Near-field Raman spectroscopy using a sharp metal tip

Near‐field Raman spectroscopy with a spatial resolution of 20 nm is demonstrated by raster scanning a sharp metal tip over the sample surface. The method is used to image vibrational modes of single‐walled carbon nanotubes. By combining optical and topographical signals rendered by the single‐walled carbon nanotubes, we can separate near‐field and far‐field contributions and quantify the observed Raman enhancement factors.     

Unique laser-scanning optical microscope for low-temperature imaging and spectroscopy

Low-temperature optical characterization of single quantum nanostructures can reveal detailed information on structure-dependent properties of these materials. We describe the development of a unique laser-scanning optical microscope capable of low-temperature single molecule/particle imaging and spectroscopy. Making use of the magnification of a microscope objective, the laser- scanning scheme of the present microscope allows for high-repeatability imaging over large sample areas. The microscope is utilized to measure the low-temperature Raman scattering spectra of individual single-walled carbon nanotubes and single molecule fluorescence spectra of conjugated polymers. The developed low-temperature microscope can be applied to study a wide array of nanomaterials at a single particle level.     

Synthesis of cobalt oxide aerogels and nanocomposite systems containing single‐walled carbon nanotubes

The synthesis and characterization of porous nanostructured cobalt oxide (Co₃O₄) aerogels using epoxide addition method is described. Cobalt‐containing monoliths were obtained by sol–gel processing of an alcoholic cobalt chloride solution with propylene oxide as the gelation agent. The alcogels were dried by supercritical CO₂ fluid extraction to obtain the highly porous amorphous cobalt (II) aerogels. To enhance and control the structural properties of the aerogels, single‐walled carbon nanotubes (SWCNT) were incorporated into the cobalt (II) aerogel network to form a homogenous composite material. The resulting materials were characterized using powder X‐ray diffraction and nitrogen adsorption/desorption analysis. The detailed microstructure of aerogel networks was investigated using scanning and transmission electron microscopy, which showed significant structural changes induced by the incorporation of SWCNT to the cobalt aerogel. Annealing of the aerogel materials at 600°C yields a highly crystalline well‐faceted Co₃O₄ network SCANNING 31: 132–138, 2009. © 2009 Wiley Periodicals, Inc.     

多壁碳纳米管增强无石棉垫片耐老化性能

为了提高无石棉垫片的耐老化性能，在无石棉垫片配方中添加一定含量经羟基化改性后的多壁碳纳米管（MWCNTs-OH），通过抄取法制备无石棉垫片试样。通过人工老化试验，测试老化前后垫片的压缩率、回弹率及拉伸强度性能，探讨羟基化多壁碳纳米管对无石棉垫片耐老化性能的影响。结果表明：在无石棉垫片配方中加入羟基化多壁碳纳米管可降低垫片试样老化前后的压缩率、回弹率及拉伸强度的变化量；随羟基化多壁碳纳米管质量分数的增大，垫片老化前后各性能变化先降低后增大，当羟基化多壁碳纳米管质量分数为1.2%时，对无石棉垫片的耐老化性提升最明显，且对力学性能有增强作用。     

HRTEM of 1DSnTe@SWNT nanocomposite located on thin layers of graphite

The method for imaging of highly sensitive nanostructures unstable under electron beam irradiation is introduced. To reduce charge and thermally generated beam damage, highly conductive multilayered graphene or thin graphite layers were used as supports for nanostructures. Well‐defined crystalline structure of graphite layers enables image reconstruction by Fourier filtering and allows maintaining high quality of images. The approach was tested for imaging of highly sensitive quasi one‐dimensional SnTe nanocrystals hosted inside single‐walled carbon nanotubes. Relying on the filtered images and the image simulation, the structure of one‐dimensional SnTe was established as a chain of fcc NaCl type unit cells, connected by the [001] edges with <110> direction coinciding with nanotube axis.     

The imaging mechanism of single-walled carbon nanotubes on Si/SiO₂ wafer in scanning electron microscopy

Scanning electron microscopy imaging of both suspended single‐walled carbon nanotubes (SWNTs) and contacted SWNTs with Si/SiO₂ substrate has been studied in this paper. The voltage contrast has been investigated by supplying external electric field around the samples. The results show that the image contrast of SWNTs attributes to both voltage contrast from the area surrounding SWNTs (tens of nanometres in both sides of the SWNTs) and electron beam induced emission from SWNTs themselves under low primary beam energy. Under high primary beam energy, however, EBIE dominates the image contrast due to the fact that the voltage contrast caused by implanted charges of the SiO₂ layer is weakened. Imaging under the primary beam energy lower than 1 keV offers widened diameter of SWNTs, which promises that the SWNTs are observable at very low magnification (lower than 100×). At a larger magnification, however, imaging under the primary beam energy higher than 10 keV can display more realistic images of the SWNTs. In addition, an appropriate external electric field can improve the images.     

Coherent nano-area electron diffraction

We describe the new coherent nano-area electron diffraction (NED) and its application for structure determination of individual nanostructures. The study is motivated by the challenge and the general lack of analytical techniques for characterizing nanometer-sized, heterogeneous phases. We show that by focusing electrons on the focal plane of the pre-objective lens using a 3rd condenser lens and a small condense aperture, it is possible to achieve a nanometer-sized highly parallel illumination or probe. The high angular resolution of diffraction pattern from the parallel illumination allows over-sampling and consequently the solution of phase problem based on the recently developed ab initio phase retrieval technique. From this, a high-contrast and high-resolution image can be reconstructed at resolution beyond the performance limit of the image-forming objective lens. The significance of NED for nanostructure characterization will be exemplified by single-wall carbon nanotubes and small metallic clusters. Imaging from diffraction patterns, or diffractive imaging, will be demonstrated using double-wall carbon nanotubes.     

In situ measurements on individual thin carbon nanotubes using nanomanipulators inside a scanning electron microscope

We demonstrate here a novel method for performing in situ mechanical, electrical and electromechanical measurements on individual thin carbon nanotubes (CNTs) by using nanomanipulators inside a scanning electron microscope. The method includes three key steps: picking up an individual thin CNT from a substrate, connecting the CNT to a second probe or an atomic force microscope cantilever for the measurements and placing the CNT onto a holey carbon film on a transmission electron microscope grid for further structure characterization. With the method, Young’s modulus, the breaking strength and the effects of axial strain on electrical transport properties of individual thin CNTs can be studied. As examples, the mechanical, electrical and electromechanical properties of a double-walled CNT (DWCNT) and a single-walled CNT (SWCNT) were measured. We observed a strain-induced metallic-to-semiconducting transition of the DWCNT and a bandgap increase of the SWCNT. More importantly, the electromechanical properties of the SWCNT were correlated to its chirality determined by electron diffraction. The method enables us to relate mechanical, electrical and electromechanical properties of the measured thin CNTs to their atomic structures.     

Cs corrected STEM EELS: Analysing beam sensitive carbon nanomaterials in cellular structures

Identification of individual single wall nanotubes (SWNTs) within a cellular structure can provide vital information towards understanding the potential mechanisms of uptake, their localisation and whether their structure is transformed within a cell. To be able to image an individual SWNT in such an environment a resolution is required that is not usually appropriate for biological sections. Standard transmission electron microscopy (TEM) techniques such as bright field imaging of these cellular structures result in very weak contrast. Traditionally, researchers have stained the cells with heavy metal stains to enhance the cellular structure, however this can lead to confusion when analysing the samples at high resolution. Subsequently, alternative methods have been investigated to allow high resolution imaging and spectroscopy to identify SWNTs within the cell; here we will concentrate on the sample preparation and experimental methods used to achieve such resolution.     

Electromechanical properties of individual single-walled carbon nanotubes grown on focused-ion-beam patterned substrates

The combined capabilities of focused-ion-beam (FIB) nano-patterning and transmission electron microscope characterization have been employed to measure the electromechanical resonance of individual single-walled carbon nanotubes (SWNTs). Suspended and isolated SWNTs of length up to 7 μm were grown on FIB-patterned molybdenum substrates. The Young's modulus of a 5 nm diameter SWNT is found to be E=1.34±0.06 TPa, which is deduced from the measured resonance frequency based on the elastic beam theory. The patterned substrates help locate the nanostructure effectively, allowing the same structure to be inspected after multiple processing steps.     

The structure of 1D CuI crystals inside SWNTs

Nanocomposites consisting of one‐dimensional CuI crystals inside single‐walled carbon nanotubes were obtained using the capillary technique. high‐resolution transmission electron microscopy investigations of the atomic structure of the encapsulated 1D CuI crystals revealed two types of 1D CuI crystals with growth direction <001> and relative to the bulk hexagonal CuI structure. Atomic structure models were proposed based on the high‐resolution transmission electron microscopy images. According to the proposed models and image simulations, the main contrast in the 1D crystal images arises from the iodine atoms whereas copper atoms, with lower atomic number giving lower contrast, are thought to be statistically distributed.     

Electron diffraction analysis of individual single-walled carbon nanotubes

We present a detailed electron diffraction study of individual single-walled carbon nanotubes. A novel sample preparation procedure provides well-separated, long and straight individual single-shell nanotubes. Diffraction experiments are carried out at 60 kV, below the threshold for knock-on damage in carbon nanotubes. We describe experimental parameters that allow single-tube electron diffraction experiments with widely available thermal emission transmission electron microscopes. Further, we review the simulation of diffraction patterns for these objects.     

碳纳米管基膨润土润滑脂的制备及摩擦学性能研究

为制备摩擦学性能优良的多壁碳纳米管基膨润土润滑脂,采用油酸对多壁碳纳米管(MWCNTs)进行修饰,在实验室自主设计的超声辅助球磨试验装置上,制备在PAO6中均匀稳定分散的多壁碳纳米管悬浮液,并以悬浮液为基础油制备MWCNTs增强的膨润土润滑脂。探讨不同分散方法(球磨分散、超声分散、超声和球磨分散)对多壁碳纳米管分散稳定性的影响,研究润滑脂的摩擦因数、磨斑直径随多壁碳纳米管质量分数的变化。实验结果表明:经油酸修饰的多壁碳纳米管在超声和球磨综合作用下分散稳定性最好;随多壁碳纳米管质量分数的增加,膨润土润滑脂的摩擦因数、磨斑直径先减小后增大,其中多壁碳纳米管质量分数为0.03%时,所制备的膨润土润滑脂摩擦学性能最佳,磨斑直径最小(0.690 mm),比美孚28号航空润滑脂(符合美国军方规格MIL-G81322C,磨斑直径0.807 mm)降低了14.5%。     

薄壁件塑性成形失稳起皱的国内外研究进展

薄壁类零件由于其塑性成形容易达到对产品精密化、轻量化、强韧化及柔性化的要求 ,广泛应用于当代航天、航空、汽车、化工和其他高技术产业中 ,成为先进塑性加工技术面向 2 1世纪研究与发展的一个重要方向。受压失稳起皱则是影响薄壁件成形过程稳定性的最主要缺陷和障碍之一 ,决定着此类产品成形潜力大小 ,并严重影响着零件的成形质量、精度、模具的寿命及后续工序的完成。因此 ,研究各种不同变形状态下的失稳起皱机理和判断准则 ,准确有效预报和控制成形中失稳现象的产生 ,在薄壁类零件的塑性加工领域就显得极为关键。本文从试验研究、理论分析和数值模拟等 3个方面 ,介绍了国内外对薄壁件特别是管材成形中失稳起皱现象所作的工作和新进展 ,提出了该领域中亟待解决的瓶颈问题     

AFM imaging of functionalized double-walled carbon nanotubes

We present a comparative study of several non-covalent approaches to disperse, debundle and non-covalently functionalize double-walled carbon nanotubes (DWNTs). We investigated the ability of bovine serum albumin (BSA), phospholipids grafted onto amine-terminated polyethylene glycol (PL-PEG₂₀₀₀-NH₂), as well as a combination thereof, to coat purified DWNTs. Topographical imaging with the atomic force microscope (AFM) was used to assess the coating of individual DWNTs and the degree of debundling and dispersion. Topographical images showed that functionalized DWNTs are better separated and less aggregated than pristine DWNTs and that the different coating methods differ in their abilities to successfully debundle and disperse DWNTs. Height profiles indicated an increase in the diameter of DWNTs depending on the functionalization method and revealed adsorption of single molecules onto the nanotubes. Biofunctionalization of the DWNT surface was achieved by coating DWNTs with biotinylated BSA, providing for biospecific binding of streptavidin in a simple incubation step. Finally, biotin-BSA-functionalized DWNTs were immobilized on an avidin layer via the specific avidin–biotin interaction.     

Electro-thermo nonlocal nonlinear vibration in an embedded polymeric piezoelectric micro plate reinforced by DWBNNTs using DQM

In the present paper, electro-thermo nonlinear vibration of a piezo-polymeric rectangular micro plate made from polyvinylidene fluoride (PVDF) reinforced by zigzag double walled boron nitride nanotubes (DWBNNTs) is studied. This plate is embedded in an elastic medium which is simulated by Winkler and Pasternak foundation models. Using nonlinear strain-displacement relations and nonlocal elasticity plate theory as well as considering charge equation for coupling between electrical and mechanical fields, the motion equations are derived based on energy method and Hamilton??s principle. The differential quadrature method (DQM) is employed to computation of nonlinear frequency for different mechanical and free-free electrical boundary conditions. The results indicate that smart composite and consequently the generated G4 improved sensor and actuator applications in several process industries, because it increases the nonlinear vibration frequency. Furthermore, it can be also found that the nonlinear frequency increases as the values of the elastic medium constants, the geometrical aspect ratios and DWBNNTs volume fraction increase but it decreases as nonlocal parameter increases.     

Cryogenic‐temperature electron microscopy direct imaging of carbon nanotubes and graphene solutions in superacids

Cryogenic electron microscopy (cryo‐EM) is a powerful tool for imaging liquid and semiliquid systems. While cryogenic transmission electron microscopy (cryo‐TEM) is a standard technique in many fields, cryogenic scanning electron microscopy (cryo‐SEM) is still not that widely used and is far less developed. The vast majority of systems under investigation by cryo‐EM involve either water or organic components. In this paper, we introduce the use of novel cryo‐TEM and cryo‐SEM specimen preparation and imaging methodologies, suitable for highly acidic and very reactive systems. Both preserve the native nanostructure in the system, while not harming the expensive equipment or the user. We present examples of direct imaging of single‐walled, multiwalled carbon nanotubes and graphene, dissolved in chlorosulfonic acid and oleum. Moreover, we demonstrate the ability of these new cryo‐TEM and cryo‐SEM methodologies to follow phase transitions in carbon nanotube (CNT)/superacid systems, starting from dilute solutions up to the concentrated nematic liquid‐crystalline CNT phases, used as the ‘dope’ for all‐carbon‐fibre spinning. Originally developed for direct imaging of CNTs and graphene dissolution and self‐assembly in superacids, these methodologies can be implemented for a variety of highly acidic systems, paving a way for a new field of nonaqueous cryogenic electron microscopy.     

An edge reversal method for precision measurement of cutting edge radius of single point diamond tools

A method, which is referred to as the edge reversal method, is proposed for precision measurement of the cutting edge radius of single point diamond tools. An indentation mark of the cutting edge which replicates the cutting edge geometry is firstly made on a soft metal substrate surface. The cutting edge of the diamond tool and its indentation mark, which is regarded as the reversal cutting edge, are then measured by utilizing an atomic force microscopy (AFM), respectively. The cutting edge radius can be accurately evaluated through removing the influence of the AFM probe tip radius, which is comparable to the cutting edge radius, based on the two measured data without characterization of the AFM probe tip radius. The results of measurement experiments and uncertainty analysis are presented to demonstrate the feasibility of the proposed method.     

厚壁筒双轴向表面裂纹尖端应力强度因子影响因素的研究

在现有文献对平面结构任意分布多裂纹间相互作用影响因素及厚壁筒轴向表面单裂纹尖端应力强度因子分析的基础上,提出了包含裂纹尖端应力强度因子影响因素的厚壁筒双轴向表面裂纹尖端应力强度因子公式.根据有限元方法,利用ANSYS软件对不同厚壁筒壁厚比、不同裂纹深度比及不同裂纹夹角情况下双轴向表面裂纹尖端应力强度因子进行了计算,分析...