Chemistry Reference
In-Depth Information
and TEM images (Fig. 2(e)) [18-19] are useful in determining the
morphology and structure of graphene. Raman spectroscopy is an
important tool to characterize graphene and provides information about
the quality and number of layers in a given sample (Fig. 2(f )) [20-24].
Single-layer graphene shows the well-known G-band around 1580 cm
-1
.
The D-band around 1350 cm
-1
arising from disorder is very weak or
absent. The 2D-band (2600 cm
-1
) which appears in both single-layer and
few-layer graphenes is sensitive to the number of layers, as well as
doping. The 2D band is intense in single layer graphene.
2. SYNTHESIS
A large majority of the studies of graphene have been directed
towards synthesis. Single-layer graphene (SG) was first prepared by
micromechanical cleavage from highly ordered pyrolyitc graphite
(HOPG) [10]. In this procedure, a layer is peeled off the HOPG crystal
by using scotch tape and then transferred on to a silicon substrate. A
chemical method to prepare single-layer graphene involves reduction of
single-layer graphene oxide (SGO) dispersion in dimethlyformamide
with hydrazine hydrate [25]. The procedure is as follows. Graphite oxide
(GO) is first prepared by oxidative treatment of graphite by employing
Hummers procedure, [26] by the reaction of graphite powder (500 mg)
with a mixture of concentrated H
2
SO
4
(12 ml) and NaNO
3
(250 mg) in a
500 ml flask kept in an ice bath. While stirring the mixture, 1.5 g of
KMnO
4
is added slowly and the temperature brought up to 35°C. After
stirring the mixture for 30 minutes, 22 ml of water is slowly added and
the temperature raised to 98°C. After 15 minutes, the reaction mixture is
diluted to 66 ml with warm water and treated with 3% of H
2
O
2
. Then
suspension so obtained is filtered to obtain a yellow-brown powder. This
is washed with warm water. GO readily forms a stable colloidal
suspension in water and the suspension is subjected to ultrasonic
treatment (300 W, 35 kHZ) to produce single-layer graphene oxide (SGO).
The SGO (0.3 mg/ml) suspension in a H
2
O+ N,N-dimethylformamide
(DMF) mixture (50 ml) is treated with hydrazine hydrate at 80°C for
12 h [25]. This yields a black suspension of reduced graphene oxide
