180 likes | 304 Views
Organized Behavior Across the Scale Boundaries. Tiara M. Dunigan MicroEP REU July 25, 2007. Objective. To explain why the same defect pattern occurs across the scale boundaries. Outline. Dislocation Deformation Shear Stress Atomic Scale Edge Dislocation Nanoscale Quantum Dots
E N D
Organized Behavior Across the Scale Boundaries Tiara M. Dunigan MicroEP REU July 25, 2007
Objective • To explain why the same defect pattern occurs across the scale boundaries
Outline • Dislocation • Deformation • Shear Stress • Atomic Scale • Edge Dislocation • Nanoscale • Quantum Dots • Macroscale • Linear Dunes • Conclusion
Scale Boundaries • Atomic Scale • Nanoscale • Macroscale
Quantum Dots(nanoscale) Edge Dislocation (atomic scale) Linear Dunes (macroscale)
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
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
Shear Stress • The type of stress observed across the scale boundaries • stress is parallel to the face of the material
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
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
Misfit Dislocation • Observed in Quantum Dots • Quantum Dots • Nanoparticle made from semi conducting material • Dislocation degrade the electronic properties of the quantum dots
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.
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
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
Acknowledgments • Dr. Ajay Malshe • Professor Vickers • Renee Hearon • Dr. Arlene Maclin
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