场离子显微镜观测单壁碳纳米管

场离子显微镜是具有原子级分辨能力的尖端表面分析工具.它适用于纳米尺度的单壁碳纳米管(SWCNTs)末端表面原子排列的观测.利用范氏力将SWCNTs组装到钨针尖上,用场离子显微镜观察了这种针尖样品.在观察过程中对针尖样品进行了加热处理,既除掉非晶的C原子,也破坏了由于碳纳米管切割制造过程使用表面活化剂引起的高电阻层,得到了开口SWCNTs的场离子显微镜像,由此推断出SWCNTs束的顶端原子结构,估算出观察到的SWCNTs的直径,并且模拟了其中一个图像所代表的SWCNTs顶端开口的原子排列,推断出产生这个图像的SWCNTs是(7,7)型结构.     

利用场发射显微镜研究单壁碳纳米管的场发射特性

利用场发射显微镜研究了单壁碳纳米管(SWCNTs)的场发射特性.由于实验中所用的SWCNTs的长度基本一致,因此能同时观察到多根SWCNTs的场发射像.SWCNTs的场发射像随着热处理温度的升高而变化,直至热处理温度过高而塌缩.在一定的实验条件下,观察到了具有精细结构的单根碳纳米管顶端"帽子"的场发射像.电流-电压(I-U)曲线分析表明,SWCNTs的电流来源于场发射.     

用于制备优质单壁碳纳米管管束的MgO负载Fe3O4纳米粒子的合成

采用沉淀方法制备了直径分布狭窄的均匀Fe3O4纳米颗粒.Fe3O4纳粒形体几近一致,平均粒径为10.33 nm±2.99 nm(平均粒径±标准偏差).在超声作用下将MgO纳米颗粒分散在一定量Fe3O4纳米颗粒的水溶液中获得MgO负载Fe3O4的纳米颗粒.以甲烷为碳源,Fe3O4/MgO为催化剂,经化学气相沉积,在Fe3O4纳粒上制得了大量直径近乎均匀的单壁碳纳米管(SWCNTs)束.TEM显示:SWCNTs的平均直径1.22rm.热重分析显示:样品在400℃～600℃温度区间失重量约19％.拉曼光谱显示:SWCNTs的ID/IG的强度比为0.03,表明采用Fe3O4/MgO催化剂可制得高石墨化程度的单壁碳纳米管.     

The matrix stiffness role on tensile and thermal properties of carbon nanotubes/epoxy composites

In this study, randomly oriented single-walled carbon nanotubes (SWCNTs)/epoxy nanocomposites were fabricated by tip sonication with the aid of a solvent and subsequent casting. Two different curing cycles were used to study the role of the stiffness of the epoxy matrix on the tensile and thermal behavior of the composites. The addition of a small amount of SWCNTs (0.25 wt.%) in rubbery, i.e., soft matrices, greatly increased Young’s modulus and tensile strength of the nanocomposites. The results showed that the tensile properties of soft epoxy matrices are much more influenced by the addition of carbon nanotubes than stiffer ones. The significant improvement in tensile properties was attributed to the excellent mechanical properties and structure of SWCNTs, an adequate dispersion of SWCNTs by tip sonication, and a stronger SWCNT/matrix interfacial adhesion in softer epoxy matrices. A slight improvement in the thermal stability of the nanocomposites was also observed.     

First-principles study of ZnO cluster-decorated carbon nanotubes

We have investigated the structural, electronic and carbon monoxide (CO) detection properties of the ZnO cluster-decorated single-walled carbon nanotubes (SWCNTs) by using density functional theory (DFT). The stable structures of hybrid ZnO/SWCNT materials are that the ZnO cluster plane is perpendicular to the surface of SWCNTs with the Zn atoms towards the SWCNTs (Zn atom above axial C-C bond or above the C atom). For the ZnO cluster-decorated semiconducting SWCNTs, the SWCNTs present p-type characteristics which may lead to the decrease of conductance upon illumination with ultraviolet (UV) light. The CO can be adsorbed on the hybrid ZnO/SWCNT materials due to the charge transfer between them. Compared with isolated ZnO clusters or bare SWCNTs, the ZnO/SWCNT network would have excellent CO detection ability due to their suitable adsorption energy and conductivity.     

Molecular-basis of single-walled carbon nanotube recognition by single-stranded DNA

Hybrids of biological molecules and single-walled carbon nanotubes (SWCNT) have proven useful for SWCNT sorting and are enabling several biomedical applications in sensing, imaging, and drug delivery. In the DNA-SWCNT system, certain short (10-20mer) sequences of single-stranded DNA recognize specific SWCNT, allowing the latter to be sorted from a chirality diverse mixture. (1) However, little is known about the DNA secondary structures that underlie their recognition of SWCNTs. Using replica exchange molecular dynamics (REMD) of multiple strands on a single SWCNT, we report that DNA forms ordered structures on SWCNTs that are strongly DNA sequence and SWCNT dependent. DNA sequence (TAT)(4) on its recognition partner, the (6,5) SWCNT, (1) forms an ordered right-handed helically wrapped barrel, stabilized by intrastrand, self-stitching hydrogen bonds and interstrand hydrogen bonding. The same sequence on the larger diameter (8,7)-SWCNT forms a different and less-stable structure, demonstrating SWCNT selectivity. In contrast, homopolymer (T)(12), with weaker tendency for intrastrand hydrogen bonding, forms a distinctly left-handed wrap on the (6,5)-SWCNT, demonstrating DNA sequence specificity. Experimental measurements show that (TAT)(4) selectively disperses smaller diameter SWCNTs more efficiently than (T)(12), establishing a relationship between recognition motifs and binding strength. The developing understanding of DNA secondary structure on nanomaterials can shed light on a number of issues involving hybrids of nanomaterials and biological molecules, including nanomedicine, health-effects of nanomaterials, and nanomaterial processing.     

Enhanced photoelectrochemical activity of the TiO2 /ITO nanocomposites grown onto single-walled carbon nanotubes at a low temperature by nanocluster deposition

High-resolution transmission electron microscopy (HRTEM) is used to observe a TiO2/ITO-coated composite nanostructure grown onto single-walled carbon nanotubes (SWCNTs). The SWCNTs, indium tin oxide (ITO), and TiO2 mixtures of anatase (A) and rutile (R) are clearly distinguished in the HRTEM images. The thickness of the SWCNT was about 3 nm, and the TiO2 shell included different polycrystalline structures.     

Analysis of clustering, interphase region, and orientation effects on the electrical conductivity of carbon nanotube-polymer nanocomposites via computational micromechanics

A multiscale model based on computational micromechanics techniques is developed for determining the effective electrical conductivity of carbon nanotube-polymer nanocomposites containing bundles of SWCNTs at a wide range of SWCNT volume fractions above and below the observed percolation concentrations. The model is applied for both randomly oriented and fully aligned nanotube bundle orientation distributions, with emphasis on the latter in elucidating the relative impact of clustering and nanoscale effects on the effective electrical conductivity of nanocomposites. Nanocomposites consisting of aligned, well-dispersed and clustered/bundled SWCNTs are studied to indicate the influence of clustering on the effective electrical conductivity. A parametric study in terms of interphase thickness and interphase conductivity for both the well-dispersed and clustered arrangements is conducted to allow for the assessment of both the independent influence of the interphase layer and of the combined effects of clustering and interphase regions on the effective electrical conductivity of nanocomposites with aligned SWCNTs. Effective nanotube bundle properties obtained from clustered nanotube arrangements both with and without interphase regions are subsequently applied in an orientation distribution homogenization technique in order to obtain the effective electrical conductivity of nanocomposites consisting of randomly oriented SWCNT bundles. The resulting nanocomposite electrical conductivities are compared with characterization data available in the literature, and are discussed in terms of two mechanisms proposed in the literature for the low volume fraction electrical percolation observed in nanocomposites.     

Synthesis and characterization of polyurethane-grafted single-walled carbon nanotubes via click chemistry

Polyurethane (PU)-grafted carbon nanotubes were synthesized by the coupling of alkyne moiety decorated single walled carbon nanotube (SWCNT) with azide moiety containing PU using Cu(I) catalyzed Huisgen [3 + 2] cycloaddition click chemistry. The azide moiety containing poly(s-caprolactone)diol was synthesized by ring-opening polymerization and further used for PU synthesis. Alkyne-functionalizion of SWCNT was completed by the reaction of p-aminophenyl propargyl ether with SWCNT using a solvent free diazotization procedure. Nuclear magnetic resonance, Fourier transform infrared, and Raman spectroscopic measurements confirmed the functionalization of SWCNT. Scanning electron microscopy and transmission electron microscopy images showed an excellent dispersion of SWCNTs, and specially debundling of SWCNTs could be observed due to polymer assisted dispersion. A quantitative grafting was successfully achieved even at high content of functional groups.     

High-performance single-wall carbon nanotube transparent conductive films

A single-wall carbon nanotube(SWCNT) has superior optical,electrical,and mechanical properties due to its unique structure and is therefore expected to be able to form flexible high-performance transparent conductive films(TCFs).However,the optoelectronic performance of these films needs to be improved to meet the requirements of many devices.The electrical resistivity of SWCNTTCFs is mainly determined by the intrinsic resistivity of individual SWCNTs and their junction resistance in networks.We analyze these key factors and focus on the optimization of SWCNTs and their networks,which include the diameter,length,crystallinity and electrical type of the SWCNTs,and the bundle size and interconnects in networks,as well as chemical doping and microgrid design.We conclude that isolated/small-bundle,heavily doped metallic or semiconducting SWCNTs with a large diameter,long length and high crystallinity are necessary to fabricate high-performance SWCNTTCFs.A simple,controllable way to construct macroscopic SWCNT networks with Y-type connections,welded junctions or microgrid design is important in achieving a low resistivity.Finally,some insights into the key challenges in the manufacture and use of SWCNT TCFs and their prospects are presented,hoping to shed light on promoting the practical application of SWCNT TCFs in future flexible and stretchable optoelectronics.     

Labeling the defects of carbon nanotubes with thiol groups

Herein, we investigate the reactivity of perfect and defective single-wall carbon nanotubes (SWCNTs) with the SH group using first principle periodic calculations. The presence of Stone–Wales (SW) defect sites significantly increases the reactivity of SWCNTs against the thiol group. The most reactive site for the addition of the SH radical is the single vacancy defect; the sulfur atom reconstructs the SWCNT framework and the hydrogen atom becomes attached to a carbon atom. The cluster model calculations performed for perfect SWCNTs confirmed a very low reactivity with the thiol group, even for the small diameter and metallic SWCNTs. The reaction between the perfect SWCNT and SH results thermodynamically unfavorable. The different reactivities observed for perfect and defective SWCNTs suggest that the SH group can be employed to perform a chemical labeling of the defect sites present in carbon nanotubes. The SH radical group is quite unique because, even though it has an unpaired electron, it does not react with sp ² carbon frameworks, unless they have defects or curvature similar to C60. The results are discussed in terms of the recent experimental investigations about thiolated SWCNTs. We were able to explain the Transmission Electron Microscopy images of thiolated nanotubes and the lack of reactivity at the tips. Finally, we discuss a possible route to synthesize sulfur-doped SWCNTs using thiol groups and their electronic properties.     

In vivo therapeutic silencing of hypoxia-inducible factor 1 alpha (HIF-1α) using single-walled carbon nanotubes noncovalently coated with siRNA

A new approach is described for delivering small interfering RNA (siRNA) into cancer cells by noncovalently complexing unmodified siRNA with pristine single-walled carbon nanotubes (SWCNTs). The complexes were prepared by simple sonication of pristine SWCNTs in a solution of siRNA, which then served both as the cargo and as the suspending agent for the SWCNTs. When complexes containing siRNA targeted to hypoxia-inducible factor 1 alpha (HIF-1α) were added to cells growing in serum containing culture media, there was strong specific inhibition of cellular HIF-1 activity. The ability to obtain a biological response to SWCNT/siRNA complexes was seen in a wide variety of cancer cell types. Moreover, intratumoral administration of SWCNT- HIF-1α siRNA complexes in mice bearing MiaPaCa-2/HRE tumors significantly inhibited the activity of tumor HIF-1α. As elevated levels of HIF-1α are found in many human cancers and are associated with resistance to therapy and decreased patient survival, these results imply that SWCNT/siRNA complexes may have value as therapeutic agents. These two authors contributed equally to the design and implementation of this study.     

Preparation of single-walled carbon nanotube/silicon composites and their lithium storage properties

Single-walled carbon nanotube (SWCNT)/silicon composites were produced from the purified SWCNTs and Si powder by high-energy ball-milling and then electrochemically inserted with Li using Li/(SWCNT/Si) cells. The highest reversible capacity and lowest irreversible capacity of the SWCNT/Si composites were measured to be 1845 and 474 mAh g(-1) after ball-milling for 60 min, respectively. During the charge/discharge process, most of the Li ions were inserted into the SWCNT/Si composites by alloying with Si particles below 0.2 V and extracted from the SWCNT/Si composites by dealloying with Si particles around 0.5 V. The enhanced capacity and cycle performance of the SWCNT/Si composites produced by high-energy ball-milling were due primarily to the fact that SWCNTs provided a flexible conductive matrix, which compensated for the dimensional changes of Si particles during Li insertion and avoided loosening of the interparticle contacts during the crumbling of Si particles. The ball-milling contributed to a decrease in the particle size of SWCNTs and Si particles and to an increase in the electrical contact between SWCNTs and Si particles in the SWCNT/Si composites.     

Zeolite Nanosheets Stabilize Catalyst Particles to Promote the Growth of Thermodynamically Unfavorable,Small‐Diameter Carbon Nanotubes

A challenge in the synthesis of single‐wall carbon nanotubes (SWCNTs) is the lack of control over the formation and evolution of catalyst nanoparticles and the lack of control over their size or chirality. Here, zeolite MFI nanosheets (MFI‐Ns) are used to keep cobalt (Co) nanoparticles stable during prolonged annealing conditions. Environmental transmission electron microscopy (ETEM) shows that the MFI‐Ns can influence the size and shape of nanoparticles via particle/support registry, which leads to the preferential docking of nanoparticles to four or fewer pores and to the regulation of the SWCNT synthesis products. The resulting SWCNT population exhibits a narrow diameter distribution and SWCNTs of nearly all chiral angles, including sub‐nm zigzag (ZZ) and near‐ZZ tubes. Theoretical simulations reveal that the growth of these unfavorable tubes from unsupported catalysts leads to the rapid encapsulation of catalyst nanoparticles bearing them; their presence in the growth products suggests that the MFI‐Ns prevent nanoparticle encapsulation and prologue ZZ and near‐ZZ SWCNT growth. These results thus present a path forward for controlling nanoparticle formation and evolution, for achieving size‐ and shape‐selectivity at high temperature, and for controlling SWCNT synthesis.     

Quantification of Uptake and Localization of Bovine Serum Albumin‐Stabilized Single‐Wall Carbon Nanotubes in Different Human Cell Types

Single‐wall carbon nanotubes (SWCNTs) possess many unique, inherent properties that make them attractive materials for application in medical and biological technologies. Development of concentrated SWCNT dispersions of isolated nanotubes that retain SWCNTs' inherent properties with minimal negative cellular effects is essential to fully realize the potential of SWCNTs in biotechnology. It is shown that bovine serum albumin (BSA), a common and well‐characterized model blood serum protein, can individually disperse SWCNTs at concentrations of up to 0.3 mg mL^?1 while retaining SWCNTs' optical properties. Uptake into human mesenchymal stem cells (hMSC) and HeLa cells is quantified, revealing strikingly high concentrations of 86 ± 33 × 10⁶ and 21 ± 13 × 10⁶ SWCNTs per cell, respectively, without any apparent acute deleterious cellular effects. Through high‐resolution confocal Raman spectroscopy and imaging, it is established that SWCNT–BSAs are preferentially localized intracellularly, especially in the cytoplasm of both hMSCs and HeLa cells. The uptake and localization results demonstrate the efficacy of BSA as a biocompatible dispersant and a mediator of bioactivity. BSA is widely available and inexpensive, which make these concentrated, highly‐dispersed, noncovalently modified SWCNT–BSAs suitable for the development of SWCNT‐based biotechnologies.     

Polydiacetylene single-walled carbon nanotubes nano-hybrid for cellular imaging applications

The functionalization of single-walled carbon nanotubes (SWCNTs) by forming self-assembled supramolecular structure of 10,12-pentacosadiynoic acid (PCDA) on the carbon nanotube wall is reported. PCDA assemblies on SWCNTs (PCDA/SWCNTs) were polymerized by UV irradiation to extensively conjugated polydiacetylene (PDA). PDA/SWCNT was identified by absorption and emission spectroscopy, scanning and transmission electron microscopies (SEM and TEM) and atomic force microscopy (AFM). PDA/SCWNTs showed strong near-infrared (NIR) fluorescence caused by fluorescence resonance energy transfer (FRET) between PDA network and semiconducting SWCNT core. The micro-patterning of biotinylated PDA/SWCNT with FITC-avidin on biotinylated glass surface demonstrated the potential application for a bio-sensing device. Furthermore, the biocompatibility for mammalian cancer cells was tested by viability experiments, which revealed that the PDA/SWCNTs had very low toxicity below 31.3 mg/L in terms of pristine SWCNTs concentration. Also, PDA/SWCNTs inside the cells can be observed by NIR microscopy. This unique modular method of preparation can contribute to diverse functionalities for practical applications in various non-invasive cellular imaging.     

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.     

Artifacts in SPM measurements of thin films and coatings

Ideally, scanning probe microscopy (SPM) should generate a three-dimensional map of a sample surface such that the result is an exact replication of the actual sample. Any measurement data that result in an image differing from the actual sample surface are artifacts. The chief sources of SPM artifacts are mechanical systems, piezoelectric crystals, electronic scanners, tip-sample interaction, and image processing. For example, choosing the proper SPM probe for a specific sample is only the first step in minimizing probe-related artifacts. In fact, geometrical effects cause the largest number of artifacts. Good quality atomic SPM images can be clearly seen in raw data and should respond appropriately when the scan range or rotation is changed. Because SPM images are often periodic, it is possible for heavily filtered “data” to sometimes be misinterpreted as “atomic resolution images”. This paper presents SPM image studies using a range of materials from hard rough diamond films to soft nanometer smooth polyimide films. The investigation brings out the hidden sources of SPM artifacts for samples with different geometries and physical properties. Ten suggestions are presented which, if implemented/followed, should minimize the number of SPM image artifacts thereby assuring high quality images.     

Effect of ending surface on energy and Young's modulus of an armchair single-walled carbon nanotubes

The energy and Young's modulus as a function of tube length for (10, 10) armchair single-walled carbon nanotubes (SWCNTs) are investigated by using a linear scaling self-consistent-charge density functional tight binding (SCC-DFTB) method. It is found that the formula derived from total energy for a zigzag SWCNT [Physica B404, 3930 (2009)] can be also used to explain these calculated length-dependent properties. Moreover, a transition occurs from fast change of length-dependent properties of the SWCNT to their slow change. This transition corresponds to the SWCNT's length of about 5 nm. The length for the armchair SWCNT is about one half of that of the corresponding Zigzag SWCNTs. In addition, a definition of volume for a short SWCNT is discussed.