| Budget Amount *help |
¥4,000,000 (Direct Cost: ¥4,000,000)
Fiscal Year 2006: ¥700,000 (Direct Cost: ¥700,000)
Fiscal Year 2005: ¥700,000 (Direct Cost: ¥700,000)
Fiscal Year 2004: ¥2,600,000 (Direct Cost: ¥2,600,000)
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| Research Abstract |
This research has been intended for development of atomic force microscopy (AFM) oriented for observation of biomolecules or microscopic properties of liquid-solid interfaces in aqueous environment. As an alternative method for conventional atomic force microscopy using a cantilever-type force sensor, which enormously suffers from sensitivity degradation due to viscous effects in liquid environment, a length-extensional quartz oscillator was employed as a novel force sensor that can implement self-oscillation and self-detection. In order to prevent viscous damping on the oscillator and electrode short circuit the oscillator was incorporated in to anti wetting housing so that only the needle probe was exposed to the solution. The Q value of the sensor that was around 6000 in ambient air dropped to about 4000 in water, implying a sensitivity degradation of only about 80 %. Under a typical condition the spatial amplitude of the probe was evaluated to of the order of 0.1 nm, a value 1-2 or
… More
ders of magnitude smaller than that of the conventional cantilever sensor and a strong advantage of the novel sensor. On the other hand, improvement of dynamic mode AFM using the conventional cantilever was also attempted. It was found theoretically and experimentally that detection of the phase of the cantilever oscillation (phase modulation, PM) can attain better sensitivity compared to the conventional amplitude modulation(AM) and also is more suited for wide-band measurement. It was also found that combination of this PM-AFM with the Q-control, a technique that enhances the resonance of the cantilever by an electrical positive feedback, enhances the sensitivity further. It was also shown that the multivalency in the oscillation spectrum of the cantilever due to the tip-sample interaction force, which often causes instability in cantilever oscillation, is successfully eliminated using an automatic gain control (AGC) in the cantilever excitation electronics so that the oscillation amplitude was kept constant regardless of the interaction force. In addition, enhancement in driving speed of the piezoelectric actuator was also attempted. As a method to directly measure the movement of the actuator, the current induced onto its electrode was detected as it was proportional to the velocity of the actuator motion. This signal was negatively fed back to the input so that the resonance was practically suppressed. The displacement of the piezo was also measured by integrating the induced current signal and was fed back to the input to eliminated the intrinsic hysteresis of the piezo. Eventually, wide-band and hysteresis-free regulation of the piezoelectric scanner was successfully implemented. Less
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