Stephen Bennington

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• Stephen Bennington
• ISIS

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Turning diamond into graphite

• People involved
• Tom Weller (STFC)
• Kate Ronayne (STFC)
• Richard Jackman (UCL)
• Rob Bewley (STFC)
• Mian Zhang (STFC)
• Leo Pisani (Imperial, STFC)
• Nic Harrison (Imperial, STFC)
• Barbara Montanari (Imperial, STFC)

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Making graphene
Method two Scotch tape
Geim - Manchester
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Edge Physics
DOS
Energy
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Magnetic edges

• The zig-zag edge is anti-ferromagnetic
• For narrow ribbons there is an long range
  magnetic interacton accros the ribbon

Interaction Strength (Independent of Decoration
and Model)
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The (111) surface

• The (111) surface of diamond is similar to
  graphite
• It will transform to graphite when
• annealed above 2000K
• Irradiated with an electron beam
• Irradiated with a high powdered

Armchair
Zig-zag
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Femtosecond laser irradiation
Femto-second irradiation
Thermal annealing
100fs laser pulse Photons 30 µm Electrons 100
nm Phonons 1 nm
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Graphite Thickness
Graphite thickness depends on pulse duration
Performed on polycrystalline diamond at various
wavelengths with energy densities between 15 and
150 J cm-2
Kononenko et. al. Quantum Electronics 35 (2005)
252
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-2 magnification
Empower 1kHz NdYLF
Spitfire Regenerative Amplifier 1kHz 5mJ 120fs
_at_ 800nm
800nm
BBO Crystals
Evolution 1kHz NdYLF
Beam Splitters
SHG
l/2
Millennia NdYVO4
Tsunami TiSapphire
Mirrors
400nm
Dichroic Mirrors
800nm
Microscope Illumination
Lenses
Piezo Stage Control PI E530
l/2
Iris
SFG
74 Reflecting Objective
Neutral Density Filter Wheel
266nm
l/2
2 magnification
l/2
CCD camera
SHG 2nd Harmonic Generation
ND Wheel
SFG
200nm
SFG Sum Frequency Genration
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Laser experiments

• 200 - 800 nm laser a pulse length of 120 fm
• 532nm in-situ Raman measurements
• CCD collection
• Piezo-stage micrometer

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Sample After Irradiation
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Strain relief

• Strain relief and device manufacture, used
  focused ion beam (FIB) milling
• Made grids with pitches of 500nm and 1000nm

Optical image of the sample with the all the FIB
cut grids
AFM image of the 500nm grid
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Raman from graphene/graphite
Raman bands using 514.5 nm G band 1582 cm-1 D
band 1350 cm-1 D band 1620 cm-1 G band 2700
cm-1
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Raman from graphene/graphite
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Raman from graphene/graphite
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In-situ raman
533 nm laser
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Raman from graphene/graphite
514.5 nm laser
The G band is sensitive to the interlayer
stacking The series shows the annealing of a
turbostratic (2D) graphite to an ordered (3D)
graphite
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Atomic Force Microscopy
10 µJ spot
1.75 µJ spot
2 µJ spot
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AFM shows
2.00 µJ spot
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Too soft to be diamond
Hiura et al.
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3
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2
3
4
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Graphite on diamond
Ex-situ micro-Raman
G-peak
2 µJ/cm3
1 µm focus 514.5 nm Raman
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Graphite on diamond
Ex-situ micro-Raman
G-peak
2 µJ/cm3
1 µm focus 514.5 nm Raman
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Graphite on diamond
Ex-situ micro-Raman
G-peak
2 µJ/cm3
1 µm focus 514.5 nm Raman
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Graphite on diamond
Run 5
Run 4
Run 3
Run 2
Run 1
1 µm focus 514.5 nm Raman
21/2/2008
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Graphite on diamond
Width of G-peak Single crystal graphite 13.5
cm-1 Graphene 14.0 cm-1
Position of G-peak HOPG 1581 cm-1 Graphene
1585cm-1
Our graphite is turbostratic
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Crystallite size
Get an average crystallite size of 80nm
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Orientation
The structures are commensurate with the
substrate
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Character of growth different on FIB structures
To confirm need EBSD, currently working with
Oxford Materials, developing the technique for
use on insulators.
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Photon absorption
Direct band gap 7.3 eV (170nm) Indirect band
gap 5.4 eV (240nm)
Energy (E)
Must involve two or more photons
Momentum (k)
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2 photon absorption
At 800nm would need a 4 photon process
Or a defect that introduces modes into the band
gap
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Other wavelengths

• At 200nm and 266nm we no longer get triangular
  features

• Smooth graphite morphology
• Initial Raman results show smaller crystallite
  size

3 µJ at 200nm
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Gold Coating

• Coating the diamond with gold
• Doing FIB milling through the gold
• Removing the gold

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Gold coating
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Gold Coating
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Conclusions

• We are producing 200 nm triangular graphite
  crystals
• The crystals are strained and 40 100 nm thick
• The FIB does appear to relieve strain and produce
  a different morphology
• Higher laser energies produce different
  morphologies
• No intermediate phase solid-solid transformation