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With the advantages of high spectral intensity and resolution, structural colors of surfaces generated by subwavelength structures whose feature sizes equal to or less than visible light wavelengths have shown great potential in scientific research and industrial application. Fabrications for subwavelength structures have gained a considerable attention of researchers. In this paper, a kind of subwavelength blazed grating structure generated on the side-walls of micro V-groove was obtained on the surface of aluminum alloy (2024) by employing a novel fabricating method that revolving a nanoindenter with nano trajectories and in the way of down-milling. It was found that whether the forming process of subwavelength grating structure was dominated by tip cutting or by tip extruding could be controlled by adjusting the revolving trajectory combined with tip orientation, which would result in the variation of grating profile. By evaluating the grating quality, the conditions able to machine the gratings of different heights and shapes with good consistency were summarized. Surface structure composed of micro/nano hierarchical gratings was prepared by machining the V-grooves into an array, which, due to the diffraction effects of micro grating and nano grating, could hide the colorized pattern and display the patten with different structural colors under different incident directions, and still had good performance after a severe pitting corrosion formed on the surface of aluminum alloy.

In order to acquire TiAl composites with a multi-scale reinforcing phase, and to improve the microstructure and tensile properties at elevated temperatures, TiAl alloys have been prepared with different added carbon content levels via vacuum arc melting. The results show that when the carbon content is greater than or equal to 1.0 at%, then Ti2AlC forms and the microstructure changes from having a dendrite morphology to an equiaxed crystal morphology. The B2 phase disappears in the Ti2AlC-containing alloys. As the carbon content increases from 0 to 3.0 at%, the lamellar colony size decreases from 148.4 to 32.8 μm and the lamellar width decreases from 441.2 to 117.6 nm. More nanoscale Ti2AlC particles form in the α2 lamellae at a higher carbon content, and there are a lot of dislocations around them. As the carbon content, the Ti2AlC content increases from 0 to 16.8 vol% and the length-diameter ratio decreases from 9.2 to 1.8. The reason for the microstructure refinement is that carbon and carbide act as heterogeneous particles during solidification, and carbide dissolves some alloy elements, improving the microstructure uniformity. Compressive testing shows that the maximum compressive strength is 2324.3 MPa at a carbon content of 1.5%. At a carbon content of 2.5%, the compression strain is higher (28.1%). Tensile testing at elevated temperatures shows that upon increasing the temperature from 750 to 850 °C, the tensile strength increases from 398 to 541 MPa, and the strain increases from 6.1 to 12.2% with a temperature increase from 750 to 950 °C. The increase in the mechanical properties is attributed to the refined lamellar colonies and lamellar width, the solid solution of elements, and the formation of nanoprecipitates.

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.

Shear deformation that dominates elementary chip formation in metal cutting greatly relies on crystal anisotropy. In the present work we investigate the influence of crystallographic orientation on shear angle in ultra-precision orthogonal diamond cutting of single crystalline copper by joint crystal plasticity finite element simulations and in-situ experiments integrated in scanning electron microscope. In particular, the experimental cutting conditions including a straight cutting edge are the same with that used in the 2D finite element simulations. Both simulations and experiments demonstrate a well agreement in chip profile and shear angle, as well as their dependence on crystallography. A series of finite element simulations of orthogonal cutting along different cutting directions for a specific crystallographic orientation are further performed, and predicated values of shear angle are used to calibrate an extended analytical model of shear angle based on the Ernst–Merchant relationship.

In the emerging field of laser-driven inertial confinement fusion, Joule heating generated via electromagnetic heating of the metal frame is a critical issue. However, there are few reported models explaining thermal damage to the aluminum alloy. The aim of this study was to build a coupled model for electromagnetic radiation and heat conversion of an ultrashort laser pulse on an aluminum alloy based on Ohm's law. Additionally, the application SiO2 films on aluminum alloy to improve the laser-induced damage threshold (LIDT) were simulated, and the effects of metal impurities in the aluminum alloy were analyzed. A model examining the relation between electromagnetic radiation and heat for a nanosecond laser irradiating an aluminum alloy was developed using a coupled model equation. The results obtained using the finite difference time domain (FDTD) algorithm can provide a theoretical basis for future improvement of the aluminum alloy LIDT.

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.

This article presents a constant force–controlled cutting approach with two different geometries of cutting tools. The methodologies for establishing two theoretical models were proposed to quantitatively predict the required applied normal forces at the expected machined depths, which were obtained with a solution to the horizontal projection of the sample–tip contact area and the multi-edge form tip based on a generalized cutting approach, respectively. The selection of the proposed theoretical models is dependent on the two material removal states, respectively, in which one is plowing for a regular triangular pyramid and the other one is cutting chips for a single-point diamond tip. To verify the feasibility and effectiveness of the proposed theoretical models and cutting strategy, a constant normal force cutting of microgrooves was implemented on a single-crystal copper substrate, while realizing constant cutting depths. The difference between the setting normal forces and the theoretical normal forces was analyzed by comparing the experimental results and the model prediction results. The aim of the present study was to investigate the effect of the geometry of the cutting tools on the material removal state and on the selection of the theoretical models.

Synergetic deformation behavior between different phases has a strongly impact on machining characteristics of composites. In the present work, we investigate ultrasonic elliptical vibration-assisted diamond cutting of reaction-bonded silicon carbide (RB-SiC) by using finite element simulations and corresponding experimental validations. In particular, a specific-cutting-energy-based criterion, considering both the material composition of two phases and the cutting tool trajectory of two-dimensional vibrations, is established to quantitatively characterize the brittle-to-ductile transition of RB-SiC. The predicted value of the critical depth of cut for the brittle-to-ductile transition of RB-SiC by finite element simulations agrees well with that derived from diamond grooving experiment. Simulation results reveal that the synergetic deformation behavior between SiC matrix and Si particle substantially affects machining results of RB-SiC, and is greatly dependent on the cutting tool trajectory. Specifically, both finite element simulations and experiments demonstrate that the ductile machinability of RB-SiC can be significantly enhanced by applying ultrasonic elliptical vibration-assisted cutting, as compared to ordinary cutting.

Paper based assays are paving the way to automated, simplified, robust and cost-effective point of care testing (POCT). We propose a method for fabricating three dimensional (3D) microfluidic paper based analytical devices (μPADs) via combining thin adhesive films and paper folding, which avoids the use of cellulose powders and the complex folding sequence and simultaneously permits assays in several layers. To demonstrate the effectiveness of this approach, a 3DμPADs was designed to conduct more assays on a small footprint, allowing dual colorimetric and electrochemical detections. More importantly, we further developed a 3D platform for implementing automated and multiplexed ELISA in parallel, since ELISA, a routine and standard laboratory method, has rarely been used in practical analyses outside of the laboratory. In this configuration, complex and multistep diagnostic assays can be carried out with the addition of the sample and buffer in a simple fashion. Using Troponin I as model, the device showed a broad dynamic range of detection with a detection limit of 0.35 ng/mL. Thus, the developed platforms allow for various assays to be cost-effectively carried out on a single 3D device, showing great potential in an academic setting and point of care testing under resource-poor conditions.

In the present study, molecular dynamics (MD) simulation and experimental tests are employed to investigate the influence of the probe orientation on the machined depth, generation of the material pile-up, and average cutting force when implementing dynamic ploughing process on a single crystal copper surface. A typical triangular pyramid diamond AFM tip is selected, and three probe orientations are studied. The energy dissipation per oscillation of the AFM cantilever is utilized to describe the interaction between the probe and sample surface experimentally. Results show that the probe orientation has a significant effect on the machined depth and material pile-up on the sides of the groove. The MD simulations mainly agree well with the experimental results. Based on the MD simulations, the difference of the machined depth results from the various material flow directions during the ploughing process. The average cutting force is also studied by the MD simulations, which shows good consistency with the variation of probe-sample contact area during the dynamic ploughing along each machined groove. These results indicate the tip orientation is also an important factor in the dynamic ploughing process, which can be used as a reference to improve the machining accuracy and optimize machining parameters in the dynamic ploughing lithography to broaden its practical application.

Polycrystalline materials like Cu–Pb alloy consist of four types of microstructural components, including grain cells, grain boundaries, triple junctions and vertex points, the mechanical propertie...

This paper proposes a probe-based force-controlled nanoindentation system employing a four-beam spring. The applied normal load is obtained by a force-modulation module with a four-beam spring and a capacitive displacement sensor, and the maximum normal force can be provided by this system is about 500 mN, which is determined by the precision approaching range of the probe in the vertical direction and the elastic yield strength of the four-beam spring. The closed-loop control accuracy of the normal force is about 0.3 mN. The penetration depth during the indentation process can be obtained by comparing the deflection of the four-beam spring with the elongation of the piezoelectric ceramic transducer (PZT). A rotating ring is utilized to control the orientation of the probe to broaden the machining diversity. The force-modulation module is set on a three-axes moving platform, and the relatively position between the probe and the sample surface can be controlled with a resolution of 1 nm in the horizontal plane, which indicates the high feeding accuracy between two adjacent indentations. Nanoindentation tests were performed using finite element (FE) simulation and experimental approaches with two typical indenters. In addition, 20 × 20 indentation arrays obtained by the probe rotation angles of 0° and 45° are also fabricated successfully. Based on these results, the feasibility of the developed system is verified for the probe-based force-controlled indentation-type micromachining.

Microstructural-related deformation behavior leads to anisotropic machining characteristics of polycrystalline materials. In the present work, we develop a crystal plasticity finite element model of ultra-precision diamond cutting of polycrystalline copper, aiming to evaluate the influence of grain boundaries on the correlation between microscopic deformation behavior of the material and macroscopic machining results. The crystal plasticity dealing with the anisotropy of polycrystalline copper is implemented in a user subroutine (UMAT), and an efficient element deletion technique based on the Johnson-Cook damage model is adopted to describe material removal and chip formation. The effectiveness of as-established crystal plasticity finite element model is verified by experiments of nanoindentation, nanoscratching and in-situ diamond microcutting. Subsequent crystal plasticity finite element simulation of diamond cutting across a high angle grain boundary demonstrates significant anisotropic machining characteristics in terms of machined surface quality, chip profile and cutting force, due to heterogeneous plastic deformation behavior in the grain level.

The dynamic plowing lithography approach is employed to fabricate nanoscale pits on polymer thin films with a high throughput based on a commercial atomic force microscope (AFM) in this study. The effects of the drive amplitude ratio and the molecular weight on the fabrication of the nanoscale pits are investigated first on the poly(methyl methacrylate) (PMMA) thin films. In particular, the critical value for the transformation of the grooves to the pits and the ratio of the experimental distance between the adjacent two pits and the calculation distance between adjacent penetrations of the AFM probe are assessed. Results show that the drive amplitude ratio and the molecular weight have little influence on the machining outcomes. The critical value is evaluated as around 100 μm/s, and the ratio described above is varied in the range of 60-80 times. As a contrast, the polycarbonate and polystyrene thin films are selected. The corresponding critical value can be evaluated as 20-30 μm/s, which is much smaller than that obtained on the PMMA thin film. The possible reason can be explained as the change of the surface elastic modulus. While the ratio of the pits distance is almost in the same range with the results given for the PMMA thin film. Furthermore, a lower drive frequency is also chosen to scratch on the polymer surface. However, only nanogrooves can be created even the scratching velocity reaches to 1000 μm/s. In this case, the machined depth of the nanogrooves is varied with the scratching velocity in the whole range of scratching velocity. Finally, 8-bit ASCII code could be obtained with the arrays of the pits with eight columns for the meaning of figures or symbols.

Dynamic ploughing lithography based on atomic force microscope (AFM) is a promising technique for fabrication of nano structures and devices. This study investigates the material removal mechanism and surface generation in dynamic ploughing of single crystal copper by molecular dynamics (MD) simulations in addition to the experimental tests, and compares it with that of static ploughing lithography. It is found that the material removal in dynamic ploughing is mainly due to downwards and sidewards slipping of workpiece material on the {1 1 1} slip planes and the subsequent elastic recovery, whereas forwards and sidewards slipping account for the material removal in static ploughing. As a result, there is little chip formation in dynamic ploughing, while significant chip formation is observed for static ploughing in both simulations and experiments. In addition, this results in smaller groove depth and width for dynamic ploughing, allowing fabrication of nanostructures with smaller features. The slipping processes in both static and dynamic ploughing can be corresponded with the periodical variations of machining forces. The average machining force in dynamic ploughing is significantly smaller than that in static ploughing. This indicates the possibility of reducing the wear of AFM tip by employing dynamic ploughing lithography, since the tip wear is greatly influenced by the magnitude of machining force. These results reveal the mechanism of material removal and surface generation in dynamic ploughing lithography, which can be of useful reference for its practical application in nanomanufacturing.

Nanofluidic chips with different numbers of nanochannels were fabricated based on a commercial AFM system using a single-scratch approach. The electrical characterization and enzymatic reactions at the nanoscale were demonstrated using the obtained chips. The effects of the number of nanochannels and the solution concentration on the measured electric current were investigated. The influence of the hydrodynamic convection generated from the induced inflow at the end of the nanochannel on the ion transport through the nanochannel was also studied. Moreover, the enzymatic reactions for trypsin towards poly-l-lysine (PLL) or thrombin were conducted with a nanofluidic chip to investigate the reaction specificity between trypsin and PLL. Results show that the electric current change during the experimental process could be used as a label-free indicator to detect the enzymatic activity.

This paper used molecular dynamics simulation to obtain an improved understanding 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 boundary leading to the initiation of plastic deformation. Furthermore, a dual slip mechanism was observed as an important factor driving plasticity in poly GaAs in sharp contrast to a single 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.

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 tip.

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.

In the present paper, the process parameters of revolving tip-based machining were optimized for the fabrication of microchannel structures. It was found that in comparison with the micromilling process, the main factor affecting the surface quality of revolving tip-based machining originated from residual materials produced in each revolution. Three process parameters, including cutting depth, feeding rate, and tool path strategy, were studied experimentally to optimize the surface quality of the machined aluminum alloy and polymethylmethacrylate (PMMA). It was noticed that at smaller cutting depths (

Surface pile-up topography is very significant for property extraction in nanoindentation tests. In the present work, we perform crystal plasticity finite element simulations of Berkovich nanoindentation of single crystalline copper with different crystallographic orientations, which derive quantitatively comparable mechanical properties and surface pile-up topographies with experimental data. Simulation results demonstrate that there is a coupled effect of crystallographic orientation of indented material and indenter geometry on surface pile-up behavior, due to the interaction between intrinsic dislocation slip events and extrinsic discrete stress distribution patterns. Based on the relative spatial orientation between crystallographic orientation of indented material and indenter geometry, a surface pile-up density factor mp is proposed to qualitatively characterize the propensity of surface pile-up behavior in nanoindentation tests of single crystalline copper.

The material removal state, which is closely related to machining quality, is an important factor in any machining process. During the machining using a non-rotational symmetric cutting tool, scratching direction manifests significant influence on the material removal state. In the present study, the relationship between material removal mode and scratching direction was investigated during the nanoscratching process on single crystal copper using an atomic force microscopy (AFM) tip. Considering the installation angle of the cantilever and the height of pile-up, a theoretical model was developed to relate machining depth with normal load for the machining of a single groove. Experimental results revealed that the theoretical normal load model was more suitable when materials were expelled in constant chip formation with small pile-ups. In addition, based on the scratching tests in different directions, the critical included cutting angle determined whether materials were expelled in chip formation or not. The height of pile-up was also influenced by the included cutting angle during the scratching in face-forward direction; however, during the machining in edge-forward direction, the distance between the cutting swept faces formed by the lateral and front edges determined the height of pile-up. Finally, an optimal machining direction is selected based on the quality of the machined grooves, which can be used in the potential application.

This study presents an atomic force microscope (AFM)-based scratching combined with reactive ion etching (RIE) method to fabricate nanopatterns on the silicon surface. All AFM-based scratching processes are performed on the polymethylmethacrylate (PMMA) film to create features in order to protect the AFM tip from wearing and enlarge its life time. Two types of resist films are selected for the RIE process. One is only PMMA thin-film resist, and the other one contains two-layer thin-film resist which are PMMA and aluminum thin films. The nanopatterns on the silicon after etching using RIE with these two types of resist film are compared. Results show that when using PMMA film, the width of the nanopattern on silicon is larger than on the PMMA film, and the material pile-ups formed during the scratching process cannot be considered as a resist. On the contrary, the aluminum thin films can improve the quality of the transfer. It indicates that the thin-film resist with bilayers can guarantee the transfer accuracy of the features, which can expand the application of the AFM tip-based scratching technique.

This paper proposes a nanogroove machined depth prediction model for the atomic force microscopy (AFM) tip-based scratching method on the polymer thin-film. This model is used to predict the normal load required to just cut through the polymer thin-film without contacting the silicon substrate excessively to reduce the tip wear. In this proposed theoretical model, the AFM tip is assumed as a rectangular pyramid with a spherical apex. The elastic recovery, material pile-up, adhesive friction coefficient and mounted angle of the tip on the AFM head are considered in the developed model. Nanogrooves are scratched on a poly(methyl methacrylate) (PMMA) thin film by a silicon AFM tip. Results show that the bulk volume of the material pile–up can be enlarged after scratching with a relatively sharp tip. The equivalent height value of the material pile-up is thus introduced into the theoretical model, and the relationship between the equivalent height values of the material pile-up and the radius of the tip is analyzed in detail. Based on the proposed model and the experimental results, the effect of the radius of the AFM tip on the flow stress and adhesive friction coefficient is studied. Finally, several nanogrooves when the tip just cutting through the polymer thin-film are achieved on the polymer thin-films with different thicknesses using the tips with various radii.

Due to the strong anisotropic property of the advanced metal materials used in automobile, aviation, and aerospace, experimental flow stress–strain relations including different stress states are necessary to provide the information of anisotropic hardening and plastic flow for constructing a constitutive model. Therefore, reasonably reproducing the experimental stress–strain relations is the most fundamental work to substitute adequate flow stress–strain curves into the constitutive equation at the same time. However, accurate and stable regression results are difficult to obtain through the current regression models such as power exponent, second-order function model, fourth-order function model, and so forth. In this paper, an optimized model named as a least square quadratic regression model (ordinary least square model) was proposed based on the most useful second-order function model. The significant difference is that all experimental points are used to reproduce the experimental stress–strain relations in ordinary least square model in place of only three experimental points adopted in second-order function model, which results in good regression accuracy. Through comparison, it is found that the regression results by power function are poor with regard to some experimental results, and the results reproduced by second-order function model or fourth-order function model are very sensitive to the experimental points selected to do the regression. The sum of squares for error (SSE) increases sharply when the selected points are unreasonable. In addition, for second-order function and fourth-order function models, only limited experimental points are adopted to do the regression, the best regression accuracy cannot be obtained even if the selected points are reasonable. In contrast, SSE of the regression curve by ordinary least square model reduces to less than 50% of the best regressed result by second-order function model, the yielding behavior and variable strain increment ratio of the anisotropic materials can be reflected more accurately. This is very important for accurately describing the plastic flow behaviors of anisotropic materials.

By introducing the mechanical motion into the confined etchant layer technique (CELT), we have developed a promising ultra-precision machining method, termed as electrochemical mechanical micromachining (ECMM), for producing both regular and irregular three dimensional (3D) microstructures. It was found that there was a dramatic coupling effect between the confined etching process and the slow-rate mechanical motion because of the concentration distribution of electrogenerated etchant caused by the latter. In this article, the coupling effect was investigated systemically by comparing the etchant diffusion, etching depths and profiles in the non-confined and confined machining modes. A two-dimensional (2D) numerical simulation model was proposed to analyze the diffusion variations during the ECMM process, which is well verified by the machining experiments. The results showed that, in the confined machining mode, both the machining resolution and the perpendicularity tolerance of side faces were improved effectively. Furthermore, the theoretical modeling and numerical simulations were proved valuable to optimize the technical parameters of the ECMM process.

In the hot metal gas forming process, the deformation conditions, such as temperature, strain rate and deformation degree, are often prominently changed. The understanding of the flow behavior of α-Ti seamless tubes over a relatively wide range of temperatures and strain rates is important. In this study, the stress–strain curves in the temperature range of 973-1123 K and the initial strain rate range of 0.0004-0.4 s−1 were measured by isothermal tensile tests to conduct a constitutive analysis and a deformation behavior analysis. The results show that the flow stress decreases with the decrease in the strain rate and the increase of the deformation temperature. The Fields–Backofen model and Fields–Backofen–Zhang model were used to describe the stress–strain curves. The Fields–Backofen–Zhang model shows better predictability on the flow stress than the Fields–Backofen model, but there exists a large deviation in the deformation condition of 0.4 s−1. A modified Fields–Backofen–Zhang model is proposed, in which a strain rate term is introduced. This modified Fields–Backofen–Zhang model gives a more accurate description of the flow stress variation under hot forming conditions with a higher strain rate up to 0.4 s−1. Accordingly, it is reasonable to adopt the modified Fields–Backofen–Zhang model for the hot forming process which is likely to reach a higher strain rate, such as 0.4 s−1.

In the present study, nanochannels are fabricated on a poly (methyl methacrylate) (PMMA) surface using an atomic force microscopy (AFM) tip-based nanomilling method. Experiments are conducted using a silicon tip with a radius around 30 nm. The influence of three typical feeding directions of the relative rotational motion between the tip and the sample on the machined results is studied in detail. Results show that the processing outcomes are obviously different when machining with various feed directions. The chip formation, machined depth and the material accumulated on the sides of the groove are considered as the evaluation indicators for the machining outcomes. Finally, the optimized feed direction is selected based on these results to guarantee the machining quality of the fabricated nanochannels, which may have the potential for the nanofluidic applications.

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.

In the present study, an atomic force microscopy tip-based nanomilling approach is used to fabricate nanochannels on a poly(methyl methacrylate) surface. A silicon atomic force microscopy tip is em...

In this work, the process of laser ablation of aluminum alloy 6061 (AA 6061) before and after silicon dioxide (SiO2) coating was studied both experimentally and by numerical simulation. Four different laser fluences (0.5 J/cm2, 1 J/cm2, 1.5 J/cm2 and 2 J/cm2) were applied to investigate laser ablation of AA 6061 before and after coated by SiO2 film. It was founded that the thermal diffusion and ablation depth of AA 6061 had been directly influenced by both laser fluence and SiO2 coating. At relatively low laser fluence (0.5 J/cm2), ablation deformation and damage of AA 6061 were not observed. While the laser fluence reached to 1 J/cm2, vaporization took place in AA 6061. With increased laser fluence, the ablation range and depth expanded. The vaporization of SiO2 films happened in the first laser fluence, however, the area of the zone affected were much less than AA 6061, that demonstrates the SiO2 film has a positive effect on AA 6061. A 3-dimensional computational model was used to compute the temperature variation in a solid material over time. The results of the model (depth to width ratio versus laser ablation) exhibited well with the experimental results in some ways.

GaAs is a hard, brittle material and its cutting at room-temperature is rather difficult, so the work explored whether hot conditions improve its cutting performance or not. Atomic force microscope (AFM) tip-based hot machining of the (0 1 0) oriented single crystal GaAs was simulated using molecular dynamics (MD). Three representative temperatures 600 K, 900 K and 1200 K (below the melting temperature of ~1511 K) were used to cut GaAs to benchmark against the cutting performance at 300 K using indicators such as the cutting forces, kinetic coefficient of friction, cutting temperature, shear plane angle, sub-surface damage depth, shear strain in the cutting zone, and stress on the diamond tip. Hotter conditions resulted in the reduction of cutting forces by 25% however, the kinetic coefficient of friction went up by about 8%. While material removal rate was found to increase with the increase of the substrate temperature, it was accompanied by an increase of the sub-surface damage in the substrate. Simulations at 300 K showed four major types of dislocations with Burgers vector 1/2, 1/6, and 1/2 underneath the cutting zone and these were found to cause ductile response in zinc-blende GaAs. Lastly, a phenomenon of chip densification was found to occur during hot cutting which referred to the fact that the amorphous cutting chips obtained from cutting at low temperature will have lower density than the chips obtained from cutting at higher temperatures.

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.

The present work investigates the friction behavior and machined depth prediction when scratching on a polymer material using an atomic force microscopy (AFM) tip. According to the calculated results based on the experimental tests and the proposed model, the flow stress during machining is demonstrated to be a logarithmic increase with the scratching speed increasing, and the adhesive friction coefficient has little change with the variation of the normal load and scratching speed. Finally, several nanochannels with expected machined depth are achieved on the polymer surface using the prediction method presented in this study and the deviation between the experimental and desired values is mainly less than 10%.

Nanocomposite multilayer TiBN coatings were prepared on Si (100) and 9Cr18Mo substrates using TiBN composite cathode plasma immersion ion implantation and deposition technique (PIIID). Synthesis of TiBN composite cathodes was conducted by powder metallurgy technology and the content of hexagonal boron nitride (h-BN) was changed from 8% to 40% (mass fraction). The as-deposited coatings were characterized by energy dispersive spectrometer (EDS), grazing incidence X-ray diffraction (GIXRD), Fourier Transform Infrared Spectroscopy (FTIR) and high resolution transmission electron microcopy (HRTEM). EDS results show that the B content of the coatings was varied from 3.71% to 13.84% (molar fraction) when the composition of the h-BN in the composited cathodes was changed from 8 % to 40% (mass fraction). GIXRD results reveal that the TiBN coatings with a B content of 8% has the main diffraction peak of TiN (200), (220) and (311), and these peaks disappear when the B content is increased. FTIR analysis of the multilayer coatings showed the presence of h-BN in all coatings. TEM images reveal that all coatings have the characteristics of self-forming nanocomposite multilayers, where the nanocomposites are composed of face-centered cubic TiN or h-BN nanocrystalline embedded in amorphous matrix. The tribological tests reveal that the TiBN coatings exhibit a marked decrease of coefficient at room temperature (~0.25). The improved properties were found to be derived from the comprehensiveness of the self-forming multilayers structure and the h-BN solid lubrication effects in the coatings.

In this study, the AFM tip-based dynamic plowing lithography (DPL) method is utilized to conduct nanoscratching tests on the poly(methyl methacrylate) (PMMA) thin-film surface. Aim to fabricate none-ridge nanogrooves, a relatively large-radius probe in wear state is employed for the whole scratching operations. Due to large contact area between the tip and the sample surface, the energy dissipation fails to break the polymer chains. The extrusion force is contributed to the formation of the none-ridge nanogrooves in the machined areas. Effects of the scratching parameters, including the drive amplitude and the scratching velocity, on the machined depth are discussed in detail. Results show that the machined depth increases linearly with the drive amplitude going up owing to more energy dissipation accumulated. Moreover, the logarithmical decrease in machined depth with respect to the scratching velocity is thought to be induced by enlarging the spacing distance between two press operations. A nanochannel can be achieved by controlling the distance between two adjacent scratching grooves which is generally called ‘feed’. The overlapping of the two adjacent scratching grooves can result in an increase of the machined depth. Finally, two geometries of controllable three-dimensional (3D) nanodot arrays are achieved by a two-step scratching approach successfully.

Scanning electrochemical microscopy (SECM) has been approved as a prospective electrochemical micromachining (ECMM) technique soon after its birth. However, it still remains challenge for SECM to fabricate arbitrary three-dimensional (3D) microstructures because of the limitation of positioning system. To solve this problem, we proposed a tip current signal/positioning close-loop mode in which the tip current signal is fed back to the positioning system in order to program the motion trial of SECM tip. Both the triedge-cone and sinusoidal microstructures were obtained by the close-loop positioning mode. The static-state etching process was demonstrated not to be disturbed by the slow motion rate of SECM tip. The unique positioning mode would be significant for both ECMM and electrochemical imaging. Keywords: Scanning electrochemical microscopy, Electrochemical micromachining, Close-loop positioning mode, SECM, ECMM

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.

This paper proposed a machining method for micro V-shaped grooves, which was achieved by introducing the revolving trajectory on the basis of tip scratching process. By coordinating the revolving direction and the tip orientation, four kinds of revolving scratches were developed which had the revolving radii larger than the groove depths. It was found that there were two revolving scratches among these four being able to eliminate the side burrs and produce much smaller cutting forces during machining grooves compared to the traditional scratch, respectively named as the up-milling of face-forward and the down-milling of edge-forward. By considering the tip geometry in the traditional scratching process, the burr formation has been studied which was mainly affected by the effect of chip interference and the amount of uncut chip thickness. By analyzing the machining trajectory, the undeformed chip, the machined surface and the chip morphology, the reason why the up-milling of face-forward and the down-milling of edge-forward had good performances for machining V-grooves was elucidated in detail. Meanwhile, the differences between these two revolving scratches were discussed, and their advantages and disadvantages were also given.

Structural phase transformation and dislocation slip are two important deformation modes of monocrystalline silicon. In the present work, we elucidate mechanisms of inhomogeneous elastic-plastic transition in spherical nanoindentation of monocrystalline silicon by means of molecular dynamics simulations. The Stillinger-Weber potential is utilized to present simultaneous phase transformations and dislocation activities in the silicon nanoindentation. And a bond angle analysis-based method is proposed to quantitatively clarify silicon phases. The influence of crystallographic orientation on the silicon nanoindentation is further addressed. Our simulation results indicate that prior to the “Pop-In” event, Si(0 1 0) undergoes inelastic deformation accompanied by the phase transformation from the Si-I to the Si-III/Si-XII, which is not occurred in Si(1 1 0) and Si(1 1 1). While the phase transformation from the Si-I to the bct-5 is the dominant mechanism of incipient plasticity for each crystallographic orientation, dislocation nucleation is also an operating deformation mode in the elastic-plastic transition of Si(0 1 0). Furthermore, interactions between phase transformations and dislocations are more pronounced in Si(0 1 0) than the other two crystallographic orientations.

Based on the tip-based continuous indentation process, a novel method for the fabrication of periodic arrayed triangular micro-cavities on copper (Cu) surfaces is presented. The indentation force is modulated and the indentation speed and moving velocity of the precision stage used to drive the workpiece are optimized to improve the machining efficiency. The deformation property of the pile-ups at the side of the pyramidal cavity is studied. Due to the overlap of the pile-ups of adjacent micro pyramidal cavities, two and three dimensional arrayed nanostructures are successfully achieved. Then, the structured Cu (110) surface is used as a surface-enhanced Raman scattering (SERS) substrate with the rhodamine 6G (R6G) probe molecule as the detecting target in the present study. Experimental results show that the Raman intensity is enhanced with a decrease in the moving velocity of the precision stage. SERS enhancement factors within the range of 105 to 3 × 106 are achieved on the structured Cu (110) surface, which demonstrates that this method is reliable, replicable, homogeneous and inexpensive for the fabrication of SERS substrates.

The atomic force microscopy tip-based nanomechanical machining method has already been employed to machine different kinds of nanostructures with the control of the normal force of the tip. The previous studies verified the feasibility of the nanomachining approach with the force control. However, there are still some shortcomings of small normal force, small machining scale, high cost and low machining efficiency. Therefore, in this study, a tip-based micromachining system with normal force closed-loop control is established based on the principle of atomic force microscopy. The control parameters are optimized based on an analysis of the control process to enable the production of a constant normal force during machining when using a tip tool. The maximum machining velocity that can be attained using this system while maintaining a constant normal force is obtained based on an analysis of the normal force variations during machining. By controlling nanoscale accuracy and high-precision stage, more complex microstructures, including microsquares, millimeter-scale microchannels and three-dimensional step microchannels, are successfully fabricated using the proposed force control method. Experimental results show that the tip-based normal force control method is a simple, low-cost and versatile micromachining method with the potential ability to machine more complex structures and is likely to find wider applications in the micromachining field.

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.

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

Atomic force microscopy (AFM) tip-based nanofabrication is as a powerful method to machine nanostructures. However, the traditional AFM scratching process suffers from low processing efficiency and a low rate of material removal. Thus, an AFM tip-based nanomilling method was previously proposed to improve the machining efficiency and material removal rate; however, the machining mechanism of the nanomilling process, especially on hard-brittle silicon crystals, is not well understood. In this study, we used an AFM tip-based nanomilling approach to machine nanochannels on single-crystal silicon to investigate the machining mechanism (i.e., the material removal state, undeformed chip thickness, the brittle-to-ductile transition, and subsurface damage). For the first time, we established a theoretical model for tip-based nanomilling with a constant normal load to predict the machined depth. Nanochannels fabricated with a wide range of feed directions, crystal orientations, and tip trajectories were obtained, which provided a reference for machining high-quality nanochannels and an in-depth understanding of the nanomilling of single-crystal silicon. The experimental results demonstrated that we could machine a nanochannel without pile-ups by selecting a specific trajectory with a feed smaller than 4 nm in the 0° direction, a normal load no greater than 120 μN, and a crystal orientation at rotation angles of 135°, 157.5°, or 180°. Moreover, transmission electron microscope analysis of the subsurface of the nanochannel revealed a large number of dislocations, stacking faults, and a layer of amorphous silicon. Our findings are of great significance for obtaining high-quality nanochannels with a predicable machined depth and understanding the nanomilling mechanism of hard-brittle materials.

Aluminum alloys are widely applied in optical turrets after coating and super-finishing. Gold films prepared on aluminum alloy substrates via electron beam (e-beam) evaporation are considered to be effective way to realize close to total reflection of incident light. Here, we investigated the optimization of the reflectivity parameters of e-beam evaporated gold films; then, the influence of different deposition parameters on the surface quality, adhesive force and reflectivity (incident light in the 650–1700 nm range) of the film at −20, 25 and 60°C were systematically studied. The results demonstrated that the reflectivity and adhesion of the gold films both increased after high temperature holding and decreased slightly after low temperature holding. However, the surface morphology of the gold film did not change substantially. After holding at 60 and −20°C, the adhesive force decreased, which indicated that the adhesion strength between the reflective membrane and the substrate decreased.

Three-dimensional molecular dynamics simulations have been performed to investigate the combination effect of the tip inclination and scratching direction on the tip-based nanomanufacturing (TBN) process of single crystal silicon. Three typical scratching directions, edge forward (EF), face forward (FF), and side-face forward (SFF), were considered in the TBN processes. By analyzing the variation of the projected area of the tip, groove morphology, and silicon atomic flow behavior, the simulation results showed that the tip inclination and scratching direction had significant influences on groove generation, which is caused by the various atomic flow directions for scratching with different inclination angles and scratching directions. The change of the contact area induced by the tip inclination and scratching direction was the main reason for the variation of the scratching forces, and the normal forces were more sensitive than the tangential forces. Moreover, the plastic behavior, including the hydrostatic stress distribution, phase transformation, and the amorphous silicon distribution, were also dependent on the combination effect of the tip inclination and scratching direction. The results will provide important guidance for the process of TBN on silicon materials.

Aiming at revealing plastic deformation mechanisms of nanoindentation tests, we investigate the crystallographic orientation-influenced indentation size effect in the Berkovich nanoindentation tests of single crystalline copper, by using the nonlocal crystal plasticity finite element approach and specifically designed experiments. In our simulation model of nanoindentation, a new geometrically necessary dislocation density-based crystal plasticity model is proposed, and the utilized model parameters are calibrated by fitting the measured load-displacement curves of indentation tests. Then the size of plastic zone of indentation tests is defined by the surface pile-up profile, i.e. the diameter of a circle consisting of material points with half of maximum pile-up height. It is found that the modified plastic zone model incorporated with the newly developed scaling factor provides good predication of the indentation depth-dependent hardness of single crystalline copper.