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We investigate the dynamics of a microcantilever subjected to the combined forcing from Brownian motion and delayed self-feedback. Specifically, the excitation of the fundamental mode of the cantilever by thermomechanical agitation is utilized as delayed external forcing and the resulting dynamical response is studied as a function of the delay and the coupling strength. A fluctuation-dissipation theorem is derived from the delay Langevin-like equation and its validity is discussed. The relaxation time scale associated with the adsorption processes is established and an experiment to determine the oscillator’s effective temperature is proposed. [ABSTRACT FROM AUTHOR]

We describe in detail the detection of deflagration of trinitrotoluene (TNT) deposited on a piezoresistive microcantilever and point out its possible use for explosive-vapor detection. The deflagration of TNT causes the cantilever to bend (due to released heat) and its resonance frequency to shift (due to mass unloading). Explosive vapors provide unique responses that are absent for" interferences" such as water or alcohol vapors. The proposed sensor makes possible a sensitive, miniature explosives detection device that may be deployed in large numbers. The minimum amount of TNT detected on the cantilever depends on the cantilever dimensions and was≈ 50 pg for the batch of cantilevers used. [ABSTRACT FROM AUTHOR]

We report direct observation of thin-film interference effects in microcantilevers, an effect that can impact the optical monitoring of the microcantilever motion. When microcantilevers are illuminated with different wavelengths of light the amount of absorption and the wavelengths of maxima in the absorption depend upon the thickness of the layers, the materials used in the layers, and the direction of illumination. Wavelengths of maximum absorption are observed as microcantilever deflections due to heat-induced bending of the bimaterial structure of the microcantilever. Results are presented for different multilayer configurations and illumination directions. These results are then compared with theoretical calculations based on multilayer thin-film analysis. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

When two surfaces at two different temperatures are separated by a distance comparable to a mean-free path of the molecules of the ambient medium, the surfaces experience Knudsen force. This mechanical force can be important in microelectromechanical systems and in atomic force microscopy. A theoretical discussion of the magnitude of the forces and the conditions where they can be encountered is discussed. A potential application of the Knudsen force in designing a cantilever-based vacuum gauge is discussed. [ABSTRACT FROM AUTHOR]

The small amplitude thermal vibrations of the microcantilever of an atomic force microscope can be enhanced via a delayed feedback system. This is verified experimentally for a triangular cantilever, and modeled theoretically as a boundary value problem resulting in a second order functional differential equation for the temporal behavior of the cantilever. The eigenvalues of the resulting delay differential equation describing the transverse vibrations of the cantilever are calculated and analyzed. These values are compared with the corresponding resonant frequencies predicted by a point mass model and with the experimentally observed values. [ABSTRACT FROM AUTHOR]

The Coulomb interaction of a dielectric probe tip with a uniform field existing above a semi-infinite, homogeneous dielectric substrate is studied. The induced polarization surface charge density and the field distribution at the bounding surface of the dielectric medium with the geometry of half of a two sheeted hyperboloid of revolution located above the dielectric half space interfaced with a uniform surface charge density is calculated. The force density on the hyperboloidal probe medium is calculated as a function of the probe tip shape. The calculation is based on solving Laplace’s equation and employing a newly derived integral expansion for the vanishing dielectric limit of the potential. The involved numerical simulations comprise the evaluation of infinite double integrals involving conical functions. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The interaction between a vapor and a thin film adsorbed on one side of a bimaterial microcantilever produces differential stress, resulting in readily measurable curvatures of the cantilever structure. Depending upon the system studied, there exist two types of gas-solid interaction: bulk-like absorption and surface-like adsorption. The absorption of hydrogen into palladium results in film expansion whose magnitude is governed by hydrogen partial pressure. The bending of a bimaterial microcantilever (palladium/silicon) due to hydrogen absorption depends on the thickness of the palladium film and is reversible but rate limited by a surface barrier. In contrast, the stress induced by adsorption of mercury onto a bimaterial (gold/silicon) cantilever is irreversible at room temperature, is rate limited by surface coverage, and is independent of the gold-film thickness. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Presents information on a study that discovered that the adsorption of molecules on cantilever surfaces can produce bending as well as resonance frequency shifts. Experimental procedure; Results and discussion on the study.

Presents information on a study which demonstrated the possibility of depositing a wide range of magnetic features, using photoassisted selective area organometallic chemical vapor deposition. Background of the study; Methodology of the study; Results and discussion.

Focuses on a study which generated cobalt nitride films in pure form and as a nanocomposite in boron nitride or silicon nitride. Experimental details; Results and discussion; Conclusion.

Examines tapping-mode atomic force microscope operation in the near-contact region in the presence of gases and liquids. Application of one-dimensional harmonic oscillator theory; Mediation of the tip-sample interaction in the fluid; Means to obtain the vibration amplitude of the model cantilever.

Lab-on-a-Chip compatible techniques for thermal characterization of miniaturized volumes of liquid analytes are necessary in applications such as protein blotting, DNA melting, and drug development, where samples are either rare or volume-limited. We developed a closed-chamber calorimeter based on a bimaterial microchannel cantilever (BMC) for sub-nanoliter level thermal analysis. When the liquid-filled BMC is irradiated with infrared (IR) light at a specific wavelength, the IR absorption by the liquid analyte results in localized heat generation and the subsequent deflection of the BMC, due to a thermal expansion mismatch between the constituent materials. The time constant of the deflection, which is dependent upon the heat capacity of the liquid analyte, can be directly measured by recording the time-dependent bending of the BMC. We have used the BMC to quantitatively measure the heat capacity of five volatile organic compounds. With a deflection noise level of ∼10 nm and a signal-to-noise ratio of 68:1, the BMC offers a sensitivity of 30.5 ms/(J g-1K-1) and a resolution of 23 mJ/(g K) for ∼150 pl liquid for heat capacity measurements. This technique can be used for small-scale thermal characterization of different chemical and biological samples. [ABSTRACT FROM AUTHOR]

Resonating strings have shown promise in a variety of applications including micron-scale mass and temperature sensors. We present microchannel string resonators (MSRs) which have resonance frequency modulated by the internal gauge pressure of silicon nitride microchannels sitting atop the strings. We present an analytical model to predict the pressure sensitivity (Hz/kPa) of the first resonance frequency as well as experimental results for three identical MSRs. While the highest experimental sensitivity of one of the resonators is 5.19 Hz/kPa (0.5 Hz/mbar), the analytical model suggests sensitivity could increase by two orders of magnitude if the microchannels are fabricated at nanometer scale with a length of 10 μm, a channel width of 600 nm, and a channel thickness of 50 nm. The average pressure resolution of the sensors is 0.4 kPa. These results are for a calibrated range of pressure from 50 kPa to 100 kPa (500 mbar to 1000 mbar). However, the analytical model shows that resonance frequency is a linear function of pressure over a range of several MPa, suggesting that the microchannel resonators could have a pressure sensing range (dynamic range) suitable for many applications. [ABSTRACT FROM AUTHOR]

Effective detection of Swine H1N1 Hemagglutinin peptide is crucial as it could be used as a positive control to screen for highly infectious flu strains such as Swine- Origin Influenza A (H1N1). Piezoresistive microcantilever arrays present a pathway towards highly sensitive and label-free detection of biomolecules by transducing the antigen-antibody binding into change in resistivity via induced surface stress variation. We demonstrate a mechanical transduction of Swine H1N1 Hemagglutinin peptide binding and suggest the employed technique may offer a potential platform for detection of the H1N1 virus, which could be clinically used to diagnose and provide subsequent relief. [ABSTRACT FROM AUTHOR]

We demonstrate a parametric energy conversion method of thermoacoustic (TA) vibrations into electrical oscillations of a LC circuit. The inductance modulation necessary to excite the parametric oscillations is achieved by varying the air gap between two halves of a ferrite E-core coil. As a proof-of-concept, the parametric converter was attached to a Sondhauss tube that converts the heat into acoustic vibrations. The maximum total acoustic power output of this thermoacoustic engine was ∼5.3 mW. A flexible metallic membrane capping the Sondhauss tube connected to the moving half E-core served as a mechanical oscillator. The resonance frequency of the membrane was matched with the operating frequency (130 Hz) of the Sondhauss tube for resonant energy extraction. We have characterized the power output of the complete system as a function of electrical load. The maximum electrical power of 2.3 mW produced by the system corresponds to an acoustic-to-electric conversion efficiency of 44%. [ABSTRACT FROM AUTHOR]

In material structures with nanometer scale curvature or dimensions, electrons may be excited to oscillate in confined spaces. The consequence of such geometric confinement is of great importance in nano-optics and plasmonics. Furthermore, the geometric complexity of the probe-substrate/sample assemblies of many scanning probe microscopy experiments often poses a challenging modeling problem due to the high curvature of the probe apex or sample surface protrusions and indentations. Index transforms such as Mehler–Fock and Kontorovich–Lebedev, where integration occurs over the index of the function rather than over the argument, prove useful in solving the resulting differential equations when modeling optical or electronic response of such problems. By considering the scalar potential distribution of a charged probe in the presence of a dielectric substrate, we discuss certain implications and criteria of the index transform and prove the existence and the inversion theorems for the Mehler–Fock transform of the order m∈N0. The probe charged to a potential V0, measured at the apex, is modeled, in the noncontact case, as a one-sheeted hyperboloid of revolution, and in the contact case or in the limit of a very sharp probe, as a cone. Using the Mehler–Fock integral transform in the first case, and the Fourier integral transform in the second, we discuss the necessary conditions imposed on the potential distribution on the probe surface. [ABSTRACT FROM AUTHOR]

In 2004, the authors reported two coupling schemes based on the thermo-optic properties of thin metallic films and their associated sub- and superstrates, by utilizing surface plasmons. These studies showed a potential for all-optical modulation at low rates that may be used for sensing purposes. In this article, they continue by investigating thermal processes involved in thin metallic films with different approaches. They first experimentally imaged the shift of the surface plasmon dispersion relation in the visible spectrum, as the thin film temperature is externally varied. They then reinforce the previous observations by collecting the absorption curves at selected visible photon energies of excitation, as the film temperature in the excitation region increases. Utilizing the absorption measurements, they briefly address how one may obtain the real and imaginary parts of the index of refraction of the thin film as a function of temperature for each involved wavelength. Finally, they investigate the local physical state of the film by optically profiling the surface plasmon excitation region. [ABSTRACT FROM AUTHOR]

We report the development of a handheld sensor based on piezoresistive microcantilevers that does not depend on optical detection, yet has high detection sensitivity. The sensor is able to detect vapors from the plastic explosives pentaerythritol tetranitrate and hexahydro-1,3,5-triazine at levels below 10 parts per trillion within few seconds of exposure under ambient conditions. A differential measurement technique has yielded a rugged sensor that is unaffected by vibration and is able to function as a “sniffer.” The microelectromechanical system sensor design allows for the incorporation of hundreds of microcantilevers with suitable coatings in order to achieve sufficient selectivity in the future, and thus could provide an inexpensive, unique platform for the detection of chemical, biological, and explosive materials. [ABSTRACT FROM AUTHOR]

A simple and cost-effective method for detecting propagation of acoustic waves based on the harmonic oscillations of a piezoresistive microcantilever is presented. Monitoring the Fourier amplitude of the microcantilever's fundamental frequency, the dependence of the detected amplitude upon the acoustic source location, is measured. At a fixed probe-source distance, the solid angular dependence of the cantilever plane relative to the source is studied. The potential use of a microelectromechanical cantilever as an acoustic leak sensor for pressurized gas reservoirs is addressed. [ABSTRACT FROM AUTHOR]

A micromechanical sensor for charged-particle flux detection utilizing the extreme force sensitivity of microcantilevers is demonstrated with alpha particles. The latter create a charge buildup on an electrically isolated collection plate, a metallic sphere. The cantilever detector measures the electric field emanating from the charge collection sphere using variations in mechanical parameters. Results are compared with responses due to fixed voltages on the sphere. Parameters investigated include cantilever deflection due to total charge and frequency and damping rate variation due to electrostatic force gradient. The minimum detectable particle fluence using this technique was calculated to be around 1000 particles in air, or about 3.2×10[sup -4] pC. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Focuses on the remote optical detection using microcantilevers. Theory of bimetallic microcantilever bending; Ability to sensitively detect physical changes resulting from thermal stress; Evaluation of the role of optical reflectivity on microcantilever response.

Discusses a novel class of highly sensitive sensors that are based on commercially available microcantilevers, such as those used in atomic force microscopy. Microcantilever preparation; Cantilever exposure and monitoring; Mercury vapor; Relative humidity; Ultraviolet radiation; Instrumental effects; Sensor optimization.

A variational method is used to calculate the deflection and the fundamental and harmonic resonance frequencies of commercial V-shaped and rectangular atomic force microscopy cantilevers. The effective mass of V-shaped cantilevers is roughly half that calculated for the equivalent rectangular cantilevers. Damping by environmental gases, including air, nitrogen, argon, and helium, affects the frequency of maximum response and to a much greater degree the quality factor Q. Helium has the lowest viscosity, resulting in the highest Q, and thus provides the best sensitivity in noncontact force microscopy. Damping in liquids is dominated by an increase in effective mass of the cantilever due to an added mass of the liquid being dragged with that cantilever. [ABSTRACT FROM AUTHOR]

The conventional deflection-mode atomic force microscope operates by optically monitoring the slope near the end of a microcantilever in contact with the sample surface. This signal is usually interpreted as a measure of height change. Lateral forces from friction, surface geometry, or inclination of the cantilever to the surface also affect the slope due to cantilever buckling. We calculate the deflection of a hollow triangular model cantilever subject to both lateral and normal forces. The measured response of the servo circuit to an inclined, loaded cantilever is then determined. This shows (1) errors are always present in height measurements of structures on inhomogeneous surfaces; (2) the sensitivity to buckling can be reduced by repositioning the laser; (3) friction measurements can be accurately made by scanning in two directions and applying the proper calibration. [ABSTRACT FROM AUTHOR]

Here, we demonstrate a variation of photoacoustic spectroscopy that can be used for obtaining spectroscopic information of surface adsorbed chemicals in a standoff fashion. Pulsed light scattered from a target excites an acoustic resonator and the variation of the resonance amplitude as a function of illumination wavelength yields a representation of the absorption spectrum of the target. We report sensitive and selective detection of surface adsorbed compounds such as tributyl phosphate and residues of explosives such as trinitrotoluene at standoff distances ranging from 0.5–20 m, with a detection limit on the order of 100 ng/cm2. [ABSTRACT FROM AUTHOR]

Standoff detection of trace explosives is gaining attention due to its immediate relevance in countering terrorist threats based on explosive devices. However, most currently available standoff techniques rely on expensive, complex, and bulky equipment. We have demonstrated highly selective and sensitive standoff detection of explosive residues on surfaces by using photothermal spectroscopy carried out with bimaterial microcantilever sensors. The demonstrated sensitivity of the technique, 100 ng/cm2, is sufficient to detect the explosive contamination generally found on explosive devices. The sensitivity of the technique can be further improved by optimizing the bimaterial cantilever and by using higher intensity infrared sources. [ABSTRACT FROM AUTHOR]

A highly sensitive potentiometric technique generally applicable for detection of gases utilizing adsorption-induced changes in surface work function is demonstrated. This technique is applied to sense hydrogen based on work function change of a Pt thin film. The surface work function changes of Pt upon exposure to pure and 1000 ppm hydrogen were found to be ∼900 and ∼270 mV, respectively. These work function changes are much higher than corresponding changes in the Schottky barrier height in Pt-semiconductor based amperometric sensor devices for similar hydrogen concentration. Using this technique, detection down to 8 ppm hydrogen concentration is demonstrated. [ABSTRACT FROM AUTHOR]