Three-dimensional molecular dynamics simulation of nanostructure for reciprocating nanomachining process

Abstract

Three-dimensional molecular dynamics simulations are conducted to investigate the effect of reciprocating nanomachining process on the subsurface damaged layers, surface integrity, cutting force, stress variation of subsurface, and changes of energy and defects in the workpiece. Results show that there is no obvious shear zone ahead the tool during nanomachining. Dislocation nucleations are near the free surface ahead the tool and the interface of the tool and the workpiece and propagate in the surface and downward in the workpiece. There are the generations of dislocation jog and dislocation loops ahead the tool during the reciprocating cutting. The values of the reciprocating cutting force for the (111) orientation and (100) orientation under offset distance of 0a0 are not zero but 11.756 and 13.0498 nN, respectively. When the offset distance of the tool is up to 10a0, the ratio of primary cutting force to reciprocating force is nearly 90%. The shape of the machined groove in the (111) orientation remains better than that in the (111) orientation in cases of both the primary cutting process and the reciprocating process. Reciprocating cutting with the offset distance of 5a0 of the tool results in the pile-up atoms filling in the primary machined groove and forming the order lattice by surface reconstruction. Primary cutting force decreases with the reduction of workpiece sizes, which shows the size effects. With the increasing cutting depths, average primary cutting force and average reciprocating force increase. It is noted that reciprocating cutting force in the case of the (111) workpiece is larger than that of the (100) orientation except for the offset distance of 0a0. With the increasing offset distance of the tool, the residual shear stress increases in the subsurface of the workpiece, and the order degree of subsurface atoms of the workpiece decreases in the cases of both the (111) orientation and (100) orientation. It is denoted that, with the offset distance at 5a0, the peak of the average shear stress is highest during the reciprocating cutting. Meanwhile, the order degree of subsurface atoms in the case of the (111) orientation is better than that of the (100) orientation.

Material Removal Mechanism during Copper Chemical Mechanical Planarization Based on Nano-Scale Material Behavior

“…49 Simulations of nanomachining of copper showed that dislocations nucleate near the surface of the workpiece and emit into the crystal. 48 When machining was conducted at previously scratched regions with high defect densities, the cutting load was decreased. 48 Also, atomistic simulation of nanoindentation of Cu, [56][57][58] Ni 59 and Mo 60 at grain boundaries predicted that lower contact stresses were required for plasticity than required in the interior of perfect crystals.…”

“…These regions of high crystallographic defect density may be plastically deformed by abrasive particles sliding on the surface of the wafer, leaving an even higher defect density in the copper, as predicted with MD simulation. 48 The crystallographic defects lower the shear strength of copper because they facilitate activation of the dislocation source 29,49,50 or function as sites for heterogeneous nucleation of dislocations. 50 MD simulations predicted that vacancies in otherwise perfect Fe crystals 51 and Ni cyrstals 30,52 reduced the stress required for the onset of plasticity.…”

Molecular Dynamics Simulation Model of AFM-Based NanoMachining

“…Numerous studies have been reported on MD simulations of nanoindentaion and nanoscratching. The effects of several parameters such as crystal orientation [41,45,46], indenter shape and orientation [33,39,40,44], penetration or scratching depth [37,42,47,48], scratching speed [47,48], feed (on nanoscratching) [34,35], and temperature [25,45,49] have been investigated on different types of bulk and thin film materials. In addition, mechanical properties including Young's modulus, friction coefficient and hardness of materials have also been reported [26,42].…”

High Performance Field Emitters

“…According to the general WKB approximation and subsequent transmission models based thereon, low φ and high β typically manifest as high J max . In practice, however, for non‐classical materials, such as nanowires and nanotubes, the intimate mechanisms which augment the emission are not yet fully understood . This study focuses on the effect of changing φ across a diverse material range in an attempt to rationalize the importance of emitter work function in comparison to the degree of perturbation in emitter geometries.…”