Cluster (physics)
Encyclopedia
In physics, the term clusters denotes small, multiatom particles. As a rule of thumb, any particle of somewhere between 3 and 3x107 atom
s is considered a cluster. Two-atom particles are sometimes considered clusters as well.
The term can also refer to the organization of protons and neutrons within an atomic nucleus, e.g. the Alpha particle
(a.k.a. as "α-cluster"), consisting of two protons and two neutrons (as in a helium
nucleus).
Although first reports of cluster species date back already to the 1940s , Cluster science emerged as a separate direction of research in the 1980s, One purpose of the research was to study the gradual development of collective phenomena which characterize a bulk solid. These are for example the color of a body, its electrical conductivity, its ability to absorb or reflect light, and magnetic phenomena such as ferro-, ferri-, or antiferromagnetism. These are typical collective phenomena which only develop in an aggregate of a large number of atoms.
It was found that collective phenomena break down for very small cluster sizes. It turned out, for example, that small clusters of a ferromagnetic material are super-paramagnetic rather than ferromagnetic. Paramagnetism
is not a collective phenomenon, which means that the ferromagnetism of the macrostate was not conserved by going into the nanostate. The question then was asked for example “How many atoms do we need in order to obtain the collective metallic or magnetic properties of a solid”? Soon after the first cluster sources had been developed in 1980, an ever larger community of cluster scientists was involved in such studies.
This development led to the discovery of fullerenes in 1986 and carbon nanotubes a few years later.
In science, a lot is known about properties of the gas
phase; however, comparatively little is known about the condensed phases (the liquid
phase and solid
phase.) The study of clusters attempts to bridge this gap of knowledge by clustering atoms together and studying their characteristics. If enough atoms were clustered together, eventually one would obtain a liquid or solid.
The study of atomic and molecular clusters also benefits the developing field of nanotechnology
. If new materials are to be made out of nanoscale particles, such as nanocatalysts and quantum computers, the properties of the nanoscale particles (the clusters) must first be understood.
Atom
The atom is a basic unit of matter that consists of a dense central nucleus surrounded by a cloud of negatively charged electrons. The atomic nucleus contains a mix of positively charged protons and electrically neutral neutrons...
s is considered a cluster. Two-atom particles are sometimes considered clusters as well.
The term can also refer to the organization of protons and neutrons within an atomic nucleus, e.g. the Alpha particle
Alpha particle
Alpha particles consist of two protons and two neutrons bound together into a particle identical to a helium nucleus, which is classically produced in the process of alpha decay, but may be produced also in other ways and given the same name...
(a.k.a. as "α-cluster"), consisting of two protons and two neutrons (as in a helium
Helium
Helium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table...
nucleus).
Although first reports of cluster species date back already to the 1940s , Cluster science emerged as a separate direction of research in the 1980s, One purpose of the research was to study the gradual development of collective phenomena which characterize a bulk solid. These are for example the color of a body, its electrical conductivity, its ability to absorb or reflect light, and magnetic phenomena such as ferro-, ferri-, or antiferromagnetism. These are typical collective phenomena which only develop in an aggregate of a large number of atoms.
It was found that collective phenomena break down for very small cluster sizes. It turned out, for example, that small clusters of a ferromagnetic material are super-paramagnetic rather than ferromagnetic. Paramagnetism
Paramagnetism
Paramagnetism is a form of magnetism whereby the paramagnetic material is only attracted when in the presence of an externally applied magnetic field. In contrast with this, diamagnetic materials are repulsive when placed in a magnetic field...
is not a collective phenomenon, which means that the ferromagnetism of the macrostate was not conserved by going into the nanostate. The question then was asked for example “How many atoms do we need in order to obtain the collective metallic or magnetic properties of a solid”? Soon after the first cluster sources had been developed in 1980, an ever larger community of cluster scientists was involved in such studies.
This development led to the discovery of fullerenes in 1986 and carbon nanotubes a few years later.
In science, a lot is known about properties of the gas
Gas
Gas is one of the three classical states of matter . Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons...
phase; however, comparatively little is known about the condensed phases (the liquid
Liquid
Liquid is one of the three classical states of matter . Like a gas, a liquid is able to flow and take the shape of a container. Some liquids resist compression, while others can be compressed. Unlike a gas, a liquid does not disperse to fill every space of a container, and maintains a fairly...
phase and solid
Solid
Solid is one of the three classical states of matter . It is characterized by structural rigidity and resistance to changes of shape or volume. Unlike a liquid, a solid object does not flow to take on the shape of its container, nor does it expand to fill the entire volume available to it like a...
phase.) The study of clusters attempts to bridge this gap of knowledge by clustering atoms together and studying their characteristics. If enough atoms were clustered together, eventually one would obtain a liquid or solid.
The study of atomic and molecular clusters also benefits the developing field of nanotechnology
Nanotechnology
Nanotechnology is the study of manipulating matter on an atomic and molecular scale. Generally, nanotechnology deals with developing materials, devices, or other structures possessing at least one dimension sized from 1 to 100 nanometres...
. If new materials are to be made out of nanoscale particles, such as nanocatalysts and quantum computers, the properties of the nanoscale particles (the clusters) must first be understood.