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. G. A. Aramayo ([email protected]) G.P. Brown ([email protected])
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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
G.P. Brown ([email protected])
O.J. Gonzalez ([email protected])
B. C. Hathorn ([email protected])
T. Kaplan ([email protected])
T. Maier ([email protected])
M. A. Majidi ([email protected])
V. Meunier ([email protected])
M. B. Nardelli ([email protected])
D. M. Nicholson ([email protected])
D. W. Noid ([email protected])
P. Nukala ([email protected])
B. Radhakrishnan ([email protected])
G. B. Sarma ([email protected])
W. A. Shelton ([email protected])
A. V. Smirnov ([email protected])
S. Simunovic ([email protected])
B. G. Sumpter ([email protected])
M. Upmanyu ([email protected])
J. C. Wells ([email protected])
L. Zhang ([email protected])
X-G Zhang ([email protected])
J. Zhong ([email protected])Computational Materials ScienceGroup Leader: Thomas Schulthess
Periodic QD arrays1D QD Array Synthesis
K.A. Stevenson, G. Muralidharan, L. Maya, J.C. Wells, J. Barhen, T.G. Thundat,
J. Nanosci. Nanotech. (2002)
Small, periodic structuresPeriodicity in QD Placement
TAGTTGCCGAGTAGGTTCTAGATAGTTGCCGAGTAGGTTCTAGATAGTTGCCGAGTAGGTTCTAGATAGTTGCCGAGTAGGTTCTAGASHTransport in QD Arrays
Current-Voltage Characteristics (Average Current):
In Collaboration with Dene Farrell, SUNY Brockport
C23/C = 2
C0/C = 1
Q1/e = -0.425
Q2 = 0
kBT/(e2/C) = 0.001
n = 1
n = 0
N (2 to 4)
courtesy: A. Mayr (SBU)
Elucidate 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.
W. Andreoni, IBM-Zurich
A. Curioni, IBM-Zurich
S.A. Shevlin, ORNL/JICS
J.C. Wells, ORNL
ORNL-IBM CRADACharging Characteristics of Monolayer-Protected Clusters
Transmission function computed through the electron-molecule-electrode system shown.
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.
R.F. Wood, Z. Zhang ORNL/CMSD
D.W. Noid, S. Pannala, B.G. Sumpter, J.C. Wells, ORNL/CSMD
Q. Zhang, U. Texas @ Arlington
ORNL-LDRDSimulation of Carbon Nanotube Nucleation and Growth
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?
Time and space evolution of carbon concentration in the catalyst
MD Simulations (Dynamic)
Time Scale ~ pico s, Length ~ nm
Mass Diffusion Rates
Rules for Segregation of carbon into the CNT
2D Continuum Simulations
Time Scale ~ ms-s, Length ~ mm
Single Carbon Atom Addition
3 sites for adsorption on Ni Electronics38.
(100), (111) hcp, and (111) fcc.
Localized relaxation of Ni38 at site.
C will remain on cluster surface.
(100), (110), (111) hcp and fcc.
Adsorption Energetics order in same sequence on surface and Ni38.
(100)Carbon Adsorption on Clusters and Surfaces
“Ring”(9 C’s) grows into the tube. Electronics
Against 9 remote/ separate C’s:-12.69eV
Against 9 adjacent C’s: ~ -9 eV
Need to compute Barriers, Dynamics.
Surface diffusion barrier (bridge site) between hcp-fcc hollow:
3 different entries for single C:
2 hexagon, DE = -1.26eV
1 pentagon, DE = +0.63eVGrowth of Baby Tubes on Ni(111) Surface
Questions: How are C-atoms incorporated into the tube?
Concerted motion, ring-by-ring growth
Single Atom Addition
Y Electronicsc = 0.03,
Yc = 0.001,
Carbon Activity = 1
dYc /dn= 0,
Zero Flux Condition
Schematic2D Continuum Calculations