As a type of thin film,two dimensional(2D) reticulate architectures built of freestanding single-walled carbon nanotube(SWCNT) bundles are suitable for scalable integration into devices and nanocomposites for many applications.The superior properties of these films,such as optical transparency,unique electrical properties and mechanical flexibility,result not only from the outstanding properties of individual SWCNTs but also from the collective behavior of the individual tubes,with additional properties arising from the tube-tube interactions.In this review,the synthesis,structure and fundamental properties,such as conductivity,transparency,optical nonlinearity and mechanical performance,of "freestanding SWCNT bundle network" thin films and nanocomposites,as well as their application as supercapacitors are highlighted.Some long-standing problems and topics warranting further investigation in the near future are addressed.
Bridged strips consisting of carbon nanotubes and poly（vinylidene fluoride） are developed, which exhibit notable deflection in response to very low driven voltages（ 1 V）, because of both the excellent conductivity of the unique carbon nanotube film and the powerful thermal expansion capability of the polymer. The actuators demonstrate periodic vibrations motivated by the alternating signals. The amplitude of displacement is dependent not only on the driven voltage but also on the applied frequency. The mechanism of actuation is confirmed to be the thermal power induced by the electrical heating. By accelerating the dissipation of heat, the vibration response at higher frequencies can be significantly enhanced.The useful locomotion shows great promise in potential applications such as miniature smart devices and micro power generators.
We provide an effective method to investigate the field gradient effect in nanoconfined plasmon-matter interaction.Aligned ultralong SWNTs without defects were grown on marked substrates, followed by assembling gold nanoparticle clusters around individual nanotubes. The Raman scattering behavior of a nanotube placed in an atomic scale nanogap between adjacent nanoparticles was studied. In addition to the expected plasmon-induced Raman enhancement up to 103,the defect-free D-mode of an individual SWNT induced by gradient field is found for the first time. When the light is confined at atomic scale, gradient field Raman scattering becomes significant and dipole-forbidden phonon modes can be activated by quadrupole Raman tensor variation, indicating breakdown of the Raman selection rules.
Lithium–sulfur（Li–S） batteries have received more and more attention because of higher specific capacity and energy density of sulfur than current lithium–ion batteries. However, the low electrical conductivity of sulfur and its discharge product, and also the high dissolution of polysulfides restrict the Li–S battery practical applications. To improve their performances, in this work, we fabricate a novel free-standing, curled and partially reduced graphene oxide（CPrGO for short） network and combine it with sulfur to form a CPrGO–S composite as a cathode for Li–S battery. With sulfur content of 60 wt%, the free-standing CPrGO–S composite network delievers an initial capacity of 988.9 m Ah·g^（-1）. After 200 cycles,it shows a stable capacity of 841.4 m Ah·g^（-1） at 0.2 C, retaining about 85% of the initial value. The high electrochemical performance demonstrates that the CPrGO–S network has great potential applications in energy storage system. Such improved properties can be ascribed to the unique free-standing and continous CPrGO–S network which has high specific surface area and good electrical conductivity. In addition, oxygen-containing groups on the partially reduced graphene oxide are beneficial to preventing the polysulfides from dissolving into electrolyte and can mitigate the ＂shuttle effect＂.
Solar cells that combine single-crystalline silicon （Si） with graphene （G） have been widely researched in order to develop next-generation photovoltaic devices. However, the power conversion efficiency （PCE） of G/Si solar cell without chemical doping is commonly low due to the relatively high resistance of graphene. In this work, through combining graphene with carbon nanotube （CNT） networks, we fabricated three kinds of hybrid nanocarbon film/Si heterojunction solar cells in order to increase the PCE of the graphene based Si solar cell. We investigated the characteristics of different nanocarbon film/Si solar cells and found that their performance depends on the heterojunctions. Specifically, a doping-free G-CNT/Si solar cell demonstrated a high PCE of 7.9%, which is nearly equal to the combined value of two individuals （G/Si and CNT/Si）. This high efficiency is attributed to the synergistic effect of graphene and CNTs, and can be further increased to 9.1% after applying a PMMA antireflection coating. This study provides a potential way to further improve the Si based heterojunction solar cells.
The predicted extraordinary properties of carbon nanotubes(CNTs)from theoretical calculations have great potential for many applications.However,reliable experimental determination of intrinsic properties at the single-tube level is currently a matter of concern,and many challenges remain because of the unhandled and nanoscale size of individual nanotubes.Here,we demonstrated a prototype to detect the intrinsic thermal conductivity of the single-wall carbon nanotube(SWCNT)and verify the significant non-resonant optical absorption behavior on tiny nanotubes by integrating the nanotube and ice into a new core-shell design.In particular,a reversible optical visualization method based on the individual suspended ultra-long SWCNT was first developed by wrapping a nanotube with ice in the cryogenic air environment.The light-induced thermal effect on the hybrid core-shell structure was used tomelt the ice shell,which subsequently acted as a temperature sensor to verify the intrinsic thermal conductivity of the core-like nanotube.More interestingly,we successfully determined for the first time the thermal response phenomenon of the tiny absorption cross section in SWCNT in the vertical-polarization configuration and the significant non-resonant absorption behavior in the parallel-polarization configuration.These investigations will provide a better understanding for the unique optical behaviors of CNT and enable the detection of intrinsic properties of various one-dimensional nanostructures such as nanotubes,nanowires,and nanoribbons.
In this work, we have presented a freestanding and flexible CNT-based film with sheet resistance of 60 ？/ and transmittance of 82% treated by nitric acid and chloroauric acid in sequence. Based on modified CNT film as a transparent electrode, we have demonstrated an ultrathin, flexible organic solar cell（OSC） fabricated on 2.5-μm PET substrate. The efficiency of OSC, combined with a composite film of poly（3-hexylthiophene）（P3HT） and phenyl-C61 butyric acid methyl ester（PCBM） as an active layer and with a thin layer of methanol soluble biuret inserted between the photoactive layer and the cathode, can be up to 2.74% which is approximate to that of the reference solar cell fabricated with ITO-coated glass（2.93%）. Incorporating the as-fabricated ITO-free OSC with pre-stretched elastomer, 50% compressive deformation can apply to the solar cells. The results show that the as-prepared CNT-based hybrid film with outstanding electrical and optical properties could serve as a promising transparent electrode for low cost, flexible and stretchable OSCs, which will broaden the applications of OSC and generate more solar power than it now does.
Continuous CNT fibers have been directly fabricated in a speed of 50 m/h-400 m/h,based on an improved chemical vapor deposition method.As-prepared fibers are further post-treated by acid.According to the SEM images and Raman spectra,the acid treatment results in the compaction and surface modification of the CNTs in fibers,which are beneficial for the electron and load transfer.Compared to the HNO3 treatment,HClSO_3 or H_2SO_4 treatment is more effective for the improvement of the fibers＇ properties.After HCISO_3 treatment for 2 h,the fibers＇ strength and electrical conductivity reach up to-2 GPa and-4.3 MS/m,which are promoted by-200%and almost one order of magnitude than those without acid treatment,respectively.The load-bearing status of the CNT fibers are analyzed based on the downshifts of the G＇ band and the strain transfer factor of the fibers under tension.The results reveal that acid treatment could greatly enhance the load transfer and inter-bundle strength.With the HCISO3 treatment,the strain transfer factor is enhanced from-3.9%to-53.6%.
A highly flexible and continuous fibrous thermoelectric(TE)module with high-performance has been fabricated based on an ultra-long single-walled carbon nanotube fiber,which effectively avoids the drawbacks of traditional inorganic TE based modules.The maximum output power density of a 1-cm long fibrous TE module with 8 p–n pairs can reach to 3436μW·cm^(-2),the power per unit weight to 2034μW·g^(-1),at a steady-state temperature difference of 50 K.The continuous fibrous TE module is used to detect temperature change of a single point,which exhibits a good responsiveness and excellent stability.Because of its adjustability in length,the flexible fibrous TE module can satisfy the transformation of the temperature difference between two distant heat sources into electrical energy.Based on the signal of the as-fabricated TE module,a multi-region recognizer has been designed and demonstrated.The highly flexible and continuous fibrous TE module with excellent performance shows a great potential in diversified applications of TE generation,temperature detection,and position identification.
Transparent conductive electrodes have pervaded modern technologies since they represent an essential component of various optoelectronic devices. Currently, indium tin oxide (ITO) is the most widely used transparent conductive material. The brittle nature and the limited resource of indium,however,present many challenges for ITO applications in flexibleelectronics.
