Carbon Nanotubes under Electron Irradiation
L. Sun, Y. Gan, J.
J. A. RodriguezRodriguez-Manzo & F. Banhart
Collaboration: A. Krasheninnikov and J. Kotakoski (University of Helsinki, Finland), M. Terrones (IPICyT, Mexico)
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Nano-engineering of carbon nanotubes under the electron beam: structuring, welding, bending, etc.
Shrinkage and deformation of nanotubes under electron irradiation
Nanotubes as deformation/extrusion cells on the nanoscale
Growth of nanotubes by injection of carbon atoms into metal crystals
Evolution of nanotubes under electron irradiation
In-situ experiments in the TEM
Irradiation and imaging of nanotubes at the same time and at the atomic scale
Electron irradiation:
• atom displacements by energetic electrons
• structural rearrangement of nanotubes
• transfer of interstitials into the central hollow of tubes
High specimen temperatures:
• annealing of irradiation defects
• high mobility of interstitials and vacancies
beam
electron
beam
t=0
axial migration
of interstitials
160 s
Imaging and manipulation of nanotubes:
Æ both at the atomic scale
Æ at the same time
340 s
ejection of interstitials
from the walls
Æ shrinkage of shell
820 s
agglomeration
of interstitials
shrinkage and
retraction of
inner shell
Irradiation effects in the nanotube lattice
• Nanotubes act as pipelines for the transport of interstitial atoms
• Stability of nanotubes increases with their diameter
Low temperatures Æ defect agglomeration
High temperatures Æ annealing of defects (> 300°C)
electron beam
interstitial
Threshold energy of electrons to displace atoms:
Single-wall nanotubes: ~ 80 keV
Multi-wall nanotubes: ~ 100 keV
reduces distance
between layers
F. Banhart, J.X. Li & A. Krasheninnikov, Phys. Rev. B 71, 241408 (2005)
A. Krasheninnikov, F. Banhart, J.X. Li, A.S. Foster, R.M. Nieminen, Phys. Rev. B 72, 125428 (2005)
atom
displacement
vacancy
curves the
layers
Cutting of single-wall nanotubes by electron beams:
Diffusion of interstitials in carbon nanotubes
dangling bonds
F. Banhart, Rep. Prog. Phys. 62, 1181 (1999)
A. Krasheninnikov & F. Banhart, Nature Materials 6, 723 (2007)
reactive sites
1st cut
2nd cut 1st cut
Cutting of SWNT bundle by focused electron beam:
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open ends close by fullerenic caps
eroded atoms migrate inside the tubes
carbon atoms in the tubes are reflected by caps
annealing of reflected atoms at second cut
Æ second cut requires higher electron dose
• measuring speed of second cut as a function of
temperature and distance to first cut Æ information
about migration barrier for C atoms in tubes: ~ 0.3 eV
Defect evolution in carbon nanotubes
Carbon nanotubes under an electron beam:
second cut requires higher electron dose than first cut
Generation of
• interstitials Æ highly mobile, vanish preferably into the central hollow
• vacancies Æ mobile, coalsece and form immobile divacancies
electron
beam
1st cut
2nd cut
Restructuring of a defetive nanotube (simulation by A. Krasheninnikov)
interstitials are reflected
and diffuse back
interstitials are lost
annealing ! Æ difficult to cut
shrinkage
under
irradiation
Closure of
dangling bonds
Y. Gan, J. Kotakoski, A. Krasheninnikov, K. Nordlund & F. Banhart, New J. Phys. (2008)
max. cutting speed as a function of temperature
and separation between cuts
Metal nanowires inside collapsing nanotubes:
Nanotubes as high-pressure cylinders and extrusion cells
single vacancy
divacancy
ad-atom
5-, 7-, 8-membered rings
• single vacancies coalesce to form divacancies
• divacancies close by saturation of dangling bonds
• formation of stable non-six-membered rings
• reduction of surface area Æ shrinkage or bending of tube
• high strength of graphitic network remains, even when defects prevail
Encapsulation of metal nanowires in carbon nanotubes:
• collapse of tubes under electron irradiation
• deformation of metal wires (thinning, defect formation)
• extrusion of metal wires
Growth of nanotubes under the electron beam
Nanotube growth under electron irradiation
Extrusion of a Co nanowire
inside a nanotube:
• Carbon atoms are ingested by the electron beam into the
metal core of the host nanotube.
collapsing tube leads to thinning of the
Co wire and sliding in the axial direction
• When the end face of the metal is round, a hemispherical graphene
cap forms and serves as the starting point for nanotube growth.
• A new nanotube grows from steps on the metal surface.
Carbon atoms are fed from the metal crystal.
thinning
sliding
Deformation of a Fe3C wire:
thinning but no visible crystal defects
Extreme deformation of a Fe3C
wire inside a collapsing nanotube
Molecular dynamics simulation (A. Krasheninnikov):
pressure inside collapsing nanotubes can reach values up to 40 GPa
Growth of a single-walled CNT
from a Co crystal inside a host nanotube
J. Rodriguez-Manzo, M. Terrones, H. Terrones, H. Kroto, L. Sun &
F. Banhart Nature Nanotechnology 2, 307 (2007)
L. Sun, F. Banhart, A. Krasheninnikov, J. Rodriguez, M. Terrones & P.M. Ajayan, Science 312 (2006)
Growth of a multi-walled CNT from a FeCo crystal
inside a host nanotube under electron irradiation
funding (2007): Deutsche Forschungsgemeinschaft (Ba 1884/4-1), NEDO/Japan (04IT4)