari †, Jing Wang †, Raj Kumar ‡, Mahasin Alam Sk. †, Siew Hooi Yeap †, Qing Zhang ‡, Siu Kwan Sze §, Kok Hwa Lim *†, and Mary B. Chan-Park *†, Journal of the Americal Chemical Society, 2013, 135 (15), pp. 5569 – 5581.
Summary: Semiconducting single-walled carbon nanotubes (s-SWNTs) have emerged as a promising class of electronic materials, but the metallic (m)-SWNTs present in all as-synthesized nanotube samples must be removed for many applications. A high selectivity and high yield separation method has remained elusive. A separation process based on selective chemistry appears to be an attractive route since it is usually relatively simple, but more effective chemicals are needed. Here we demonstrate the first example of a new class of dual selective compounds based on polycyclic aromatic azo compounds, specifically Direct Blue 71 (I), for high-purity separation of s-SWNTs at high yield. Highly enriched (93% purity) s-SWNTs are produced through the simple process of standing arc-discharge SWNTs with I followed by centrifugation. The s-SWNTs total yield is up to 41%, the highest yet reported for a solution-based separation technique that demonstrates applicability in actual transistors. 91% of transistor devices fabricated with these s-SWNTs exhibited on/off ratios of 103 to 105 with the best devices showing mobility as high as 21.8 cm2/V s with on/off ratio of 104. Raman and X-ray photoelectron spectroscopic shifts and ultraviolet–visible–near-infrared (UV–vis–NIR) show that I preferentially complexes with s-SWNTs and preferentially suspends them. Preferential reaction of naphthyl radicals (generated from I with ultrasonication) with m-SWNTs is confirmed by changes in the D-band in the Raman spectroscopy, matrix-assisted desorption–ionization time-of-flight mass spectrometry (MALDI-TOF-MS), and molecular simulation results. The high selectivity of I stems from its unique dual action as both a selective dispersion agent and the generator of radicals which preferentially attack unwanted metallic species.
Summary: We demonstrate a practical sensing platform, consisting of SnO2 nanoparticle-decorated semiconducting single-walled carbon nanotubes assembled on gold electrodes via a dielectrophoretic process, for highly sensitive CO detection with fast response at room temperature. The highest sensitivity obtained was 0.27 and the response time was ~2 s for 100 ppm CO detection. The lower detection limit was ~1 ppm. These results indicate that the sensing performance of our device is among the best of CO sensors implemented with SWNTs. Further, we observed a significant increase in sensitivity to 0.67 after subjecting the device to an electrical breakdown at 8 V. We also proposed a theoretical model to reveal the relationship between the sensitivity and the gas concentration. The new model not only resulted in a nice fit to our data, but also allowed us to estimate the contact resistance between an individual SWNT and the gold electrodes.
Citation: Guillaume Mercier, Claire Hérold, Jean-François Marêché, Sébastien Cahen, Jérôme Gleize, Jaafar Ghanbaja, Gianrico Lamura, Christine Bellouarda, Brigitte Vigolo, New Journal of Chemistry 2013, 37, 790 – 795.
Summary: Large scale production of high quality CNT samples is still challenging. The presence of structural defects and metallic particles in pristine single walled carbon nanotubes (SWNTs) is responsible for the alteration of both their chemical stability and their magnetic and electrical properties. The commonly used purification procedures are based on multi-step treatments that are often too aggressive towards the CNTs, leading to disappointing yields. Here, we propose an alternative process that allows preparing high-quality and high-purity SWNT samples. The proposed process merely consists of heating up SWNT powder under high chlorine partial pressure and high temperature. These thermodynamic conditions favor high chlorine diffusion to metal impurities embedded in carbon shells thus inducing an avalanche process of metal chloride formation and sublimation. The purified samples have been characterized by transmission electron microscopy, thermogravimetric analysis, magnetic measurements and Raman spectroscopy. We show that the developed process combines selective elimination of catalytic impurities and high yields. More importantly, we show that this process preserves the quality of the resulting purified nanotubes.p>
Citation: Constantine Y. Khripin , Xiaomin Tu , John M. Heddleston , Carlos Silvera-Batista , Angela R. Hight Walker , Jeffrey Fagan , and Ming Zheng , Analytical Chemistry, 2013, 85 (3), pp 1382 – 1388.
Summary: Length fractionation of colloidal single-wall carbon nanotube (SWCNT) dispersions is required for many studies. Size-exclusion chromatography (SEC) has been developed as a reliable method for high-resolution length fractionation of DNA-dispersed SWCNTs but has not been applied to surfactant-dispersed SWCNTs due to their lower dispersion stability and tendency to adsorb onto SEC stationary phases. Here, we report that SEC length fractionation can be achieved for bile salt dispersed SWCNTs by using porous silica-based beads as the stationary phase and bile salt solution as the mobile phase. We demonstrate that the SEC length sorting method can be combined with existing ultracentrifugation SWCNT sorting methods to produce “orthogonally sorted” samples, including length sorted semiconducting SWCNTs, which are important for electronics applications as well as length sorted empty-core SWCNTs. Importantly, we show that unlike simple length fractionation by SEC or any other method, orthogonal sorting produces samples of consistent quality for different length fractions, with similar UV–vis-nearIR absorption and Raman spectral features.
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.
Citation: G. Dinesha M. R. Dabera, K. D. G. Imalka Jayawardena, M. R. Ranga Prabhath, Iskandar Yahya, Y. Yuan Tan, N. Aamina Nismy, Hidetsugu Shiozawa, Markus Sauer, G. Ruiz-Soria, Paola Ayala, Vlad Stolojan, A. A. Damitha T. Adikaari, Peter D. Jarowski, Thomas Pichler, and S. Ravi P. Silva , ACSNano 2013, 7 (1), pp. 556-565.
Summary: Transparent, highly percolated networks of regioregular poly(3-hexylthiophene) (rr-P3HT)-wrapped semiconducting single-walled carbon nanotubes (s-SWNTs) are deposited, and the charge transfer processes of these nanohybrids are studied using spectroscopic and electrical measurements. The data disclose hole doping of s-SWNTs by the polymer, challenging the prevalent electron-doping hypothesis. Through controlled fabrication, high- to low-density nanohybrid networks are achieved, with low-density hybrid carbon nanotube networks tested as hole transport layers (HTLs) for bulk heterojunction (BHJ) organic photovoltaics (OPV). OPVs incorporating these rr-P3HT/s-SWNT networks as the HTL demonstrate the best large area (70 mm2) carbon nanotube incorporated organic solar cells to date with a power conversion efficiency of 7.6%. This signifies the strong capability of nanohybrids as an efficient hole extraction layer, and we believe that dense nanohybrid networks have the potential to replace expensive and material scarce inorganic transparent electrodes in large area electronics toward the realization of low-cost flexible electronics.
Summary: In the last three decades, zero-dimensional, one-dimensional, and two-dimensional carbon nanomaterials (i.e., fullerenes, carbon nanotubes, and graphene, respectively) have attracted significant attention from the scientific community due to their unique electronic, optical, thermal, mechanical, and chemical properties. While early work showed that these properties could enable high performance in selected applications, issues surrounding structural inhomogeneity and imprecise assembly have impeded robust and reliable implementation of carbon nanomaterials in widespread technologies. However, with recent advances in synthesis, sorting, and assembly techniques, carbon nanomaterials are experiencing renewed interest as the basis of numerous scalable technologies. Here, we present an extensive review of carbon nanomaterials in electronic, optoelectronic, photovoltaic, and sensing devices with a particular focus on the latest examples based on the highest purity samples. Specific attention is devoted to each class of carbon nanomaterial, thereby allowing comparative analysis of the suitability of fullerenes, carbon nanotubes, and graphene for each application area. In this manner, this article will provide guidance to future application developers and also articulate the remaining research challenges confronting this field.p>
Summary: Carbon nanotube networks in thin-film type transistors were studied experimentally, comparing the use of pre-separated semiconducting enriched nanotubes (90% and 99% purity) to examine how topology affects the properties of the devices. Measurements are reported for two deposition methods used for network formation: random and spin-aligned deposition methods. The results show that the thin-film transistors fabricated via spin-aligned deposition demonstrate better electrical uniformity and performance than those produced by the random network deposition method. Our results imply that coverage and alignment are strongly correlated with the properties of the devices and should therefore be simultaneously optimized for improved electrical uniformity and performance.
Summary: Horseradish peroxidase (HRP) multimer on a graphene modified glassy carbon electrode (GCE) has been fabricated by carbodiimide coupling reaction. The possible adsorption sites of HRP on graphene were predicted by Lamarckian genetic algorithm. It has been observed that HRP has five possible sites for its adsorption to graphene. Scanning electron microscopy and atomic force microscopy measurements support the evidence of formation of HRP multimer graphene. The graphene–HRP multimer film showed good electrocatalytic activity for the reduction of hydrogen peroxide. The electrochemical studies showed that graphene on the GCE increased the effective surface area, reduced the charge transfer resistance of the electrode and enhanced the electrochemical signal. The detection limit of H2O2 (9 nM) at graphene–HRP multimer was also lower than that of other electrodes studied in this work. The sensitivity of the graphene–HRP multimer film towards H2O2 determination was 7.8 μA μM−1 cm−2. Differential pulse voltammetry and selectivity studies revealed that GCE modified by graphene–HRP multimer film can be efficiently used for H2O2 determination in real samples.
Summary: The ultraviolet optical properties of semiconducting-enriched and metallic-enriched single-walled carbon nanotube (semi-enriched and m-enriched SWCNT) networks were studied using spectroscopic ellipsometry. According to calculated energy loss function, the energy loss peak assigned to the maximum intensity of π-plasmon energy was found to increase from 4.5 eV to 5.0 eV as SWCNT network composition was changed from m-SWCNT enriched to semi-SWCNT enriched. These results clearly demonstrate that the dielectric response in the 4–6 eV range is sensitive to changes in the surrounding dielectric environment depending on the semi-/m-SWCNT content. Therefore, the spectral shift of this energy loss is attributed to the enhanced electron confinement by the presence of the surface plasmon due to a small amount of m-SWCNT, which is an important phenomenon at the SWCNT network.
Summary: A processable approach to fabricate suspended and aligned single-walled carbon nanotube (SWNT) beams and cantilevers is presented in this article. Suspended dense SWNT membranes were aligned and deposited by a controlled dielectrophoresis process. A gallium focused ion beam at 30 keV and 50 pA with an optimized dose bombarded the SWNT membranes to prepare them for suspended nanoscale beams and cantilevers. To demonstrate the application of this process to nanoelectromechanical systems (NEMS), an SWNT switch was realized with a pull-in voltage of ∼ 7.8 V. Accordingly, the fabrication process of SWNT beams and cantilevers is believed to be very promising for prototyping of many NEMS devices such as switches, resonators, and biosensors.
Summary: Solution-processed thin-films of semiconducting carbon nanotubes as the channel material for flexible electronics simultaneously offers high performance, low cost, and ambient stability, which significantly outruns the organic semiconductor materials. In this work, we report the use of semiconductor-enriched carbon nanotubes for high-performance integrated circuits on mechanically flexible substrates for digital, analog and radio frequency applications. The as-obtained thin-film transistors (TFTs) exhibit highly uniform device performance with on-current and transconductance up to 15 μA/μm and 4 μS/μm. By performing capacitance–voltage measurements, the gate capacitance of the nanotube TFT is precisely extracted and the corresponding peak effective device mobility is evaluated to be around 50 cm2V–1s–1. Using such devices, digital logic gates including inverters, NAND, and NOR gates with superior bending stability have been demonstrated. Moreover, radio frequency measurements show that cutoff frequency of 170 MHz can be achieved in devices with a relatively long channel length of 4 μm, which is sufficient for certain wireless communication applications. This proof-of-concept demonstration indicates that our platform can serve as a foundation for scalable, low-cost, high-performance flexible electronics.
Summary: Carbon nanotubes (CNTs) are novel materials with considerable potential in many areas related to nanomedicine. However, a major limitation in the development of CNT-based therapeutic nanomaterials is a lack of reliable and reproducible data describing their chemical and structural composition. Knowledge of properties including purity, structural quality, dispersion state, and concentration are essential before CNTs see widespread use in in vitro and in vivo experiments. In this work, we describe the characterization of several commercially available and two in-house-produced CNT samples and discuss the physicochemical profiles that will support their use in nanomedicine.
Summary: An improved layer-by-layer vacuum filtration method was adopted for the fabrication of single-walled carbon nanotube (SWCNT) films aiming at a series of SWCNT films with controllable thickness and density. The electrical transport properties of the multilayered SWCNT films have been investigated. With the constant film density, the decrease of the layer number of the SWCNT film results in an increase of the temperature coefficient of resistance (TCR). SWCNT film with 95% metallic nanotubes has shown a lower TCR than that of the SWCNT films with a low percentage of metallic nanotubes. The effect of thermal annealing and subsequent acid (HNO3) treatment on the electrical properties of the SWCNT films has also been investigated.
Summary: The conduction responses of semiconducting single-walled carbon nanotube (SWCNT) films irradiated by 6 and 15 MV X-rays were evaluated. Results indicate that the average resistance–dose rate relations of the SWCNT network are quasi-linear and can be used for dosimetry measurements in medical radiation applications. The dynamic responses exhibit fluctuations which reveal an intrinsic feature of SWCNT networks due to the large number of interconnections between individual SWCNTs.
Integrating carbon nanotubes (CNTs) and nanowires into devices for sensing, actuation and other nanoelectronic applications has the potential to increase device efficiency and lower power consumption. Examples include ultra-high frequency CNT filters and resonators for high sensitivity gas/mass detection. Reliable operation requires careful mechanical and electrical characterization of the integrated CNTs and their contact with electrodes. In this work, we demonstrate a fabrication strategy and integration of suspended single walled CNTs (SWCNTs) on a chip for investigation of the metal nanotube interfacial adhesion strength. A multi-step etching process is used to prepare SWCNTs integrated on TEM compatible chips. Alternating current (AC) dielectrophoresis (DEP) is used for selective SWCNT integration simultaneously overcoming localization issues. The suspended tubes are conducive to mechanical manipulation or electrostatic actuation. In addition, our approach provides fully suspended electrodes for TEM analysis with reduced charging issues that are typically caused by supporting insulating layers. This enables the visualization of failure modes of the tube/electrode contact that have not been previously observed.
Summary: This paper reports the radio frequency (RF) and linearity performance of transistors using high-purity semiconducting carbon nanotubes. High-density, uniform semiconducting nanotube networks are deposited at wafer scale using our APTES-assisted nanotube deposition technique, and RF transistors with channel lengths down to 500 nm are fabricated. We report on transistors exhibiting a cutoff frequency (ft) of 5 GHz and with maximum oscillation frequency (fmax) of 1.5 GHz. Besides the cutoff frequency, the other important figure of merit for the RF transistors is the device linearity. For the first time, we report carbon nanotube RF transistor linearity metrics up to 1 GHz. Without the use of active probes to provide the high impedance termination, the measurement bandwidth is therefore not limited, and the linearity measurements can be conducted at the frequencies where the transistors are intended to be operating. We conclude that semiconducting nanotube-based transistors are potentially promising building blocks for highly linear RF electronics and circuit applications.
Summary: Over the past decade, one-dimensional nanostructures (1D-NS) have been studied for the detection of biological molecules. These nanometre-scale materials, with diameters comparable to the size of individual biomolecules, offer the advantage of high sensitivity. In this feature article we discuss different techniques of biosensing using 1D-NS, namely electrical, electrochemical, optical, and mechanical methods, with a focus on the advancement of these techniques. Advantages and disadvantages of various synthesis and functionalization methods of 1D-NS, as well as biosensor device fabrication procedures are discussed. The main focus of this review is to demonstrate the progress of protein and DNA sensors based on 1D-NS over the past decade, and in addition we present an outlook for the future of this technology.
Summary: The electrochemical sensing of hydrogen peroxide is of substantial interest to the operation of oxidase-based amperometric biosensors. We explore the fabrication of a novel and highly sensitive electro-analytical biosensor using well characterised commercially available graphene and compare and contrast responses using Nafion -graphene and -graphite modified electrodes. Interestingly we observe that graphite exhibits a superior electrochemical response due to its enhanced percentage of edge plane sites when compared to graphene. However, when Nafion, routinely used in amperometric biosensors, is introduced onto graphene and graphite modified electrodes, re-orientation occurs in both cases which is beneficial in the former and detrimental in the latter; insights into this contrasting behaviour are consequently presented providing acuity into sensor design and development where graphene is utilised in biosensors.
Summary: Wafer-scale fabrication and characterization of local back gate semiconducting nanotube thin-film transistors (SN-TFTs) are reported in this paper. The local back gate voltage of the corresponding SN-TFT controls the individual transistor switching. In order to achieve high performance, a high-k dielectric material is employed as a gate oxide and this helped to achieve low-voltage operations, much steeper sub-threshold voltage swings and higher transconductance values. A simple procedure to deposit a high-density single-walled carbon nanotube thin film on an amino-silane-treated hafnium oxide (HfOX) surface is suggested such that a good density of nanotubes is realized without degrading the device on–off current ratio and mobility values. The density of the nanotubes achieved on the silanized HfOX surface is about 40–45 nanotubes µm−2. SN-TFTs exhibit an excellent p-type output characteristic with distinct linear and saturation regions. Local back gate SN-TFTs exhibit an on–off current ratio exceeding 104 and a steep sub-threshold slope of 400 mV/decade. SN-TFTs achieve a maximum current density of 13 μA µm−1, an average threshold voltage of −0.5 V, a maximum normalized transconductance of 18.5 μS µm−1 and exhibit a maximum carrier mobility of 60.6 cm2(Vs)−1.
Summary: Carbon nanotubes (CNTs) are one of the advanced functional materials of today and has been researched extensively since its discovery. Although much is still not known about the physical and chemical properties of CNTs, it has already found potential applications in many industries, from defense to electronics and even in environmental remediation. CNTs possess many desirable mechanical and chemical properties, which supercedes many of the advanced materials of today. It was also found that CNTs have excellent electronic properties like unprecedented mobilities of up to 100,000 cm2/V s, which can potentially result in a quantum leap in the electronics industry. Over the recent years, CNT and their derivatives (decorated/functionalized) were also intensively studied, especially in the field of bio and chemical sensing owing to the size similarity of nanotubes with the analytes such as biospecies that enable strong interactions between them. However, despite intensive research, commercialization of these potential applications still remains elusive mainly due to the lack of control in synthesis of specific chirality, diameter and length of CNTs, which influences the device performance. This short review focuses on addressing recent advances in CNT research especially on aspects such as controlled synthesis, decoration/functionalization for specific recognition, sensor device fabrication and commercialization strategies.
Summary: Due to extraordinary electrical properties, preseparated, high purity semiconducting carbon nanotubes hold great potential for thin-film transistors (TFTs) and integrated circuit applications. One of the main challenges it still faces is the fabrication of air-stable n-type nanotube TFTs with industry-compatible techniques. Here in this paper, we report a novel and highly reliable method of converting the as-made p-type TFTs using preseparated semiconducting nanotubes into air-stable n-type transistors by adding a high-κ oxide passivation layer using atomic layer deposition (ALD). The n-type devices exhibit symmetric electrical performance compared with the p-type devices in terms of on-current, on/off ratio, and device mobility. Various factors affecting the conversion process, including ALD temperature, metal contact material, and channel length, have also been systematically studied by a series of designed experiments. A complementary metal−oxide−semiconductor (CMOS) inverter with rail-to-rail output, symmetric input/output behavior, and large noise margin has been further demonstrated. The excellent performance gives us the feasibility of cascading multiple stages of logic blocks and larger scale integration. Our approach can serve as the critical foundation for future nanotube-based thin-film macroelectronics.
Summary: Surfactants are routinely used in the production of graphene and additionally in their solubilisation with the aim of reducing the likelihood of coalescing. We demonstrate that surfactants, which are an inherent property of graphene, are a major contribution to the electrochemical performance. Using well characterised commercially available graphene we demonstrate that the surfactant may be detrimental in electrochemical processes, for example in the electrochemical oxidation of NADH, used prolifically as the basis of over 300 biosensors, and in the electrochemical oxidation of acetaminophen, an analgesic and antipyretic drug which requires routine monitoring in a plethora of areas. The use of control experiments in the form of surfactant modified carbon electrodes is particularly encouraged in de-convoluting the origin of the electrochemical response of graphene modified electrodes.
Summary: Use of random network carbon nanotube (CNT) transistors and their applications to complementary logic gates have been limited by several factors such as control of CNT density, existence of metallic CNTs producing a poor yield of devices, absence of stable n-dopant and control of precise position of the dopant, and absence of a scalable and cost-effective fabrication process. Here, we report a scalable and cost-effective fabrication of complementary logic gates by precisely positioning an air-stable n-type dopant, viologen, by inkjet printing on a separated semiconducting CNTs network. The obtained CNT transistors showed a high yield of nearly 100% with an on/off ratio of greater than 103 in an optimized channel length (9 μm). The n-doped semiconducting carbon nanotube transistors showed a nearly symmetric behavior in the on/off current and threshold voltage with p-type transistors. CMOS inverter, NAND, and NOR logic gates were integrated on a HfO2/Si substrate using the n/p transistor arrays. The gain of inverter is extraordinarily high, which is around 45, and NAND and NOR logic gates revealed excellent output on and off voltages. These series of whole processes were conducted under ambient conditions, which can be used for large-area and flexible thin film technology.
Summary: The sources of broad backgrounds in visible−near-IR absorption spectra of single-walled carbon nanotube (SWCNT) dispersions are studied through a series of controlled experiments. Chemical functionalization of nanotube sidewalls generates background absorption while broadening and red-shifting the resonant transitions. Extensive ultrasonic agitation induces a similar background component that may reflect unintended chemical changes to the SWCNTs. No major differences are found between spectral backgrounds in sample fractions with average lengths between 120 and 650 nm. Broad background absorption from amorphous carbon is observed and quantified. Overlapping resonant absorption bands lead to elevated backgrounds from spectral congestion in samples containing many SWCNT structural species. A spectral modeling method is described for separating the background contributions from spectral congestion and other sources. Nanotube aggregation increases congestion backgrounds by broadening the resonant peaks. Essentially no background is seen in sorted pristine samples enriched in a single semiconducting (n,m) species. By contrast, samples enriched in mixed metallic SWCNTs show broad intrinsic absorption backgrounds far from the resonant transitions. The shape of this metallic background component and its absorptivity coefficient are quantitatively assessed. The results obtained here suggest procedures for preparing SWCNT dispersions with minimal extrinsic background absorptions and for quantifying the remaining intrinsic components. These findings should allow improved characterization of SWCNT samples by absorption spectroscopy.
Summary: We demonstrate for well characterised and commercially available graphene that the surfactant used in its fabrication inhibits the electro-analytical sensing of cadmium(II) via anodic stripping voltammetry. Inspection of the deposition and stripping steps reveals that the surfactant inhibits the latter corresponding to the transition of cadmium metal to cadmium ions; this observation is in distinct contrast to the current electrochemical literature of graphene for metal analysis.
Summary: Thin fibers were spun from a colloidal solution of single-walled carbon nanotubes (SWNTs) using an electrophoretic method. Sodium dodecylbenzenesulfonate (NaDDBS) was chosen as a surfactant and showed good performance owing to its special chemical structure. The highest spinning velocity reached 0.5 mm s−1. The resulting SWNT fibers had a tensile strength of 400 MPa and a conductivity of 355 S cm−1. Their mechanical and electrical properties were markedly improved after adding NaDDBS as the dispersant in water.
Summary: The electronic properties of arrays of carbon nanotubes from several different sources differing in the manufacturing process used with a variety of average properties such as length, diameter, and chirality are studied. We used several common surfactants to disperse each of these nanotubes and then deposited them on Si wafers from their aqueous solutions using dielectrophoresis. Transport measurements were performed to compare and determine the effect of different surfactants, deposition processes, and synthesis processes on nanotubes synthesized using CVD, CoMoCAT, laser ablation, and HiPCO.
Summary: The flexible cancer sensor based on layer-by-layer self-assembled graphene reported in this letter demonstrates features including ultrahigh sensitivity and low cost due to graphene material properties in nature, self-assembly technique, and polyethylene terephthalate substrate. According to the conductance change of self-assembled graphene, the label free and labeled graphene sensors are capable of detecting very low concentrations of prostate specific antigen down to 4 fg/ml (0.11 fM) and 0.4 pg/ml (11 fM), respectively, which are three orders of magnitude lower than carbon nanotube sensors under the same conditions of design, manufacture, and measurement.
Summary: We demonstrate that graphene modified electrodes do not suffer from thin layer effects which is commonly observed in carbon nanotube modified electrodes which precludes mechanistic information to be deduced and false claims of electro-catalysis to be inferred. A simple methodology is presented allowing the electron transfer sites of graphene, viz edge plane sites to be readily determined, allowing researchers to make comparisons in the graphene field such as electrochemical generation and storage devices where graphene has been beneficially applied. Interestingly we find that in comparison of graphene orientated on a surface with that of multi-walled carbon nanotubes, the latter has an identical % of electron transfer sites (edge plane content) with that of the former.
Summary: 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 SiO2-Si substrates from 98% pure semiconducting SWCNTs separated by density gradient ultracentrifugation. Optical and Raman characterization, in concert with measured drain current Ion/Ioff ratios, up to 104, 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 SiO2 and SiO2-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.
Summary: We have studied the solvation dynamics and rotational relaxation of Coumarin 153 (C-153) in SDS dispersed two different types of single walled carbon nanotubes (SWNTs), namely metallic and semiconducting, using picosecond fluorescence spectroscopy. It has been observed that solvation dynamics of C-153 in SWNTs is severely retarded compared to pure water and SDS micelle. Time resolved fluorescence anisotropy study suggests that C-153 molecules are located on the surface of SWNT, where the rotational motion of the probe is severely hindered compared to SDS micelle due to the restriction imposed by SWNT surface as well as surrounding SDS monomers or SDS half-cylindrical micelles adsorbed on SWNT surface.
Citation: Megumi Kinoshita, Mathias Steiner, Michael Engel, Joshua P. Small, Alexander A. Green, Mark C. Hersam, Ralph Krupke, Emilio E. Mendez, Phaedon Avouris, Opt. Express (2010), 18, 25, 25738-25745.
Summary: We demonstrate a light emitting p-i-n diode made of a highly aligned film of separated (99%) semiconducting carbon nanotubes, self- assembled from solution. By using a split gate technique, we create p- and n-doped regions in the nanotube film that are separated by a micron-wide gap. We inject p- and n-type charge carriers into the device channel from opposite contacts and investigate the radiative recombination using optical micro-spectroscopy. We find that the threshold-less light generation efficiency in the intrinsic carbon nanotube film segment can be enhanced by increasing the potential drop across the junction, demonstrating the LED- principle in a carbon nanotube film for the first time. The device emits infrared light that is polarized along the long axes of the carbon nanotubes that form the aligned film.
Summary: Macroelectronic integrated circuits are widely used in applications such as flat panel display and transparent electronics, as well as flexible and stretchable electronics. However, the challenge is to find the channel material that can simultaneously offer low temperature processing, high mobility, transparency, and flexibility. Here in this paper, we report the application of high-performance separated nanotube thin-film transistors for macroelectronic integrated circuits. We have systematically investigated the performance of thin- film transistors using separated nanotubes with 95% and 98% semiconducting nanotubes, and high mobility transistors have been achieved. In addition, we observed that while 95% semiconducting nanotubes are ideal for applications requiring high mobility (up to 67 cm2 V-1 s-1) such as analog and radio frequency applications, 98% semiconducting nanotubes are ideal for applications requiring high on/off ratios (>104 with channel length down to 4µm). Furthermore, integrated logic gates such as inverter, NAND, and NOR have been designed and demonstrated using 98% semiconducting nanotube devices with individual gating, and symmetric input/output behavior is achieved, which is crucial for the cascading of multiple stages of logic blocks and larger scale integration. Our approach can serve as the critical foundation for future nanotube-based thin-film macroelectronics.
Summary: Electrochemical (EC) sensing approaches have exploited the use of carbon nanotubes (CNTs) as electrode materials owing to their unique structures and properties to provide strong electrocatalytic activity with minimal surface fouling. Nanofabrication and device integration technologies have emerged along with significant advances in the synthesis, purification, conjugation and biofunctionalization of CNTs. Such combined efforts have contributed towards the rapid development of CNT-based sensors for a plethora of important analytes with improved detection sensitivity and selectivity. The use of CNTs opens an opportunity for the direct electron transfer between the enzyme and the active electrode area. Of particular interest are also excellent electrocatalytic activities of CNTs on the redox reaction of hydrogen peroxide and nicotinamide adenine dinucleotide, two major by-products of enzymatic reactions. This excellent electrocatalysis holds a promising future for the simple design and implementation of on-site biosensors for oxidases and dehydrogenases with enhanced selectivity. To date, the use of an anti-interference layer or an artificial electron mediator is critically needed to circumvent unwanted endogenous electroactive species. Such interfering species are effectively suppressed by using CNT based electrodes since the oxidation of NADH, thiols, hydrogen peroxide, etc. by CNTs can be performed at low potentials. Nevertheless, the major future challenges for the development of CNT-EC sensors include miniaturization, optimization and simplification of the procedure for fabricating CNT based electrodes with minimal non-specific binding, high sensitivity and rapid response followed by their extensive validation using “real world” samples. A high resistance to electrode fouling and selectivity are the two key pending issues for the application of CNT-based biosensors in clinical chemistry, food quality and control, waste water treatment and bioprocessing.
Summary: High mobility and high on/off ratio thin-film transistors are fabricated using solution-based deposition of purified semiconducting carbon nanotubes. A comprehensive spectrum of the density starting from less than 10 tubes μm-2 to the high end of around 100 tubes μm-2 is investigated. This study provides the first important roadmap for the tradeoffs between mobility and on/off ratio in nanotube-based semiconducting inks.
Summary: Convincing evidence is presented demonstrating that the electro-catalytic nature of graphene resides in electron transfer from the edge of graphene which structurally resembles the behaviour of edge plane (rather than basal plane) of highly ordered pyrolytic graphite. The impact of surfactants intrinsic to graphene on the electrochemical response is highlighted.
Summary: We report photodetection in a very large spectral bandwidth, which encompasses ultraviolet, visible and near infrared, using graphene inks or graphene inks functionalized with either gold or silver nanoparticles, or gold nanoparticles further encapsulated with bovine serum albumin deposited on interdigitated electrodes fabricated on a silicon dioxide/silicon substrate. In contrast to gold-functionalized graphene inks, which have responsivities better than 1 mA W-1 at a 0.1 V bias over the huge bandwidth extending from 215 to 2500 nm, Ag-functionalized inks show at least a four-fold increased responsivity, with a record value of 13.7 mA W-1 in near infrared.
Summary: We compare electrochemical response of single-, few-, and multilayer graphene sheets and conclude that there is no significant difference between them. Therefore, there is no need for single-layer graphene sheets for electrochemical applications because multilayer graphene provides equal voltammetric performance.
Summary: We used tip-enhanced Raman spectroscopy to study defect induced D-band Raman scattering in metallic single-walled carbon nanotubes with a spatial resolution of 15 nm. The spatial extent of the D-band signal in the vicinity of localized defects is visualized and found to be about 2 nm only. Using the strong optical fields underneath the tip, we photogenerate localized defects and derive a relation between defect density and resulting D-band intensity.
Summary: This paper reports a mechanically flexible, transparent thin film transistor that uses graphene as a conducting electrode and single-walled carbon nanotubes (SWNTs) as a semiconducting channel. These SWNTs and graphene films were printed on flexible plastic substrates using a printing method. The resulting devices exhibited a mobility of ~ 2 cm2 V -1 s -1, On/Off ratio of ~ 102, transmittance of ~ 81% and excellent mechanical bendability.
Summary: An electrostatic force microscope (EFM) was used to characterize single-walled carbon nanotube (SWNT)-based nanoswitches in this paper. A conductive atomic force microscopy (AFM) tip acted as a mechanical probe as well as a positioning electrode in the experiment. The resonance frequency of the SWNT beams was computed from the measured SWNTs’ dimension and spring constant. The pull-in voltages and the corresponding gaps were extracted simultaneously from a set of force curves at different EFM probe bias voltages. The adhesive force between the AFM tip and the SWNT beam was measured through the analysis of retract force curves. The relationship between the pull-in voltage and the SWNT nanoswitch gap was in agreement with the electrostatic pull-in theory. Long-range forces such as meniscus force or electrostatic force from surface charges engaged the SWNT beam when the gap was below 6 nm in atmosphere. The SWNT beam with a resonance frequency of 1.1 GHz was actuated by a voltage of 2 V for a gap of 6.5 nm. The average adhesive force between an SWNT beam and a platinum/iridium (PtIr5)-coated tip was found to be about 50 nN. Considering the stiffness of the 1.1 GHz SWNT beam, the elastic restoring force at 6.5 nm exceeds 53 nN, which will overcome the adhesive force and release the 1.1 GHz SWNT beam. Finally, some possible approaches to further improve the behavior of SWNT nanoswitches are discussed.
Summary: Single-walled carbon nanotubes (SWNTs) have been previously observed to be strong antimicrobial agents, and SWNT coatings can significantly reduce biofilm formation. However, the SWNT antimicrobial mechanism is not fully understood. Previous studies on SWNT cytotoxicity have concluded that membrane stress (i.e., direct SWN–bacteria contact resulting in membrane perturbation and the release of intracellular contents) was the primary cause of cell death. Gene expression studies have indicated oxidative stress may be active, as well. Here, it is demonstrated for the first time how SWNT electronic structure (i.e., metallic versus semiconducting) is a key factor regulating SWNT antimicrobial activity. Experiments were performed with well-characterized SWNTs of similar length and diameter but varying fraction of metallic nanotubes. Loss of Escherichia coli viability was observed to increase with an increasing fraction of metallic SWNTs. Time-dependent cytotoxicity measurements indicated that in all cases the majority of the SWNT antimicrobial action occurs shortly after (<15 min) bacteria–SWNT contact. The SWNT toxicity mechanism was investigated by in vitro SWNT-mediated oxidation of glutathione, a common intracellular thiol that serves as an antioxidant and redox state mediator. The extent of glutathione oxidation was observed to increase with increasing fraction of metallic SWNTs, indicating an elevated role of oxidative stress. Scanning electron microscopy images of E. coli in contact with the SWNTs demonstrated electronic structure-dependent morphological changes consistent with cytotoxicity and glutathione oxidation results. A three-step SWNT antimicrobial mechanism is proposed involving (i) initial SWN–bacteria contact, (ii) perturbation of the cell membrane, and (iii) electronic structure-dependent bacterial oxidation.
Summary: Semiconducting networks were found to be extremely sensitive to charges, which promises the electrical detection of ultralow concentrations of DNA (down to 0.1 fM, ∼100 DNA molecules).
Summary:A tactile sensor utilizing a patterned, aligned, and suspended SWNT film as a sensing element is reported in this paper. The sensor was prepared on both silicon and polymer substrates to expand its potential applications to different working conditions. First, a trench 10 μm deep with Cr/Au electrodes on both sides of the trench was realized. Next, dense and oriented SWNT films were self-assembled using dielectrophoresis through in-situ control of the dc resistance of the film. Follow that, the SWNT film was patterned by lithography and oxygen plasma etching to prepare a suspended SWNT beam. Finally, PDMS primer was spin-coated on the structure and cured to protect the SWNT beam and realize a robust tactile sensor. In nanoindentation test, a piezoresistive sensitivity of 5%/mN and a detection limitation of 2 μN were demonstrated. This simple and low temperature fabrication technology is believed to be very promising for flexible tactile sensor and sensor array in applications to smart robots, implantable clinic tools, or embedded pressure sensors in micro fluidic systems.
Summary: This review outlines the use of one-dimensional nanostructures (1D-NS) for the detection of biomolecules on a chip. The materials discussed here include carbon nanotubes, metallic and semiconducting nanowires and nanochannels. While nanotubes and naowires have predominantly been used as electrical detectors, nanochannels are promising frameworks for optical detection in applications such as separation, preconcentration and DNA mapping. The primary expectation for all the three types of 1D-NS lies in the promise for ultimate single molecule detection. Furthermore, the electrical double layer governs the physics behind biosensing in all the three systems. The review starts by shedding light on the advantages arising due to the use of 1D nanostructures, followed by a discussion of fundamental aspects such as double layer effects and sensing methodologies. After this, the three kinds of 1D-NS are introduced. The main focus of the review is an in-depth analysis of the current achievements in the field and the major challenges that are to be overcome for the widespread use of such nanostructures in applications such as lab-on-a-chip devices and point-of-care diagnostics.
Citation: Liping Huang, Hongliang Zhang, Bin Wu, Yunqi Liu, Dacheng Wei, Jianyi Chen, Yunzhou Xue, Gui Yu, Hisashi Kajiura, Yongming Li, The Journal of Physical Chemistry (2010), 114, 28, 12095–12098.
Summary:A general and useful method has been developed to evaluate the metallic-to-semiconducting (M/S) ratio for separated single-walled carbon nanotubes (SWNTs). By virtue of measuring UV−vis−NIR spectra of a variety of solutions with different ratios of metallic-rich to semiconducting-rich SWNTs, the commercial IsoNanotubes samples as well as metallic-rich HiPCO SWNTs (HiPCO-M) separated by an Agarose gel method have been evaluated. Values of 99.5% metallic contents for IsoNanotubes-M, 98.9% semiconducting contents for IsoNanotubes-S, and 1.24 for the absorption coefficient of IsoNanotubes, whereas 80.4% metallic contents for HiPCO-M and 1.05 for the absorption coefficient of HiPCO SWNTs were obtained. This method does not need pure metallic (M-) or semiconducting (S-) SWNTs as references. Furthermore, we found that this method can also be applied to evaluate the M/S ratio for any SWNT samples.
Summary: We performed low-temperature electron transport spectroscopy to evaluate defects in individual single-walled carbon nanotube (SWNT) devices assembled via dielectrophoresis from a surfactant-free solution. At 4.2 K, the majority of the devices show periodic and well-defined Coulomb diamonds near zero gate voltage corresponding to transport through a single quantum dot, while at higher gate voltages, beating behavior is observed due to small potential fluctuations induced by the substrate. The Coulomb diamonds were further modeled using a single electron transistor simulator. Our study suggests that SWNTs derived from stable solutions in this work are free from hard defects and are relatively clean. Our observations have strong implications on the use of solution-processed SWNTs for future nanoelectronic device applications.
Summary: In this report, we present a description of the optical and electronic properties of as-deposited, annealed, and chemically treated single-walled carbon nanotube (SWNT) films showing metallic or semiconducting behavior. As-deposited and annealed semiconducting SWNT films were significantly less conductive than metallic SWNT films; however, chemical treatment of semiconducting SWNT films resulted in sheet resistance values as low as 60 Ω·sq−1 in comparison to 76 Ω·sq−1 for similarly processed metallic SWNT films. We conclude that the greater improvement of electrical conductivity observed in the semiconducting SWNT film results from the difference in the density of available electronic states between metallic and semiconducting SWNTs. A corroborative investigation of the change in surface work function and the chemical composition of SWNT films, as revealed by X-ray photoelectron spectroscopy, is provided to support these conclusions and to give new perspective to the formation of electronically homogeneous SWNT networks.
Summary: We report a comprehensive study of the gate-induced electromodulated transmittance of infrared light by single-walled carbon nanotube (SWNT) thin films. The observed electromodulation is significantly enhanced by utilizing large diameter SWNTs, increasing the ratio of semiconducting to metal SWNTs, and by decreasing the SWNT film thickness. The amplitude of the effect reported herein (∼7%) is more than an order of magnitude larger than in previous SWNT thin film solid state devices.
Summary: We report on the memory effect of single-walled carbon nanotubes (SWNTs (placed on a nitride-oxide layer structure designed as a charge storage medium. The conductance of the SWNT was modulated by the injected charge in the nitride-oxide interface and the polarities of injected charges were then detected. A large on/off-state current ratio ≶104(was obtained at a small program/erase voltage range ≶3 V(. We also studied the effect of a half-selected cell on the conductance of the SWNTs to identify the issues with cross-point memory architecture.
Summary: The noncovalent functionalization of single-walled carbon nanotubes (SWNTs) is important in the development of advanced materials and nanoelectronic sensors and devices. A cobalt-terpyridine transition metal complex with pendant pyrene moieties has been shown to successfully functionalize SWNTs via noncovalent π−π stacking interactions. Cyclic voltammetry at SWNT coated platinum electrodes has been utilized to investigate the process of surface modification and provides conclusive evidence of robust surface functionalization. The electrochemical methodology for examining surface functionalization of SWNTs described herein is generalizable to any redox-active system and provides a simple and powerful means for in situ examination of processes occurring at the surface of nanostructured materials.
Summary: This paper demonstrates a functioning OLED display device based on a waferscale
assembly of carbon nanotube thinfilm transistors. Using IsoNanotubes S 95%, the University of California produced transistors with high yield (>98%), low sheet resistance (25kΩ/sq), high current density ( 10µA/µm), and superior mobility (52 cm 2 V-1s-1). Moreover, on/off rations of >10^4 were achieved in devices with channel length L>20µm. To the best of our knowledge, these are the best concurrent CNT transistor numbers reported in the literature to date.
Summary: In this study, solutions of 99% pure semiconducting nanotubes were used to fabricate SWNT field-effect transistors (FETs) with extrinsic and intrinsic current gain cutoff frequencies of ~15 and ~80 GHz, respectively. Importantly, this study also demonstrates that precise nanotube alignment is not required to achieve excellent performance in high-frequency devices.
Summary: The IBM T.J. Watson Research Center with Northwestern University fabricated thin-film transistors (TFTs) from DGU produced semiconducting CNTs. To confirm the semiconducting purity of the CNTs, the team synthesized 83 single nanotube transistors from the same DGU produced source material. 82 of the 83 transistors were found to contain a semiconducting nanotube, empirically confirming the material’s calculated level (99%) of semiconducting enrichment.
Summary: This paper discusses the advantages of DGU over other nanotube sorting strategies, such as dielectrophoresis, selective chemistry, controlled electrical breakdown, and chromatography. In brief, the principle advantages of DGU are its:
- Demonstrated scalability
- Compatibility with a wide range of starting materials
- Use of reversible functionalization chemistry
- Iterative repeatability
Summary: This paper discusses the performance of DGU-produced metallic nanotubes in transparent conductive films. In comparison to unsorted-CNT films, metallic films were found to be up to 5.6x more conductive in the visible spectrum, and 10x more conductive in the near infrared (NIR) at similar transparencies.