A Course in Micro- and Nanoscale Mechanics

At small scales, mechanics enters a new regime where the role of surfaces, interfaces, defects, material property variations, and quantum effects play more dominant roles. A new course in nanoscale mechanics for engineering students was recently taught at the University of Wisconsin - Madison. This course provided an introduction to nanoscale engineering with a direct focus on the critical role that mechanics needs to play in this developing area. The limits of continuum mechanics were presented as well as newly developed mechanics theories and experiments tailored to study and describe micro- and nano-scale phenomena. Numerous demonstrations and experiments were used throughout the course, including synthesis and fabrication techniques for creating nanostructured materials, bubble raft models to demonstrate size scale effects in thin film structures, and a laboratory project to construct a nanofilter device. A primary focus of this paper is the laboratory content of this course, which includes an integrated series of laboratory modules utilizing atomic force microscopy, self-assembled monolayer deposition, and microfluidic technology

Who Wants to be an Engineer? - Or Better Teaching Through Game Shows

A 50 (or 60 or 70) -minute lecture is inherently incompatible with the typical attention spans of students. The author has developed a teaching technique that successfully re-captures attention in the classroom. The technique, loosely based on a popular prime-time game show, consists of quizzing a student on the spot while allowing a life-line of polling the audience for help. The game is enjoyable for students and professor alike, but also allows review, clarification, and reinforcement of concepts. The technique is effective while only requiring minimal preparation and lecture time to be implemented

Directional shear force microscopy

We describe a technique, based on shear force microscopy, that allows one to detect shear forces in a chosen direction at the nanometer scale. The lateral direction of an oscillating probe tip is determined by selecting which of the four quadrants are excited on the piezo driver. The shear forces depend directly on this lateral direction if structural anisotropies are present, as confirmed with polydiacetylene monolayers. (C) 2001 American Institute of Physics

Negative stiffness and enhanced damping of individual multiwalled carbon nanotubes

The mechanical instabilities and viscoelastic response of individual multiwalled carbon nanotubes and nanofibers (MWCNTs/Fs) under uniaxial compression are studied with atomic force microscopy. Specific buckling events are evident by regimes of negative stiffness, i.e., marked drops in force with increasing compression. Uniaxial cyclic loading can be repeatedly executed even in initially postbuckled regimes, where the CNTs/Fs display incremental negative stiffness. Increases in mechanical damping of 145–600 % in these initially postbuckled regimes, as compared to the linear prebuckled regimes, are observed. Increased damping is attributed to frictional energy dissipation of walls in buckled configurations of the MWCNTs/Fs. This represents the extension of the concept of negative stiffness to the scale of nanostructures and opens up possibilities for designing nanocomposites with high stiffness and high damping simultaneously

Calibration of frictional forces in atomic force microscopy

The atomic force microscope can provide information on the atomic-level frictional properties of surfaces, but reproducible quantitative measurements are difficult to obtain. Parameters that are either unknown or difficult to precisely measure include the normal and lateral cantilever force constants (particularly with microfabricated cantilevers), the tip height, the deflection sensor response, and the tip structure and composition at the tip-surface contact. We present an in situ experimental procedure to determine the response of a cantilever to lateral forces in terms of its normal force response. This procedure is quite general. It will work with any type of deflection sensor and does not require the knowledge or direct measurement of the lever dimensions or the tip height. In addition, the shape of the tip apex can be determined. We also discuss a number of specific issues related to force and friction measurements using optical lever deflection sensing. We present experimental results on the lateral force response of commercially available V-shaped cantilevers. Our results are consistent with estimates of lever mechanical properties using continuum elasticity theory

Lateral stiffness: A new nanomechanical measurement for the determination of shear strengths with friction force microscopy

We present a technique to measure the lateral stiffness of the nanometer-sized contact formed between a friction force microscope tip and a sample surface. Since the lateral stiffness of an elastic contact is proportional to the contact radius, this measurement can be used to study the relationship between friction, load, and contact area. As an example, we measure the lateral stiffness of the contact between a silicon nitride tip and muscovite mica in a humid atmosphere (55% relative humidity) as a function of load. Comparison with friction measurements confirms that friction is proportional to contact area and allows determination of the shear strength

Atomic Friction Studied by Modeling the Buried Inteface

Molecular dynamics simulation is carried out to model the single-asperity friction in atomic force microscope experiments. Superlubricity is achieved through misalignment between the AFM tip and substrate. Direct observation of the buried interface reveals that incommensurability-induced inhomogeneous shear stress can cause ultra-low atomic scale friction

Friction and Molecular Deformation in the Tensile Regime

Recent molecular level studies of energy dissipation in sliding friction have suggested a contribution from adhesive forces. In order to observe this directly, we have constructed a scanning force microscope with decoupled lateral and normal force sensors to simultaneously observe the onset of both friction and attractive forces. Measurements made on self-assembling alkanethiol films with chemically different tail groups show that friction can increase with stronger adhesive intermolecular forces and from the associated tensile deformation and collective motion of the thiol chains

Imaging and manipulation of nanometer-size liquid droplets by scanning polarization force microscopy

Using atomic force microscopy in noncontact mode, we have imaged nanometer-size liquid droplets of KOH water solutions on the surfaces of highly oriented pyrolitic graphite and mica. On graphite the droplets prefer to be adsorbed on atomic step edges. Droplets on the same step tend to be evenly spaced and of similar size. The droplets can be manipulated by the atomic force microscopy tip allowing the controllable formation of droplet patterns on the surface