[Show abstract][Hide abstract] ABSTRACT: We present a chemical sensor based on a microfabricated array of eight silicon cantilevers actuated at their resonance-frequency and functionalized by polymer coatings. The operating principle relies on transduction of chemical or physical processes into a mechanical response. After exposure to analyte vapor, analyte molecules diffuse into the cantilever coating, which begins to swell. Jointly with the mass increase, a change of interfacial stress between coating and cantilever occurs, resulting in a bending of the cantilevers. Our setup allows the simultaneous detection of cantilever oscillation and bending of eight cantilevers by time-multiplexed optical beam de¯ection readout. The ac component of the cantilever response is demodulated, and the cantilever resonance-frequency is tracked by a custom-built phase-locked loop. By ®ltering out the ac component (oscillation), the dc signal (bending) is extracted, yielding information on mass as well as surface stress changes simultaneously. Detection results of water, primary alcohols, alkanes and perfumes are presented. # 2001 Elsevier Science B.V. All rights reserved.
Sensors and Actuators B Chemical 06/2001; · 3.54 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We present quantitative and qualitative detection of analyte vapors using a microfabricated silicon cantilever array. To observe transduction of physical and chemical processes into nanomechanical motion of the cantilever, swelling of a polymer layer on the cantilever is monitored during exposure to the analyte. This motion is tracked by a beam-deflection technique using a time multiplexing scheme. The response pattern of eight cantilevers is analyzed via principal component analysis (PCA) and artificial neural network (ANN) techniques, which facilitates the application of the device as an artificial chemical nose. Analytes tested comprise chemical solvents, a homologous series of primary alcohols, and natural flavors. First differential measurements of surface stress change due to protein adsorption on a cantilever array are shown using a liquid cell.
[Show abstract][Hide abstract] ABSTRACT: Force microscopy in atomic resolution with an oscillating tip has been performed across monatomic steps of the Si(111)-(7×7) surface using the tunnelling current or frequency shift as the feedback parameter. The contrast of simultaneously recorded images in both feedback modes is discussed. A significant difference between tip–sample interactions on the upper and lower terrace close to a step is analyzed in detail by means of Kelvin-type measurements. No contact potential variation across the step is found. A simple model for the force contrast is suggested which takes into account the different effective interaction areas or volumes on the upper and the lower terrace.
[Show abstract][Hide abstract] ABSTRACT: A novel chemical sensor based on a micromechanical array of silicon cantilevers is presented. Chemical reactions are transduced by sensitization of cantilevers with coatings such as metals, self-assembled monolayers, or polymers into a mechanical response. This is read out using an optical beam-deflection technique by a sequential readout scheme. Reference cantilever sensors permit subtraction of background signals (differential measurement). Coating of each cantilever sensor with a different sensitive layer allows operation of the array-device as a new form of chemical nose. Detection of hydrogen, primary alcohols, natural flavors, and water vapor is demonstrated. We show that the magnitude of sensor response is proportional to the amount of analyte present.
[Show abstract][Hide abstract] ABSTRACT: We present a novel chemical sensor based on a microfabricated
array of silicon cantilevers. Individual cantilevers are sensitized for
the detection of analytes using metal coatings. Analyte molecules
chemisorbing or physisorbing on the cantilever coating and chemical
reactions produce a change in interfacial stress between analyte
molecules and cantilever. This leads to a nanomechanical response of the
cantilever, i.e. bending. The bending is read out using a
time-multiplexed optical beam-deflection technique. From magnitude and
temporal evolution of the bending, quantitative information on analyte
species and concentration is derived. Here, we demonstrate the detection
of ethene and water vapor with such a nanomechanical nose
[Show abstract][Hide abstract] ABSTRACT: We present a novel chemical sensor based on a micromechanical array of silicon cantilevers sensitized for the detection of analytes using cantilever coatings such as metals, self-assembled monolayers, or polymers. Chemical reactions are transduced into a mechanical response and read out using an optical beam-deflection technique. Detection of primary alcohols, natural flavors, and water vapor is demonstrated.
IBM Research Division, Zurich Research Laboratory, Zurich, Switzerland. 01/1999;
[Show abstract][Hide abstract] ABSTRACT: This work presents constant amplitude Dynamic Force Microscopy (DFM) measurements under ultra-high vacuum conditions performed with home-built digital electronics based on the principle of phase locked loop (PLL) techniques. In DFM so-called topography is often measured in constant frequency shift (Δf) mode. This study describes the influence of phase shifts on constant Δf imaging. Therefore, phase variation experiments were acquired, leading to information about the cantilever resonance behaviour close to the surface. As sample, an evaporated thin film of NaCl on a Cu(111) substrate was chosen in order to obtain a heterogeneous system with clean Cu and NaCl areas. The atomic structure of both materials was resolved, which is the first time true atomic resolution was obtained on a metal. Large apparent topography variations are observed on this heterogeneous sample when changing the phase between the excitation and oscillation of the cantilever end. Such artefacts can be explained by comparison with phase variation experiments.
[Show abstract][Hide abstract] ABSTRACT: A feedback mechanism based on fuzzy logic has been applied to operate a combined atomic force microscope (AFM)/scanning tunneling microscope (STM), which is able to measure the resonance frequency shift Deltaf of the cantilever-type spring and the mean tunneling current It simultaneously. Using a decision making logic, the microscope can be scanned over a heterogeneous surface without tip crash. On the conductive parts of the sample, the STM mode is preferred, whereas the noncontact (nc)-AFM mode is used on the poorly conductive parts of the surface. The transition from the STM mode to nc-AFM mode is performed smoothly with the fuzzy logic feedback.
[Show abstract][Hide abstract] ABSTRACT: One way to improve imaging in dynamic force microscopy is to increase
the cantilever resonance frequency. Higher frequencies require faster
electronics. This work presents fast new digital electronics based on
the principle of phase-locked loop techniques. First results show very
high frequency resolution and very stable imaging.
Applied Physics A 01/1998; 66:S215-S218. · 1.69 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We investigate interaction effects which occur in scanning tunneling
microscopy (STM) by performing local force spectroscopy with an
oscillating tip while imaging Si(111)7×7 terraces in the dynamic
lever STM mode (constant time-averaged current). It is found that true
atomic resolution is achieved close to the minimum of the resonance
frequency vs. distance curve and even closer to the sample. On the other
hand true atomic resolution in noncontact AFM (constant frequency shift)
is expected several nm away from this minimum, in the range where the
frequency shift becomes more negative with decreasing distance.
Applied Physics A 01/1998; 66:S245-S248. · 1.69 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: can be detected by its adsorption on aPt-coated sensor because achange in surface stress causes astatic bending of the
sensor. The diffusion of various alcohols into polymethylmethacrylate induces resonance frequency shifts in adynamic measuring
mode and bending in the static mode, which allows one to distinguish between the various alcohols.
Applied Physics A 01/1998; 66:S61-S64. · 1.69 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: t simultanously. Depending on the conductivity of the surface the fuzzy logic controller decides whether it has to use the
AFM feedback or the STM feedback. On conductive regions of the sample STM mode is used, whereas on poorly conducting regions
the non-contact AFM mode is preferred. This allows one to scan over heterogenous surfaces avoiding atip crash.
Applied Physics A 01/1998; 66:S49-S53. · 1.69 Impact Factor