Chemistry Reference
In-Depth Information
It is particularly important to show the evidence on the presence
of edge state using scanning tunneling microscopy/spectroscopy
(STM/STS) technique in atomic resolution.
11-15
However, the as-prepared
graphene edges are usually covered with oxygen-containing functional
groups due to the easy oxidation of graphene edges in the ambient
condition.
22
STM observations with well defined graphene edges are
required to examine the electronic structure of the graphene edges.
For this reason, the graphene edges are heat-treated to remove the
functional groups and hydrogen terminated in ultra-high vacuum (UHV)
condition.
11,13
Figure 3 exhibits the typical examples of the UHV-STM
lattice images and STS spectra of graphene edges which are hydrogen
terminated.
11
Figures 3(a) and (b) are the STM and STS results for a
(a)
(b)
(c)
(d)
Fig. 3. (a) Atomically resolved UHV STM images (5.6×5.6 nm
2
) of a homogeneous
armchair edge in constant-height mode with bias voltage
V
s
=0.02 V and current
I
=0.7 nA.
For clarity of edge structures, a model of the honeycomb lattice is drawn on the image.
(b) A d
I
/d
V
s
curve from STS measurements taken at the edge in (a). (c) An atomically-
resolved UHV STM image of zigzag and armchair edges (9×9 nm
2
) observed in constant-
height mode with bias voltage
V
s
=0.02 V and current
I
=0.7 nA. (d) The d
I
/d
V
s
curve from
STS data at a zigzag edge (From reference 11).
