What is a Thin film? and how to prepare them?

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Credit: Codex-international

     Thin film is the layer of material on the substrate like metals or glass. Thin films are 2-dimensional materials where the third dimension of these materials are suppressed to a nanometer scale. Due to the surface geometry of this material, we call it thin-film.

How thin is thin film?

     Thin-films are a relative layer on the substrate. Here thin means a few nanometers to the several micrometres. Mostly thin films are a few microns on the substrate. 

Application of Thin films:

     Thin films are used to reduce the structure of the material. Recent development in this department increases the industrial applications in the thermal barriers in aerospace industries, solar cells, semiconductor devices etc. In thin-film, the materials in the film are reduced to atom size. Due to the change in surface to volume ratio of the materials have peculiar properties than bulk materials. 

Credit: Researchgate

For an example:

     Gold Film annealed at different temperatures results in various colour properties in the thin films.

Thin film Deposition methods:

     Based on the preparation, we can classify this into two different groups is Physical and Chemical deposition.

Physical deposition method:

  • Evaporation
  • Sputtering

Chemical vapour deposition method:

  • Sol-gel
  • Spray Pyrolisis
  • Chemical Bath
  • Chemical Vapour evaporation

Evaporation Technique:

Evaporation is the method where the target elements(or anode) evaporate thermally and becomes gaseous form. These gaseous atoms cover the layer of the substrate to form the thin film. Based on the source used in the processes, we name it Arc evaporation,

Laser evaporation, electron beam evaporation.

Sputtering:

Sputtering is another physical method where plasma or argon like gaseous atoms are used to hit the elements on the surface of the target element. These free atoms of the target element cover the thin film.

Sol-gel:

Sol-gel is a bottom-up method where the solution or gel-like material is dried by cold or heat method to get the thin-film

Spray Pyrolisis:

The Spray method is the most common in chemical deposition methods. Where the desired solution is forced by the high pressured spray to get the thin film.

Chemical Bath:

A chemical bath is quite simple submerging the thin film inside the desired solution, like dipping cookies inside the tea.

Chemical vapour evaporation:

This is the same as the physical vapour deposition method, but thermally induced chemical reactions lead to this reaction.

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Conclusion:

Unlike the Chemical deposition method, physical methods are more expensive. They need a vacuum process that’s so expensive and time-consuming. But the physical deposition methods have a high deposition rate and high sample utilization rate.

Like-wise there are plenty of methods available in thin-film preparation.

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