Pulsed Laser Deposition (PLD) is a powerful method to grow thin films and multilayers of complex materials.

It consists of a target holder and a substrate holder housed in a vacuum chamber. A high-power laser is used as an external energy source to vaporize materials and grow thin films. A set of optical components is used to focus and raster the laser beam over the target.

 

  1. The distinct advantage of PLD include its simplicity of use, since the laser is totally decoupled from the growth chamber, and the ability to preserve the stoichiometry of compound materials. The deposited film has the same chemical structure as the target material.
  2. The second advantage makes this technique so flexible that is easily adaptable to different operational modes without the constraints imposed by the use of internally powered evaporation sources.
  3. The last advantage has make PLD an effective method for synthesizing thin films of complex composition.

 

In our case, the PLD will be used to grow aluminium oxide (Al2O3) thin films on buffered NiAl or NiAl3, and La0.66Ca0.33O3 onto SrTiO3 substrate.

The PLD system uses a pulsed neodymium-doped yttrium-aluminium-garnet (Nd:YAG) Quantel 981C model having the following parameters: wavelength 1064 nm; maximum pulse energy 1200 mJ, wavelength 532 nm; maximum pulse energy 600 mJ and wavelength 355 nm; maximum pulse energy 280 mJ. The repetition rate of the three wavelengths is 10 HZ and the pulse width is 8 ns.

Between the output port of the laser and the laser port of the deposition chamber, various optical components are required to guide and focus the laser beam onto the target surface. Dielectric multilayer mirrors are used in order to deflect the laser beam into the port window. After the mirror, a 50 cm focal length UV grade fused silica lens focalises the laser beam onto the target.

The deposition chamber is cylindrical with a diameter of 30 cm and 45 cm height. All flanges and feedthroughs are standard CF flanges sealed with copper gaskets. The chamber has a substrate manipulator with a continuous rotation to homogenize the thin film deposition and two translations, one to change the distance between the target and the substrate and other to move away the substrate from the ablation plume. The samples are mounted onto a heating system that raises the substrate temperature up to 1500ºC.

The chamber also houses a target carrousel which can hold up to six targets. These targets can be rastered for uniform erosion and by rotating the carrousel, it is possible to change targets in situ for multilayer thin films fabrication. In PLD technique, gas mixture atmosphere may be necessary in order to obtain complex stoichiometries. The gas mixture is introduced into the chamber through a variable-leak valve.

The substrate/sample and target replacements are carried out with the same load-lock system and through the same port. The load-lock consists of an additional baby chamber which can be evacuated separately. The sample and targets are transported into the ablation chamber with a transfer rod and they can be removed instantly after the deposition.

Film growth can be monitored using a RHEED (Reflective High Energy Electron Diffraction). A differentially pumped electron gun, STAIB RH 30KeV makes possible to perform RHEED studies at standard deposition gas pressure up to 10 mtorr.