Study On AFM-based Nanomachining Models Of Machined Depth And Processing Technology Of Multi-scale Nanostructures

With the rapid development of nanotechnology, nanoparns are increasingly employed in the fields of nanophotonics, nanofluidics and nanoelectronics. However, to create nanopatterns with accurate dimensions is a challenge owing to the complexity and/or cost of the existing methods that greatly impede nanopattern fabrication, such as focused ion beam nanolithography, laser processing and nanoimprint lithography. Atomic force microscopy(AFM), invented in 1986, was originally employed as a high-precision surface profiler with nano-Newton scale interaction forces between the AFM probe and the sample. However, when the interaction force is large enough to generate plastic deformation in the sample, the obsevered AFM-based nanoscratching method can be considered as a nanofabrication technique. The AFM-based direct scratching method is currently known as a simple and feasible method for fabricating nanoscale patterns, owing to its low cost, simplicity, high accuracy and low environmental requirement. Howerver, this technique is still in the stage of preliminary study. The material removal mechanism and processing method of large-scale nanostructure fabrication when using AFM-based nanoscratching method need to be further studied, which leads to very difficult to fabricate nanopatterns with controllable machined depth and large-scale length. Therefore, according to the issues mentioned above, the AFM-based nanoscratching technique is investigated in three aspects: mechanism, theory and processing. The detailed contents of this thesis contain:A load-controlled molecular dynamics simulation model is developed to study the material removal process during the multi-passes scrarching and analyze the influence of the crystal orientation of the single crystal metal on the machined depth and the profile of the machined grooves. Based on the experimental method, the actual normal load applied on the sample in the single groove scratching process can be detected when scratching in different directions and the materials removeal states in different scratching directions can be obtained. Moreover, in the two/three dimensional nanostructure machining process, the effect of the feed direction on the chip formation, the quality of the machined grooves and the machined depth is analyzed and the cutting angles of different feed direction are obtained. The influence of the cutting angles on the material removeal state is also analyzed.Theoretical models applied to metal materials are establish to study the relationship between the applied normal load and the machined depth during single-groove multi-passes and two/three dimensional nanostructure machining process. In these models, the AFM probe is simplified as a cone with a spherical apex, which is verified by the experiments. In addition, a theoretical model applied to polymer material is also developed to study the relationship between the normal load and the machined depth during single groove scraching process. The geometrical shape of the probe, the height of the material pile-up and the elastic recovery of the material are considered in this model.The experimental normal load for the expected machined depth in the multi-passes scratching process is compared with the calculated theoretical normal load. Based on the difference between the experimental and theoretical values, the model for multi-passes scratching process is amended and the machined depth is predicted successfully. Moreover, the range of application of the theoretical model for two/three dimensional nanostructures machining is also studied and a sine wave nanostructure is obtained successfully. For the polymer material, the effects of the normal load and scratching velocity on the material pile-up and the elastic recovery of the material are studied and they are introduced into the theoretical model of the relationship between the normal load and the machined depth. The theoretical machiend depth for a given normal load is obtained, which is closed to the experimental value. The feasibility of the established theoretical model is verified.Novel AFM-based nanoscratching methods combining the probe trajectory with the high-precision stage movement are proposed. The effects of the machining parameters on the machined groove are analyzed and the optimized parameters are obtained. The large-scale nanochannels array with good quality are fabricated successfully. For the fabrication of nanochannels with ladder nanostructure at the bottom, the inflence of the matching relations between the feed speed of the tip and the moving velocity of the stage on the machined results is studied. The large-scale nanochannels array with ladder nanostructure at the bottom are also obtained successfully. In addition, a novel AFM-based nanoscratching method to fabricate nanochannel with complex three dimensional nanostructures at the bottom by controlling the feed during the scratching process is presented. The limiting inclined angle of the machined nanostructures is evaluated when using a diamond AFM tip. The nanochannel with typical three dimensional nanostructures are obtained.A five-axis nanomechanical processing equipment is established to conduct AFM-based nanoscratching process on a micro-ball. The solutions of some key issues such as aligning procedure of the rotation center of the micro-ball and detection of the distance between the micro-ball center and the rotation center of the AFM head are presented. Different nanostructures are machined on different rings of the micro-ball successfully. An AFM-based methodology for measuring axial and radial error motions of the air-bearing is proposed and the machining position errors caused by the axial and radial error motions of the air-bearing and the offset of the micro-ball are also studied.