Chemistry and Properties of Nanocrystals of Different Shapes
Clemens Burda,*
,†,‡
Xiaobo Chen,
†
Radha Narayanan,
§
and Mostafa A. El-Sayed*
,§
Center for Chemical Dynamics and Nanomaterials Research, Department of Chemistry, Case Western Reserve UniversitysMillis 2258,
Cleveland, Ohio 44106, and Laser Dynamics Laboratory, School of Chemistry and Biochemistry, Georgia Institute of Technology,
Atlanta, Georgia 30332-0400
Received July 22, 2004
Contents
1. General Introduction and Comments 1025
2. Preparation of Nanostructures of Different
Shapes
1027
2.1. Introduction: Nucleation and Particle Growth 1027
2.2. Preparation Methods 1028
2.2.1. Sol Process 1028
2.2.2. Micelles 1031
2.2.3. Sol−Gel Process 1034
2.2.4. Chemical Precipitation 1034
2.2.5. Hydrothermal Synthesis 1036
2.2.6. Pyrolysis 1036
2.2.7. Vapor Deposition 1038
2.3. Growth Mechanism of Nanostructures of
Different Shapes
1040
2.3.1. Effect of Monomer Concentration on the
Shape of the Semiconductor QDs
1040
2.3.2. Vapor−Liquid−Solid Growth for Nanowire
by CVD and PVD Methods
1041
2.3.3. Light-Induced Shape Change Mechanism
of Metal Nanorods
1042
3. Surface Chemical Modification of Nanoparticles 1042
4. Assembly of Nanoparticles 1042
5. Optical, Thermal, and Electrical Properties of
Particles of Different Sizes and Shapes
1047
5.1. Semiconductor Nanoparticles 1047
5.1.1. Discrete Electronic Structure 1047
5.1.2. Optical Transitions in Nanostructures of
Different Shapes
1048
5.2. Metallic Nanoparticles 1057
5.3. High Surface-to-Volume Ratio 1059
5.4. Melting Point 1060
5.5. Conductivity and Coulomb Blockade 1061
6. Nonradiative Relaxation of Nanoparticles of
Different Shapes
1063
6.1. Nonradiative Relaxation in Metal
Nanostructured Systems
1063
6.1.1. Background 1063
6.1.2. Theoretical Modeling of the Transient
Optical Response
1063
6.1.3. Electron−Electron Thermalization in Gold
Nanoparticles
1063
6.1.4. Electron−Phonon Relaxation in Gold
Nanoparticles
1064
6.1.5. Shape and Size Dependence on the
Electron−Phonon Relaxation Rate
1065
6.1.6. Pump Power Dependence of the
Electron−Phonon Relaxation Rate
1066
6.2. Nonradiative Relaxation in Semiconductor
Nanostructured Systems
1066
6.2.1. II−VI Semiconductor Systems 1067
6.2.2. I−VII Semiconductor Systems 1074
6.2.3. III−V Semiconductor Systems 1074
6.2.4. Group IV Semiconductor Systems 1074
6.2.5. Metal Oxides Systems 1075
6.2.6. Other Systems 1075
6.3. Hot Electrons and Lattice Temperatures in
Nanoparticles
1076
6.4. Phonon Bottleneck 1078
6.5. Quantized Auger Rates 1079
6.6. Trapping Dynamics 1079
7. Nanocatalysis 1081
7.1. Introduction 1081
7.2. Homogeneous Catalysis 1081
7.2.1. Chemical Reactions Catalyzed Using
Colloidal Transition Metal Nanocatalysts
1083
7.3. Heterogeneous Catalysis on Support 1086
7.3.1. Lithographically Fabricated Supported
Transition Metal Nanocatalysts
1087
7.3.2. Chemical Reactions Catalyzed Using
Supported Transition Metal Nanocatalysts
1087
8. Summary 1090
8.1. Reviews 1090
8.1.1. Synthesis 1090
8.1.2. Properties 1090
8.1.3. General 1091
8.2. Books 1091
8.2.1. Metal Nanoparticles 1091
8.2.2. Semiconductor Nanoparticles 1091
8.2.3. Carbon Nanotubes and Nanoparticles 1091
8.2.4. Nanoparticles in General 1092
9. Acknowledgment 1092
10. References 1092
1. General Introduction and Comments
The interest in nanoscale materials stems from the
fact that new properties are acquired at this length
scale and, equally important, that these properties
* To whom correspondence should be addressed. Phone, 404-894-
0292; fax, 404-894-0294; e-mail, mostafa.el-sayed@
chemistry.gatech.edu.
†
Case Western Reserve UniversitysMillis 2258.
‡
Phone, 216-368-5918; fax, 216-368-3006; e-mail, burda@case.edu.
§
Georgia Institute of Technology.
1025Chem. Rev. 2005, 105, 1025−1102
10.1021/cr030063a CCC: $53.50 2005 American Chemical Society
Published on Web 03/18/2005

change with their size or shape. The change in the
properties at this length scale is not a result of scaling
factors. It results from different causes in different
materials. In semiconductors, it results from the
further confinement of the electronic motion to a
length scale that is comparable to or smaller than
the length scale characterizing the electronic motion
in bulk semiconducting material (called the electron
Bohr radius, which is usually a few nanometers).
As noble metals are reduced in size to tens of
nanometers, a new very strong absorption is observed
resulting from the collective oscillation of the elec-
trons in the conduction band from one surface of the
particle to the other. This oscillation has a frequency
that absorbs the visible light. This is called the
Prof. Clemens Burda is the Director of the Center for Chemical Dynamics
and Nanomaterials Research in the Chemistry Department at Case
Western Reserve University. He is appointed as Professor of Physical
Chemistry specializing in Nanoscience and technology. His research
evolves around optically useful nanocrystals, applied toward diverse areas
such as photovoltaics, photocatalysis, photobiology, and biomedical
applications, including bioimaging, therapy, and tissue targeting for drug
delivery. Prof. Burda received his chemistry education in Basel, Switzer-
land, and graduated as a doctor of philosophy and science with honors
in 1997 from the Jakob Wirz group at the University of Basel. Prof. Burda
was a postdoctoral research fellow with Prof. Mostafa El-Sayed before
assuming his current position at Case. Dr. Burda is a reviewer for several
nanoscience journals, an editorial board member for the International
Journal of Nanotechnology, and an organizer of the Nanomaterials
Conference at the 50th annual SPIE meeting in 2005.
Xiaobo Chen did his undergraduate research at Peking University and
did his Master’s research on inorganic membranes at Dalian Institute of
Chemical Physics (Chinese Academy of Sciences). His current research
interest as a Ph.D. candidate on Prof. Burda’s research team is focused
on the development of photocatalytic nanomaterials. In his spare time
Xiaobo is an excellent cook and ping-pong player.
Radha Narayanan was born in Savannah, GA. She got her B.S. in
Chemistry from Armstrong Atlantic State University. She is currently a
Ph.D. Candidate in chemistry under the direction of Professor Mostafa A.
El-Sayed at Georgia Institute of Technology. She will be graduating with
a Ph.D. in May 2005. Her Ph.D. research involves investigating the stability
and recycling potential of differently shaped colloidal transition metal
nanoparticles during their catalytic function. She has compared the stability
and catalytic activity of tetrahedral, cubic, and spherical platinum
nanoparticles during the catalytic process. Her other research interests
include the rational design of nanoparticles for various applications such
as sensing, molecular transport, and so forth.
Professor Mostafa A. El-Sayed was born in Zifta, Egypt. He obtained his
B.S. degree in chemistry from Ain Shams University at Cairo, Egypt. He
got his Ph.D. degree in Chemistry from Florida State University. During
his Ph.D. studies, he worked with Professor Michael Kasha, Professor
Ray Sheline, and Professor R. Wolfgang. He was a research associate
at Harvard, Yale, and California Institute of Technology. In 1961, he was
appointed to the faculty of University of California, Los Angeles. In 1994,
he became the Julius Brown Chair in the School of Chemistry and
Biochemistry at Georgia Institute of Technology. He is also the Regents’
Professor and Director of the Laser Dynamics Laboratory at Georgia Tech.
He has served as the Editor-in-Chief of The Journal of Physical Chemistry
from 1980 to 2004. He has received numerous fellowships such as Alfred
P. Sloan Fellow, John Simon Guggenheim Fellow, Sherman Fairchild
Distinguished Scholar, and Senior Alexander von Humboldt Fellow. He
was elected to the National Academy of Sciences and the Third World
Academy of Science. He became an elected fellow of the American
Academy of Arts and Sciences, the American Physical Society, and the
American Association for the Advancement of Science. He has also
received numerous national awards such as the Fresenius Award, the
McCoy Award, the Harris Award, and the Irving Langmuir ACS National
Award as well as regional ACS awards from the California, Southern
California, Florida, Eastern Tennessee, and Northeastern sections. He
has also received the King Faisel International Award in Science. His
research interests include understanding the optical properties and ultrafast
dynamics of metal and semiconductor nanoparticles and the catalytic
properties of transition metal nanoparticles of different shapes. His other
research interests include the study of the primary processes involved in
the photoisomerization and the proton pump in bacteriorhodopsin
photosynthesis.
1026 Chemical Reviews, 2005, Vol. 105, No. 4 Burda et al.