Dariusz M. Jarząbek

Precise and direct method for the measurement of the torsion spring constant of the atomic force microscopy cantilevers

A direct method for the evaluation of the torsional spring constants of the atomic force microscope cantilevers is presented in this paper. The method uses a nanoindenter to apply forces at the long axis of the cantilever and in the certain distance from it. The torque vs torsion relation is then evaluated by the comparison of the results of the indentations experiments at different positions on the cantilever. Next, this relation is used for the precise determination of the torsional spring constant of the cantilever. The statistical analysis shows that the standard deviation of the calibration measurements is equal to approximately 1%. Furthermore, a simple method for calibration of the photodetectors lateral response is proposed. The overall procedure of the lateral calibration constant determination has the accuracy approximately equal to 10%.

Method for lateral force calibration in atomic force microscope using MEMS microforce sensor

In this paper we present a simple and direct method for the lateral force calibration constant determination. Our procedure does not require any knowledge about material or geometrical parameters of an investigated cantilever. We apply a commercially available microforce sensor with advanced electronics for direct measurement of the friction force applied by the cantilevers tip to a flat surface of the microforce sensor measuring beam. Due to the third law of dynamics, the friction force of the equal value tilts the AFM cantilever. Therefore, torsional (lateral force) signal is compared with the signal from the microforce sensor and the lateral force calibration constant is determined. The method is easy to perform and could be widely used for the lateral force calibration constant determination in many types of atomic force microscopes.

The Influence of Alkali Metal Chloride Treatments on the Wear Resistance of Silicon Surfaces for Possible Use in MEMS

ABSTRACT The wear of contacting silicon surfaces in microelectromechanical systems (MEMS) has been a longstanding concern. To address this issue, the effects of immersing silicon surfaces into alkali metal chloride solutions (LiCl, NaCl, CsCl) on their sliding friction and wear were investigated. A custom-built reciprocating tribometer was used with a sapphire ball as the counterbody. Results indicated that the friction coefficient between the silicon surface (p-doped, orientation (100)) and a sapphire ball can be reduced by up to 30% by treating the silicon surfaces in aqueous salt solutions (concentration 1 mol/L, exposure for 24 h). These modified surfaces also have higher wear resistance and a significant change in wettability. After immersion, the contact angle between the silicon surface and water was reduced by approximately 50%. These results may lead to new, simple, and inexpensive methods to increase the wear resistance of silicon surfaces for use in MEMs devices.

Piezoelectric bimorph as a high-sensitivity viscosity resonant sensor to test the anisotropy of magnetorheological fluid

In this paper, we present a device which is very sensitive for small changes in the viscosity of the investigated fluid. The main part of the device is a piezo-electric bimorph which consists of the brass shim with two piezo-ceramic layers on the opposite sides. One of them is responsible for generating vibrations, whereas the second one is meant to measure system response which is produced by the damping properties of the surrounding fluid. During the experiment, the cylindrical bar is forced to move by the series of sinusoidal waves with different frequencies and at constant amplitudes. The probe is immersed in the fluid and then the amplitude vs frequency and phase vs frequency curves are obtained. Next, one can determine the viscosity according to a proper mathematical model. The resonant frequency is related to the damping coefficient which depends on the viscosity of the surrender fluid and immersion depth of the probe. The coefficients necessary for calculating viscosity are obtained by fitting the resonance curve to the amplitude vs frequency data obtained from the experiment. The device has been applied to study the anisotropy of magnetorheological fluids. The weak anisotropy of viscosity has been observed. The highest value of viscosity was observed in the case of viscosity measurement in the direction orthogonal to the magnetic field and the lowest in the direction parallel to the magnetic field.

Surface mechanical properties

Surface mechanical properties play an essential role in the development of nanotechnology and novel materials, i.e., biocomposites. Hence, in this chapter the methods for determination of hardness, Youngs modulus, adhesion, friction, and wear at the micro and nanoscale are described. Firstly, the methods with use of atomic force microscope (AFM) are shown. Force-distance curves made by AFM can be used for determination of adhesion force and Youngs modulus of soft materials, i.e., polymers. AFM is also necessary in nanotribology. It is possible to measure friction coefficients with the use of so-called friction loops. However, in order to achieve proper results one should apply precise methods for AFM calibration which are also provided in the chapter. Furthermore, the instrumented nanoindentation is described. Similarly to the classical indentation an indenter, usually a diamond tip of known geometry, is pressed into the test surface. From the drawing of a loading and unloading curve of the applied load as a function of the penetration depth one can determine Youngs modulus and hardness of an investigated surface. This technique is usually used for metals and ceramics. In this chapter, the most popular method of analyzing the results of nanoindentation—Oliver and Pharr method—is described. Finally, some modern aspects of nanoindentation are discussed: indentation size effects and mechanical dynamic analysis.