A frequency modulation atomic force microscope(AFM) using a tuning fork as the force sensor is developed.Utilizing the piezoelectricity and ultra high quality factor characteristics of tuning forks,a positive feedback loop is used to oscillate a tuning fork at its resonant frequency.An automatic gain control loop is used to keep the oscillating amplitude of the tuning fork constant.By a simple and accurate method,the quantitative amplitude of the tuning fork can be easily calibrated using the cu...