Organized Behavior Across the Scale Boundaries

1. Organized Behavior Across the Scale Boundaries Tiara M. Dunigan MicroEP REU July 25, 2007

2. Objective • To explain why the same defect pattern occurs across the scale boundaries

3. Outline • Dislocation • Deformation • Shear Stress • Atomic Scale • Edge Dislocation • Nanoscale • Quantum Dots • Macroscale • Linear Dunes • Conclusion

4. Scale Boundaries • Atomic Scale • Nanoscale • Macroscale

5. Quantum Dots(nanoscale) Edge Dislocation (atomic scale) Linear Dunes (macroscale)

6. Dislocation • Linear Defect where some of the atoms in the crystal lattice are misaligned • Allows deformation to occur at the lowest possible stress level • Allows for elasticity in a material in order to reduce stress

7. Deformation • Deformation occurs when the defect is moving through a material • There are two types of deformation • Plastic • The material undergoes a change in shape that is not reversible • Elastic • Deformation is reversible

8. Shear Stress • The type of stress observed across the scale boundaries • stress is parallel to the face of the material

9. Edge Dislocation • Takes place on the atomic scale • Moves under the application of external stress by the breaking of existing bonds and forming new bonds with neighboring atoms • Fault in a crystalline structure

10. Edge Dislocation • Takes place on the atomic scale • Moves under the application of external stress by the breaking of existing bonds and forming new bonds with neighboring atoms • Fault in a crystalline structure

11. Quantum Dots

12. Misfit Dislocation • Observed in Quantum Dots • Quantum Dots • Nanoparticle made from semi conducting material • Dislocation degrade the electronic properties of the quantum dots

13. Quantum Dots • Lattice Mismatch • Two materials featuring different lattice constants are brought together by deposition of one material on top of another • In order to compensate for the lattice mismatch a misfit dislocation will form.

14. Linear Dunes

15. Linear Dunes • Linear Dunes • Found in deserts around the world • When the wind strength is strong enough, individual sand grains are lifted by the direct action of the shear stress exerted by the wind on the sand surface. • The change in wind direction causes the reorientation of a bed form thus producing the defect pattern

16. Conclusion • In each case the defect pattern occurs as a means to relieve stress • In each the case the type of stress induced was shear stress • Shear stress causes an angle to form when shifting from the initial state to the final state

17. Acknowledgments • Dr. Ajay Malshe • Professor Vickers • Renee Hearon • Dr. Arlene Maclin

18. References • http://www.jwave.vt.edu/crcd/farkas/lectures/dislocations/tsld003.htm • http://www.cmse.ed.ac.uk/AdvMat45/CrystalBasics.pdf • Lattice defects in InAs quantum dots on the GaAs(315)B surface; T. Suzuki, Y. Temko, M.C.Xu, K.Jacobi; Physical Review B 69; The American Physical Society (2004) • Defect reduction with quantum dots in GaN grown on sapphire substrates by molecular beam epitaxy; D. Huang, M.A. Reshchikov, F. Yun, T. King, A.A. Baski, H Morkoc; Applied Physics Letters Vol. 80 #2 (2002) • N. Jin-Phillipp, F. Phillipp;(1999) Defect formation in self assembling quantum dots of InGaAs: a case study of direct measurements of local strain from HREM Journal of Microscopy, Vol.194, pt.1 (1999) • Dynamics of Aeolian sand ripples; Z. Csah´ok1,, C. Misbah, F. Rioual, and A. Valance; European Physical Journal • Physical Review E; Volume 60, number 1; July 1999; Nonlinear Dynamics of Aeolian Sand Ripples; Leonid Prigozhin • Geology; September 1997;Bedform Dynamics: Does the tail wag the dog?, B. Werner, G. Kocurek