Research On High-speed Atomic Force Microscopy And Its Applications In 3D Nanoprinting

Three dimensional(3D)printing technique,which has been recognized as a symbol of the third industrial revolution,is changing the way of manufacturing.When printing components,the model generated by computer aided design is sliced into thin layers with given thicknesses,and then added layer by layer until obtaining the expected object.Compared with traditonal methods,3D printing approach can afford the production of highly complex components,in a much more effec ient manner.At the micro-and nano-scale,3D printing technique has also shown enormous potentials.Traditional micro-and nano-fabrication techniques such as photolithography,soft lithography,e-beam lithography and nanoindentation lithography are only suitable for fabricating 2D patterns.In addition,complicate working procedure,high cost and long lead time further complicate the situation.However,by using 3D printing techniques,complex nanostructures can be fabricated in a diret-write way,without using masks and resists.To date,focused electron beam induced deposition(FEBID),a promising 3D nanoprinting approach,has driven a large amount of innovations to happen in the fields of nano-optics,nanoelectronics and nanometrology.However,the bott leneck of this technique lies in the fact that the fabrication precision can not be fully controlled,which is particularly important for manufacturing multilayer functional nanostructures.To break through this bottleneck,we propose a new concept of "close-loop 3D nanoprinting technique".By customizing high-performance characterization tools,printing outcomes and parameter tuning process can be linked together.Based on this,we have built a high-speed atomic force microscope(HS-AFM)compatible with FEBID process.In this design,detecting optics,scanner,control electronics and data aquisition system have been redesigned.The integrated HS-AFM/FEBID not only enables in situ and online probing of the 3D printed nanostructures,but also allows for new type of experiments such as exploring the evolving dynamics just after deposition.To be specific,we first modelled the cantilever dynamics in both constant force contact mode and tapping mode.Based on this,key parameters determining scanning speed such as quality factor and resonance frequency have been analyzed in detail.Also,the influence of the mechanical bandwidth of scanner and cantilever on imaging quality is clarified.As a result,it is clear that in vacuum chamber of the dual beam microscope(DBM),constant force contact mode is suitable for high-speed AFM imaging.The scanner was redesigned using flexure based mechanism.The Castigliano theorem was adopted to analyze the stiffness of the flexure,so that the scan size is more 90% of the stroke.Then finite element analysis(FEA)simulation was conducted to further evaluate the dynamic performance of the design,before real implementation.The experimental results demonstrate the feasibility of the proposed high-bandwidth scanner.According to these,hysteresis nonlinearity,vibration and crosstalk between X-and Y-axes have been identified.To compensate them,a field programmable analog array has been chosen to implement feedforward controllers.Then self-sensing cantilever readout circuit and high-speed data acquisition system have been built.User interface to set scan parameters was programmed based on Lab VIEW development enviroment.By doing these,both cantilever signal and controller output were sampled and recorded for constructing AFM images.To compensate the rate-dependent hysteretic effect,a novel charge control method has been proposed,aiming to eliminate the observed under-compensation and over-compensation effects.As a consequence,motion precision and effective operating range have been significantly improved.The sensorless and model-free natures of the proposed method make it particularly suitable for real-time industrial applications,since both the cost and system complexity have been reduced to a large extent.Finally,the custom-built high-speed AFM was integrated with FEBID.The effectiveness of the design was first demonstrated by imaging standard grit sample in the air,and further demonstrated by monitoring the growth process of a multi-layer Matterhorn replica inside the vacuum chamber.By coordinating the operation strategy between HS-AFM and FEBID,simultaneous imaging and fabrication has been achieved,which opens up a revenue for exploring evolving properties of the printed nano-structures.To sum up,the proposed high-speed AFM can serve as an high-performance characterization tool towards close-loop 3D nanoprinting.Future works should focus on making full use of the obtained spatial information to tune printing parameters of FEBID process.