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GODDARD - MSC/Caltech PASI-Caltech 1/5/04 1 First principles Simulations of Nanoscale Materials Technology William A. Goddard III Charles and Mary Ferkel.

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Presentation on theme: "GODDARD - MSC/Caltech PASI-Caltech 1/5/04 1 First principles Simulations of Nanoscale Materials Technology William A. Goddard III Charles and Mary Ferkel."— Presentation transcript:

1 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 1 First principles Simulations of Nanoscale Materials Technology William A. Goddard III Charles and Mary Ferkel Professor of Chemistry, Materials Science, and Applied Physics Director, Materials and Process Simulation Center California Institute of Technology, Pasadena, California 91125 [] NSF Pan-American Advanced Studies Institutes (PASI) Workshop January 5-16, 2004 Computational Nanotechnology and Molecular Engineering MSC/Caltech: Dr. Mario Blanco and Dr. Mamadou Diallo

2 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 2 Who is Goddard? Born El Centro, California (in Southern California desert east San Diego) Public schools of El Centro, Delano, Indio, Lodi, Firebaugh, MacFarland, Oildale (Bakersfield), Modesto, Yuma BS Engineering, UCLA, June, 1960 PhD Engineering Science (Minor physics) Caltech Oct. 1964 Caltech Chemistry Faculty Nov. 1964-2024 108 PhD’s, 550 publications, Member National Academy of Science, Int. Acad. Quantum Molec. Sci. 8 patents in protein structure prediction, new polymerization catalysts, semiconducting processing modeling Co-founded 5 companies (all still thriving) William Goddard PhD (Engr. Sci. 1965,Caltech) advisor: Pol Duwez Pol Duwez DSc (1933, Brussels) advisor: Emile Henriot Emile Henriot DSc (Phys, 1912, Sorbonne, Paris) advisor: Marie Curie Marie Curie DSc (1903, Ecole Phys. Chim. Ind, Paris) advisor: Becqeurel

3 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 3 What is Caltech? Throop University founded in 1891 (at Green and Fair Oaks, near old town Pasadena). vocational college, high school, grammar school ~1905 George Ellery Hale, Astronomer came to Pasadena to build Mt. Wilson Observatory (because of clear air) In ~ 1907 changed from to Throop Polytechnic Institute (engineering college) In ~1910 Throop moved to current site (previously a citrus grove) ~1915 Arthur Amos Noyes came from MIT to start science (chemistry) at Caltech ~1918 Noyes attracted Robert A. Millikan to Caltech In ~ 1920 changed to California Institute of Technology In 1920’s Nobel Prizes to Mulliken (Physics), Morgan (Biology)

4 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 4 Caltech Today Six Divisions: Chemistry and Chemical Engineering Biology Geosciences Physics, Math, and Astronomy Engineering and Applied Science Humanities and Social Science ~1000 undergraduates ~1200 graduate students ~350 faculty

5 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 5 What is Beckman Institute? Gift by Arnold and Mabel Beckman (Arnold got PhD at Caltech, stayed of faculty for 10 years, then started Beckman Instruments) Construction finished July,1990 Resource Centers in Chemistry and Biology Imaging Lasers Materials Synthesis Materials and Process Simulation Center (MSC)

6 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 6 What is Materials and Process Simulation Center? (MSC) Senior Staff: All involved in nanotechnolgy William A. Goddard III, Director Blanco, Director Process Simulations and Industrial Technology Cagin, Director Mesoscale and Materials Science Technology van Duin, Director Force Field and Materials Technology Vaidehi, Director of Biotechnology and Pharma Meulbroek, Director Software Integration and Databases Oxgaard, Director of Quantum and Catalysis Technology Diallo, Manager Molecular Environmental Technology Molinero, Manager of Complex Materials Simulations Willick, Manager of Computer Technology and Networks Staff: (over 60) Trained in Chem., Phys., Mat. Sci., Appl. Phys., Biol., Envir. Engr., Chem. Eng., Comp. Sci., Elect. Engr. Excellent team for complex problems Critical Mass of Expertise in Most areas of Atomistic Theory and Applications to Materials, Chemistry, and Biology Including QM, FF, MD, MesoDyn, Stat. Mech. Biochem., Catalysis, Ceramics, Polymers, Semicond., Metal Alloys, Nanotechnology, Environmental Technology

7 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 7 Vision of MSC: First Principles Modeling: Base on QM To predict macroscale from QM use Multiscale Strategy EOS of different phases, vacancy energy, surface energy femtosec time distance Å nm micron mm meters MESO Continuum (FEM) QM MD MD simulations of deformation Fracture, Plasticity, Creep, Fatigue with application scales of time-space ELECTRONS ATOMS GRAINS GRIDS First principles Force Field Constitutive relations mechanisms plastic deformation Mesoscale FF (beads) FF hours seconds microsec nanosec picosec Build from QM  FF  MD  Meso  Continuum

8 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 8 Materials and Process Simulation Center (MSC) Each student involved with both  developing tools (theory and software) to solve impossible problems (1/2 effort) using simulation (and experiment) to develop new materials and processes materials (1/2 effort) Nearly every project has a strong coupling with experiment  Experiment stimulates current theory with impossible problems  Results from simulation guide and interpret experiments  Experiment essential to validate theory and simulation Ultimately, de novo simulation will be at the heart of chemistry, biology, materials science

9 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 9 Theory Essential to solve Grand Challenges in Technology Materials Science: Nanoscale Technology Opportunity: Tremendous potential for new functional materials (artificial machines smaller than cells) Problems: Synthesis, Characterization, Design Need Multiscale Modeling: couple time/length scales from electrons/atoms to manufacturing Biology: Protein Folding: Predict all structures of life Opportunity Will soon have Genomes for All Life Now: Over 700,000 genes but only ~10,000 protein structures Problem: experiment can do only ~ 2000/year ($200 million) Need: Prediction of Reliable Protein Structure and Function for 1,000,000 proteins Chemistry: Methane (CH 4 ) Activation, Gas to Liquid Opportunity Enormous reserves of CH 4 for energy, chemicals, and materials, mostly wasted Problem: no efficient, selective, low temperature catalyst Need: Predictive Mechanism to predict new catalysts First Principles Theory will lead developments of new technologies in 21 st Century

10 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 10 BIOTECHNOLGY: Membrane Proteins (GPCR), non-natural Amino Acids, Pharma (VLS) POLYMERS: PEM (nafion), Dendrimers, Gas diffusion, Surface Tension, Biobased CATALYSTS: Methane Activation, Selective Oxidation, ElectroCat (O 2 ), Polar Olefins SEMICONDUCTORS: Dielectric Breakdown, Si/SiO 2 /Si 3 N 4 interfaces, B diffusion CERAMICS: Ferroelectrics, Zeolites, Exfoliation Clays METAL ALLOYS: Glass Formation, Plasticity (dislocations, crack propagation, spall) NANOSYSTEMS: DNA based Machines, Carbon Nanotubes, nanoelectronics ENVIRONMENTAL: Dendrimers for Selective Encapsulation, Humic acid INDUSTRIAL APPLICATIONS (GM-GAPC, ChevronTexaco, GM-R&D, Asahi Kasei, Toray) Polymers: Gas Diffusion, Surface Tension Modification, Water solubility Polymerization Catalysts for Polar Monomers Catalysts: CH 4 activation, Alkylation phenols, zeolites (Acid sites/templates) Semiconductors: Dielectric Breakdown nanometer oxides, nitrides, B Diffusion in Si Automobile Engines: Wear Inhibitors (iron and aluminum based engines) Oil Pipelines: Inhibitors for Corrosion, Scale, Wax; Hydrates, Demulsifiers Oil Fields: Surfactants for low water/oil interface energy, Basin models Ceramics: Bragg Reflection Gratings Catalysts: ammoxidation of propane Fuel Cells: H 2 Storage, Polymer Electrolyte Membranes, Electrocatalysis Applications Focus at the MSC

11 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 11 GM advanced propulsion: Fuel Cells (store H 2, membrane, cathode) Chevron Corporation: CH 4 to CH 3 OH, Alkylation, Wax Inhibition General Motors - Wear inhibition in Aluminum engines Seiko-Epson: Dielectric Breakdown in nm oxide films, TED (B/Si) Asahi Kasei: Ammoxidation Catalysis, polymer properties Berlex Biopharma: Structures and Function of CCR1 and CCR5 (GPCRs) Aventis Pharma: Structures and Function of GPCR’s Stimulation toward solving impossible problems Collaborations with Industry Asahi Glass: Fluorinated Polymers and Ceramics Avery-Dennison: Nanocomposites for computer screens Adhesives, Catalysis BP Amoco: Heterogeneous Catalysis (alkanes to chemicals, EO) Dow Chemical: Microstructure copolymers, Catalysis polymerize polar olefins Exxon Corporation: Catalysis (Reforming to obtain High cetane diesel fuel) Hughes Satellites/Raytheon: Carbon Based MEMS Hughes Research Labs: Hg Compounds for HgCdTe from MOMBE Kellogg: Carbohydrates/sugars (corn flakes) Structures, water content MMM: Surface Tension and structure of polymers Nippon Steel: CO + H2 to CH3OH over metal catalysts Owens-Corning: Fiberglas (coupling of matrix to fiber) Saudi Aramco: Demulsifiers, Asphaltenes Each project (3 Years) supports full time postdoc and part of a senior scientist

12 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 12 Method Developments in MSC Quantum Mechanics Solvation (Poisson-Boltzmann) Periodic Systems (Gaussians) New Functionals DFT (bond breaking) Quantum Monte Carlo methods Time Dependent DFT (optical spectra) Force Fields Polarizable, Charge Transfer Describe Chemical Reactions Describe Phase Transitions Mixed Metal, Ceramic, Polymer MesoScale Dynamics Coarse Grained FF Kinetic Monte Carlo (Gas Diffusion, Epitaxial Growth) Hybrid MD and Meso Dynamics Tribology Utilization: Integrated, Web-based Molecular Dynamics Non-Equilibrium Dynamics –Viscosity, rheology –Thermal Conductivity Solvation Forces (continuum Solv) –surface tension, contact angles Hybrid QM/MD Plasticity –Formation Twins, Dislocations –Crack Initiation Interfacial Energies Process Simulation Vapor-Liquid Equilibria Reaction Networks Method Development critical to progress Generally not supported by US government or industry

13 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 13 Nanotechnology: Experiment and Theory Closing the Gap Opportunity: Nanotechnology provides tremendous potential for new functional materials (artificial machines smaller than cells) Problems to be solved before commercialization: –Synthesis –Characterization –Design In each area there are tremendous experimental challenges. In each case the time to solution will be dramatically decreased by the use of de novo simulations Multiscale Modeling that couples the time and length scales from electrons and atoms to manufacturing

14 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 14 Nanoelectronics Many experimental efforts to make nanoscale electronic devices based on molecules sandwiched between conducting surfaces (e.g., Jim Heath/UCLA-Caltech, Charley Lieber/Harvard, Jan Schön/Lucent, Phaedon Avouris/IBM) This could be most useful. For example a future MEMS-scale device (say 20 microns in size) might have an onboard computer based on nanometer sized elements with built in sensors and logic to respond to local environment without the necessity of communicating to remote computer. Thus to be useful the nanosized switches need not be as fast as current computer elements (GHz). They could be even as slow as KHz and still be useful. Unfortunately little is known about the atomic-level structure and properties of these nanoelectronics systems, making difficult the design of improved devices.

15 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 15 Computational Nanoelectronics Step 1: Use theory to predict the structures and mechanical properties of Nanoelectronics systems Step 2: Use theory to predict electrical performance from 1st principles. To predict electrical performance of experimental systems we must develop QM based methods to predict current/voltage (I/V) performance from first principles. We have been working on this over the last 2 years (with support from an industrial partner). We can now predict I/V both for isolated molecules and for 2-dimensional slabs (still need to make the software faster for routine use). We are now in the position to design new systems that can be synthesized and tested.

16 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 16 CBPQT=cyclobis(paraquat-p-phenylene) DNP=1,5-dioxynaphthalene [2]Rotaxane TTF=tetrathiafulvalene; Stoddart-Heath-Type [2]Rotaxane Molecular Switch OFF Weiqiao Deng Yun Hee Jang Seung Soon Jang Hoon Kim

17 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 17 11_26C KAN242 Volts 01 Current 0 +2.5 V  -2.5 V Return Switch diode orientation at –2.3V NDR=AcceptorCharging(?) redox D D + + + + D D + + + + s O Me ON Fraser Stoddart (UCLA) Jim Heath Caltech) OFF TTF Naphthyl TTF Naphthyl Molecular Switch Napthyl and TTF nearly equally good donors Rotaxane ring binds to TTF > 300K Rotaxane binds to napthyl > 250K Assume ring moves when apply external voltage which cause diode to switch. ON OFF

18 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 18 Electrode 2 Transmission function:  p(E,V) difference in the Fermi-Dirac occupations between electrodes, 1 and 2 Green’s function: H MM obtained from ab initio QM calculation: Molecule Spectrum functions: Green’s functions for electrodes g 1 and g 2 : Describe as Cluster, slab and surface Electrode 1 Overlap matrix S Fock matrix H Ab initio Self energy: Formalism due to Mark Ratner Atomic level simulation of Current/Voltage Finite (non periodic) case

19 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 19 Naphthyl TTF ON OFF TTF, OFF Naphthyl, ON V(energy) I(transmission) I(current) Voltage H = H M +  Predicted I(transmission) -V(energy) Not known experimentally which state is on and which is off

20 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 20 Rotaxane on TTF, OFFRotaxane on Naphthyl, ON Nearly degenerate, thus strongly coupled. ~metallic HOMOLUMOHOMOLUMO Big gap not coupled. ~insulating Switch mechanism: Location of HOMO and LUMO

21 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 21 Next step on Heath-Stoddart molecular devices The theory has already shown which site blue box sits on in the On/Off states We are now determining how the blue box moves: applied voltage or chemical reductant Get fundamental understanding of how the device is switched. Currently the switching is done using chemical oxidants, reductants (experiments may take minutes) or by applying a voltage step It is not known what the limiting speed is or how it depends on the design –2e – +2e – + 2 + – e – + e – – e – + e –

22 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 22 Research plan: Optimize molecules for devices Connection between molecule tail and electrode R = NO 2, CN, COOH, OH etc Can do computational experiments in hours Lab experiments sometimes months R = CN:30% increase

23 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 23 Failure of Theory? Bell Labs Molecular Transistor (Sch ö n) Drain SiO 2 Source Gate PURE SAM SAM transistor: Nature (2001) Vol, 413, p. 713 Ion/Ioff = 10 6 Single molecule transistor: Science (2001) Vol 294, p. 2138 I on /I off = 450 at 1:5000 4K temperature Goals in theoretical Study: Validate the ability to predict field-effect modulation behavior Determine the reason for the difference in behavior of these systems Design new improved systems SiO 2 Source Gate Drain MIXED SAM Conducting molecules mixed with insulator molecules These papers are now in dispute, Results may have been faked

24 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 24 Shift in Gate voltage can modify MOs near Fermi energy leading to a transistor effect but the maximum effect is only a factor or 20 not the 450 that Schoen reported. Also this value of 20 depends on the optimum placement of the energies of the MOs. Our work was done in Sept. 2001 and not published since it seemed so inconsistent with experiment. Since then the experimental results have been withdrawn because of possible fraud. Thus the theory might be ok. Molecular orbitals shift under Gate voltage, can shift to fermi energy of electrodes Predicted field- effect modulation under Gate voltage Experiment (Schoen) Field-effect modulation behavior Single molecule transistor Ion/Ioff = 450 theory Gate voltage Drain bias gate field theory Ion/Ioff = 20

25 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 25 Luo – Collier – Jeppesen – Nielsen – DeIonno – Ho – Perkins – Tseng – Yamamoto – Stoddart – Heath Best performance  Ordered Self Assembled Monolayer What is the arrangement of Rotaxanes on surface?

26 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 26 Started with half rotaxane 1 (fewer conformations) SAM structures at various packing density Determine How the SAM structure affects (1) the shuttling motion and (2) the I-V (current-voltage) characteristics Bryce, et al. Tetrahed. Lett. (2001), 42, 1143 Bryce, et al. J. Mater. Chem. (2003) 13, 1 1 SAM of Rotaxane on Au(111)

27 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 27 X-ray structure vs. average from MD Density 1.59 1.546 (3 %  ) 1.801 1.789 (0.67 %  ) (g/cm 3 ) @ 295 K @ 295 K @ 160 K @ 160 K Cooke, Tetrahed. Lett. (2001) UBULUY (TTF  PQT 2+  2 PF 6  ) VOLMEO (TTF  CBPQT 4+  4 PF 6   4 CH 3 CN) R = 0.094; Philp, JCS, Chem. Commun. (1991) Validate Force field - Crystal structure

28 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 28 1/48 (6  4r3) 3.46 nm 2 /1 1/36 (6  3r3) 2.59 1/27 c(9  3r3) 1.94 1/24 c(6  4r3) 1.73 1/18 c(9  2r3) 1.30 1/12 (3  2r3) 0.86 Uncomplexed Complexedlie downTilt around y-axisUp along yUp along x SAM at various coverages n(1)/n(Au (111) surf) highlow

29 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 29 SAM 1/15 (footage 1.08 nm 2 /1) SAM 1/12 (footage 0.86 nm 2 /1) Stand up! Ring face (PQT or Ph) parallel to surface:  -contact? Most stable packing  coverage of [0.9, 1.3] (nm 2 /1)

30 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 30 Good  -contact between stations SAM 1/12 (footage 0.86 nm 2 /2)SAM 1/24 (footage 1.73 nm 2 /2) 2 Now do full rotaxane 2 (DNP added with ethylene oxide linker)

31 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 31 need to understand the “shoulder-to-shoulder sticking” versus “  -stacking” on the surface. This Could be better... ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++  -Stacking arrangement in [2]rotaxane SAM?

32 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 32 (TTF)(CBPQT)(PF 6 ) 4  (DNP) “CBPQT@TTF” Only  orbitals around E F (TTF)  (DNP)(CBPQT)(PF 6 ) 4 “CBPQT@DNP” Electronic Structure of Model [2]Rotaxane (with shuttle) HOMO  1 (DNP) HOMO (TTF + CBPQT) LUMO (CBPQT) LUMO (CBPQT) HOMO (TTF) HOMO  1 (DNP) Significant overlap Shifted to lower energy LUMO+1: CBPQT + TTF LUMO, LUMO+1 Splitting Ring provides low-lying LUMO’s. Ring stabilizes energy level of nearby station.

33 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 33 extended configuration Better tunneling between aligned HOMOs (each at each station: folded configuration Better tunneling between aligned HOMO (free station) and LUMO (ring): Need direct contact between free station and CBPQT such as folding and  -contact Two Plausible, Conformation-Dependent, Tunneling Mechanisms in [2]Rotaxane

34 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 34 Started without “non-  ” linker or anchor I-V Characteristics of  -Stacked [2]Rotaxane Components between Au(111) Electrodes

35 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 35 Exper. UCLA Theory: Goddard, Caltech

36 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 36 Manipulate Graphene, Graphite, and Single Walled Carbon Nanotubes Motivation: Hongjai Dai, J. Am. Chem. Soc. 2001, 123, 3838-3839 The experiment provided evidence of 1-PBSE absorption by imaging gold clusters presumably attached to the ester tails of the molecules absorbed on SWNT, but what is really happening? 1-Pyrene Butanoic Acid Succinimidyl Ester Purpose: Understand the interaction of 1-PBSE with carbon nanotubes and with one another so that we can use non-covalent sidewall functionalization of carbon nanotubes to for molecular electronics and self assembly. concept

37 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 37 Methods Step One: Find out how different parts of PBSE interact with one another in free space. Step Two: Do the same with a PBSE dimer. Step Four: Examine packed configurations for pyrene and PBSE on graphene and graphite (check this against experimental results if possible). Step Three: Look at the dynamics of isolated PBSE clusters on graphene and graphite. Each pyrene covers 50 graphene atoms, each PBSE can cover 24 or 40 atoms.

38 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 38 More on Methods Step Six: Put PBSE on (10,10) nanotube and compare the free energies of different packing configurations. Try different nanotube sizes and chiralities. Validating Tools – Friction: Our tools need to produce the right energy barrier for translation of the absorbed molecules on the graphene surface. We should have the correct stresses for the shearing of graphite. Validating Tools – Bonding forces: We should have the right shape for our molecules. Validating Tools – Non-Bond forces: We should produce the correct inter-plane separation in graphite. Our QEq parameters should give the right charges.

39 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 39 Surprises So Far For isolated PBSE clusters on graphite, both the ester tail and the pyrene part of PBSE like to lay flat. Van der Waals interaction is responsible for absorption onto graphite, graphene, and nanotube, but there is strong Coulombic interaction between absorbed PBSE’s. On Graphene, Coulombic interactions between neighboring PBSE’s has led to tighter than expected optimum packing of PBSE. Whereas a single pyrene covered 50 graphene atoms, a single PBSE can cover 24 or 40 graphene atoms. Results on graphite and nanotubes are pending. Ester tail Pyrene PBSE 4x3 PBSE 4x5

40 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 40 SAM packing on Au(111) from MD simulation  Coverage-dependence conformation (  -stacking) (1) Electronic structure of essential components from QM  Role of the ring 1: provide low-lying LUMO’s  Role of the ring 2: stabilize levels of nearby stations   -orbitals dominant around HOMO-LUMO (Aliphatic linkers and anchors negligible?) (3) I-V Calculation from periodic QM and Green’s matrix on a. Fully extended (unfolded) form b. Fully folded form c. Fully folded form w/o linker/anchor Conformation effect on I-V Thru-bond effect on I-V Summary nanoelectronics

41 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 41 Application: Ferroelectric Actuators Must understand role of domain walls in mediate switching Switching gives large strain, … but energy barrier is extremely high! E 90° domain wall Domain walls lower the energy barrier by enabling nucleation and growth Essential questions: Are domain walls mobile? Do they damage the material? In polycrystals? In thin films? Experiments in BaTiO 3 1 2 010,000-10,000 0 1.0 Electric field (V/cm) Strain (%) Use MD with ReaxFF

42 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 42 P-QEq Force Field Model Proper description of Electrostatics is critical Pair-wise Nonbond Terms between all atoms Short range Pauli Repulsion plus Dispersion (EvdW) Include Electrostatic interactions between all atoms (E Coulomb ) Describe Charges as distributed (Gaussians) not point charges Core charge is fixed to the mass of the atom (total charge +4 for Ti) Electron or shell charge is allowed to move wrt the core (atomic polarizability) This includes Shielding as charges overlap Allow charge transfer (shell charges not fixed) Self-consistent charge equilibration

43 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 43 Charge Equilibration (QEq): Environment dependent charges: Charge Equilibration (QEq) Require that the chemical potential (dE/dQ i ) be the same at every atom Fix core charge, allow valence charge to transfer and to shift center Electrostatic energy Atomic self energy Pairwise electrostatic interaction (Shielded Coulomb) Five universal parameters for each element describes charge distribution, polarization Original Paper: Rappe and Goddard, J. Phys. Chem. 1991 QEq parameters are fitted to reproduce QM charges on molecules and polarizability of atoms

44 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 44 Use simple Morse Form with 3 universal parameters per ij (R 0, D 0,  ): Same parameters for same pair of atoms in all environments Determine from QM at very close separations Distance energy Pauli Principle and Dispersion Terms 44

45 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 45 Phase transitions in BaTiO 3 from MD Rhomb.Ortho.Tetra.Cubic Polarizable ReaxFF

46 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 46 Transition Temperature (K) 46 Transition Temp. Rhombohedral to Orthorhombic Orthorhombic to Tetragonal Tetragonal to Cubic Experiment183278393 ReaxFFBetween 200-300Between 300-400Between 400-500 PhaseRhombohedra l OrthorhombicTetragonalCubic Exp.*8-910-1115-160 ReaxFF810210 * Merz, W. J., Phys. Rev. 76, 1221 (1949) Spontaneous Polarization ( Spontaneous Polarization ( uC/cm 2 )

47 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 47 Hysterisis Loop of BaTiO3 at 300K, 25GHz by MD 47 Apply Dz at f=25GHz (T=40ps). T=300K. Monitor Pz vs. Dz. Get Pz vs. Ez. Ec = 0.05 V/A at f=25 GHz. D z (V/A) Time (ps) Applied Field (25 GHz) Applied Field (V/A) Polarization (  C/cm 2 ) Dipole Correction Electric Displacement Correction EcEc PrPr

48 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 48 O Vacancy Jump When Applying Strain 48 X-direction strain induces x-site O vacancies (i.e., neighboring Ti’s in x direction) to y or z-sites. x z y x z y o O atom O vacancy site

49 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 49 Effect of O Vacancy on the Hystersis Loop 49 Introducing O Vacancy reduces both P r & E c. O Vacancy jumps when domain wall sweeps. Perfect Crystal without O vacancy Crystal without 1 O vacancy. O Vacancy jumps when domain wall sweeps. Supercell: 2x32x2 Total Atoms: 640/639 Can look at bipolar case where switch domains from x to y EcEc PrPr

50 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 50 Computational design: Nano-actuator Nano-assembled structures Isolated PVDF chains prefer combination of Trans and Gauch conformations Control the packing density by assembling PVDF chains between Si slabs when packing density is low  structure contains Trans and Gauch conformations Can convert to All Trans with an electric field (get large strains, high frequency) Pt electrodes Si substrate PVDF chains

51 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 51 Computational design: nano-actuator Si (111) surface PVDF: 1/2 coverage 10 monomer long chains Play movie

52 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 52 Computational design: Nano-actuator strain Zero field Electric field Actuation principle T and G bonds All trans bonds Electric field All trans bonds

53 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 53 Strain-electric field curves All trans bonds Electric field All trans bonds Zero field T and G bonds

54 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 54 Strain-polarization field curves External Electric Field: E(t) = E 0 sin(2  t / T) T = 240 ps  ~4 GHz E 0 = 0.64 C/m 2 =~40 MV/m 5 % strain @ 4 GHz Polarization (C/m 2 ) strain (%)  = Q P 2 Strain is proportional to square of polarization Electrostrictive behavior Obtain from analyze dynamics

55 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 55 Strain-electric field curves External Electric Field: E(t) = E 0 sin(2  t / T) T = 120 ps  ~8 GHz E 0 = 0.64 C/m 2 =64  C/cm 2 40 MV/m Double the frequency

56 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 56 Strain-electric field curves External Electric Field: E(t) = E 0 sin(2  t / T) T = 120 ps  ~8 GHz E 0 = 0.32 C/m 2 =32  C/cm 2 Half the electric field It does not work

57 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 57 Biosynthetic Strategies for Nanoscale Assemblies Use CURRENT biosynthetic processes to make elements for functional nanoscale devices. NEED: fasteners- nanorope, nanorivets (covalent attachments) containers- fill and empty upon change in pH, T permanent disposal Sensors- detect change in local state Energy source - nano fuel cell (H 2 /O 2 ) Templates- to organize parts into a regular array Use Multiscale Theory to design and characterize systems

58 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 58 Nadrian Seeman (NYU) DNA Double Crossover – JACS 118 6131 (96), Biochem. 32 3211 (93) Nanomechanical Device – Nature 397 144 (99) Borromean Ring DNA – Nature 386 137 (97) 3 Arm Junctions – Nucleic Acid Res. 14 9745 (86) DNA Cube Topology – Nature 350 631 (91) DNA Nanotechnology – Ann. Rev. Biophy. Biomed.Structures 27 225 (98) Demonstated DNA Bionanotechnology Synthesis

59 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 59 Nanodevice based on DNA B-Z motor Double cross over DX in light blue. Each circle represents a DNA double helix. Dark blue circle has a fluorescent quencher B-Z device shown in red. After B-Z transition - quenching several such motors can be mounted in a 2-D array that could cause circles in light blue to move Before operation After operation Design and experimental synthesis and testing: Ned Seeman NYU Theory: Testing and modify: Goddard Caltech Funding: NSF-NIRT (Mike Roco

60 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 60 Current Projects in Polymers Nanostructure in Nafion membranes for fuel cells Mesoscale simulations of polysaccharides Controlled Assembly of Dendrimers into 3D structures (Percec, U. Penn) Controlled Recognition Sites using Cored Dendrimers (Zimmermann, U. Illinois) Properties of PAMAM Dendrimers as a function of generation New Polymers with Low Surface Tension (3M) Design of polymer membranes for selective Gas Diffusion (Avery Dennison) Solvent dependent structures of Dendrimer Assemblies (Frechet Berkeley)

61 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 61 Overview of projects on Fuel Cells 2 (~200  m) ~10  m~100  m Pt, 2nm Polymer electrolyte membrane fuel cell (PEMFC) Performance is not adequate but considerable uncertainly regarding: The mechanism of Cathode catalysis, Transport of proton from anode to electrolyte to cathode Role of polymer nanostructure and interfaces Use atomistic simulations to explain current system and then improve performance

62 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 62 Nafion: Polymer electrolyte Membrane in Fuel Cells Nafion used in PEMFC (Polymer Electrolyte Membrane Fuel Cell) due to its high proton conductivity as well as electrochemical and mechanical stability. Molecular level study of nanostructure and transport in hydrated Nafion using atomistic simulation Most studies on this system have focused on 1. Structure of Nafion 2. Transport characteristics under the various conditions (water content, temperature etc) Motivation for study Need to run catalyst at 120C to avoid CO poisoning of catalyst, but nafion operates only <80C Need to develop new generation of non-water membranes that operate at 120C and also do not freeze at -20C Need first to understand nafion

63 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 63 less blocky (DR=1.1) not phase-separate Red: hydrophilic Green: hydrophobic more blocky (DR=0.1) Get phase separation hydrophilic domain How is nanostructure affected by monomeric sequence? Nanophase-segregation Objective: investigate the effect of monomeric sequence on the nanophase-separated structure and on water transport in hydrated Nafion Results reported for hydrated Nafion (20 wt % water content) We find that the monomeric sequence affects Nanophase-segregated structure Heterogeneity of water/Nafion interface Diffusion of water Electro-osmotic drag coefficient

64 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 64 ionized D.R.=1.1 (20 wt % water) 353.15 K DR (degree of randomness)=1.1DR (degree of randomness)=0.1 ionized D.R.=0.1 (20 wt % water) 353.15 K blocky Nafion has well- developed phase- separated structure: get large hydrophilic channel which percolates and retains bulk-water structure. 80 Å Effect of DR on Nanophase-segregation

65 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 65 q: reciprocal vector between i and j (q=2  / ) r ij : real space vector between i and j  i : local density contrast at location i L: length of simulation system Structure factor, S(q) We find that for low q, DR=0.1 has larger intensity than the DR=1.1. This implies that DR=0.1 (blocky Nafion) has more phase-segregation than DR=1.1. Use calculated structure to predict the results of Small-angle scattering experiments. SAXS: electron density contrast SANS: deuteron density contrast How measure the extent of phase-segregation? Theory can predict many details about how structure and properties and predicts S(q) Experimental measurement of S(q) not give detailed structure Combining theory and experiment to conclude full detail about structure and properties blocky dispersed

66 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 66 Atomistic three-phase interface: Catalyst, electrolyte, gasPolymerElectrolyte Pt Catalyst Gas Polymerelectrolyte How does the proton get from the membrane to the catalyst and delivered to the O to get H 2 O? We are using ReaxFF to determine atomistic rates. To obtain low overpotential (activation barrier) may require optimized electrolyte-catalyst interface

67 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 67 Nafion-Platinum interfaces: structures Equilibrated structure 2.0x2.0x7.3 nm 3 Local composition 240 H 2 O molecules 10 S (37 %w/w) 300 Pt atoms (5x5x3 fcc unit cells) NPT MD T=300 K zero pressure Pt

68 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 68 Fuel-Cell-Related Catalysts Oxygen reduction reaction (ORR) electrocatalyst (Cathod) O 2 + 4 H + + 4 e -  2 H 2 O Pt  Lower Pt loading (Pt-Co, Pt-Ru) CO tolerant electrocatalyst (Cathod in low-temp fuel cell) Pt-CO + Ru + H 2 O  (Ru-OH)  Pt + Ru + CO 2 + H 2 Water-gas-shift reaction (WGSR) catalyst (Fuel reform) CO + H 2 O  CO 2 + H 2 on Au, Ru (More H 2 and inhibit CO poisoning) Go for Ru!! Then Pt-Ru! (Ru 44 ; 4d 7 5s 1 ; hcp)

69 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 69 Modeling the cathode reaction in PEM fuel cells Reduce or eliminate Pt as catalyst in fuel cell electrodes Understand the chemistry of the cathode reaction Clustersperiodic systemsReaxFF Study different other possible materials and the influences of the electrolyte on the cathode reaction (Find suitable model)

70 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 70 Ultrashallow junction fabrication Junction depth (x j ) gate length (L) gate electrode gate oxide source drain e-e- MOSFET device silicon substrate Greatly decreased gate length (100 nm) requires ultrashallow junctions (30nm) to minimize short channel effects. x j (nm) 30-80 20-70 15-45 10-30 Year 2001 2004 2007 2010 L (  m) (0.18) (0.13) (0.10) (0.07)

71 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 71 What are the issues? Requires Better understanding of low-energy implantation transient enhanced dopant diffusion (TED) defect/dopant clustering Requires Development of predictive numerical models Process requirements maximize dopant activation minimize dopant diffusion attain box-like doping profiles Annealing (~ 1000 o C) B + implantation (< 1 keV) Si substrate z CBCB B B z TED z CBCB

72 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 72 Multiscale modeling and simulation fundamental data Kinetic Monte Carlo simulations [long time (>1 sec)] Atomic-scale calculations density functional theory tight binding MD classical MD explanation/ prediction validation Experimental data 100 B+B+ 200 300 400 500 600 700 Depth, Å B concentration, cm -3 10 21 10 22 10 20 10 19 10 18 as implanted after annealing (1-10 sec) Technological Problem: Transient Enhanced Diffusion Long range tail. Made worse by pronounced shoulder Explanation: Bs-SiI migration + BsB migration

73 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 73 Orange balls = Si atoms green balls = B atoms [B-B] s B s -B i B s -B s - I TS (a) (b) (c) (e) (d) (f) (g) diffusion pathway for a boron-boron pair.

74 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 74 Kinetic Monte Carlo simulation (C B =C si =10 19 cm -3, T=900 K) Boron Si interstitial Si cluster I2I2 t=0 sec I3I3 I5I5 I2I2 I 10 t=10 -6 sec t=10 -3 sec t=1 sec

75 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 75 10 18 10 19 10 20 10 21 0300 200100 400500 600 Depth, A Concentration, cm -3 1 keV B + implantation 1000 o C 950 o C kink formation concave & shouldering diffusion profile evolution experimental vs. simulation

76 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 76 Computational Materials Design Facility (CMDF) Funded by DARPA To integrate these disparate software into a Virtual Test Facility We are developing the CMDF (an integrated Materials Design Facility) ICARUS visualization and GUI environment Common-Generalized Materials Data Model External-Plug in Materials Properties Simulation Tools as modules Driven by Python as scripting Language Archiving MP simulations in MP Database Query/Search MP database Generate and regenerate Materials Properties Sockets for 3rd party MP application modules Materials Properties Modeling software spans modeling scales from electrons, to atoms, to mesoatoms (QM, FF, MM/MD/MC, unit processes, analysis)

77 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 77 First Principles Reactive force fields: strategy Describe Chemistry (i.e., reactions) of molecules -Fit QM Bond dissociation curves for breaking every type of bond (X n A-BY m ), (X n A=BY m ), (X n A ≡ BY m ) -Fit angle bending and torsional potentials from QM -Fit QM Surfaces for Chemical reactions (uni- and bi-molecular) -Fit Ab initio charges and polarizabilities of molecules Pauli Principle: Fit to QM for all coordinations (2,4,6,8,12) Metals: fcc, hcp, bcc, a15, sc, diamond Defects (vacancies, dislocations, surfaces) cover high pressure (to 50% compression or 500GPa) Generic: use same parameters for all systems (same O in O 3, SiO 2, H 2 CO, HbO 2, BaTiO 3 ) Require that One FF reproduces all the ab-initio data (ReaxFF)

78 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 78 ReaxFF Electrostatics energy Three universal parameters for each element: 1991 paper : use experimental IP, EA, R i ; ReaxFF get from fitting QM Keeping: Self-consistent Charge Equilibration (QEq) Describe charges as distributed (Gaussian) Thus charges on adjacent atoms shielded (interactions  constant as R  0) and include interactions over ALL atoms, even if bonded (no exclusions) Allow charge transfer (QEq method) Electronegativity (IP+EA)/2 Hardness (IP-EA) interactions atomic J ij r ij 1/r ij r i 0 + r j 0 I 2

79 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 79 Reactive Force Field - ReaxFF Valence energy Electrostatic energy short distance Pauli Repulsion + long range dispersion (pairwise Morse function) Valence Terms (E Val ) based on Bond Order: dissociates smoothly Bond distance  Bond order  Bond energy Allow angle, torsion, and inversion terms where needed Includes resonance (benzene, allyl) describes forbidden (2 s + 2 s ) and allowed (Diels-Alder) reactions Atomic Valence Term (sum of Bond Orders gives valency) Pair-wise Nonbond Terms between all atoms Short range Pauli Repulsion plus Dispersion (E vdW )

80 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 80 Applications of ReaxFF Decomposition of High Energy (HE) Density Materials (HEDM) MD simulations of shock decomposition and of cook-off Reaction Kinetics from MD simulations Ferroelectric oxides (BaTiO 3 ) domain structure, Pz/Ez Hysteresis Loop of BaTiO 3 at 300K, 25GHz by MD Catalysts: Pt Fuel cell anode, cathode, CH transformations Ni catalyzed growth of bucky tubes MoO x catalysts: catalyzed growth of bucky tubes Si-SiO 2 and Si-SiO x N y interfaces Metal alloy phase transformations (crystal-amorphous) Enzyme Proteolysis Si-Al-Mg oxides: Zeolites, clays, mica, intercolation with polymers MoVNbTaTeO x (Mitsubishi) ammoxidation catalysts

81 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 QM/ReaxFF interaction: new RDX decomposition pathway discovered by ReaxFF; validated by QM HONO elimination NO 2 dissociation concerted New mechanism QM ReaxFF 8 membered ring New unimolecular reaction Inspired by ReaxFF MD simulation More important than concerted pathway Concerted, NO 2 and HONO- dissociation pathways (part of the original training set)

82 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 82 QM + ReaxFF opens door to Complex Reactions Use QM to Extend and develop the detailed reaction mechanism for reactions of organics, organometallics –Unimolecular and bimolecular reactions Extend ReaxFF to fit all possible unimolecular and bimolecular reactions. Use ReaxFF in computational experiments to describe fundamental processes as function temperature and pressure including uni-,bi-,ter, -tetra-molecular reactions Include defects, finite grain size, binder, plasticizer in these simulations to determine models for their effect on microstructure and performance of materials ReaxFF references: 1: van Duin, A.C.T.; Dasgupta, S.; Lorant, F.; Goddard III, W.A. J. Phys. Chem. A 2001, 105, 9396. 2: van Duin, A.C.T.; Strachan, A.; Stewman,S; Zhang, Q.; Goddard III, W.A., J. Phys. Chem. A 2003, 107, 3803. 3: Strachan, A.; van Duin, A.C.T.; Chakraborty, D.; Dasgupta, S.;Goddard III, W.A. Phys. Rev. Letters. 2003, 91, 098301. 4. Zhang. Q.; Cagin, T.; van Duin, A.C.T.; Goddard III, W.A. Phys. Rev. B, subm

83 GODDARD - MSC/Caltech PASI-Caltech 1/5/04 83 Conclusions Goddard Support people: ARO ONR NIH NSF DARPA DOE ASCI DOE FETL ChevronTexaco Seiko-Epson General Motors Asahi Kasei Toray Beckman Institute Facilities (computers) DARPA DURIP NSF MRI IBM SUR Dell Software Schrodinger Accelrys (MSI)

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