surface, with a scale factor of a million to one. Optical tweezers provide another
approach to holding and moving nanometer structures, a capability especially useful in investigating the dynamics of molecules and particles. Questions such as,
how does a polymer move, generate force, respond to an applied force and unfold,
can be answered by the use of optical tweezers. It is noteworthy that the positioning of nanoparticles accurately and reliably on a surface by using the tip of an
atomic force microscope as a robot has already been accomplished. Large-scale operations requiring parallel tip arrays are being explored in several laboratories.
(a)
10
15
20
25
30
35
40
45
50
400
600
800
1000
1200
1400
1600
1800
Melting Temperature (K)
Radius(Å)
10
12
14
16
18
20
22
3.4
3.6
3.8
4.0
4.2
4.4
4.6
4.8
5.0
Transition pressure (GPa)
Radius(Å)
(b)
bulk
Fig. 1.4. (a) Size dependence of the melting temperature of
CdS nanocrystals. (b) Size dependence of the pressure-induced
wurtzite–rock salt transformation in CdSe nanocrystals [from
A. P. Alivisatos, J. Phys. Chem., 1996, 100, 13226.].
1 Nanomaterials – An Introduction
6