Experimental progress in graphene since 2004

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Experimental progress in graphene since 2004
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Before the invention of the so called scotch
tape technique
Zhang et.al., Appl. Phys. Lett. 86, 073104 (2005)
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The scotch tape technique
Kim group (Columbia) and Geim group (Manchester)
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Finding graphene from the crowd
Judy G. Cherian UW REU
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With the scotch tape technique
2-dimensional crystal matter. (a) NbSe2, (b)
graphite, (c) Bi2Sr2CaCu2Ox (d) MoS2
visualized by AFM (a,b), SEM (c) optical
microscope (d). All scale bars 1µm. The 2D
crystallites are on top of an Si wafer with 300
nm of thermal SiO2 (a-c) and on top of a holey
carbon film (d). Novoselov et.al., PNAS, 2005
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Suspended graphene
Meyer et.al., Nature, 2007
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Electron diffraction of suspended graphene
Meyer et.al., Nature, 2007
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Electron diffraction of suspended graphene at a
tilted angle
Meyer et.al., Nature, 2007
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Electron diffraction of suspended graphene at a
tilted angle
Meyer et.al., Nature, 2007
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Fluctuation in the 3rd dimension
Ripples are 0.5 nm in height and their typical
size is 5 nm laterally. Calculated diffraction
patterns agree well with our experimental data.
Meyer et.al., Nature, 2007
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Suspended graphene oscillator
Bunch et.al., Science, 2007
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Suspended graphene oscillator in resonance

• Amplitude versus frequency for a 15-nm-thick
  multilayer graphene resonator taken with optical
  drive. (Inset) An optical image of the resonator.
  Scale bar, 5 mm.
• (B) Amplitude versus frequency taken with optical
  drive for the fundamental mode of the
  single-layer graphene resonator shown in Fig. 1B.
  A Lorentzian fit of the data is shown in red.
• Bunch et.al., Science, 2007

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First devices for electrical measurements
a, SEM image of one device (the width of the
central wire is 0.2mm). b, c, Changes in
conductivity j (b) and Hall coefficient RH (c) as
a function of gate voltage Vg. j and RH were
measured in magnetic fields B of 0 and 2 T,
respectively. d, Maximum values of resistivity
(circles) exhibited by devices with different
mobilities m (left y axis). Several of the
devices shown were made from two or three layers
of graphene, indicating that the quantized
minimum conductivity is a robust effect and does
not require ideal graphene. Novoselov et.al.,
Nature, 2005
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QHE in graphene, Berrys phase
Examples of fan diagrams used in our analysis to
find BF. N is the number associated with
different minima of oscillations. The lower and
upper curves are for graphene and a 5-nm-thick
film of graphite with a similar value of BF,
respectively. Novoselov et.al., Nature, 2005
Hall conductivity and longitudinal resistivity of
graphene as a function of their concentration at
B 14 T and T 4K. Inset Hall conductivity in
two-layer graphene where the quantization
sequence is normal and occurs at integer n.
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QHE in graphene, room temperature
(A) Optical micrograph of one of the devices
used in the measurements. The scale is given by
the Hall bars width of 2 µm. (B) - sxy (red)
and ?xx (blue) as a function of gate voltages Vg
in a magnetic field of 29 T. The inset
illustrates the Landau level quantization for
Dirac fermions. (C) - Hall resistance Rxy for
electrons (red) and holes (green) shows the
accuracy of the observed quantization at 45 T.
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Graphene exposed to different molecules
Concentration of chemically-induced carriers in a
graphene sensor exposed to different
concentrations C of NO2. Upper inset SEM Lower
inset Characterisation of graphene sensors with
B 1T was applied.
Changes in zero-field resistivity of single-layer
devices caused by their exposure to various
active gases diluted in concentration 1 ppm. The
positive (negative) sign of changes in ? is
chosen here to indicate electron (hole) doping.