● Flash Evaporation:

The flash evaporation process is similar to the thermal evaporation techniques with the difference that only a small amount of the charge in powder form is fed at a time to a white-hot boat of tungsten, molybdenum or tantalum, so that an instantaneous evaporation of the total charge takes place without leaving any residue. There will be no time for constituents to build up by differential vapor pressure. Hence, the composition of the gaseous phase is more or less same as that of the charge and it is expected that on condensation the deposits will retain the composition of the evaporant.

● Laser Ablation:

Figure 38.2 shows the typical arrangement of a laser ablation apparatus with the main components of a pulsed laser (Nd: YAG, Excimer) and a rotatable target carrier combined with a heated substrate holder and a Reflection high energy electron diffraction (RHEED), or a low energy electron diffraction (LEED) system for epitaxial film preparation. The evaporation mechanism in laser ablation is somewhat complicated. It consists of radiation induced decomposition by pair breaking, resulting in emission of atoms, molecules, clusters and macroparticles with different velocities. Deposition in ultrahigh vacuum chamber for the growth of high quality epitaxial films as well as high rate deposition and reactive deposition at high reactive gas pressure are possible. The primary disadvantages of this technique are the incorporation of droplets and the limitation to small uniform deposition areas on the substrate.

Figure 38.2: Schematic diagram of a typical laser ablation set up for preparation of thin films.