viii
Preface
determining role in the cluster structure evolution, stability, and electronic transition of frontier orbitals. Meanwhile, various theoretical methods including global
structure search and intelligent machine learning enable to provide a fundamental
understanding of the properties of nanomaterials and to guide scientific thinking in
the future.
In many cases, people have worked from the top-down; that is, subdividing matter to get it
smaller and smaller. We’re trying to work with atoms and molecules and put them together-working our way from the bottom up. If we can retain the properties of aggregates, as
we put them together, perhaps we will be able to construct new nanoscale materials.—A.
W. Castleman, Jr. (Evan Pugh Professor of Chemistry and Physics and the Eberly Family
Distinguished Chair in Science at Penn State University).
The current interest in the field of cluster science continues on a rapidly expanding
trajectory in large measure due to two considerations. First, novel behaviors are found
to emerge as the cluster size is reduced to the sub-nanometer scale. The electronic,
chemical, and optical properties are all found to change with size, and in many
cases, clusters of nonmagnetic solids are found to become magnetic. The second
consideration is the connection to the field of nanoscale science where clusters offer
the exciting prospect of serving as building blocks for new materials whose desired
properties may be tailored through the selection of size and composition. Indeed, the
fundamental research activity is inspired by the joint work of Castleman, Khanna,
Luo, and others as a major goal of acquiring the underpinning knowledge for undertaking the formation of new materials “from the bottom up”. This contrasts with the
more conventional “top-down method” which typically involves the subdivision of
matter of bulk dimensions. Particularly interesting and significant are systems whose
properties vary dramatically with size and composition, one atom at a time, and don’t
simply scale with size or surface area directly. Most appealing among these are clusters that display interesting behaviors, whose composition can be selectively chosen
and individual characteristics could be retained when assembled into an extended
material. As Castleman, Khanna, Luo et al. demonstrated, some stable metallic clusters mimic the chemical behavior of elements in the periodic table and hence can
be regarded as “superatoms” providing an unprecedented ability to design novel
materials.
The focus of the current book is the reactivity of clusters. The chemical properties of matter depend on its energy levels which are greatly influenced by boundaries
which restrict sizes. At the mesoscale, a large fraction of atoms are near the surface
and are not interacting through bonding with as many neighboring atoms as in the
case of the bulk substance. Frequently, they have different bonding characteristics,
and hence their chemical properties are different. It is important to elucidate the
details of the behavior and reactivity of metal cluster species in reaction cells or flow
tube reactors, to apply the level of understanding obtainable for gas-phase species to
the systems of practical interest in condensed phase chemistry.
The field of cluster science has developed along a few directions, including gasphase clusters, monolayer-protected clusters (or termed as ligand-protected metal
clusters), and surface-supported clusters. Around these fields, abundant efforts have
been devoted to the investigations on carbon clusters, metal and semiconductor
Preface
determining role in the cluster structure evolution, stability, and electronic transition of frontier orbitals. Meanwhile, various theoretical methods including global
structure search and intelligent machine learning enable to provide a fundamental
understanding of the properties of nanomaterials and to guide scientific thinking in
the future.
In many cases, people have worked from the top-down; that is, subdividing matter to get it
smaller and smaller. We’re trying to work with atoms and molecules and put them together-working our way from the bottom up. If we can retain the properties of aggregates, as
we put them together, perhaps we will be able to construct new nanoscale materials.—A.
W. Castleman, Jr. (Evan Pugh Professor of Chemistry and Physics and the Eberly Family
Distinguished Chair in Science at Penn State University).
The current interest in the field of cluster science continues on a rapidly expanding
trajectory in large measure due to two considerations. First, novel behaviors are found
to emerge as the cluster size is reduced to the sub-nanometer scale. The electronic,
chemical, and optical properties are all found to change with size, and in many
cases, clusters of nonmagnetic solids are found to become magnetic. The second
consideration is the connection to the field of nanoscale science where clusters offer
the exciting prospect of serving as building blocks for new materials whose desired
properties may be tailored through the selection of size and composition. Indeed, the
fundamental research activity is inspired by the joint work of Castleman, Khanna,
Luo, and others as a major goal of acquiring the underpinning knowledge for undertaking the formation of new materials “from the bottom up”. This contrasts with the
more conventional “top-down method” which typically involves the subdivision of
matter of bulk dimensions. Particularly interesting and significant are systems whose
properties vary dramatically with size and composition, one atom at a time, and don’t
simply scale with size or surface area directly. Most appealing among these are clusters that display interesting behaviors, whose composition can be selectively chosen
and individual characteristics could be retained when assembled into an extended
material. As Castleman, Khanna, Luo et al. demonstrated, some stable metallic clusters mimic the chemical behavior of elements in the periodic table and hence can
be regarded as “superatoms” providing an unprecedented ability to design novel
materials.
The focus of the current book is the reactivity of clusters. The chemical properties of matter depend on its energy levels which are greatly influenced by boundaries
which restrict sizes. At the mesoscale, a large fraction of atoms are near the surface
and are not interacting through bonding with as many neighboring atoms as in the
case of the bulk substance. Frequently, they have different bonding characteristics,
and hence their chemical properties are different. It is important to elucidate the
details of the behavior and reactivity of metal cluster species in reaction cells or flow
tube reactors, to apply the level of understanding obtainable for gas-phase species to
the systems of practical interest in condensed phase chemistry.
The field of cluster science has developed along a few directions, including gasphase clusters, monolayer-protected clusters (or termed as ligand-protected metal
clusters), and surface-supported clusters. Around these fields, abundant efforts have
been devoted to the investigations on carbon clusters, metal and semiconductor