So far, we've dealt with surface coating processes based on the liquid state, either by sol-gel or electrochemical deposition. Here we deal more specifically with the use of gaseous precursors for thin-film deposition via methods listed under the headings PVD (for physical vapor deposition) or CVD (for chemical vapor deposition). The aim of this lecture is to define the benefits of thin-film deposition at both fundamental and applied levels. The benefits at the fundamental level are manifold, including the possibility of injecting new properties/functions into materials via the elaboration of heterostructures and superlattices of oxides or chalcogenides. As a result, new metastable phases can be obtained thanks to enhanced reactivity (diffusion, nucleation, growth) at the interface. A particular phase can often be obtained by depositing these constituents in an ordered sequence corresponding to the atomic arrangement of these constituents in the desired phase. In this way, all n-members of the Aurivillius Bi2O2(An-1BnO3n+1) phase family can be synthesized, which is not possible with conventional synthesis methods.
We also discuss substrate and epitaxial issues, to show how these epitaxial constraints (extensive or compressive) can be played with to stabilize new phases or even tune/control magnetic or ferroelectric properties (e.g.: paraelectric → ferroelectric transition) in BaTiO3. On the basis of these fundamental aspects, we describe the various deposition techniques - MOCVD (metal-organic chemical vapor deposition), ALD(atomic layer deposition), MBE (molecular beam electrodeposition), PLD (laser ablation deposition) and sputtering (sputter deposition) - and highlight their advantages/disadvantages. The same applies to layer growth monitoring techniques such as grazing incidence electron diffraction (RHEED) and scanning tunneling microscopy.
By way of conclusion, we mention the varied applications of oxide and chalcogenide layers and superlattices, which are of considerable importance for a multitude of applications such as glazing, and play a vital role in microelectronics.
