Measurement of Mechanical Properties of Cantilever Shaped Materials

Beyond biology: alternative uses of cantilever-based technologies

Micromechanical cantilever sensors are attracting a lot of attention because of the need for characterizing, detecting, and monitoring chemical and physical properties, as well as compounds at the nanoscale. The fields of application of micro-cantilever sensors span from biological and point-of-care, to military or industrial sectors. The purpose of this work focuses on thermal and mechanical characterization, environmental monitoring, and chemical detection, in order to provide a technical review of the most recent technical advances and applications, as well as the future prospective of micro-cantilever sensor research.

A cantilever torque magnetometry method for the measurement of Hall conductivity of highly resistive samples

We present the first measurements of Hall conductivity utilizing a torque magnetometry method. A Corbino disk exhibits a magnetic dipole moment proportional to Hall conductivity when voltage is applied across a test material. This magnetic dipole moment can be measured through torque magnetometry. The symmetry of this contactless technique allows for the measurement of Hall conductivity in previously inaccessible materials. Finally, we calculate a low-temperature noise bound, demonstrate the lack of systematic errors, and measure the Hall conductivity of sputtered indium tin oxide.

Graphene Foam Cantilever Produced via Simultaneous Foaming and Doping Effect of an Organic Coagulant

Inspired by the role of cellular structures, which give three-dimensional robustness to graphene structures, a new type of graphene cantilever with mechanical resilience is introduced. Here, NH₄SCN is incorporated into graphene oxide (GO) gel using it as a coagulant for GO fiber self-assembly, a foaming agent, and a dopant. Subsequent thermal treatment of the GO fiber at 600 °C results in the evolution of gaseous species from NH₄SCN, yielding internally porous graphene cantilevers (NS-GF cantilevers). The results reveal that NS-GF cantilevers are doped with N and S and thus exhibit higher electrical conductivity (150 S cm^-1) than that of their nonporous counterparts (38.4 S cm^-1). Unlike conventional fibers, the NS-GF cantilevers exhibit mechanical resilience by bending under applied mechanical force but reverting to the original position upon release. The tip of the NS-GF cantilevers is coated with magnetic Fe₃O₄ particles, and fast mechanical movement is achieved by applying the magnetic field. Since the NS-GF cantilevers are highly conductive and elastic, they are employed as bendable, magnetodriven electrical switches that could precisely read on/off signals for >10 000 cycles. Our approach suggests a robust fabrication strategy to prepare highly electroconductive and mechanically elastic foam structures by introducing unique organic foaming agents.

Laterally Driven Resonant Pressure Sensor with Etched Silicon Dual Diaphragms and Combined Beams

A novel structure of the resonant pressure sensor is presented in this paper, which tactfully employs intercoupling between dual pressure-sensing diaphragms and a laterally driven resonant strain gauge. After the resonant pressure sensor principle is introduced, the coupling mechanism of the diaphragms and resonator is analyzed and the frequency equation of the resonator based on the triangle geometry theory is developed for this new coupling structure. The finite element (FE) simulation results match the theoretical analysis over the full scale of the device. This pressure sensor was first fabricated by dry/wet etching and thermal silicon bonding, followed by vacuum-packaging using anodic bonding technology. The test maximum error of the fabricated sensor is 0.0310%F.S. (full scale) in the range of 30 to 190 kPa, its pressure sensitivity is negative and exceeding 8 Hz/kPa, and its Q-factor reaches 20,000 after wafer vacuum-packaging. A novel resonant pressure sensor with high accuracy is presented in this paper.

A Micro-Preconcentrator Combined Olfactory Sensing System with a Micromechanical Cantilever Sensor for Detecting 2,4-Dinitrotoluene Gas Vapor

Preventing unexpected explosive attacks and tracing explosion-related molecules require the development of highly sensitive gas-vapor detection systems. For that purpose, a micromechanical cantilever-based olfactory sensing system including a sample preconcentrator was developed to detect 2,4-dinitrotoluene (2,4-DNT), which is a well-known by-product of the explosive molecule trinitrotoluene (TNT) and exists in concentrations on the order of parts per billion in the atmosphere at room temperature. A peptide receptor (His-Pro-Asn-Phe-Ser-Lys-Tyr-Ile-Leu-His-Gln-Arg) that has high binding affinity for 2,4-DNT was immobilized on the surface of the cantilever sensors to detect 2,4-DNT vapor for highly selective detection. A micro-preconcentrator (µPC) was developed using Tenax-TA adsorbent to produce higher concentrations of 2,4-DNT molecules. The preconcentration was achieved via adsorption and thermal desorption phenomena occurring between target molecules and the adsorbent. The µPC directly integrated with a cantilever sensor and enhanced the sensitivity of the cantilever sensor as a pretreatment tool for the target vapor. The response was rapidly saturated within 5 min and sustained for more than 10 min when the concentrated vapor was introduced. By calculating preconcentration factor values, we verified that the cantilever sensor provides up to an eightfold improvement in sensing performance.

Spin-coatable, photopatternable magnetic nanocomposite thin films for MEMS device applications

Magnetic nanomaterials' (especially metals) air stability and compatibility with standard micro-fabrication technologies are often a concern for development of MEMS-based magnetic devices.

Detecting both the mass and position of an accreted particle by a micro/nano-mechanical resonator sensor

In the application of a micro-/nano-mechanical resonator, the position of an accreted particle and the resonant frequencies are measured by two different physical systems. Detecting the particle position sometimes can be extremely difficult or even impossible, especially when the particle is as small as an atom or a molecule. Using the resonant frequencies to determine the mass and position of an accreted particle formulates an inverse problem. The Dirac delta function and Galerkin method are used to model and formulate an eigenvalue problem of a beam with an accreted particle. An approximate method is proposed by ignoring the off-diagonal elements of the eigenvalue matrix. Based on the approximate method, the mass and position of an accreted particle can be decoupled and uniquely determined by measuring at most three resonant frequencies. The approximate method is demonstrated to be very accurate when the particle mass is small, which is the application scenario for much of the mass sensing of micro-/nano-mechanical resonators. By solving the inverse problem, the position measurement becomes unnecessary, which is of some help to the mass sensing application of a micro-/nano-mechanical resonator by reducing two measurement systems to one. How to apply the method to the general scenario of multiple accreted particles is also discussed.

Determining the effects of surface elasticity and surface stress by measuring the shifts of resonant frequencies

Both surface elasticity and surface stress can result in changes of resonant frequencies of a micro/nanostructure. There are infinite combinations of surface elasticity and surface stress that can cause the same variation for one resonant frequency. However, as shown in this study, there is only one combination resulting in the same variations for two resonant frequencies, which thus provides an efficient and practical method of determining the effects of both surface elasticity and surface stress other than an atomistic simulation. The errors caused by the different models of surface stress and mode shape change due to axial loading are also discussed.

Nanomusical systems visualized and controlled in 4D electron microscopy

Nanomusical systems, nanoharp and nanopiano, fabricated as arrays of cantilevers by focused ion beam milling of a layered Ni/Ti/Si(3)N(4) thin film, have been investigated in 4D electron microscopy. With the imaging and selective femtosecond and nanosecond control combinations, full characterization of the amplitude and phase of the resonant response of a particular cantilever relative to the optical pulse train was possible. Using a high repetition rate, low energy optical pulse train for selective, resonant excitation, coupled with pulsed and steady-state electron imaging for visualization in space and time, both the amplitude on the nanoscale and resonance of motion on the megahertz scale were resolved for these systems. Tilting of the specimen allowed in-plane and out-of-plane cantilever bending and cantilever torsional motions to be identified in stroboscopic measurements of impulsively induced free vibration. Finally, the transient, as opposed to steady state, thermostat effect was observed for the layered nanocantilevers, with a sufficiently sensitive response to demonstrate suitability for in situ use in thin-film temperature measurements requiring resolutions of <10 K and 10 μm on time scales here mechanically limited to microseconds and potentially at shorter times.

Generating and measuring the anisotropic elastic behaviour of Co thin films with oriented surface nano-strings on micro-cantilevers

In this research, the elastic behaviour of two Co thin films simultaneously deposited in an off-normal angle method was studied. Towards this end, two Si micro-cantilevers were simultaneously coated using pulsed laser deposition at an oblique angle, creating a Co nano-string surface morphology with a predetermined orientation. The selected position of each micro-cantilever during the coating process created longitudinal or transverse nano-strings. The anisotropic elastic behaviour of these Co films was determined by measuring the changes that took place in the resonant frequency of each micro-cantilever after this process of creating differently oriented plasma coatings had been completed. This differential procedure allowed us to determine the difference between the Young's modulus of the different films based on the different direction of the nano-strings. This difference was determined to be, at least, the 20% of the Young's modulus of the bulk Co.PACS: 62.25.-g; 81.16.Rf; 68.60.Bs; 81.15.Fg; 68.37.Ef; 85.85.+j.

Fano-like resonance in an optically driven atomic force microscope cantilever

We observe Fano-like resonance in the vibration spectrum of an optically driven atomic force microscope cantilever system. The vibration of the cantilever is photothermally induced by exciting it with a 780-nm laser diode. The asymmetry of the resonance curve strongly depends on the position of the excitation spot along the central axis of the cantilever. By using a simple physical model, we could extract and analyze the hidden resonance and continuous components in the vibration spectrum.

Investigation of the frequency shift of a SAD circuit loop and the internal micro-cantilever in a gas sensor

Micro-cantilever sensors for mass detection using resonance frequency have attracted considerable attention over the last decade in the field of gas sensing. For such a sensing system, an oscillator circuit loop is conventionally used to actuate the micro-cantilever, and trace the frequency shifts. In this paper, gas experiments are introduced to investigate the mechanical resonance frequency shifts of the micro-cantilever within the circuit loop(mechanical resonance frequency, MRF) and resonating frequency shifts of the electric signal in the oscillator circuit (system working frequency, SWF). A silicon beam with a piezoelectric zinc oxide layer is employed in the experiment, and a Self-Actuating-Detecting (SAD) circuit loop is built to drive the micro-cantilever and to follow the frequency shifts. The differences between the two resonating frequencies and their shifts are discussed and analyzed, and a coefficient α related to the two frequency shifts is confirmed.

Approaches to increasing surface stress for improving signal-to-noise ratio of microcantilever sensors

Microcantilever sensor technology has been steadily growing for the last 15 years. While we have gained a great amount of knowledge in microcantilever bending due to surface stress changes, which is a unique property of microcantilever sensors, we are still in the early stages of understanding the fundamental surface chemistries of surface-stress-based microcantilever sensors. In general, increasing surface stress, which is caused by interactions on the microcantilever surfaces, would improve the S/N ratio and subsequently the sensitivity and reliability of microcantilever sensors. In this review, we will summarize (A) the conditions under which a large surface stress can readily be attained and (B) the strategies to increase surface stress in case a large surface stress cannot readily be reached. We will also discuss our perspectives on microcantilever sensors based on surface stress changes.

Magnetic molecule on a microcantilever: quantum magnetomechanical oscillations

We study the quantum dynamics of a system consisting of a magnetic molecule placed on a microcantilever. The amplitude and frequencies of the coupled magnetomechanical oscillations are computed. Parameter-free theory shows that the existing experimental techniques permit observation of the driven coupled oscillations of the spin and the cantilever, as well as of the splitting of the mechanical modes of the cantilever caused by spin tunneling.

An iterative curve fitting method for accurate calculation of quality factors in resonators

A new method for eliminating the noise effect in interpreting the measured magnitude transfer characteristic of a resonator, in particular in extracting the Q-factor, is proposed and successfully tested. In this method the noise contribution to the measured power spectral density of resonator is iteratively excluded through a sequence of least-square curve fittings. The advantage of the presented method becomes more tangible when the signal to noise power ratio (SNR) is close to unity. A set of experiments for a resonant cantilever vibrating at different amplitudes has shown that when SNR is less than 10, the calculation results of conventional methods in extracting the Q-factor, i.e., the 3 dB bandwidth and single least-square curve fit, exhibit significant deviations from the actual Q-factor, while the result of the proposed iterative method remains in 5% margin of error even for a SNR of unity. This method is especially useful when no specific data is available about the measurement noise, except the assumption that the noise spectral density is constant over the measured bandwidth.

Nonlinear Dynamics and Chaos of Microcantilever-Based TM-AFMs with Squeeze Film Damping Effects

In Atomic force microscope (AFM) examination of a vibrating microcantilever, the nonlinear tip-sample interaction would greatly influence the dynamics of the cantilever. In this paper, the nonlinear dynamics and chaos of a tip-sample dynamic system being run in the tapping mode (TM) were investigated by considering the effects of hydrodynamic loading and squeeze film damping. The microcantilever was modeled as a spring-mass-damping system and the interaction between the tip and the sample was described by the Lennard-Jones (LJ) potential. The fundamental frequency and quality factor were calculated from the transient oscillations of the microcantilever vibrating in air. Numerical simulations were carried out to study the coupled nonlinear dynamic system using the bifurcation diagram, Poincaré maps, largest Lyapunov exponent, phase portraits and time histories. Results indicated the occurrence of periodic and chaotic motions and provided a comprehensive understanding of the hydrodynamic loading of microcantilevers. It was demonstrated that the coupled dynamic system will experience complex nonlinear oscillation as the system parameters change and the effect of squeeze film damping is not negligible on the micro-scale.