1. Micro/Nanoscale Thermal Science Laboratory Department of Mechanical Engineering URL: http://www.engr.unl.edu/~nanolab Large-scale Atomistic Modeling of Laser-assisted Surface Nanostructuring Xinwei Wang Department of Mechanical Engineering The University of Nebraska – Lincoln Lincoln, NE 68588-0656 E-mail: xwang3@unl.eduxwang3@unl.edu Phone: 402-472-3089; Fax: 402-472-1465

2. Micro/Nanoscale Thermal Science Laboratory Department of Mechanical Engineering URL: http://www.engr.unl.edu/~nanolab Outline  Physical background: laser-assisted STM  Design and conduction of large-scale modeling  Unique physical phenomena discovered  Current and future work  Acknowledgment

3. Micro/Nanoscale Thermal Science Laboratory Department of Mechanical Engineering URL: http://www.engr.unl.edu/~nanolab Physical background: laser-assisted STM STM tip Pulsed laser Si substrate Enhanced optical field ~10 nm

4. Micro/Nanoscale Thermal Science Laboratory Department of Mechanical Engineering URL: http://www.engr.unl.edu/~nanolab Parallel Computation Enhanced optical field x y z 12 3 36 354 19.... 18........ Distribution of the computation domain on computing points. More than 200,000,000 atoms are modeled in the system to capture the physical process.

5. Micro/Nanoscale Thermal Science Laboratory Department of Mechanical Engineering URL: http://www.engr.unl.edu/~nanolab Parallel Computation 36 of the 52 computing points are used in the parallel MD simulation. Prairie Wind

6. Micro/Nanoscale Thermal Science Laboratory Department of Mechanical Engineering URL: http://www.engr.unl.edu/~nanolab Construction of Prairie Wind

7. Micro/Nanoscale Thermal Science Laboratory Department of Mechanical Engineering URL: http://www.engr.unl.edu/~nanolab Completed and current projects  Thermal transport in nanoscale materials  Thermal transport in nanocrystalline materials  Thermophysical properties of single-wall silicon nanotubes  Surface nanostructuring using laser-assisted scanning tunneling microscope  Multi-laser beam open-air diamond coating  Long-time nanosecond-laser materials interaction

8. Micro/Nanoscale Thermal Science Laboratory Department of Mechanical Engineering URL: http://www.engr.unl.edu/~nanolab Temperature Evolution (side view)

9. Micro/Nanoscale Thermal Science Laboratory Department of Mechanical Engineering URL: http://www.engr.unl.edu/~nanolab Sub-surface Nanostructure

10. Micro/Nanoscale Thermal Science Laboratory Department of Mechanical Engineering URL: http://www.engr.unl.edu/~nanolab Epitaxial re-growth

11. Micro/Nanoscale Thermal Science Laboratory Department of Mechanical Engineering URL: http://www.engr.unl.edu/~nanolab Epitaxial re-growth

12. Micro/Nanoscale Thermal Science Laboratory Department of Mechanical Engineering URL: http://www.engr.unl.edu/~nanolab Multi-scheme modeling of nanosecond laser materials interaction Si wafer domain II: MD simulation domain I: finite difference method thin Si (~nanometers) layer to provide the connection between the two domains Si wafer region experiencing phase change Targeted computational time: 1  s Targeted domain size: 2 mm

13. Micro/Nanoscale Thermal Science Laboratory Department of Mechanical Engineering URL: http://www.engr.unl.edu/~nanolab Multi-laser energy open-air diamond coating Substrate Diamond coating C atoms Velocity, pressure, specie concentration, and temperature are provided by the micro- to macroscopic modeling

14. Micro/Nanoscale Thermal Science Laboratory Department of Mechanical Engineering URL: http://www.engr.unl.edu/~nanolab Acknowledgement National Science Foundation (NSF) Office of Naval Research Air Force Office of Scientific Research Office of Vice Chancellor for Research Nebraska Research Initiative (NRI) Layman Foundation Sumitomo Foundation