Graphene: facts and perspectives - O.V. Lounasmaa Laboratory

Graphene project meeting

Graphene nanoribbons Romain Danneau

r.danneau@boojum.hut.fi

Nano GroupLow Temperature Laboratory

Helsinki University of Technology

LTL20th of April 2007

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Graphene: definition Band structure: semi-metal Nano-ribbons: can be semiconducting Two kind of samples: exfoliation and epitaxial Nano-ribbons: first experiments Future and perspective

Outline

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Graphene: definition

Atomic orbitals sp2

0DFullerene

1DNanotube

3DGraphite

2D Graphene

For a review: A.K. Geim and K.S. Novoselov, Nature Mat. 6. 183 (2007).

Graphene is a 2D allotropeof carbon

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Graphene: a semi-metal

A.K. Geim and K.S. Novoselov, Nature Mat. 6. 183 (2007).

Linear dispersion around the Dirac point: carrier act like massless relativistic particles

Two sublattices: notion of chiralityNew physics!!

Anomalous QHE (even at room temperature)Applications in microelectronics: great potential

(high mobility, high current density, high thermal conductivity, large MFP)But no gap... no real on-off transistor

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Graphene nano-ribbons: metallic or semiconductor

armchair edgesSC

zigzag edgesSC or M

K. Nakada et al., Phys. Rev. B 54, 17954 (1996).

Y.-W. Son et al., Phys. Rev. Lett 97, 216803 (2006).

Graphene nano-circuit: gap controled either by the orientation or the width of the ribbon

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Graphene: two type of samples (so far…)

Mechanical exfoliation (using tape for example) of highly orientated

pyrolytic graphite (HOPG) bulk.

H.B. Heersche, PhD thesis, TU Delft, 2006.

A.K. Geim and K.S. Novoselov, Nature Mat. 6. 183 (2007).

Grown by graphitization processin commercial SiC wafers.

C. Berger et al., Science 312, 1191 (2006).

Work supportedBy Intel inc.

P. Mallet et al., cond-mat/0702406

Single layer possiblebut no transport measurements

published so far

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Already some results on nano-ribbons…

M.Y. Han et al., Phys. Rev. Lett. (in press), cond-mat/0702511.

Si-SiO2 substrateCr-Au contact

contact resistance ~1 kΩDifferent widths

and different relative orientations

Columbia University (P. Kim group)

IBM New York (P. Avouris group)

Patterned by e-beamOxigen plasma etch

Z. Chen et al., cond-mat/0701599.

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Graphene nano-ribbons: a semiconductor

M.Y. Han et al., Phys. Rev. Lett. (in press), cond-mat/0702511.

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Graphene nano-ribbons: a semiconductor

M.Y. Han et al., Phys. Rev. Lett. (in press), cond-mat/0702511.

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A- Introductioni-

Also Qdots!

A.K. Geim and K.S. Novoselov, Nature Mat. 6. 183 (2007).

CB is observed and the system can be pinch-off even at room temperature

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Projects:Nano-circuits in the ballistic regime using nano-ribbons ribbons and metallic side-gatesQdots, Josephson junctions, SET, RF-SET…Working with both HOPG and epitaxial graphene

Conclusion and perspectives

Conclusions:Graphene can become a semiconductorOn-off transistors are possible

Thank you!