Y.C. Liang

Influence of coherent twin boundaries on three-point bending of gold nanowires

In the present work we elucidate the deformation mechanisms of twinned Au nanowires (NWs) under three-point bending by means of molecular dynamics simulations. We further investigate the effects of twin boundary orientation, NW diameter and twin boundary spacing on the mechanical properties and deformation behaviors of NWs. Our simulation results reveal that dislocation slip, twin boundary associated mechanisms and deformation twinning work in parallel in the heterogeneous localized plastic deformation of twinned Au NWs under bending. The dislocation–twin boundary interactions can be significantly altered by changing the twin boundary orientation as well as the bending direction. Furthermore, the NW diameter and twin boundary spacing strongly influence the competition between individual deformation mechanisms, which in turn leads to extrinsic and intrinsic size effects on the strength and the bending ductility of the NWs.

Nanobending of nanowires: A molecular dynamics study

Three-dimensional molecular dynamics simulations of the nanobending of copper nanowires are carried out. Simulation results show that the loading and unloading cycles of the nanobending test can reveal the full spectrum of the nanowires’ mechanical properties. Up-tensile and bottom-compressive features have been observed along with the neck zone formation. Amorphous region formation is the mechanism of fracture and final breakage. The measured elastic modulus and yield stress are 49 and 7.6 GPa, respectively. Moreover, the effect of the adhesion on the nanobending process is revealed.

An investigation of nanoindentation tests on the single crystal copper thin film via an atomic force microscope and molecular dynamics simulation

Abstract Nanoindentation tests performed in an atomic force microscope have been utilized to directly measure the mechanical properties of single crystal metal thin films fabricated by the vacuum vapour deposition technique. Nanoindentation tests were conducted at various indentation depths to study the effect of indentation depths on the mechanical properties of thin films. The results were interpreted by using the Oliver-Pharr method with which direct observation and measurement of the contact area are not required. The elastic modulus of the single crystal copper film at various indentation depths was determined as 67.0 > 6.9 GPa on average, which is in reasonable agreement with the results reported by others. The indentation hardness constantly increases with decreasing indentation depth, indicating a strong size effect. In addition to the experimental work, a three-dimensional nanoindentation model of molecular dynamics (MD) simulations with embedded atom method (EAM) potential is proposed to elucidate the mechanics and mechanisms of nanoindentation of thin films from the atomistic point of view. MD simulations results show that due to the size effect no distinct dislocations were observed in the plastic deformation processes of the single crystal copper thin films, which is significantly different from the plastic deformation mechanism in bulk materials.

MD Simulation of Effect of Crystal Orientation and Cutting Direction on Nanometric Cutting Using AFM Pin Tool

Three-dimensional molecular dynamics simulations of nanometric cutting monocrystalline copper using atomic force microscopy pin tool are conducted to investigate the effect of crystal orientation and corresponding cutting direction on the deformation characteristics. EAM potential and Morse potential are utilized respectively to compute the interactions between workpiece atoms, interactions between workpiece atoms and tool atoms. The results reveal that the nanometric cutting processes are significantly affected by crystal orientation and cutting direction. Along the [110] cutting direction, better quality of chip pattern and smaller workpiece material deformation region can be obtained than along the [100] cutting direction. Cutting the workpiece material (110) crystal orientation, samaller chip volume and smaller subsurface deformed region can be obtained than cutting the workpiece material (100) crystal orientation. The variations of workpiece atoms potential energy in different cutting processes are investigated.

Mechanical Properties of Machined Nanostructures

Three-dimensional molecular dynamics simulations have been carried out to predict the mechanical properties of a single crystalline copper with different scratching depths and no defects by embedded-atom method potential respectively. The mechanical properties for nanostructure with no defects and machined groove are investigated by various strain rates, scratched depths and scratching directions. Through the visualization technique of atomic coordination number, the onset and movement of defects in workpiece such as dislocations are analyzed under tensile loads. Work-harden formation, recrystallization behavior and the properties of rupturing process of nanostructure are exhibited at the atomic view. The relation between stress and the onset and evolvement of defects in specimen is analyzed for fundamental understanding the mechanical properties of nanostructure.

Modulated wrinkle patterns in a gold thin film deposited onto an elastomeric polymer

Modulated wrinkle patterns could be yield on a gold thin film covering an elastomeric polymer with the following simple process. The simple, efficient ultra-precision turning technique was used to prepare patterned surface of Al samples, which served as a hard master to replicate reverse patterns on the elastomeric polydimethylsiloxane (PDMS) surface by replica molding. The surface patterns in PDMS have the irregular section, different from those fabricated by optical lithography. And then a gold thin film was deposited by ion sputtering onto the patterned surface of PDMS substrates. Due to great difference in heat expansion coefficient between the metal and elastomeric polymer, modulated wrinkle patterns spontaneously appeared on the gold thin film, including stripe and herringbone. When the wavelength of the wrinkle pattern is approximately close to or more than height and width of the microstructures on the PDMS substrates, the herringbone wrinkles appear and entirely overlay the grating pattern; and otherwise the stripe pattern occurred on patterned surface of PDMS substrates and distributed perpendicularly to the step. Due to obvious difference in metal film depth, modulated wrinkle patterns, including regular striped and herringbone pattern, could be generated on gold thin films deposited onto PDMS surface.

Influential Factors of Low-energy C36 Cluster Deposition on Diamond (100) Crystal Plane

Brenner-LJ potential is adopted to describe the interactivity between diamond and C36 cluster, and the deposition mechanism of multi-C36 on the diamond surface is researched by molecular dynamics simulation. Through simulative experiments the incident energy, incident point, incident posture, incident angle and other factors are analyzed. Studies discover that the minimal deposition threshold is 20 eV and the maximum is 60 eV with the different incident point locations and incident postures of C36 clusters. When the incident angle is not over 60, C36 may roll or slip to the region of smaller bonding energy and then bond. So the bonding probability is raised. Research results show that when incident angle is between 0 and 20 and incident energy range is from 30 eV to 60 eV, it is the optimal condition of single C36 cluster deposition on diamond (100) crystal plane.