ABSTRACT
Carbon nanotubes (CNTs) can be used as atomic force microscopy (AFM) tips for high-resolution scanning due to their small diameter, high aspect ratio and outstanding wear resistance. However, previous approaches for fabricating CNT probes are complex and poorly controlled. In this paper, we introduce a simple method to selectively fabricate a single CNT on an AFM tip by controlling the trigger threshold to adjust the amount of growth solution attached to the tip. The yield rate is over 93%. The resulting CNT probes are suitable in length, without the need for a subsequent cutting process. We used the CNT probe to scan the complex nanostructure with a high aspect ratio, thereby solving the long-lasting problem of mapping complex nanostructures.
ABSTRACT
Carbon nanotube (CNT) probes are used in atomic force microscopes (AFMs) for high-resolution imaging, especially in the measurement of high aspect ratio micro/nano structures. Due to the use of a longer CNT tip leading to the degradation of image resolution, researchers have used several methods to cut CNTs. However, the principle of the selection of the cutting length has hardly been reported. Moreover, the influence of the effect of size on the mechanical properties of a CNT tip is not fully understood. In this study, an accurate model of finite element simulations is constructed on the basis of scanning electron microscopy data to investigate the mechanical properties of a CNT probe. An elastic model is employed to study the factors that influence the critical buckling force at the CNT tip during the measurement process. The calculation shows that the mechanical stiffness of the probe is affected by the diameter and the length-to-diameter ratio of the CNT tip. The changes in the von Mises stress at the bond between the AFM probe and the CNT tip as well as the variation of the strain energy at the CNT tip are discussed. It is hoped that this study will provide guidance for the selection of the cutting length of CNT-AFM probes and propose a basis for probe selection and design in practical measurements.
ABSTRACT
Nanowires have been widely studied due to their outstanding mechanical and electrical properties; however, their practical applications are limited to the lack of an effective technique for controlled assembly. In the present work, zinc oxide (ZnO) nanowire arrays were assembled via a combing process using a makeup brush and the nanodevice was fabricated. The current–voltage (I–V) and ultraviolet (UV) characteristics of the device indicate stable and repeatable electrical properties. The carbon monoxide (CO) sensing properties were tested at operating temperatures of 200, 300 and 400 °C. It was found that ZnO based sensor exhibited the highest sensitivity to CO at 300 °C due to the change of dominant oxygen species. Comparing with others result, the sensitivity of the fabricated sensor exhibits higher sensing performance. The sensing mechanism of the CO sensor is also discussed.
