Atomic Scale Computational Simulation for Nano-materials and Devices: A New Research Tool for NanotechnologyKwang-Ryeol Lee

Future Technology Research Division, KIST, Seoul, Korea2nd International Symposium on Bio- and Nano-Electronics in Sendai, Dec. 9-10, 2006

Todays TalkIntroduction to computational simulationRole of atomic scale simulation in nano-materials and devices researchCase Study : Asymmetry in atomic scale intermixing during deposition of thin metallic multilayers

What is Computational Simulation?Research method to investigate a complex system based on the reasonable principles of a simple system. 10keV Ar on Au75eV C on diamond

Molecular Dynamics Simulation

Hierarchy of Computer Simulation

Computation & Simulation in Atomic ScaleAb initio CalculationMolecular Dynamic Simulation

Nanomaterials

Characteristics of NanotechnologyContinuum media hypothesis is not allowed.

Band Theory

Diffusion and Mechanics

Size Dependent Properties

Scale Down Issues1~2nmKinetics based on continuum media hypothesis is not sufficient.

Chracteristics of NanotechnologyContinuum media hypothesis is not allowed.

Large fraction of the atom lies at the surface or interface.Abnormal WettingAbnormal Melting of Nano ParticlesChemical Instabilities

GMR Spin ValveMajor materials issue is the interfacial structure in atomic scale

Nanoscience or Nanotechnologyneeds atomic scale understandings of structure, kinetics and properties.

Insufficient Experimental Tools

Methodology of Conventional R&D

Methodology of Nanotechnology

Computation & Simulation in Atomic ScaleAb initio CalculationMolecular Dynamic Simulation1nm = 1,000 atoms10nm= 1,000,000 atoms100nm=1,000,000,000 atoms

Cluster Supercomputer & VisualizationBeowulf Cluster @ CALTECH

Devices with Thin MultilayersMajor materials issue is the interfacial structure in atomic scale1~2nmGMR Spin Valve

Thin Film Growth Model (conventional)

Adatom (normal incident 0.1 eV)Co-Al EAM potential*x,y-axis : Periodic Boundary Conditionz-axis : Open SurfaceDeposition rate: 1.306 10-1 nm/nsecMD calc. step : 0.1fs300K Initial Temperature300K Constant TemperatureFixed Atom PositionCalculation MethodsR. Pasianot et al, Phys. Rev. B45, 12704 (1992).A. F. Voter et al , MRS Proc. 82, 175 (1987).C. Vailhe et al, J. Mater. Res. 12, 2559 (1997).

Deposition in Co-Al SystemCo on Al (001)Al on Co (001)

Asymmetry in Interfacial Intermixing

Radial Distribution Function of Interface CoAl compound layer of B2 structure was formed spontaneously.

Al on Co(111)/(0001)Co on Al(111)Atomic deposition behavior

Asymmetry in Interfacial Intermixing Deposition at 300K Initial kinetic energy 0.1eV

Activation Barrier for IntermixingReaction Coordinate

Adatom (normal incident 0.1 eV)Co-Al EAM potential*x,y-axis : Periodic Boundary Conditionz-axis : Open SurfaceDeposition rate: 1.306 10-1 nm/nsecMD calc. step : 0.1fs300K Initial Temperature300K Constant TemperatureFixed Atom PositionCalculation MethodsR. Pasianot et al, Phys. Rev. B45, 12704 (1992).A. F. Voter et al , MRS Proc. 82, 175 (1987).C. Vailhe et al, J. Mater. Res. 12, 2559 (1997).

Acceleration of Adatoms near Surface

Kinetic Criteria for IntermixingLocal Acceleration3.5eV(1)(2)(3)(4)Activation Barrier for MixingReaction Coordinate

Deposition in Co-Al SystemCo on Al (001)Al on Co (001)

New Chinese Proverb?

Asymmetry of Surface ReactionDo you have experimental evidence?

FCC - AlMagnetic Properties of Co-Al systemSpin resolved DOS

Magnetic properties of Co-Al Thin LayerSi substrateSi substrateSi substrateCu buffer layer (1500)Cu buffer layer (1500)Co (30)Co (30)Co (30)Al (30)Al (840)Cu Capping layer (50)Cu Capping layer (50)Cu Capping layer (50)MOKE(Magneto-Optic Kerr effects)

Effect of Coating SequenceAlSi substrateCu buffer layer (1500)Co (30)Capping layer (50)

Co Thickness Effect

Effect of Coating SequenceAlSi substrateCu buffer layer (1500)Co (30)Capping layer (50)

How thick is the nonmagnetic (B2) interlayer?

Thickness of B2 Layer : 3ML3ML ~ 10

SummaryAl on CoCo on AlAsymmetry in interfacial intermixing was observed in both MD simulation and experiment.

AcknowledgementFinancial SupportCore Capability Enhancement Program of KIST (V00910, E19190)

CollaboratorsKISTMr. Sang-Pil KimDr. Seung-Cheol LeeHanyang UniversityProf. Yong-Jae Chung Yonsei UniversityProf. Chungnam Whang Dr. Jae Young ParkMs. Hyunmi Hwang

Computational Materials Simulation Lab.http://diamond.kist.re.kr/SMS