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The interaction between a semi-infinite crack and a screw dislocation under antiplane mechanical and in-plane electrical loading in a linear piezoelectric material is studied in the framework of linear elasticity theory. A straight dislocation with the Burgers vector normal to the isotropic basal plane near a semi-infinite crack tip is considered. In addition to having a discontinuous electric potential across the slip plane, the dislocation is subjected to a line-force and a line-charge at the core. The explicit solution for the model is derived by means of complex variable and conformal mapping methods. The classical 1/[square root of r] singularity is observed for the stress, electric displacement, and electric field at the crack tip. The force on a screw dislocation due to the existence of a semi-infinite crack subjected to external electromechanical loads is calculated. Also, the effect of the screw dislocation with the line-force and line-charge at the core on the crack-tip fields is observed through the field intensity factors and the crack extension force. [S0021-8936(00)01501-4]

The contrast mechanisms of domain imaging experiments assisted by atomic force microscope (AFM) have been investigated by model experiments on nonpiezoelectric (silicon oxide) and piezoelectric [Pb(Zr,Ti)O[sub 3]] thin films. The first step was to identify the electrostatic charge effects between the tip, the cantilever, and the sample surface. The second step was to explore the tip-sample piezoelectric force interaction. The static deflection of the cantilever was measured as a function of dc bias voltage (V[sub dc]) applied to the bottom electrode (n-type Si wafers) for noncontact and contact modes. In addition, a small ac voltage (V[sub ac] sin ωt) was applied to the tip to measure the amplitude (A[sub ω]) and phase (Φ[sub ω]) of the first harmonic (ω) signal as a function of V[sub dc]. By changing from the noncontact to the contact mode, a repulsive contribution to the static deflection was found in addition to the attractive one and a 180° phase shift in Φ[sub ω] was observed. These results imply that in the contact mode the cantilever buckling is induced by the capacitive force between the cantilever and the sample surface. This interaction adds to the tip-sample piezoelectric interaction thereby overlapping the obtained tip vibration signal. Therefore, the antiparallel ferroelectric domain images obtained at zero dc bias voltage will show a variation in A[sub ω] but a negligible one in Φ[sub ω]. The capacitive force contribution to the tip vibration signal was further verified in piezoelectric hysteresis loop measurement assisted by the AFM. The observed vertical offset of the loops was explained by the contact potential difference between the cantilever and the bottom electrode. The shape of the curve could be explained by the capacitive force interaction combined with the tip-sample piezoelectric interaction. The experimental results obtained in this study support the interpretation of the ... [ABSTRACT FROM AUTHOR]

In this study, we explored magnetic nanoparticles translocating through a nanopore in the presence of an inhomogeneous magnetic field. By detecting the ionic current blockade signals with a silicon nitride nanopore, we found that the translocation velocity that is driven by magnetic and hydrodynamic forces on a single magnetic nanoparticle can be accurately determined and is linearly proportional to the magnetization of the magnetic nanoparticle. Thus, we obtained the magneto-susceptibility of an individual nanoparticle and the average susceptibility over one hundred particles within a few minutes. [ABSTRACT FROM AUTHOR]

The structures used in microelectromechanical system (MEMS) such as sensors and actuators have been miniaturized, and the use of macroinstruments in testing mechanical properties has become limited by the physical size of the materials involved. We propose an electrostatically actuated test device for measuring the elastic and yield properties of Al thin films for MEMS applications. The test device we have designed consists of electrostatically actuated micrometer-sized comb drives for loading a suspended beam. The device was fabricated by surface micromachining. On the basis of the test device, the elastic modulus is determined by analyzing the initial linear load–displacement behavior of the suspended beam, and the yield strength is determined as the deviation from linear elastic behavior. [Copyright &y& Elsevier]

We have characterized the immobilization of thiol-modified oligomers on Au surfaces and subsequent hybridization with a perfectly matched or single-base mismatched target using a quartz crystal microbalance (QCM) and fluorescence spectroscopy. The surface density of immobilized probe molecules and the hybridization efficiency depending on the type of buffer and salt concentration were investigated. We observed some ambiguities in surface coverage deduced from QCM measurement and adopted a complementary fluorescence displacement method. Direct comparison of surface coverage deduced from frequency change in QCM measurement and determined by the fluorescence exchange reaction revealed that QCM results are highly overestimated and the amount of overestimation strongly depends on the type of buffer and the structure of the film. Discrimination capability of the surface attached 15-mer probe was also examined using a single-base mismatched target at various hybridization temperatures. Hybridization efficiency depending on the type of single base mismatch was investigated using surface plasmon resonance (SPR). [Copyright &y& Elsevier]

In this study, we explored magnetic nanoparticles translocating through a nanopore in the presence of an inhomogeneous magnetic field. By detecting the ionic current blockade signals with a silicon nitride nanopore, we found that the translocation velocity that is driven by magnetic and hydrodynamic forces on a single magnetic nanoparticle can be accurately determined and is linearly proportional to the magnetization of the magnetic nanoparticle. Thus, we obtained the magneto-susceptibility of an individual nanoparticle and the average susceptibility over one hundred particles within a few minutes.