Analysis And Application Of Vibration In Scanning Probe Microscopy

Vibration is an important research topic in the field of scanning probe microscopy.This thesis is concentrated on theoretical and experimental research on externalvibration criteria of scanning probe microscope (SPM), influence of externalvibration on SPM performance, vibration compensation plans, micro vibrationmeasurement using the principle of SPM, etc. The main work of the thesis includes:1. Tip-sample interaction, which is the key structure of SPM, was theoretically analyzed. Static and dynamic mechanics models are built up on cantilever SPM, which is widely used. In vibration frequency band concerned in this thesis, far below 10 kHz, the harmonic spring oscillator is used as the model of cantilever. Point-mass model of tip-sample interaction is then decided, omitting the effect of low frequency vibration propagating spatially along the cantilever.2. A SPM base vibration measurement system is set up. A laser interferometer is used for measurement. A BK vibrator and an arbitrary waveform generator, AWG2021, are used for vibration stimulation. The frequency band concerned in this thesis is decided as 0 - 100 Hz, by means of vibration response experiments on SPM.3. A concept of SPM vibration rejection ratio is proposed, which is defined as the amplitude ratio of external stimulating vibration and tip-sample interaction change. The SPM vibration rejection ratio is theoretical analyzed under the conditions of open loop and close loop operation. It comes to a conclusion that, under the conditions of open loop operation, vibration rejection ratio is approximately inverse-proportional with the square of stimulating frequency, and restricted by effective mass, spring constant and air damping constant of cantilever, contact elasticity constant and contact damping constant between tip and sample. The relationship between SPM vibration rejection ratio and external vibration amplitude, sample scanner size, sample hardness, cantilever length, tip-sample pre-force and SPM open/close loop, etc., is experimentally proved.4. SPM imaging mechanism is analyzed. The influence of the combination of external vibration and tip-sample scanning movement on SPM imaging is idiscussed. It is proved by experiments that scanning rate (frequency) and number of sampling points of SPM will directly influence the direction and distribution of the fringes (spatial periodical wave), generated by certain frequency external vibration, on SPM image, which is the main form of SPM image distortion caused by external vibration.5. Two compensation plans of external vibration, which influences the quality of SPM imaging, are proposed. One is to measure the tip-sample interaction change caused by external vibration, the result of which is used for compensation of the distorted image scanned by SPM. The other is to stimulate the cantilever at its fixed end with the signal measured from the tip-sample interaction change, in order to eliminate the distance change caused by external vibration, so as to realize online vibration compensation.6. The research status quo on micro and nano vibration measurement and sensor technology is analyzed. Mechanism and structure design of micro and nano vibration sensor are studied. A sensor system is built up. The measuring technique of the weak tunneling current is discussed. Measuring and controlling circuits of STM nano scale vibration sensor system are designed and realized.