Large-scale molecular dynamics simulation of surface nanostructuring with a laser-assisted scanning tunnelling microscope

Abstract

In this work, large-scale molecular dynamics simulations are conducted to explore the thermal and mechanical phenomena in surface nanostructuring with a laser-assisted scanning tunnelling microscope. Employing a super parallel computer, more than 200 million atoms are modelled to provide substantial details about how the localized thermal and mechanical perturbations result in surface nanostructures. Extremely localized stress accumulation beneath the sample surface leads to an explosion of the melted/vaporized material, leaving a nanoscale hole in the sample surface. Normal and shear stress development are observed. Stress propagation in space is strongly influenced by the anisotropic nature of the crystal. The high pressure in the melted/vaporized region pushes the melt adjacent to the solid to move, thereby forming a protrusion at the edge of the hole. More importantly, visible sub-surface nanoscale structural damages are observed in a direction 45˚with respect to the axial direction. Detailed study of the lattice structure reveals atomic dislocations in the damaged regions. Both temporary and permanent structural damages are observed in the material. The temporary structural damage is featured with a formation, propagation and disappearing procedure.

Hybrid atomistic-macroscale modeling of long-time phase change in nanosecond laser–material interaction

“…Absorption of laser in the sample is achieved by only exciting the kinetic energy of atoms while keeping their momentum conserved. Details of the computational principles and laser energy absorption are described in our previous work [21][22][23][24][25].…”

“…After it separates from the molten region, it is gradually decomposed into small parts of liquid or gas-phase atoms. Compared with the picosecond laser-material interaction we studied before [23], under the same laser fluence input the nanosecond laser-material interaction is much less intense and shows limited nucleation and bubble formation. It is seen from Fig.…”

Dynamic Structure and Mass Penetration of Shock Wave in Picosecond Laser-Material Interaction

“…Details of laser beam absorption and treatment of MD simulation can be found in our recent work about laser-assisted surface nanostructuring. 14) The half-step leap-frog scheme is used in this work with a time step of 25 fs. Computation of the force between an atom and its neighbors is arranged by the cell structure and linked-list method.…”

Fabrication of nanostructures with high electrical conductivity on silicon surfaces using a laser-assisted scanning tunneling microscope

“…It has several advantages over STM-only counterpart such as versatile material processing and correlated property characterization. [9][10][11][12][13][14][15][16][17] This technique, stemming from the tipenhanced Raman spectroscopy, employs a focused laser radiation at the tip apex. A local intensity enhancement of optical radiation near the tip apex with the resolution much beyond the optical diffraction can be achieved.…”