Liviu Nicu

Viscosity measurements based on experimental investigations of composite cantilever beam eigenfrequencies in viscous media

Experimental investigations have been conducted to study the multimode dynamic response of composite cantilever beams in various viscous media and to determine their viscosity. Theoretical eigenfrequencies are computed using the analytical model proposed by Sader [J. Appl. Phys. 84, 64 (1998)] based on the analysis of the hydrodynamic function of cantilever beams. A good agreement is found between theory and experiment for the first two resonant frequencies of composite beams operated in air and in water. The same experimental approach is used to determine the viscosity of ultrapure ethanol. Thus, it is established that Sader’s model represents an accurate alternative for the determination of liquid viscosity in small volumes (about 50 μl) which might be of great importance for microfluidics applications. Finally, the limits of the method are underlined by monitoring the dynamic response of cantilever beams in silicon oil.

Piezoelectric properties of PZT films for microcantilever

The investigation of piezoelectric properties of materials in the thin layer form has become an important task because of the increased range of their applications as actuators and sensors. The sensor magnitude, is a direct function of the e31 piezoelectric constant. Pb(Zr,Ti)O3 thin films and the modified compositions have attracted great attention in recent years as promising for use in microelectromechanical systems. To determine this constant we use an unusual experimental method. A remanent piezoelectric constant of −4.7 C/m2 was obtained. The parameters as, coercive field, saturation field, curve of first polarization, and self polarization of the remanent piezoelectric hysteresis loop are presented for 1.6 μm thick PZT thin film. We will associate also dielectric results. To show the possible integration of the piezoelectric films in microelectromechanical systems, we have deposited PZT thin film on a 100 μm long, 20 μm wide, 1 μm thick silicon oxide beam to control the z actuation.

Biosensors and tools for surface functionalization from the macro- to the nanoscale: The way forward

Most of review articles or even books dedicated to biosensing issues are organized by the generally admitted scheme of a biosensor. Subsequently, biological receptors, modified surfaces (and ways to specifically modify those surfaces using established biological and/or chemical recipes), and transduction techniques are thoroughly addressed in this precise order. In this review, we deliberately decided to break the conventional way of providing biosensing review by uniquely addressing biomolecules’ immobilization methods onto a solid surface and biosensing-related transduction techniques. The aim of this review is to provide a contemporary snapshot of the biosensing landscape without neglecting the seminal references or products where needed. The main guiding line of the review is the downscaling (from the macro- to the nanoscale) of biosensors and their respective most known applications. To conclude, a brief overview of the most popularized nanodevices applied to biology is given before attempting to com...

Rheological behavior probed by vibrating microcantilevers

The aim of this paper is to demonstrate that vibrating microcantilevers can be used to quantify fluid properties such as density and viscosity. Contrary to classical rheological measurements using microcantilevers, the development of the proposed microrheometer is based on the measurement of fluid properties over a range of vibration frequencies, without necessarily being restricted to resonant phenomena. To this end, an analytical model is implemented and, when combined with measurements, allows the determination of the viscosity as a function of frequency. The preliminary results are encouraging for the development of a useful microrheometer on a silicon chip for microfluidic applications.

The Microcantilever: A Versatile Tool for Measuring the Rheological Properties of Complex Fluids

Silicon microcantilevers can be used to measure the rheological properties of complex fluids. In this paper two different methods will be presented. In the first method the microcantilever is used to measure the hydrodynamic force exerted by a confined fluid on a sphere that is attached to the microcantilever. In the second method the measurement of the microcantilever’s dynamic spectrum is used to extract the hydrodynamic force exerted by the surrounding fluid on the microcantilever. The originality of the proposed methods lies in the fact that not only may the viscosity of the fluid be measured but also the fluid’s viscoelasticity, i.e., both viscous and elastic properties, which are key parameters in the case of complex fluids. In both methods the use of analytical equations permits the fluid’s complex shear modulus to be extracted and expressed as a function of shear stress and/or frequency.

Individual Blood‐Cell Capture and 2D Organization on Microarrays

The image shows living B lymphocytes captured on a microcantilever-arrayed biochip. Antibodies targeting cellular antigens are pyrrole-modified and then electropolymerized into polypyrrole films on a gold surface. The arrayed feature size is close to a lymphocyte size and thus allows efficient cell capture and organization. Gold layers can thus be arrayed in a predetermined manner that gives access to organized blood cells on surfaces. Each line is separated from the other by 50 µm.

Large‐Scale Assembly of Single Nanowires through Capillary‐Assisted Dielectrophoresis

An innovative technique is proposed for the precise and scalable placement of 1D nanostructures in an affordable manner. This approach combines the dielectrophoresis phenomenon and capillary assembly to successfully align thousands of single nanowires at specific locations at the wafer. The nanowires are selectively trapped by taking advantage of the material--specific frequence dependence.

Current Switching Coupled to Molecular Spin-States in Large-Area Junctions

The fabrication of large-area vertical junctions with a molecular spin-crossover complex displaying concerted changes of spin degrees of freedom and charge-transport properties is reported. Fabricated devices allow spin-state switching in the spin-crossover layer to be triggered and probed by optical means, while detecting associated changes in electrical resistance in the junctions.

Determination of the d31 piezoelectric coefficient of PbZrxTi1−xO3 thin films using multilayer buckled micromembranes

The aim of this paper consists in the determination of the piezoelectric transverse coefficient d31 of PbZrxTi1−xO3 (PZT) thin films integrated in dedicated multilayer silicon-based micromembranes exhibiting an initial buckled profile. An analytical model specific to this configuration was built and used for the calculation of d31 starting with the static profiles of the microfabricated devices determined by means of a double-beam interferometer. The influence of dc voltage and buckling effects on the d31 piezoelectric coefficient at the microscale were investigated, and high values were obtained, from 30to75pm∕V, within a hysteresyslike cycle. These results demonstrated the good electrical behavior of PZT thin films at the microscale with a low influence of buckling effects and determined optimal operation conditions for high values of d31.

Energy study of buckled micromachined beams for thin-film stress measurements applied to SiO2

Measurements of maximal deflection amplitude were carried out on arrays of clamped-clamped SiO2 microfabricated beams buckling under the effect of thin-film built-in compressive stress. The experimental deflection determination of these deflections yields the residual stress value in the SiO2 film. This proposal is confirmed by appropriate theory that considers the issue of microfabricated beam buckling from an energy point of view. In this model, the total potential energy stored in a buckled microbeam is computed and the residual stress value is given by considering the measured buckling maximal deflection and by making approximations about the shape of the microbeam deflection curve. The SiO2 film residual stress evaluated with the help of the energy method is in good agreement with values reported in the literature.