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ENEA - Fusion division

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You are in: Home » Labs & Plants » Thin Film Deposition Lab. » Laser Ablation

Thin Film Deposition Laboratory: Laser Ablation

Ablation is a process that involves very complex physics mechanisms due to the high energy and the high power used. In the case of laser ablation, a pulsed laser source (Pulsed Laser Ablation) is employed, which, once focused through a suitable lens, engraves on the surface of the material that should be ablated (target material).

Laser ablation processLaser ablation process

In the case of thin films deposition, such material is ablated and the resulting material cloud is deposited on a substrate in the form of film. The evaporation regime, which can be varied from atomic to cluster evaporation, is selected by the energy density resulting on the target and it depends on the intrinsic characteristics of the target as the coefficient of absorption of the radiation from the material. The heating of the material (T>2000K) brings to the consequent formation of a plasma of electrons and ions, further to atoms and molecular aggregates, that expand themselves in the peculiar form of plume toward the substrate.
PLD is a technique used for its versatility and because it allows to deposit very complex materials though maintaining the correct target-film stechiometry transfer.

PLD system schematicPLD system schematic Plume created by the laser-target interactionPlume created by the
laser-target interaction

The experimental setup for PLD consists of a vacuum system, in which background pressure is of the order of 10-7 Torr. One of the most used lasers for ablation is the Excimer laser (XeCl), characterized by high energy densities and by a wavelength (308 nm) which is in the ultraviolet range and it is mostly used for the deposition of ceramic materials and oxides. Inside the vacuum chamber are present, one in front of the other, a multiple target holder and a sample holder constituted by a cylindrical block of steel, inside which a spiral of resistive material (Thermocoax) that allows the resisive heating of the substrate. The laser beam, once focused, enters the vacuum chamber through a ultraviolet transparent window and touches the target at 45 with respect to the target-substrate normal. The vacuum chamber is equipped with gas lines and flowmeters in order to manage depositions in different gas atmospheres, such as Ar, O2, N2 etc., depending on the deposition needs.

In the laboratory we have two devices for laser ablation deposition (PLD) of high critical temperature superconductor films, mainly YBCO-based, on monocrystalline and/or metallic substrates with the purpose of realizing high temperature superconductor tapes (coated conductors) for power applications. This research line asks for the possibility of developing the whole structure of the tape beginning from ceramic films generally constituted by oxides (CeO2, Y2O3, MgO etc.), that must have the role of buffer layers, up to the superconductor film itself. The buffer layers generally have the role to limit and/or control the diffusion of metal atoms from the substrate to the superconductor film, which is a limiting factor for its superconducting properties, to limit the metallic substrate oxidation during the deposition at high temperatures and in oxidizing atmosphere and to adapt the physical-chemical properties of the substrate and of the superconductor film. Both the lasers which are available in our laboratories are XeCl excimer lasers, even if with different features. The first one has a maximum energy of 150mJ and a maximum frequency of 100Hz, while the other one has a maximum energy of 200mJ and a maximum frequency of 200Hz.

PLD plant with a 200Hz/200mJ laserPLD plant with a 200Hz/200mJ laser PLD plant with a 100Hz/150mJ laserPLD plant with a 100Hz/150mJ laser