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 To explain why the same defect pattern occurs across the scale boundaries

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

4 Scale Boundaries Atomic Scale Atomic Scale Nanoscale Nanoscale Macroscale Macroscale

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

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

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

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

9 Edge Dislocation Takes place on the atomic scale 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 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 Fault in a crystalline structure

10 Edge Dislocation Takes place on the atomic scale 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 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 Fault in a crystalline structure

11 Quantum Dots

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

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

14 Linear Dunes

15 Linear Dunes Linear Dunes Linear Dunes Found in deserts around the world 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 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 case the defect pattern occurs as a means to relieve stress In each the case the type of stress induced was shear 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 Shear stress causes an angle to form when shifting from the initial state to the final state

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

18 References 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) 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) 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) 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 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 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 Geology; September 1997;Bedform Dynamics: Does the tail wag the dog?, B. Werner, G. Kocurek