文档介绍：NT’06
NAGANO JAPAN
Tutorial Program
June 18, 2006
Electrical and thermal transport in macroscopic
carbon nanotube assemblies, and posites
John E. (Jack) Fischer
Department of Materials Science and Engineering
University of Pennsylvania
3231 Walnut St.
Philadelphia PA 19104-6272
OUTLINE
• Brief review of macroscopic (3-D) electrical conductors
• Electrical conductivity of nanotube assemblies:
pure tubes, SWNT/posites
– How do we even begin to think about macroscopic NT assemblies (mats,
fibers, films)? Certainly not a collection of perfect ballistic conductors!
– Beyond “free electron gas”– effects of disorder, interfaces, carrier
localization, variable-range hopping, tunneling thru barriers, …..
– How do we identify the macro-scale mechanism for a particular material?
Experiments vs. temperature, ic field, doping.
– Composites – dispersion, interfaces, SWNT alignment, percolation,…
• Brief review of macroscopic (3-D) thermal conductors:
heat capacity, mean free path, phonon dispersion and sound velocity
• Fundamentals of thermal transport in SWNT: effect of 1-D subbands
– SWNT – lots of theory, sparse experiments
– Individual MWNT – experiments
– SWNT assemblies posites
• Application to peapods - a case study
Excuse me, Prof. Tomanek, but….
The beautiful physics of ideal tubes is largely ruined
(or obscured) in real materials, by
1. Diameter polydispersity broadens everything.
2. Coupling between tubes (bundles, ropes, …..)
3. Inhomogeneities
4. Residual impurities (metals, amorphous carbon)
from the growth process
5. Characterization problems, . luminescence
is quenched by interactions in assemblies.
Macroscopic electron transport;
disorder effects T materials
Free electron gas: inelastic (e-ph) and elastic (defects,impurities) scattering
(elemental metals and alloys, doped semiconductors, )
Strong localization: phonon-assisted variable range hopping (VRH) a la Mott:
(impurity bands, a