5
Nanotubes, Nanorods, and Nanoplates
5.1
General Considerations
Nanotubes, nanorods, and nanoplates are frequently observed. While nanotubes
and nanorods are often referred to as one-dimensional nanoparticles, nanoparticles
and fullerenes, in contrast, are generally denominated as zero-dimensional structures. Consequently, nanoplates, in particular graphenes, could be considered as twodimensional nanoparticles. Although, nanorods and nanoplates are often found as
more or less spherical or facetted particles, their one- or two-dimensionality is clearly
visible. Notably, as very few routes of synthesis are available for the preferential
delivery of aggregates that are not zero-dimensional, interest has centered on these
specially shaped nanoparticles and continues to be promoted by the wide range of
interesting physical properties associated with these structures.
A typical example of nanorods (in this case ZnO) is shown in Figure 5.1. These
rods are over 5 mm long (most are about 15 mm long), with diameters ranging from
120 to 140 nm, and are clearly separated. (According to the definitions of nanomaterials, rods with linear dimensions over 100 nm are, strictly speaking, no longer
nanomaterials. However, the perfection of this micrograph guaranteed its selection
as an example.) The most important point is that a bulb is visible on one end of most
particles, this being typical of the synthesis process via the gas phase.
ZnO nanoparticles and nanorods are of special interest because of their excellent
luminescence properties in ultraviolet (UV) light. The intensity of the UV emission
line that is found in the wavelength range from 380 to 390 nm of the nanorods as a
function of the intensity of the excitatory light as shown in Figure 5.1 can be clearly
seen in Figure 5.2.
The graph in which luminescence intensity is plotted against pumping power
(¼ intensity of the exciting light) (Figure 5.2) is of special interest, since above a
pumping power of 600 kW cm
À2 is stimulated emission observed rather than only
luminescence, as the ZnO nanorods act as lasers. In fact, this is one reason why
nanorods are of special importance. In this example, the excitation power for
conventional luminescence ranges from about 200 to 600 kW cm
À2 and this is
demonstrated graphically in the insert of Figure 5.2.
Nanomaterials: An Introduction to Synthesis, Properties and Applications, Second Edition. Dieter Vollath.
Ó 2013 Wiley-VCH Verlag GmbH & Co. KGaA. Published 2013 by Wiley-VCH Verlag GmbH & Co. KGaA.
j89
Nanotubes, Nanorods, and Nanoplates
5.1
General Considerations
Nanotubes, nanorods, and nanoplates are frequently observed. While nanotubes
and nanorods are often referred to as one-dimensional nanoparticles, nanoparticles
and fullerenes, in contrast, are generally denominated as zero-dimensional structures. Consequently, nanoplates, in particular graphenes, could be considered as twodimensional nanoparticles. Although, nanorods and nanoplates are often found as
more or less spherical or facetted particles, their one- or two-dimensionality is clearly
visible. Notably, as very few routes of synthesis are available for the preferential
delivery of aggregates that are not zero-dimensional, interest has centered on these
specially shaped nanoparticles and continues to be promoted by the wide range of
interesting physical properties associated with these structures.
A typical example of nanorods (in this case ZnO) is shown in Figure 5.1. These
rods are over 5 mm long (most are about 15 mm long), with diameters ranging from
120 to 140 nm, and are clearly separated. (According to the definitions of nanomaterials, rods with linear dimensions over 100 nm are, strictly speaking, no longer
nanomaterials. However, the perfection of this micrograph guaranteed its selection
as an example.) The most important point is that a bulb is visible on one end of most
particles, this being typical of the synthesis process via the gas phase.
ZnO nanoparticles and nanorods are of special interest because of their excellent
luminescence properties in ultraviolet (UV) light. The intensity of the UV emission
line that is found in the wavelength range from 380 to 390 nm of the nanorods as a
function of the intensity of the excitatory light as shown in Figure 5.1 can be clearly
seen in Figure 5.2.
The graph in which luminescence intensity is plotted against pumping power
(¼ intensity of the exciting light) (Figure 5.2) is of special interest, since above a
pumping power of 600 kW cm
À2 is stimulated emission observed rather than only
luminescence, as the ZnO nanorods act as lasers. In fact, this is one reason why
nanorods are of special importance. In this example, the excitation power for
conventional luminescence ranges from about 200 to 600 kW cm
À2 and this is
demonstrated graphically in the insert of Figure 5.2.
Nanomaterials: An Introduction to Synthesis, Properties and Applications, Second Edition. Dieter Vollath.
Ó 2013 Wiley-VCH Verlag GmbH & Co. KGaA. Published 2013 by Wiley-VCH Verlag GmbH & Co. KGaA.
j89