A general surface-treatment-free approach to fabrication of alignment layers using a super-aligned carbon nanotube film template

We develop a general approach to the fabrication of films with unidirectional grooves, such as silicon nitride, silicon dioxide and aluminium oxide, in which the surface is not required to be treated. Super-aligned carbon nanotube （SACNT） film may be used as a template and as sacrificial layer, which is subsequently removed by heating in an atmosphere of air. The unidirectional morphology of the SACNT film turns into a desired film, which is found to possess the ability to align liquid crystal molecules. This approach also features high efficiency, low cost and easy scaling-up for mass production.

Multiplexed Five-Color Molecular Imaging of Cancer Cells and Tumor Tissues with Carbon Nanotube Raman Tags in the Near-Infrared

Single-walled carbon nanotubes(SWNTs)with five different C13/C12 isotope compositions and well-separated Raman peaks have been synthesized and conjugated to five targeting ligands in order to impart molecular specificity.Multiplexed Raman imaging of live cells has been carried out by highly specific staining of cells with a five-color mixture of SWNTs.Ex vivo multiplexed Raman imaging of tumor samples uncovers a surprising up-regulation of epidermal growth factor receptor(EGFR)on LS174T colon cancer cells from cell culture to in vivo tumor growth.This is the first time five-color multiplexed molecular imaging has been performed in the near-infrared(NIR)region under a single laser excitation.Near zero interfering background of imaging is achieved due to the sharp Raman peaks unique to nanotubes over the low,smooth autofluorescence background of biological species.

Applications of carbon nanotubes in high performance lithium ion batteries

The development of lit;triton ion batteries （LIBs） relies on the improvement in the performance of electrode materials with higher capacity, higher rate capability, and longer cycle lift;. In this review article, the recent advances in carbon nanotube （CNT） anodes, CNT-based composite electrodes, and CNT current collectors for high performance LIBs are concerned. CNT has received considerable attentions as a candidate material for the LIB applications. In addition to a possible choice for anode, CNT has been recognized as a solution in improving the performance of the state-of-the-art electrode materials. The CNT-based composite electrodes can be fabricated by mechanical or chem- ical approaches. Owing to the large aspect ratio and the high electrical conductivity, CNTs at very low loading can lead to an efficient conductive network. The excellent mechanical strength suggests the great potential in forming a structure scaffold to accommodate nano-sized electrode materials. Accordingly, the incorporation of CNTs will enhance the conductivity of the composite electrodes, mitigatc the agglomeration problem, decrease the dependence on inactive binders, and improve the clcctrochenfical properties of both anode and cathode materials remarkably. Freestanding CNT network can be used as lightweight current collectors to increase the overall energy density of LIBs. Finally, research perspectives for exploiting CNTs in high-performance LIBs are discussed.

A process study of electron beam nano-lithography and deep etching with an ICP system

A systemic process study on an electron beam nanolithography system operating at 100kV was pre-sent.The exposure conditions were optimized for resist ZEP520A.Grating structures with line/space of 50nm/50nm were obtained in a reasonably thick resist which is beneficial to the subsequent pattern transfer technique.The ICP etching process conditions was optimized.The role of etching parameters such as source power,gas pressure,and gas flow rate on the etching result was also discussed.A grating structure with line widths as small as 100nm,duty cycles of 0.5,depth of 900nm,and the side-wall scalloping as small as 5nm on a silicon substrate was obtained.The silicon deep etching technique for structure sizes smaller than 100nm is very important for the fabrication of nano-optical devices working in the visible regime.

High temperature performance of coaxial h-BN/CNT wires above 1,000 ℃:Thermionic electron emission and thermally activated conductivity

The development of wires and cables that can tolerate extremely high temperatures will be very important for probing extreme environments, such as in solar exploration, fire disasters, high-temperature materials processing, aeronautics and astronautics. In this paper, a lightweight high-temperature coaxial h-boron nitride (BN)/carbon nanotube (CNT) wire is synthesized by the chemical vapor deposition (CVD) epitaxial growth of h-BN on CNT yarn. The epitaxially grown h-BN acts as both an insulating material and a jacket that protects against oxidation. It has been shown that the thermionic electron emission (1,200 K) and thermally activated conductivity (1,000 K) are two principal mechanisms for insulation failure of h-BN at high temperatures. The thermionic emission of h-BN can provide the work function of h-BN, which ranges from 4.22 to 4.61 eV in the temperature range of 1,306-1,787 K. The change in the resistivity of h-BN with temperature follows the ohmic conduction model of an insulator, and it can provide the “electron activation energy”(the energy from the Fermi level to the conduction band of h-BN), which ranges from 2.79 to 3.08 eV, corresponding to a band gap for h-BN ranging from 5.6 to 6.2 eV. However, since the leakage current is very small, both phenomena have no obvious influence on the signal transmission at the working temperature. This lightweight coaxial h-BN/CNT wire can tolerate 1,200 ℃ in air and can transmit electrical signals as normal. It is hoped that this lightweight high-temperature wire will open up new possibilities for a wide range of applications in extreme high-temperature conditions.

二硫化钼/石墨烯异质结在电子束辐照轰击下发光能量的鲁棒特性（英文）

在许多恶劣的工作环境中,器件难免会曝露在电子束辐照下.对于单原子层厚度的二维材料而言,电子束辐照经常会造成其本征性能的衰减.如何避开这一影响对于多功能化的二维异质结器件来讲至关重要.然而,电子束辐照对于二维异质结的影响至今仍缺乏充分深入的研究.本工作发现利用异质结的堆垛可以阻碍单层二硫化钼(MoS_2)由于电子束辐照带来的性能衰退.通过在MoS_2与基底之间插入单层石墨烯,在同样剂量的电子束辐照轰击下,异质结区域的光致发光强度始终大于纯单层MoS_2;而且与纯单层区域明显的发光能量变化相比,MoS_2/石墨烯异质结区域的发光能量具有更佳的稳定性.这一现象归因于石墨烯的阻隔效应:由于单层石墨烯的存在抑制了基板对MoS_2的影响.此外,我们也系统地揭示了电子束辐照对MoS_2/石墨烯异质结拉曼光谱及电学传输特性的影响.本工作不仅有助于加深人们对二维异质结辐照效应的认知,同时也为新型抗辐射器件的设计开辟了新的途径.

Crossover from 2D metal to 3D Dirac semimetal in metallic PtTe2 films with local Rashba effect

PtTe2 and PtSe2 with trigonal structure have attracted extensive research interests since the discovery of type-II Dirac fermions in the bulk crystals. The evolution of the electronic structure from bulk 3D topological semimetal to 2D atomic thin films is an important scientific question. While a transition from 3D type-II Dirac semimetal in the bulk to 2D semiconductor in monolayer(ML) film has been reported for PtSe2, so far the evolution of electronic structure of atomically thin PtTe2 films still remains unexplored.Here we report a systematic angle-resolved photoemission spectroscopy(ARPES) study of the electronic structure of high quality PtTe2 films grown by molecular beam epitaxy with thickness from 2 ML to 6 ML.ARPES measurements show that PtTe2 films still remain metallic even down to 2 ML thickness, which is in sharp contrast to the semiconducting property of few layer PtSe2 films. Moreover, a transition from 2D metal to 3D type-II Dirac semimetal occurs at film thickness of 4–6 ML. In addition, Spin-ARPES measurements reveal helical spin textures induced by local Rashba effect in the bulk PtTe2 crystal, suggesting that similar hidden spin is also expected in few monolayer PtTe2 films. Our work reveals the transition from2D metal to 3D topological semimetal and provides new opportunities for investigating metallic 2D films with local Rashba effect.

In Situ TEM Observation of the Gasification and Growth of Carbon Nanotubes Using Iron Catalysts

We report the in situ transmission electron microscope (TEM) observation of the catalytic gasification and growth of carbon nanotubes (CNTs). It was found that iron catalysts can consume the CNTs when pumping out the precursor gas, acetylene, at the growth temperature, and reinitiate the growth when acetylene is re-introduced. The switching between gasification and growth of CNTs can be repeated many times with the same catalyst. To understand the phenomenon, thermogravimetric analysis (TGA) coupled with mass spectroscopy was used to study the mechanism involved. It was shown that the residual water molecules in the growth chamber of the TEM react with and remove carbon atoms of CNTs as carbon monoxide vapor under the action of the catalyst, when the precursor gas is pumped out. This result contributes to a better understanding of the water-assisted and oxygen-assisted synthesis of CNT arrays, and provides useful clues on how to extend the lifetime and improve the activity of the catalysts.

Free-standing hybrid films comprising of ultra-dispersed titania nanocrystals and hierarchical conductive network for excellent high rate performance of lithium storage

The construction of advanced electrode materials is key to the field of energy storage.Herein,a free-standing anatase titania(TiO_(2))nanocrystal/carbon nanotube(CNT)film is reported using a simple and scalable sol-gel method,followed by calcination.This unique free-standing film comprises ultra-small TiO_(2) nanocrystals(~5.9 nm)and super-aligned CNTs,with ultra-dispersed TiO_(2) nanocrystals on the surfaces of the CNTs.On the one hand,these TiO_(2) nanocrystals can significantly decrease the diffusion distance of the charges and on the other hand,the cross-linked CNTs can act as a three-dimensional(3D)conductive network,allowing the fast transport of electrons.In addition,the film is free-standing,without requiring electrode fabrication and additional conductive agents and binders.Owing to these above synergistic effects,the film is directly used as an anode in Li-ion batteries,and delivers a high discharge capacity of~105 mAh·g^(−1) at high rate of 60 C(1 C=170 mA·g^(−1))and excellent cycling performance over 2,500 cycles at 30 C.These results indicate that the free-standing anatase TiO_(2) nanocrystal/CNT film affords a superior performance among the various TiO_(2) materials and can be a promising anode material for fast-charging Li-ion batteries.Moreover,the TiO_(2)/CNT film exhibits an areal capacity of up to 2.4 mAh·cm^(−2),confirming the possibility of its practical use.

Direct laser patterning of two-dimensional lateral transition metal disulfide-oxide-disulfide heterostructures for ultrasensitive sensors

Two-dimensional(2D)heterostructures based on the combination of transition metal dichalcogenides(TMDs)and transition metal oxides(TMOs)have aroused growing attention due to their integrated merits of both components and multiple functionalities.However,nondestructive approaches of constructing TMD-TMO heterostructures are still very limited.Here,we develop a novel type of lateral TMD-TMO heterostructure(NbS2-Nb2O5-NbS2)using a simple lithography-free,direct laser-patterning technique.The perfect contact of an ultrathin TMO channel(Nb2O5)with two metallic TMDs(NbS2)electrodes guarantee strong electrical signals in a two-terminal sensor.Distinct from sensing mechanisms in separate TMOs or TMDs,this sensor works based on the modulation of surface conduction of the ultrathin TMO(Nb2O5)channel through an adsorbed layer of water molecules.The sensor thus exhibits high selectivity and ultrahigh sensitivity for room-temperature detection of NH3(ΔR/R=80%at 50 ppm),superior to the reported NH3 sensors based on 2D materials,and a positive temperature coefficient of resistance as high as 15%–20%/℃.Bending-invariant performance and high reliability are also demonstrated in flexible versions of sensors.Our work provides a new strategy of lithography-free processing of novel TMD-TMO heterostructures towards high-performance sensors,showing great potential in the applications of future portable and wearable electronics.

SEM imaging of insulating specimen through a transparent conducting veil of carbon nanotube

Observing the morphology of insulating specimen in scanning electron microscope(SEM)is of great significance for the nanoscale semiconductor devices and biological tissues.However,the charging effect will cause image distortion and abnormal contrast when observing insulating specimen in SEM.A typical solution to this problem is using metal coating or water-removable conductive coating.Unfortunately,in both cases the surface of the specimen is covered by a thin layer of conductive material which hides the real surface morphology and is very difficult to be completely removed after imaging.Here we show a convenient,residue-free,and versatile method to observe real surface morphology of insulating specimen without charging effect in SEM with the help of a nanometer-thick film of super-aligned carbon nanotube(SACNT).This thin layer of SACNT film,like metal,can conduct the surface charge on insulating specimen through the sample stage to the ground,thus eliminating the charging effect.SACNT film can also be used as the conductive tape to carry and immobilize insulating powder or particles during SEM imaging.Different from the metal coating,SACNT film is transparent,so that the real microstructure of the insulating specimen surface can be observed.In addition,SACNT film can be easily attached to and peeled off from the surface of specimen without any residue.This convenient,residue-free,and versatile method can open up new possibilities in nondestructive SEM imaging of a wide variety of insulating materials,semiconductor devices,and biological tissues.

Bidirectional micro-actuators based on eccentric coaxial composite oxide nanofiber

It is of great importance to develop new micro-actuators with high performance by optimizing the structures and materials.Here we develop a VO2/AI2O3/CNT eccentric coaxial nanofiber,which can be potentially applied as a micro-actuator.The specific eccentric coaxial structure was efficiently fabricated by conventional thin film deposition methodology with individual CNT templet.Activated by thermal and photothermal stimuli,the as-developed actuator delivers a bidirectional actuation behavior with large amplitudes and an ultra-fast response,〜2.5 mS.A tweezer can be further made by assembling two such nanofibers symmetrically onto a tungsten probe.Clamping and unclamping can be realized by laser stimulus.More experimental and simulation investigations indicated that the actuation behaviors could be attributed to the nanostructured eccentric coaxial geometry,the thermal coefficient mismatch between layers and the fast phase transition of V02.The micro-actuators will have potentials in micro manipulators,nanoscaled switches,remote controls and other autonomous systems.Furthermore,a large variety of coaxial and eccentric coaxial nanofibers with various functions can also be developed,giving the as-developed methodology more opportunities.

Visualizing nonlinear resonance in nanomechanical systems via single-electron tunneling

Numerous reports have elucidated the importance of mechanical resonators comprising quantum-dot-embedded carbon nanotubes(CNTs)for studying the effects of single-electron transport.However,there is a need to investigate the single-electron transport that drives a large amplitude into a nonlinear regime.Herein,a CNT hybrid device has been investigated,which comprises a gate-defined quantum dot that is embedded into a mechanical resonator under strong actuation conditions.The Coulomb peak positions synchronously oscillate with the mechanical vibrations,enabling a single-electron Chopper*1 mode.Conversely,the vibration amplitude of the CNT versus its frequency can be directly visualized via detecting the time-averaged single-electron tunneling current.To understand this phenomenon,a general formula is derived for this time-averaged single-electron tunneling current,which agrees well with the experimental results.By using this visualization method,a variety of nonlinear motions of a CNT mechanical oscillator have been directly recorded,such as Duffing nonlinearity,parametric resonance,and double-,fractional-,mixed-frequency excitations.This approach opens up burgeoning opportunities for investigating and understanding the nonlinear motion of a nanomechanical system and its interactions with electron transport in quantum regimes.

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 SiOdSi substrate under enhanced accelerating voltages. With this identification technique, a CNT transistor with an on/off ratio of 〉10s 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.