Lateral Cantilever Research Articles

Cantilever tip-surface contact as a catastrophe machine

The contact of a cantilever tip with a sample surface in a scanning-probe microscopy is considered for the first time as a catastrophe machine. Using an approach of the catastrophe theory, behavior of the tip-surface system is analyzed depending on the internal parameters (stiffness and coordinates of the cantilever holder). The tip jumps and the adhesion force variations in the course of the vertical and lateral cantilever motions are calculated. Projections of the equilibrium surface are constructed and the regimes are established that eliminate the “jumps to contact” and “ microslips.” A new method for the surface vacancy diagnostics and a new algorithm for the controlled tip approach to the surface are proposed.

Fabrication and characterization of nanoresonating devices for mass detection

We report on a novel fabrication process and preliminary characterization of a nanomechanical resonating device, which is to be used for mass detection. The fabrication of the device is based on laser lithography on Al coated SiO2/p++Si/SiO2/Si structures, followed by dry and wet etching. We have fabricated highly doped polysilicon free-hanging cantilevers and anchored drivers for lateral cantilever vibration, where the motion of the cantilever is parallel to the substrate. The cantilevers are actuated electrically by applying an ac voltage between the cantilever and driver. The laterally vibrating cantilever structures are approximately 30–50 μm in length, 1.8 μm in height, and 500 nm in width. The characterization of the resonators was performed by direct observation of the cantilever through an optical microscope. An electrical measuring technique is also presented and discussed. Typical values of resonant frequency and quality factor, at 1 atm, are approximately 500 kHz and 50, respectively. Moreover, a dependence of the resonant frequency on the applied dc voltage between the cantilever and driver has been found.

Tribological Properties of Iron Powder Subjected to Various Surface Treatments

The role of organic additives in dry pressing of metallic powders can be studied with the atomic force microscope (AFM) in terms of interaction forces, friction forces and shearing behavior. Material dependent properties in contact can be determined with the appropriate calibration of instrument sensitivities and spring constants. Force-distance curves give information about particle-particle interactions; measurement of static and dynamic friction provide additional information directly related to surface deformation. We present a fast and simple method for calibration of lateral cantilever deflection, independent of experimental setup. Experimental results on iron surfaces in contact show how adsorption of 12-hydroxy stearic acid yields different contact behaviour than commercial lubricants. This information also explains the hysteresis in friction-load experiments which can not be obtained from normal force curves or standard friction measurements alone.

Combined Scanning Force Microscopy and Electrochemical Quartz Microbalance in-Situ Investigation of Specific Adsorption and Phase Change Processes at the Silver/Halogenide Interface

Specific adsorption of halogenides and silver halogenide phase formation was investigated by the combination of electrochemical quartz microbalance measurements (EQMB), topographical in-situ scanning force microscopy (SFM), and in-situ lateral force microscopy (LFM). In-situ LFM can be employed to monitor specific adsorption and, more generally, chemical conversion reactions in submonolayers of atomic species which are inaccessible to topological imaging by SFM. Reorganization of the electrochemical double layer during specific adsorption caused nanotribological changes. Hydrated anions in the outer Helmholtz plain are not locally bonded to a specific site and give low LFM friction values. Specifically adsorbed anions and ion pairs, on the other hand, impede the lateral cantilever translation, resulting in increased friction. EQMB measurements yielded data corresponding to the formation of up to one monolayer of specifically adsorbed cation−halogenide ion pairs. Anodic dissolution of silver to AgO- and th...

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 forces during atomic force microscopy of graphite in air

Highly oriented pyrolytic graphite and boronated pyrolytic graphite were imaged in air by simultaneous normal and lateral force microscopy. A number of effects occurred when scanning over steps, including an increase in attractive forces from surface contamination which could be detrimental to the imaging of soft or weakly bonded samples. Contamination may also give rise to regions of high lateral force which do not seem to be associated with any topographic features. Finally, in atomic resolution images of graphite, atomic corrugation was clearer in the lateral cantilever deflection images than in the simultaneous topography and normal cantilever deflection images, demonstrating the high sensitivity of lateral force detection to topographic features.

Torsion of Box Girders with Deformable Cross Sections

This paper studies thin‐walled trapezoidal cross‐section beams with lateral cantilevers subjected to a torsional load, considering the distortion of the cross section. Transverse and longitudinal displacements of the walls are governed by six shape functions, which describe bending in the horizontal plane, as well as torsion and distortion of the cross section; the shearing strain in the middle plane of the walls is considered; the shear center is not used. The theorem of minimum total potential energy is used to derive the governing equilibrium equations (and boundary conditions), whose solution is given in closed form. A wide set of constraints is studied (rigid or flexible transverse diaphragms, mixed kinematic and static boundary conditions), from a theoretical point of view and in numerical examples. The following results were obtained: (1) Torsion and distortion are a pair of coupled problems: distortion and warping stresses are always present; in particular, the longitudinal stress at the side cant...

Biomechanical analysis of internal fixation techniques for proximal interphalangeal joint arthrodesis

Although numerous fixation techniques have been developed for performing small joint arthrodesis, no previous study of the biomechanical properties of these constructs has been published. The strength of specimens of arthrodesis of the proximal interphalangeal joint performed with cadaver material was determined for three-point anteroposterior bending, axial torsion, and lateral cantilever bending stress. Crossed Kirschner wires, intraosseous wiring, and figure of eight tension-band wiring were studied. Figure of eight tension-band wiring demonstrates superior strength in anteroposterior bending and torsion. For lateral bending stress, no significant difference exists among the techniques studied.

Nonuniform Bending‐Stress Distribution (Shear Lag)

Nonuniform normal longitudinal stress distribution in a trapezoidal box beam with lateral cantilever is discussed. The problem is solved by the variational method assuming as unknown the displacement of the beam axis and three functions which describe the warping of the horizontal flanges; the unknowns are reduced in case of vertical walls. The state of stress of stress in each structural element is analyzed and an example is given to illustrate the results.

On the effect of shear center location on the values of axial and lateral cantilever buckling loads for singly symmetric cross-section beams

A generalization of Kirchhoff's beam equations, in which account is taken of deformations due to cross sectionalforces, in addition to those due to cross-sectionalmoments, is used to obtain results on the effect of cross-sectional shear center location on the values of Euler and Michell-Prandtl buckling loads. The analysis of these problems appears to be outside the scope of the original Kirchhoff equations.

The influence of axial load on eigen-frequencies of a vibrating lateral restraint cantilever

The solution for frequencies of transverse oscillations of a vertical cantilever with continuous lateral restraints under uniformly distributed gravity load is developed. The solution includes the influence of axial load, while the dynamic equilibrium is established for the deflected form of the cantilever. The restraining media is distributed along the centroidal axis and the shear forces are assumed to be proportional to the respective derivative.