Study On Atomic Force Microscope Tip-sample Interaction For Controllable Two-Dimensional Manipulation Of Nanowires

As a comprehensive discipline with strong crossed nature,nano science and technology leads the development of frontier technologies in multiple fields,and it has been regarded by many countries as commanding height of science and technology competition.As one of the important components of nano science and technology,nanomanipulation technology is a key method to realize the displacement,splicing and deformation of nanomaterials,and plays an indispensable role in nanodevices manufacturing.Atomic force microscope(AFM)is a common instrument which can be employed for the nanomanipulation.At present,due to the lack of investigating the adhesion between a nanowire and a substrate,as well as the interaction between an AFM tip and a nanowire,the accuracy of the manipulation is limited;besides,most AFM-based nanomanipulation technologies are carried out in contact mode,which are more likely to induce substrate wear by the tip.For a comparison,the wear can be effectively reduced when the manipulation process is conducted in tapping mode.The research on the tip-sample interaction contributes to improve the accuracy of AFM-based nanowire manipulation technologies,and lays a foundation for the development of nanomanipulation technology in tapping-mode AFM.In addition,the tip-sample interaction has a significant influence on probe vibration in a tapping-mode AFM,causing the decrease of measurement accuracy and even image distortion.Studying the tip-sample interaction provides a theoretical basis for improving the measurement and imaging accuracy of tapping-mode AFM.Currently,researchers mainly study the tip-sample interaction through the force,amplitude and phase of an AFM probe;but they hardly investigated the interaction through these simultaneously collected values,making it hard to systematically study the interaction in multiple fields,including attractive forces,energy dissipation and hysteresis.In this thesis,the force,amplitude and phase of a probe retracting from different surfaces with different velocities or voltages were simultaneously collected through an AFM,aiming to investigate the mechanism of the tip-sample interaction in multiple aspects.On this basis,the effects of probe retracting velocity and voltage on the interaction between an AFM tip and a silver nanowire were investigated.Finally,by optimizing the probe voltage and amplitude parameters,the controllable bending of a silver nanowire was conducted in a tapping-mode AFM.The main research contents in this thesis are as follows:(1)The effects of probe retracting velocity and voltage on the tip-sample interaction were investigated.In this thesis,an AFM was employed to simultaneously collect the force,amplitude and phase of a probe retracting from a silicon surface with different velocities or voltages,aiming to analyze the probe vibration and further reflect the tip-sample interaction during the experiment.The results obtained through the analysis indicate that the increase of probe retracting velocity or voltage causes the strengthening of the tip-sample interaction.(2)The effects of surface hardness and wettability on the tip-sample interaction were studied.Silicon samples with different wettability and a polyvinyl chloride sample were used as research subjects.An AFM was employed to simultaneously collect the force,amplitude and phase of a probe when it retracted from the surfaces of these research objects with different velocities,and the tip-sample interaction was further analyzed through the obtained data.The results indicate that the reduce of surface hardness causes the increase of energy dissipation in probe vibration;and the increase of surface wettability causes the tip-sample interaction to strengthen.(3)The effects of probe retracting velocity and voltage on the interaction between the tip and a silver nanowire were researched.An AFM was employed to simultaneously measure the force,amplitude and phase of a probe retracting from the surface of a silver nanowire with different velocities or voltages,in order to investigate the discrepancy of the interaction under different experimental conditions.The analysis shows that the increase of probe retracting velocity or voltage can lead to the strengthening of the interaction between the tip and a silver nanowire.(4)The controllable two-dimensional manipulation of a silver nanowire was conducted in the tapping mode of an AFM.Based on the above research,the interaction between an AFM tip and the hydrophobic silicon surface is relatively weaker,thus the hydrophobic silicon is beneficial for nanowire manipulation.Correspondingly,a silicon sample coated with a self-assembled monolayer of PFDS was selected as the substrate for two-dimensional nanowire manipulation.Based on the optimized probe voltage and amplitude parameters,the controllable bending of a silver nanowire was conducted in the tapping mode of an AFM.Tapping-mode AFM is widely used in micro-nano scale mechanical characterization,morphology detection and manipulation,etc.,and the tip-sample interaction has significant influences on the mechanical behavior of the probe in these applications.In this thesis,the effects of probe retracting velocity and voltage,as well as the hardness and wettability of material surface,on the tip-sample interaction were investigated,and the influence mechanisms were also addressed.Through the investigation of the interaction between the tip and a silver nanowire surface with different probe retracting velocities or voltages,a reasonable probe voltage and amplitude were determined to conduct the controllable twodimensional manipulation of a silver nanowire on a silicon substrate,which was coated with a self-assembled monolayer of PFDS.This thesis further enriches the research on the tipsample interaction in atmosphere,and contributes significantly to realizing the twodimensional manipulation of silver nanowires in tapping-mode AFM.