Inspired by rich physics and functionalities of graphenes, scientists have taken an intensive interest in two-dimensional (2D) crystals of h-BN (analogue of graphite, so-called "white" graphite). Recent calculations have predicted the exciting potentials of BN nanoribbons in spintronics due to tunable magnetic and electrical properties; however no experimental evidence has been provided since fabrication of such ribbons remains a challenge. Here, we show that few- and single-layered BN nanoribbons, mostly terminated with zigzag edges, can be produced under unwrapping multiwalled BN nanotubes through plasma etching. The interesting stepwise unwrapping and intermediate states were observed and analyzed. Opposed to insulating primal tubes, the nanoribbons become semiconducting due to doping-like conducting edge states and vacancy defects, as revealed by structural analyses and ab initio simulations. This study paves the way for BN nanoribbon production and usage as functional semiconductors with a wide range of applications in optoelectronics and spintronics.
Tensile loading and pullouts of individual multi-walled BNNTs were studied for the first time by in-situ tests in the integrated HRTEM-AFM setup. Most important mechanical parameters, such as the ultimate tensile strength and strain, maximum sustainable load and the Young's modulus of tubes, were measured. Under parallel HRTEM observations the measured mechanical parameters were correlated to experimental conditions and tube structures.
Herein the recent experiments performed by the authors on fabricated multi walled BN nanotubes and monoatomic BN graphene like nanosheets are reviewed The re suits are presented in several sections namely (i) method for high yield synthesis of thin, defect free BN nanotubes of only a few layers, with external diameters below 10 nm, (ii) verification of BN nanotube piezoelectrical behavior and its electrically induced thermal decomposition under combined resistive heating and electrical charging in a transmission electron microscope, (iii) the first direct measurements of the true tensile strength and Young's modulus of BN nanotubes, using newly developed nanotensile tests inside an electron microscope, the measured values were found to be similar to 30 GPa and similar to 900 GPa, respectively, and (iv) diverse kinetic processes taking place within the prepared monoatomic BN sheets (so called "white graphenes") affiliated with intensive knock on B and N atom displacements under high energy electron beam irradiation in an aberration corrected medium voltage high resolution transmission electron microscope
We report here a method for measurement of thermoelectric power of quasi-one dimensional nano-materials with a simple platform, where individual nanomaterial is assembled with nano-probes in a scanning electron microscope. This approach allows repeated manipulation and thermoelectric measurement of the same loaded nanosample with adjustable number of individual nanotubes or nanowires. It also allows assembly of multiple samples on one measurement stage. For multi-walled carbon nanotube bundles, we have observed a weak trend that, when the number of individual tubes in a bundle varies from ten millions to around a hundred thousand, the thermoelectric power almost remains at around 10 mu V/K. When the tube number in the bundle is further reduced, the up-limit of the thermoelectric power gradually increases to a value near 20 mu V/K.
Through nanomanipulation inside scanning electron microscope, a carbon nanotube scanning probe microscope tip was made by connecting a carbon nanotube with a silicon atomic force microscope tip. The carbon nanotube scanning probe microscope tip was then tailored to the desired length and end structure by a "nanoknife," which is a carbon nanotube adhered to a metal tip. Through mapping the same carbon nanotube on SiO(2) substrate, it was found that the lateral resolution of the carbon nanotube tips can be improved significantly through sharpening the tip ends, and the sharpened carbon nanotube tips had better performance than commercial silicon tips.
CdS nanowire (NW) ring cavities were fabricated and studied for the first time. The rings with radii from 2.1 to 5.9 mu m were fabricated by a nanoprobe system installed in a scanning electron microscope. Radius dependent whispering gallery modes (WGMs) were observed. A straight CdS NW with Fabry-Perot (F-P) cavity structure was fabricated and placed by the side of a NW ring cavity to form 6 coupled ring-F-P cavity. When the NW ring was excited by a focused laser, a bright green light spot was observed at the output end of the straight NW, indicating that the latter had served as an effect waveguide to couple the light out from the ring cavity. The corresponding light spectrum showed that the WGMs had been modulated. We confirmed that the NW F-P cavity had served as a modulator. Such a coupled cavity has potential application in a nanophotonic system.
Single-walled carbon nanotube field-effect transistors (SWCNT FETs) with multi-walled carbon nanotubes (MWCNTs) as interconnects were fabricated, and their field effect properties were measured and compared with those of the case with metal leads as interconnects. Both cases showed almost the same direct current (DC) response, while the MWCNTs interconnected case showed a little better alternating current (AC) properties. AC measurement showed that the MWCNTs interconnected SWCNT FETs worked well at frequency up to 20 MHz.
The mechanical properties of individual WS(2) nanotubes were investigated and directly related to their atomic structure details by in situ transmission electron microscope measurements. A brittle mode deformation was observed in bending tests of short (ca. 1 mu m in length) multilayer nanotubes. This mode can be related to the atomic structure of their shells. In addition, longer nanotubes (6-7 mu m in length) were deformed in situ scanning electron microscope, but no plastic deformation was detected. A "sword-in-sheath" fracture mechanism was revealed in tensile loading of a nanotube, and the sliding of inner shells inside the outermost shell was imaged "on-line". Furthermore, bending modulus of 217 GPa was obtained from measurements of the electric-field-induced resonance of these nanotubes.