Mark C. Strus

Imaging artefacts in atomic force microscopy with carbon nanotube tips

Dynamic atomic force microscopy (dynamic AFM) with carbon nanotube tips has been suggested as an enabling tool for high precision nanometrology of critical dimension features of semiconductor surfaces. We investigate the performance of oscillating AFM microcantilevers with multi-walled carbon nanotube (multi-walled CNT) tips interacting with high aspect ratio structures while in the attractive regime of dynamic AFM. We present experimental results on SiO2 gratings and tungsten nanorods, which show two distinct imaging artefacts, namely the formation of divots and large ringing artefacts that are inherent to CNT AFM probe operation. Through meticulous adjustment of operating parameters, the connection of these artefacts to CNT bending, adhesion, and stiction is described qualitatively and explained.

Strain energy and lateral friction force distributions of carbon nanotubes manipulated into shapes by atomic force microscopy

The interplay between local mechanical strain energy and lateral frictional forces determines the shape of carbon nanotubes on substrates. In turn, because of its nanometer-size diameter, the shape of a carbon nanotube strongly influences its local electronic, chemical, and mechanical properties. Few, if any, methods exist for resolving the strain energy and static frictional forces along the length of a deformed nanotube supported on a substrate. We present a method using nonlinear elastic rod theory in which we compute the flexural strain energy and static frictional forces along the length of single walled carbon nanotubes (SWCNTs) manipulated into various shapes on a clean SiO(2) substrate. Using only high resolution atomic force microscopy images of curved single walled nanotubes, we estimate flexural strain energy distributions on the order of attojoules per nanometer and the static frictional forces between a SWCNT and SiO(2) surface to be a minimum of 230 pN nm(-1).

Nanomechanical Peeling of Carbon Nanotubes and Nanocoils Studied Using the Atomic Force Microscope

The physics of adhesion of one-dimensional nanostructures such as nanotubes, nanocoils, and nanowires is of great interest to the functioning and reliability of nanoelectronic devices and the development of high-strength, lightweight nanocomposites. Here, we extend previous work using the Atomic Force Microscope (AFM) to investigate quantitatively the physics of nanomechanical peeling of carbon nanotubes (CNTs) and nanocoils on different substrates. We summarize previous modeling results which predict that an initially straight nanotube peeled from a surface may transition suddenly between different geometric configurations with vastly different interfacial energies. In contrast, nanocoils display a sawtooth peeling force curve indicating the sequential release of discrete pinning points. We resolve differences in nanotube peeling energies at attoJoule levels on different materials, thus opening up the possibility of sensitive screening of fiber coatings or material surfaces for improved adhesion in nanocomposites.© 2008 ASME

Nanomechanics of Peeling Studied Using the Atomic Force Microscope

Through adaptation of an atomic force microscope, we have developed a peel test at the micro- and nanoscale level that has the capability of investigating how long flexible nanotubes, nanowires, nanofibers, proteins, and DNA adhere to various substrates. This novel atomic force microscopy (AFM) peeling mode extends existing AFM “pushing” and “pulling” force spectroscopies by offering practical knowledge about the complex interplay of nonlinear flexure, friction, and adhesion when one peels a long flexible molecule or nanostructure off a substrate. The static force peeling spectroscopies of straight multiwalled carbon nanotubes suggest that a significant amount of the total peeling energy is channeled into nanotube flexure. Meanwhile dynamic force spectroscopies offer invaluable information about the dissipative physical processes involved in opening and closing a small “crack” between the nanotube and substrate.