- LN2-cooled target pocket
- retractable pocket with garage
- fully compatible with conventional PLD target manipulator
- PLD and MAPLE usable in the same experiment
- optional multi laser setup for optimal PLD and MAPLE wavelengths
- multi-layer structures from organic and inorganic materials
- target filling and freezing in-situ under protective dry atmosphere
- 2-axis laser scanner for even target usage and laser-generated heat distribution
Organic Thin Film Deposition by Laser Ablation?
Laser ablation of organic materials is challenging. A conventional PLD (pulsed laser deposition) approach is often not feasible, because complex organic molecules tend to be damaged by the ablation process and the UV light involved. On the other hand, a deposition technique is desireable that allows the study of thin film interfaces of organic/inorganic substances or superlattices thereof. MAPLE (matrix-assisted pulsed laser evaporation) can be a solution for this problem.
Instead of directly ablating the desired organic compound, for MAPLE the material is mixed with a suitable – that means volatile and UV-absorbing – solvent and then frozen. The frozen solution is then used as a target in a PLD-like setup. The incident laser pulses heat up the solvent, which evaporates and entrains the organic compound to be deposited. A plume of material forms, and the organic compound can be deposited onto a substrate, whereas the volatile solvent can be pumped away by the vacuum pump.
Compared to conventional deposition techniques like spin coating, MAPLE offers advantages like better film thickness and morphology control. At the same time, the deposition can be combined with conventional PLD of inorganic materials. This opens a path to study interfaces and superlattices between these materials!
The SURFACE MAPLE target system
To utilize solutions of organic materials as PLD target, they have to be frozen. This usually means cryogenic cooling with nitrogen is necessary. To accomplish this, SURFACE has developed a special target holder. The holder is cooled by liquid nitrogen, so the MAPLE target material can be filled into the holder in its liquid phase – under protective atmosphere – and then be frozen before the chamber is evacuated. This process avoids cumbersome pre-freezing of targets and ensures clean and moisture-free conditions.
The MAPLE module is compatible with the conventional SURFACE target manipulator, so both can be installed and used at the same time, enabling deposition of interfaces and superstructures as mentioned above. The cold MAPLE target pocket can be retracted manually or motorically into a protective shell while other process steps are running, avoiding cross contamination.
Because of the cryogenic cooling, a conventional rotation appoach as for standard PLD targets is not feasible. To ensure even utilization of the MAPLE target, a computer controlled 2-axis laser scanner is added to the system.
Due to the solvent-based nature of MAPLE, it is less important than in conventional PLD to have high photon energies for stoichiometric transfer. Good absorption of the incident laser wavenlength by the solvent used is more important. For greater flexibility, SURFACE also offers dual-laser setups, combining an excimer laser for UV light pulses with a YAG laser for infrared light pulses (optionally with harmonic converter for shorter wavelengths, e.g. green).