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Organized Behavior Organized Behavior Across the Scale Across the Scale

BoundariesBoundaries

Tiara M. DuniganTiara M. DuniganMicroEP REUMicroEP REU

July 25, 2007July 25, 2007

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ObjectiveObjective

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

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OutlineOutline

DislocationDislocation DeformationDeformation Shear StressShear Stress Atomic ScaleAtomic Scale

Edge DislocationEdge Dislocation NanoscaleNanoscale

Quantum DotsQuantum Dots MacroscaleMacroscale

Linear DunesLinear Dunes ConclusionConclusion

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Scale BoundariesScale Boundaries

Atomic ScaleAtomic ScaleNanoscaleNanoscaleMacroscaleMacroscale

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Quantum Dots

(nanoscale)

Linear Dunes(macroscale)

Edge Dislocation(atomic scale)

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DislocationDislocation

Linear Defect where some of the atoms in the crystal Linear Defect where some of the atoms in the crystal lattice are misalignedlattice are misaligned

Allows deformation to occur at the lowest possible stress Allows deformation to occur at the lowest possible stress levellevel

Allows for elasticity in a material in order to reduce stressAllows for elasticity in a material in order to reduce stress

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DeformationDeformation

Deformation occurs when the defect is moving Deformation occurs when the defect is moving through a materialthrough a material

There are two types of deformationThere are two types of deformationPlasticPlastic

The material undergoes a change in shape that is not The material undergoes a change in shape that is not reversible reversible

ElasticElastic Deformation is reversibleDeformation is reversible

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Shear StressShear Stress

The type of stress The type of stress observed across the observed across the scale boundariesscale boundariesstress is parallel to the stress is parallel to the

face of the materialface of the material

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Edge DislocationEdge Dislocation Takes place on the atomic scaleTakes place on the atomic scale

Moves under the application of external stress by the breaking of Moves under the application of external stress by the breaking of existing bonds and forming new bonds with neighboring atomsexisting bonds and forming new bonds with neighboring atoms

Fault in a crystalline structureFault in a crystalline structure

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Edge DislocationEdge Dislocation Takes place on the atomic Takes place on the atomic

scalescale

Moves under the application of Moves under the application of external stress by the breaking external stress by the breaking of existing bonds and forming of existing bonds and forming new bonds with neighboring new bonds with neighboring atomsatoms

Fault in a crystalline structureFault in a crystalline structure

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Quantum DotsQuantum Dots

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Misfit DislocationMisfit Dislocation

Observed in Quantum DotsObserved in Quantum DotsQuantum DotsQuantum Dots

Nanoparticle made from semi conducting materialNanoparticle made from semi conducting material

Dislocation degrade the electronic properties Dislocation degrade the electronic properties of the quantum dotsof the quantum dots

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Quantum DotsQuantum Dots

Lattice MismatchLattice Mismatch Two materials featuring Two materials featuring

different lattice constants different lattice constants are brought together by are brought together by deposition of one material deposition of one material on top of anotheron top of another

In order to compensate In order to compensate for the lattice mismatch a for the lattice mismatch a misfit dislocation will form.misfit dislocation will form.

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Linear DunesLinear Dunes

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Linear DunesLinear Dunes

Linear DunesLinear Dunes Found in deserts around the worldFound 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 The change in wind direction causes the reorientation of a bed form thus producing the defect patternof a bed form thus producing the defect pattern

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ConclusionConclusion In each case the defect pattern occurs as In each case the defect pattern occurs as

a means to relieve stress a means to relieve stress

In each the case the type of stress In each the case the type of stress induced was shear stressinduced was shear stressShear stress causes an angle to form when Shear stress causes an angle to form when

shifting from the initial state to the final stateshifting from the initial state to the final state

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AcknowledgmentsAcknowledgments

Dr. Ajay MalsheDr. Ajay MalsheProfessor VickersProfessor VickersRenee HearonRenee HearonDr. Arlene MaclinDr. Arlene Maclin

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ReferencesReferences 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; 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)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. 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)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 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) direct measurements of local strain from HREM Journal of Microscopy, Vol.194, pt.1 (1999)

Dynamics of Aeolian sand ripples; Z. Csah´ok1Dynamics of Aeolian sand ripples; Z. Csah´ok1 ,,, C. Misbah, F. Rioual, and A. Valance; European Physical , C. Misbah, F. Rioual, and A. Valance; European Physical JournalJournal

Physical Review E; Volume 60, number 1; July 1999; Physical Review E; Volume 60, number 1; July 1999; Nonlinear Dynamics of Aeolian Sand Ripples;Nonlinear Dynamics of Aeolian Sand Ripples; Leonid PrigozhinLeonid Prigozhin

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