Kindly note as you are referring to thin films in your question

There is no question of particle size in the case of thin films.

A particle has dimensions, it should be possible to see it physically, like tiny sugar/ salt/dust particle. Dr. Alan in the previous response has really explained it well. A particle when reduced to the smallest size (let us say by crushing to the limits) would result in  the smallest entity known as single crystal unit cell. This can be smallest crystallite on can get. So therefore a largely a particle can consists of many crystallites, or one single crystal unit cell at the smallest level.   

In thin films sometimes having a very rough morphology, we would find aggregates a random collection of many large sized particles.

A Crystallite refers to region of coherrent diffraction, and can be estimated using x-ray diffraction. Now a crystallite can be equal to a particle, and both can have the same size. This is what Prof. Hugh is referring to. Hence in the case of thin films we will not see separated particles, rather a cluster of particles normally called aggregate.

A grain  can be a collection of many crystallites having the same orientation. A polycrystalline film would have grains of different orientation. An XRD pattern many a times can reveal the film to be polycrystalline very easily showing a number of peaks. This means that that the film is having grains of different orientation. Grains can be seen, and grain boundaries can be distinguished, and different grains having different orientation can be identified through electron diffraction.

A film having a single grain (with a single specific) orientation can be obtained via epitaxial growth on a matched substrate. IN comparison a solid with a specific orientation with a single grain is called single crystal, and in a similar way when a film is grown on a perfectly matched epitaxial substrate would be called a single crystal film.

My simple question is how are you determining the particle size in the case of a thin film, and the crystallite size in your film.

K. Sreenivas

How do you define/measure particle size? If a particle is crystalline, and many of them combine in a polycrystalline film, then particle size is the same as crystallite size, is the same as grain size.

i am satisfied with that polycrystalline films may have same particle and crystallite sizes but grain consists of a single material, but may be crystalline, or polycrystalline. An individual crystallite consists of a single phase, so how grain size and crystallite size will be same in case of polycrystalline films? but i think the correct oder of sizes is crystallite

Agree with Prof. Hugh.

The have been literally tens of discussions on ResearchGate on this exact point.  A little research will help here...

It depends on your definitions - to me a particle is free standing.... not part of a film, and the grains of a film can be crystalline domains. There is no correct order of size - a particle can be subatomic, or micron size.

NIST definition of a particle (from SP 960-3 Section 2.2.2):

'Any condensed-phase tridimensional discontinuity in a dispersed system may generally be considered a particle; e.g., droplets in an emulsion or solids dispersed in a liquid. The term is normally used in reference to solid materials.  An aggregate may also be regarded as a particle'.

Kindly note as you are referring to thin films in your question

There is no question of particle size in the case of thin films.

A particle has dimensions, it should be possible to see it physically, like tiny sugar/ salt/dust particle. Dr. Alan in the previous response has really explained it well. A particle when reduced to the smallest size (let us say by crushing to the limits) would result in  the smallest entity known as single crystal unit cell. This can be smallest crystallite on can get. So therefore a largely a particle can consists of many crystallites, or one single crystal unit cell at the smallest level.   

In thin films sometimes having a very rough morphology, we would find aggregates a random collection of many large sized particles.

A Crystallite refers to region of coherrent diffraction, and can be estimated using x-ray diffraction. Now a crystallite can be equal to a particle, and both can have the same size. This is what Prof. Hugh is referring to. Hence in the case of thin films we will not see separated particles, rather a cluster of particles normally called aggregate.

A grain  can be a collection of many crystallites having the same orientation. A polycrystalline film would have grains of different orientation. An XRD pattern many a times can reveal the film to be polycrystalline very easily showing a number of peaks. This means that that the film is having grains of different orientation. Grains can be seen, and grain boundaries can be distinguished, and different grains having different orientation can be identified through electron diffraction.

A film having a single grain (with a single specific) orientation can be obtained via epitaxial growth on a matched substrate. IN comparison a solid with a specific orientation with a single grain is called single crystal, and in a similar way when a film is grown on a perfectly matched epitaxial substrate would be called a single crystal film.

My simple question is how are you determining the particle size in the case of a thin film, and the crystallite size in your film.

K. Sreenivas

Many thanks to Prof. Sreenivas for shedding more light on this subject. Indeed crystal size could be obtained XRD analysis by considering the characteristic peaks of the material. During recrystallization and recovery process, crystallites are formed as a result of grain growth. Therefore it is tenable to say that grain size is similar to crystal size. Particcle size is the average diameter of a discrete piece of material, different from a region in the material with a specific crystal orientation. Particles can be amorphous, single crystals or polycrystalline. Particle size can be determined by using particle size analyzer.

 Thanks dear Dr. K. Sreenivas for your valuable answer.

For crystallite size i use the scherrer's formula for preffered orientation as my material is polycrystalline and for actual particle size and grain size i go for TEM and HRTEM.

Dear Burhanuz,

while we are seeing the image on TEM for a thin film,

It is important to understand, how do we distinguish a certain region as a particle,

and the other region as grain.

K. Sreenivas

Dr. K. Srinivas, will you please elaborate this for me?

In a general sense both crystallite size and particle size refer the average diameter of the discrete particles. But the difference lies in that, cystallite size particularly used to denote the average size of the discrete single crystals whereas particle size sometimes refers the average diameter of agglomerated particles too as well as indicating the discrete ones.

Grain size usually used to denote the average diameter of the individual crystal orientations in a polycrystalline material.

For example, if u synthesize some nano particles then the average size of the particles will be refered as particle size or crystallite size. But if u sinter the particles in a bulk form, then the average diameter of the crystals will be refered as grain size. 

And there shouldn't be arised any questions of particle size or crystallite size in case of thin film rather film thickness.

Hope this will help.