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

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

Molecular dynamics simulation of AFM tip-1 based hot scratching of nanocrystalline GaAs

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

Nanoindentation induced anisotropy of deformation and damage behaviors of MgF2 crystals

The competition mechanism between the slip motions and cleavage fractures is related to the anisotropy of deformation behaviors, which is essential to manufacture complex optical components. To identify competition mechanism between the slip motions and cleavage fractures and reveal the anisotropy of deformation and damage behaviors of MgF2 crystals, the nanoindentation tests were systematically conducted on different crystal planes. In addition, the stress induced by the nanoindentation was developed and decomposed along the slip systems and cleavage planes, and cleavage factors and Schmid factors were calculated. The stress, cleavage factors and Schmid factors indicated that the activation degree of the slip motions and cleavage fractures determined the indentation morphologies. Under the same indentation conditions, the nanoindentation of the (001) crystal plane activated most slip motions, so the plastic deformation is most prone to occur on this crystal plane. The nanoindentation of the (010) crystal plane activated less slip motions and most cleavage fractures, resulting in the severest brittle fractures on the (010) crystal plane. The theoretical results consisted well with the experimental results, which provides the theoretical guidance to the low-damage manufacturing of MgF2 components

Oblique nanomachining of gallium arsenide explained using AFM experiments and MD simulations

Gallium Arsenide (GaAs) continues to remain a material of significant importance due to being a preferred semiconductor substrate for the growth of quantum dots (QDs) and GaAs-based quantum devices used widely in fifth-generation (5G) wireless communication networks. In this paper, we explored aspects of oblique nanomachining to investigate the improvement in the machining quality as well as to understand plasticity and transport phenomena in GaAs using atomic scale machining experiments and simulations. We studied the influence of the direction vector of the cutting tip (e.g. tip alignment) during the surface generation process in GaAs. We noticed a novel observation that when the AFM tip's cutting edge presented two acute angles (i.e., 30° angles each) between the cutting face and the cutting direction (which can be regarded as an oblique cutting condition), the cutting configuration involved early avalanche of dislocations compared to other tip configurations (e.g., orthogonal cutting). Orthogonal cutting involved the least coefficient of friction but the highest specific cutting energy compared to oblique cutting. High-resolution transmission electron microscopy (HRTEM) examination revealed that the shuffle-set slip on the {1 1 1} slip system due to the 〈1 1 0〉 type dislocation paves the way for plasticity during nanometric cutting of GaAs. Overall, a particular condition of oblique cutting was inferred to be the best for nanofabrication of high-quality wafers using an AFM

Fabrication of nanoscale pits with high throughput on polymer thin film using AFM tip-based dynamic plowing lithography

We show that an atomic force microscope (AFM) tip-based dynamic plowing lithography (DPL) approach can be used to fabricate nano-scale 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 one second using this proposed method. Both experiments and theoretical analysis are presented that fully determine the potential of this proposed method to fabricate pits efficiently

Insight into atomic-scale adhesion at the C/Cu interface during the initial stage of nanoindentation

Adhesion is a common phenomenon in nanomachining which affects processing accuracy and repeatability. As material removal approaches the atomic or close-to-atomic scale, quantum mechanics becomes the dominant principle behind the atomic-level interaction. However, atomic-scale effects cannot be properly described by empirical potential function-based molecular dynamics simulations. This study uses a first-principles method to reveal the atomic-scale adhesion between a diamond tip and a copper slab during initial-stage nanoindentation. Using a simplified tip and slab model, adhesion energy, electronic distribution and density of states are analysed based on quantum chemistry calculation. Results show that atomic adhesion is primarily due to the covalent bonding interaction between C and Cu atoms, which can induce structural changes to the diamond tip and copper slab. The effects of tip position and angles on adhesion are further studied through a series of simulation. The results show that adhesion between the tip and slab is sensitive to the lattice structure and a variant in angstroms is enough to cause different adhesion and structural changes. The actual determinants of adhesion can only be the atomic and electronic structures at the tip-slab interface. Bond rotation and breakage are observed during simulation and their effects on adhesion are further discussed. To conclude, the first-principles method is important for the analysis of an atomic-scale interaction system, even if only as an aid to describing adhesion at atomic and electronic scales

Processing outcomes of atomic force microscope tip-based nanomilling with different trajectories on single-crystal silicon

Atomic force microscope (AFM) tip-based nanomilling is an emerging technology for machining nanostructures with a high rate of material removal and slight tip wear. However, subsurface damage induced by nanomilling is poorly understood. In this study, we investigated nanomilling-induced subsurface damage of single-crystal silicon experimentally and with molecular dynamics simulations. We studied the effect of clockwise and anticlockwise trajectories on the nanochannel morphology. The clockwise trajectory resulted in a 'U'-shaped nanochannel at a relatively low normal load. Transmission electron microscopy and Raman spectroscopy analysis of the nanochannel subsurface revealed atomic-scale defects, including dislocations, stacking faults, and amorphous silicon. Molecular dynamics simulations described the evolution of the phase transformation and subsurface damage. This work reveals the mechanism of subsurface damage of single-crystal silicon in nanomilling, which will facilitate the machining of nanostructures with minimal subsurface damage

Study on the vertical ultrasonic vibration-assisted nanomachining process on single-crystal silicon

Subsurface damage that is caused by mechanical machining is a major impediment to the widespread use of hard–brittle materials. Ultrasonic vibration-assisted macro- or micromachining could facilitate shallow subsurface damage compared with conventional machining. However, the subsurface damage that was induced by ultrasonic vibration-assisted nanomachining on hard–brittle silicon crystal has not yet been thoroughly investigated. In this study, we used a tip-based ultrasonic vibration-assisted nanoscratch approach to machine nanochannels on single-crystal silicon, to investigate the subsurface damage mechanism of the hard–brittle material during ductile-machining. The material removal state, morphology, and dimensions of the nanochannel, and the effect of subsurface damage on the scratch outcomes were studied. The materials were expelled in rubbing, plowing, and cutting mode in sequence with an increasing applied normal load and the silicon was significantly harder than the pristine material after plastic deformation. Transmission electron microscope analysis of the subsurface demonstrated that ultrasonic vibration-assisted nanoscratching led to larger subsurface damage compared with static scratching. The transmission electron microscopy results agreed with the Raman spectroscopy and molecular dynamic simulation. Our findings are important for instructing ultrasonic vibration-assisted machining of hard–brittle materials at the nanoscale level