Thin film

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A familiar application of thin films is the household mirror, which typically has a thin metal coating on the back of a sheet of glass to form a reflective interface. The process of silvering was once commonly used to produce mirrors. A very-thin-film coating (less than about 50 nanometers thick) is used to produce two-way mirrors.

The performance of optical coatings (e.g., antireflective, or AR, coatings) are typically enhanced when the thin-film coating consists of multiple layers having varying thicknesses and refractive indices. Similarly, a periodic structure of alternating thin films of different materials may collectively form a so-called superlattice which exploits the phenomenon of quantum confinement by restricting electronic phenomena to two-dimensions.

Work is being done with ferromagnetic and ferroelectric[1] thin films for use as computer memory. It is also being applied to pharmaceuticals, via thin-film drug delivery. Thin-films are used to produce thin-film batteries and thin film solar cells.


Research is being done on a new class of thin-film inorganic oxide materials, called amorphous heavy-metal cation multicomponent oxides, which could be used to make transparent transistors that are inexpensive, stable, and environmentally benign.[2]


The act of applying a thin film to a surface is thin-film deposition – any technique for depositing a thin film of material onto a substrate or onto previously deposited layers. "Thin" is a relative term, but most deposition techniques control layer thickness within a few tens of nanometres. Molecular beam epitaxy allows a single layer of atoms to be deposited at a time.


Deposition techniques fall into two broad categories, depending on whether the process is primarily chemical or physical.[3]

Chemical deposition[edit]


Chemical deposition is further categorized by the phase of the precursor:

  • Spin coating or spin casting, uses a liquid precursor, or sol-gel precursor deposited onto a smooth, flat substrate which is subsequently spun at a high velocity to centrifugally spread the solution over the substrate. The speed at which the solution is spun and the viscosity of the sol determine the ultimate thickness of the deposited film. Repeated depositions can be carried out to increase the thickness of films as desired. Thermal treatment is often carried out in order to crystallize the amorphous spin coated film. Such crystalline films can exhibit certain preferred orientations after crystallization on single crystal substrates.[4]
  • Atomic layer deposition (ALD) uses gaseous precursor to deposit conformal thin films one layer at a time. The process is split up into two half reactions, run in sequence and repeated for each layer, in order to ensure total layer saturation before beginning the next layer. Therefore, one reactant is deposited first, and then the second reactant is deposited, during which a chemical reaction occurs on the substrate, forming the desired composition. As a result of the stepwise, the process is slower than CVD, however it can be run at low temperatures, unlike CVD.

Physical deposition[edit]



Examples of physical deposition include:

  • Electrohydrodynamic deposition (electrospray deposition) is a relatively new process of thin film deposition. The liquid to be deposited, either in the form of nano-particle solution or simply a solution, is fed to a small capillary nozzle (usually metallic) which is connected to a high voltage. The substrate on which the film has to be deposited is connected to ground. Through the influence of electric field, the liquid coming out of the nozzle takes a conical shape (Taylor cone) and at the apex of the cone a thin jet emanates which disintegrates into very fine and small positively charged droplets under the influence of Rayleigh charge limt. The droplets keep getting smaller and smaller and ultimately get deposited on the substrate as a uniform thin layer.

Growth modes[edit]

Frank-van-der-Merwe mode
Stranski-Krastanow mode
Volmer-Weber mode
  • Frank-van-der-Merwe[5][6][7] ("layer-by-layer"). In this growth mode the adsorbate-surface and adsorbate-adsorbate interactions are balanced. This type of growth requires lattice matching, and hence considered an "ideal" growth mechanism.
  • Stranski–Krastanov growth[8] ("joint islands"). In this growth mode the adsorbate-surface interactions are stronger than adsorbate-adsorbate interactions.
  • Volmer-Weber[9] ("isolated islands"). In this growth mode the adsorbate-adsorbate interactions are stronger than adsorbate-surface interactions, hence "islands" are formed right away.

Thin-film photovoltaic cells[edit]

Further information: Thin film solar cell

Thin-film technologies are also being developed as a means of substantially reducing the cost of solar cells. The rationale for this is thin film solar cells are cheaper to manufacture owing to their reduced material costs, energy costs, handling costs and capital costs. This is especially represented in the use of printed electronics (roll-to-roll) processes. Other thin-film technologies, that are still in an early stage of ongoing research or with limited commercial availability, are often classified as emerging or third generation photovoltaic cells and include, organic, dye-sensitized, and polymer solar cells, as well as quantum dot, copper zinc tin sulfide, nanocrystal and perovskite solar cells.

Thin-film batteries[edit]


See also[edit]


  1. ^ Thinfilm and InkTec awarded IDTechEx' Technical Development Manufacturing Award IDTechEx, April 15th 2009
  2. ^ "Major advance made in transparent electronics". December 28, 2004. Retrieved 2009-09-09. 
  3. ^ Functional Polymer Films Eds. R. Advincula and W. Knoll – Wiley, 2011, ISBN 978-3527321902.
  4. ^ Hanaor, D; Triani G.; Sorrell C.C.; (2011). "Morphology and photocatalytic activity of highly oriented mixed phase titanium dioxide thin films". Surface and Coatings Technology: 205 (12): 3658–3664. doi:10.1016/j.surfcoat.2011.01.007. 
  5. ^ Frank, F. C.; van der Merwe, J. H. (1949). "One-Dimensional Dislocations. I. Static Theory". Proceedings of the Royal Society of London. Series A, Mathematical and Physical Sciences 198 (1053): 205–216. Bibcode:1949RSPSA.198..205F. doi:10.1098/rspa.1949.0095. JSTOR 98165. 
  6. ^ Frank, F. C.; van der Merwe, J. H. (1949). "One-Dimensional Dislocations. II. Misfitting Monolayers and Oriented Overgrowth". Proceedings of the Royal Society of London. Series A, Mathematical and Physical Sciences 198 (1053): 216–225. Bibcode:1949RSPSA.198..216F. doi:10.1098/rspa.1949.0096. JSTOR 98166. 
  7. ^ Frank, F. C.; van der Merwe, J. H. (1949). "One-Dimensional Dislocations. III. Influence of the Second Harmonic Term in the Potential Representation, on the Properties of the Model". Proceedings of the Royal Society of London. Series A, Mathematical and Physical Sciences 200 (1060): 125–134. Bibcode:1949RSPSA.200..125F. doi:10.1098/rspa.1949.0163. JSTOR 98394. 
  8. ^ Stranski, I. N.; Krastanov, L. (1938). "Zur Theorie der orientierten Ausscheidung von Ionenkristallen aufeinander". Sitzungsber. Akad. Wiss. Wien. Math.-Naturwiss. 146: 797–810. 
  9. ^ Volmer, M.; Weber, A. (1926). "Keimbildung in übersättigten Gebilden". Z. Phys. Chem 119: 277–301. 
  10. ^ Flexible Cell Construction. Retrieved on 2012-01-15.

Further reading[edit]


  • M. Birkholz, with contributions by P.F. Fewster and C. Genzel (2005). Thin Film Analysis by X-Ray Scattering. Weinheim: Wiley-VCH. ISBN 978-3-527-31052-4.  Table of contents
  • M. Ohring (2001). Materials Science of Thin Films (2nd ed.). Boston: Academic Press. ISBN 9780125249751. 
  • K. Seshan, ed. (2012). Handbook of Thin Film Deposition (3rd ed.). Amsterdam: Elsevier. ISBN 978-1-4377-7873-1.