SPMW FIRAT: A fast and sensitive probe structure for SPM
05 Jan 2007 | Online Presentations | Contributor(s): F. Levent Degertekin
A new SPM probe, called the force sensing integrated readout and active tip (FIRAT), is described and initial experimental results obtained on commercial AFM systems are presented. FIRAT combines a micromachined integrated electrostatic actuator to move the tip and an integrated optical interferometric displacement detector in a microscale volume. The current implementation of the probe uses surface micromachined aluminum structures on quartz substrate as the mechanical force sensing structure, and the probe tips are fabricated by focused ion beam assisted deposition . Interferometric detection is achieved by monitoring the reflected diffraction pattern generated when the diffraction grating on the quartz substrate surface beneath the probe tip is illuminated by a laser. This robust interferometer structure has been shown to provide detection levels down to 13.6fm/√Hz with 60µW laser power, close to the shot noise level .
The probe is integrated to several commercial AFM systems for imaging and material characterization experiments. Tapping mode images using FIRAT probes with resonance frequencies in the 600-900 kHz range with 60 Hz line scan rate are obtained, where the electrostatic actuator is used for both AC vibration and Z position control. In addition to regular tapping mode imaging, the broad bandwidth of the probe enables non-resonant tapping mode imaging where the transient interaction forces can be measured with regular imaging speeds. When used in the time resolved interaction force (TRIF) mode, the FIRAT probe provides quantitative information such as surface adhesion and elasticity through model based inversion, while simultaneously imaging the topography. TRIF mode images and inversion results on various polymer and carbon nanotube samples are presented. FIRAT probe design and fabrication for specific applications for operation in air are also discussed. Fabricated probes have resonance frequencies about 1MHz, quality factors in the .5 to 16, spring constants in the 10-40 N/m range. Finally, FIRAT probes for applications in liquids are described and initial single molecule force spectroscopy results are presented.
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W. Lee, N. A. Hall, Z. Zhou, and F. L. Degertekin, “Fabrication and Characterization of a Micromachined Acoustic Sensor with Integrated Optical Readout,” IEEE J. Selected Topics on Quantum Electronics, 10, pp. 643-51, 2004.