1,721,196 research outputs found
Laterally driven electrostatic repulsive-force microactuators using asymmetric field distribution
No full textWe present a new electrostatic actuation method using a lateral repulsive-force induced by an asymmetric distribution of planar electrostatic field. The lateral repulsive-force has been characterized by a simple analytical equation, derived from a finite element simulation. Quality-factors are estimated from the computer simulation based on creep flow model. A set of repulsive-force polycrystalline silicon microactuators has been designed and fabricated by a four-mask surface-micromachining process. Static and dynamic response of the fabricated microactuators has been measured at the atmospheric pressure for the driving voltage range of 0-140 V. The static displacement of 1.27 Irm is obtained at the de voltage of 140 V. The resonant frequency of the repulsive-force microactuator increases from 11.7 kHz to 12.7 kHz when the de induction voltage increases from 60 V to 140 V. The measured quality-factors are increased from 12 to 13 in the voltage range of 60-140 V. Fundamental characteristics of the force, frequency and quality-factor of the electrostatic repulsive-force microactuator have been discussed and compared with those of the conventional electrostatic attractive-force microactuator
Electrostatic control of mechanical quality factors for surface-micromachined lateral resonators
No full textWe investigate a laterally driven, surface-micromachined microstructure, whose mechanical quality factor can be adjusted electrostatically after fabrication. An electrical method for the mechanical quality factor control is presented and applied for laterally driven micromechanical resonators. The present method is based on the damping-gap change caused by an electrostatic force between parallel planar microstructures. Micromechanical resonators for quality factor control tests have been designed and fabricated by a 4-mask surface-micromachining process, including the dry etching of a 6 mu m-thick LPCVD polycrystalline silicon layer. In the experimental test performed at atmospheric pressure, the quality factors of the microfabricated resonators have been reduced rapidly at the rate of 120 V-1 in the control voltage range of 1.75-2.25 V; thereby demonstrating that 50% reduction of the mechanical quality factor of a microfabricated resonator can be achieved in the control voltage range of 1.75-2.25 V with the maximum 0.8% modification of resonant frequency
A triangular electrostatic comb array for micromechanical resonant frequency tuning
No full textA new electrostatic comb structure has been presented for the post-fabrication frequency tuning of laterally driven micromechanical resonators. The frequency tuning comb structure, composed of a triangular comb array of linearly varied finger lengths, generates a linear electrostatic tuning force from the translational motion of the DC-biased comb array. Simple analytic formulae for the electrostatic tuning force, the modified stiffness, and the resonant frequency have been derived in terms of the tuning bias voltage. A set of frequency tunable microresonators has been designed and fabricated by the 4-mask surface-micromachining process. The resonant frequency of the microfabricated microresonator has been measured as 2.42 kHz at the reduced pressure of 1 Torr. The resonant frequency has been reduced by 3.3% for a tuning voltage increase of 20 V. The theoretical frequency shift, including the electrostatic levitation effect, is compared with the experimental results. The higher tuning voltage results in the lower effective stiffness, thereby decreasing resonant frequency of the microresonator. (C) 1998 Elsevier Science S.A. All rights reserved
Evidence for spin coating electrostatic self-assembly of polyelectrolytes
No full textThe influence of molecular mass on the formation of polyelectrolyte multilayers on an oppositely charged surface of a rotating substrate was explored for a combination of strong cationic and anionic polyelectrolytes, such as poly(1-(N-benzylpyridinio-2-yl)ethylene bromide) (PVP-2B) and i-carrageenan. UV/visible spectroscopy and ellipsometry measurements confirmed that the amount of material deposited on a substrate is inversely proportional to the logarithm of the molecular weight of PVP-2B at a low concentration of 1 mM in the spin-coated as well as the solution-dipped multilayer assemblies. A quantitative evaluation of the data shows that an increase of the molecular weight M-w of PVP-2B from 3.8K to 6.0M leads to 50 and 23% decreases in the average amount and thickness per bilayer deposited using the spin coating electrostatic self-assembly technique, respectively. Studies were also carried out to determine the effect of polymer concentration and spin speed on the adsorption rate of high molecular weight (HMW) and low molecular weight (LMW) polyelectrolytes. Increase of the spin speed leads to almost the same decrease in the average deposition rate of LMW and HMW polymers on a substrate. In sharp contrast, increasing the concentration of the polymer solution causes a higher increase in the average amount of the layer pair for HMW polyelectrolytes than for LMW. It was also found that there exists a critical concentration in which an equivalent amount of polymer is adsorbed on a solid substrate for two different HMW and LMW polymers; more LMW polyelectrolyte is adsorbed until a critical concentration, above which the trends are reversed. The observation would indicate the fact that the spin coating is less and less determined by the self-assembly process with increasing the concentration, causing enhanced nonspecific interactions among polymer chains. Particularly, some evidence is found for the self-assembly process that plays an essential role in the formation of polyelectrolyte multilayers on a rotating substrate.X113637sciescopu
Effect of the nitrogen partial pressure on the preferred orientation of TiN thin films
No full textX1112sciescopu
Pattern generation of cells on a polymeric surface using surface functionalization and microcontact printing
No full textDiffuse x-ray scattering study of interfacial structure of self-assembled conjugated polymers
No full textThe interfacial structures of self-assembled heterostructures through alternate deposition of conjugated and nonconjugated polymers were studied by x-ray reflectivity and nonspecular scattering. We found that the interfacial width including the effects of both interdiffusion and interfacial roughness (correlated) was mainly contributed by the latter one. The self-assembled deposition induced very small interdiffusion between layers. The lateral correlation length xi(parallel to) grew as a function of deposition time (or film thickness) described by a power law xi(parallel to)proportional tot(beta/H) and was also observed from the off-specular scattering.open112sciescopu
Diffuse x-ray reflectivity study of interface roughness in Mo/Si multilayers
No full textDiffuse x-ray reflectivity intensities mere measured to characterize interface morphologies of Mo/Si multilayers with and without interleaved carbon thin layers. Parameters related to the interface morphologies can be obtained by fitting the measured intensities within the distorted wave Born approximation in such a way that intermixing widths of graded interfaces, correlated interface roughness amplitudes and vertical correlation lengths are obtained. The interface parameters of Mo/Si and Mo/C/Si/C multilayers are compared for as-grown samples and annealed ones.110sciescopu
The structure and magnetotransport properties of (PZT,LCMO) bilayer films
No full textGrowth of bilayered thin films of ferroelectric PbZr0.52Ti0.48O3 and ferromagnetic La0.7Ca0.3MnO3 on MgO(100) substrates by the pulsed laser deposition is reported. Resistance and magnetoresistance measurements of the bilayered films were performed. The effects of ferroelectric polarization on the magnetoresistance (electromagnetotransport effect) of La0.7Ca0.3MnO3 thin films are discussed. It is seen that the electric field due to the ferroelectric polarization completely suppresses the sharp peak in magnetoresistance near the ferromagnetic transition point.112sciescopu
Fisher-Langer relation and scaling in the specific heat and resistivity of La0.7Ca0.3MnO3
No full textWe have measured the specific heat and resistivity of mixed valence manganite La0.7Ca0.3MnO3 as a function of temperature and magnetic field. We demonstrate that the magnetic contribution to the specific heat in this system is proportional to the temperature coefficient of the resistivity in the magnetic phase transition region, following the Fisher-Langer relation. We also show that the specific heat and the temperature coefficient of resistivity measured as a function of temperature at various magnetic fields can be superposed to a single curve if they are properly scaled. (C) 1998 Elsevier Science B.V. All rights reserved.116sciescopu
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