One-dimensional Carbon Nanotubes Research Articles

Theoretical Modelling of Charge Transport Properties of Individual Single-Wall Carbon Nanotubes

Experimental projection of transport properties of semiconductor devices faces a challenge nowadays. As devices scale to nanometre scale range, the classical transport equations used in current device simulators can no longer be applied. Conversely, the use of a more accurate and better non-equilibrium green function (NEGF) is limited by the fact that it requires excessive quantum of memory and computational time, having quasi-separable matrices that are extremely convoluted to solve. This work exploits the Boltzmann Transport Equation (BTE) to assess the transport properties of carbon nanotubes. Previous works on solving the BTE have employed either a stochastic method or an approximate method, both of which do not possess the necessary properties for practical device applications. Therefore, this work represents the first direct theoretical solution of the BTE for one-dimensional carbon nanotubes that can be utilized for practical device applications. The complete spectrum of transport in CNTs extending from ohmic to high-field through ballistic transmission is examined to delineate plethora of transport properties. The transport for arbitrary values of the electric field is based on the BTE applied to experimental data on CNTs. In the limit of low field, the mobility expressions are obtained in terms of the mean free path (mfp) that is distinctly shorter than the length of the sample. The ohmic resistance is quantized a value of 6.453k-ohms consistent with experimental findings with transmission approaching unity as channel length shrinks below the carrier mfp. The emission of a quantum was observed to lower the saturation velocity that is independent of scattering and hence ballistic. Transition to ballistic domain was found to occur when the channel length is scaled below the ballistic limit that is shown to be the extended version of the long-channel mfp modulated by injections from the contacts, yet the mobility degrades. The mobility degradation is shown to be the cause of resistance quantum in the low-channel length limit. These findings are important in predicting the transport properties of low-dimensional CNTs.

Synergistic improvement of electrical and thermal conductivities of carbon-based nanocomposites and its prediction by Mori-Tanaka scheme with interfacial resistances

Carbon-based nanomaterials have widely been used to enhance the thermal and electrical properties of polymer composites with the aid of miniaturization of electronic devices that require fast heat dissipation and electromagnetic interference shielding at a desired level. A combination of different carbon nanofillers can lead to a strong synergistic effect by creating the electron hopping pathway and conductive network. Here, we fabricate the hybrid nanocomposites composed of two-dimensional graphite nanoplatelets, one-dimensional microscale carbon fibers, and one-dimensional nanoscale multiwalled carbon nanotubes. The synergistic improvement of electrical and thermal conductivities of the hybrid nanocomposites is achieved by a three-dimensional network formation among the microscale and nanoscale fillers. A Mori-Tanaka averaging scheme with perfect and imperfect interfacial resistances under uni-directional and random fiber orientations is presented to predict the synergistic improvement of thermal conductivity of the nanocomposites. A transient temperature response in the nanocomposites is investigated to evaluate heat dissipation capability in which heat transfer rate is enhanced in the case of hybrid nanocomposites. Finite element simulation results are in a good agreement with the transient temperature response experimentally obtained.

Ultrafast response of spray-on nanocomposite piezoresistive sensors to broadband ultrasound

We present a nano-engineered thin-film-type piezoresistive sensor, coatable or sprayable on a medium surface for in-situ acquisition of broadband ultrasound up to 1.4 MHz – a trait of nanocomposite-based piezoresistive sensing devices that has until now not been discovered and explored. With polyvinylidene fluoride as the matrix, fabrication of the spray-on sensor is attempted in a comparative manner, with multiscale nanofillers ranging from zero-dimensional carbon black, through one-dimensional multiwalled carbon nanotubes, to two-dimensional graphene nanoparticles. With a morphologically optimal nano-architecture, the quantum tunneling effect can be triggered in the percolating nanofiller network when ultrasound signals traverse the sensor, inducing dynamic alteration in the piezoresistivity manifested by the sensor. In-situ morphological analysis and experiment reveal high fidelity, ultrafast responses, and high sensitivity of the sensor to dynamic disturbance, from static strain to ultrasound in a regime of megahertz yet with an ultralow magnitude (of the order of microstrain or nanostrain). These findings are remarkable as no other investigation has probed the response of nanocomposite piezoresistive sensors over such a broad frequency spectrum.

Heteroatom-doped carbon dots based catalysts for oxygen reduction reactions

Carbon materials doped with heteroatoms are a class of cost-effective and stable electrocatalysts for oxygen reduction reactions (ORR), whose activities are mainly based on the heteroatom-related active sites. Besides the widely reported one-dimensional carbon nanotubes and two-dimensional graphene materials, carbon dots (CDs), as a new kind of zero-dimensional carbon materials, exhibit a range of unique structures and promising catalytic activities for ORR. In order to optimize the complex conditions of carbon-based catalysts, composites consisting of doped CDs and reduced graphene oxide (rGO) (designated as CD/rGO) are prepared hydrothermally, in comparison with directly doped rGO. All produced composites outperform their corresponding directly doped rGO counterparts in ORR measurements. It is noted that nitrogen and sulfur co-doped samples perform better than those doped by individual N or S. Mechanistic relationships between the ORR catalytic activities and the catalyst features are proposed, including type, location, bonding, fraction and synergistic effects of dopants, as well as the composition and structure of the carbon substrates. It is apparent that doping heteroatoms and constructing carbon substrates play a synergistic role in yielding high-performance carbon based catalysts.

Electrical and Mechanical Properties of Ink Printed Composite Electrodes on Plastic Substrates

Printed flexible electrodes with conductive inks have attracted much attention in wearable electronics, flexible displays, radio-frequency identification, etc. Conventional conductive inks contain large amount of polymer which would increase the electrical resistivity of as-printed electrodes and require high sintering temperature. Here, composite electrodes without cracks were printed on polyimide substrate using binder-free silver nanoparticle based inks with zero-dimensional (activated carbon), one-dimensional (silver nanowire and carbon nanotube) or two-dimensional (graphene) fillers. The effect of fillers on resistivity and flexibility of printed composite electrodes were evaluated. The graphene filler could reduce the resistivity of electrodes, reaching 1.7 × 10−7 Ω·m after low power laser sintering, while the silver nanowire filler improved their flexibility largely during bending tests. The microstructural changes were examined to understand the nanojoining process and their properties.

Strain sensing behaviors of stretchable conductive polymer composites loaded with different dimensional conductive fillers

Herein, we investigate the dependence of the strain sensing behaviors of isoprene rubber (IR) based conductive composites on filler dimensionality. It is found that carbon black (CB)/IR composites display ultrahigh strain sensitivity and good recoverability since CB-networks are easily broken under stretching and fast rebuilt under releasing. However, the drawback of CB/IR composites is the high electrical percolation threshold (8.01 phr), leading to the complex processing, poor mechanical properties, and high cost. In contrast, carbon nanotubes (CNTs)/IR composites possess low percolation threshold (1.44 phr) but also low sensitivity and poor recoverability because CNT-networks are more stable under strain. Interestingly, it is observed that combining zero-dimensional CB and one-dimensional CNTs to construct the hybrid CNT-CB networks is an effective route to overcome the drawbacks of CB-networks and CNT-networks, which endows the stretchable CNTs/CB/IR composites with low percolation threshold, high strain sensitivity and good recoverability. Moreover, the demonstration experiments show that the stretchable CNTs/CB/IR composites could be used to detect human motions and emotional expressions. This study provides a deeper understanding of the strain sensing behaviors of the stretchable conductive polymer composites loaded with different dimensional conductive fillers, which helps to design strain sensing materials.

A Geometry Effect of Carbon Nanomaterials on Flame Retardancy and Mechanical Properties of Ethylene-Vinyl Acetate/Magnesium Hydroxide Composites.

This study was aimed at investigating the effects of carbon nanomaterials with different geometries on improving the flame retardancy of magnesium hydroxide–filled ethylene-vinyl acetate (EM). The thermal stability and flame retardancy were studied by thermogravimetric analysis (TGA), limiting oxygen index (LOI), UL-94 test, and cone calorimeter test (CCT). The in situ temperature monitoring system and interrupted combustion offered direct evidence to link flame retardancy and composite structure. Results demonstrated that carbon nanomaterials enhanced the thermal stability and fire safety of EM. The geometry of carbon nanomaterials played a key role in synergistic flame retardancy of EM, with the flame-retardant order of carbon nanotube > nanoscale carbon black > graphene. Based on an online temperature monitoring system and interrupted combustion test, one-dimensional carbon nanotube was more inclined to form the network structure synergistically with magnesium hydroxide in ethylene-vinyl acetate, which facilitated the generation of more continuous char structure during combustion. In parallel, the mechanical property was characterized by a tensile test and dynamic mechanical analysis (DMA). The incorporation of carbon nanomaterials presented a limited effect on the mechanical properties of the EM system.

Catalytic performance of non-platinum-based hybrid carbon hetero-structure for oxygen reduction and hydrogen oxidation reactions in proton exchange membrane fuel cell

The present work describes the potential of a hybrid carbon hetero-structure having the unique properties of one-dimensional carbon nanotubes and two-dimensional graphene as a catalyst support material for platinum-free electrocatalysts in polymer electrolyte membrane fuel cell (PEMFC) for hydrogen oxidation reaction (HOR) or oxygen reduction reaction (ORR). Partially exfoliated carbon nanotubes (PCNT), which have the synergistic effect of good electrical conductivity and high surface area, have been used as the support material for Pd3Co alloy catalysts. This provides more active sites for the dispersion of catalyst particles along with quick electron transport through the carbon structure. This unique characteristic increases the catalytic activity of the electrocatalysts. The electrochemical half-cell studies confirm that, ORR on Pd3Co/PCNT proceeds via a four-electron process. The single cell measurements were carried out by preparing a membrane electrode assembly (MEA) using Pd3Co/PCNT at the anode, cathode separately as well as simultaneously at both the anode and cathode. A maximum power density of 327 mW cm−2, 240 mW cm−2 and 96 mW cm−2 is attained from the use of Pd3Co/PCNT nanocomposite at anode, cathode and at both electrodes simultaneously in a PEMFC at 60 °C, respectively.

Amorphous Molybdenum Sulfide on Three-Dimensional Hierarchical Hollow Microspheres Comprising Bamboo-like N-Doped Carbon Nanotubes as a Highly Active Hydrogen Evolution Reaction Catalyst

Novel amorphous-MoSx-coated three-dimensional (3D) hierarchical hollow microspheres comprising one-dimensional bamboo-like N-doped carbon nanotubes (BNCNT/MoSx-HM) are developed as a highly active electrocatalyst for the hydrogen evolution reaction (HER). The 3D hierarchical microspheres are easily prepared via the growth of bamboo-like N-doped CNTs (BNCNTs) on both the inner and outer surfaces of Co3O4–MgO/carbon hollow microspheres, which are prepared by spray pyrolysis, followed by uniform MoSx coating of the surface. Metallic Co nanocrystals play a key role in the growth of BNCNTs, acting as catalysts for their nucleation. Owing to the electrostatic attraction between the N-doped sites in BNCNTs and the thiomolybdate precursor anions, few-layered amorphous MoSx catalysts are well deposited on BNCNT surfaces, even at low temperature. The 3D hierarchical hollow structure facilitates electrolyte access, and the synergistic effect between the MoSx catalyst material with ample active sites and the conducti...

Co metal nanoparticles deposition inside or outside multi-walled carbon nanotubes via facile support pretreatment

Decoration of one-dimensional multi-walled carbon nanotubes (MWCNTs) with zero-dimensional Co nanoparticles leads to hybrid structures with chemical and electromagnetic features that are not available to the individual components. This work addresses the influence of the nature and structure of MWCNTs on the localization of Co nanoparticles. Depending on synthesis conditions, Co can be deposited on the external or in inner surfaces of the nanotubes. Co/MWCNTs hybrids have been characterized by in situ X-ray powder diffraction, high-resolution transmission electron microscopy and 59Co internal field nuclear magnetic resonance. It has been shown that the average diameter (7.2, 9.4 and 18.6 nm), number of walls (5–7, 12–15, 15–20), and functional composition of the MWCNTs have a remarkable effect on the size of Co nanoparticles and their distribution in the structure of MWCNTs. The observed phenomenon has been rationalized in terms of nanotubes surface properties. Parent MWCNTs being hydrophobic and having limited porosity do not stabilize Co nanoparticles and, therefore, they are localized on the outside surface with relatively large average size and broad size distribution. On the other hand, the oxidation of the MWCNTs resulted in the penetration of Co nanoparticles inside of the nanotubes, presumably because of pore opening as well as increased hydrophilicity of the nanotubes.

Three-dimensionally integrated carbon tubes/MoS2 with reduced graphene oxide foam as a binder-free anode for lithium ion battery

Three-dimensional foam with integrated core-shell carbon nanotubes-MoS2 with reduced graphene oxide (MoS2/CNT/rGO) has been fabricated by a hydrothermal reaction together with freeze drying. Thin MoS2 nanosheets are coated on the carbon nanotubes (CNT) and distributed on the surface of reduced graphene oxide (rGO) nanosheets. One-dimensional CNT and two-dimensional rGO conductive network not only effectively improves the electron transport and mechanical property, but also prevents the aggregation of MoS2 nanosheets. MoS2 with large interlayer spacing provides more active sites and channels for insertion of lithium ions, while CNT and rGO network acts as a conductive skeleton. The 3D porous and interconnected foam can directly as electrode without any binders and conductive agents. After optimizing the ratio of CNT to rGO, the MoS2/CNT/rGO foam as a freestanding electrode for lithium ion batteries exhibits a high specific capacity of 745 mAh g−1 at a current density of 0.1 A g−1 after 170 cycles and 420 mAh g−1 at 0.5 A g−1 after 200 cycles. This method is easily extended to prepare the other electrode materials, especially the freestanding and flexible electrode.

Rational design of coaxial MWCNTs@Si/SiOx@C nanocomposites as extending-life anode materials for lithium-ion batteries

One-dimensional (1D) uniform multi-walled carbon nanotubes (MWCNTs)@Si/SiOx@C nanocomposites were prepared by the magnesiothermic reduction of MWCNT@SiO2 nanocables and subsequent carbon coating process. Through simply altering the acid-treatment conditions, SiOx were reserved on the surface of MWCNTs to seal and fix the Si nanoparticles, along with the carbon coating layer, the reducted Si nanoparticles (Si NPs) were entirely encapsulated in the 1D coaxial nanocomposites. Due to the multiple volume expansion limit effects of inner Si nanoparticles, the cycling stability has been greatly improved. When worked as anodes for lithium-ion batteries, the MWCNTs@Si/SiOx@C electrode exhibits better electrochemical properties than bulk Si and MWCNTs, as well as an extending cycle life of 500 cycles in comparsion to our previous MWCNTs@Si nanocomposites. It is believed that the MWCNTs can provide structural support and enhance the electronic mobility, while the SiOx and carbon buffer component would anchor the Si NPs firmly and accommodate the volume expansion of Si.

The effect of crystalline defects and geometry factors of multi-walled carbon nanotubes on electrical conductivity of silver-nitrile butadiene rubber composites

It is important to construct effective electrical network to achieve high electrical conductivity of soft polymer matrix composites. We previously employed one-dimensional multi-walled carbon nanotubes (MWNTs) decorated with silver nanoparticles (nAg-MWNTs) and micron-sized silver flakes in a nitrile butadiene rubber matrix to develop highly conductive flexible adhesive (CFA) films. However, the effect of intrinsic physical properties of MWNTs on the conductivity of CFA was not explored in detail. Here we investigated the influence of crystalline defects and geometry factors of MWNTs on the electrical conductivity of CFA films. The nAg-MWNTs were synthesized using five different MWNTs. The electrical conductivity of the CFA films decreased significantly with an increase in Raman D- to G-mode ratio demonstrating the crystallinity effect. There was the tube diameter dependence. The conductivity increased as the diameter of MWNTs decreased. The dispersion was also a determining factor. The strongly entangled structure of MWNTs originated from the initial synthesis process caused aggregation of tubes in the polymer matrix resulting in a low conductivity of CFA film. However, the tube length dependence was not obvious in the investigated range (5–20 μm). It was possible that all the tubes were long enough not to differentiate the length effect on percolation. These findings may provide a guideline for selection of MWNTs to achieve high conductivity of flexible composites.

Construction of 3D Carbon Nanostructure: Carbon Nanosheets Decorated Carbon Nanofiber As a Three-Dimensional Carbon Hybrid for High Performance Lithium-Sulfur Battery

Among the emerging energy storage methods, lithium-sulfur battery (LiS) has drawn plenty of attentions due to its high theoretical energy density (2600 Wh kg-1),1 economical cost and environmental benignity. Nevertheless, the insulating nature of sulfur and notorious polysulfides shuttling result in a low sulfur utilization and short cycling life.2 To address these problems, carbon material has been confirmed as an ideal sulfur host to promote LiS’s performance because of their low cost, high conductivity and controllable structure such as carbon spheres, carbon nanotube/fibers and carbon nanosheets. For example, one-dimensional carbon nanotube can increase the sulfur utilization by providing better electrical conductivity. However, its “open-to-electrolyte” structures cannot effectively prevent shuttling effect.3 As for zero-dimension carbon materials, core/yolk shell carbon spheres in particular, are less capable of establishing conductive networks, which in turns, compromise the sulfur utilization and rate capability.4 Thus, it is of great necessity to develop three-dimensional (3D) carbon materials with multiple functions in order to achieve high-performance lithium-sulfur batteries. Along this line, we prepared a three-dimensional carbon nanosheets modified carbon nanofiber (3DCNF) as high porosity sulfur host. After decorated with vertically aligned carbon nanosheets, the surface area of pristine carbon nanofiber was dramatically increased from 30 m2/g to 500 m2/g due to the expanded dimension. Although both 1D nanofiber and 2D nanosheets cannot effectively prevent polysulfides shuttling by themselves, the delicate combination of them endows new functions, where 3D carbon hybrid is capable of accommodating sulfur expansion and deterring polysulfides dissolution by the hierarchical porous structure and interconnected carbon nanosheets. At the same time, the 3D porous carbon nanofiber can also form conductive network that allows rapid electron transfer. With the structural advantages, the 3DCNF and sulfur composite delivered a capacity as high as 1266, 977 mAh/g at 0.1 and 0.5 C, respectively. After 500 cycles at 0.5 C, it still retains a capacity of 607 mAh/g (0.07% capacity fading per cycle), exhibiting excellent cycling capability. Reference M. K. Song, E. J. Cairns and Y. Zhang, Nanoscale, 2013, 5, 2186-2204.Y. Yang, G. Zheng and Y. Cui, Chem. Soc. Rev., 2013, 42, 3018-3032.X. Liang, Z. Wen, Y. Liu, H. Zhang, J. Jin, M. Wu and X. Wu, J. Power Sources, 2012, 206, 409-413.Y. J. Hong, J.-K. Lee and Y. Chan Kang, J. Mater. Chem. A, 2017, 5, 988-995. Figure 1

Probing Phonon Dynamics in Individual Single-Walled Carbon Nanotubes.

Interactions between elementary excitations, such as carriers, phonons, and plasmons, are critical for understanding the optical and electronic properties of materials. The significance of these interactions is more prominent in low-dimensional materials and can dominate their physical properties due to the enhanced interactions between these excitations. One-dimensional single-walled carbon nanotubes provide an ideal system for studying such interactions due to their perfect physical structures and rich electronic properties. Here we investigated G-mode phonon dynamics in individual suspended chirality-resolved single-walled carbon nanotubes by time-resolved anti-Stokes Raman spectroscopy. The improved technique allowed us to probe the intrinsic phonon information on a single-tube level and exclude the influences of tube-tube and tube-substrate interactions. We found that the G-mode phonon lifetime ranges from 0.75-2.25 ps and critically depends on whether the tube is metallic or semiconducting. In comparison with the phonon lifetimes in graphene and graphite, we revealed structure-dependent carrier-phonon and phonon-phonon interactions in nanotubes. Our results provide new information for optimizing the design of nanotube electronic/optoelectronic devices by better understanding and utilizing their phonon decay channels.

Self-sensing and mechanical performance of CNT/GNP/UHMWPE biocompatible nanocomposites

Ultra-high molecular weight polyethylene (UHMWPE)-based conductive nanocomposites with reduced percolation and tunable piezoresistive behavior were prepared via solution mixing followed by compression molding using carbon nanotubes (CNT) and graphene nanoplatelets (GNP). The effect of varying wt% of GNP with fixed CNT content (0.1 wt%) on the mechanical, electrical, thermal and piezoresistive properties of UHMWPE nanocomposites was evaluated. The combination of CNT and GNP enhanced the dispersion in UHMWPE matrix and lowered the probability of CNT aggregation as GNP acted as a spacer to separate the entanglement of CNT with each other. This has allowed the formation of an effective conductive path between GNP and CNT in UHMWPE matrix. The thermal conductivity, degree of crystallinity and degradation temperature of the nanocomposites increased with increasing GNP content. The elastic modulus and yield strength of the nanocomposites were improved by 37% and 33%, respectively, for 0.1/0.3 wt% of CNT/GNP compared to neat UHMWPE. The electrical conductivity was measured using four-probe method, and the lowest electrical percolation threshold was achieved at 0.1/0.1 wt% of CNT/GNP forming a nearly two-dimensional conductive network (critical value, t = 1.20). Such improvements in mechanical and electrical properties are attributed to the synergistic effect of the two-dimensional GNP and one-dimensional CNT which limits aggregation of CNTs enabling a more efficient conductive network at low wt% of fillers. These hybrid nanocomposites exhibited strong piezoresistive response with sensitivity factor of 6.2, 15.93 and 557.44 in the linear elastic, inelastic I and inelastic II regimes, respectively, for 0.1/0.5 wt% of CNT/GNP. This study demonstrates the fabrication method and the self-sensing performance of CNT/GNP/UHMWPE nanocomposites with improved properties useful for orthopedic implants.

Shape matters: Cr(VI) removal using iron nanoparticle impregnated 1-D vs 2-D carbon nanohybrids prepared by ultrasonic spray pyrolysis

Iron nanoparticles (Fe NPs) are used for treating water contaminated with metals or organic compounds. One-dimensional (1-D) carbon nanotubes (CNTs) and two-dimensional (2-D) graphenes act as useful nanocarbon (NC) supports for Fe NPs by resisting aggregation and enhancing adsorption and redox activity. However, no study showed how shape difference between tubular CNT and planar graphene structures dictates the physicochemical properties and pollutant removal potential of their iron-based nanohybrids. In this work, ultrasonic spray pyrolysis was used to continuously prepare Fe-CNT and Fe-rGO nanohybrids. Both NC shape and Fe/NC ratio influenced Fe NP size, loading, and oxidation states. High Fe content (precursor Fe/NC mass ratio = 2) resulted Fe NPs with diameters of 30.97 ± 7.00 and 24.11 ± 4.42 nm for Fe-CNT and Fe-rGO, respectively; however, low Fe content (Fe/NC = 0.2) provided more uniformly dispersed Fe NPs of 15.65 ± 3.06 and 9.67 ± 1.49 nm, respectively, while unsupported Fe NPs were 285.71 ± 132.42 nm. The USP-derived nanohybrids, for the first time, were used for removal of pollutant, i.e., chromium (Cr(VI)) from aqueous media. Both CNT and rGO provided synergistic effects to significantly enhance Fe NPs’ ability to remove Cr(VI); the effect was more pronounced in Fe-rGO than Fe-CNT and also for low Fe content in both cases. Fe-rGO with low Fe/NC ratio and smallest Fe NPs provided the highest Cr(VI) removal capacity (25 mg/g), which was a multifold improvement over bare Fe NPs and other synthesized nanohybrids (range 7–14 mg/g). Overall, 2-D rGO improved contaminant removal capacity of the nanohybrids more than 1-D CNT indicating towards shape effect of NC supports.

A comparison of the twisted and untwisted structures for one-dimensional carbon nanotube assemblies

The way how carbon nanotubes (CNTs) are assembled together determines the utilization efficiency of mechanical property in their macroscopic assembly materials. For one-dimensional (1D) assemblies, CNTs are often assembled under drawing and twisting into a fiber structure with a twist angle. In this study, an untwisted 1D assembly, CNT strip, is introduced, inside which the CNTs are not only aligned but also overall parallel to strip axis. Due to the shielding effect of the twisted fiber surface, the interior of CNT fiber is loosely packed, and the fiber is more stretchable and hard to become stiff. On the contrary, CNT strip with high straightness or undirectionality can utilize the CNT's mechanical property much more efficiently, as reflected by its higher strength and modulus. These insights can guide different applications of CNT fibers and strips in textile.

Memristic Characteristics from Bistable to Tristable Memory with Controllable Charge Trap Carbon Nanotubes.

The incorporation of the one-dimensional carbon nanomaterial carbon nanotubes (CNTs) in poly(methyl methacrylate) (PMMA) was found to successfully develop a resistive switching. It implements memristic characteristics which shift from bistable to tristable memory. The localized current pathways in the organic nanocomposite layers for each intermediate resistive state (IRS) are attributed to the trapping mechanism consistent with the fluorescent measurements. Multi-bit organic memories have attracted considerable interest, which provide an effective way to increase the memory density per unit cell area. This study will be useful for the development and tuning of multi-bit storable organic nanocomposite memory device systems.

Enriching the hydrogen storage capacity of carbon nanotube doped with polylithiated molecules

In a quest to find optimum materials for efficient storage of clean energy, we have performed first principles calculations to study the structural and energy storage properties of one-dimensional carbon nanotubes (CNTs) functionalized with polylithiated molecules (PLMs). Van der Waals corrected calculations disclosed that various PLMs like CLi, CLi2, CLi3, OLi, OLi2, OLi3, bind strongly to CNTs even at high doping concentrations ensuring a uniform distribution of dopants without forming clusters. Bader charge analysis reveals that each Li in all the PLMs attains a partial positive charge and transform into Li+ cations. This situation allows multiple H2 molecules adsorbed with each Li+ through the polarization of incident H2 molecules via electrostatic and van der Waals type of interaction. With a maximum doping concentration, that is 3CLi2/3CLi3 and 3OLi2/3OLi3 a maximum of 36 H2 molecules could be adsorbed that corresponds to a reasonably high H2 storage capacity with the adsorption energies in the range of −0.33 to −0.15 eV/H2. This suits the ambient condition applications.