Yanquan Geng

Effect of cantilever deformation and tip-sample contact area on AFM nanoscratching

The present work investigates the effect of cantilever deformation and tip-sample contact area on the performance of atomic force microscopy (AFM)-based scratching tests. Nanoscratching tests are carried out using a pyramidal diamond tip on aluminum alloy surfaces. Three typical AFM cantilever deformation states are illustrated, and the actual normal loads applied on the surface of the sample are obtained using a new method. A theoretical model for AFM-based nanoscratching using a three-sided pyramidal tip is also established to calculate the effect of the tip-sample contact area for different scratching directions. The corresponding theoretical normal loads can be obtained with this model. Experimental and theoretical results are compared for the normal loads at an expected machined depth, with different scratching directions. The contact length between the chip and the rake face of the tip is found to be the key factor leading to an increase in the tip-sample contact area. This results in an actual norm...

Fabrication of nanochannels with ladder nanostructure at the bottom using AFM nanoscratching method

This letter presents a novel atomic force microscopy (AFM)-based nanomanufacturing method combining the tip scanning with the high-precision stage movement to fabricate nanochannels with ladder nanostructure at the bottom by continuous scanning with a fixed scan size. Different structures can be obtained according to the matching relation of the tip feeding velocity and the precision stage moving velocity. This relationship was first studied in detail to achieve nanochannels with different ladder nanostructures at the bottom. Machining experiments were then performed to fabricate nanochannels on an aluminum alloy surface to demonstrate the capability of this AFM-based fabrication method presented in this study. Results show that the feed value and the tip orientation in the removing action play important roles in this method which has a significant effect on the machined surfaces. Finally, the capacity of this method to fabricate a large-scale nanochannel was also demonstrated. This method has the potential to advance the existing AFM tip-based nanomanufacturing technique of the formation these complex structures by increasing the removal speed, simplifying the processing procedure and achieving the large-scale nanofabrication.

Investigation of the nanoscale elastic recovery of a polymer using an atomic force microscopy-based method

An atomic force microscopy (AFM)-based method to reveal the elastic recovery behavior of a polymer material after the nanoscratching process is presented. The machined depth during scratching is obtained by monitoring the position of the piezoceramic tube (PZT) of the AFM system. By comparison with the measured depth of the nanogroove, the elastic recovery of the machined depth can be achieved. Experiments are also undertaken to study the effects of the scratching velocity and the applied normal load on the elastic recovery of the machined depth when scratching on polycarbonate (PC). Results show that the elastic recovery rate has a logarithmically proportional relationship to the scratching velocity, while it has little change with the variation of the applied normal load. In addition, the constitutive model of the polymer material is also used to verify the obtained conclusions, indicating that this is a potential method for measuring the elastic recovery of the material under the mechanical process on the nanoscale.

Machining complex three-dimensional nanostructures with an atomic force microscope through the frequency control of the tip reciprocating motions

A novel method relying on atomic force microscope (AFM) tip based nanomachining is presented to enable the fabrication of microchannels that exhibit complex three-dimensional (3D) nanoscale floor surface geometries. To achieve this, reciprocating lateral displacements of the tip of an AFM probe are generated, while a high-precision stage is also actuated to move in a direction perpendicular to such tip motions. The width and length of microchannels machined in this way are determined by the amplitude of the tip motion and the stage displacement, respectively. Thus, the processing feed can be changed during the process as it is defined by the combined control of the frequency of the tip reciprocating motions and the stage speed. By employing the built-in force feedback loop of conventional AFM systems during such operations, the variation of the feed leads to different machined depths. Thus, this results in the capability to generate complex 3D nanostructures, even for a given normal load, which is set by the AFM user prior to the start of the process. In this paper, the fabrication of different microchannels with floor surfaces following half triangular, triangular, sinusoidal, and top-hat waveforms is demonstrated. It is anticipated that this method could be employed to fabricate complex nanostructures more readily compared to traditional vacuum-based lithography processes.

Insight into mechanics of AFM tip-based nanomachining: bending of cantilevers and machined grooves

Atomic force microscope (AFM) tip-based nanomachining is currently the object of intense research investigations. Values of the load applied to the tip at the free end of the AFM cantilever probe used for nanomachining are always large enough to induce plastic deformation on the specimen surface contrary to the small load values used for the conventional contact mode AFM imaging. This study describes an important phenomenon specific for AFM nanomachining in the forward direction: under certain processing conditions, the deformed shape of the cantilever probe may change from a convex to a concave orientation. The phenomenon can principally change the depth and width of grooves machined, e.g. the grooves machined on a single crystal copper specimen may increase by 50% on average following such a change in the deformed shape of the cantilever. It is argued that this phenomenon can take place even when the AFM-based tool is operated in the so-called force-controlled mode. The study involves the refined theoretical analysis of cantilever probe bending, the analysis of experimental signals monitored during the backward and forward AFM tip-based machining and the inspection of the topography of produced grooves.

An AFM-based methodology for measuring axial and radial error motions of spindles

This paper presents a novel atomic force microscopy (AFM)-based methodology for measurement of axial and radial error motions of a high precision spindle. Based on a modified commercial AFM system, the AFM tip is employed as a cutting tool by which nano-grooves are scratched on a flat surface with the rotation of the spindle. By extracting the radial motion data of the spindle from the scratched nano-grooves, the radial error motion of the spindle can be calculated after subtracting the tilting errors from the original measurement data. Through recording the variation of the PZT displacement in the Z direction in AFM tapping mode during the spindle rotation, the axial error motion of the spindle can be obtained. Moreover the effects of the nano-scratching parameters on the scratched grooves, the tilting error removal method for both conditions and the method of data extraction from the scratched groove depth are studied in detail. The axial error motion of 124 nm and the radial error motion of 279 nm of a commercial high precision air bearing spindle are achieved by this novel method, which are comparable with the values provided by the manufacturer, verifying this method. This approach does not need an expensive standard part as in most conventional measurement approaches. Moreover, the axial and radial error motions of the spindle can both be obtained, indicating that this is a potential means of measuring the error motions of the high precision moving parts of ultra-precision machine tools in the future.

Characterization study on machining PMMA thin-film using AFM tip-based dynamic plowing lithography

This paper presents a reliable nanolithography technique, namely dynamic plowing lithography (DPL) based on a commercial atomic force microscope (AFM). The poly(methyl methacrylate) (PMMA) solution spinning on a silicon substrate is utilized to be scratched directly with an oscillating tip at its resonance frequency. The films with different thickness are obtained by adjusting the concentration of solution and post baked time. A new silicon tip is employed to conduct DPL on PMMA film surface. The geometry of nano-line structure scratched on the film with high adhesion force is shown with a transition process, including total protuberance, protuberance with groove and groove with pile-up. The scratching direction has less influence on the scratched depth of groove, while the shape of pile-up is varied with directions. The depth of groove on thin films is increasing with the drive amplitude until the value of the depth reaches to the threshold value. Moreover, owing to smaller elastic modulus, the film with relatively large thickness could be modified by the tip more easily using this DPL method. SCANNING 38:612-618, 2016.

Experimental and Theoretical Investigation of Crystallographic Orientation Dependence of Nanoscratching of Single Crystalline Copper.

In the present work, we perform experiments and molecular dynamics simulations to elucidate the underlying deformation mechanisms of single crystalline copper under the load-controlled multi-passes nanoscratching using a triangular pyramidal probe. The correlation of microscopic deformation behavior of the material with macroscopically-observed machining results is revealed. Moreover, the influence of crystallographic orientation on the nanoscratching of single crystalline copper is examined. Our simulation results indicate that the plastic deformation of single crystalline Cu under the nanoscratching is exclusively governed by dislocation mechanisms. However, there is no glissile dislocation structure formed due to the probe oscillation under the load-controlled mode. Both experiments and MD simulations demonstrate that the machined surface morphologies in terms of groove depth and surface pile-up exhibit strong crystallographic orientation dependence, because of different geometries of activated slip planes cutting with free surfaces and strain hardening abilities associated with different crystallographic orientations.

Direction-identical scratching method for fabricating nanostructures using a modified AFM nanoscratching system

To machine nanostructures with consistent depth and quality, a novel direction-identical scratching method based on a modified atomic force microscopy (AFM) probe-based machining system is proposed. During scratching, the optimized scratching direction is precisely maintained by rotating or/and moving the sample mounted on the stage of a modified AFM system. The specific procedures of this scratching method are described in detail and, compared to the conventional method, have the multiple advantages of optimized quality and consistent depth. Also, nanoline and nanochannel patterns are machined using this direction-identical scratching method, which is proved to be highly efficient.

A novel AFM-based 5-axis nanoscale machine tool for fabrication of nanostructures on a micro ball

This paper presents a novel atomic force microscopy (AFM)-based 5-axis nanoscale machine tool developed to fabricate nanostructures on different annuli of the micro ball. Different nanostructures can be obtained by combining the scratching trajectory of the AFM tip with the movement of the high precision air-bearing spindle. The center of the micro ball is aligned to be coincided with the gyration center of the high precision to guarantee the machining process during the rotating of the air-bearing spindle. Processing on different annuli of the micro ball is achieved by controlling the distance between the center of the micro ball and the rotation center of the AFM head. Nanostructures including square cavities, circular cavities, triangular cavities, and an annular nanochannel are machined successfully on the three different circumferences of a micro ball with a diameter of 1500 μm. Moreover, the influences of the error motions of the high precision air-bearing spindle and the eccentric between the micro ball and the gyration center of the high precision air-bearing spindle on the processing position error on the micro ball are also investigated. This proposed machining method has the potential to prepare the inertial confinement fusion target with the expected dimension defects, which would advance the application of the AFM tip-based nanomachining approach.