Constant Amplitude Feedback Control in Near-field Scanning Optical Microscopy in Shear Force Mode
剪切力模式近场扫描光学显微镜的恒幅反馈控制方法研究

A method is described to control the amplitude of the tuning fork probe while scanning on the surface of the sample in the Near-field Scanning Optical Microscopy(NSOM).The phase signal is used as the signal of distance control signal between tip and sample in the shear-force detection mode.Meanwhile the PI feedback technique is introduced to feedback control both the amplitude and phase of the probe resonance,the amplitude and phase of the tuning fork probe keep a constant value while scanning imaging.The NSOM images of the standard CD_RW grating with amplitude feedback circuit and without amplitude feedback circuit in different scanning speeds are obtained,and the two sets of images are compared.The experiment results shows that the introduce of constant amplitude feedback circuit can increase the response of the tuning fork probe system,meanwhile can improve the quality and resolution of the images gained by shear-force SNOM with bi-feedback control system of amplitude and phase.