Narrow Results

We review the results of our current research on quantum engineering which include the theory, modeling and simulations of quantum devices for potential applications to threat reduction and homeland security. In particular, we discuss: (i) scalable solid-state quantum computation with qubits based on (a) nuclear spins of impurity atoms in solids, (b) superconducting junctions, and (c) unpaired electron spins of spin radicals in self-assembled organic materials; (ii) quantum neural devices; (iii) quantum annealing; (iv) novel magnetic memory devices based on magnetic tunneling junctions with large tunneling magnetoresistance; (v) terahertz detectors based on microcantilever as a light pressure sensor; (vi) BEC based interferometers; (vii) quantum microscopes with a single-spin resolution based on (a) a magnetic resonant force microscopy and (b) an optically detected magnetic resonance; and (viii) novel approach for suppression of fluctuations in free space high-speed optical communication. Finally, we describe the similarities between the behavior of cross sections in reactions with heavy nuclei in the regions of strongly overlapped resonances and electron conductivity in semiconductor heterostructures.

A feasibility study was done on a novel concept to design and develop a low-cost disdrometer and wind turbulence hybrid sensor in a single device. It employs the principles of electromagnetic induction and response of a cantilever to impulses. Based on these principles, a device was designed and fabricated to detect the rain droplet size and wind turbulence. It was fabricated from readily available materials. The testing of the device in laboratory conditions yielded satisfactory results as compared to the standard commercial instruments.

Modeling and analysis of a MEMS piezoelectric (PZT-Lead Zirconate Titanate) unimorph cantilever with different substrates are presented in this paper. Stainless steel and Silicon $〈110〉$ are considered as substrate. The design is intended for energy harvesting from ambient vibrations. The cantilever model is based on Euler–Bernoulli beam theory. The generated voltage and power, the current density, resonance frequencies and tip displacement for different geometry (single layer and array structure) have been analyzed using finite element method. Variation of output power and resonant frequency for array structure with array elements connected in parallel have been studied. Strain distribution is studied for external vibrations with different frequencies. The geometry of the piezoelectric layer as well as the substrate has been optimized for maximum power output. The variation of generated power output with frequency and load has also been presented. Finally, several models are introduced and compared with traditional array MEMS energy harvester.

In this study, the length and width effects of metal films on the stress-induced bending of a surface micromachined cantilever curved grating are systematically investigated. A characterization of cantilever curved gratings with various lengths and widths was conducted to observe out-of-plane deformation. A finite element model was established to analyze the deformation. Finite element analysis and experimental results indicate that the commonly used beam theory formula for predicting the deformation of surface micromachined cantilever curved gratings is not valid for these devices. Experiments show that the shape of a cantilever curved grating and residual stress have a close relationship. As the length increases, the residual stress of the metal increases, resulting in a larger out-of-plane deformation of the cantilever curved grating. The tip deflection gradually decreases as the length-to-width ratio of the cantilever curved grating increases. A more reliable shape design of metal films on the stress-induced bending of surface micromachined cantilever curved gratings can thus be achieved.

In this study, the residual stress of boron-doped diamond (BDD) films is investigated as a function of boron doping level using X-ray diffraction (XRD) analysis. Boron doping level is controlled from 1000ppm to 9000ppm by dissolving trimethyl borate into acetone. BDD films are deposited on silicon wafers using a bias-enhanced hot filament chemical vapor deposition (BE-HFCVD) system. Residual stress calculated by ${sin}^2\psi$ method varies linearly from $-$2.4GPa to $-$1.1GPa with increasing boron doping level. On the BDD film of $-$1.75GPa, free standing BDD cantilevers are fabricated by photolithography and ICP-RIE processes, then tested by laser Doppler vibrometer (LDV). A cantilever with resonant frequency of 183KHz and $Q$ factor of 261 in the air is fabricated.

In this paper, a new process to fabricate nanosized silicon oxide apertures on a cantilever array is presented. The various semiconductor processes such as alkine etching, stress-dependent thermal oxidation, dilute HF etching and Au sputter deposition were utilized. With the dilute HF etching process, the opening of the nanosized oxide aperture could be fabricated in a controlled manner. The Au thin layer was deposited on the oxide apertures on the cantilever array so that the 160 nm apertures on a (5×1) cantilever array were successfully fabricated.

The nanosize silicon oxide aperture on the cantilever array has been successfully fabricated as nearfield optical probe. The various semiconductor processes were utilized for subwavelength size aperture fabrication. The anisotropic etching of the Si substrate by alkaline solutions followed by anisotropic crystal orientation dependent oxidation, anisotropic plasma etching, isotropic oxide etching was carried out. The 3 and 4 micron size dot array were patterned on the Si(100) wafer. After fabrication of the V-groove shape by anisotropic TMAH etching, the oxide growth at 1000°C was performed to have an oxide etch-mask. The oxide layer on the Si(111) plane have been utilized as an etch mask for plasma dry etching and water-diluted HF wet etching for nanosize aperture fabrication. The Au thin layer was deposited on the fabricated oxide nanosize aperture on the cantilever array. The 160 nm metal apertures on (5×1) cantilever array were successfully fabricated using electron beam evaporator.

Vibrations can be a good source of energy and can be harvested and utilized by simple design and fabrication using the MEMS technology. Energy harvesting provides unending sources of energy for low-power electronics devices where the use of batteries is not feasible. Piezoelectric energy harvesters are widely considered because of their compact design, compatibility to MEMS devices and ability to respond to a wide range of frequencies freely available in the environment. In this project, a rectangular model for cantilever-based piezoelectric energy harvester is proposed with different designs like two layer, two layer with proof mass, four layer and four layer with proof mass designed with dimensions as 50$\mu$m$\times$50$\mu$m$\times$1$\mu$m for each layer using COMSOL Multiphysics 5.0. Simulation results were obtained using silicon as substrate, aluminium as electrodes and PZT-5H and ZnO as piezoelectric materials and the respective stress and voltages were obtained by applying a force acting on foot, train, roller coaster and a general value of 10N/m² on top of the cantilever. The effects of varying geometrical dimensions of the device were also investigated.

This paper presents the simulation and the experimental results of various bimorph and multimorph structures, which are formed using Si, SiO₂, and Al. These results include effects of thickness variation of the single/ composite material. The effect of multiple heat cycles, on the stress of various structural materials is investigated. The cantilever tip bending mainly due to intrinsic stresses, is measured using Optical Interferometer and compared with the simulated data which is obtained by an analytical model developed using ANSYS. A combination of various materials is predicted that are suitable for released cantilevers with variable bending. Finally, the bimorph and multimorph structures that have yielded the high and low intrinsic stresses are also discussed.

In this paper, a nonlinear model is used to analyze the dynamic pull-in instability and vibrational behavior of a microcantilever gyroscope. The gyroscope has a proof mass at its end and is subjected to nonlinear squeeze film damping, step DC voltages as well as base rotation excitation. The electrostatically actuated and detected microgyroscopes are subjected to coupled flexural-flexural vibrations that are related by base rotation. In order to detune the stiffness and natural frequencies of the system, DC voltages are applied to the proof mass electrodes in drive and sense directions. Nonlinear integro differential equations of the system are derived using extended Hamilton principle considering nonlinearities in curvature, inertia, damping and electrostatic forces. Afterward, the Gelerkin decomposition method is implemented to reduce partial differential equations of microgyroscope deflection to a system of nonlinear ordinary equations. By using the 4th order Runge–Kutta method, the nonlinear ordinary equations are solved for various values of damping coefficients, air pressures, base rotation and various initial gaps between the proof mass electrodes and the substrates. Results show that the geometric nonlinearity increases the dynamic pull-in voltage and also consideration of the base rotation gives an improved evaluation of the dynamic instability. It is shown that the squeeze film damping has a considerable influence on the dynamic deflection of the microgyroscopes.

Nanomechanical biosensors based on atomic force microscopy (AFM) cantilevers have garnered considerable attention. AFM cantilevers are devices that can detect a target either via a surface functionalization process based on immobilization through molecular adsorption, or through the selective chemical binding of a specific molecule, transforming the device into a specific biosensor. In this study, we demonstrate that functionalized AFM cantilevers could be used, in a process involving self-assembling layers, to create a homogeneous surface layer of the widely used herbicide mesotrione. Controlled experiments to evaluate its detection were performed, and binding between mesotrione and its target molecule, 4-hydroxyphenylpyruvate dioxygenase (HPPD), was evaluated using deflection curves of functionalized cantilevers interacting with mesotrione. The cantilevers worked as nanomechanical sensors inside a fluid cell device, under different concentrations of HPPD diluted in PBS. After evaluating increasing concentrations of HPPD, the deflection curves showed a clear, dose-dependent pattern. The homogeneous dispersion of mesotrione on the cantilevers was assessed by confocal microscopy, and this corroborated the functionalization method. Thus, the results obtained by this functionalized cantilever presented a high efficiency in detecting binding between HPPD and mesotrione molecules at concentrations as low as 17ng mL${}^{-1}$. In this way, as a preliminary step for a future environmental contaminants nanosensor development, the described detection method showed a suitable capability for molecular recognition at the nanoscale.

Flexible piezoelectric cantilever beam has been realized by depositing lead zirconate titanate (PZT) thin film (4.5 μm) by chemical solution deposition (CSD) onto very thin aluminium foil (16 μm). The tip deflection of the beam has been measured as a function of the frequency of the applied sinusoidal voltage to the PZT film for different amplitudes. Resonance curves have been compared to a classical model of an oscillating system under sinusoidal stress with a very good agreement. Despite of weak ferroelectric properties (remnant polarization: 13 μC/cm²), ultra-large deflection amplitudes have been measured under very moderate applied voltage values: 750 μm@10 V for quasi-static mode and 5 mm@10 V at the resonance frequency (~12 Hz), which makes this PZT/aluminium composite film very promising for highly flexible actuation applications where large displacements are wanted.

This paper presents the application of the Pareto-based multicriteria optimization technique to problems of increasing the efficiency of piezoelectric generators (PEGs). The optimization problem was solved for two types of generators: cantilever and stack. For the cantilever generator, the task was to optimize the design in such a way as to obtain the maximum output power for a given mechanical excitation. The optimization process was divided into several stages, which significantly reduced the amount of calculations. The task of optimizing the stack type for a given form of mechanical loading consisted in finding the geometric parameters of the generator at which the output voltage and power would be maximum. In the result of solving both problems, sets of geometric design parameters of PEGs were obtained, on the basis of which efficient transducers can be developed for specific operating conditions. It turned out that this technique is more suitable for optimizing the design of cantilever generators than for stack ones in given constraints. The solution of both problems was realized using the finite element method.

Over the last period, increasing attention has been paid to measurement of small forces which play a more important role in nanotechnology and other significant areas such as MEMS (Micro-Electro-Mechanical Systems) and NEMS (nano-electro-mechanical systems) which can be found into everyday products (mobile phones, MP3 players, PCs, cars). In this respect, the development of mass standards and measurement techniques below the current limit of 1 milligram is vital to provide traceability to the SI for such measurements. In Romania, the Mass laboratory of INM considered it necessary to extend the dissemination of the mass unit below 1 mg, in order to meet current needs. Using the subdivision method and starting from the national prototype kilogram No. 2, all necessary experiments were performed for the first time in Romania to extend mass unit traceability till 100 μg. This extension also supports the provision of mass calibrations for low force measurements. The associated measurement procedure and measurement uncertainty results obtained in the calibration are described. In the article are also presented some of the worldwide methods currently used for measuring small forces.

Micro-nanomachining technologies based on extended microfabrication for integrated circuit have been applied for minimal invasive medical tools such as catheter and for highly sensitive sensors and actuators. Hydraulic suction type active catheters were developed. Micromachined quartz crystal microbalances designed especially for use in solution were fabricated to detect absorbed molecules gravimetrically. Micro fluidic channel made of quartz glass was fabricated for the purpose of electrophoresis. Thin cantilever resonators have potentials of extremely sensitive magnetic sensors for micro magnetic resonance imaging. Not only fabrication but also the noise reduction of the cantilever resonating sensor have been studied. Electrostatically actuated bow-tie antenna probe was developed for the purpose of high resolution near-field scanning optical microscope.

We review the results of our current research on quantum engineering which include the theory, modeling and simulations of quantum devices for potential applications to threat reduction and homeland security. In particular, we discuss: (i) scalable solid-state quantum computation with qubits based on (a) nuclear spins of impurity atoms in solids, (b) superconducting junctions, and (c) unpaired electron spins of spin radicals in self-assembled organic materials; (ii) quantum neural devices; (iii) quantum annealing; (iv) novel magnetic memory devices based on magnetic tunneling junctions with large tunneling magnetoresistance; (v) terahertz detectors based on microcantilever as a light pressure sensor; (vi) BEC based interferometers; (vii) quantum microscopes with a single-spin resolution based on (a) a magnetic resonant force microscopy and (b) an optically detected magnetic resonance; and (viii) novel approach for suppression of fluctuations in free space high-speed optical communication. Finally, we describe the similarities between the behavior of cross sections in reactions with heavy nuclei in the regions of strongly overlapped resonances and electron conductivity in semiconductor heterostructures.

Atomic force microscopy (AFM) was originally developed for atomic resolution surface topography observations. Nowadays, it is also widely used for nanolithography. AFM-based lithography is an effective method compared to conventional photolithographic processes due to its simplicity, high resolution, and low cost. It can provide nanoscale stage control and the probing tip can be used as a lithographic tool. Therefore, various AFM-based nanoscale fabrication methods have been proposed using electrochemical oxidation, material transfer, mechanical lithography, and thermally induced modifications. This chapter will introduce the detailed processes and applications of AFM-based lithographic techniques.