Introduction to in-situ nanomanipulation for nanomaterials engineering

Abstract

Nanomanipulation represents the logical next step in applications of electron microscopy: why simply image when one can image and manipulate in real time simultaneously with no loss of resolution? The incorporation of robotic manipulators in scanning electron microscopes (SEM) began as a way to characterize the mechanical properties of novel nanostructures [1]. However, the applications for nanomanipulators have expanded to include electrical characterization of nanostructures [2], as well as contact level integrated circuit (IC) probing, and the manipulation of virus nanoblocks [3]. The term nanomanipulator can be loosely defined as any kind of electromechanical device used for controlled placement of an end effector with better than 100 nm resolution. The restriction on the resolution of the tool arises from the industry standard length scale definition of nanotechnology: structures with one or more dimensions at sub-100 nm. Obviously, the positioning resolution of the nanomanipulator must conform to the length scales of the materials to be characterized and/or manipulated. Constructing a nanomanipulator requires conforming to several other restrictions that will be discussed later. Before the introduction of nanomanipulators, scientists were forced to resort to arduous and time-consuming techniques in order to characterize nanostructures. For example, to measure the electrical properties of a nanotube, one had to deposit nanotubes onto a surface, locate an isolated nanotube using atomic force or SEM, deposit metal contacts with lithographical techniques, and finally perform the electrical characterization using microprobes. Although this technique has produced excellent data [4], the overhead in equipment and personnel is prohibitive. The nanomanipulator operated inside an SEM allows the scientist to locate a nanostructure using SEM imaging, connect electrodes or other end effectors to it using the manipulator, and perform mechanical and/or electrical measurements all in a single experiment. Essentially, an SEM with a nanomanipulator is a direct analog of an optical light microscope with a microprober station. The SEM can image nanometer-scale structures in real time, and the vacuum pressures allow measurements to be made in a clean, dry environment. Additional advantages over previous techniques come from the ability to make dynamic measurements on nanostructures, such as measuring the electrical response of a multiwalled carbon nanotube (MWNT) to a mechanical deformation [5]. Since the end effectors serve as the electrodes, moving them to deform a nanotube does not affect the metal-nanotube contact or contact resistance. Performing similar experiments using AFM resulted in strained contacts, which obviously affect the outcome of the experiment [6]. Nanomanipulators are also compatible with focused ion beam (FIB) systems. FIB systems are used for milling sections out of semiconductor devices for failure analysis (FA). Materials and structures can be extracted with high precision using nanomanipulators for transmission electron microscopy (TEM) characterization [7]. However, they can also be used to deposit metal to modify probe tips and create electrodes on surfaces. FIB systems coupled with nanomanipulators form the tool of choice for nanotechnology applications in physical characterization of nanostructures and nanomaterials. Nanomanipulators have also been adapted for use in transmission electron microscopes. Nanostructures can be analyzed and even altered with the added functionality of manipulation systems in situ to the TEM [8,9]. TEM manipulation of multiwalled nanotubes yielded some of the first insights into the engineering of nanoelectromechanical systems (NEMS). © 2006 Springer Science+Business Media, LLC.