PHYS01200704032 Debes Ray - Homi Bhabha National Institute

Chapter 1: Synthesis, Characterization and Applications of Gold Nanoparticles
In the size range of approximately 2 nm and below, single particles can be considered
as quantum dots.
With modern microelectronics, transistors and other microelectronic
devices get smaller and smaller. Along with miniaturization, distances between transistors
and related switching elements on a chip get shorter and quantum effects become relevant.
Today‟s nanolithographic fabrication techniques allow scaling down to 50nm or below. This
has already made a great impact on the performance of traditional semiconductor circuits, and
it opens up new opportunities utilizing quantum effects. Following the utilization of charging
effects, the so-called Coulomb effects, in metallic circuits comprising tunnel junctions with
submicron sizes, allow us to handle individual charge carriers. This field has been named
single electronics (SE). It relies on the discreteness of the electric charge, and the tunneling of
electrons [single electron tunneling (SET)] in a system of such junctions can be affected by
Coulomb interaction of electrons, which can be varied by an externally applied voltage or by
injected charges [8,26]. As the continuous miniaturization in microelectronics reaches its
physical limits, new concepts are used to achieve component sizes of tens of nanometers or
less, or, ideally, the molecular level. Thus, the idea of utilizing the principle of SE for the
development of logic and memory cells, which in principle could lead to the construction of a
computer working on single electrons, realizing a „single-electron logic‟, has triggered
intense research activities related to SET phenomena.
(iii) Surface Properties
The surface properties of nanoparticles including surface reactivity are distinctly different
from larger particles and have an effect on surface composition, termination, charge and
functionalization for nanoparticles [27,28]. Gold nanoparticles are surrounded by a shell of
stabilizing molecules. With one of their ends these molecules are either adsorbed or
chemically linked to the gold surface, while the other end points towards the solution and
7