Pulsed laser deposition

Called Laserstrahlverdampfen, also laser vaporization or laser deposition, (English pulsed laser deposition, PLD) is a method of physical vapor deposition ( PVD process ) and closely related to the thermal evaporation. It refers to the deposition of films by laser ablation. For this purpose, both of the deposited coating material (target) and the support on which the layer is to be deposited (substrate ) is placed (recipient ) in a vacuum vessel.

Method

The material of the target is in a vacuum chamber with pulsed laser radiation of high intensity lights ( ≈ 10 MW/cm2 ) and thereby evaporated. The evaporation process of the target material takes place through the absorption of the energy of the laser beam through the material to be vaporized. From a certain ( sufficient ) amount of energy forms at a target plasma from which atoms can detach from the target itself. Using large process gas pressures (> 1 mbar) is possible in the gas phase, the condensation of the vapor material in clusters ( groups of atoms ). This material vapor moves through the vacuum chamber away from the target towards the substrate where it is condensed into a thin layer. For the preparation of the crystalline layers, the substrate is additionally heated, in order to allow diffusion processes and therefore rearrangement of the atoms. In this manner, other particles may be incorporated in the crystal, either in order to produce complex materials or to produce a dopant.

Particularly good results are achieved with UV lasers (e.g., XeCl, or KrF excimer laser ), since the radiation has a high photon energy, which is absorbed by a variety of materials, since it is above the plasma frequency. More pulsed laser for PLD are transversely excited CO2 laser, Q-switched Nd: YAG laser and increasingly pulsed femtosecond laser. The pulse duration is typically in the range of 10-50 ns at a repetition frequency of a few Hertz.

Pros and Cons

Advantages:

  • An advantage of the method over other deposition methods is that one can define the exact amount of the number of laser pulses, which can be deposited on the substrate. This is always the same amount of material is removed from the target, the target is crazy a little bit after each laser pulse, otherwise the laser will always suggest in the same place.
  • A further advantage is that you can even complicated ( stoichiometric ) can transfer compositions of elements exactly where other methods, the composition of the elements when transferring is often changed, so that one has on the substrate is not exactly the same chemical compounds as the target.
  • Simple production of complex documents (English multilayers )
  • Simultaneous production of high quality layers of different classes of materials such as ceramics, metals, semiconductors, and some polymers

Cons:

  • Slower separation than other PVD methods such as electron beam
  • Formation of droplets on the substrate possible
  • Clusters are often undesirable
  • No large areas possible in contrast to the sputtering
  • Comparatively expensive

Areas of application

The PLD method is used in materials science to novel materials with many components, in particular metastable structures such as amorphous diamond-like carbon ( engl. diamond-like carbon, DLC ), ceramics (such as the high-temperature superconductor yttrium barium copper oxide short YBaCuO ) or special function ferromagnetic layers ( AMR, GMR or GMI layers) to produce.

List of coating techniques Cluster (physics) Plasma oscillation Electron beam physical vapor deposition
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