Fabrication of periodic nanostructures using dynamic plowing lithography with the tip of an atomic force microscope

The fabrication of periodic nanostructures with a fine control of their dimensions is performed on poly(methyl methacrylate) (PMMA) thin films using an atomic force microscope technique called dynamic plowing lithography (DPL). Different scratching directions are investigated first when generating single grooves with DPL. In particular, the depth, the width and the periodicity of the machined grooves as well the height of the pile-up, formed on the side of the grooves, are assessed. It was found that these features are not significantly affected by the scratching direction, except when processing took place in a direction away from the cantilever probe and parallel to its main axis. For a given scratching direction, arrays of regular grooves are then obtained by controlling the feed, i.e. the distance between two machining lines. A scan-scratch tip trace is also used to reduce processing time and tip wear. However, irregular patterns are created when combining two layers oriented at different angles and where each layer defines an array of grooves. Thus, a “combination writing” method was implemented to fabricate arrays of grooves with a well-defined wavelength of 30 nm, which was twice the feed value utilized. Checkerboard, diamond-shaped, and hexagonal nanodots were also fabricated. These were obtained by using the combination writing method and by varying the orientation and the number of layers. The density of the nanodots achieved could be as high as 1.9 × 109 nanodots per mm2

A simulated investigation of ductile response of GaAs in single point diamond turning and experimental validation

In this paper, molecular dynamic (MD) simulation was adopted to study the ductile response of single-crystal GaAs during single-point diamond turning (SPDT). The variations of cutting temperature, coordination number, and cutting forces were revealed through MD simulations. SPDT experiment was also carried out to qualitatively validate MD simulation model from the aspects of normal cutting force. The simulation results show that the fundamental reason for ductile response of GaAs during SPDT is phase transition from a perfect zinc blende structure (GaAs-I) to a rock-salt structure (GaAs-II) under high pressure. Finally, a strong anisotropic machinability of GaAs was also found through MD simulations

Fabrication of periodic nanostructures using AFM tip-based nanomachining: combining groove and material pile-Up topographies

This paper presents an atomic force microscopy (AFM) tip-based nanomachining method to fabricate periodic nanostructures. This method relies on combining the topography generated by machined grooves with the topography resulting from accumulated pile-up material on the side of these grooves. It is shown that controlling the distance between adjacent and parallel grooves is the key factor in ensuring the quality of the resulting nanostructures. The presented experimental data show that periodic patterns with good quality can be achieved when the feed value between adjacent scratching paths is equal to the width between the two peaks of material pile-up on the sides of a single groove. The quality of the periodicity of the obtained nanostructures is evaluated by applying one- and two-dimensional fast Fourier transform (FFT) algorithms. The ratio of the area of the peak part to the total area in the normalized amplitude–frequency characteristic diagram of the cross-section of the measured AFM image is employed to quantitatively analyze the periodic nanostructures. Finally, the optical effect induced by the use of machined periodic nanostructures for surface colorization is investigated for potential applications in the fields of anti-counterfeiting and metal sensing

AFM tip-based nanomachining with increased cutting speed at the tool-workpiece interface

This paper reports a study towards enhancing the throughput of the Atomic Force Microscope (AFM) tip-based nanomachining process by increasing the cutting speed at the interface between the tool and the workpiece. A modified AFM set-up was implemented, which combined the fast reciprocating motions of a piezoelectric actuator, on which the workpiece was mounted, and the linear displacement of the AFM stage, which defined the length of produced grooves. The influence of the feed, the feed direction and the cutting speed on the machined depth and on the chip formation was studied in detail when machining poly(methyl methacrylate). A theoretical cutting speed over 5 m/min could be achieved with this set-up when the frequency of the piezoelectric actuator reciprocating motions was 40 kHz. This is significantly better than the state of the art for AFM-based nanomachining, which is currently less than 1 m/min.</p

Macro and nanoscale wear behaviour of Al-Al 2 O 3 nanocomposites fabricated by selective laser melting

Aluminium-based composites are increasingly applied within the aerospace and automotive industries. Tribological phenomena such as friction and wear, however, negatively affect the reliability of devices that include moving parts; the mechanisms of friction and wear are particularly unclear at the nanoscale. In the present work, pin-on-disc wear testing and atomic force microscopy nanoscratching were performed to investigate the macro and nanoscale wear behaviour of an Al-Al2O3 nanocomposite fabricated using selective laser melting. The experimental results indicate that the Al2O3 reinforcement contributed to the macroscale wear-behaviour enhancement for composites with smaller wear rates compared to pure Al. Irregular pore surfaces were found to result in dramatic fluctuations in the frictional coefficient at the pore position within the nanoscratching. Both the size effect and the working-principle difference contributed to the difference in frictional coefficients at both the macroscale and the nanoscale

AFM tip-based mechanical nanomachining of 3D micro and nano-structures via the control of the scratching trajectory

This paper presents a novel mechanical material removal method to produce nanostructures with a precise control of their three dimensional (3D) surface topography. The method employs the tip of an atomic force microscope (AFM) probe as the cutting tool and a closed-loop high precision stage to control the machining path of the tip. In this approach, the tip only describes vertical motions while the stage is actuated along lateral directions in a raster scan strategy. The machining of features with 3D nanoscale topography in this way is the combined result of the tip applying a constant normal load on the sample while varying the distance (i.e. the feed) between two parallel lines of cut. More specifically, an increased feed leads to a reduced machining depth and vice-versa. Thus, the main difference with mechanical milling or turning at such small scale is that this method relies on the control of the feed to determine the machined depth. To support the interpretation of the process outcomes, an analytical model is developed. This model expresses the relationship between the feed and the machined depth as a function of the contact area between the tip and the material. The critical achievable slope of produced nanostructures was derived from this model and validated using experimental tests. This parameter corresponds to the maximum inclination of the surface of a nanostructure that can be machined with the proposed method. From the knowledge of the critical slope, the machining of periodic nanostructures was demonstrated on a single crystal copper workpiece. In principle, the method reported here could be implemented to any instrument with micro- and nano-indentation capabilities by exploiting their load-control feedback mechanism

Processing outcomes of the AFM probe-based machining approach with different feed directions

We present experimental and theoretical results to describe and explain processing outcomes when producing nanochannels that are a few times wider than the atomic force microscope (AFM) probe using an AFM. This is achieved when AFM tip-based machining is performed with reciprocating motion of the tip of the AFM probe. In this case, different feed directions with respect to the orientation of the AFM probe can be used. The machining outputs of interest are the chip formation process, obtained machined quality, and variation in the achieved channel depth. A three-sided pyramidal diamond probe was used under load-controlled conditions. Three feed directions were first investigated in detail. The direction parallel to and towards the probe cantilever, which is defined as “edge forward”, was then chosen for further investigation because it resulted in the best chip formation, machining quality, and material removal efficiency. To accurately reveal the machining mechanisms, several feed directions with different included angles for the pure edge-forward direction were investigated. Upon analysis of the chips and the machined nanochannels, it was found that processing with included angles in the range 0–30° led to high-quality channels and high material-removal efficiency. In this case, the cutting angles, such as the rake angle, clearance angle, and shear angle, have an important influence on the obtained results. In addition, a machining model was developed to explain the observed machined depth variation when scratching in different feed directions

Origins of ductile plasticity in a polycrystalline gallium arsenide during scratching: MD simulation study

This paper used molecular dynamics simulation to reveal the origins of the ductile plasticity in polycrystalline gallium arsenide (GaAs) during its nanoscratching. Velocity-controlled nanoscratching tests were performed with a diamond tool to study the friction-induced deformation behaviour of polycrystalline GaAs. Cutting temperature, sub-surface damage depth, cutting stresses, the evolution of dislocations and the subsequent microstructural changes were extracted from the simulation. The simulated MD data indicated that the deformation of polycrystalline GaAs is accompanied by dislocation nucleation in the grain boundaries (GBs) leading to the initiation of plastic deformation. Furthermore, the 1/2〈1 1 0〉 is the main type of dislocation responsible for ductile plasticity in polycrystalline GaAs. The magnitude of cutting forces and the extent of sub-surface damage were both observed to reduce with an increase in the scratch velocity whereas the cutting temperature scaled with the cutting velocity. As for the depth of the scratch, an increase in its magnitude increased the cutting forces, temperature and damage-depth. A phenomenon of fluctuation from wave crests to wave troughs in the cutting forces was observed only during the cutting of polycrystalline GaAs and not during the cutting of single-crystal GaAs

An atomistic investigation on the wear of diamond during atomic force microscope tip-based nanomachining of gallium arsenide

This paper investigated the wear mechanism of diamond during the atomic force microscope (AFM) tip-based nanomachining of Gallium Arsenide (GaAs) using molecular dynamics (MD) simulations. The elastic-plastic deformation at the apex of the diamond tip was observed during the simulations. Meanwhile, a transition of the diamond tip from its initial cubic diamond lattice structure sp3 hybridization to graphite lattice structure sp2 hybridization was revealed. Graphitization was, therefore, found to be the dominant wear mechanism of the diamond tip during the nanometric cutting of single crystal gallium arsenide for the first time. The various stress states, such as hydrostatic stress, shear stress, and von Mises stress within the diamond tip and the temperature distribution of the diamond tip were also estimated to find out the underlying mechanism of graphitization. The results showed that the cutting heat during nanomachining of GaAs would mainly lead to the graphitization of the diamond tip instead of the high shear stress-induced transformation of the diamond to graphite. The paper also proposed a new approach to quantify the graphitization conversion rate of the diamond ti

AFM tip-based nanomachining with increased cutting speed at the tool-workpiece interface

This paper reports a study towards enhancing the throughput of the Atomic Force Microscope (AFM) tip-based nanomachining process by increasing the cutting speed at the interface between the tool and the workpiece. A modified AFM set-up was implemented, which combined the fast reciprocating motions of a piezoelectric actuator, on which the workpiece was mounted, and the linear displacement of the AFM stage, which defined the length of produced grooves. The influence of the feed, the feed direction and the cutting speed on the machined depth and on the chip formation was studied in detail when machining poly(methyl methacrylate). A theoretical cutting speed over 5 m/min could be achieved with this set-up when the frequency of the piezoelectric actuator reciprocating motions was 40 kHz. This is significantly better than the state of the art for AFM-based nanomachining, which is currently less than 1 m/min