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 non-destructive SEM imaging of a wide variety of insulating materials, semiconductor devices, and biological tissues.

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" 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.

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, 306Ƀ1, 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 pelectron activation energyq (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.

The emerging applications of nanoelectromechanical systems (NEMS) in ground-state cooling, quantum manipulation, communication devices, etc., call for a nanoresonator with high frequency, quality factor, and tunability, as well as easy integration. Here we show that such a nanoresonator can be achieved by using a unique assembly technique that transfers the stressed inner shell of carbon nanotubes (CNTs) to a self-aligned device geometry. The as-fabricated nanoresonator shows excellent comprehensive performance, i.e., high frequency (2–3 GHz), high tunability (80–110 MHz/V), high quality factor (3 × 10⁴), and single mode operation. The defect-free nature of the inner shell of the CNT gives rise to a high quality factor, and the preloaded tension improves the resonant frequency and tunability. This resonator with excellent performance also enables the integration of homogeneous devices and will play a key role in the emerging applications of NEMS.

Scanning electron microscopy (SEM) plays an indispensable role in nanoscience and nanotechnology because of its high efficiency and high spatial resolution in characterizing nanomaterials. Recent progress indicates that the contrast arising from different conductivities or bandgaps can be observed in SEM images if single-walled carbon nanotubes (SWCNTs) are placed on a substrate. In this study, we use SWCNTs on different substrates as model systems to perform SEM imaging of nanomaterials. Substantial SEM observations are conducted at both high and low acceleration voltages, leading to a comprehensive understanding of the effects of the imaging parameters and substrates on the material and surface-charge signals, as well as the SEM imaging. This unified picture of SEM imaging not only furthers our understanding of SEM images of SWCNTs on a variety of substrates but also provides a basis for developing new imaging recipes for other important nanomaterials used in nanoelectronics and nanophotonics.

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.

Single-walled carbon nanotubes (SWCNTs) illuminated by white light should appear colored due to resonance Rayleigh scattering. However, true-color imaging of SWCNTs on substrates has not been reported, because of the extremely low scattering intensity of SWCNTs and the strong substrate scattering. Here we show that Rayleigh scattering can be greatly enhanced by the interface dipole enhancement effect. Consequently colorful SWCNTs on substrates can be directly imaged under an optical microscope by wide field supercontinuum laser illumination, which facilitates high throughput chirality assignment of individual SWCNTs. This approach, termed "Rayleigh imaging microscopy", is not restricted to SWCNTs, but widely applicable to a variety of nanomaterials, which enables the colorful nanoworld to be explored under optical microscopes.

Aligned carbon nanotube films coated with amorphous carbon were developed into novel templates by atomic layer deposition. Freestanding macroscopic metal-oxide nanotube films were then successfully synthesized by using these templates. The reactive amorphous carbon layer greatly improved the nuclei density, which ensured the high quality of the films and allowed for precise control of the wall thickness of the nanotubes. Using template-synthesized alumina nanotube films, we demonstrate a humidity sensor with a high response speed, a transmission electron microscopy (TEM) grid, and a catalyst support. The cross-stacked assembly, ultrathin thickness, chemical inertness, and high thermal stability of the alumina nanotube films contributed to the excellent performance of these devices. In addition, it is expected that the metal-oxide nanotube films would have significant potential owing to their material richness, macroscopic appearance, flexibility, compatibility with the semiconducting technologies, and the feasibility of mass production.

The optical effect of a nanometer or sub-nanometer interfacial layer of condensed molecules surrounding individual nanomaterials such as single-walled carbon nanotubes (SWCNTs) has been studied theoretically and experimentally. This interfacial layer, when illuminated by light, behaves as an optical dipole lattice and contributes an instantaneous near field which enhances the local field on neighboring atoms, molecules, or nanomaterials, which in turn may lead to enhanced Rayleigh scattering, Raman scattering, and fluorescence. The theory of this interface dipole enhanced effect (IDEE) predicts that a smaller distance between the nanomaterials and the plane of the interfacial layer, or a larger ratio of the dielectric constants of the interfacial layer to the surrounding medium, will result in a larger field enhancement factor. This prediction is further experimentally verified by several implementations of enhanced Rayleigh scattering of SWCNTs as well as in situ Rayleigh scattering of gradually charged SWCNTs. The interface dipole enhanced Rayleigh scattering not only enables true-color real-time imaging of nanomaterials, but also provides an effective means to peer into the subtle interfacial phenomena.

Transfer printing of nanomaterials onto target substrates has been widely used in the fabrication of nanodevices, but it remains a challenge to fully avoid contamination introduced in the transfer process. Here we report a metal-film-assisted method to realize an ultra-clean transfer of single-walled carbon nanotubes (SWCNTs) mediated by poly(methyl methacrylate) (PMMA). The amount of PMMA residue can be greatly reduced due to its strong physical adhesion to the metal film, leading to ultra-clean surfaces of both the SWCNTs and the substrates. This metal-film-assisted transfer method is efficient, nondestructive, and scalable. It is also suitable for the transfer of graphene and other nanostructures. Furthermore, the relatively low temperature employed allows this technique to be compatible with nanomaterial-based flexible electronics.