Carbon Nanotube Channel Research Articles

Donor doping of single-walled carbon nanotubes by filling of channels with silver

The channels of single-walled carbon nanotubes (SWNTs) are filled with metallic silver. The synthesized nanocomposites are studied by Raman spectroscopy and optical absorption spectroscopy, and these data indicate a substantial modification of the electronic structure of the nanotubes upon their filling. Moreover, X-ray photoelectron spectroscopy shows that the incorporation of the metal leads to a change in the work function of SWNTs due to the Fermi level upshift and to the transfer of an electron density from inserted nanoparticles to the nanotube walls. Thus, the filling of the channels with silver results in donor doping of the nanotubes.

Simultaneously grown single wall carbon nanotube channel and electrodes in a thin film transistor

Abstract

A molybdenum disulfide/carbon nanotube heterogeneous complementary inverter

We report a simple, bottom-up/top-down approach for integrating drastically different nanoscale building blocks to form a heterogeneous complementary inverter circuit based on layered molybdenum disulfide and carbon nanotube (CNT) bundles. The fabricated CNT/MoS2 inverter is composed of n-type molybdenum disulfide (MOS2) and p-type CNT transistors, with a high voltage gain of 1.3. The CNT channels are fabricated using directed assembly while the layered molybdenum disulfide channels are fabricated by mechanical exfoliation. This bottom-up fabrication approach for integrating various nanoscale elements with unique characteristics provides an alternative cost-effective methodology to complementary metal–oxide–semiconductors, laying the foundation for the realization of high performance logic circuits.

Comparison of metallic silver and copper doping effects on single-walled carbon nanotubes

In this work we performed the filling of single-walled carbon nanotube channels with metallic silver and copper by means of two-step synthesis including imbuing with metal nitrate aqueous solution and further annealing. It has been shown that metal insertion into the nanotube cavities results in the Fermi level upshift and the charge transfer from metal to carbon atoms, thus donor doping of single-walled carbon nanotubes takes place. At the same time, encapsulated silver has a larger donor effect on the carbon nanotubes that has been proved by Raman spectroscopy and X-ray photoelectron spectroscopy.

Enhanced catalytic performance of CeO2 confined inside carbon nanotubes for dehydrogenation of ethylbenzene in the presence of CO2

Carbon nanotubes (CNTs) filled with CeO2 particles are prepared by wet impregnation assisted by capillary force. Compared to CeO2 outside CNTs, these composites show superior catalytic performance of oxidative dehydrogenation (ODH) of ethylbenzene (EB) to styrene in the presence of CO2. Transmission electron microscopy, temperature-programmed reduction, Raman and X-ray photoelectron spectroscopy are used to investigate the effect of CNT confinement on the catalytic performance of CeO2 inside CNTs. The results indicate that CNT tubular structure results in strengthened interaction between CeO2 and inner wall, which induces distortion and reducibility of CeO2 lattices to promote the activation of surface lattice oxygen and the formation of oxygen vacancy. The activated surface oxygen and oxygen vacancy from CeO2–CNT composites play an important role in two-step ODH reaction by promoting reverse water–gas shift reaction. In addition, CeO2 filled into shorter CNTs exhibits higher catalytic activities due to decreasing the diffusion resistance of reactants and products in CNT channels. The fact that CeO2–CNT composites exhibit excellent thermostability in the atmosphere of CO2 provides a positive choice for enhancing catalytic efficiency at elevated temperature using CNTs as supports.

Molecular simulation of CO2/N2 separation using vertically-aligned carbon nanotube membranes

The CO2/N2 permeation through carbon nanotube (CNT) membrane was studied using molecular simulations to explore its potential for flue gas separation. The theory of gas permeation was derived on the basis of the Maxwell–Stefan formulas. Adsorption isotherms calculated using grand-canonical Monte Carlo methods show a higher loading of pure CO2 than that of N2, while an approximately identical loading was found for CO2/N2 mixture with a feed pressure ratio of 1:9. The molecular snapshot indicates a concentrically layered structure inside the cylindrical channel of CNT. Results of molecular dynamics simulations show that the diffusion of N2 is a few times faster than that of CO2. For binary mixtures, the diffusion coefficients of CO2/N2 mixtures become identical at high concentrations due to the correlation effect that causes a slowing-down of the mobile species, and a speed-up of the other tardy component. The calculated N2 permeance agrees with the experimental measurement. The computed CO2 flux through CNT membranes is higher than N2 for single components, while they become nearly equal under flue gas conditions.

A spiking neuron circuit based on a carbon nanotube transistor

A spiking neuron circuit based on a carbon nanotube (CNT) transistor is presented in this paper. The spiking neuron circuit has a crossbar architecture in which the transistor gates are connected to its row electrodes and the transistor sources are connected to its column electrodes. An electrochemical cell is incorporated in the gate of the transistor by sandwiching a hydrogen-doped poly(ethylene glycol)methyl ether (PEG) electrolyte between the CNT channel and the top gate electrode. An input spike applied to the gate triggers a dynamic drift of the hydrogen ions in the PEG electrolyte, resulting in a post-synaptic current (PSC) through the CNT channel. Spikes input into the rows trigger PSCs through multiple CNT transistors, and PSCs cumulate in the columns and integrate into a ‘soma’ circuit to trigger output spikes based on an integrate-and-fire mechanism. The spiking neuron circuit can potentially emulate biological neuron networks and their intelligent functions.

MnOx supported on carbon nanotubes by different methods for the SCR of NO with NH3

In order to modify the catalytic properties of MnOx via confinement within the channels of carbon nanotubes (CNTs), a series of MnOx catalysts supported by CNTs were prepared by different methods, in which MnOx was introduced on the outside surface only or on the inside and outside surface of CNTs. The catalysts showed different activity in SCR of NOx with NH3 in the temperature range of 80–300°C. The catalyst in which some MnOx was introduced into CNT channels exhibited higher NOx conversion than that in which all the MnOx was on the outside surface of CNTs. From the result of the activity test, it was indicated that the internal diffusion of molecules may not be the key influencing factor on the catalytic activity when the particle diameter was very smaller comparing with the tubes. In addition, the result of characterization showed that MnOx confined in the channels had better abilities of supplying oxygen and adsorbing NO which played an important role in the NH3-SCR, and it can partially be attributed to the electronic interaction between MnOx and the inner surface of nanotubes.

Driving Forces and Transportation Efficiency in Water Transportation Through Single-Walled Carbon Nanotubes

Based on the concept of an energy pump, water transportation in a carbon nanotube (CNT) is studied by molecular dynamics simulations. The influences of CNT pretwist angle, water mass, environmental temperature, CNT diameter, CNT channel length, and CNT channel restrain condition on driving force and transportation efficiency are investigated. It is found that in order to initiate the transportation, the pretwist angle must be larger than certain threshold, 80 deg, for the case of one water molecule in a restrained (8,0) CNT. Furthermore, driving force decreases with increasing water mass and it is more efficient to transport multiple water molecules than one water molecules. The water molecule is found to have higher degrees of collisions in a (8,0) CNT in elevated environmental temperature. By comparing three CNT channel lengths, the channel length of 19.80 nm is identified as a faster and more efficient transporter in an unrestrained (8,8) CNT. Finally, molecular dynamics (MD) simulation indicates that a water molecule can only be transported below 300 K in an unrestrained (8,8) CNT due to the large friction caused by severely deformed channel and the Brownian motion.

New method of the directional modification of the electronic structure of single-walled carbon nanotubes by filling channels with metallic copper from a liquid phase

A method has been proposed and successfully implemented for filling the channels of single-walled carbon nanotubes with metallic copper by permeating with an aqueous solution of copper nitrate with subsequent thermal treatment. It has been demonstrated that the introduction of metallic copper into the channels of nanotubes leads to donor doping accompanied both by an increase in the Fermi energy of nanotubes and by the transfer of the electron density from introduced metal nanoparticles to the walls of nanotubes.

Local structure of titania decorated double-walled carbon nanotube characterized by scanning transmission X-ray microscopy

Scanning transmission X-ray microscopy was demonstrated to deliver detailed local structure and chemical composition of a complicated system with titania nanoparticles dispersed inside and outside the double-walled carbon nanotube (DWNT) channels. Areas with inhomogeneous distribution of titania and the associated water were particularly investigated at the C K-edge, Ti L-edge, and O K-edge. The results show that titania nanoparticles located inside DWNTs are present as amorphous, while those unsuccessfully introduced into the channels behave more like bulk materials in forms of anatase and rutile. Strong interaction was detected between the confined titania and DWNTs, as evidenced by up to 0.6 eV energy shift at the Ti L-edge. Strong hydration was observed for the as-prepared samples. Functionalization due to reduction and oxidation between titania and carbon layer is observed upon heat-treatment. This detailed structural information of specific areas cannot be provided by other techniques such as HRTEM, XRD, and XANES.

High-Density Monodispersed Cobalt Nanoparticles Filled into Multiwalled Carbon Nanotubes

Magnetic cobalt-based nanoparticles (NPs) with homogeneous size were selectively cast inside the channel of multiwalled carbon nanotubes (CNTs). The proposed synthesis method allows for filling only the CNTs channel with an unprecedented high density. The CNTs act as “nanoreactors” and provide protection against oxidation.

The translocation of DNA oligonucleotide with the water stream in carbon nanotubes

The translocation of biomolecule within carbon nanotubes (CNTs) has attracted great interest and has opened up exciting opportunities for drug delivery, gene detection and sequencing technology. To understand the fundamental interaction and the properties of translocation is indispensable but remains a challenge for both theoretical and experimental investigations. The present work focuses on the dynamics process of a single-stranded deoxyribonucleic acid (ssDNA) oligonucleotide through CNTs with a water-driven field using the steered molecular dynamics simulation. The van der Waals interaction and translocation time τ is used for analyzing the translocation process. The propulsion and obstruction forces for the movement of ssDNA are described. It is observed that both the strength of the water-driven field and the CNT channel size exert significant influence on the translocation process of ssDNA. Interestingly, both forces, the repulsive force from the water molecules behind ssDNA and the attractive interaction from water molecules in front of ssDNA, drive the ssDNA to move. The relationship between the translocation time and the water velocity is also examined. The present results can provide some helpful ideas for controlling biomolecule translocation process in CNT.

Iron nanoparticles in aligned arrays of pure and nitrogen-doped carbon nanotubes

Arrays of aligned carbon nanotubes (CNTs) and nitrogen-doped carbon (CNx) nanotubes have been grown on silicon substrates as the result of thermolysis of ferrocene/toluene and ferrocene/acetonitrile mixture. The microstructure of materials was studied by transmission and scanning electron microscopy, and X-ray diffraction was used to control the carbon and iron forms. The composition and properties of iron nanoparticles developed in the CNT and CNx nanotube samples were determined from Mössbauer spectroscopy data. The total iron content in CNx nanotubes was found to be considerably higher than that in CNTs. Three forms of iron nanoparticles α-Fe, γ-Fe, and Fe3C were detected in CNTs and only two last of them in CNx nanotubes. In the interior of CNT channels the α-Fe and Fe3C nanoparticles were observed to be coupled by a strong exchange interaction and to exhibit magnetic behavior at room temperature.

Synthesis of nanocomposites on basis of single-walled carbon nanotubes intercalated by manganese halogenides

In this work MnCl2@SWNT and MnBr2@SWNT nanocomposites were prepared via capillary filling of single-walled carbon nanotube channels by melts of manganese halogenides with slow cooling to room temperature for better crystallization. Electronic properties of MnHal2@SWNT nanocomposites have been investigated by X-ray photoelectron spectroscopy, optical absorption spectroscopy and Raman spectroscopy. It was found that the manganese halogenides show acceptor behavior and there is the charge transfer from the carbon nanotube walls to intercalated nanocrystals.

Electrophoretically induced aqueous flow through single-walled carbon nanotube membranes

Electrophoresis, the motion of charged species through liquids and pores under an external electric field, has been principle source of chemical pumping for numerous micro- and nano-fluidic devices platforms. Recent studies of ion current through single or few carbon nanotube channels range from near bulk mobility to 2-7 orders of magnitude of enhancement but cannot directly measure ion flux. Membranes, with large number of nanotube pores, allow independent confirmation of ion current and flux. Here we report that the aqueous electrophoretic mobility of ions within the graphitic cores of carbon nanotube membranes, with a uniform pore size of 0.9 ± 0.2 nm, is enhanced ∼3 times that of bulk mobilities. The induced electroosmotic velocities are 4 orders of magnitude faster than those measured in conventional porous materials. We also show that a nanotube membrane can function as a rectifying diode due to ionic steric effects within tightly controlled nanotube diameter.

Fermi energy level tuning for high performance dye sensitized solar cells using sp2 selective nitrogen-doped carbon nanotube channels

Here, we find that doping sp(2) selective nitrogen, N sp(2), into carbon nanotube (CNT) channels induces a positive shift in the Fermi level of TiO(2) photoelectrodes. It is found that this results in the large diffusion coefficient of solar driven electrons for increasing the photocurrent as well as in the low recombination rate for improving open circuit voltage with 0.74 V, which could not be overcome by using pristine CNT channels with 0.66 V.

A novel CeO2 supported on carbon nanotubes coated with SiO2 catalyst for catalytic cracking of naphtha

Carbon nanotubes (CNTs) supported ceria catalysts coated with silica were used in catalytic cracking of naphtha to increase the yield of ethylene and propylene. Coating of CNTs was carried out with a pH control chemical deposition method using Si precursor. TGA results on coated CNTs showed 80°C improvement in the thermal stability compared to uncoated CNT. XRD, SEM, and TEM analysis indicated that the structure of the CNT remained intact after modification. The silicon partly coated the CNT walls and the CeO2 entered the CNT channel or was deposited on the wall. Measurement of the total acidity and number of Brønsted acid sites with NH3-TPD and FTIR measurements exhibited that the total acid concentration and Brønsted acid sites of modified CNTs increased. TPR results showed that the presence of Si species slightly improved the reduction of CeO2. As a result, catalyst Si–Ce/CNT showed a better catalytic cracking performance than catalysts Ce/CNT, Si/CNT or CNT.

Improvement of transfer characteristic for carbon nanotube field effect transistor with poly crystalline PbZrxTi1-xO3 gate by ionic liquid

We have investigated the transfer characteristics of carbon nanotube (CNT) field effect transistors (FETs) with poly crystalline PbZrxTi1-xO3 (PZT) gate with the application of ionic liquid. The transconductance of the devices was improved more than three times by applying ionic liquid with high reproducibility. In addition, the FETs including metallic CNTs are preferable to obtain clockwise hysteresis induced by polarization reversal of the PZT gate because of the efficient electric field concentration just beneath the CNT channel. The low voltage operation around 1 V has been achieved due to the electric field concentration even for the polycrystalline PZT gate.

Single Carbon Nanotube Schottky Diode Microwave Rectifiers

We report the fabrication of single and few-channel carbon nanotube (CNT) Schottky diodes on high-frequency compatible substrates using horizontally aligned CNT arrays and dissimilar metal contacts in a coplanar-waveguide geometry. Rectification of ac signals in the range of 100 MHz-40 GHz is examined and the observed cutoff frequencies are used to compute the Schottky junction capacitance of the devices, which is strongly CNT-length-dependent and appears dominated by stray capacitance between the CNT channel and metal electrode, in agreement with electrostatic simulations.