Resonance Frequency Of Cantilever Research Articles

Determination of the Young's modulus of pulsed laser deposited epitaxial PZT thin films

We determined the Young's modulus of pulsed laser deposited epitaxially grown PbZr0.52Ti0.48O3 (PZT) thin films on microcantilevers by measuring the difference in cantilever resonance frequency before and after deposition. By carefully optimizing the accuracy of this technique, we were able to show that the Young's modulus of PZT thin films deposited on silicon is dependent on the in-plane orientation, by using cantilevers oriented along the ⟨1 1 0⟩ and ⟨1 0 0⟩ silicon directions. Deposition of thin films on cantilevers affects their flexural rigidity and increases their mass, which results in a change in the resonance frequency. An analytical relation was developed to determine the effective Young's modulus of the PZT thin films from the shift in the resonance frequency of the cantilevers, measured both before and after the deposition. In addition, the appropriate effective Young's modulus valid for our cantilevers’ dimensions was used in the calculations that were determined by a combined analytical and finite-element (FE) simulations approach. We took extra care to eliminate the errors in the determination of the effective Young's modulus of the PZT thin film, by accurately determining the dimensions of the cantilevers and by measuring many cantilevers of different lengths. Over-etching during the release of cantilevers from the handle wafer caused an undercut. Since this undercut cannot be avoided, the effective length was determined and used in the calculations. The Young's modulus of PZT, deposited by pulsed laser deposition, was determined to be 103.0 GPa with a standard error of ± 1.4 GPa for the ⟨1 1 0⟩ crystal direction of silicon. For the ⟨1 0 0⟩ silicon direction, we measured 95.2 GPa with a standard error of ± 2.0 GPa.

Functionalized Mesoporous Silica for Microgravimetric Sensing of Trace Chemical Vapors

Featuring a huge surface-to-volume ratio, synthesized SBA-15 mesoporous silica is functionalized by inner-channel-wall modification of sensing groups for highly specific chemical-vapor detection at trace level. With the developed sensing material loaded on resonant microcantilevers, the specifically adsorbed chemical-vapor molecules act as an added mass to shift the cantilever resonant frequency for gravimetric sensing signal readout. Two kinds of sensing materials for trinitrotoluene (TNT) and ammonia/amine are respectively prepared by inner-wall layer-by-layer grafting functionalization. By using hexafluoro-2-propanol-functionalized mesoporous silica (HFMS), experimental results show highly specific and rapid detection of TNT vapor, with a ppt-level detection limit; functionalized with a carboxyl (COOH) group, the mesoporous silica is loaded onto the cantilever resonating sensor that experimentally exhibits an ultrafine detection limit of tens of ppb to ammonia/amine gases.

Measurement and modelling of non-contact atomic force microscope cantilever properties from ultra-high vacuum to normal pressure conditions

The resonance frequency and Q-factor of cantilevers typically used for non-contact atomic force microscopy (NC-AFM) are measured as a function of the ambient pressure varied from 10−8 mbar to normal pressure. The Q-factor is found to be almost constant up to a pressure in the range of 10−2–10−1 mbar and then decreases by about three orders of magnitude when increasing the pressure further to normal pressure. The decrease in the resonance frequency measured over the same pressure range amounts to less than 1% where a significant change is observed in the range of 10–103 mbar. The pressure dependence of the effective Q-factor and resonance frequency is approximated by analytical models accounting for different processes in the molecular and viscous flow regimes. By introducing a heuristic approach for describing the pressure dependence in the transition regime, we are able to well approximate the cantilever properties over the entire pressure range.

Fabrication and Characterization of an Integrated Microsystem for Protein Preconcentration and Sensing

We report on a fabrication and packaging process for a microsystem consisting of a mass-based protein detector and a fully integrated preconcentrator. Preconcentration of protein is achieved by means of a nanofluidic concentrator (NC), which takes advantage of fast nonlinear electroosmotic flow near a nanochannel-microchannel junction to concentrate charged molecules inside a volume of fluid on the order of 1 pL. Detection of preconcentrated protein samples is accomplished by passing them through a suspended microchannel resonator (SMR), which is a hollow resonant cantilever serially connected to the NC on the same device. The transit of a preconcentrated sample produces a transient shift in the cantilever's resonance frequency that is proportional to the density of the sample and, hence, the concentration of protein contained in it. A device containing both NC and SMR structures was produced using a novel fabrication process which simultaneously satisfies the separate packaging requirements of the two structures. The initial testing of this prototype device has demonstrated that the integrated SMR can accurately measure the concentration of a bovine serum albumin solution, that was preconcentrated using the integrated NC. Future improvements in the fabrication process will allow site-specific surface modification of the device and compatibility with separation methods, which will create opportunities for its application to immunoassays and universal detection.

High throughput label-free platform for statistical bio-molecular sensing

Sensors are crucial in many daily operations including security, environmental control, human diagnostics and patient monitoring. Screening and online monitoring require reliable and high-throughput sensing. We report on the demonstration of a high-throughput label-free sensor platform utilizing cantilever based sensors. These sensors have often been acclaimed to facilitate highly parallelized operation. Unfortunately, so far no concept has been presented which offers large datasets as well as easy liquid sample handling. We use optics and mechanics from a DVD player to handle liquid samples and to read-out cantilever deflection and resonant frequency. Also, surface roughness is measured. When combined with cantilever deflection the roughness is discovered to hold valuable additional information on specific and unspecific binding events. In a few minutes, 30 liquid samples can be analyzed in parallel, each by 24 cantilever-based sensors. The approach was used to detect the binding of streptavidin and antibodies.

Prototype of Frame-Type Cantilever for Biosensor and Femtogram Detection

The possibility of realizing femtogram mass detection using a frame-type microcantilever has been studied in bioscience. To realize highly sensitive mass detection by reducing the viscose resistance in liquids, we designed frame-type cantilevers using finite element modeling (FEM). We fabricated prototypes of mesh-type, hole-type and conventional-type cantilevers using a semiconductor process. The properties of the cantilevers were measured by a conventional atomic force microscope (AFM) system. The measured resonance frequencies of the cantilevers were almost consistent with the calculated results of the FEM simulation in air. The resonance frequency and quality (Q) factor of the mesh-type cantilever were larger than those of the conventional-type cantilever in water. We measured the frequency change due to gold film deposition on the mesh-type cantilever. Then, we estimated the mass sensitivity of the cantilever at about 16.6 fg/Hz. This value is more than 10 times smaller than that of the conventional-type cantilever. These results indicate that the mesh-type cantilever has the advantage of reducing the viscous resistance and achieving high sensitivity in liquids.

Batch-Fabrication of Cantilevered Magnets on Attonewton-Sensitivity Mechanical Oscillators for Scanned-Probe Nanoscale Magnetic Resonance Imaging

We have batch-fabricated cantilevers with ∼100 nm diameter nickel nanorod tips and force sensitivities of a few attonewtons at 4.2 K. The magnetic nanorods were engineered to overhang the leading edge of the cantilever, and consequently the cantilevers experience what we believe is the lowest surface noise ever achieved in a scanned probe experiment. Cantilever magnetometry indicated that the tips were well magnetized, with a ≤ 20 nm dead layer; the composition of the dead layer was studied by electron microscopy and electron energy loss spectroscopy. In what we believe is the first demonstration of scanned probe detection of electron-spin resonance from a batch-fabricated tip, the cantilevers were used to observe electron-spin resonance from nitroxide spin labels in a film via force-gradient-induced shifts in cantilever resonance frequency. The magnetic field dependence of the magnetic resonance signal suggests a nonuniform tip magnetization at an applied field near 0.6 T.

Influence of random roughness on cantilever resonance frequency

In this paper we investigate the influence of random roughness on the oscillation frequency of cantilevers coated with thin film overlayers. First the theory expressions for the roughness-induced frequency shift are derived using the cantilever equation of motion. Subsequently it is shown that the roughness induced shift depends on the particular roughness parameters, assuming the general case of self-affine rough surfaces for the overlayer film, the material properties of the overlayer film, and the dimensions mainly of the bare cantilever. Indeed it is shown that the roughness influence becomes significant for relatively thin cantilevers $(\ensuremath{\le}1\text{ }\ensuremath{\mu}\text{m})$, and increased local surface slopes $(>0.5)$ within the limits of applicability of the proposed formalism. The results of this study can be used in high precision frequency sensing applications in the field of micro/nanomechanics.

Some considerations of effects-induced errors in resonant cantilevers with the laser deflection method

Micro/nano resonant cantilevers with a laser deflection readout have been very popular in sensing applications over the past years. Despite the popularity, however, most of the research has been devoted to increasing the sensitivity, and very little attention has been focused on effects-induced errors. Among these effects, the surface effects and the so-called readout back-action are the two most influential causes of errors. In this paper, we investigate (1) the influence of the surface effects such as water adsorption, gas adsorption, and generally surface contaminations, and (2) the effect of the laser deflection detection, including power and positions of the laser, on the resonance frequency of silicon cantilevers. Our results show that both the surface contaminations and the laser back-action effects can significantly change the resonant response of the cantilevers. We conclude that the effects have to be taken into account, particularly in the case of ultra high sensitivity cantilevers.

Characterization of epitaxial Pb(Zr,Ti)O3 thin films deposited by pulsed laser deposition on silicon cantilevers

This paper reports on the piezoelectric-microelectromechanical system micro-fabrication process and the behavior of piezoelectric stacks actuated silicon cantilevers. All oxide layers in the piezoelectric stacks, such as buffer-layer/bottom-electrode/film/top-electrode: YSZ/SrRuO3/Pb(Zr,Ti)3/SrRuO3, were grown epitaxially on the Si template of silicon-on-insulator substrates by pulsed laser deposition. By using an analytical model and finite element simulation, the initial bending of the cantilevers was calculated. These theoretical analyses are in good agreement with the experimental results which were determined using a white light interferometer. The dependences of the cantilever displacement, resonance frequency and quality factor on the cantilever geometry have been investigated using a laser-Doppler vibrometer. The tip displacement ranged from 0.03 to 0.42 µm V−1, whereas the resonance frequency and quality factor values changed from 1010 to 18.6 kHz and 614 to 174, respectively, for the cantilevers with lengths in the range of 100–800 µm. Furthermore, the effect of the conductive oxide electrodes on the stability of the piezoelectric displacement of the cantilevers has been studied.

Ultrasensitive detection of Vibrio cholerae O1 using microcantilever-based biosensor with dynamic force microscopy

This work presents the first demonstration of a cantilever based cholerae sensor. Dynamic force microscopy within atomic force microscope (AFM) is applied to measure the cantilever's resonance frequency shift due to mass of cell bound on microcantilever surface. The Vibrio cholerae O1, a food and waterborne pathogen that caused cholera disease in human, is a target bacterium cell of interest. Commercial gold-coated AFM microcantilevers are immobilized with monoclonal antibody (anti- V. cholerae O1) by self-assembled monolayer method. V. cholerae O1 detection experiment is then conducted in concentrations ranging from 1 × 10 3 to 1 × 10 7 CFU/ml. The microcantilever-based sensor has a detection limit of ∼1 × 10 3 CFU/ml and a mass sensitivity, Δ m/Δ F, of ∼146.5 pg/Hz, which is at least two orders of magnitude lower than other reported techniques and sufficient for V. cholerae detection in food products without pre-enrichment steps. In addition, V. cholerae O1 antigen–antibody binding on microcanilever is confirmed by scanning electron microscopy. The results demonstrate that the new biosensor is promising for high sensitivity, uncomplicated and rapid detection of V. cholerae O1.

Energy levels of few-electron quantum dots imaged and characterized by atomic force microscopy

Strong confinement of charges in few-electron systems such as in atoms, molecules, and quantum dots leads to a spectrum of discrete energy levels often shared by several degenerate states. Because the electronic structure is key to understanding their chemical properties, methods that probe these energy levels in situ are important. We show how electrostatic force detection using atomic force microscopy reveals the electronic structure of individual and coupled self-assembled quantum dots. An electron addition spectrum results from a change in cantilever resonance frequency and dissipation when an electron tunnels on/off a dot. The spectra show clear level degeneracies in isolated quantum dots, supported by the quantitative measurement of predicted temperature-dependent shifts of Coulomb blockade peaks. Scanning the surface shows that several quantum dots may reside on what topographically appears to be just one. Relative coupling strengths can be estimated from these images of grouped coupled dots.

Fabrication and characterization of PMN-PT single crystal cantilever array for cochlear-like acoustic sensor

We have successfully fabricated piezoelectric PMN-PT single crystal cantilever array. Each PMN-PT cantilever has a different length to achieve different resonance frequencies. The width and thickness of PMN-PT cantilever array are 200 μm and 10 μm, respectively. Resonance frequencies of PMN-PT cantilevers were measured with laser interferometer, and charge sensitivity was measured with charge-measuring device. PMN-PT cantilever array was installed in a noise-shield case. The array was then exposed to sound pressure frequency corresponding to resonance frequency to measure its sensitivity. The experimental results show that the PMN-PT cantilever array has high sensitivity to the sound pressure. This implies that the single crystal PMN-PT cantilever array is a potential candidate for a cochlear-like acoustic sensor.

Micromachining of thin 3C-SiC films for mechanical properties investigation

AbstractIn this work, the mechanical properties of cubic silicon carbide are explored through the analysis of the static and dynamic behavior of 3C-SiC cantilevers. The investigated structures were micro-machined using Inductively Coupled Plasma (ICP) etching of thin 3C-SiC films grown on silicon. The aim was to evaluate the influence of some basic parameters (film orientation, film thickness, defect density) on the mechanical properties of the material.X-Ray Diffraction was used to evaluate the crystalline quality of the epilayers. Scanning Electron Microscopy observations of static cantilever deflection highlight the major difference between the stress states of (100) and (111) oriented layers for which the intrinsic stresses are of opposite signs. The cantilever deflection is highly dependent on the film thickness, as stated for (100) oriented epilayers. The lowest deflection is obtained for the thickest layer. The Young's modulus of 3C-SiC is calculated from the resonance frequency of clamped-free cantilevers, measured by laser Doppler vibrometry. The relatively low and orientation independent value of Young's modulus (~350GPa) found on the samples is probably associated with the high defect density usually observed in very thin 3C-SiC films grown on Si.

Resonance tunability of clamped–free piezoelectric cantilevers

Piezoelectric cantilevers often form a crucial part in actuating and sensing devices. Many dynamic applications require them to operate at the basic resonance. To ensure optimal performance, the eigenfrequency has to be adjustable to match varying application demands. Within this publication, it is demonstrated that the resonance frequency of a piezoelectric bimorph cantilever can be tuned about 20% by an applied static electrical field. This beneficial feature is explained by an extended analytical model including nonlinear properties of piezoelectric materials.

Substantial Contribution to a Cantilever Resonance Frequency Shift in Magnetic Resonance Force Microscopy

We report a cantilever resonance frequency shift due to the magnetic resonance force gradient in magnetic resonance force microscopy. Our experimental results obtained for a phantom sample of diphenylpicrylhydrazil (DPPH) at T =14 K can be quantitatively understood with the magnetic force gradient containing the first derivative of spin magnetization. This substantial contribution should be explicitly treated when calculating an equipment function and estimating the number of spins through the deconvolution process for image restoration.

Microcantilevers with nanowells as moisture sensors

An anodic aluminum oxide (AAO) layer with hexagonally ordered nanowells was fabricated on an aluminum specimen with two-step anodization, and then AAO cantilevers were fabricated with photolithography and electrochemical etching. Each resulting AAO cantilever has a larger surface area and a lower modulus than that of a plain cantilever with the same dimensions due to the presence of the nanowells. We measured the variations in the resonance frequency and deflection of the cantilevers when exposed to moisture and found that the sensitivity in both mass and stress measurements of the porous AAO cantilever is superior to that of the nonporous cantilever. The changes in the deflection and resonance frequency of the AAO cantilever were found to be reproducible and proportional to moisture concentration.

A novel method for the measurement of mechanical mobility

We describe a novel technique for direct measurement of the unloaded driving-point mechanical mobility of a structure. The method uses an electrically-excited inertial motor/actuator attached directly to the structure under test (SUT) to induce sinusoidal motion in the frequency range 7.5–750 Hz. Two accelerometers, one attached to the actuator frame and the other to the vibrating actuator mass, separately measure the induced motion of the SUT and the vibrating mass. We develop an expression for the driving-point mobility of the SUT using these two measurements and show analytically that any mass-loading effect of the actuator on the measured mobility can be removed mathematically so that the unloaded mobility of the SUT can be determined. In this study we validate the method using a cantilever as a mobility standard. Measured mobility, mode shape and resonant frequency of cantilevers with various lengths were consistent with theoretical predictions for an unloaded cantilever. We conclude that the method can be used to conveniently determine the mobility of a range of structures, without the limitations associated with some of the traditional methods of mobility measurement.

Detection of microviscosity by using uncalibrated atomic force microscopy cantilevers

In this letter, we provide evidence that the vibrating resonance frequency of an uncalibrated atomic force microscope cantilever can be precisely related to the viscosity of the fluid in which it is immersed, independent of any knowledge of the cantilever’s geometry and spring constant. Reverse geometry, density, and spring constants of a cantilever immersed in a fluid of known viscosity can be recovered with ease. The methods for monitoring viscosity we propose are of relevance to all biorheologic and microfluidic applications where functionalized cantilevers have to be used, and a simple, yet reliable nondestructive procedure is called for.

Improvement of a dynamic scanning force microscope for highest resolution imaging in ultrahigh vacuum

We report on a modification of a commercial scanning force microscope (Omicron UHV AFM/STM) operated in noncontact mode (NC-AFM) at room temperature in ultrahigh vacuum yielding a decrease in the spectral noise density from 2757 to 272 fm/Hz. The major part of the noise reduction is achieved by an exchange of the originally installed light emitting diode by a laser diode placed outside the vacuum, where the light is coupled into the ultrahigh vacuum chamber via an optical fiber. The setup is further improved by the use of preamplifiers having a bandpass characteristics tailored to the cantilever resonance frequency. The enhanced signal to noise ratio is demonstrated by a comparison of atomic resolution images on CeO(2)(111) obtained before and after the modification.