According to the Oxford English Dictionary, the meaning of the word 'cluster' has not varied significantly since its Anglo-Saxon origin; it is a collection or accumulation of a particular thing, such as a cluster of grapes. This implies an agglomeration of a particle, which comes from the French (Latin). Again according to the OED, a particle is the smallest discernible part of an aggregation or mass. Thus, if a cluster of atoms or molecules emerges with different properties than its constituent parts than you might call the cluster a particle. You might feel the difference if I threw grapes or clusters of grapes at you.

Clusters are aggregate of crystals in different orientations like ice. Small particles is non defined term since nano-particle is defined to be in the nano-scale, so to what level small is not so clear, nano-technology is just playing around the crystal normal size or arrangement to get novel electronic characters.

Dear Miguel

I am totally agree with Hassan.

Dear Walid and Niranjan,

The questions are: where are the limit between nanoparticles and clusters or small particles? and why this limit? exist?

Now you have rephrased your question, I think there should be no limit or boundary between them, they can break to much smaller or aggregate to larger systems, depending the possible Media molecular bands and themselves Molecular Bands that comes out by combining their molecular orbitals. in a surfaial words it is like splitting a huge stuff when u break it down it will not be atoms but smaller stable pieces that can be further divided to much smaller pieces by another strike even atom itself can be broken to another atoms or smaller components by stronger strike so it looks like moving from local minimum to another local minimum and to do so you need to give enough energy to jump over that transition in between them. without going much away from the subject, if there is a clear limit between bulk and isolated quantum dots and nano-materials there will be a limit but in fact this is just different names to different stable quantum dots of size = infinity, All these topics rotates around to basic quantum phenomena (particle in a box-then changing size of this box) and (Molecular bands, where overlap of similar atoms make change to molecular orbitals to form different band gaps) . this is just my idea about it.

If our discussion is in the frames of condensed matter, then the terms "small" or "nano-" particles" come from many studies where properties of particles' surface become to be important and different from properties of the same material consisting of bigger particles. The area of particle surface is proportional to square of particle size but volume is proportional to its cubic degree. So surface become more important when the size is smaller. Thus for different materials and for different physical/chemical properties a boundary between small, nano and large particles could be different.

I think that "cluster" more in use for description of atomic structure of material, when chemical bonds inside of definite group of atoms much stronger than chemical bonds between these groups-clusters and also between the clusters and other atoms in the structure. Sometimes such clusters can be stored as a single group in solution or liquid and gaseous phases.

The term cluster is a general one, it exists in contemporary music (clusters of notes), astronomy (clusters of galaxies), computing (compute clusters) and also in "small particle" science, i.e. as "atomic clusters" (= clusters of atoms) or "molecular clusters (= clusters of molecules). With respect to "nanoparticles", it is imho vaguely understood that you'd roughly expect 'clusters' to be somewhat smaller than nanoparticles. Note, though, that the term "nanoclusters" has also become abundant in the pertinent literature.

So there are no clear delineations between the terms. In my experience you will find the term "cluster" more often (but by no means exclusively) in contexts where people do bother about the number of atoms in the object. This may, however cover a large range of sizes, since people have built mass spectrometers able to do atomic mass resolution way up into thousands of atoms per particle. That brings you in the range of nm's in diameter and obviously the term nanoparticle applies as well. So, there's a large overlap in terminology!

I guess there is not much to add: in molecular sciences a cluster is a (chemically or physically) bound ensemble of a countable number of atoms or molecules and the number usually matters for the properties. For nanoparticles the total number of building blocks is usually not considered to be that important, but just the overall dimension. Nevertheless there is no strict difference in the use of the two terms, maybe only when speaking about the smallest clusters that are much smaller than 1 nm.

But of course there is overlap also with the definition of molecules.

One probably can spend a lot of time arguing what the C60 buckyball is, a cluster or a molecule, or even already a nanoparticle? Nobody would call linear alkanes as clusters, but still they form a series where one unit is added after another and their properties scale with size (chain length).

According to the Oxford English Dictionary, the meaning of the word 'cluster' has not varied significantly since its Anglo-Saxon origin; it is a collection or accumulation of a particular thing, such as a cluster of grapes. This implies an agglomeration of a particle, which comes from the French (Latin). Again according to the OED, a particle is the smallest discernible part of an aggregation or mass. Thus, if a cluster of atoms or molecules emerges with different properties than its constituent parts than you might call the cluster a particle. You might feel the difference if I threw grapes or clusters of grapes at you.

It looks like that our discussion of the term "cluster" came to such definition: cluster is a collection of any homogenous (more or less) particles. But, what is "particle"? Electron, proton, neutron, atom, molecule are the particles by their definitions. In such a way, atoms are clusters of elementary particles, atomic nuclei are clusters of nucleons, molecule is cluster of atoms, crystal is cluster of atoms and molecules. It, may be, is correct from linguistic point of view but I didn't see that it is in use so in scientific literature. Opposite, "Cluster of atoms" or "cluster of molecules" are in use to distinguish those clusters from "molecule" or "crystal" if they are not the same. Particles, which are aggregations of many atoms/molecules and they are small crystals, amorphous solids, grains, etc., also could form units, or be combined in clusters.

Atomic cluster is a some collection of atoms. It has not itself physical and chemincal properties, not distinct doundary with its matrix media, not a specific dimensions, only change the physical and chemincal properties of its matrix media.