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If one had a metal block (lets say tantalum) in a vacuum chamber, what would be the most efficient way of evaporating it in regards to the proportion of the input energy directly going into removing atoms from the metal into a vapor. From researching around a bit, it seems that there are three main techniques to do this:

  • Placing the metal block into a crucible, like boron nitride and heat with a filament joule heater.

  • Sputtering of the metal block using a biased ion plasma

  • Directly heating the metal via a laser beam

Now I imagine that out of these three, laser heating would be the most efficient due to the direct illumination of the surface by the laser so the efficiency is primarily limited by the reflectivity of the metal. But I am unsure as I have not seen much data around regarding any limits regarding the evaporation efficiency of the first two methods.

Does anyone know what is the most efficient evaporation process in a vacuum? Are there any fundamental limits to the efficiency of the evaporation process here for each technique?

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    $\begingroup$ The electron beam does not sputter - it just heats the material allowing you to get hotter than a normal filament heater will reliably and repeatably achieve. E-beam evaporators are indeed a standard tool. Sputtering is accomplished by lighting a plasma of a suitable gas and biasing it to accelerate the ions into the material to be sputtered. $\endgroup$
    – Jon Custer
    Commented May 25, 2022 at 19:31
  • $\begingroup$ thanks, made the appropriate changes $\endgroup$
    – tjsmert44
    Commented May 25, 2022 at 19:36
  • $\begingroup$ Well, reconsider your sentence on imagining - what is the 'reflectivity' of the electron beam... $\endgroup$
    – Jon Custer
    Commented May 25, 2022 at 19:38
  • $\begingroup$ that sentence refers to the reflectivity of the metal for the wavelength of the laser. $\endgroup$
    – tjsmert44
    Commented May 25, 2022 at 19:40
  • $\begingroup$ Yes, and an energetic electron coming onto the surface basically does not get reflected. So, the most 'efficient' way of pumping energy into a block of material is likely to be the e-beam. But the penetration depth of the electrons is likely longer, so less energy is deposited in the near-surface layer. Are you interested solely in heating some chunk of material in vacuum, or selecting an appropriate deposition method, or what? $\endgroup$
    – Jon Custer
    Commented May 25, 2022 at 19:43

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It is quite sure that W (tungsten) crucibles are applied when people evaporate rare earth metal such as Sc (Scandium). BN can't be used as it decomposed in vacuum at about 1800-1900C according to some BN supplier's document.

Another good option is to halogenate the metal, because metal halides have relatively low boiling points. For example, this process is used in the production of high-purity zirconium and hafnium.

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