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Nanoscale Science

Jack C. Wells

Computational Material Science Group

Computer Science Division

Oak Ridge National Laboratory

Research Alliance for Minorities (RAM)

Spring '03 Workshop for

Faculty and Mentors

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Computational Materials ScienceGroup Leader: Thomas Schulthess

G. A. Aramayo (aramayoga@ornl.gov)

G.P. Brown (browngp@ornl.gov) O.J. Gonzalez

(gonzalezoj@ornl.gov) B. C. Hathorn

(hathornb@ornl.gov) T. Kaplan (kaplant@ornl.gov) T. Maier (maierta@ornl.gov) M. A. Majidi (majidima@ornl.gov) V. Meunier (meunierv@ornl.gov) M. B. Nardelli

(buongiornonm@ornl.gov) D. M. Nicholson

(nicholsondm@ornl.gov) D. W. Noid (noiddw@ornl.gov)

P. Nukala (nukalapk@ornl.gov) B. Radhakrishnan

(radhakrishnb@ornl.gov) G. B. Sarma (sarmag@ornl.gov) W. A. Shelton

(sheltonwajr@ornl.gov) A. V. Smirnov

(smirnovav@ornl.gov) S. Simunovic

(simunovics@ornl.gov) B. G. Sumpter

(sumpterbg@ornl.gov) M. Upmanyu (agor@ornl.gov) J. C. Wells (wellsjc@ornl.gov) L. Zhang (zhangl@ornl.gov) X-G Zhang (zhangx@ornl.gov) J. Zhong (zhongjn@ornl.gov)

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Computational Materials Science (CMS)

From nano-science to engineering applications. Engineering sciences Nano science Applied mathematics Soft materials (polymers) Surface science (catalysis) Magnetism and magneto transport in nanostructures Light-weight materials Carbon based nanostructures Molecular electronics

Intersection of Two Strategic Thrusts Computational Sciences (www.ccs.ornl.gov) Advanced Materials & Nanoscale Science (www.cnms.ornl.g

ov, www.ssd.ornl.gov/cnms/workshops)

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Directed assembly of QDs along engineered DNA.DNA modified with amine groups as binding sites.Covalent QD attachment to DNA.

Advantages Particles at desired locations. Achieve desired nanometer-scale periodicity. Long-range order. Stable backbone along the length of duplex DNA.

Research Issues:Control site occupation along DNA template.

Methylamine blocks excess binding sites. Improved control of chemical binding sites on QD.

1D QD Array Synthesis

K.A. Stevenson, G. Muralidharan, L. Maya, J.C. Wells, J. Barhen, T.G. Thundat, J. Nanosci. Nanotech. (2002)

Periodic QD arrays

AFM Image

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Periodicity in QD Placement Regular 1D Arrays Method to covalently bond inorganic nanoparticles to

duplex DNA in a programmable fashion. Fabrication of nanostructures with nanoscale

periodicity.

Gold nanoparticles bound to DNA strand with 10 nm spacing.

Small, periodic structures

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HSGATCTA*CAACGGCTCA*CCAAGATCTA*CAACGGCTCA*CCAAGATCTA*CAACGGCTCA*CCAAGATCTA*CAACGGCTCA*CCAA

TAGTTGCCGAGTAGGTTCTAGATAGTTGCCGAGTAGGTTCTAGATAGTTGCCGAGTAGGTTCTAGATAGTTGCCGAGTAGGTTCTAGASH

Electron transport via tunneling

Transport in QD ArraysAfter assembly, DNA can be removed by UV-ozone technique.Current measurement through array.

Develop techniques to measure I-V curves. Use AFM / STM, with probe tip acting as electrode.

Two electrode measurements.

ElectrodeElectrode

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Master Equation and CurrentsTunneling Rates:

Fermi’s Golden Rule with approximations, Tunneling between nearest neighbors only, Neglects the effects of co-tunneling, Rk, effective resistance of tunneling junction.

Master Equation: Time-development of probabilities for charge

configurations, Most often solved by Monte-Carlo techniques.

Current-Voltage Characteristics (Average Current):

1 1 1

1

,ˆ ˆ ˆ ˆ( , ) ( , )

( , ).

k k k k k kk

N

k kk

dP n tn u P n u t n u P n u t

dt

n n P n t

, ,k SD k SD k SDn

I V e P n n V n V

1

2, ( , ) 1 expk k

k SD k k SDk B

E En V E n V

e R k T

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The Coulomb Ladder

In Collaboration with Dene Farrell, SUNY Brockport

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Single-Electron Latching Switch

Modeling Results:

(orthodox theory)C23/C = 2C0/C = 1

Q1/e = -0.425Q2 = 0

Q3/e= -0.2kBT/(e2/C) = 0.001

-0.1 0.0 0.1 0.2 0.3-0.1

0.0

0.1

0.2

0.3

Cur

ren

t (e/

RC

)

Voltage (e/C)

n = 0

n = 1

Vinj

Molecular Implementation:

Va

1

axon dendrite

tunnel barrier

C0

single-electron island

2 3

S

R

R

C C

R

C

R

C N S

R’’R’’

CC

R R

CCN

0

0

0

SiO2 insulation

p-Si substrate

goldnanowire

goldnanowire

S

RR

C

R’’ R’’

CCNN (2 to 4)

00

00

NR’

R

R R

R”

R”

R

0

C

courtesy: A. Mayr (SBU)

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6 4 2 0 -2 -42

3

4

C

harg

ing

Ene

rgy

(IP

- E

A)

(eV

)

Excess Charge (e)

Charging Characteristics of Au38

Symmetric Disordered

Charging Characteristics of Monolayer-Protected Clusters

ObjectivesElucidate the charging characteristics of monolayer-protected clusters.

Describe ligand-cluster interface in MPC.

Interpret the charging spectrum of MPCs to provide to distinguish between possible structural configurations for the clusters.

ParticipantsW. Andreoni, IBM-ZurichA. Curioni, IBM-ZurichS.A. Shevlin, ORNL/JICSJ.C. Wells, ORNL

FundingDOE/BES/DMSEORNL-IBM CRADA

Computational Approach•Ab-Initio Density-Functional Theory

–Pseudopotential Plane Wave (PSPW)

– CPMD, NWChem,

–Gaussian-type Obitals (LCAO)

– NWChem

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Structure and Charge Transport in Molecular-Scale Electronics

Objectives•Elucidate the role of the atomic structure of the molecule-electrode interface.

•Role of charging and Coulomb blockade for molecular-scale latching switches.

•Discrimination of bio-molecules (e.g., proteins, DNA. etc.) by their unique “conductance signature”.

Participants•D.J. Dean, P.S. Krstic, J. C. Wells, X.-G. Zhang ORNL

•P.T. Cummings, Y. Leng Vanderbilt•D. Keffer, U. Tennessee

Funding•ARDA/ONR•DOE/BES/DMSE•ORNL-LDRD

-0.4 -0.3 -0.2 -0.1 0.00.0

0.2

0.4

0.6

0.8

1.0

Tra

nsm

issi

on

Energy (a.u.)

Transmission function computed through the electron-molecule-electrode system shown.

Computational Approach•Ab-Initio Density-Functional Theory

•Tight-binding Approach for Physically Realistic Electrode-molecule interface.

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Simulation of Carbon Nanotube Nucleation and GrowthObjectives

Elucidate fundamental catalytic nucleation and growth mechanisms for carbon nanotubes.

Develop expertise in multiscale modeling of carbon nanotube growth processes.

Support ORNL’s experimental program in carbon nanotube growth.

ParticipantsR.F. Wood, Z. Zhang ORNL/CMSDD.W. Noid, S. Pannala, B.G. Sumpter, J.C. Wells, ORNL/CSMD

Q. Zhang, U. Texas @ Arlington

FundingORNL-LDRD

Computational Approach•Continuum Mass and Heat Transfer

•Ab-Initio Density-Functional Theory–Pseudopotential Plane Wave (PSPW)

– CPMD, NWChem,

–Gaussian-type Obitals (LCAO)– NWChem

Decomposition Rates: Dependence on Concentration, Temperature, Composition?

Surface Carbide formation? How stable is it?

Diffusion pathways? Catalyst clogging? Is diffusion the growth rate-limiting step?

Precipitation of carbon? Is precipitation rate limiting? Control of length, diameter chirality?

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Multiscale Modeling (Overview)

Mass Diffusion Rates

Time and space evolution of carbon concentration in the catalyst

Growth Interface

2D Continuum Simulations Time Scale ~ s-s, Length ~ m

MD Simulations (Dynamic)Time Scale ~ pico s, Length ~ nm

Rules for Segregation of carbon into the CNT

Single Carbon Atom Addition(DFT Calculations)

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-0.2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

Rela

tive

En

erg

y (e

V)

(100)

fcc (111)hcp (111)

Interstitial

Carbon Adsorption on Clusters and Surfaces

3 sites for adsorption on Ni38. (100), (111) hcp, and (111) fcc.

Localized relaxation of Ni38 at site. C will remain on cluster surface.

Stable sites: (100), (110), (111) hcp and fcc.

Adsorption Energetics order in same sequence on surface and Ni38.

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

Rel

ativ

e E

ner

gy

(eV

)

(100)

(110)

(111) hcp (111) fcc

Fundamental, new predictions on small NixCy clusters and Ni surfaces. Insight into adsorption, nucleation for large clusters in CVD growth.

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Growth of Baby Tubes on Ni(111) Surface

“Ring”(9 C’s) grows into the tube. Energy:

Against 9 remote/ separate C’s:-12.69eV

Against 9 adjacent C’s: ~ -9 eVReaction-limited growth.Need to compute Barriers, Dynamics.

Questions: How are C-atoms incorporated into the tube?

Single Atom Addition Concerted motion, ring-by-ring growth

Surface diffusion barrier (bridge site) between hcp-fcc hollow: E=0.26 eV.

3 different entries for single C: 2 hexagon, E = -1.26eV 1 pentagon, E = +0.63eV

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2D Continuum Calculations

Yc /n= 0, Zero Flux Condition

Schematic

Yc = 0.001, Carbon Activity = 1

Yc = 0.03, Typical Value

Inputs to the Model

Diffusion Rates

Temperature

Inlet Composition

Shape of Catalyst Particle

Location of CNT formation

Size of Catalyst

Predictions

Spatio-temporal distribution of Carbon

Inner Diameter of NT

Single Vs. Double Vs. Multi-wall NTs

Growth Rates

Insight into growth and control of NTs

0)(1

)(1

0),(1

),(1

z

TTrk

zrr

TTrk

rrt

T

z

YYTrD

zrr

YYTrD

rrt

Y cc

cc

c

Model

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Concluding Comments

Diversity of Computational Materials Science Research

Favorable collaboration would include RAM student, Faculty Advisor, and ORNL Staff, and remain active outside the constraints of one summer’s project.

Challenge of Undergraduate Research Match project to student’s knowledge base More knowledge is better, but we can often “make

progress” with limited knowledge/experience.

Motivated, enthusiastic, “self-starters” wanted!