Chirality-enriched semiconducting carbon nanotubes synthesized on high surface area MgO-supported catalyst

Single-walled carbon nanotubes (SWCNTs) with a narrow diameter distribution were synthesized by radio frequency-Catalytic Chemical Vapor Deposition (RF-CCVD) through the pyrolysis of CH4. Fe-Co bimetallic catalytic nanoclusters were supported on high-surface area MgO nanopowders and used in the nanotube synthesis process. Nanolog absorption fluorescence analysis was used to characterize the chiralities of the as-produced SWCNTs over this nanostructural catalyst. In the final SWCNT sample, the (7,5) semiconducting carbon nanotube species were found to be dominant, with a low chirality variation.     

Length-sorted semiconducting carbon nanotubes for high-mobility thin film transistors

We have developed a process for chemical purification of carbon nanotubes for solution-processable thin-film transistors (TFTs) having high mobility. Films of the purified carbon nanotubes fabricated by simple drop coating showed carrier mobilities as high as 164 cm²V⁻¹s⁻¹, normalized transconductances of 0.78 Sm⁻¹, and on/off current ratios of 10⁶. Such high performance requires the preparation of a suspension of micrometer-long and highly purified semiconducting single-walled carbon nanotubes (SWCNTs). Our purification process includes length and electronic-type selective trapping of SWCNTs using recycling gel filtration with a mixture of surfactants. The results provide an important milestone toward printed high-speed and large-area electronics with roll-to-roll and ink-jet device fabrication.      

Electronic devices based on purified carbon nanotubes grown by high-pressure decomposition of carbon monoxide

The excellent properties of transistors, wires and sensors made from single-walled carbon nanotubes (SWNTs) make them promising candidates for use in advanced nanoelectronic systems. Gas-phase growth procedures such as the high-pressure decomposition of carbon monoxide (HiPCO) method yield large quantities of small-diameter semiconducting SWNTs, which are ideal for use in nanoelectronic circuits. As-grown HiPCO material, however, commonly contains a large fraction of carbonaceous impurities that degrade the properties of SWNT devices. Here we demonstrate a purification, deposition and fabrication process that yields devices consisting of metallic and semiconducting nanotubes with electronic characteristics vastly superior to those of circuits made from raw HiPCO. Source-drain current measurements on the circuits as a function of temperature and backgate voltage are used to quantify the energy gap of semiconducting nanotubes in a field-effect transistor geometry. This work demonstrates significant progress towards the goal of producing complex integrated circuits from bulk-grown SWNT material.     

Disposable planar reference electrode based on carbon nanotubes and polyacrylate membrane

In this technical note, we report a new all-solid-state planar reference electrode based on single-walled carbon nanotubes and photocured poly(n-butylacrylate) (poly(nBA)) membrane containing the Ag/AgCl/Cl(-) ion system. Single-walled carbon nanotubes functionalized with octadecylamide (SWCNT-ODA) and deposited by drop-casting onto a disposable screen-printed electrode are an excellent all-solid-state transducer. The novel potentiometric planar reference electrode shows low potential variability (calibration slopes inferior to 2 mV/dec) for a wide range of chemical species (i.e., ions, small molecules, proteins) in a wide calibration range, redox pairs, changes in pH, and changes in ambient light. Potentiometric medium-term signal stability (-0.9 ± 0.2 mV/h) and electrochemical impedance characterization confirm the correct solid contact between the SWCNT-ODA layer and photocured poly(nBA) membrane. Overall, the materials used and the simple fabrication by screen-printing and drop-casting enable a high throughput and highly parallel and cost-effective mass manufacture of the new disposable reference electrode. Moreover, the reference electrode has a long shelf life, a characteristic that can be of special interest in decentralized and multiplexing potentiometric analysis.     

Gel-based separation of single-walled carbon nanotubes for metallic and semiconducting fractions

Common technique for biomaterials recovery in genetics is freeze-squeeze procedure. However, this method found a new application in carbon nanotubes field in a selective separation of metallic and semiconducting nanotubes. None-commercial agarose gel acts as a selective absorbent for semiconducting nanotubes and allows to separate them from metallic type of nanotubes. In this work we point out the great potential of freeze-squeeze technique in the field of separation of nanotubes and prove that the post-separation purification procedure is crucial to perform the quality and quantity estimation of the fractionated samples. Furthermore, the detailed quantitative analysis of the efficiency of this process is shown. Additionally, we emphasize that this technique can be used for high-scale separation of metallic counterparts of single-walled carbon nanotubes due to its simplicity and low cost.     

Direct discrimination between semiconducting and metallic single-walled carbon nanotubes with high spatial resolution by SEM

Single-walled carbon nanotube (SWCNT) films with a high density exhibit broad functionality and great potential in nanodevices,as SWCNTs can be either metallic or semiconducting in behavior.The films greatly benefit from characterization technologies that can efficiently identify and group SWCNTs based on metallic or semiconducting natures with high spatial resolution.Here,we developed a facile imaging technique using scanning electron microscopy (SEM) to discriminate between semiconducting and metallic SWCNTs based on black and white colors.The average width of the single-SWCNT image was reduced to ～9 nm,～1/5 of previous imaging results.These achievements were attributed to reduced surface charging on the SiO2/Si substrate under enhanced accelerating voltages.With this identification technique,a CNT transistor with an on/off ratio of ＞105 was fabricated by identifying and etching out the white metallic SWCNTs.This improved SEM imaging technique can be widely applied in evaluating the selective growth and sorting of SWCNTs.     

Radio frequency transistors based on ultra-high purity semiconducting carbon nanotubes with superior extrinsic maximum oscillation frequency

In this paper, we report polyfluorene-separated ultra-high purity semiconducting carbon nanotube radio frequency transistors with a self-aligned T-shape gate structure. Because of the ultra-high semiconducting tube purity and self-aligned T-shape gate structure, these transistors showed an excellent direct current and radio frequency performance. In regard to the direct current characteristics, these transistors showed a transconductance up to 40 μS/μm and an excellent current saturation behavior with an output resistance greater than 200 kΩ·μm. In terms of the radio frequency characteristics, an extrinsic maximum oscillation frequency (f _max) of 19 GHz was achieved, which is a record among all kinds of carbon nanotube transistors, and an extrinsic current gain cut-off frequency (f _T) of 22 GHz was achieved, which is the highest among transistors based on carbon nanotube networks. Our results take the radio frequency performance of carbon nanotube transistors to a new level and can further accelerate the application of carbon nanotubes for future radio frequency electronics.

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多孔碳化聚苯胺/碳纳米管的制备及性能研究

具有较高电化学性能的一种新型多孔碳化的聚苯胺包覆碳纳米管电极材料被成功的制备,它是先通过原位聚合形成聚苯胺包覆碳纳米管复合材料,然后在氩气条件下850℃碳化制得的。该电极材料在0.5A.g-1电流密度下和1mol/L H2SO4电解液中拥有209F.g-1的比电容,远高于相同条件下碳纳米管的比电容20F.g-1。这应该归因于该电极材料比表面积的提高和来自碳化聚苯胺层中氮原子掺杂诱导的赝电容效应,同时也说明了该材料在超级电容器应用中是一种比较有希望的电极材料。     

Electrocatalysis for the oxidation of NADH based on beta-cyclodextrin/multi-walled carbon nanotubes modified ITO electrode

In this study, the new nanocomposites of beta-cyclodextrin (beta-CD) and multi-walled carbon nanotubes (MWNTs) have been prepared and deposited on the indium tin oxide (ITO) electrodes to form the beta-CD/MWNTs modified ITO electrodes. These novel modified electrodes exhibited the abilities to lower the electrooxidation potentials of NADH substantially (ca. 600 mV) in comparison with bare ITO electrodes. Furthermore, a linear response to NADH in the concentration range of 4.0 x 10(-6) to 3.2 x 10(-3) mol/L was observed, with a detection limit of 8.0 x 10(-7) mol/L. Such ability of the novel nanocomposites to promote the electron-transfer reaction of NADH suggests great promise for dehydrogenase-based amperometric biosensors.     

Membrane-electrode assemblies with high specific power based on functionalized carbon nanotubes

It is demonstrated that the efficiency of catalysis and platinum usage in electrochemical energy converters can be improved by employing chemically functionalized multiwalled carbon tubes. On this basis, membrane-electrode assemblies for air-hydrogen fuel cells with specific powers up to 581 mW/cm² have been obtained.     

半导体型与金属型单壁碳纳米管的分离技术

目前用任何技术上可行的方法制备出的可用于商品化的单壁碳纳米管(SWCNTs)均为金属型和半导体型碳纳米管的混合物,极大地阻碍了SWCNTs在纳电子器件领域的应用研究进程。实现不同结构与性能SWCNTs的分离是解决当前SWCNTs研究困境的有效途径。通过概述SWCNTs分离研究的最新进展,分析和比较近几年发展的分离金属型和半导体型SWCNTs的主要技术和方法,认为研发具有操作简便、高效、可规模化分离,且成本低廉等特点的SWCNTs分离技术仍是今后研究的重点。     

Water-assisted self-sustained burning of metallic single-walled carbon nanotubes for scalable transistor fabrication

Nano Research - Although aligned arrays of semiconducting single-walled carbon nanotubes (s-SWNTs) are promising for use in next-generation electronics owing to their ultrathin bodies and ideal...     

A nanostructured electrode of IrOx foil on the carbon nanotubes for supercapacitors

IrO(x) nanofoils (IrO(x)NF) of high surface area are sputtered on multi-wall carbon nanotubes (CNT) in the preparation of a structured electrode on a stainless steel (SUS) substrate for supercapacitor applications. This IrO(x)/CNT/SUS electrode is featured with intriguing IrO(x) curved foils of 2-3 nm in thickness and 400-500 nm in height, grown on top of the vertically aligned CNT film with a tube diameter of ～ 40 nm. These nanofoils are moderately oxidized during reactive sputtering and appeared translucent under the electron microscope. Detailed structural analysis shows that they are comprised of contiguous grains of iridium metal, iridium dioxide, and glassy iridium oxide. Considerable Raman line broadening is also evidenced for the attributed nanosized iridium oxides. Two capacitive properties of the electrode are significantly enhanced with addition of the curved IrO(x) foils. First, IrO(x)NF reduces the electrode Ohmic resistance, which was measured at 3.5 Ω cm(2) for the CNT/SUS and 2.5 Ω cm(2) for IrO(x)NF/CNT/SUS using impedance spectroscopy. Second, IrO(x)NF raises the electrode capacitance from 17.7 F g(-1) (CNT/SUS) to 317 F g(-1) (IrO(x)/CNT/SUS), measured with cyclic voltammetry. This notable increase is further confirmed by the galvanostatic charge/discharge experiment, measuring 370 F g(-1) after 2000 uninterrupted cycles between - 1.0 and 0.0 V (versus Ag/AgCl).     

PN-junction diode behavior based on polyaniline nanotubes field effect transistor

Polyaniline (PANI) nanotubes configured as a field effect transistor (FET) exhibits a p–n junction diode behavior. The forward-bias current can be modulated by a gate voltage; turning on at negative gate voltage and turning off at positive gate voltage. An energy band diagram model has been proposed to explain the rectifying effect of the PANI nanotubes FET (PNT-FET). All the four different forward bias conduction mechanisms of a typical p–n junction diode can be identified for this PNT-FET using a semi-log graph to confirm this resemblance.     

Selective determination of sucrose based on electropolymerized molecularly imprinted polymer modified multiwall carbon nanotubes/glassy carbon electrode

A novel and selective electrochemical sensor was successfully developed for the determination of sucrose by integrating electropolymerization of molecularly imprinted polymer with multiwall carbon nanotubes. The sensor was prepared by electropolymerizing of o-phenylenediamine in the presence of template, sucrose, on a multiwall carbon nanotube-modified glassy carbon electrode. The sensor preparation conditions including sucrose concentration, the number of CV cycles in the electropolymerization step, pH of incubation solution, extraction time of template from the imprinted film and the incubation time were optimized using response surface methodology (RSM). A mixture of acetonitrile/acetic acid was used to remove the template. Hexacyanoferrate(II) was used as a probe to characterize the sensor using electrochemical impedance spectroscopy, cyclic voltammetry and differential pulse voltammetry. Capturing of sucrose by the modified electrode causes decreasing the response of the electrode to hexacyanoferrate(II). Calibration curve was obtained in the sucrose concentration range of 0.01–10.0 mmol L^? 1 with a limit of detection 3 μmol L^? 1. This sensor provides an efficient way for eliminating interferences from compounds with similar structures to sucrose. The sensor was successfully used to determine sucrose in sugar beet juices with satisfactory results.     

多壁纳米碳管电极电吸附脱盐性能的研究

利用透射电镜(TEM)和X射线衍射(XRD)对多壁纳米碳管形貌和晶型结构进行分析,发现多壁纳米碳管管径分布范围窄,其层间距大于高定向石墨,且随着管径的增大逐渐减小;利用多壁纳米碳管对氮气吸附实验分析其表面结构,发现其比表面积和孔容随管径的增大而减小,所形成的空隙绝大部分为中孔;将多壁纳米碳管处理后,压制成电极,组装成电吸附脱盐器,研究纳米碳管管径对电极电容和脱盐性能的影响,结果表明多壁纳米碳管管径越小,电极比电容越高,脱盐能力越强,随着中孔比表面积增大电极比电容和电极单位脱盐量均呈线性增加。     

Electrochemical properties of ferrocene adsorbed on multi-walled carbon nanotubes electrode

The adsorbed process of ferrocene on a glassy carbon (GC) electrode modified by multi-walled carbon nanotubes (MWNTs) and electrochemical properties of the adsorbed layers are investigated. It is found that the redox process of ferrocene in solution is controlled by diffusion and surface electrochemical steps on the MWNT/GC electrode in contrast to the diffusion-controlled process of ferrocene on the GC electrode. The adsorbed ferrocene exhibits a pair of well-defined redox waves in the potential range from − 0.2 V to 0.6 V. Interestingly, two pairs of obvious redox waves for the adsorbed ferrocene are observed at the switching potential over 0.8 V and the peak current values of redox waves in more positive potential increase with the enlarging switching potential. The electrochemical reaction model of ferrocene adsorbed on the MWNT/GC electrode is proposed.     

Preferential syntheses of semiconducting vertically aligned single-walled carbon nanotubes for direct use in FETs

We have combined fast heating with plasma enhanced chemical vapor deposition (PECVD) for preferential growth of semiconducting vertically aligned single-walled carbon nanotubes (VA-SWNTs). Raman spectroscopic estimation indicated a high yield of up to 96% semiconducting SWNTs in the VA-SWNT array. The as-synthesized semiconducting SWNTs can be used directly for fabricating FET devices without the need for any postsynthesis purification or separation.