
130 Nanosensors: Physical, Chemical, and Biological
forces. As a result, the graphene sheets slide easily across each other mak-
ing graphite a good lubricant and drawing tool. For the same reason,
graphite of the pencil is not so strong although a layer of graphite is very
strong.
2.13.3 Structure of SWCNT
The innitely many possibilities of rolling a sheet into a cylinder lead to a
variety of diameters and microscopic structures of the nanotubes. A diver-
sity of possible congurations is found in practice, and no particular type is
preferentially formed.
What is chiral angle? Figure 2.17 shows the unrolled two-dimensional gra-
phene sheet.