Grinding a Nanotube

Abstract

Field evaporation phenomena, the removal of atoms from positively charged surfaces at strong field of tens of volts per nanometer, are of tremendous scientific and technological importance. The technique of field-ion microscopy (FIM) has been developed based on this phenomenon, and is historically the first technique to have achieved atomic resolution. [1,2] The atom probe, a variation of FIM, came later and is generally used to identify the species of atoms that are being individually evaporated from the surface of a FIM tip. [2] Recently, atom-probe tomography (APT) [3,4] has been developed as a powerful analytical characterization technique that ties compositional information to structure. This is the only approach that is capable of determining the 3D location and elemental identity of atoms in a sample with near atomic precision. In principle, the field evaporation phenomenon can be utilized not only for materials characterization, but also for materials processing and morphology control with extremely high precision because of its unique atom-by-atom removal capability. However, FIM and atom probe investigations only provide access to structural information on the tip surface or the evaporated segments of the specimen, and it is not possible to directly observe the structural evolution of the sample. This limitation has greatly restricted the potential applications of field evaporation as a materials-processing tool.Here, we have investigated the positive field evaporation of nanomaterials by transmission electron microscopy (TEM). Direct TEM observations of the details of the structural evolution during field evaporation have been obtained for the first time. In previous work, the shortening of individual positively biased carbon nanotubes (CNTs) has been observed by scanning electron microscopy (SEM), [5] but the observed phenomenon may perhaps arise from the electron ablation effect because of electrons emitted from the counter CNT electrodes. Detailed information about the end caps of CNTs is difficult to obtain because of the limited spatial resolution of SEM. On the other hand, structural changes in individualCNTs have also been observed in previous in situ field-emission measurements. [6][7][8][9][10][11][12] However, it is likely that the observed structural changes do not arise from "pure" field evaporation phenomena. The reason for this is that when CNTs are negatively charged, the large field-emission current can induce very irregular tip structures and can even damage the emitters. In contrast, as will be demonstrated here, positive field evaporation is much more controllable. Indeed, we demonstrate that positive field evaporation in combination with in situ TEM may actually provide a very simple and effective means for controlling the morphology of nanomaterials with atomic precision. All the in situ experiments have been carried out using a 200 kV Tecnai G20 transmission electron microscope with a vacuum level of about 1×10 -5 Pa. The manipulations and measurements have been made using a Nanof...

Electrical Characteristics of a Carbon Nanotube-Functionalized Probe for Kelvin Probe Force Microscopy

“…21,22 As suggested in previous studies, the end of a CNT subjected to an electrical field of a few tens V nm −1 could undergo a structural evolution via positive field evaporation. 23 Meanwhile, the contaminants at the CNT apex can also be removed efficiently by this method (See Figure S2). 24 After this treatment, the resulting CNT tip usually exhibited consistent performance in the following experiment of imaging and work function measurements (See Supporting Information for details).…”

In Situ TEM of Carbon Nanotubes

“…The possibility of using the fi eld emission process to controllably modify the freestanding tip of a CNT was again picked up in 2008 [ 71 ]. Previously, sharpening of the CNT had been reported but this required direct contact of the tip to another CNT [ 63 ].…”

Combining Scanning Probe Microscopy and Transmission Electron Microscopy

“…Sveningsson et al [5] measured the electron emission from carbon nanotubes and observed that for low currents the emission was of a standard Fowler-Nordheim type, while for higher emission currents a nonlinear behavior occurred due to thermally enhanced emission caused by Joule heating of the carbon nanotube. A detailed study of the correlation of the structure of carbon nanotubes and electron emission as well as the structural change during emission was done by Wang et al [55]. An interesting combination of the resonance method to determine the work function [56,57] and field emission was done by Xu et al [58].…”