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Graphene is a useful solid lubricant for flexible micro/nanoelectromechanical systems (MEMS/NEMS) because of its beneficial mechanical properties. However, understanding the tribological and wear characteristics of graphene on polymer substrates under high-temperature conditions is essential for predicting whether graphene will fail as a solid lubricant for flexible substrates in high-temperature environments. Herein, the friction and wear characteristics of monolayer graphene on flexible polydimethylsiloxane (PDMS) substrates are studied by atomic force microscopy using a heated tip. The friction of graphene before wear is more stable than that of PDMS, demonstrating that graphene can be used as a solid lubricant to stabilize the stick-slip motion of the tip on the flexible substrate at elevated temperatures. The friction of graphene shows an increasing trend with the heating temperature increasing due to an enlarged tip-graphene contact area. However, the friction of graphene considerably decreases with the tip sliding velocity increasing at a speed of less than 0.5 µm/s, resulting from a reduced tip-graphene contact area. The thermally-induced wear of graphene is caused by the coupling effect of the temperature and the sliding velocity. These results can provide an in-depth understanding of graphene as a solid lubricant for flexible polymer-based MEMS/NEMS devices in high-temperature environments.

Abstract The bundle structure formed perpendicular to the scratching direction is a type of wear-induced structure for thermoplastics. In this study, the formation mechanism of bundle structures on polycarbonate (PC) surfaces is investigated by reciprocal scratching experiments. Based on the analysis of the morphologies, friction forces, and height signals, the formation of the bundle structure is reproduced. The influence of scratching parameters, including the feed value and scratching direction, on the formation of the bundle structure is also studied. It is found that the bundle structure is accumulated by the continuous stacking of the sample materials plowed by the tip in stick—slip motion, and that the stick—slip behavior is enhanced with increased scratching times. This work reproduces the formation process of bundle structure in experiments for the first time and demonstrates that the stick—slip enhancement mechanism exists in the reciprocal scratching process, providing further insight into the friction behavior of polymers.

Abstract This paper presents a probe-based force-controlled nanoindentation method to fabricate ordered micro/nanostructures. Both the experimental and finite element simulation approaches are employed to investigate the influence of the interval between the adjacent indentations and the rotation angle of the probe on the formed micro/nanostructures. The non-contacting part between indenter and the sample material and the height of the material pile-up are two competing factors to determine the depth relationship between the adjacent indentations. For the one array indentations, nanostructures with good depth consistency and periodicity can be formed after the depth of the indentation becoming stable, and the variation of the rotation angle results in the large difference between the morphology of the formed nanostructures at the bottom of the one array indentation. In addition, for the indentation arrays, the nanostructures with good consistency and periodicity of the shape and depth can be generated with the spacing greater than 1 μm. Finally, Raman tests are also carried out based on the obtained ordered micro/nanostructures with Rhodamine probe molecule. The indentation arrays with a smaller spacing lead to better the enhancement effect of the substrate, which has the potential applications in the fields of biological or chemical molecular detection.

Micro diamond tools are indispensable for the efficient machining of microstructured surfaces. The precision in tool manufacturing and cutting performance directly determines the processing quality of components. The manufacturing of high-quality micro diamond tools relies on scientific design methods and appropriate processing techniques. However, there is currently a lack of systematic review on the design and manufacturing methods of micro diamond tools in academia. This study systematically summarizes and analyzes modern manufacturing methods for micro diamond tools, as well as the impact of tool waviness, sharpness, and durability on machining quality. Subsequently, a design method is proposed based on the theory of cutting edge strength distribution to enhance tool waviness, sharpness, and durability. Finally, this paper presents current technical challenges faced by micro diamond tools along with potential future solutions to guide scientists in this field. The aim of this review is to contribute to the further development of the current design and manufacturing processes for micro diamond cutting tools.

The laser ablation of aluminum alloy 6061 was studied both experimentally and by computational modeling in this work. Six variations of the number of pulses of irradiation (1, 5, 10, 20, 50, and 100 pulses) combined with four different laser fluence (2.0 J/cm2, 1.5 J/cm2, 1.0 J/cm2, and 0.5 J/cm2) were chosen to study the effect of heat input and laser action time on microstructural changes and the generation of particulate pollutants. Laser fluence and the number of pulses of laser irradiation were found to have a direct influence on thermal diffusion and the ablation depth of aluminum alloy 6061. At a relatively high laser fluence (2 J/cm2) and with the application of 10 pulses of irradiation, ablation cracks were observed on the surface of aluminum alloy 6061 and the production of pollutant particles increased according to a particle counter. Maintaining the laser fluence at 0.5 J/cm2 while increasing the number of pulses of irradiation to 50 also enhanced the depth of thermal diffusion while laser ablation continued to occur. The occurrence of vaporization in the surface region was influenced largely by laser fluence and the number of pulses of irradiation, as evident from the simulation and from experimental results. The single laser pulse duration was 6 ns and the repetition rate was 1 s−1. This article provides a novelty numerical model which could reveal the metal alloys' evapotation at a high-fluence nanosecond laser ablation. A 3D computational model was used to predict the temperature variation upon laser irradiation in a solid material over time. The results of the model (thermal diffusion versus laser ablation) agreed well with the experimental results.

Abstract Fabrication of periodic nanostructures has drawn increasing interest owing to their applications of such functional structures in optics, biomedical and power generation devices. Nano-indentation technique has been proven as a method to fabricate periodic nanostructures. In this study, the molecular dynamic simulation approach is employed to investigate the nano-indentation process for fabricating periodic nano-pit arrays using a single indenter and an indenter array. The morphologies of indentations that machined using these two kinds of indenters are compared. The indentation force and the defect evolution during the nano-indentation process are further studied. Results show that indentation morphologies obtained by single indenter are mainly depended on the spacing of indenters, and a nano-pit array with a better shape and consistency can be obtained easier using the indenter array compared with using a single indenter. The stacking faults and dislocations induced by indentation are depended on the spacing of the indenters. Our findings are significant for understanding the differences of indentation processes using a single indenter and an indenter array and machining a high-quality periodic nano-pit array with high machining efficiency. Graphical Abstract

Au nanowires have been promoted in flexible electronics, micro-nano bioelectrodes, and micro-electrochemical detection benefit from their inherent size effect, unique chemical stability, and biocompatibility. Nanoskiving methodology has been confirmed as a feasible approach to preparing multidimensional nanostructures simply and efficiently utilizing ultramicrotome. However, the morphology, dimension, and microstructure of the nanowires will be altered by the tool geometry under extrusion and shearing during the nanoskiving process. Herein, a molecular dynamics simulation and experiments of cutting polycrystalline Au utilizing nanoskiving were performed, and the nanowire formation behavior caused by the variation of the tool geometry was analyzed. Smaller rake angle and larger tool cutting edge radius favor thicker chip thickness, larger high-stress areas, increased machining forces, as well as a shift in cutting formation mechanism from shear to extrusion shear. The reduction in the clearance angle only increases the high-stress areas and machining forces. The stress state and dislocation density within the chip and plastic deformation zone were closely related to the tool topography. The conclusions provide a thorough technical analysis of the mechanism of polycrystalline Au nanowire formation as well as theoretical guidance for the design and selection of tools for nanoskiving processes.

To calculate the shear yield stress and effect of the gold film thickness on sandwich structures, a force transducer was used to measure cutting forces during nanoskiving, and an orthogonal cutting model, which considered liquid parameters, was used for analysis the slicing process. Sandwich structures with gold film thicknesses of 50 nm and 150 nm were prepared. The contact angles between the water surface in the trough and its edge line were 0° (horizontal) and 35° (protruding) during slicing. The cutting feed of the slab should be

Abstract Tip-based nanomachining (TBN) approaches has proven to be a powerful and feasible technique for fabrication of microstructures. The molecular dynamics (MD) simulation has been widely applied in TBN approach to explore the mechanism which could not be fully revealed by experiments. This paper reviews the recent scientific progress in MD simulation of TBN approach. The establishing methods of the simulation model for various materials are first presented. Then, the analysis of the machining mechanism for TBN approach is discussed, including cutting force analysis, the analysis of material removal, and the defects analysis in subsurface. Finally, current shortcomings and future prospects of the TBN method in MD simulations are given. It is hopeful that this review can provide certain reference for the follow-up research.

Nanostructures have been widely employed in surface-enhanced Raman scattering (SERS) substrates. Recently, in order to obtain a higher enhancement factor at a lower detection limit, hierarchical structures, including nanostructures and nanoparticles, appear to be viable SERS substrate candidates. Here we describe a novel method integrating the nanoindentation process and chemical redox reaction to machine a hierarchical SERS substrate. The micro/nanostructures are first formed on a Cu(110) plane and then Ag nanoparticles are generated on the structured copper surface. The effect of the indentation process parameters and the corrosion time in the AgNO3 solution on the Raman intensities of the SERS substrate with hierarchical structures are experimentally studied. The intensity and distribution of the electric field of single and multiple Ag nanoparticles on the surface of a plane and with multiple micro/nanostructures are studied with COMSOL software. The feasibility of the hierarchical SERS substrate is verified using R6G molecules. Finally, the enhancement factor using malachite green molecules was found to reach 5.089 × 109, which demonstrates that the production method is a simple, reproducible and low-cost method for machining a highly sensitive, hierarchical SERS substrate.

Abstract In current research realm, polydimethylsiloxane (PDMS)-based nanofluidic devices are widely used in medical, chemical, and biological applications. In the present paper, a novel nanomilling technique (consisting of an AFM system and a piezoelectric actuator) was proposed to fabricate nanochannels (with controllable sizes) on PDMS chips, and nanochannel size was controlled by the driving voltage and frequency inputted to the piezoelectric actuator. Moreover, microchannel and nanochannel molds were respectively fabricated by UV lithography and AFM tip-based nanomilling, and finally, PDMS slabs with micro/nanochannels were obtained by transfer process. The influences of PDMS weight ratio on nanochannel size were also investigated. The bonding process of microchannel and nanochannel slabs was conducted on a homemade alignment system consisted of an optical monocular microscope and precision stages. Furthermore, the effects of nanochannel size on electrical characteristics of KCl solution (concentration of 1 mM) were analyzed. Therefore, it can be concluded that PDMS nanofluidic devices with multiple nanochannels of sub-100-nm depth can be efficiently and economically fabricated by the proposed method.

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. Keywords: Atomic force microscopy, Nanomachining, Periodic nanostructure, Single-crystal copper

We conducted thermomechanical nanolithography to realize nanoscale manipulation of materials patterning on a polymethyl methacrylate thin film. We used atomic force microscopy with a heated tip make a single scratch on the film surface. The error in the machining force caused by the thermal expansion of the tip cantilever was corrected to guarantee the accuracy of machining force by calibrating the machining parameters, including the spring constant of the tip cantilever and the sensitivity coefficient of the optical lever for different tip temperatures. Three kinds of nanostructure including polymer nanowires, nanopit arrays, and nanogrooves were regulated via controlling scratching velocity and the heated temperature. Inspection of the nanopit arrays proved that fabrication of continuous bundles with desired dimensions can be realized by controlling the feed between adjacent scratching paths. The good agreement between the calculated stick–slip friction and observed machining outcomes demonstrated the feasibility of using stick–slip friction to predict the generation of nanopit structures.

High-throughput and high-accuracy nanofabrication methods are required for the ever-increasing demand for nanoelectronics, high-density data storage devices, nanophotonics, quantum computing, molecular circuitry, and scaffolds in bioengineering used for cell proliferation applications. The scanning probe lithography (SPL) nanofabrication technique is a critical nanofabrication method with great potential to evolve into a disruptive atomic-scale fabrication technology to meet these demands. Through this timely review, we aspire to provide an overview of the SPL fabrication mechanism and the state-the-art research in this area, and detail the applications and characteristics of this technique, including the effects of thermal aspects and chemical aspects, and the influence of electric and magnetic fields in governing the mechanics of the functionalized tip interacting with the substrate during SPL. Alongside this, the review also sheds light on comparing various fabrication capabilities, throughput, and attainable resolution. Finally, the paper alludes to the fact that a majority of the reported literature suggests that SPL has yet to achieve its full commercial potential and is currently largely a laboratory-based nanofabrication technique used for prototyping of nanostructures and nanodevices.

Using the tip-based continuous indentation process, arrays of three-dimensional pyramidal cavities have been successfully machined on a copper template and the structures were successfully transferred to a polydimethylsiloxane (PDMS) surface using a reverse nanoimprinting approach. The structured PDMS surface is coated with a thin Au film, and the final substrate is demonstrated as a surface-enhanced Raman spectroscopy (SERS) substrate. Rhodamine 6G (R6G) was used as a probe molecule in the present study to confirm the SERS measurements. Arrays of micro/nanostructures of different dimensions were formed by the overlap of pyramidal cavities with different adjacent distances using the tip-based continuous indentation process. The effects of the reverse nanoimprinting process and coating process on the final topography of the structures are studied. The experimental results show that the Raman intensity of the Au-film-coated PDMS substrate is influenced by the topography of the micro/nanostructures and by the thickness of the Au film. The Raman intensity of 1362 cm−1 R6G peak on the structured Au-film-coated PDMS substrate is about 8 times higher than the SERS tests on a commercial substrate (Q-SERS). A SERS enhancement factor ranging from 7.5 × 105 to 6 × 106 was achieved using the structured Au-film-coated PDMS surface, and it was demonstrated that the method proposed in this paper is reliable, replicable, homogeneous and low-cost for the fabrication of SERS substrates.

Abstract We show that an atomic force microscope (AFM) tip-based dynamic plowing lithography (DPL) approach can be used to fabricate nanoscale pits with high throughput. The method relies on scratching with a relatively large speed over a sample surface in tapping mode, which is responsible for the separation distance of adjacent pits. Scratching tests are carried out on a poly(methyl methacrylate) (PMMA) thin film using a diamond-like carbon coating tip. Results show that 100 μm/s is the critical value of the scratching speed. When the scratching speed is greater than 100 μm/s, pit structures can be generated. In contrast, nanogrooves can be formed with speeds less than the critical value. Because of the difficulty of breaking the molecular chain of glass-state polymer with an applied high-frequency load and low-energy dissipation in one interaction of the tip and the sample, one pit requires 65–80 penetrations to be achieved. Subsequently, the forming process of the pit is analyzed in detail, including three phases: elastic deformation, plastic deformation, and climbing over the pile-up. In particular, 4800–5800 pits can be obtained in 1 s using this proposed method. Both experiments and theoretical analysis are presented that fully determine the potential of this proposed method to fabricate pits efficiently.

In relevant investigations and applications of the heated atomic force microscope (AFM) probes, the determination of the actual thermal distribution between the probe and the materials under processing or testing is a core issue. Herein, the polyphthalaldehyde (PPA) film material and AFM imaging of the decomposition structures (pyrolytic region of PPA) were utilized to study the temperature distribution in the nano/microscale air gap between heated tips and materials. Different sizes of pyramid decomposition structures were formed on the surface of PPA film by the heated tip, which was hovering at the initial tip−sample contact with the preset temperature from 190 to 220 °C for a heating duration ranging from 0.3 to 120 s. According to the positions of the 188 °C isothermal surface in the steady-state probe temperature fields, precise 3D boundary conditions were obtained. We also established a simplified calculation model of the 3D steady-state thermal field based on the experimental results, and calculated the temperature distribution of the air gap under any preset tip temperature, which revealed the principle of horizontal (

As a brand new nanomachining method, the tip-based nanomachining/nanoscratching (TBN) method has exhibited a powerful ability at machining on polymer materials and various structures have been achieved using this approach, ranging from the nanodot, nanogroove/channel, bundle to 2D/3D (three-dimensional) nanostructures. The TBN method is widely used due to its high precision, ease of use and low environmental requirements. First, the theoretical models of machining on polymer materials with a given tip using the TBN method are presented. Second, advances of nanostructures achieved by this method are given, including nanodots/nanodot arrays, a nanogroove/channel, 2D/3D nanostructures and bundles. In particular, a useful approach called the ultrasonic vibration-assisted method introduced to integrate with TBN method to reduce the wear of the tip is also reviewed, respectively. Third, the typical applications of the TBN method and the nanostructures achieved by it are summarized in detail. Finally, the existing shortcomings and future prospects of the TBN method are given. It is confirmed that this review will be helpful in learning about this method and push the technology toward industrialization.

Annular polishing technology is an important optical machining method for achieving a high-precision mirror surface on silicon carbide. However, the inevitable over-polishing of the specimen edge in annular polishing deteriorates achieved surface quality. In the present work, we first analytically investigate the kinematic coupling of multiple relative motions in the annular polishing process and subsequently derive an analytical model that addresses the principle of material removal at specimen edge based on the Preston equation and the rigid body contact model. We then perform finite element simulations and experiments involving annular polishing of silicon carbide (SiC), which jointly exhibit agreement with the derived analytical model of material removal.

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.