4
Mesoscopic Assembly and Other Properties of
Metal and Semiconductor Nanocrystals
G. U. Kulkarni, P. J. Thomas, and C. N. R. Rao
Abstract
The properties of metal and semiconductor nanocrystals are briefly reviewed. The
organization of metal and semiconductor nanocrystals into mesostructures is an
important aspect of nanoscience. New methods of nanocrystal synthesis and functionalization relevant to mesoscopic assembly are described, with emphasis on
procedures that deal with monodispersed nanocrystals. Programmed assemblies
of nanocrystals in one, two and three dimensions are discussed together with attempts to measure the properties of such lattices. Future directions and potential
applications of ordered assemblies are indicated.
4.1
Introduction
A nanocrystal is a tiny chunk of the bulk measuring a few nanometers with a finite
number of atoms in it. Nanocrystals in the size range 1–50 nm are considered
important and are obtainable as sols: a dispersion of a solid in a liquid, also called a
colloidal sol. Metal sols possess fascinating colors and have long been used as dyes.
That such dyes indeed consist of tiny metal chunks was established as early as
1857 by Faraday [1], but a similar realization in the case of semiconducting nanocrystals had to wait for over a century [2, 3]. Modern techniques of synthesis enable
one to obtain sols of metals and semiconductors that can be dried and re-dissolved
like water colors. The colloidal particles display a remarkable tendency to remain
single-crystalline and are hence named as nanocrystals. Nanocrystals posses high
surface area, a large fraction of the atoms in a nanocrystal are on its surface. A
small nanocrystal of 1 nm diameter will have as much as 30% of its atoms on the
surface, while a larger nanocrystal of 10 nm (@1000 atoms) will have around 15%
of its atoms on the surface [4].
An added dimension to research on nanocrystals is their size-dependent properties. The electronic, magnetic and optical properties of a nanocrystal depend on its
size [4]. In small nanocrystals, the electronic energy levels are not continuous as
51
Mesoscopic Assembly and Other Properties of
Metal and Semiconductor Nanocrystals
G. U. Kulkarni, P. J. Thomas, and C. N. R. Rao
Abstract
The properties of metal and semiconductor nanocrystals are briefly reviewed. The
organization of metal and semiconductor nanocrystals into mesostructures is an
important aspect of nanoscience. New methods of nanocrystal synthesis and functionalization relevant to mesoscopic assembly are described, with emphasis on
procedures that deal with monodispersed nanocrystals. Programmed assemblies
of nanocrystals in one, two and three dimensions are discussed together with attempts to measure the properties of such lattices. Future directions and potential
applications of ordered assemblies are indicated.
4.1
Introduction
A nanocrystal is a tiny chunk of the bulk measuring a few nanometers with a finite
number of atoms in it. Nanocrystals in the size range 1–50 nm are considered
important and are obtainable as sols: a dispersion of a solid in a liquid, also called a
colloidal sol. Metal sols possess fascinating colors and have long been used as dyes.
That such dyes indeed consist of tiny metal chunks was established as early as
1857 by Faraday [1], but a similar realization in the case of semiconducting nanocrystals had to wait for over a century [2, 3]. Modern techniques of synthesis enable
one to obtain sols of metals and semiconductors that can be dried and re-dissolved
like water colors. The colloidal particles display a remarkable tendency to remain
single-crystalline and are hence named as nanocrystals. Nanocrystals posses high
surface area, a large fraction of the atoms in a nanocrystal are on its surface. A
small nanocrystal of 1 nm diameter will have as much as 30% of its atoms on the
surface, while a larger nanocrystal of 10 nm (@1000 atoms) will have around 15%
of its atoms on the surface [4].
An added dimension to research on nanocrystals is their size-dependent properties. The electronic, magnetic and optical properties of a nanocrystal depend on its
size [4]. In small nanocrystals, the electronic energy levels are not continuous as
51