Optical detection system for probing cantilever deflections parallel to a sample surface (original) (raw)
Related papers
Journal of Applied Physics, 1998
The detection sensitivity of an atomic force microscope with optical beam deflection for small cantilevers is characterized experimentally and theoretically. An adjustable aperture is used to optimize the detection sensitivity for cantilevers of different length. With the aperture, the signal-to-noise ratio of cantilever deflection measurements is increased by a factor of 1.5 to nearly 3. A theoretical model is set up that generally describes the optical beam deflection detection in an atomic force microscope. This model is based on diffraction theory and includes the particular functional shape of the cantilever.
A detailed analysis of the optical beam deflection technique for use in atomic force microscopy
Journal of Applied Physics, 1992
A Michelson interferometer and an optical beam deflection configuration (both shot noise and diffraction limited) are compared for application in an atomic force microscope. The comparison shows that the optical beam deflection method and the interferometer have essentially the same sensitivity. This remarkable result is explained by indicating the physical equivalence of both methods. Furthermore, various configurations using optical beam deflection are discussed. All the setups are capable of detecting the cantilever displacements with atomic resolution in a 10 kHz bandwidth.
Calibrating laser beam deflection systems for use in atomic force microscopes and cantilever sensors
Applied Physics Letters, 2006
Most atomic force microscopes and cantilever-based sensors use an optical laser beam detection system to monitor cantilever deflections. We have developed a working model that accurately describes the way in which a position sensitive photodetector interprets the deflection of a cantilever in these instruments. This model exactly predicts the numerical relationship between the measured photodetector signal and the actual cantilever deflection. In addition, the model is used to optimize the geometry of such laser deflection systems, which greatly simplifies the use of any cantilever-based instrument that uses a laser beam detection system.
Noninvasive determination of optical lever sensitivity in atomic force microscopy
Review of Scientific Instruments, 2006
Atomic force microscopes typically require knowledge of the cantilever spring constant and optical lever sensitivity in order to accurately determine the force from the cantilever deflection. In this study, we investigate a technique to calibrate the optical lever sensitivity of rectangular cantilevers that does not require contact to be made with a surface. This noncontact approach utilizes the method of Sader et al. ͓Rev. Sci. Instrum. 70, 3967 ͑1999͔͒ to calibrate the spring constant of the cantilever in combination with the equipartition theorem ͓J. L. Hutter and J. Bechhoefer, Rev. Sci. Instrum. 64, 1868 ͑1993͔͒ to determine the optical lever sensitivity. A comparison is presented between sensitivity values obtained from conventional static mode force curves and those derived using this noncontact approach for a range of different cantilevers in air and liquid. These measurements indicate that the method offers a quick, alternative approach for the calibration of the optical lever sensitivity.
Optical lever calibration in atomic force microscope with a mechanical lever
Review of Scientific Instruments, 2008
A novel method that uses a small mechanical lever has been developed to directly calibrate the lateral sensitivity of the optical lever in the atomic force microscope ͑AFM͒. The mechanical lever can convert the translation into a nanoscale rotation angle with a flexible hinge that provides an accurate conversion between the photodiode voltage output and torsional angle of a cantilever. During the calibration, the cantilever is mounted on a holder attached on the lever, which brings the torsional axis of the cantilever and rotation axis of the lever into line. By making use of its nanomotion on the Z-axis and using an external motion on the barrier, this device can complete the local and full-range lateral sensitivity calibrations of the optical lever without modifying the actual AFM or the cantilevers.
MODEL OF THE CANTILEVER USED AS A WEAK FORCE SENSOR IN ATOMIC FORCE MICROSCOPY
2005
New types of weak forces measurements with Atomic Force Microscope (AFM) are very challenging for experimental physics and call for new studies on control strategies operating the AFM. It is thus necessary to first develop a precise model of the cantilever with its sharp tip, in interaction with the scanned sample. This paper presents a model of the cantilever, that is based on beam theory and taking into account the influence of the long distance interaction forces.
Optical excitation of atomic force microscopy cantilever for accurate spectroscopic measurements
EPJ Techniques and Instrumentation, 2020
Reliable operation of frequency modulation mode atomic force microscopy (FM-AFM) depends on a clean resonance of an AFM cantilever. It is recognized that the spurious mechanical resonances which originate from various mechanical components in the microscope body are excited by a piezoelectric element that is intended for exciting the AFM cantilever oscillation and these spurious resonance modes cause the serious undesirable signal artifacts in both frequency shift and dissipation signals. We present an experimental setup to excite only the oscillation of the AFM cantilever in a fiber-optic interferometer system using optical excitation force. While the optical excitation force is provided by a separate laser light source with a different wavelength (excitation laser : λ = 1310 nm), the excitation laser light is still guided through the same single-mode optical fiber that guides the laser light (detection laser : λ = 1550 nm) used for the interferometric detection of the cantilever deflection. We present the details of the instrumentation and its performance. This setup allows us to eliminate the problems associated with the spurious mechanical resonances such as the apparent dissipation signal and the inaccuracy in the resonance frequency measurement.
Review of Scientific Instruments, 2008
We present here a method to calibrate the lateral force in the atomic force microscope. This method makes use of an accurately calibrated force sensor composed of a tipless piezoresistive cantilever and corresponding signal amplifying and processing electronics. Two ways of force loading with different loading points were compared by scanning the top and side edges of the piezoresistive cantilever. Conversion factors between the lateral force and photodiode signal using three types of atomic force microscope cantilevers with rectangular geometries ͑normal spring constants from 0.092 to 1.24 N / m and lateral stiffness from 10.34 to 101.06 N / m͒ were measured in experiments using the proposed method. When used properly, this method calibrates the conversion factors that are accurate to Ϯ12.4% or better. This standard has less error than the commonly used method based on the cantilever's beam mechanics. Methods such of this allow accurate and direct conversion between lateral forces and photodiode signals without any knowledge of the cantilevers and the laser measuring system.
Beilstein Journal of Nanotechnology, 2014
We present a theoretical framework for the dynamic calibration of the higher eigenmode parameters (stiffness and optical lever inverse responsivity) of a cantilever. The method is based on the tip–surface force reconstruction technique and does not require any prior knowledge of the eigenmode shape or the particular form of the tip–surface interaction. The calibration method proposed requires a single-point force measurement by using a multimodal drive and its accuracy is independent of the unknown physical amplitude of a higher eigenmode.
Laser Actuation of Cantilevers for Picometre Amplitude Dynamic Force Microscopy
Scientific Reports, 2014
As nanoscale and molecular devices become reality, the ability to probe materials on these scales is increasing in importance. To address this, we have developed a dynamic force microscopy technique where the flexure of the microcantilever is excited using an intensity modulated laser beam to achieve modulation on the picoscale. The flexure arises from thermally induced bending through differential expansion and the conservation of momentum when the photons are reflected and absorbed by the cantilever. In this study, we investigated the photothermal and photon pressure responses of monolithic and layered cantilevers using a modulated laser in air and immersed in water. The developed photon actuation technique is applied to the stretching of single polymer chains.